US3638761A

US3638761A - Three-stage mast assembly for a lift truck

Info

Publication number: US3638761A
Application number: US10481A
Authority: US
Inventors: Shuji Ohta
Original assignee: Toyoda Automatic Loom Works Ltd
Current assignee: Toyota Industries Corp
Priority date: 1969-02-25
Filing date: 1970-02-11
Publication date: 1972-02-01
Anticipated expiration: 1989-02-01
Also published as: DE7006907U; DE2008841A1; GB1253772A; JPS4833578B1

Abstract

A three-stage mast assembly for a lift truck, consisting of an outer mast channel, an intermediate mast channel and an inner mast channel, all of I- or L-shaped cross section, wherein the forward and rearward flanges, respectively, of the intermediate mast channel are arranged rearwardly from the forward and rearward flanges, respectively, of the outer and inner mast channels.

Description

[ 5] Feb.l,l972

[56] References Cited UNITED STATES PATENTS [54] THREE-STAGE MAST ASSEMBLY FOR A LIFT TRUCK d 0 0 w n e e r m 0 m M J mm .L h 5 mm m w K m... n O n N a SK mu n n8 i s .mA 1] 23 77 [i Selsakusho, Aichi Prefecture, Japan Feb. 11, 1970 Primary Examiner-Harvey C. Homsby Attorney-Wenderoth, Lind & Ponack [22] Filed:

211 Appl. No.:

ABSTRACT [30] Foreign Application Priority Data Feb. 25, 1969 A three-stage mast assembly for a lift truck, consisting of an outer mast channel, an intermediate mast channel and an [51] Int. [58] Field of 2 Claims, 7 Drawing Figures PATENTED FEB H972 SHEET 1 BF 2 FIG.

3 IAZ A 21 a L SHUJI OHTA,

ATTORNEY S PATENTEU FEB 1 I972 SHEEY 2 0F 2 FIG.

Jr's

FIG.

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JNVENTOR ATTORNEY THREE-STAGE MAST ASSEMBLY FOR A LIFT TRUCK This invention relates to a three-stage mast assembly for lift truck comprising three channels, viz an outer mast channel, an intermediate mast channel and an inner mast channel.

An object of this invention is to provide an improved arrangement of the mast assembly of the three-stage type, in which the mast assembly has an improved construction, removing the disadvantage inherent in a presently known arrangement of a mast construction of this type. Other objects of the invention will become apparent from the following detailed description taken in conjunction with the accompanying drawings.

In the accompanying drawings,

FIGS. 1 and 2 are side elevations of the three-stage mast assembly for lift trucks heretofore in use;

FIGS. 3 and 4 are explanatory plan views partly in transverse section of said mast assembly shown in FIGS. 1 and 2 respectively;

FIG. 5 is a side view of the mast assembly according to the present invention;

FIG. 6 is an explanatory plan view partly in transverse section of the mast assembly of this invention; and

FIG. 7 is a plan view similar to FIG. 6 showing a modified form of the arrangement of the mast assembly of this invention.

Referring to the drawings, FIGS. 1-4 show the arrangement of the three-stage mast assembly of a type extensively used in lift trucks, the outer mast channel 1, the intermediate mast channel 2 and the inner mast channel 3 being telescopically associated with each other through mast rollers. The forward and rearward flanges 2A-2B of the intermediate mast channel 2 being arranged in line with the forward and rearward flanges lA-lB of the outer mast channel 1 as well as with the forward and rearward flanges 3A-3B of the inner mast channel 3, as shown in FIG. 3. In another type (FIG. 4), the forward and rearward flanges 2A-2B are arranged in the position slightly offset from the forward and rearward flanges lA-lB of the outer mast channel 1 and from the forward and rearward flanges 3A-3B of the inner mast channel 3. In the first example, the intermediate and inner

mast guide rollers

14, 15, I6 and 17 which are in engagement with the adjacent masts receive a moment in the fore and aft direction, and more than two guide rollers will have to be provided within the range of overlap formed at the uppermost position of the intermediate and inner masts. Short distances A and C should be selected and this is constant, so that durability of such mast guide rollers and the bearing surfaces of the masts will be affected. In view of the above, for the purpose of improving the durability of the bearing surfaces of the mast channels and guide rollers, it has heretofore been proposed to employ a three-stage type mast assembly comprising an inner mast, intermediate mast and outer mast, in which the distance between adjacent mast channels may be varied according to the amount of overlap (FIGS. 2 and 4). In such an arrangement, however, the foreand-aft moment varies in proportion to the amount of said overlap, and the distances A and C between the

