JP2005133801A - Balancer shaft - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To miniaturize an engine itself by miniaturizing a balancer shaft as small as possible. <P>SOLUTION: In the engine wherein the balancer shaft 80 is mounted in parallel with a crank shaft 5, and rotated from the crank shaft 5 through gears 82, 83, a fitting part 90 for fitting the gear 83 is mounted on an end part of the balancer shaft 80, a flange part 90b is formed on a machine body central side of the fitting part, a stepped part 83b is formed on the machine body central-side end part of a shaft hole 83a formed on the gear 83, a recess 80e is formed on the balancer shaft at a side opposite to a balance weight 80c mounted on the balancer shaft, and a bottom part of the recess 80e is located at a balance weight side with respect to a shaft center of the balancer shaft. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a configuration of a balancer shaft that is provided in an engine crankcase in parallel with a crankshaft to reduce vibration, noise, and the like. More specifically, the present invention relates to a technique for improving the balancer shaft to make the engine compact.

Conventionally, a crankshaft is horizontally mounted on the crankcase of an engine, the crankshaft and a piston are connected by a connecting rod, the piston is slidably inserted into a cylinder, and fuel is sucked into the cylinder. By burning, the piston is reciprocated, the crankshaft is rotated via the connecting rod, and power is taken out using one or both ends of the crankshaft as an output shaft.
In such an engine, since the reciprocating motion of the piston is converted into the rotational motion of the crankshaft, vibration is inevitably generated in the crankshaft. In order to reduce this vibration, a balancer shaft is arranged in parallel with the crankshaft, and the balancer shaft is rotated in the opposite direction to the crankshaft so as to cancel vibrations generated during operation of the engine.

In this way, in the engine, the balancer shaft is arranged in parallel with the crankshaft. However, in order to reduce the weight of the engine itself and make the crankcase compact, the balance weight must be reduced, and the crankshaft and balancer shaft can be connected as much as possible. It is preferable to arrange them close to each other. However, if the balance weight is reduced in size, it is difficult to reduce the vibration by reducing the weight. If the crankshaft and the balancer shaft are too close together, the weight provided on the balancer shaft will hit the large end of the connecting rod during rotation.
Therefore, a technique is known in which an escape portion is formed on the balance weight so that the balance weight provided on the balancer shaft and the large end of the connecting rod do not contact (do not interfere with each other) (see, for example, Patent Document 1).

Japanese Patent Laid-Open No. 11-94026

In the technique disclosed in Patent Document 1, since the balance weight portion where the large end of the connecting rod interferes is simply shaved, the crankshaft and the balancer shaft cannot be brought closer to each other. Therefore, there was a limit to downsizing the engine.
Further, in order to transmit a driving force from the crankshaft to the balancer shaft, gears are provided on one side of the crankshaft and the balancer shaft, and are arranged in mesh with each other. The gear provided on the balancer shaft is as thin as possible and can contribute to downsizing by forming the shaft support portion as short as possible, but the bearing portion can be shortened or the weight abutting on the side of the gear can be omitted. Then there was a problem that the gears collapsed. In order to prevent this collapse, a C ring or the like can be arranged on both sides of the gear, but the number of parts increases and the number of assembly steps also increases.

  The problems to be solved by the present invention are as described above. Next, means for solving the problems will be described.

  That is, according to the first aspect of the present invention, in the engine in which the balancer shaft is disposed in parallel with the crankshaft and the balancer shaft is rotated from the crankshaft through the gear, the gear is fitted on the end of the balancer shaft. A fitting portion is provided, and a flange portion is formed on the machine body center side of the fitting portion, and a step portion is formed on the machine body center side end portion of the shaft hole formed in the gear.

  According to a second aspect of the present invention, the shaft shape on the side opposite to the balance weight disposed on the balancer shaft is flattened.

  According to a third aspect of the present invention, a recess is formed on the balancer shaft opposite to the balance weight disposed on the balancer shaft, and the bottom of the recess is disposed on the balance weight side with respect to the balancer shaft axis.

  According to a fourth aspect of the present invention, the depression center, the balance weight center, and the connecting rod center are arranged on the same plane.

  According to a fifth aspect of the present invention, the cross-sectional shape of the recess is configured to be substantially the same shape as the locus of the large end portion of the connecting rod.

  As effects of the present invention, the following effects can be obtained.

