Industrial truck with supported mast lift cylinder

Abstract

An industrial truck (1) comprises a stationary mast frame (21) and a first moveable mast frame (22), the first moveable mast frame being moveable in a vertical direction in relation to the stationary mast frame. A load handling arrangement (25) is displaceably connected to the first moveable mast frame, the load handling arrangement being moveable in a vertical direction. At least one mast lift cylinder (23) is arranged to move the first moveable mast frame in relation to the stationary mast frame. The mast lift cylinder comprises a piston (231). A moveable support (25) is slidably arranged around the piston of the mast lift cylinder and a receiver (26) is fixedly arranged on the first moveable mast frame, wherein the moveable support and the receiver comprise complementary engagement parts (251, 261) arranged to releasably engage the moveable support and the receiver when brought together as the first moveable mast frame is moved upwards.

Description

TECHNICAL FIELD OF THE INVENTION

[0001] The present invention relates to an industrial truck with a telescopic mast arrangement.BACKGROUND OF THE INVENTION

[0002] Extendable mast arrangements are used in certain industrial trucks, such as in reach trucks. The mast arrangement typically comprises a stationary mast which is vertically fixedly connected to the vehicle frame. One or more additional masts are telescopically displaceable in relation to the stationary mast. The telescopic displaceability may be provided in the form of profile rails or the like, connecting the frames to each other.

[0003] If mast frames are used, the stationary mast may be arranged as an outer frame fixedly connected to the vehicle and the moveable mast may be arranged as an inner mast, being telescopically displaceable in relation to the outer mast.

[0004] If three mast frames are used, a second telescopically displaceable, moveable frame may be arranged between the inner mast and the outer mast.

[0005] A load handling arrangement, typically in the form of a fork carriage, may be displaceable along a guiding structure arranged on the inner mast.

[0006] The fork carriage is conventionally hydraulically lifted by one or more hydraulically actuated cylinder(s). The cylinder(s) may be arranged to bring the displaceable mast along, telescoping together with the fork carriage motion. Alternatively, the cylinder(s) may be arranged to lift the fork carriage without bringing any displaceable mast along - a so called free-lift function, where separate cylinder(s), mast cylinders, are used for lifting the displaceable mast(s). For example, two mast cylinders may be provided, one mast lift cylinder e.g. being arranged close to each side of the mast structure.

[0007] Examples of such known telescopic mast arrangements for industrial trucks are disclosed in EP 2465812, EP 0866026, EP 0622331 and US6557456.

[0008] The free-lift cylinder(s) and the mast lift cylinder(s) may be operated by the same hydraulic system. The internal cross-sectional areas of the cylinders may then determine in which order the cylinders are operated. When the hydraulic pressure is increased, the cylinder which is easiest to move, i.e. the cylinder with the greatest cross-sectional area, will be lifted first. This will typically be the free-lift cylinder(s). When the free-lift cylinder(s) has been maximally extended, the inner mast will then be lifted by the mast lift cylinders.

[0009] The cylinders typically comprise an outer tube / sleeve and a piston rod being telescopically displaceable in relation to the outer tube / sleeve. The lift length of the mast lift cylinders can be great, such as several meters. The mast lift cylinders consequently need to be dimensioned to be able to withstand both the (possibly) heavy load and the great height, without deforming, buckling, or in other ways being damaged during use. However, lifting and lowering speeds benefit from keeping the cylinders' diameters limited. These contradictory factors generate a need for improvement.

[0010] Since the free-lift cylinder would generally need to have a greater cross-sectional area than the mast lift cylinders, also this cylinder must have large dimensions, thereby restricting the piston movement speed.

[0011] In total, this makes the cylinders and the hydraulic system costly and also slow in operation.

[0012] A solution to address this problem may be to control the cylinders separately and independently, by use of electric valves. However, even if this may increase the lifting and lowering speed of the free-lift movement, this solution would make the system still more complicated and costly. Further, the increased lifting and lowering speed hereby obtained is only related to the free-lifts, since it does not address the deformation / buckling problem, which is setting the required dimensions for the mast lift cylinders.

[0013] There is therefore a need for an improved extendable mast arrangement for an industrial truck addressing these problems in the prior art. In particular, there is a need for an extendable mast arrangement which can be operated at a higher speed, which is more cost-effective and / or with higher resistance against damages, such as buckling and other forms of deformation.SUMMARY OF THE INVENTION

[0014] It is therefore an object to provide an industrial truck which alleviates all, or at least some, of the above-discussed drawbacks and problems of the prior art.

