JPH0893746A - Crankshaft structure of multicylinder engine - Google Patents

Abstract

PURPOSE: To obtain an excellent balance rate, and reduce engine vibration and a bearing load by positioning a tooth bottom part of a gear formed in one of crank webs of both end parts of a crank pin outside of a crank web edge part of the other. CONSTITUTION: In a crank web 12d2 on which a separate balance weight 18 is installed, an outside diametrical dimension D1 of an edge part 12d2' on the opposite side of its crank pin 10d, is set smaller than a tooth bottom diameter D2 of a primary drive gear 14. Therefore, after the gear 14 is ground in a condition where the separate weight 18 having a circular arc part 18b opposed to a tooth side surface of the gear 14 is not installed on a crank shaft 6, the weight 18 can be fixed to the edge part 12d2' of the crank web 12d2. Therefore, as the whole balance weight 16, an outside diametrical dimension D3 can be made larger than the tooth bottom diameter D2 of the gear 14. Therefore, when mass of the weight 18 is properly set, inertia force of a piston system can be reliably cancelled, and an excellent balance rate can be obtained.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a crankshaft structure for a multi-cylinder engine.

[0002]

2. Description of the Related Art An example of a crankshaft structure in a conventional multi-cylinder engine is shown in FIG. FIG. 5 is a sectional view of the crankshaft. The crankshaft a is used in a four-cycle four-cylinder engine, and has crankpins b, c, d, which are connected to the large ends of the connecting rods of the respective cylinders.
e, and a pair of crank webs b1, b2, c1, c2, d1 ,.
d2, e1 and e2 are integrally formed by forging or casting. Also, the crank webs b1 and b2
The balance weights b1 ', b2', c1 ', c2', d are provided on the opposite side of the crankpins b to e from e1 to e2.
1 ′ · d2 ′, e1 ′ · e2 ′ are integrally provided, and the inertial force of the reciprocating mass of the piston of each cylinder and the centrifugal force of the rotating mass around the large end of the connecting rod are These balance weights b1 ', b2' to e1 ', e2'
It is designed to be balanced by the inertial force of.

In many four-cycle four-cylinder engines, one of the crank webs is also used as a primary drive gear, which is a gear for extracting power, in order to reduce the width of the engine as much as possible. For example, in the crankshaft a, the primary drive gear g is formed on the right crank web d2 of the pair of crank webs d1 and d2 corresponding to the second cylinder from the right in the plane of FIG. We are trying to miniaturize.

[0004]

However, in the above-described conventional crankshaft structure, the tool of the gear cutting machine is located on both sides of the primary drive gear g when the gear of the primary drive gear g is ground.
Since they hit 1'and e1 ', their outer diameter dimension is restricted, and further, the outer diameter dimension cannot be made larger than the root diameter dimension of the primary drive gear g.

Therefore, it becomes difficult to cancel the inertial force due to the reciprocating mass and the rotating mass of the piston system, which increases engine vibration and rotatably supports the journal of the crankshaft a and the crankpins b to e. There is a problem that the load on the bearing metal is increased.

Further, since it becomes difficult to cancel the inertial force such as the reciprocating motion of the piston system, the insufficient mass of the balance weights d1 'and e1' is provided on the side portion of the primary drive gear g, or the primary gear is not provided. It is necessary to increase the outer diameter of g, which increases the overall length of the crankshaft a, and the distance between the crankshaft and the counter shaft provided with the primary driven gear of the primary reduction gear increases. There is also a problem that the engine becomes large by doing so.

The present invention has been made in view of the above-mentioned problems of the prior art, and it is a multi-cylinder engine capable of obtaining a good balance ratio to reduce the engine vibration and the load on the bearing metal and to downsize the engine. It is an object of the present invention to provide a crankshaft structure of.

[0008]

The present invention has the following constitution in order to solve the above problems. That is, the invention of claim 1 holds a crank pin that pivotally supports a connecting rod for converting reciprocating motion of a piston in an engine into rotational motion of a crank shaft on the crank shaft side, and holds the crank pin from both ends of the crank pin. A pair of crank webs, a gear for extracting rotational power of the crank shaft formed at one edge of the pair of crank webs, and the other of the pair of crank webs with the crank pin In a crankshaft structure of a multi-cylinder engine having a holding side and a balance weight provided on the opposite side across the crankshaft center, at least a part of the balance weight is formed separately, and The edge of the crank web is located substantially closer to the center of the crank shaft than the tooth bottom of the gear. A crankshaft structure of a multi-cylinder engine, characterized in that the further body weights to the edges of the crank web is mounted in.

