GB2032883A

GB2032883A - Improved Lift Truck Mast

Info

Publication number: GB2032883A
Application number: GB7928057A
Authority: GB
Original assignee: ASEA AB
Current assignee: ABB Norden Holding AB
Priority date: 1978-08-14
Filing date: 1979-08-13
Publication date: 1980-05-14
Also published as: FI68599B; NO151657C; DE2931703C2; NL7905989A; NO792614L; NO151657B; NL189558C; DE2931703A1; FI68599C; FI792490A; GB2032883B

Abstract

A mast for a lift truck, in particular a fork lift truck, comprises a first pair of guides 1 carried by the lift truck (not shown), a movable second pair of guides 8 controlled by the guides 1, a fork carriage 9 controlled by the guides 8, and at least one operating piston and cylinder assembly 2 which includes a main cylinder 20, fixedly connected to the guides 1, a tubular piston rod 5, movable in the cylinder 20 and having a first annular piston 22 with a seal 23 which moves in the main cylinder 20, and a piston rod 4b with a second piston 29 which moves in the piston rod 5, the tubular piston rod 5 and the piston rod 4b projecting through respective end walls 24, 30 of the main cylinder 20 and being connected by means of ropes or chains 11, 13 to the movable guides 8 and the fork carriage 9, respectively. The stroke of the piston 4a is restricted by an annular flange 28 on this piston engaging an inwardly- facing flange 34 on the piston rod 5, so that when the tubular piston rod 5 is pushed out by the supply of pressure medium to the channel 39, the piston 4a therein accompanies the piston rod 5 into the main cylinder 20. There is a permanently open connection via axial slots 29 and 38 between a first space 36 between the inner end of the piston rod 4b and an end wall 25 of the tubular piston rod 5 and a second space 37 between the annular piston 22 and the end wall 30 of the main cylinder 20. <IMAGE>

Description

SPECIFICATION Improved Lift Truck Mast This invention relates to a mast for a lift truck, in particular for a fork lift truck, the mast being of the kind comprising a first mast section intended to be mounted on a truck, a second mast section arranged for movement relative to the first mast section, a lifting carriage arranged for movement relative to the second mast section, and fluidoperated piston and cylinder means for effecting said relative movements.

The invention aims to provide a mast of the kind referred to, which gives a large free field of vision for the operator of the truck on which the mast is mounted.

According to the invention a lift truck mast of the kind referred to is characterised in that said piston and cylinder means comprises a main cylinder secured to the first mast section, a first annular piston movable in the main cylinder and joined to a first tubular piston rod which passes through one end wall of the main cylinder, a second piston movable in the first tubular piston rod and joined to a second piston rod which passes through the end wall of the main cylinder opposite to said one end wall, and stop means for preventing the second piston from moving out of the inner end of the first tubular piston rod, and in that flexible elongate members, which are joined to said second mast section and to said lifting carriage, respectively, are influenced by said piston rods to effect said relative movements.

Preferably, the axis of the main cylinder is disposed substantially parallel to the axis of the first mast section, and in this case it is preferred that, in use of the mast, the first tubular piston rod passes through the end wall of the main cylinder which is uppermost and that the second piston rod passes through the end wall of the main cylinder which is lowermost.In this case, it is convenient for the first tubular piston rod to influence, for example via a deflector pulley, a first flexible elongate member, for example a rope or chain, in a region intermediate points of attachment of the first flexible elongate member to the first mast section (or the main cylinder) and second mast section, respectively, and for the second piston rod to influence, for example via another deflector pulley, a second flexible elongate member, for example a rope or chain, in a region intermediate points of attachment of the second flexible elongate member to the first mast section (or the main cylinder) and the lifting carriage, respectively. This second flexible elongate member may pass around yet a further deflector pulley at the upper part of the second mast section when the mast is in use.