[0015] This object is achieved with an industrial truck as defined in the appended claims.

[0016] According to a first aspect of the invention there is provided an industrial truck comprising: a stationary mast frame; a first moveable mast frame, the first moveable mast frame being moveable in a vertical direction in relation to the stationary mast frame; a load handling arrangement displaceably connected to the first moveable mast frame, the load handling arrangement being moveable in a vertical direction; at least one mast lift cylinder arranged to move the first moveable mast frame in relation to the stationary mast frame, the mast lift cylinder comprising a piston; a moveable support slidably arranged around the piston of the mast lift cylinder; and a receiver fixedly arranged on the first moveable mast frame, wherein the moveable support and the receiver comprise complementary engagement parts arranged to releasably engage the moveable support and the receiver when brought together as the first moveable mast frame is moved upwards.

[0017] The piston may also be referred to as a rod. The piston may be tubular, i.e. tube-shaped, but may alternatively be solid. The piston preferably has a circular cross-section, but other cross-sectional shapes are also feasible.

[0018] The new solution enables use of essentially the same set-up as has been used previously, with an outer, stationary mast frame and an inner displaceable mast frame, and optionally one or more additional mast frames in between. Further, the displaceable mast frame(s) is moved by one or more mast lift cylinder, and a load handling arrangement, such as a fork, is displaceable along the inner mast frame, e.g. by use of a free-lift cylinder.

[0019] The new solution provides an additional support and stabilization for the piston(s) of the mast lift cylinder(s), thereby protecting the cylinder(s), and in particular the piston(s), against buckling, deforming and other types of related damage.

[0020] Due to the moveable support it becomes possible to use smaller and less costly mast lift cylinders, and consequently also a smaller and less costly free-lift cylinder(s). The smaller cylinders also increase the operational speed for lifting and lowering the mast frames and forks.

[0021] The moveable support is relatively loosely arranged around the piston of the mast lift cylinder, thereby allowing it to slide axially along the length of the piston.

[0022] In a retracted position, the movable support may be arranged on top of the outer sleeve of the mast lift cylinder.

[0023] The moveable support preferably has a base plate with an opening loosely holding the moveable support on the piston, allowing the moveable support to glide over the piston.

[0024] As the receiver is moved upwards when the first moveable mast frame is lifted, it is brought into contact with the movable support. Upon contact, the complementary engagement parts are releasably engaged, whereby the movable support is lifted together with the receiver upon continued lifting of the first moveable mast frame. Hereby, the moveable support will slide along the piston. Since the receiver is fixedly connected to the first moveable mast frame the moveable support it connects the piston to the first moveable mast frame in lateral directions, thereby providing support to the piston in horizontal directions.

[0025] Thus, differently put, the operation may be described as follows. When the cylinder is in a retracted position, the moveable support is preferably in contact with, or in the vicinity of, the upper end of the outer sleeve / tube of the first mast lift cylinder. In an embodiment, the moveable support rests on the outer sleeve of the mast lift cylinder. At the same time, when the first moveable mast frame is in a retracted position, the receiver block is at a distance from the moveable support.

[0026] When the first mast cylinder is operated, the piston is expelled out from the outer sleeve. However, the moveable support maintains its position at the end of the outer sleeve. At the same time, the inner mast frame moves upwards in conjunction with the piston, and, consequently, the receiver block is moved closer to the moveable support.

[0027] At a certain height, e.g. when the first moveable mast frame has been lifted a distance corresponding to the height when the support becomes positioned close to the middle of the piston, the receiver block reaches the moveable support, and the complementary engagement parts of the moveable support and the receiver engage.

[0028] Upon continued lifting, the moveable support is moved together with the receiver and the inner mast frame. Hereby, the moveable support maintains its position relative to the piston, whereas the distance from the outer sleeve increases.

[0029] At the fully extended position, the moveable support is preferably at a height corresponding to 20-80% of the length of the fully extended piston, e.g. about 50% of the length of the fully extended piston. At this position, and also previously during the entire lifting operation, the moveable support stabilizes the piston to the inner frame. This significantly reduces the risk of kinking, deformation, bending and other damages occurring to the piston.