According to the invention of claim 2, the separate weight has a fitting hole that fits into a mounting portion formed around the center of the crankshaft, and the fitting hole has the mounting hole. The crankshaft structure for a multi-cylinder engine according to claim 1, wherein the crankshaft structure is fastened in a thrust direction to a side surface of the other crank web in a thrust direction by a screw member in a state of being fitted in.

[0010]

According to the invention of claim 1, since the edge portion of the other crank web is located closer to the crank shaft center side than the tooth bottom portion of the gear, the gear of the gear for extracting the rotational power is provided. Since the separate weight can be attached to the edge portion of the other crank web after grinding, the outer diameter dimension of the entire balance weight can be made larger than the root diameter of the gear. Therefore, by appropriately setting the mass of the separate weight, it becomes possible to reliably cancel the inertial force of the piston system.

Therefore, since it is not necessary to provide a weight portion on the side portion of the gear or to increase the outer diameter of the gear,
The overall length of the crankshaft and the axial distance between the primary reduction gears can be shortened, and the engine can be downsized.

Further, according to the invention of claim 2, since the fitting hole is fitted in the mounting portion of the crankshaft,
Since the inertial force (centrifugal force) of the separate weight during engine operation is received as a tensile load by the attachment portion, attachment of the separate weight is advantageous in terms of strength. That is, since the inertial force of the separate weight is not applied to the screw member as a shear load, the screw diameter of the screw member can be reduced.

On the other hand, in the case where the separate weight is simply fixed to the crank web by the through bolt, the inertial force of the separate weight is applied to the through bolt as a shear load, so that the through bolt is increased in order to increase the mounting strength. It is necessary to increase the screw diameter of.

[0014]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a sectional view of an engine according to this embodiment. FIG. 2 is a vertical sectional view of the crankshaft of this embodiment.
FIG. 3 is a side view of the crankshaft viewed from the direction A in FIG. 4A and 4B are views showing a comparative example with respect to the present embodiment, in which FIG. 4A is a vertical cross-sectional view of the crankshaft, and FIG. 4B is a side view of the crankshaft seen from the direction B in FIG.

As shown in FIG. 1, the engine 2 according to the present embodiment is, for example, a 4-cycle parallel 4-cylinder engine used in a motorcycle, and includes a crankcase 22 having a crankshaft 6 incorporated therein, and a crank. The pistons 4a, 4b, 4
A cylinder block 24 on which c and 4d slide, a cylinder head 26 that has a valve mechanism inside and is mounted and fixed on the upper surface of the cylinder block 24, and a cylinder head cover 28 that closes the cylinder head 26 from above. .

The pistons 4a-4d are connected to the small ends of the connecting rods 8a, 8b, 8c, 8d through piston pins 32a, 32b, 32c, 32d, respectively, and the large ends of the connecting rods 8a-8d are connected. The parts are crank pins 10a, 10b, 10c, 1
It is connected to 0d. As shown in FIG. 2, each of the crank pins 10a to 10d has a pair of crank webs 12a1, 12a2, 12b1, 12b2, 12c from both ends.
It is held by 1 · 12c2, 12d1 · 12d2.

The crankshaft 6 has the crankpin 10a.
-10d and the crank webs 12a1-12d2
Is integrally formed by casting or forging, and has journal portions 6c at a total of 5 positions between both end portions and each cylinder. Each journal 6c is rotatably supported by a pair of bearing metals 34 (see FIG. 1) fixed to the crankcase 22.

The crankshaft structure of this embodiment, as shown in FIGS. 2 and 3, includes a primary drive gear 14 for extracting rotational power of the crankshaft 6 formed at the edge of the crank web 12d1. Crank web 1
2d2, a balance weight 1 provided on the opposite side of the holding side of the crankpin 10d and the crankshaft center 6a.
6 and the balance weight 16 has
A part is formed separately and the crank web 12d2
12d2 'is located closer to the crankshaft center 6a side than the tooth bottom 14a of the primary drive gear 14, and a separate weight 18 is attached to the edge 12d2' of the crank web 12d2. . In the crankshaft 6, the balancers 36a1, 36a2, 36b1 ... are provided on the crank webs 12a1, 12a2-12c1, 12c2 of the other cylinders.
36b2, 36c1 and 36c2 are formed.

