JPH061594A - Mast supporting system for forklift truck - Google Patents

Abstract

PURPOSE:To reduce the stress concentration of welded parts to outer masts and to enhance the strength of lower mast parts by securing a lower beam positioned on a pair of right and left masts at their back lower parts to outer mask back surfaces through a reinforcing member comprising an oblong plate member. CONSTITUTION:A right and a left outer masts 1 (11) on a forklift truck are mutually connected at their lower ends by means of a lower beam 2 (14) at their back surface sides. The right and left outer masts 1 are mounted tiltably before and after on a base at its pivot shaft 12 through a right and a left mast pivot brackets 13 positioned on their lower back sides. In this case, a reinforcing member 8 comprising an oblong plate member having a longitudinally long rectangular shape in its cross section is positioned at the lower end back sides of the right and left outer masts 1 and also at the outer side position from a lift cylinder 16. The lower beam 2 is secured to the right and left reinforcing members 8 at their inside lower ends by welding. Thus, the stress concentration of the welded parts to the outer masts 1 is relieved.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a mast support device for a forklift in which lift cylinders are arranged behind a pair of left and right masts.

[0002]

2. Description of the Related Art FIGS. 5 and 6 show a mast support device of this type which is generally known in the prior art. As shown, the outer mast 11 of the mast unit has a lower end supported by a pivot shaft at the lower front end of the vehicle body, specifically, a front axle housing 12 via a mast pivot bracket 13 so as to be able to tilt forward and backward, and not shown. It is tilted back and forth by a tilt cylinder. Also,
The left and right mast pivot brackets 13 are fixed to the lower beam 14 which is horizontally arranged on the lower side of the rear surface of the outer mast 11 and extends left and right, and the rear end surface of the beam 15 which is arranged above the lower beam 14. Both beams 14 and 15 have a structure in which the front end edges of the outer mast 11 are fixed to the rear surface of the outer mast 11 by welding. It should be noted that the lift cylinders 16 arranged at the rear of the left and right masts, respectively.
Are supported by the lower beam 14 arranged at the lower end of the mast.

[0003]

However, in the case of the above-described mast support device, a backward bending moment M acts on the lower beam 14 supporting the lift cylinder 16 as shown in FIG. Then, due to the bending moment M, the stress is concentrated particularly at the point A in the figure in the welded portion between the lower beam 14 and the outer mast 11, which may cause cracks in the outer mast 11.
In the conventional mast support device, as shown in FIGS. 7A and 7B, the load applied to the cylinder support center of the lower beam 14 is F, the distance from the rear end surface of the outer mast 11 to the cylinder support center is a, and the lower beam is If the thickness of 14 is h and the stress generated in the welded portion A is σ, this stress σ
Shows that the cross-sectional modulus Z of the welded portion, which is indicated by hatching in FIG. 7B, is Z = 1 / 6H (BH ³ −bh ³ ) ... (1), so σ = Fa / Z .... …………… (2). If the stress σ generated in the welded portion A is to be reduced, B and b are limited by the flange width W of the outer mast 11, and therefore the thickness h of the lower beam 14 having flexibility is set to a large value to obtain a section coefficient. Although it can be achieved by increasing Z, however, such a countermeasure to increase the thickness h of the lower beam 14 causes other problems such as an increase in overall height and an increase in weight. become.

In view of the above-mentioned problems, therefore, the present invention is to solve the technical problem to be solved by providing a mast support device for a forklift truck capable of increasing the strength of the mastro section without causing other problems. And

[0005]

In order to solve the above problems, the present invention is configured as follows. That is, a lift cylinder arranged on the rear surface of the mast is erected on the lower beam arranged on the lower part of the rear surface of the pair of left and right masts, and a mast pivot bracket fixed to the rear end of the lower beam is a pivot shaft of the machine base. A mast support device for a forklift mounted in a tiltable manner at a lower part of a rear surface of the mast and at a position outside the lift cylinder, the reinforcement consisting of a vertically long plate member having a substantially rectangular cross section in the front-rear direction. While arranging the members, the front edge of the reinforcing member is fixed to the rear surface of the mast, while the end portion of the lower beam is fixed to the lower end portion on the inner surface side of the reinforcing member with a gap left from the rear surface of the mast. Is characterized by.

[0006]

In the mast support device according to the present invention constructed as described above, the reinforcement members are fixed to the rear surfaces of the left and right outer masts, respectively, and the lower beam is fixed to the left and right reinforcement members. As a result, it becomes possible to set the welding portion A shown in FIG. 1 where a large stress is generated among the welding portions of the reinforcing member and the outer mast at a position higher than the upper surface of the lower beam. As a result, the stress generated in the welded portion A is greatly reduced, and the strength of the mastro part is increased.

[0007]

Embodiments of the present invention will be described below in detail with reference to the drawings. The outer masts 1 on the left and right of the mast unit in the forklift truck are connected to each other on the rear surface side by an upper beam (not shown) in the upper portion, a middle beam (not shown) in the middle portion, and a lower beam 2 in the lower portion. Also, the left and right outer masts 1
Is attached to the pivot shaft of the machine base, specifically, the front axle housing 6 through left and right mast pivot brackets 4 installed on the lower rear surface side thereof so as to be tiltable forward and backward, and tilted forward and backward by a tilt cylinder (not shown). It
Furthermore, lift cylinders 3 are provided behind the mast.
And the lift cylinder 3 is supported by the lower beam 2.