[0030] A lift height corresponding to 50% of the length of the fully extended piston represents the most effective support position from a buckling prevention point of view, since it minimizes the bending of the cylinder rod and minimizes the horizontal counteracting forces in the most critical cylinder rod position.

[0031] However, it also feasible to use other maximum heights, within the range from 20-80% of the length of the fully extended piston. The position can be varied quite freely since the moveable support constitutes a "third hand" when placed somewhere at the free length of the cylinder rod when the rod extends. It may be activated earlier or later during the staging by selecting the position of the receiver. If load limitations are applied against height, another, lower critical height position than at 50% may exist where it is favorable to activate the moveable support earlier. Other cases may occur where it is favorable to activate the moveable support later due to practical circumstances.

[0032] When the first moveable mast is again lowered, the same steps are repeated in a reverse order.

[0033] In embodiments, it is possible to move the load handling arrangement, such as forks, in various ways, such as by electric motors, by chains, etc. However, preferably, the load handling arrangement is moved by a hydraulic cylinder, i.e. a free-lift cylinder.

[0034] Thus, in an embodiment, the industrial truck further comprises a free-lift cylinder arranged to move the forks in relation to the moveable mast frame.

[0035] In embodiments, the mast lift cylinder(s) and the free-lift cylinder are hydraulic cylinders actuated by the same hydraulic system. Preferably, the internal cross-sectional areas of the at least one mast lift cylinder(s) and the free-lift cylinder are such that the free-lift cylinder is moved before the mast lift cylinder(s) upon operation of the hydraulic system. In such embodiments the support of the piston of the first mast cylinder(s), as discussed in the foregoing, is of particular importance and advantage.

[0036] In an embodiment, the first moveable mast frame is arranged as an inner mast frame in relation to the stationary mast frame, and wherein a second moveable mast frame is arranged as an intermediate mast frame, arranged between the stationary mast frame and the first moveable mast frame. Thus, in such an embodiment the telescopic mast arrangement comprises three mast sections - one stationary and two moveable masts frames. The second moveable mast frame may be moved by one or several additional second mast lift cylinder(s). Such additional piston(s) of such second mast lift cylinder(s) may be stabilized in the same way as for the piston(s) of the first mast lift cylinder, by use of additional moveable support(s) and receiver(s). Alternatively, the second moveable mast, and even a possible third moveable mast, fourth moveable mast, etc., will be connected, e.g via chains to move together with the first moveable mast in a way where all the moveable masts telescope the complete mast simultaneously, in one joint movement. In such embodiments, only one cylinder, or one set of cylinders, connected to the moveable mast closest to the stationary mast is / are needed to move all moveable masts frames.

[0037] In an embodiment, the first moveable mast frame is arranged as an inner mast frame in relation to the stationary mast frame, and wherein a second moveable mast frame is arranged as an intermediate mast frame, arranged between the stationary mast frame and the first moveable mast frame, wherein at least one of said mast lift cylinder(s) is connected to the moveable mast frame closest to the stationary mast.

[0038] In an embodiment, the moveable support, in a retracted position, is arranged at, or in the vicinity of, a top end of an outer sleeve of the mast lift cylinder.

[0039] The moveable support preferably comprises a base plate with an opening therein, the opening having an internal diameter exceeding an outer diameter of the piston of the mast-lift cylinder, and wherein at least one of the engagement parts is arranged at, or in the vicinity of, an end side of the base plate. The opening of the base plate may consequently be arranged to closely encircle the piston, thereby providing lateral support in all horizontal directions.

[0040] The complementary engagement parts may comprise at least one vertically protruding element, arranged on the moveable support or the receiver, and at least one hole dimensioned to receive the vertically protruding element, the at least one hole being arranged on the other of the moveable support and the receiver.

[0041] In an embodiment, the moveable support comprises the at least one vertically protruding element, the vertically protruding element(s) having a downwardly directed free end, and wherein the receiver comprises the at least one hole arranged to engage with the vertically protruding element(s).

[0042] In an embodiment, the vertically protruding element(s) have over at least a part of the length a tapered, conical shape, thereby having a smaller cross-sectional area at a free end and a greater cross-sectional area at a base or at an intermediate position. This presents a smaller, more pointed forward end, which facilitates insertion of the vertically protruding element(s) into the corresponding holes.