In one embodiemnt of a mast in accordance with the invention, said main cylinder has a permanently open connection between a first space inside the first tubular piston rod between said second piston and said one end wall of the moin cylinder and a second space between said first annular piston and the opposite end wall of the main cylinder. In the use of the mast, lowering of the lifting carriage is brought about by the weight of the second mast section, the lifting carriage itself and any load supported by this carriage. The mast suitable includes a locking device which, in use of the mast, locks the first and second mast sections in the lower position of the second mast section while lifting the lifting carriage to its upper limit position in relation to the second mast section.A further locking device may interconnect the lifting carriage and the second mast section in said upper limit position of the lifting carriage while lifting the second mast section and the lifting carriage. This embodiment makes possible a very simple arrangement for the supply of pressurised fluid to the piston and cylinder means, since only one almost rigid pressure pipe is necessary. In the case where the first mast section is tiltably mounted on a truck, this pipe can be arranged near to the tilting point, so that movement and bending of the pipe are insignificant during use of the mast, which is vary favourable and results in a long service life.

In a second embodiment, the main cylinder may be constructed without the above-mentioned permanently open connection between said first and second cylinder spaces. In this case, said second piston is provided with a sealing ring which seals against the inner surface of the first tubular piston rod. The movements are then completely determined by the supply of pressure medium to the respective cylinder spaces. In this embodiment it is possible, in use of the mast, to lift the second mast section with the lifting carriage in its lowermost position. Also simultaneous lifting of the lifting carriage in relation to the second mast section and the second mast section in relation to the first mast section can be carried out, should this be desirable. A forced lowering of the lifting carriage and the second mast section is also possible.This second embodiment, however, involves a more complicated valve equipment and a less favourable arrangement of pipes for the supply of pressure medium.

Conveniently, each of said mast sections comprises a pair of spaced-apart guides with a large free field of vision between the guides. In this case, it is convenient to arrange for the piston and cylinder means to be in the form of two piston and cylinder assemblies, one closely adjacent to each guide of the first mast section.

Since the maximum lift of the lifting carriage is achieved with two piston rods of the piston and cylinder assembly, these rods can be shorter than if a single rod were used. Consequently, the risk of buckling of the rods is reduced and small diameter rods can be used. By employing a high working pressure for the fluid medium, the main cylinder (or cylinders) of the piston and cylinder means can have a small diameter. All these factors assist in giving the operator of a lift truck on which the mast is mounted a large unobstructed field of vision.

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 mast in accordance with the invention for a fork lift truck, the three views showing different relative positions of the mast sections and lifting carriage, Figures 4 to 6 are sectional views of the piston and cylinder means of the mast of Figures 1 to 3, with its pistons in the three positions they assume when the lifting carriage is in the positions shown in Figures 1 to 3, respectively, Figures 7 to 9 are schematic views of a locking mechanism for coupling the lifting carriage to the second mast section and for coupling the second mast section to the first mast section, and Figures 10 to 12 are views similar to Figures 4 to 6, respectively, of an aiternative embodiment of the piston and cylinder means of the mast of Figures 1 to 3.

In Figures 1 to 3, the numeral 1 designates a pair of spaced-apart guides forming the first mast section of a mast which is joined to a fork lift truck (not shown) in a known manner. Operating cylinders 2-one for each guide-are attached to the upper portion of the guides 1 by means of two brackets 3. The cylinders 2 include two piston rods 4b and 5, which support deflector pulleys 6 and 7 at their ends. The mast comprises a second vertically movable mast section in the form of a pair of spaced-apart guides 8 which are guided by the guides 1. In the guides 8 there runs a lifting carriage 9 with forks 10 for supporting a load M.

