GB2077224A

GB2077224A - Load handling mast for a truck

Info

Publication number: GB2077224A
Application number: GB8116846A
Authority: GB
Original assignee: ASEA AB
Current assignee: ABB Norden Holding AB
Priority date: 1980-06-03
Filing date: 1981-06-02
Publication date: 1981-12-16
Also published as: NL8102560A; DK230181A; GB2077224B; DE3120235A1; NL192614B; FR2483386B1; FI68600C; DK148681C; DK148681B; NO811858L; JPS5723593A; FR2483386A1; FI811670L; DE3120235C2; NO151235C; SE8004116L; FI68600B; NO151235B; NL192614C; JPH0336760B2

Abstract

A load handling mast for a truck, in particular for a fork lift truck, includes a first mast section 1 intended to be mounted on a truck, a second mast section 2 mounted on, and movable substantially vertically relative to, the first mast section 1, a third mast section 3 mounted on, and movable substantially vertically relative to, the second mast section 2, a load carrying member, for example a fork carrier 4, mounted on, and movable substantially vertically relative to, the third mast section 3, and fluid- operated piston and cylinder means 5 mounted in the second mast section 2 for effecting these relative movements. The piston and cylinder means 5 has a first upwardly projectable piston rod 7 on which is mounted a first pulley wheel 9 and a second downwardly projectable piston rod 6 on which is mounted a second pulley wheel 8. A first rope or chain 11 is attached at one end to the upper portion of the first mast section 1, passes around the pulley wheel 8, passes around a third pulley wheel 10 mounted on the upper portion of the third mast section 3 and has its other end attached to the fork carrier 4. A second rope or chain 12 is attached at one end to the second mast section 2, passes around the pulley wheel 9 and is attached at its other end to the lower portion of the third mast section 3. <IMAGE>

Description

SPECIFICATION Load handling mast for a truck This invention relates to a load handling mast for a truck, in particular for a fork lift truck, the mast being of the kind comprising a first mast section intended to be mounted in a truck, a second mast section mounted on, and movable substantially vertically relative to, the first mast section, a third mast section mounted on, and movable substantially vertically relative to, the second mast section, a load carrying member, for example a fork carrier, mounted on, and movable substantially vertically relative to, the third mast section, and fluid-operated piston and cylinder means for effecting said relative movements.

Fork lift trucks which are required to work in spaces with low headroom but at the same time permit a high lifting height, can suitably be provided with a triple mast of the kind referred to above. The mast should also be designed as a free lifting mast, that is, the load carrying member should be raisable to its highest position before the lifting movement of the second and third mast sections is started.

The present invention aims to provide a load handling mast of the kind referred to which has an improved arrangement of the means for effecting the relative movements between the various parts of the mast, which leads to a simple and inexpensive construction of the mast.

According to the invention, a load handling mast for a truck comprises a first mast section intended to be mounted on a truck, a second mast section mounted on, and movable substantially vertically relative to, said first mast section, a third mast section mounted on, and movable substantially vertically relative to, said second mast section, a load carrying member mounted on, and movable substantially vertically relative to, said third mast section, fluid-operated piston and cylinder means for effecting said relative movements, said piston and cylinder means comprising a first upwardly projectable piston rod on which is mounted a first pulley wheel means and a second downwardly projectable piston rod on which is mounted a second pulley wheel means, a first flexible elongate member attached at one end to the upper portion of said first mast section, passing around said second pulley wheel means, passing around a third pulley wheel meanC mounted on the upper portion of said third mast section and having its other end attached to said load carrying member, and a second flexible elongate member attached at one end to said second mast section, passing around said first pulley wheel means and attached at its other end to the lower portion of said third mast section.

Said fluid-operated piston and cylinder means may comprise a single cylinder from the opposite ends of which said first and second piston rods are respectively projectable. Alternatively, said fluidoperated piston and cylinder means may comprise two cylinders in which the first and second piston rods, respectively, are mounted. In each case, it is preferred that the effective cross-sectional area of said first piston rod is greater than, but less than twice, the effective cross-sectional area of said second piston rod.

Preferably, each of said mast sections comprises a pair of spaced-apart, parallel guides for guiding the substantially vertical movement of the adjacent mast section or the load carrying member. With the mast sections constructed in this way, and with the fluid-operated piston and cylinder means in the form of two spaced-apart piston and cylinder assemblies, each having said first and second piston rods, good visibility is obtained through the mast for the operator of the mast.

The invention will now be described, by way of example, with reference to the accompanying drawings, in which: Figures 1 to 3 are schematic side views of a load handling mast according to the invention in different operating positions, and Figures 4 and 5 are sectional side views of the piston and cylinder assemblies of the mast of Figure 1 with the piston rods in retracted and extended positions, respectively.

Figures 1 to 3 show a mast intended to be mounted on a fork lift truck. The mast comprises three relatively movable mast sections. The first mast section comprises a first pair of spaced-apart guides 1 (only one of which can be seen in the drawings) which is articulatedly joined to the frame of a fork lift truck (not shown). The second mast section comprises a second pair of spacedapart guides 2 (only one of which can be seen in the drawings) which are guided by the guides 1.