[0043] For example, in embodiments where the moveable support comprises a base plate, engagement parts may be arranged as a a side of the base plate, e.g. in the form of one or more downwardly extending fingers or pins. In a preferred embodiment, two such downwardly extending fingers are provided. The fingers preferably have a tapering, conical shape, at least towards the lowermost end, with a gradually decreasing cross-sectional area in the downward direction. A corresponding receiver block may be fixedly arranged on the first moveable mast frame. The receiver block is here provided with openings corresponding to the fingers of the moveable support.

[0044] The receiver is preferably arranged at a height position on the first moveable mast frame so that the moveable support is lifted to a position between 25% and 75% of the length of the fully extended piston, i.e. when the length of the piston protruding out from the cylinder when the piston is maximally extended, and preferably to a position at about the middle of the piston. The receiver block is hereby arranged at a height so that the support is provided close to the middle of the piston when in a maximally extended state, thereby offering maximum support.

[0045] The receiver is preferably arranged at a height position on the first moveable mast frame which is closer to a top end than a bottom end of the first moveable mast frame. Preferably, the receiver is arranged at a height position of the first moveable mast frame corresponding to 50-90% of the height of the first moveable mast frame, and preferably 60-80%, and most preferably about 75%. Thus, the receiver may be arranged at an intermediate height, between the far ends of the first moveable mast, such as at height corresponding to at least half the height of the inner mast, and preferably at about ¾ of the height of the inner mast.

[0046] According to another aspect of the invention there is provided a method for operating the industrial truck of the type discussed in the foregoing, comprising: moving the first moveable mast frame, together with the fixedly arranged receiver, upwards in relation to the stationary mast frame; bringing the receiver into engagement with the moveable support when in a retracted position; moving the moveable support upwards together with the receiver upon continued movement of the first moveable mast frame, the moveable support thereby sliding along the piston of the mast lift cylinder to an extended position.

[0047] The industrial truck is preferably of a type referable to as a reach truck. The truck is preferably arranged to enable loading and off-loading at great heights. However, the novel solution could also be used for other types of trucks having one or more masts which carry the forks and which are telescopically displaceable in relation to the main body of the truck.

[0048] Other aspects, benefits and advantageous features of the invention will be apparent from the following description and claims.BRIEF DESCRIPTION OF THE DRAWINGS

[0049] The present invention will be described in more detail with reference to the appended drawings, showing currently preferred embodiments of the invention. Fig. 1 illustrates an overview of an exemplifying industrial truck in accordance with a first embodiment of the present disclosure; Fig. 2 is a block diagram illustrating the control system of the industrial truck of Fig. 1; Figs. 3A and 3B are views of the telescopic lifting arrangement of an industrial truck in accordance with an embodiment of the present disclosure; and Fig. 4 is a schematic illustration of a part of the telescopic lifting arrangement of Figs. 3A and 3B. DETAILED DESCRIPTION OF CURRENTLY PREFERRED EMBODIMENTS

[0050] The present invention will now be described more fully hereinafter with reference to the accompanying drawings, in which currently preferred embodiments of the invention are shown. This invention may, however, be embodied in many different forms and should not be construed as limited to the embodiments set forth herein; rather, these embodiments are provided for thoroughness and completeness, and fully convey the scope of the invention to the skilled addressee. Like reference characters refer to like elements throughout.

[0051] Fig. 1 illustrates an overview of an exemplifying industrial truck 1 in accordance with a first embodiment of the present disclosure. In a preferred embodiment, the industrial truck is a reach truck. The industrial truck 1 comprises a body frame 11, to which are mounted the major operating components of the vehicle 1, such as a telescoping mast arrangement 2, for lifting of a load handling arrangement, such as forks 3, an operator compartment 4, two non-steerable wheels 51, and a drive wheel 52 (not visible in fig 1). The drive wheel 52 may be arranged generally underneath the operator compartment. The dive wheel may also function as the steered wheel, for steering the truck. The two non-steerable wheels 51 may be arranged on a pair of outriggers 24 that extend from the body of the truck in a direction opposite the driving direction, so as to flank either side of the load handling arrangement and the forks. The operator compartment 4 may be open at the side positioned opposite to the load handling arrangement, to provide easy access thereto for the operator.

[0052] The truck may be adapted such that a user operating the vehicle 1 is seated transversely to a driving direction D. For seating, an operator's seat 6 is provided comprising an essentially horizontal seat section 61 for supporting the seated user's buttocks, along with a backrest 62 for supporting the seated operator's vertebral column.