  According to the first aspect of the present invention, it is possible to easily position the gear and the balancer shaft only by bringing the side surface of the gear into contact with the collar portion. And it can attach easily at right angle with respect to an axis | shaft, A collar part receives the end surface of a gearwheel, and can prevent a fall. Further, by providing the collar portion, a positioning member such as a C-ring can be omitted, and the cost can be reduced. Furthermore, by providing a step portion on the side surface of the shaft hole of the gear, the flange portion can be inserted, and the length of the balancer shaft in the axial direction can be shortened. Or since a collar part can be further arrange | positioned now at a side end side, the space which arrange | positions a balance weight can be enlarged and the weight of a balance weight can also be increased.

  According to the second aspect of the present invention, the eccentric amount can be increased while suppressing an increase in the weight of the balancer shaft, and the balancer shaft can be made compact. And since the weight of a balancer axis | shaft can be reduced, an engine itself can be reduced in weight.

  According to the third aspect, it is possible to increase the eccentricity without increasing the balance weight on the balancer shaft. That is, even if the weight is the same, the amount of eccentricity can be increased, which can contribute to downsizing. Moreover, the space on the opposite side to the balance weight can be made large by the depression. Therefore, it can be brought close to the crankshaft located on the opposite side.

  In claim 4, the recess, the balance weight, and the connecting rod are arranged in a row in a direction perpendicular to the crankshaft, and the large end of the connecting rod is positioned in the recess when the balance weight is positioned on the opposite side of the connecting rod. Therefore, it can be arranged efficiently, and the vibration during rotation can be suppressed and balanced.

  According to the fifth aspect of the present invention, interference with the connecting rod can be avoided by the depression, and the large end portion of the connecting rod enters the depression, so that the balancer shaft can be brought as close to the crankshaft as possible. That is, the distance between the balancer shaft and the crankshaft can be shortened, and the engine itself can be made compact.

Next, embodiments of the invention will be described.
1 is a front sectional view of an engine according to the present invention, FIG. 2 is a plan sectional view of a lower portion of the engine according to the present invention, FIG. 3 is a plan sectional view of a balancer shaft portion according to the present invention, and FIG. 5 is a cross-sectional view of the balancer shaft drive gear, FIG. 6 is a cross-sectional view taken along the line AA in FIG. 4, and FIG. 7 is a cross-sectional view taken along the line BB in FIG.

The overall configuration of the engine according to the present invention will be described with reference to FIGS.
As shown in FIG. 1, the main body of the engine 1 is composed of an upper cylinder block 2 and a lower crankcase 3. A cylinder 2a is formed in the center of the cylinder block 2 in the vertical direction. The piston 4 is accommodated. A cylinder head 7 is disposed on the cylinder block 2, and a valve arm case 8 is disposed on the cylinder head 7, and upper end portions of the valve arm 27, the intake valve and the exhaust valve, and an upper end portion of the push rod 25. Etc., a valve arm chamber 8a is formed. A muffler 9 is disposed on one side (left side in FIG. 1) of the valve arm case 8 above the engine 1, and a fuel tank 10 is disposed on the other side (right side in FIG. 1).

  A crankshaft 5 is supported on the crankcase 3 in the front-rear horizontal direction, and the crankshaft 5 and the piston 4 are connected by a connecting rod 6. A balancer shaft 80 and a cam shaft 13 which will be described later are horizontally mounted on the crankcase 3 in parallel with the crankshaft 5, and a governor device 11 is disposed in the crankcase 3 below the camshaft 13. A fuel injection pump 12, a tappet 23, and the like are disposed above the camshaft 13. A cam gear 17 is fixed to one end of the cam shaft 13. The cam gear 17 is engaged with a gear 18 fixed to one end of the crankshaft 5 so that a driving force can be transmitted from the crankshaft 5 to the camshaft 13 via the gear 18 and the cam gear 17.

  An intake cam, a fuel injection cam 14 and an exhaust cam are provided on the cam shaft 13 at predetermined intervals. A tappet is brought into contact with each of the intake cam and the exhaust cam, and each tappet is brought into contact with the lower end of one side of the intake valve arm 27 and the exhaust valve arm in the valve arm case 8 via the intake push rod and the exhaust push rod. ing. The upper ends of the intake valve and the exhaust valve arm are in contact with the lower ends of the intake valve arm 27 and the exhaust valve arm, respectively.

