JPH09111796A - Boom for hydraulic shovel - Google Patents

Abstract

PROBLEM TO BE SOLVED: To enhance the fatigue life of a bracket by forming a spacing between the ends at a hydraulic cylinder side and at opposite side of a pair of plate members of the bracket narrower than the interval of portions with holes for coupling hydraulic cylinders. SOLUTION: A pair of plate members 31 and 32 constituting a bracket are bent symmetrically at almost vertical lines A about a center line between the plate members almost at the middle of the plate members longitudinally, and end portions 31a and 32a at the opposite side of a position, where a hydraulic cylinder is arranged, are welded with a gap (d), which is narrower than the gap d0 where the hole 8 is provided. Then, the gap d0 is set in a range of 0.4-0.8 of the gap (d). Next, a force acting to a bucket during excavation is applied to a boom, and a compressive force and a tensile stress occurred at the boom are canceled each other by shifting the ends 31a and 32b of a pair of plate members where the maximum compressive stress occurs to a central portion in a boom width direction where the tensile stress becomes the maximum, and the fatigue life of the bracket can be improved by reducing this compressive stress.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a hydraulic excavator boot having a bracket for connecting hydraulic cylinders.
The present invention relates to a boom for a hydraulic excavator having an improved fatigue life of a bracket, particularly a bracket.

[0002]

2. Description of the Related Art Conventionally, hydraulic excavators have been widely used in civil engineering, construction work and the like. As shown in FIG. 5, this hydraulic excavator has a main body having a steering section 11, a prime mover section 12, a traveling unit 13, and a swivel base 14, and a set of booms 2 and an arm.
The arm 3 is connected so that it can bend and extend, and the bucket 9 is attached to the tip of the arm 3 so as to be able to drive and swing. Both the boom 2 and the arm 3 are collectively referred to as a boom for a hydraulic excavator in the present invention.

A hydraulic cylinder 7 is provided in each of the booms 2 and 3.
a and 7b are provided, and the boom 3 is a hydraulic cylinder.
The bucket 7 can be bent and stretched with respect to the boom 3 by a hydraulic cylinder 7b. The hydraulic cylinders 7a and 7b are arranged along the booms 2 and 3, and a bracket 1 is provided in each of the booms 2 and 3 to connect the hydraulic cylinders 7a and 7b.

A typical example of the booms 2 and 3 for the hydraulic excavator will be described with reference to the boom 2 as an example with reference to FIG. The boom 2 is formed by combining the upper plate 4, the lower plate 5 and the both side plates 6 so as to have a rectangular cross section, and has a dogleg shape as a whole. A bracket 1 for connecting a hydraulic cylinder 7a arranged along the main body is mounted on the upper plate of the boom 2. As shown in FIG. 7, the bracket 1 has a pair of plate members 21 and 22 arranged facing each other at equal intervals, and the plate members 21 and 22 are provided with holes 8 for connecting the hydraulic cylinder 7a. . In addition, 8a is a boss provided as needed. The plate members 21 and 22 of the bracket 1 are configured to be welded to either the upper plate 4 or the lower plate 5 of the boom symmetrically and parallel to the center in the plate width direction. The bracket 1 has a function of supporting the hydraulic cylinder 7a at a portion of the hole 8 via a pin and transmitting the thrust of the hydraulic cylinder 7a to the boom 2 during operation.

When the bracket 1 receives the thrust force of the hydraulic cylinder 7a, the bracket 1 is welded to the pair of plate members 21 and 22 through a hole 8 for connecting the hydraulic cylinder 7a.
The mechanism is such that stress is transmitted to the upper plate 4 of the boom 2 and thrust is transmitted to the boom 2. When the thrust of the hydraulic cylinder 7a is received during excavation work, the upper plate 4 of the boom 2 to which the pair of plate members 21 and 22 are welded is bent inward and deformed. Further, stress concentration occurs on the upper plate 4 of the boom 2 where the ends of the pair of plate members 21 and 22 are in contact with each other. In particular, it has been confirmed that high compressive stress is generated at the ends 21a and 22a on the side opposite to the side where the hydraulic cylinder 7a is arranged.