mast rollers

6 and 7 and 4-5 will vary in proportion to the amount of overlap, so that the durability of the bearing surfaces of the

mast rollers

4', 5, 6' and 7 would be improved. However, the space B between the rearward flange 1B of the outer mast 1 and the forward flange 3A of the inner mast 3 will be increased, so that the center of gravity will be displaced in a forward direction. Moreover, with an enlargement of said distance B, the position of the lift fork will also be displaced forwardly from the front end of the truck chassis, and the distance between the center of gravity of the load materials and the center of the front wheel axle of the truck will be increased, resulting in displacing the center of gravity of the truck, forwardly, thus deteriorating the stability of the truck, and the weight of the balance weight will have to be increased in order to prevent the aforementioned disadvantage. Increase of weight of the said balance weight will result in increase of its size, and the distance between the front wheel axle of the truck, and the rear end of the balance weight will have to be increased accordingly. As a result, the turning radius of the truck will have to be increased, reducing the maneuverability of the truck. With respect to the above-mentioned three-stage mast assembly, the rearward flange 1B of the outer mast l is positioned in the vicinity of the brake drum 19 on the front wheel axle in order to bring the center of gravity of the mast assembly into the vicinity of the truck chassis. In such an arrangement, however, another disadvantage will occur. Arranging the outer mast l in a position as near as possible to the drum 19, means that the rearward flange 1B of the outer mast 1 is arranged behind the forward side of the differential gear case 20, and that the rear side of the lift cylinder 9 can not be arranged in a position in line with the rear flange 18 of the outer mast 1, even if the rear side of the lift cylinder 10 were disposed as near as possible to said gear case 20. Moreover, the lift cylinder 9 for a three-stage mast assembly has a larger diameter in contradistinction to the lift cylinder for a twostage mast assembly, so that the forward side of said lift cylinder 9 will have to project beyond the forward flange IA of the outer mast 1. Consequently, during lifting of the fork said cylinder 9 would contact with any obstacle such as shelves, so that the cylinder 9 would be subject to damage.

Accordingly, an object of the present invention is to provide an improved arrangement of the three-stage mast assembly for a lift truck of the above-mentioned character which is not subject to the foregoing disadvantages. The new arrangement according to this invention will now be described in detail referring to the drawings, FIGS. 5 through 7. The reference numeral l designates the outer mast with the lower end pivoted to the forward part of the lift truck chassis and adapted to be oscillated fore and aft by means of a tilt cylinder (not shown). 2 is an intermediate mast vertically and telescopically slidable relative to said outer mast l, and consists of I- or L-cross section channel. The forward and rearward flanges 2A and 28 thereof are disposed behind the forward and

rearward flanges

1A and 18, respectively of said outer mast l, and nearest to the brake drum l9. 3 is an inner mast consisting of a channel of I- or L-shaped cross section, and is movable in telescopical movement along the said intermediate mast 2. Forward and

rearward flanges

3A, 3B are disposed in front of the forward and

rearward flanges

2A and 2B respectively of the intermediate mast 2, and substantially in line with the forward and rearward flanges 1A 1B of the outer mast l. 4 is a guide roller pivotally mounted on the upper part of the outer mast and engaging with the intermediate mast channel 2. 5 is a guide roller pivotally mounted on the lower part of the intermediate mast 2 and engaging with the outer mast channel 1. Said two

rollers

4 and 5 are engaging with the adjacent masts, so that the intermediate mast 2 is telescopically associated with the outer mast 1, and the fore-and-aft moment of the intermediate mast 2 is transmitted to and the intermediate mast is supported by the outer mast l, as guided by the roller 4. 6 is a guide roller pivotally mounted on the upper part of the intermediate mast 2 and engaging with the inner mast 3. 7 is a guide roller pivotally mounted on the lower part of the inner mast 3 and engaging with the intermediate mast 2. Said two

rollers

6 and 7 are in engagement with the adjacent masts, and the foreand-aft moment of the inner mast 2 is transmitted to and the inner mast is supported by the intermediate mast 2. 9 is a lift cylinder mounted in a position near the differential gear casing 20, from which extends the

piston rods

10 and 11. The upper end of the uppermost piston rod I1 is associated with the upper end of the inner mast 3. I2 is an engagement member on the lower end of the

inner mast

3, and 13 is another engagement member or a supporter on the intermediate mast 2, adapted to transmit the lifting motion of the inner mast and to support said inner mast in the desired position. 8 is a lift bracket adapted for vertical movement by the engagement of the lift roller 21 with the inner mast 3.