As shown in FIG. 1, the primary drive gear 14 meshes with a primary driven gear 40 which is provided on a counter shaft 38, which is a driven shaft of the crankshaft 6, so as to rotate freely.
Transmits power to the counter shaft 38 via the clutch 42. The power transmitted to the counter shaft 38 is output from the engine 2 through the transmission 44 in a state of a predetermined rotation speed to drive the rear wheels.

As shown in FIGS. 2 and 3, the crank web 12d2 is set so that the outer diameter dimension D1 of the edge portion 12d2 'on the side opposite to the crank pin 10d is smaller than the root diameter D2 of the primary drive gear 14. In addition to the above, it has female screw holes 20a penetrating at three locations in the circumferential direction inside the edge portion 12d2 '. Also, the crank web 12
The crankshaft center 6a is provided on the side surface of the crankshaft end side of d2.
A boss-shaped mounting portion 6b is formed around the periphery.

The separate weight 18 has a substantially horseshoe shape when viewed in the crankshaft direction, has a circular fitting hole 18a that fits in the mounting portion 6b, and the fitting hole 18a is in the mounting portion 6b. Crank web 12d when fitted
A hexagon socket head cap screw (an example of a screw member) 20 is tightened in the thrust direction on the side surface of the No. 2 side. Further, the separate weight 18 has a thick arc portion 18b having an inner diameter dimension substantially the same as the outer diameter dimension D1 of the edge portion 12d2 ′ of the crank web 12d2 and fitted into the edge portion 12d2 ′. Prepare Further, a screw insertion hole 20b having a plain counterbore and penetrating therethrough is provided at a portion corresponding to the three female screw holes 20a. Therefore, in the separate weight 18, the hexagon socket head cap screw 20 is screwed into the screw insertion hole 20b with the fitting hole 18a fitted into the mounting portion 6b and the circular arc portion 18b continuing to the lower side of the edge portion 12d2 '. By being screwed into the female screw hole 20a through the through hole, it is fastened and fixed to the side surface of the crank web 12d2 in the thrust direction.

According to the present embodiment having the above-mentioned configuration, the primary weight is not attached to the crankshaft 6 without the separate weight 18 having the arc portions 18b facing the side surfaces of the teeth of the primary drive gear 10. After the gear grinding of the drive gear 14 is performed, the separate weight 18 can be fixed to the edge portion 12d2 'of the crank web 12d2. Therefore, the outer diameter dimension D3 (see FIG. 2) of the balance weight 16 as a whole is set as the primary weight. The diameter can be made larger than the root diameter D2 of the drive gear 14. Therefore, by appropriately setting the mass of the separate weight 18, the inertial force of the piston system can be reliably canceled by the inertial force of the separate weight 18, and a good balance ratio can be obtained.

Therefore, it is not necessary to provide a heavy weight portion on the primary drive gear 14 or to increase the outer diameter of the primary drive gear 14, so that the crankshaft 6
It is possible to shorten the overall length of the engine and the axial distance between the crank shaft 6 and the counter shaft 38, and to downsize the engine 2.

Further, in the mounting portion 6b of the crankshaft 6,
Since the fitting hole 18a of the separate weight 18 is fitted, the inertial force of the separate weight 18 during engine operation is received as a tensile load on the outer peripheral surface of the mounting portion 6b, as shown in FIG. Since no shear load is applied to the hexagon socket head cap bolt 20, the mounting structure of the separate weight 18 is advantageous in strength. That is, the screw diameter of the hexagon socket head cap screw 20 can be reduced.

In contrast, FIG. 4 (a) and FIG. 4 (b)
As in the crankshaft structure shown as a comparative example in FIG. 1, by inserting the through bolt 46 into the crankshaft 6 and the separate weight 48 through the nut 50 in the direction in which the crankshaft is twisted with respect to the crankshaft center 6a, Body weight 48
In the case where the weight of the through bolt 46 is fastened, the inertial force of the separate weight 48 is applied as a shear load to the cross section of the through bolt 46, so that the screw diameter of the through bolt 46 is increased in order to increase the attachment strength of the separate weight 48. It becomes necessary to thicken it. In FIG. 4, reference numerals 52a and 52b are crank webs, 54 is a crank pin, and 56 is a knock pin.