[0053] As best seen in Fig. 2, the lift truck may comprise a vehicle controller 12 which receives operator input signals from operator controls 13, such as handles, key switches, pedals, stick controllers, steer wheels, control buttons etc. Based on the received signals, the controller provides command signals to electric motors, such as a lift motor 14 and a traction motor 15, as is per se known in the art. The drive motor provides a force for driving the truck in a selected direction, through the drive wheel 52, while the lift motor drives forks 3 along the mast 2 to raise or lower a load. The lift truck 1, including the vehicle controller 12 and the motors, may be powered by an electric energy source in the form of one or more battery.

[0054] The vehicle controller 12 may be a separate unit, possibly integrating several controller functions, or be arranged as a distributed controller system, including a plurality of connected controller units.

[0055] The speed of the traction motor 15 and associated wheels is selected by the operator by a speed control 131, such as an operator control handle, a pedal or the like. The drive wheel 52 may also be connected to a friction brake through the drive motor, providing both a service and parking brake function for the lift truck 1. The traction motor 15 is typically an electric motor. A speed detector 17 may be provided to estimate a current speed of the truck.

[0056] Steering of the steerable wheel, here the drive wheel 52, can be made through a steering control 132, such as a steering wheel or a steering tiller. The steering control may be arranged in front of the operator, but may alternatively be arranged towards one of the sides, such as on the lefthand side of the operator. The steering can be made manually, i.e. by a direct mechanical connection between the drive wheel 52 and the steering control 132, or by a steer motor, to steer the wheel in a direction selected by the operator. A steering angle detector 16 or other feedback device may be coupled to the steer motor or the steering wheel, to detect the current steering direction. This may be used by the controller to maintain the direction of travel of the lift truck 1 within a predetermined range of the selected direction of motion. The steerable wheel and the drive wheel need not be the same, but may also be arranged as different wheels.

[0057] A lift motor control 133 provides command signals to control the lift motor 14. The lift motor is connected to a hydraulic circuit including a pump for driving hydraulic cylinders for movement of the load handling arrangement and telescopic mast arrangement to be discussed in the following.

[0058] As illustrated in more detail in Figs. 3A and 3B, the telescopic mast arrangement 2 comprises a stationary mast frame 21, fixedly connected to the body of the industrial truck, and a first moveable mast frame 22. The first moveable mast frame 22 is moveable in a vertical direction in relation to the stationary mast frame 21. More than one moveable mast frame may also be provided, such as a second moveable mast frame (not shown).

[0059] A load handling arrangement, such as forks 3, is displaceably connected to the first moveable mast frame 22. Hereby, the load handling arrangement 3 is moveable in a vertical direction.

[0060] For movement of the load handling arrangement 3 and the one or more moveable mast frames, one or more hydraulic cylinders are provided.

[0061] The load handling arrangement 3 may be moved by a free-lift cylinder 24. However, other ways of moving the load handling arrangement 3 are feasible, as would be known by the skilled reader.

[0062] At least one mast lift cylinder 23 is arranged to move the first moveable mast frame 22 in relation to the stationary mast frame 21. The mast lift cylinder 23 comprises a cylinder tube or outer tube 232 and a piston 231. Preferably, two mast lift cylinders 23 are provided, arranged on opposite sides of the frame. Further, in case more than one moveable mast frame is used, one or more additional mast lift cylinders may be used to operate such additional mast frames. Alternatively, the second moveable mast, and even a possible third moveable mast, fourth moveable mast, etc., will be connected, e.g via chains to move together with the first moveable mast in a way where all the moveable masts telescope the complete mast simultaneously, in one joint movement. In such embodiments, only one cylinder, or one set of cylinders, connected to the moveable mast closest to the stationary mast is / are needed to move all moveable masts frames.

[0063] The free-lift cylinder 24 and the mast lift cylinder(s) 23 are preferably operated by the same hydraulic system, and connected to the same hydraulic pump 27. Hereby, the hydraulic pressure provided by the hydraulic pump 27 is distributed to all cylinders simultaneously, which means that the hydraulic cylinders with the lowest resistance, i.e. with the greatest cross-sectional area, will move first. Preferably, the internal cross-sectional areas of the at least one mast lift cylinder(s) 23 and the free-lift cylinder 24 are such that the free-lift cylinder 24 is moved before the mast lift cylinder(s) 23 upon operation of the hydraulic pump 27.