A rope or chain 11, which is attached to the carriage 9 and the lower one of the brackets 3, runs over the deflector pulley 6 on the piston rod 4b and a deflector pulley 12 at the upper portion of a guide 8. Thus, when the parts are in the positions shown in Figure 1, downward movement of the pulley 6 causes the carriage 9 to move upwardly on the guides 8 to the position shown in Figure 2. The upper position of the carriage 9 on the guides 8 is determined by a stop means (not shown). Another rope or chain 1 3 is attached to the lower portion of a guide 8 and to the upper one of the brackets 3 and runs over the deflector pulley 7 on the piston rod 5. Thus, when the parts are in the positions shown in Figure 2, upward movement of the pulley 7 causes the movable guides 8 to move upwardly relative to the fixed guides 1 to the position shown in Figure 3.The lower position of the guides 8 relative to the guides 1 is determined by a stop means (not shown). Arrows 14 and 1 5 indicate the direction of the tensions in the ropes or chains 11 and 1 3, respectively, and arrows 16, 1 7 and 1 8 indicate the loads on the deflector pulleys 12, 6 and 7, respectively, as a function of the load M on the forks 10.

Referring now to Figures 4 to 6, each of the operating cylinders 2 comprises an outer main cylinder 20, which is attached to the guides 1 of the mast. The piston rod 5 is tubular and joined to an annular piston 22 which is slidable in the cylinder 20. A sealing ring 23 provides a seal between the piston 22 and the cylinder 20. The piston rod 5 passes through the upper end wall 24 of the cylinder 20. At its upper end the piston rod 5 is provided with a transverse wall 25 having two lugs 26 for a shaft 27 which supports the deflector pulley 7 (see Figures 1 to 3). The piston rod 4b is a solid rod and is joined to a piston 4a slidable inside the piston rod 5. The piston 4a is formed by an annular flange 28 on the rod 4b, the flange 28 having at least one axial slot 29 in its peripheral surface.The piston rod 4b passes through the lower end wall 30 of the cylinder 20 and is provided with two lugs 31 for a shaft 32 which supports the deflector pulley 6 (see Figures 1 to 3). A sealing ring 33 provides a seal between the piston rod 4b and the end wall 30. The lower open end of the piston rod 5 is formed with an inwardly-directed annular flange 34, the internal diameter of which is smaller than the external diameter of the flange 28. Thus, the flange 34 acts as a stop means for the piston 4a, so that when the piston rod 4b is in its fully extended position relative to the piston rod 5 (as shown in Figure 5) is will become interconnected with the piston rod 5 and accompany the latter upon its upward movement (see Figure 6). Adjacent its lower end the cylinder 20 is formed with an inwardly-directed annular flange 35 which acts as a stop means for the annular piston 22.The space 36 in the piston rod 5 between the end wall 25 and the piston 4a and the space 37 in the cylinder 20 between the end wall 30 and the piston 22 are in permanent communication with each other through an axial gap 38 between the flange 34 and the piston rod 4b and slot(s) 29 in the flange 28. The space 37 is supplied with pressure medium through a channel 39 from a pressure medium source (not shown). Through an opening 21 and possibly a drainage hose (not shown) the space 40 between the cylinder 20 and the piston rod 5 communicates with a collecting container for pressure medium, so that air or pressure medium leaking into the space 40 does not prevent the movements of the pistons.

When lifting the load M on the forks 10, the space 37 is supplied with pressure medium. If the area of the piston rod 4b is chosen to be equal to or greater than the area of the annular piston 22, the force relations will be such that the piston rod 4b will be forced out of the cylinder 20, whereas the piston rod 5 will maintain its position with respect to the cylinder 20 up to the moment when the movement of the piston rod 4b is arrested when the flange 28 of the piston 4a makes contact with the flange 34 of the piston rod 5. The carriage 9 is then lifted from the position shown in Figure 1 to that shown in Figure 2. During continued supply of pressure medium, the pressure medium acting on the annular piston 22 and on the area of the end wall 25 will force out the piston rod 5. The piston 4a and the piston rod 4b will then accompany the piston rod 5 during this movement, the carriage 9 maintaining its position with respect to the movable guides 8.