Since the hydraulic cylinder is repeatedly operated,
The upper plate of the boom is repeatedly deformed, and the fatigue strength at the ends 21a and 22a of the bracket 1 where compressive stress with higher stress concentration occurs is reduced, which is a problem. In order to prevent this decrease in fatigue strength, the following measures have been conventionally proposed. That is, (a) the plate member 2 of the bracket 1
The ends 21a and 22a of Nos. 1 and 22 are bent and joined to form an annular shape and then welded to disperse the load applied to the upper plate.
No. 95754) and (b) Plate material 2 of bracket 1
Place the mounting positions of 1, 22 on the side plates 6, 6 of the boom,
The load is borne by the side plates 6 and 6 (Actual No. Sho 58-63254)
Is what you do.

In the method (a), the stress from the hydraulic cylinder is dispersed by the end of the bracket which is bent and joined to form an annular shape. In the method (b), the stress acting on the upper plate 4 or the lower plate 5 from the bracket can be borne by the side plates 6, 6 of the boom, whereby the upper plate 4 or the lower plate 5 of the boom can be loaded. It is considered possible to prevent stress concentration.

[0008]

However, in the above-mentioned item (a) in which both ends of the bracket 1 are bent and joined and welded in an annular shape, the tip of the bracket 1 is also welded in an annular shape. In consideration of the bending of 4 as well, there is a problem that stress concentration occurs in the center of the upper plate 4 and conversely the fatigue strength may be reduced. Furthermore, the shape of the bracket 1 becomes complicated, and an increase in processing and welding construction costs cannot be avoided. Further, in the case of (B) where the plate members 21 and 22 of the bracket 1 are mounted on the side plates 6 and 6 of the boom, the width direction of the bracket 1 is abnormal due to the relationship between the boom width and the hydraulic cylinder size. It is expected that it will become too large to implement.

Therefore, the present invention provides a boom for a hydraulic excavator which does not complicate the shape of the bracket and fits within the width of the boom so that stress concentration at the end of the bracket can be relaxed. The purpose is to do.

[0010]

In order to achieve the above-mentioned object, the invention according to claim 1 of the present invention is characterized in that (A) an upper plate, a lower plate and both side plates are combined to form a rectangular cross section. The booms 2 and 3 formed on the upper and lower bodies are welded to one of the upper plate and the lower plate.
The bracket 1 for connecting the hydraulic cylinders 7a, 7b arranged along the main body is provided, and the bracket 1 has a pair of plate members 31, 32 arranged to face each other. In the hydraulic excavator booms 2 and 3 provided with the holes 8 for connecting the hydraulic cylinders 7a and 7b, (B) the pair of plate members 31 and 32 are
The upper plate 4 and the lower plate 5 are symmetrical with respect to the center in the width direction, and are attached so as to be spaced apart from each other so as not to ride on the side plates 6, 6, and (C) the pair of plate members 31, 32. The pair of plate members are formed in such a shape that the distance between the ends 31a, 32a on the side opposite to the side where the hydraulic cylinders 7a, 7b are arranged is smaller than the distance at the portion where the holes 8 are provided. It is the formed structure.

During excavation work of the hydraulic excavator, the booms 2 and 3 are bent in the longitudinal direction thereof, and the upper plate 4 or the lower plate 5 is deformed so as to bulge outward. Due to this deformation, a tensile stress is generated on the surface of the upper plate 4 or the lower plate 5, and becomes the largest at the center in the width direction of the boom. This tensile stress and bracket 1
The ends of the pair of plate members 31 and 32 are offset by the compressive stress exerted on the upper plate 4 or the lower plate 5. In order to make this offset effective, if the edges of the plate materials are attached, the concentration of compressive stress will be greater. Therefore, it is effective to make it narrow enough not to stick together.