[0064] A moveable support 25 is slidably arranged around the piston 231 of the mast lift cylinder 23. Correspondingly, a receiver 26 is fixedly arranged on the first moveable mast frame 22.

[0065] The moveable support 25 and the receiver 26 comprise complementary engagement parts arranged to releasably engage the moveable support 25 and the receiver 26 when brought together as the first moveable mast frame 22 is moved upwards.

[0066] The moveable support 25 closely encircles the piston 231 of the first mast cylinder 23. Thus, the moveable support 25 preferably has an inner diameter which is essentially the same as, or only slightly larger, than an outer diameter of the piston 231. Hereby, the moveable support 25 may offer support to the piston 231 in all horizontal directions, and at the same time be easily moveable along the piston 231. To facilitate sliding of the moveable support 25 over the piston 231, the moveable support may, at an internal surface facing the piston, be provided with a low friction surface.

[0067] In the exemplary embodiment, the moveable support comprises a base plate 253, providing an opening or hole 254 closely surrounding the exterior surface of the piston 231 of the first mast lift cylinder 23. However, other realizations of the moveable support are also feasible. For example, the moveable support may have a flexible structure surrounding the piston 231, such as a chain or the like.

[0068] In the illustrative embodiment, the engagement parts of the moveable support 25 comprises one or more vertically protruding elements 251, in the form of taps, pins, fingers or the like. The vertically protruding elements are preferably generally cylindrical in shape, and preferably have a tapered, conical shape, at least towards the free, downwardly directed ends. In the illustrative example, the vertically protruding elements 251 have generally pointed, conical ends directed downwardly, i.e. at the free ends, followed by a generally cylindrical base part.

[0069] In the illustrative example, two parallel vertically protruding elements 251 are provided. However, in alternative embodiments, only one vertically protruding element 251 may be used. It is also feasible to use more than two vertically protruding elements 251.

[0070] In the illustrative example, where the moveable support is realized as a base plate, the engagement parts, i.e. here the vertically protruding elements 251, may be arranged at a side of the base plate. In the illustrative example, the vertically protruding elements 251 are arranged as one or more downwardly extending fingers or pins, directed vertically downwardly from a part of the base plate extending out from the enclosed piston 231.

[0071] The receiver 26 may be arranged as a receiver block, fixedly arranged on the first moveable mast frame. The receiver block is here, in the illustrative example, provided with openings or holes 261 corresponding to the vertically protruding elements, such as fingers / taps / pins, of the moveable support 25. However, the receiver need not be rectangular, and other shapes are also feasible. For example, the receiver may have the shape of a plate, a cylinder, a wedge, or the like. Any shape capable of forming the openings to receive the vertically protruding elements could be used.

[0072] However, other types of engagement parts are also feasible. For example, the receiver may be provided with vertically protruding elements, directly upwardly, and the moveable support may be provided with corresponding holes or openings. Further, other types of engagement elements, such as wedge-shaped engagement parts, are also feasible, as would be appreciated by the skilled reader.

[0073] In the illustrative embodiment, the moveable support 25, in its retracted position, is arranged at, or in the vicinity of, a top end 233 of an outer sleeve 232 of the mast lift cylinder 23.

[0074] Upon use, the receiver 26 is moved upwards when the first moveable mast frame 22 is lifted. At a certain point, the receiver 26 is brought into contact with the movable support 25. Upon contact, the complementary engagement parts are releasably engaged, whereby the movable support 25 is lifted, together with the receiver 26, upon continued lifting of the first moveable mast frame 22. Hereby, the moveable support 25 will slide along the piston 231. Since the receiver 25 is fixedly connected to the first moveable mast frame 22 the moveable support 25 connects the piston 231 to the first moveable mast frame 22 in all lateral. horizontal directions, thereby providing support to the piston 231.

[0075] Thus, differently put, the operation may be described as follows. When the cylinder 231 is in a retracted position, the moveable support 25 is preferably in contact with, or in the vicinity of, the upper end 233 of the outer sleeve / tube 232 of the first mast lift cylinder 23. Preferably, the moveable support 25 in this state rests on the outer sleeve 232 of the mast lift cylinder 23. At the same time, when the first moveable mast frame 22 is in a retracted position, the receiver block 26 is at a distance from the moveable support 25.

[0076] When the first mast cylinder 23 is operated, the piston 231 is expelled out from the outer sleeve 232. However, the moveable support 25 maintains its position at the end 233 of the outer sleeve 232. At the same time, the inner mast frame 22 moves upwards in conjunction with the piston 231, and, consequently, the receiver 26 is moved closer to the moveable support 25.