Further, according to this embodiment, the fitting hole 18a of the separate weight 18 and the mounting portion 6b of the crankshaft 6 are attached.
Since the and spigots are fitted together at the spigot part, the manufacture of the spigot part is easy and generally easy. Therefore, the weight 18 which is a separate body is easier to manufacture than the crankshaft structure of the comparative example. The remarkable effect that it can be achieved is also obtained.

In this embodiment, the inertial moment of the separate weight 18 due to the angular acceleration of the crankshaft 6 is applied as a shearing load to the shaft portion of the hexagon socket head cap bolt 20, but is different from the mounting portion 6b. Body weight 1
By fitting a knock pin or the like for fixing the rotation of the separate weight 18 between the 8 and 8, the backlash of the separate weight 18 with respect to the crankshaft 6 is reduced, and the weight 18 is separated by the inertial force moment related to the angular acceleration. If the impact force received by the threaded portion of the body weight 18 is reduced, the attachment strength of the separate weight 18 with respect to the shear load can be further improved.

The present embodiment is a preferred embodiment of the present invention, and the technical scope of the present invention is not limited to this embodiment. For example, in the present embodiment, the present invention is applied to the crank webs 12d1 and 12d2 corresponding to the cylinder located on the rightmost side in FIG. 1, but the primary drive gear 14 is the crank web 12a2 related to the leftmost cylinder.
Crank web 12 on the left side of the
By attaching a separate weight 18 to a1,
The same effect as that of the present embodiment can be obtained.

The position of the edge portion 12d2 'of the crank web 12d2 is closer to the crankshaft center 6a than the position shown in FIG. 2, or, conversely, slightly to the crank bottom than the tooth bottom portion 14a of the primary drive gear 14. The position may be separated from the axis center 6a. The point is that it can be set as appropriate as long as the existence of the edge portion 12d2 'does not affect the gear grinding of the primary drive gear 14.

[0030]

As described above, according to the present invention, it is possible to reliably cancel the inertial force of the piston system by the separate weight, so that a good balance ratio can be obtained. The engine vibration and the load on the bearing metal can be reduced. At the same time, the total length of the crankshaft and the axial distance between the primary reduction gears can be shortened, so that the engine can be downsized.

[Brief description of drawings]

FIG. 1 is a cross-sectional view of an engine according to this embodiment.

FIG. 2 is a vertical sectional view of a crankshaft structure of the present embodiment.

FIG. 3 is a side view of the crankshaft structure as viewed from the direction A in FIG.

FIG. 4 is a diagram showing a comparative example with respect to the present embodiment,
(A) is a longitudinal cross-sectional view of the crankshaft, (b) is a side view of the crankshaft seen from the B direction in (a).

FIG. 5 is a vertical sectional view of a conventional crankshaft.

[Explanation of symbols]

2 Multi-cylinder engine 4d Piston 6 Crankshaft 6a Crankshaft center 6b Attachment part 8d Connecting rod 10d Crank pin 12d1 Crank web (corresponding to one crank web) 12d2 Crank web (corresponding to the other crank web) 12d2 'Crank web edge Part (corresponding to the edge of the other crank web) 14 Primary drive gear (corresponding to a gear for extracting rotational power) 14a Gear bottom 16 Balance weight 18 Separate weight 18a Fitting hole 20 Hexagon socket head cap screw (for screw member) One case)

Claims (2)

[Claims] 1. A crank pin for pivotally supporting a connecting rod for converting a reciprocating motion of a piston in an engine into a rotary motion of a crank shaft on the crank shaft side, and a pair of crank webs for holding the crank pin from both ends of the crank pin. And a gear for extracting rotational power of the crankshaft formed on one edge of one of the pair of crank webs, and the other of the pair of crank webs on the holding side of the crank pin and the crank pin. In a crankshaft structure of a multi-cylinder engine having a balance weight provided on the opposite side across the center of the crankshaft, at least a part of the balance weight is formed separately, and an edge of the other crank web. Part is located closer to the crankshaft center side than the tooth bottom of the gear, and the other crankshaft Crankshaft structure of a multi-cylinder engine, characterized in that it said further body weight is attached to the edge of the probe. 2. The separate weight has a fitting hole that fits in a mounting portion formed around the center of the crankshaft, and in a state where the fitting hole is fitted in the mounting portion, 2. The crankshaft structure for a multi-cylinder engine according to claim 1, wherein the crankshaft structure is fastened to a side surface of the other crank web in a thrust direction by a screw member.