The guides 8 will then be lifted from the position shown in Figure 2 to that shown in Figure 3 together with the carriage 9. If the pressure medium is now allowed to exhaust from the space 37, the above described movements of the lifting carriage 9 and the guides 8 take place in the opposite directions and in the opposite order, the pressure medium being forced out as a result of the pressure caused by the weight of the guides 8 and the carriage 9 and any loads carried thereby. When the length of the stroke of each of the piston rods 4b and 5 is S, the total lifting height will be 4 S with the shown connections of the ropes or chains 11 and 13.

In order to prevent the movable guides 8 from being lifted before the carriage 9 has reached its upper position due, for example, to excessive friction between the different elements, the coupling mechanism shown in Figures 7 to 9 may be used. This mechanism comprises two latches 41 and 42 which are journalled so as to rotate around fixed pins 43 and 44, respectively, on the guides 8. The latches are provided with slots 47 and 48, respectively. Pins 49 and 50 protrude from the guides 1 and from the carriage 9, respectively. When the carriage 9 is in the position shown in Figure 1 and during lifting to the position shown in Figure 2, the guides 8 are locked with respect to tiie guides 1 by the pin 49 extending into the slot 47 of the latch 42. The latch 42 is held locked against rotation in the clockwise direction in this position by the latch 41.During the last part of the lifting movement of the carriage 9, from the position shown in Figure 7 to that shown in Figure 8, the pin 50 is moved into the slot 48, and the latch 41 is rotated to the position shown in Figure 8 so that it not longer locks the latch 42. When the movable guides 8 commence to move upwardly from the position of figures 2 and 8 to the position of Figures 3 and 9, the pin 49 turns the latch 42 around the pin 44 from the position shown in Figure 8 to that shown in Figure 9. In that position the latch 42 locks the latch 41 against rotation in the anticlockwise direction, the carriage 9 and the guides 8 thus being coupled together during the lifting and lowering of the guides 8. When lowering the carriage 9 from the position of Figures 3 and 9, a corresponding disengagement and engagement is obtained, but in the inverse order.

As will be clear from the description, there need only be a single connection for the pressure medium between the cylinder 2 and the truck proper. Since the cylinder 2 is also fixedly mounted on the guides 1, the connection is very simple. Only a very short, flexible high-pressure hose need be used, since only the tilting movement of the mast involves a change of distance between the truck and the point of connection of the fluid medium to the cylinder 20.

The above-described mast considerably improves the field of view of the operator of the fork lift trcuk on which the mast is mounted, as compared with hitherto used masts. Particularly good visibility is obtained when two parallelworking cylinders 2 are used and these are arranged behind the guides 8. The described construction also gives the possibility of lifting the carriage 9 to the top of the movable guides 8 without affecting the total height, so that a socalled free lift stroke is obtained. The entire cylinder contains only two seals 23 and 33 which are required to seal against a high fluid pressure.

Otherwise, only guiding surfaces between the units of the operating cylinder are used.

In the embodiment of the cylinder according to Figures 10 to 12 the same reference numerals have been used to designate the same or similar items as in the embodiment of Figure 4 to 6. In Figures 10 to 12 there is a seal 51 in the end wall 24, a seal 52 around the piston 4a, and a seal 53 in the annular piston 22. The space 36 communicates with a pressure medium source through a channel 54 in the end wall 25. By supplying pressure medium to the space 36, the piston 4a and the piston rod 4b are displaced downwards (to the position shown in Figure 11), By supplying pressure medium to the space 37 through the channel 39, the piston 22 and the piston rod 5 are displaced upwards and the piston rod 4b accompanies the piston rod 5 (to the position shown in Figure 12). Then, by supplying pressure medium to the space 40 through the channel 21, the piston 22 can be returned to its lower position together with the piston rod 5.

Alternatively, with the parts in the position shown in Figure 11, by supplying pressure medium to the space 55 through a channel 56 in the piston rod 4b, the piston 4a with the piston rod 4b can be returned to the position shown in Figure 10.

