JPH0794848B2 - Multi-cylinder engine crankshaft - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a crankshaft suitable for a multi-cylinder engine such as a motorcycle.

(Prior Art) Generally, a multi-cylinder engine of this type is mounted laterally with respect to a vehicle body, but since it is a multi-cylinder engine, the crankshaft becomes long and the crankcase extends to the side of the vehicle body. . That is, since the crankshaft for a multi-cylinder engine has crankpins connected to the connecting rods of the pistons and crank arms connected to both sides of these crankpins, the shaft length becomes long because of the number of cylinders. It is necessary to shorten the total length of the crankshaft as much as possible in order to narrow the width.

By the way, as a power transmission means for transmitting the output given to the crankshaft to the camshaft and the generator, it is general to drive the output through a drive gear such as a sprocket coaxially formed on the crankshaft. In this case, the total length of the crankshaft has to be lengthened by the amount of the drive gear to be created, so that there is a problem that the width of the crankcase is further increased.

That is, in a crankshaft of a multi-cylinder engine, particularly in the case of a high-power engine, it is common to provide journal parts, that is, bearing parts supported by bearing parts, on both sides of the crank arm in terms of strength. If a sprocket for driving a cam shaft or cam chain is created in the center of the engine in a cylinder engine,
Since the span between the crank arms of the set corresponding to the third cylinder and the third cylinder is expanded, the right side of the crank arm corresponding to the second cylinder (the first cylinder is the left end) and the crank arm corresponding to the third cylinder are A journal section is provided on each of the left sides, for a total of six journal sections.

However, in order to further reduce the overall width of the engine, when a generator (generator) conventionally attached to the end of the crankshaft is attached to the back side of the crankcase, the generator provided on the backside is driven to correspond to the second cylinder. If a gear or sprocket is created between the crank arm and the sprocket for driving the camshaft, the journal part on the right side of the crank arm corresponding to the second cylinder cannot be provided.
It will be 5 journals. Therefore, the bearing span of the crank arm corresponding to the second cylinder is inevitably wider than that corresponding to the other cylinders.

Such a crankshaft is disclosed, for example, in JP-A-56-1185.
This is disclosed in Japanese Patent No. 23, which will be described below with reference to FIG. 1a, 1b, 2a, 2b, 3a, 3b and 4a, 4b are pairs of crank arms respectively corresponding to the first to fourth cylinders, 5 is a crank pin connected to the piston of each cylinder, 6 Is a journal portion of the pair of crank arms corresponding to the second cylinder and the third cylinder, and is located between the crank arms 2b and 3a from the crank arm 2b side coaxially with the journal portion for driving the generator sprocket 7 and the cam shaft. A sprocket 8 and a journal section 6 are provided. The crank arm 3b is coaxial with the journal portion 6 and is provided with a driving gear 9 on the outer periphery for extracting the output. In order to provide the sprocket 7 for driving the generator in this way,
A pair of crank arms corresponding to the adjacent second cylinder
The spans of the bearings arranged on both sides of 2a and 2b are wider than the others.

On the other hand, an appropriate balance weight w, w ′ is attached to the crank arm in order to balance the rotational mass and the mass, and this balance weight w, w ′ is normally dispersed on the crank arm and also serves as the crank arm. It is provided. That is, the balance weight w'of the crank arms 2b and 2a corresponding to the second cylinder and the third cylinder and the balance weight w of the crank arm 3a have a shape bulging to one side of the journal portion 6, and The total of the balance weights w ', w'of the crank arm 2b and the amount of the balance weight w of the crank arm 3a are the same. Further, in the inner crank arms 1b and 4a of the first and fourth cylinders, the balance weight w part is relative to the journal part 6, and the balance weight w'parts of the crank arms 2b and 2a and the balance of the crank arm 3a. It has a shape that bulges out on the side opposite to the weight w part.

Now, as shown in FIG. 6 (b), when focusing on the through crank arms 2a and 2b corresponding to the second cylinder, the balance weight w'is evenly divided, but during engine operation, the inertia force due to crankshaft rotation is generated. And the engine explosive force through the piston and connecting rod is applied to the crankpin 5. However, since the bearing span of the crank arm pair corresponding to the second cylinder is wide, the stress applied to the crank pin 5 in this portion, that is, the bending moment is higher than that of the other crank arm pairs. This stress is large in part A of FIG. 6 (b), and therefore in a high speed engine,
This part may be damaged.

(Object of the Invention) The present invention has been made in view of the above-mentioned problems of the related art, in which drive means including a camshaft and a sprocket for driving a generator are arranged in parallel between opposed crank arms. (EN) A crankshaft for a multi-cylinder engine that can prevent the crankshaft from becoming long and reduce stress on the crankpin to improve robustness.

(Structure of the Invention) A crankshaft of a multi-cylinder engine of the present invention includes a crank pin connected to a piston of each cylinder, a plurality of pairs of crank arms connected to both sides of each crank pin, and a journal portion. In a crankshaft of a multi-cylinder engine, for driving one journal portion and a camshaft, etc., between opposed crank arms of a crank arm pair provided corresponding to at least one set of adjacent cylinders. A driving means such as a sprocket is provided in parallel, the journal portion is arranged adjacent to one of the crank arms facing each other, and the driving means is arranged adjacent to the other of the crank arms facing each other, The balance weight provided on the pair of crank arms disposed on the side of the drive means is The one closer to the driving means is lighter, and the one farther from the driving means is heavier.