[0077] At a certain height, e.g. when the first moveable mast frame 22 has been lifted a distance corresponding to the height when the support becomes positioned close to the middle of the piston 231, the receiver 26 reaches the moveable support 25, and the complementary engagement parts 251, 261 of the moveable support 25 and the receiver 26 engage.

[0078] Upon continued lifting, the moveable support 25 is moved together with the receiver 26 and the inner mast frame 22. Hereby, the moveable support 25 maintains its position relative to the piston 231, whereas the distance from the outer sleeve 232 increases.

[0079] At the fully extended position, the moveable support 25 is at a height corresponding to e.g. ½ or ¾ of the height of the piston 231. At this position, and also previously during the entire lifting operation, the moveable support stabilizes the piston to the inner frame. This significantly reduces the risk of kinking, deformation, bending and other damages occurring to the piston.

[0080] When the first moveable mast 22 is again lowered, the same steps are repeated in a reverse order.

[0081] In an embodiment, the first moveable mast frame 22 is arranged as an inner mast frame in relation to the stationary mast frame 21. A second moveable mast frame (not shown) may be arranged as an intermediate mast frame, arranged between the stationary mast frame 21 and the first moveable mast frame 22. Thus, in such an embodiment the telescopic mast arrangement comprises three mast sections - one stationary and two moveable masts frames. The second moveable mast frame may be moved by one or several additional second mast lift cylinder(s). Such additional piston(s) of such second mast lift cylinder(s) may be stabilized in the same way as for the piston(s) of the first mast lift cylinder, by use of additional moveable support(s) and receiver(s). Alternatively, the second moveable mast, and even a possible additional moveable mast(s), may be operated by the first mast lift cylinder, e.g. by being connected via chains to move together with the first moveable mast in a way where all the moveable masts telescope the complete mast simultaneously, in one joint movement.

[0082] As best seen in Fig. 4, the receiver 26 is preferably arranged at a height position on the first moveable mast frame 22 so that the moveable support 25 is lifted to a position between 20-80%, and preferably 25-75%, of the length of the piston 231 when maximally extended, and preferably to a position at about the middle of the piston 231. The receiver 26 is hereby arranged at a height so that the support is provided close to the middle of the piston 231 when in a maximally extended state, thereby offering maximum support.

[0083] The length of the fully extended piston, i.e. the length protruding out from the cylinder when maximally extended, may be denominated L1, and the height of the receiver 26 and the moveable support 25, i.e. the length from the top end of the cylinder to the moveable support 25 and the receiver 26, at the fully extended position may be denominated L2. Thus, in a preferred embodiment L2 = L1 * 0.5 when the cylinder is fully extended. This represents the most effective support position from buckling prevention point of view, since it minimizes the bending of the cylinder rod and minimizes the horizontal counteract forces in the most critical cylinder rod position.

[0084] However, in embodiments, the length L2 could also assume other values within the range L2 = L1 * 0.2 .. L1 * 0.8 when the cylinder is fully extended. The position can be varied quite freely since the moveable support constitutes a "third hand" when placed somewhere at the free length of the cylinder rod when the rod extends. It may be activated earlier or later during the staging by selecting the position of the receiver. If load limitations are applied against height, another, lower critical height position L1 * 0.5 may exist where it is favorable to activate the moveable support earlier. Other cases may occur where it is favorable to activate the moveable support later due to practical circumstances.

[0085] Further, the receiver 26 is preferably arranged at a height position on the first moveable mast frame 22 which is closer to a top end than a bottom end of the first moveable mast frame 22. Preferably, the receiver 26 is arranged at a height position of the first moveable mast frame 22 corresponding to 50-90% of the height of the first moveable mast frame 22, and preferably 60-80%, and most preferably about 75%. Thus, the receiver 26 may be arranged at an intermediate height, between the far ends of the first moveable mast 22, such as at height corresponding to at least half the height of the first moveable mast 22, and preferably at about ¾ of the height of the first moveable mast 22.

[0086] The person skilled in the art realizes that the present invention by no means is limited to the preferred embodiments described above. On the contrary, many modifications and variations are possible within the scope of the appended claims. For example, many types of engagement parts are possible to releasably connect the receiver and the moveable support. Further, the industrial truck may comprise only one moveable mast frame, or two or even more moveable mast frames. In such embodiments, the solution with a movable support may be used only to support the cylinder operating the outermost, first moveable mast frame, but may also be used to support cylinders operating one or more intermediate mast frames.

