JPH0821426A - Bolt fastening method - Google Patents

Abstract

PURPOSE:To reduce lowering of axial tension for fastening and prevent deformation of member to be fastened from generating by interposing a washer between a bolt head and the member to be fastened, and applying a specified load in the axial direction of bolt to the projection face of bolt shaft section of belt head which is not fastened. CONSTITUTION:Between a bolt head 44 and a seat face 45 of fastening part on the side of rod main body 40 a washer 46 having almost the same shape as the head 44 is interposed. As a material for the washer 46 one is used which is weaker in its endurance than a material for the rod main body 40 and by which the temperature to generate high temperature creep is made higher than the temperature at use. A load over the specified fastening load for a bolt 43 is applied to the head 44 before fastening operation in the axial direction of the bolt 43 to meet the projection face of section of shaft part 47 in the bolt head 44. A nut is then set on the tip of the bolt 43 and fastening operation is carried out. The endurance of the washer 46 is lower than that of the rod body 40, and thereby the washer 46 sinks so that the face pressure of the bolt head is made uniform. The maximum face pressure value on the side of the rod main body 40 is reduced to prevent the rod main body 40 from being damaged and to secure a good fastening condition.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a bolt fastening method for engine parts.

[0002]

2. Description of the Related Art High-strength bolts are used for fastening engine parts, and as a fastening method there is, for example, the method shown in FIG.

This is an example of a connecting rod, and a connecting rod 15 made of a light alloy such as aluminum is composed of a rod portion 16 having an H-shaped cross section, and small ends 17 and large ends 18 at both ends thereof. . The small end 17 is the piston pin and the large end 18
Are connected to crank pins, respectively, and the connecting rod 15 is used to convert the explosion energy on the piston side into the rotation of the crank shaft.

The large end portion 18 of the connecting rod 15 is divided into two parts, and one of the two divided large end parts is integrally formed with the rod part 16 and the small end part 17 as a bifurcated end part 19 to form the two divided large end part. The other part is separately molded as a curved connecting member 20.

The bifurcated portion 19 and the connecting member 20 which are the large two-divided end portions are connected by using two tightening bolts 21 which are high-strength bolts so that their mating surfaces 191 and 201 are overlapped with each other. Both cooperate to support the bearing metal 22 made of white metal.

The tightening bolts 21 are fitted in bolt holes 23 formed at both ends of the large end portion 18, respectively. The bolt head 211 of the tightening bolt 21 is perpendicular to the center line L of the bolt hole 23, and faces the bearing surface 24 around the opening of the bolt hole on the bifurcated portion 19 side, and the nut 25 also contacts the center line L of the bolt hole. It is vertical and faces the bearing surface 26 around the opening of the bolt hole on the connecting member 20 side.

The bearing surfaces 24 and 26 are subjected to a cold surface treatment before the tightening bolt 21 is mounted. That is, the bearing surfaces 24 and 26 have the center line L of the bolt hole 23.
A set amount of load P is applied in the bolt axial direction, which is the direction of.

The load P is the large end 18 of the tightening bolt 21.
Depending on the mass of the connecting rod 15, the tightening axial force P1 which is the initial load (when the large end 18 does not change with time) and the inertial force generated by the rotational movement of the large end 18 Inertial force sharing load P
2 and a thermal expansion force P3 corresponding to the thermal expansion of the large end portion 18 in the bolt axial direction, or a value equal to or more than that value. Such a load P is applied to the both seating surfaces 24 through the pressure contactors 27, 28 (shown by a chain double-dashed line) made of a highly rigid material after forming the outer shapes of the seating surfaces 24, 26 by using a known press machine. , 26 at the same time.

Instead of using a pressing machine, a load P may be applied to both bearing surfaces 24, 26 using a bolt-nut tightening device (not shown) made of a rigid material that also serves as a pressure contact.

Due to the load applied in this way, the lower surface layers 241 and 261 of the seating surfaces 24 and 26 are settled and are depressed by an amount δ corresponding to the load (one point in the figure). The chain line shows the state before surface treatment). That is, each surface layer 24
1, 261 is work-hardened in the cold, and the hardness of the structure in that portion becomes high.