  In addition, the fuel injection amount of the fuel injection pump 12 is changed by turning a control lever 16 connected to the governor device 11. The fuel injection pump 12 communicates with a fuel injection nozzle 15 disposed above the cylinder 2a through a high-pressure pipe, and injects a predetermined amount of fuel into the cylinder 2a in synchronization with the rotation of the crankshaft 5 and the vertical movement of the piston 4. It is assumed to be configured.

As shown in FIGS. 1 and 2, one side of the crankshaft 5 is an output shaft, and a flywheel 81 is fixed on the other side. A large end portion 6a of the connecting rod 6 is pivotally supported at the front and rear central portions of the crankshaft 5. The pivot portion 5a of the large end portion 6a is arranged eccentrically, and both the front and rear sides of the pivot portion 5a extend to the opposite side of the pivot portion 5a to form weight portions 5b and 5b.
In this way, vibrations during engine driving are reduced by the weight portions 5b and 5b.

  A gear 82 is fixed on the rear side of the crankcase 3 on the crankshaft 5, and the gear 82 meshes with a drive gear 83 fixed on the balancer shaft 80. Thus, the rotational force of the crankshaft 5 is transmitted to the balancer shaft 80 via the gear 82 and the drive gear 83, and the balancer shaft 80 is rotationally driven in the reverse direction of the crankshaft 5.

Next, the balancer shaft 80 of the present invention will be described with reference to FIGS.
Bearing portions 80a and 80a are formed at both front and rear ends of the balancer shaft 80, and the bearing portions 80a and 80a are rotatably supported by the crankcase 3 via bearings 84 and 84. In this embodiment, the front surface of the crankcase 3 is covered with a gear case 85, and the bearing portion 80 a at the front end of the balancer shaft 80 is supported by the gear case 85 via a bearing 84.

A gear fitting portion 90 is formed at one end of the balancer shaft 80, in this embodiment, at the front portion of the rear bearing portion 80a. The gear fitting portion 90 forms an attachment shaft portion 90 a that matches the width of the drive gear 83. The length of the mounting shaft portion 90a in the axial center direction is set to a length sufficient to prevent the drive gear 83 from shrink-fitting and slipping in the axial direction. A key 86 is interposed between the balancer shaft 80 and the drive gear 83 so that they do not rotate relative to each other.
A flange 90b is formed on the center side of the mounting shaft 90a. A vertical surface 90c formed in a direction perpendicular to the shaft center on the mounting shaft portion 90a side of the flange portion 90b attaches the drive gear 83 to the drive gear 83 at a right angle to the positioning surface of the drive gear 83 and the balancer shaft 80. The contact surface for this purpose.
In addition, a taper portion 90d whose diameter gradually decreases on the center side of the body of the flange portion 90b is formed. In this way, stress concentration is prevented.

On the other hand, as shown in FIG. 5, the drive gear 83 has a stepped portion (stepped portion) 83b on the flange 90b side of a shaft hole 83a provided at the center. The inner diameter of the step portion 83b is configured to be slightly larger than the outer diameter of the flange portion 90b, and the width of the step portion 83b is substantially the same as the width of the flange portion 90b.
With this configuration, the side surface of the step portion 83b abuts on the vertical surface 90c of the flange portion 90b, and the drive gear 83 can be attached to the balancer shaft 80 at a right angle. The flange portion 90b enters the step portion 83b to shorten the axial length to form a compact structure, eliminates the protrusion from the drive gear 83, and increases the space for arranging the balance weight as much as possible. I am doing so.

A front balance weight 80b and a center balance weight 80c are formed at the center of the body of the bearing 80a on the front side of the balancer shaft 80 and at the front and rear center, respectively. Specifically, the front balance weight 80b is disposed between the gear case 85 and the weight portion 5b, and the central balance weight 80c is disposed between the weight portions 5b and 5b. A weight portion 5b is disposed between the central balance weight 80c and the drive gear 83. The front balance weight 80b and the center balance weight 80c are located alternately and do not overlap in plan view when the crankshaft 5 and the balancer shaft 80 rotate and rotate to positions facing the weight portions 5b and 5b. And the gap between the two is configured to be as small as possible so that the amount of eccentricity is as large as possible.
With this arrangement, the balance weight is efficiently arranged between the crankshaft 5 and the balancer shaft 80 so that the length in the front-rear direction is as short as possible, so that the engine body is compact, The space in the case 3 can be used effectively.