According to a second aspect of the present invention, in the configuration of the first aspect of the invention, the pair of plate members 3 of the bracket 1 are provided.
The distance between the narrowed ends of 1, 32 is 0.4 to the distance between the plate materials 31, 32 in the portion where the hole 8 is provided.
It is characterized by being in the range of 0.8. When the space between the narrowed ends 31a and 32a of the plate materials 31 and 32 satisfies the above condition, the stress at the edge of the plate material and the tensile stress of the upper plate or the lower plate are offset, and a stress reduction of about 10% is expected. it can.

According to a third aspect of the present invention, in the configuration according to the first or second aspect of the invention, the side where the hydraulic cylinder 7a is disposed from the hole 1 of the pair of plate members 31 and 32 of the bracket 1. Bend the upper plate 4 or the lower plate 5 inward at appropriate positions up to the ends 31a, 32a on the opposite side,
It is characterized in that the narrowed end is formed.

A pair of plate members 31, 32 of the bracket 1
It is possible to reduce the generated stress by not bending the shape of the bracket 1 and making the ends 31a and 32a of the bracket that are narrowed by bending inward.

[0015]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiments of the present invention will be described with reference to illustrated examples. FIG. 1 is a schematic view of a bracket arranged in a boom for a hydraulic excavator, and FIG. 2 is a schematic view of another bracket arranged in a boom for a hydraulic excavator.

Since the hydraulic excavator and the boom described with reference to FIGS. 5 and 6 are the same as those of the present invention, the description thereof will be omitted. 1 is different from FIG. 7 in that the vertical line A in the middle of the longitudinal direction of the pair of plate members 31 and 32 forming the bracket.
Are bent symmetrically inward with respect to each other, and the distance between the portions where the holes 8 are provided; the distance narrower than d ₀ ; the ends 31a and 32a opposite to the side where the hydraulic cylinder 7a is arranged at d are welded. It is configured. 2 is different from FIG. 7 in that the plate members 31 and 32 forming the bracket are provided with the holes 8 for connecting the hydraulic cylinders 31c,
The spacing of 32c remains d ₀ , and the remaining portions of the pair of plate members are attached near the center of the boom 2 in the width direction. Cylinder side end 31 of the pair of plate members 31, 32 of the blanket 1
b, 32b and the distance between the ends 31a, 32a on the opposite side of the cylinder; d is the distance between the portions 31c, 32c provided with the holes 8;
It is configured to be welded narrower than d ₀ .

Next, the operation of the boom shown in FIGS. 1 and 2 will be described. The boom 2 exerts a force on the bucket 9 during excavation.
In addition to the boom 2, the boom 2 is bent, the rectangular cross section of the boom 2 is dented in the center of the side plate 6, and the upper plate 4 and the lower plate 5 are formed.
Then, the deformation that the center protrudes occurs. As a result, a tensile stress is generated on the front side of the upper plate 4 of the boom 2, and the place where the maximum stress is generated is the central portion in the width direction of the boom 2.
On the other hand, the thrust acting from the hydraulic cylinder 7a to the boom 2 during operation is compressive stress, and the ends 31a, 3a of the pair of plate members of the bracket 1 on the side opposite to the side on which the hydraulic cylinder 7a is arranged.
It was stated that stress concentrates on 2a.