The third mast section comprises a third pair of spaced-apart guides 3 (only one of which can be seen in the drawings) which are guided by the guides 2. A load carrying member in the form of a fork carrier 4 is guided by the guides 3. A fluidoperated piston and cylinder assembly 5 has its cylinder fixedly joined to the second pair of guides 2. The piston and cylinder assembly 5 is of a type having two piston rods 6, 7, respectively, projectable from opposite ends of the cylinder. The piston rods 6, 7 support pulley wheels 8 and 9, respectively. At the upper portion of the third pair of guides 3 there is a pulley wheel 10. A flexible elongate member, such as a chain or rope 11, is attached at one of its ends to the upper portion of the first pair of guides 1 and at its other end to the fork carrier 4.The rope 11 runs around the pulley wheels 8 and 1 0. Another elongate flexible member, such as a chain or rope 12, is attached at one of its ends to the second pair of guides 2 and at its other end to the lower portion of the third pair of guides 3. The rope 12 runs around the pulley wheel 9.

The piston and cylinder assembly 5 may be constructed in the manner shown in Figures 4 and 5. In these Figures, the piston and cylinder assembly is shown as comprising a cylinder 1 3 which contains a downwardly projectable piston rod 6 and an upwardly projectable, tubular piston rod 7. In the retracted position of the two piston rods see Figure 4) the piston rod 6 is disposed within the tubular piston rod 7. The space 14 in the cylinder 13 is supplied with pressurised fluid medium through a conduit 1 5.

When, in use of the mast, pressurised medium is supplied to the cylinder space 14, the force acting on the piston rod 7 is greater than the force acting on the piston rod 6. By choosing the effective cross-sectional area of the piston rod 6 somewhat larger than half the effective crosssectional area of the piston 7, the fork carrier 4 may be caused to move to its upper position on the guides 3 (as shown in Figure 2) before the guides 2 and 3 are lifted relative to the guides 1.

Possibly it may be suitable to arrange a locking device (not shown) which locks the fork carrier 4 in its upper position and maintains it locked in this position during lifting and lowering of the pairs of guides 2 and 3. When the load carrier 4 has been lifted to its upper position shown in Figure 2 by projection of the piston rod 6 from the cylinder 1 3, the pressure in the space 14 rises until the force acting on the piston rod 7 is overcome. The piston rod 7 is then projected upwardly from the cylinder 13 (see Figure 5) and the fork carrier 4 is lifted together with the pairs of guides 2 and 3, see Figure 3. When lowering the mast, the pairs of guides 2 and 3 are first lowered with the fork carrier 4 in its highest position relative to the guides 3. When the guides 2 and 3, have been returned to their lower positions (Figure 2), the fork carrier 4 is lowered relative to the guides 3.

The above-described mast permits the fork carrier 4 to work with a constant lifting speed during the entire lifting movement. The pressure of the pressure medium in the cylinder 1 3 is largely constant during the entire lifting movement if the effective cross-sectional area of the piston rod 7 is chosen to be almost twice the effective crosssectional area of the piston rod 6.

Claims

1. A load handling mast for a truck, comprising a first mast section intended to be mounted on a truck, a second mast section mounted on, and movable substantially verically relative to, said first mast section, a third mast section mounted on, and movable substantially vertically relative to, said second mast section, a load carrying member mounted on, and movable substantially vertically relative to, said third mast section, fluid-operated piston and cylinder means for effecting said relative movements, said piston and cylinder means comprising a first upwardly projectable piston rod on which is mounted a first pulley wheel means and a second downwardly projectable piston rod on which is mounted a second pulley wheel means, a first flexible elongate member attached at one end to the upper portion of said first mast section, passing around said second pulley wheel means, passing around a third pulley wheel means mounted on the upper portion of said third mast section and having its other end attached to said load carrying member, and- a second flexible elongate member attached at one end to said second mast section, passing around said first pulley wheel means and attached at its other end to the lower portion of said third mast section.

2. A load handling mast according to claim 1, wherein said fluid-operated piston and cylinder means comprises a cylinder from the opposite ends of which said first and second piston rods are respectively projectable.

3. A load handling mast according to claim 1, wherein said fluid-operated piston and cylinder means comprises two separate cylinders in one of which said first piston rod is mounted and in the other of which said second piston rod is mounted.

4. A load handling mast according to claim 1 or claim 2 wherein the effective cross-sectional area of said first piston rod is greater than, but less than twice, the effective cross-sectional area of said second piston rod.

5. A load handling mast according to any of the preceding claims, wherein each of said mast sections comprises a pair of spaced-apart guides, for guiding the substantially vertical movement of an adjacent mast section or the load carrying member.

6. A load handling mast constructed and arranged substantially as herein described with reference to, and as illustrated in, the accompanying drawings.

7. A fork lift truck comprising the load handling mast claimed in any of the preceding claims.