The three-stage mast assembly according to the invention being arranged in the manner substantially as described and illustrated, it will be seen that when the

piston rods

10 and 11 are extended by operating the lift cylinder 9, the inner mast 3 will be elevated. When the mast 3 reaches the predetermined position, the engaging element 12 will engages with the engaging element 13 of the intermediate mast 2, finishing thereby the first stage elevating operation. By continued operation of the lift cylinder 9, the said piston rod 1 1 will be extended, so that the intermediate mast 2 will be elevated, being pulled by the inner mast 3.

From the foregoing, it will be understood that the characterizing feature of the present invention resides in the fact that the intermediate mast channel 2 of I- or L-shaped cross section is arranged with its forward and rearward flanges 2A and 28 arranged rearwardly from the forward and

rearward flanges 1A

1B and 3A 3B, respectively, of the outer mast 1 and of the inner mast 3, as shown in H0. 6, all masts being so arranged that the forward and

rearward flanges

3A and 3B of the inner mast 3 are positioned substantially in line with the forward and rearward flanges 1A 1B of the outer mast 1. In the prior arrangement of a three-stage mast assembly, the front part of the lift cylinder 9 will have to be disposed forwardly from the forward flange 1A of the outer mast 1. In contradistinction to the above, according to the present invention, the forward flange 1A of the outer mast 1 can be placed forwardly from the forward flange 2A of the intermediate mast 2 which is nearest to the truck chassis in the vicinity of the brake drum 19, so that the forward flange 1A of the outer mast 1 may be disposed forwardly of the front part of the lift cylinder 9. Consequently, said rearward flange 1A serves to protect the lift cylinder 9, thus removing the disadvantage of damage to the lift cylinder liable to occur due to the interference thereof with shelves provided in a low position.

Moreover, the distance B (FIG. 6) between the

forward flanges

3A and 1A, respectively, of the

masts

3, 1 and the rearward flange 2B of the intermediate mast 2 is shorter than the corresponding distance B in case of the prior art arrangement of the mast assembly (FIG. 4). As a result of such improvement, the center of gravity of the mast assembly is displaced to a position rearwardly from the center of the outer mast 1, viz.

nearer to the truck chassis. Consequently, the distance between the center of gravity of the load materials on the lift fork and the center of the front wheel axle of the lift truck is shortened. The center of gravity of the truck per se remains on the rear side of the truck, resulting in an increase of the stability of the truck, minimizing the size of the required balance weight as well as minimizing the distance between the front wheel axle and the rear end of the chassis, whereby the turning radius of the truck can be minimized.

According to the present invention, as will be seen from the foregoing, the forward and

rearward flanges

2A and 2B of the intermediate mast are arranged rearwardly from the forward and

rearward flanges

1A and 1B and 3A and 38, respectively, of the outer and inner masts, thereby attaining the advantageous result for to the mast assembly consisting of channels of lor L-shaped cross section.

I claim:

1. In a three-stage mast assembly for a lift truck having a pair of outer mast channels, a pair of intermediate mast channels between and telescopically associated with said outer mast channels respectively, and a pair of inner mast channels between and telescopically associated with said intermediate mast channels respectively, each of said mast channels having opposed forward and rearward, with respect to the truck, flanges, the distance between said flanges being equal on all channels; the improvement wherein said forward and rearward flanges of each said intermediate mast channel are positioned rearwardly of said forward and rearward flanges each said outer mast channel respectively, and said forward and rearward flanges of each said inner mast channel are arranged forwardly of said forward and rearward flanges of each said in termediate mast channel.

2. The improvement as claimed in claim I wherein said forward and-rearward flanges on said outer mast channels are aligned, in the direction between the channels of the pairs of channels, with the flanges or said ipne; mast channels.

Claims

1. In a three-stage mast assembly for a lift truck having a pair of outer mast channels, a pair of intermediate mast channels between and telescopically associated with said outer mast channels respectively, and a pair of inner mast channels between and telescopically associated with said intermediate mast channels respectively, each of said mast channels having opposed forward and rearward, with respect to the truck, flanges, the distance between said flanges being equal on all channels; the improvement wherein said forward and rearward flanges of each said intermediate mast channel are positioned rearwardly of said forward and rearward flanges each said outer mast channel respectively, and said forward and rearward flanges of each said inner mast channel are arranged forwardly of said forward and rearward flanges of each said intermediate mast channel.

2. The improvement as claimed in claim 1 wherein said forward and rearward flanges on said outer mast channels are aligned, in the direction between the channels of the pairs of channels, with the flanges on said inner mast channels.