Hydraulic cylinder 7a which produces the maximum compressive stress
The compressive stress and the boom are generated by moving the ends 31a, 32a of the pair of plate materials of the bracket 1 on the side opposite to the side where the is arranged to the central portion in the boom width direction where the tensile stress is maximum. It is possible to cancel the tensile stress. As shown in FIGS. 1 and 2, the pair of plate members 31, 3 of the bracket 1
Of the two ends, the distance between the ends 31a and 32a on the side opposite to the side on which the hydraulic cylinder 7a is arranged; d is the hydraulic cylinder 7a.
Are arranged so as to be narrower than the distance; d ₀ at the portion where the holes 8 provided in the bracket for connecting the are connected. Tensile stress is generated on the front side of the upper plate 4 or the lower plate 5 of the boom 2 during excavation work of the hydraulic excavator, and the compressive stress exerted by the ends 31a, 32a of the pair of plate members of the bracket 1 on the upper plate or the lower plate is offset. Then, this compressive stress is reduced. Further, the ends 31a and 32a of the pair of plate members of the bracket 1 are attached to the boom 2
When approaching the central portion in the plate width direction, the compressive stress exerted on the upper plate 4 or the lower plate 5 is further reduced, but on the other hand, the stress concentration increases and the effect of reducing the compressive stress decreases. Finally, the sticking maximizes the stress concentration, and conversely increases the compressive stress exerted on the upper plate 4 or the lower plate 5 by the ends 31a and 32a of the pair of plate members of the bracket 1.

As shown in FIG. 1, a pair of plate members 31 and 32 of the bracket 1 are bent inward to form the narrowed ends 31a and 32a of the bracket 1 so that the shape of the bracket 1 is complicated. It is possible to reduce the generated stress without increasing the stress and improve the fatigue life. Further, as shown in FIG. 2, by disposing both ends of the pair of plate members 31 and 32 of the bracket 1 from the center in the width direction of the boom 2, it is possible to reduce the stress generated at both ends and to reduce the fatigue life. Can be further improved.

In the above embodiment, the boom 2 on the main body side of the hydraulic excavator is used as the boom.
It can also be applied to program 3. The hydraulic cylinder may be attached to the lower plate instead of the upper plate, and the present invention can be applied to this case as well.

[0021]

EXAMPLE A specific example of using the boom of FIG. 1 in a hydraulic excavator of a 20-ton class will be described below. Bracket plate length is 1140mm, thickness is 2
5 mm, the distance between the portions in which the holes in which the cylinders are provided are provided; d ₀ is 180 mm, and the length from the holes in the plate material to the end on the opposite side to the side in which the cylinders are arranged is 750 mm. The width of the upper plate of the boom is 370 mm. 3 from the hole of the plate to the end opposite to the side where the cylinder is installed.
The 00 mm portion was bent toward the upper plate of the boom and welded so that the distance d between the ends of the bracket was 120 mm. In addition, it was actually measured that the stress generated at the end of the bracket was reduced by 30% as compared with the stress generated at the end of the bracket having the same shape shown in FIG. 7.

Also, as shown in FIG. 2, in the case where two brackets are arranged in advance on the lower plate of the boom from the center in the width direction of the boom, the stress generated at the end of the bracket is reduced. I was able to do it. Further, in any of the hydraulic cylinders used in any of the embodiments, it was difficult to mount the bracket on the side plate of the boom.

Further, among the ends of the pair of plate members of the bracket, the distance between the ends on the side opposite to the side on which the cylinder is arranged;
It was examined by the finite element method that the generated stress is reduced by making the shape such that d is narrower than the distance d ₀ in the portion where the holes are provided. Figure 3 shows the effect of bracket spacing on the stress generated at the bracket ends. For the calculation, the model of the hydraulic excavator boom shown in FIG. 8 was used to analyze the actual excavation conditions by the finite element method.

From these results, it has been found that the stress at the tip of the annularly welded bracket is not reduced by the method of bending and joining both ends of the bracket of the above-mentioned (c), which is welded in an annular shape. did. That is, when the ends of the brackets are aligned, stress concentration occurs on the ends of the brackets. In some cases, stress may increase.

As shown in FIG. 3, the distance between the ends of the bracket; the distance between the portions where holes for connecting the cylinders d are provided; d ₀ within the range of 0.4 to 0.8 ,
It has been found that the stress at the end of the bracket opposite the side where the cylinder is located is reduced by more than 10%. Fatigue design guideline / commentary shown in Fig. 4 (edited by Japan Steel Structure Association, 199)
3 years, p33) SN diagram
It was estimated that the fatigue life was increased by about 2 times by the decrease of 0%, and it was found that the fatigue life was significantly improved. It was confirmed that the stress generated at the end of the bracket can be reduced and the fatigue life can be improved by narrowing the interval between the ends of the bracket.