Claims

1. A lift truck mast comprising a first mast section intended to be mounted on a truck, a second mast section arranged for movement relative to the first mast section, a lifting carriage arranged for movement relative to the second mast section, and fluid-operated piston and cylinder means for effecting said relative movements, characterised in that said piston and cylinder means comprises a main cylinder secured to the first mast section, a first annular piston movable in the main cylinder and joined to a first tubular piston rod which passes through one end wall of the main cylinder, a second piston movable in the first tubular piston rod and joined to a second piston rod which passes through the end wall of the main cylinder opposite to said one end wall, and stop means for preventing the second piston from moving out of the inner end of the first tubular piston rod, and in that flexible elongate members, which are joined to said second mast section and to said lifting carriage, respectively, are influenced by said piston rods to effect said relative movements.

2. A mast according to claim 1, in whicheach of said mast sections comprises a pair of spacedapart guides.

3. A mast according to claim 1 or 2, wherein the axis of said main cylinder is disposed substantially parallel to the axis of the first mast section.

4. A mast according to claim 3, in which, in use of the mast, the first tubular piston rod projects through the upper end wall of the main cylinder and influences a first flexible elongate member intermediate its points of attachment to the first mast section (or the main cylinder) and the second mast section, and the second piston rod projects through the lower end wall of the main cylinder and influences a second flexible elongate member intermediate its points of attachment to the first mast section (or the main cylinder) and the lifting carriage.

5. A mast according to claim 4, in which each piston rod influences its associated flexible elongate member via a respective deflector pulley.

6. A mast according to claim 4 or 5, in which said second flexible elongate member passes round a further deflector pulley at the upper part of the second mast section when the mast is in use.

7. A mast according to any of the preceding claims, in which each of said flexible elongate members is a rope or chain.

8. A mast according to any of the preceding claims, in which said main cylinder has a permanently open connection between a first space inside the first tubular piston rod between said second piston and said one end wall and a second space between said first annular piston and the opposite end wall of the main cylinder.

9. A mast according to any of the preceding claims, comprising a locking device which, in use of the mast, locks the first and second mast sections with respect to each other until the lifting carriage has reached its upper limit positon in relation to the second mast section.

10. A mast according to claim 9, comprising a further locking device for locking the lifting carriage and the second mast section in the upper limit position of the lifting carriage when lifting the second mast section and the lifting carriage.

11. A mast according to any of claims 1 to 7, in which said second piston seals against the inner surface of the first tubular piston rod and the piston and cylinder means comprises means for supplying pressure medium through separate supply channels to a space in the first tubular piston rod between said second piston and said one end wall of the main cylinder and a space in the main cylinder between the first annular piston and said opposite end wall of the main cylinder.

12. Lift truck mast comprising a first pair of guides intended to be supported by a truck, a second movable pair of guides controlled by said first pair of guides, a fork carriage controlled by said second pair of guides, and at least one vertical lifting cylinder having a main cylinder with piston rods rigidly connected to the first pair of guides, which main cylinder achieves lifting of the movable pair of guides and the fork carriage by means of ropes or chains, characterised in that a first piston, which is made in the form of an annular piston, is movably arranged in the main cylinder and joined to a tubular first piston rod which passes through an end wall of the main cylinder, in that a second piston is movably arranged in the tubular piston rod and joined to a second piston rod which passes through the second end wall of the main cylinder, and in that the tubular piston rod at its inner end is provided with stop means which limit the movement of the second piston and force it to accompany the first piston during its movement. whereby said ropes or chains which are joined to the movable pair of guides and to the fork carriage, respectively, and are influenced by way of the piston rods, achieve the lifting of the fork carriage and the movable pair of guides, respectively.

13. A lift truck mast constructed and arranged substantially as herein described with reference to, and as illustrated in, Figures 1 to 9, or Figures 1 to 3 and 10 to 12, of the accompanying drawings.

14. A lift truck comprising a mast as claimed in any of the preceding claims.