With this configuration, the bending stress applied to the crank pin is reduced despite the fact that the bearing between the two crank arms of the set adjacent to the driving means is omitted and the bearing span is widened.

(Example) A case where the present invention is applied to a four-cylinder four-cycle engine of a motorcycle will be described below with reference to Figs.
In these figures, the same numbers as above indicate the same members, 20 is a cylinder block of a multi-cylinder engine, 21 to 24 are cylinders for each cylinder, 25 is a piston housed in each cylinder,
26 is a connecting rod, 30 is a crankshaft, 31 is a crankcase, the connecting rod 26 is connected to each pin 5 of the crankshaft 30, and the journal portion 6 is axially supported by a bearing provided in the crankcase 31. Has been done.
The driven gear 9 is in mesh with a driven gear 9'provided in a transmission case arranged behind the crankcase 31. Further, the driving means such as the sprocket 7 for driving the generator and the sprocket 8 for driving the camshaft include a transmission means such as a chain or a gear for transmitting the output to the generator and the camshaft mounted on the rear surface of the crankcase 31. (Not shown) are connected.

Further, each pair of crank arms 32 corresponding to the second cylinder and the third cylinder adjacent to each other on the crankshaft 30.
Crank arm 32b facing each other among a, 32b and 3a, 3b
And 3a, a sprocket 7 for driving a generator, a sprocket 8 for driving a camshaft, and a journal portion 6 are juxtaposed from the crank arm 32b side. Of the crank arm pair 32a, 32b arranged on the side of the installation portion of the generator driving sprocket 7, the crank arm 32b closer to the generator driving sprocket 7 is not provided with a balance weight. A balance weight w is attached to the crank arm 32a farther from the driving sprocket 7. That is, as shown in FIG. 3 and FIG.
A balance weight w is provided on 32a, and the crank arm 32b has a disk shape coaxial with the journal portion 6, and the balance weight w is not provided. As a method of applying the balance weight w, the crank arm 32b side closer to the generator driving sprocket 7 is lightened and the balance weight w is farther from the generator driving sprocket 7, that is, the first cylinder and the second cylinder. It suffices to make the crank arm 32a side adjacent to the journal portion 6 disposed therebetween heavy. Then, the total of the weights w thus lightly weighted is set to be substantially the same as the total in the case of the conventional equal division.

The portions of the crank arms 32a, 32B to which the balance weight w is thus distributed are shown in FIG. 6 (a). As is clear from this figure, the bearing spans of the finished crank arms 32a and 32b, that is, the first journal portion 6 located on the left side of the crank arm 3a and the second journal portion located on the left side of the crank arm 32a. Distance from part 6 (see Fig. 2)
However, since the balance weight w is not attached (or made lighter) to the crank arm 32b far from the second journal portion 6, the bending moment stress applied to the crank pin 5 is larger than that of the conventional one. Reduce to. Therefore, the risk of breakage at the boundary between the crank arms 32a and 32b and the crank pin 5 as in the conventional case is greatly reduced.

It should be noted that although the four-cylinder, four-cycle engine has been described in the above embodiment, the present invention is not limited to this example, and may be a three-cylinder or six-cylinder engine, or a two-cycle engine.

(Effect of the Invention) As described above, according to the present invention, the drive means for driving one journal portion and the cam shaft and the like are provided in parallel between the crank arms corresponding to the adjacent cylinders, and the drive means is provided. By equipping the pair of crank arms on the side where the means are adjacent to each other, the balance weight is lighter on the side closer to the drive means and heavier on the side farther, so that means for driving other devices can be provided in the crankshaft. Regardless, the crankshaft does not become long, it is possible to satisfy the demand for shortening the overall length, and the weight of the arm farther from the journal portion immediately adjacent to the pair of crank arms becomes smaller. The bending moment stress applied to the crank pin is Therefore, it is possible to reduce the possibility that the joint between the crank pin and the crank arm will be damaged, improve the robustness of the crankshaft, and ensure high reliability.

[Brief description of drawings]

1 is a partial sectional view showing an embodiment of a crankshaft of a multi-cylinder engine of the present invention, FIG. 2 is a plan view of the crankshaft, FIG. 3 is a sectional view taken along line III-III of FIG. 3 is a sectional view taken along line IV-IV in FIG. 3, FIG. 5 is a plan view of a conventional crankshaft, and FIGS. 6A and 6B are plan views of essential portions of the present invention and the conventional crankshaft. 5 ... Crank pin, 6 ... Journal part, 7 ... Generator driving sprocket (driving means), 8 ... Camshaft driving sprocket (driving means), 30 ... Crankshaft, 32a, 32b ... Crank arm.

Claims (1)

[Claims] 1. A crankshaft of a multi-cylinder engine comprising a crankpin connected to a piston of each cylinder, a plurality of pairs of crank arms connected to both sides of each crankpin, and a journal portion, and at least one crankshaft. One journal portion and a driving means such as a sprocket for driving a camshaft and the like are provided in parallel between the crank arms of a pair of crank arms provided corresponding to the adjacent cylinders of a set, The journal portion is disposed adjacent to one of the crank arms facing each other, the driving means is disposed adjacent to the other of the crank arms facing each other, and is installed on the side of the driving means. The balance weight provided on the pair of crank arms is lighter on the side closer to the drive means and farther from the drive means. Crankshaft of a multi-cylinder engine, characterized in that the heavy.