[0026]

According to the first and second aspects of the present invention, in the boom for a hydraulic excavator, the pair of plate members of the bracket arranged in the boom is either an upper plate or a lower plate. The brackets are symmetric with respect to the center in the width direction and are attached so as not to ride on the side plate, and the distance between the ends of the bracket is the side of the pair of plate members of the bracket on which the cylinder is arranged. The distance between the ends on the opposite side is set to be narrower than the distance in the portion of the plate member provided with the hole for connecting the cylinders. Specifically, the distance between the narrowed ends of the plate material is 0.4 to 0.8 with respect to the distance between the plate materials in the portion where the holes are provided,
It is a configuration in which the pair of plate members are formed. As a result, during the operation of the hydraulic excavator, the compressive stress generated at the end of the bracket on the side opposite to the side where the cylinder is arranged and the tensile stress of the upper plate or the lower plate are canceled out, and the fatigue life of the bracket. Is improved.

According to the second aspect of the invention, since the pair of plate members constituting the blanket are simply bent,
The effect is that the increase in manufacturing cost will be small.

[Brief description of the drawings]

FIG. 1 is a schematic view of a bracket arranged in a boom for a hydraulic excavator according to the present invention.

FIG. 2 is a schematic view of another bracket arranged in the boom for a hydraulic excavator of the present invention.

FIG. 3 is a diagram showing an influence of a bracket interval on a stress generated at an end of the bracket.

FIG. 4 is an SN diagram of a steel structure.

FIG. 5 is an overall view of a hydraulic excavator.

FIG. 6 is a side view and a top view of a boom for a hydraulic excavator.

[Fig. 7] Fig. 7 shows a conventional example, and is a hydraulic excavator boom.
FIG. 3 is a schematic view of a bracket arranged on the frame.

FIG. 8: A hydraulic excavator boom analyzed by the finite element method.
FIG.

[Explanation of symbols]

1 bracket 2 boom 3 boom (arm) 4 upper plate of boom 5 lower plate of boom 6 side plate of boom 7a hydraulic cylinder 7b hydraulic cylinder 8 bracket for connecting hydraulic cylinders Hole 8a provided in the bracket 8 boss of a hole provided in the bracket 9 bucket 11 control section 12 motor section 13 strike device 14 swivel base 21 pair of plate members of bracket 22 pair of plate members of bracket 31 pair of plate members of the bracket of the present invention 32 A pair of plate materials of the bracket of the present invention d ₀ Interval of portions provided with holes for connecting cylinders d Interval of brackets on the side opposite to the side where the cylinders are arranged

Claims (3)

[Claims] 1. A boom main body formed by combining an upper plate, a lower plate and both side plates so as to have a rectangular cross section, and attached to either of the upper plate and the lower plate by welding.
A bracket for connecting the hydraulic cylinders arranged along the boom body, the brackets having a pair of plate members arranged opposite to each other, for connecting the hydraulic cylinders to the plate members. In the boom for a hydraulic excavator provided with the holes, the pair of plate members are symmetrical with respect to the center of either the upper plate or the lower plate in the width direction and do not ride on the side plate. Of the pair of plate members, the pair of plate members having a shape in which the distance between the ends on the side opposite to the side where the hydraulic cylinder is arranged is narrower than the distance in the portion where the holes are provided. A boom for a hydraulic excavator, which is characterized in that a plate material of is formed. 2. The distance between the narrowed ends of the plate members is the distance between the pair of plate members in the portion where the holes are provided,
The boom for a hydraulic excavator according to claim 1, wherein the boom is in the range of 0.4 to 0.8. 3. The sheet is narrowed by being bent toward the inside of the upper plate and the lower plate at a proper position from the hole of the pair of plate members to the end opposite to the side where the hydraulic cylinder is arranged. The boom for a hydraulic excavator according to claim 1 or 2, wherein an end is formed.