By the way, the depression caused by the settling on the seat surfaces 24 and 26 is stopped after a predetermined elapsed time t from the start of applying a predetermined load P0 as shown in FIG. This is because the work hardening of the surface layer portion, that is, the surface layer portion receives the load P0 by the pressing surface having a predetermined area and changes into a structure capable of withstanding the limit surface pressure at the time when the deformation no longer progresses. The amount δ of depression caused by such a tendency is determined by the load P, the hardness of each material, the bolt head 211, the nut 25 and the seat surface 2.
4, 26 and the contact area.

Thus, the bearing surfaces 24, 2 of the connecting rod 15 are
A contact area, a material, and a load P are set in 6, and the load P is continuously applied for a predetermined elapsed time to perform a surface treatment for causing a depression as a plastic deformation. Then, after this surface treatment, a tightening bolt 21 is fitted into the bolt hole 23, and the forked portion 19 and the connecting member 20 are tightened with a tightening axial force P1 for fastening (Japanese Utility Model Publication No. 57-71810, etc.). reference).

As a result of such surface treatment, the deformation (depression) of the seat surfaces 24, 26 does not proceed during engine operation, and the initial tightening axial force is maintained.

[0014]

However, depending on the operating conditions of the engine, the connecting rod 15 is used under the temperature condition in which high temperature creep occurs (for example, 150 to 200 ° C. in the case of a light alloy connecting rod such as aluminum). There is a possibility that, in this case, the portion worked and hardened by the plastic deformation returns to the original structure by the recovery, and the seat surface 24,
There is a problem that the deformation of 26 progresses and the tightening axial force decreases.

Further, as shown in FIGS. 7 and 8, stress is likely to be concentrated in the plastically deformed depressed portion, which makes it difficult to secure durability on the connecting rod 15 side.

According to the present invention, a bolt capable of uniforming the surface pressure distribution of the member to be fastened at the time of fastening to reduce the maximum surface pressure value itself, avoiding the deformation of the member to be fastened and maintaining the initial tightening axial force. It is intended to provide a conclusion method.

[0017]

According to a first aspect of the present invention, a washer is interposed between a bolt head and a member to be fastened, and before fastening, only the projection surface of the bolt shaft cross section of the bolt head is bolt shaft. Apply a specified load in the direction.

In a second aspect based on the first aspect, the load applied is larger than the bolt tightening load.

A third aspect of the present invention uses the washer of the first and second aspects, which has a lower yield strength than the member to be fastened and a temperature at which high temperature creep occurs is higher than the operating temperature.

According to a fourth aspect of the present invention, in the first to third aspects, the member to be fastened is an engine connecting rod, and the large split end that is connected to the crank pin is fastened with a bolt.

[0021]

In the first aspect of the invention, the washer between the bolt head and the member to be fastened is such that when a predetermined load is applied in the bolt axial direction only to the projection surface of the bolt axial section of the bolt head, It is depressed so that the surface pressure is uniform. Thereby, the surface pressure distribution of the member to be fastened is made uniform at the time of fastening, the maximum surface pressure value is reduced, and the deformation of the member to be fastened is avoided.

In a second aspect of the present invention, the surface pressure is made more uniform by applying a load larger than the bolt tightening load in the first aspect.

According to a third invention, in the first and second inventions,
By using a washer made of a material that has a lower yield strength than the fastened member and the temperature at which high temperature creep occurs is higher than the operating temperature, it is possible to reliably prevent the fastened member from sinking and avoid creep deformation of the washer. Further, a better fastening state can be obtained.

According to the fourth aspect of the invention, the large end portion of the connecting rod of the engine is securely fastened.

[0025]

Embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 is an example applied to a connecting rod of an engine, and shows a main part of a large end portion 41 on the rod body 40 side of a connecting rod connecting structure to a crank pin which has a split structure.

At the fastening portion of the large end portion 41 on the side of the rod body 40, another fastening member (not shown) of the large end portion of the split structure is fastened so that the mating surfaces thereof are superposed and fastened. Also, a bolt hole 42 penetrating the connecting member is provided.

As the bolt 43, a bolt head 44 having an asymmetrical shape is used. According to the shape of the bolt head 44, the bearing surface 4 around the bolt hole 42 of the rod body side fastening portion is used.
A cutout 5 is formed.

A washer 46, which is formed in substantially the same shape as the bolt head 44, is interposed between the bolt head 44 and the seat surface 45 of the rod body side fastening portion.

This washer 46 has a lower proof stress (softer) than the material of the rod body 40, and creep does not occur at the operating temperature (for example, 150 to 200 ° C.) of the connecting rod, that is, the temperature at which high temperature creep occurs is lower than the operating temperature. It is also formed of a high material such as S10C (carbon steel for machine structure) which is close to pure iron.