In the mast support device having the above structure, however, the lower beam 2 arranged horizontally in the left-right direction is fixed to the outer mast 1 via the reinforcing member 8. That is, reinforcing members 8 are arranged on the rear surface side of the lower end portions of the left and right outer masts 1 and at positions outside the lift cylinders 3, and these reinforcing members 8 are vertically long and have a substantially rectangular transverse cross section. Of the plate member, the front end edge of which is fixed to the rear surface of the outer mast 1 by welding. The left and right edges of the lower beam 2 are fixed to the lower ends of the inner side surfaces of the left and right reinforcing members 8 by welding, and face the rear surface of the outer mast 1 with a slight gap.

The mast pivot bracket 4 is a vertically elongated member having a substantially T-shaped cross section similar to the conventional one, and the lower end edge of the front plate 5 is fixed to the rear end surface of the lower beam 2 by welding, and the upper end edge is It is fixed to the lower end of the beam 7 arranged above the lower beam 2 by welding. The beam 7 is arranged rearward of the lift cylinder 3 so as to avoid interference with the lift cylinder 3, and both ends of the beam 7 are bent forward on the outside of the lift cylinder 3, and the front edge of the beam 7 is bent. Is fixed to the rear surface of the outer mast 1 by welding.

In the mast support device of the present embodiment constructed as described above, the lower beam 2 supporting the lift cylinder 3 has a lower beam 2 as shown in (a) and (b) of FIG. As in the conventional case, a backward bending moment M as shown by an arrow in the figure acts, and due to this bending moment M, stress concentrates particularly at a point A in the figure in the welded portion between the reinforcing member 8 and the outer mast 1. The stress σ ′ generated in the welded portion A is F, the load applied to the cylinder support center of the lower beam 2 of the reinforcing member 8, a is the distance from the rear end surface of the outer mast 1 to the cylinder support center, and h is the height of the reinforcing member 8. If this is the case, this stress σ ′ is determined by the cross-sectional modulus Z ′ of the welded portion indicated by diagonal lines in FIG. 3B: Z ′ = 1 / 6H ′ (B′H ′ ³ -b′h ′ ³ ) Since (1), σ '= Fa / Z' ………………………… To become (2). When the lower beam 2 is fixed to the outer mast 1 via the reinforcing member 8 as in this embodiment, the height h'of the reinforcing member 8 is the same as that of the conventional lower beam 2 shown in FIG. It is possible to set it to be much larger than the thickness h. That is, since the welded portion A can be set far above the upper surface of the lower beam 2,
"Stress σ'of this embodiment <conventional stress σ" can be set, and the stress in the vicinity of the welded portion A can be significantly reduced as compared with the conventional case.

This can also be confirmed from the stress test example. That is, FIG. 4 is a stress comparison diagram of the welded portion A between the mast support device according to the present embodiment and the conventional mast support device. The stress test is performed by applying the maximum lift and maximum load of the mast unit. In the stationary state, the magnitude of stress generated in the welded portion A was measured using a strain gauge. However, the height h ′ of the reinforcing member 8 was set to about 3 times the thickness h of the lower beam 2, and the other conditions were the same as the conventional one. Therefore, according to the above stress test example, the stress σ generated in the conventional welded portion A is Pkg.
/ Thing was cm ² is the stress in the case of the present embodiment sigma 'is
It has been reduced to 0.4 Pkg / cm ² . As described above, when the configuration in which the lower beam 2 is fixed to the outer mast 1 through the vertically long reinforcing member 8 is adopted, the stress of the welded portion A is reduced and the strength of the mastroe portion is increased as compared with the conventional case. It

It is desirable that the height of the reinforcing member 8 be the upper limit near the tilt center of the outer mast 1.
This is because a forward bending moment acts on the outer mast 1, and this bending moment is maximized at the center of connection with the tilt cylinder and gradually decreases below that, and becomes zero at the tilt center. That is, the height of the reinforcing member 8 should be set within a range in which the forward bending moment acting on the outer mast 1 with respect to the welded portion A does not influence.

[0013]

As described in detail above, according to the present invention,
By fixing the lower beam to the rear surface of the outer mast via a reinforcing member consisting of a vertically long plate member, it is possible to reduce the stress concentration of the welded part on the outer mast and increase the strength of the mastro part, which helps improve safety, and Since the lower beam having the same thickness as the conventional one can be used, there is no adverse effect such as an increase in overall height and an increase in weight.

[Brief description of drawings]

FIG. 1 is a side view showing a mast support device according to an embodiment of the present invention.

FIG. 2 is a view on arrow X in FIG.

FIG. 3 is a stress explanatory view of an outer mast welded portion according to the present embodiment.

FIG. 4 is a stress test comparison diagram between the present embodiment and the conventional example.

FIG. 5 is a side view showing a conventional mast support device.

6 is a view on arrow Y of FIG.

FIG. 7 is a stress explanatory diagram of a conventional outer mast welded portion.

[Explanation of symbols]

1 ... Outer mast 2 ... Lower beam 3 ... Lift cylinder 4 ... Mast pivot bracket 8 ... Reinforcing member

Claims (1)

[Claims] 1. A lift cylinder disposed on the rear surface of the mast is erected on a lower beam disposed on the lower portion of the rear surface of the pair of left and right masts, and a mast pivot bracket fixed to the rear ends of the lower beams is a machine base. Is a mast support device for a forklift that is tiltably attached to the pivot shaft of the vertical plate member having a substantially rectangular cross section at the lower part of the rear surface of the mast and outside the lift cylinder. While arranging a reinforcing member consisting of, while fixing the front end edge of the reinforcing member to the rear surface of the mast, at the lower end portion on the inner surface side of the reinforcing member with the end portion of the lower beam leaving a gap with respect to the rear surface of the mast. A fixed forklift mast support device.