Further, as shown in FIGS. 4 and 6, the shaft portion where the front balance weight 80b is located and the shaft portion located on the front-rear center side from the flange portion 90b are substantially semicircular as shown in FIGS. The shaft portion on the opposite side to the balance weight is configured as a flat plane 80d. However, a cross-sectional area having rigidity that is not deformed by the load of the balance weight and the centrifugal force received during rotation is secured.
In this way, by shaving the shaft portion opposite to the balance weight, the amount of eccentricity with respect to the shaft center can be increased, the balancer shaft 80 can be reduced in size, and the crankshaft 5 can be brought closer. It is.

Further, as shown in FIGS. 4 and 7, the shaft portion where the center balance weight 80c is located has a small diameter on the opposite side of the balance weight in the front and rear center on the balancer shaft 80, that is, in the center portion in the axial center direction. It is said. Thus, the amount of eccentricity can be increased without increasing the balancer, and the space on the opposite side of the balancer can be increased.

A small-diameter portion formed on the balancer shaft portion on the opposite side to the central balance weight 80c disposed on the balancer shaft 80 is formed as a recess 80e. The recess 80e is configured such that its bottom is positioned on the balance weight side with respect to the axis O of the balancer shaft 80, and enters the center balance weight 80c side. Note that the surface from the flat surface 80d to the recess 80e is an inclined surface.

  By configuring in this way, the recess 80e cuts the weight on the opposite side of the central balance weight 80c (projecting side), and the center of gravity of the central balance weight 80c is located when the recess is not provided (a perfect circle axis). Compared with the shaft center O, it can be positioned farther away, the amount of eccentricity can be increased, and the weight can be efficiently arranged to balance vibrations during rotation.

Further, the center in the front-rear direction (axial direction) of the recess 80e, the center in the front-rear direction of the central balance weight 80c, and the center in the front-rear direction of the connecting rod 6 are arranged on substantially the same plane. In other words, the recess 80e, the central balance weight 80c, and the connecting rod 6 are arranged in a row in a direction perpendicular to the crankshaft 5. And the planar cross-sectional shape of this hollow 80e is comprised in the shape substantially the same as the locus | trajectory (outside in sectional view) of the big end part 6a of the connecting rod 6. FIG.

  By configuring in this way, when the balance weights 80b and 80c and the weight portions 5b and 5b are separated from each other during rotation of the crankshaft 5, the large end portion 6a of the connecting rod 6 approaches the recess 80e. Since the shape is substantially the same, it can rotate without contacting through a slight gap. That is, the balancer shaft can be rotated while avoiding interference between the connecting rod 6 and the balancer shaft 80. Then, the balancer shaft 80 can be brought as close as possible to the large end portion 6a of the connecting rod 6, that is, the crankshaft 5, and the distance between the crankshaft 5 and the balancer shaft 80 can be arranged to be shorter than the conventional one. It can be configured compactly.

The front sectional view of the engine concerning the present invention. The plane sectional view of the engine lower part concerning the present invention. The plane sectional view of the balancer axis part concerning the present invention. The top view of a balancer axis | shaft. Sectional drawing of a balancer shaft drive gear. AA arrow sectional drawing in FIG. BB arrow sectional drawing in FIG.

Explanation of symbols

5 Crankshaft 6 Connecting rod 6a Large end 80 Balancer shaft 80c Balance weight 80e Depression 82/83 Gear 83a Shaft hole 83b Step 90 Fitting 90b Hut

Claims (5)

  In an engine in which a balancer shaft is arranged in parallel with a crankshaft and the balancer shaft is rotated from the crankshaft via a gear, a fitting portion for fitting a gear is provided on an end portion of the balancer shaft. A balancer shaft characterized in that a flange portion is formed on the machine body center side of the joint and a step portion is formed on the machine body center side end portion of the shaft hole formed in the gear.   The balancer shaft according to claim 1, wherein a shaft shape opposite to a balance weight disposed on the balancer shaft is flattened.   2. The recess according to claim 1, wherein a recess is formed on a balancer shaft opposite to the balance weight disposed on the balancer shaft, and a bottom portion of the recess is disposed on the balance weight side with respect to the axis of the balancer shaft. Balancer shaft.   4. The balancer shaft according to claim 3, wherein the center of the recess, the center of the balance weight, and the center of the connecting rod are arranged on the same plane. The balancer shaft according to claim 3, wherein a cross-sectional shape of the recess is configured to be substantially the same shape as a locus of a large end portion of the connecting rod.

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