Before the bolt 43 is fastened, a predetermined pressing device is used to apply a predetermined load to the bolt head 44 in the bolt axial direction.

In this case, as shown in FIG. 2, a load is applied by aligning a press rod 48 having substantially the same diameter as the shaft portion 47 of the bolt 43 with the projection surface of the shaft portion 47 cross section of the bolt head 44.

The load is set so as to exceed the set tightening load of the bolt 43.

Then, after this, the bolt 43 on the connecting member side
A nut (not shown) is attached to the tip of and fastened.

As described above, when a predetermined load is applied to the bolt head 44, the washer 46 interposed between the bolt head 44 and the seat surface 45 of the rod body side fastening portion is depressed.

In this case, the proof stress of the washer 46 is the rod body 4
Since it is lower than 0, the rod body 40 side does not sink, and the load is applied in the bolt axial direction only to the projection surface of the bolt axial section of the bolt head 44. Depending on the shape of the portion 44 and the like, the portion having a higher surface pressure is depressed, that is, the bolt head 44 is depressed so that the surface pressure is uniform.

Therefore, the asymmetrical shape of the bolt head 44,
The influence on the surface pressure due to the rigidity distribution, the squareness error of the bolt head 44 and the shaft portion 47, etc. is prevented, and at the time of fastening,
As described above, the surface pressure distribution on the rod body 40 side is made uniform.

As a result, the maximum surface pressure value on the rod body 40 side is reduced, so that the occurrence of high temperature creep in the rod body 40 is avoided, and the temperature at which high temperature creep occurs is made of a material higher than the operating temperature. The occurrence of high temperature creep of the washer 46 is avoided.

Therefore, the rod body 40 is prevented from being damaged, a good fastening state is secured, and the tightening axial force of the bolt 43 is maintained as set.

The holding ratio of the tightening axial force is 82.9% when there is no washer and no load as compared with the condition when the engine is continuously operated at a working temperature of 200 ° C. for 100 hours.
Which was 93.6% in the present invention.
It has been confirmed that the retention rate is improved.

Since the load to be applied is larger than the set tightening load of the bolt 43, the rod body 40 is fastened at the time of tightening.
The surface pressure distribution on the side is surely made uniform.

[0042]

As described above, according to the first aspect of the present invention, due to the recessed state of the washer, the surface pressure distribution of the member to be fastened is made uniform, and it is possible to prevent the tightening axial force of the bolt from being lowered and to achieve a good fastening. The state is obtained.

According to the second aspect of the invention, the surface pressure distribution of the member to be fastened can be surely made uniform.

According to the third aspect of the present invention, it is possible to avoid the depression of the member to be fastened and the creep deformation of the washer, so that a better fastening state can be obtained.

According to the fourth invention, high reliability of bolt fastening of engine parts is secured.

[Brief description of drawings]

FIG. 1 is a partial perspective view.

FIG. 2 is a sectional view showing a state before a load is applied.

FIG. 3 is a cross-sectional view showing a state when a load is applied.

FIG. 4 is a sectional view showing a surface pressure distribution at the time of fastening.

FIG. 5 is a front view showing a conventional connecting rod fastening method.

FIG. 6 is a characteristic diagram showing a progressive state of depression of the surface layer of the bolt seat surface.

FIG. 7 is a cross-sectional view when fastening the bolt.

FIG. 8 is a cross-sectional view showing the surface pressure distribution.

[Explanation of symbols]

 40 Rod Main Body 41 Large End 42 Bolt Hole 43 Bolt 44 Bolt Head 45 Seat Face 46 Washer 47 Shaft 48 Press Rod

Claims (4)

[Claims] 1. A washer is interposed between a bolt head and a member to be fastened, and a predetermined load is applied in the bolt axial direction only to a projection surface of the bolt axial section of the bolt head before fastening. Bolt fastening method. 2. The bolt fastening method according to claim 1, wherein the applied load is larger than the tightening load of the bolt. 3. The bolt fastening method according to claim 1, wherein a washer made of a material having a lower proof stress than that of a member to be fastened and a temperature at which high temperature creep is generated is higher than an operating temperature is used. 4. The bolt fastening method according to claim 1, wherein the member to be fastened is a connecting rod of an engine, and the large end portion divided into two parts connected to the crankpin is fastened with a bolt.