[0087] Such and other obvious modifications must be considered to be within the scope of the present invention, as it is defined by the appended claims. It should be noted that the above-mentioned embodiments illustrate rather than limit the invention, and that those skilled in the art will be able to design many alternative embodiments without departing from the scope of the appended claims. In the claims, any reference signs placed between parentheses shall not be construed as limiting to the claim. The word "comprising" does not exclude the presence of other elements or steps than those listed in the claim. The word "a" or "an" preceding an element does not exclude the presence of a plurality of such elements. Further, a single unit may perform the functions of several means recited in the claims.

Examples

Embodiment Construction

[0050]The present invention will now be described more fully hereinafter with reference to the accompanying drawings, in which currently preferred embodiments of the invention are shown. This invention may, however, be embodied in many different forms and should not be construed as limited to the embodiments set forth herein; rather, these embodiments are provided for thoroughness and completeness, and fully convey the scope of the invention to the skilled addressee. Like reference characters refer to like elements throughout.

[0051]Fig. 1 illustrates an overview of an exemplifying industrial truck 1 in accordance with a first embodiment of the present disclosure. In a preferred embodiment, the industrial truck is a reach truck. The industrial truck 1 comprises a body frame 11, to which are mounted the major operating components of the vehicle 1, such as a telescoping mast arrangement 2, for lifting of a load handling arrangement, such as forks 3, an operator compartment 4, two non-s...

TECHNICAL FIELD OF THE INVENTION

[0001] The present invention relates to an industrial truck with a telescopic mast arrangement.BACKGROUND OF THE INVENTION

[0002] Extendable mast arrangements are used in certain industrial trucks, such as in reach trucks. The mast arrangement typically comprises a stationary mast which is vertically fixedly connected to the vehicle frame. One or more additional masts are telescopically displaceable in relation to the stationary mast. The telescopic displaceability may be provided in the form of profile rails or the like, connecting the frames to each other.

[0003] If mast frames are used, the stationary mast may be arranged as an outer frame fixedly connected to the vehicle and the moveable mast may be arranged as an inner mast, being telescopically displaceable in relation to the outer mast.

[0004] If three mast frames are used, a second telescopically displaceable, moveable frame may be arranged between the inner mast and the outer mast.

[0005] A load handling arrangement, typically in the form of a fork carriage, may be displaceable along a guiding structure arranged on the inner mast.

[0006] The fork carriage is conventionally hydraulically lifted by one or more hydraulically actuated cylinder(s). The cylinder(s) may be arranged to bring the displaceable mast along, telescoping together with the fork carriage motion. Alternatively, the cylinder(s) may be arranged to lift the fork carriage without bringing any displaceable mast along - a so called free-lift function, where separate cylinder(s), mast cylinders, are used for lifting the displaceable mast(s). For example, two mast cylinders may be provided, one mast lift cylinder e.g. being arranged close to each side of the mast structure.

[0007] Examples of such known telescopic mast arrangements for industrial trucks are disclosed in EP 2465812, EP 0866026, EP 0622331 and US6557456.

[0008] The free-lift cylinder(s) and the mast lift cylinder(s) may be operated by the same hydraulic system. The internal cross-sectional areas of the cylinders may then determine in which order the cylinders are operated. When the hydraulic pressure is increased, the cylinder which is easiest to move, i.e. the cylinder with the greatest cross-sectional area, will be lifted first. This will typically be the free-lift cylinder(s). When the free-lift cylinder(s) has been maximally extended, the inner mast will then be lifted by the mast lift cylinders.

[0009] The cylinders typically comprise an outer tube / sleeve and a piston rod being telescopically displaceable in relation to the outer tube / sleeve. The lift length of the mast lift cylinders can be great, such as several meters. The mast lift cylinders consequently need to be dimensioned to be able to withstand both the (possibly) heavy load and the great height, without deforming, buckling, or in other ways being damaged during use. However, lifting and lowering speeds benefit from keeping the cylinders' diameters limited. These contradictory factors generate a need for improvement.

[0010] Since the free-lift cylinder would generally need to have a greater cross-sectional area than the mast lift cylinders, also this cylinder must have large dimensions, thereby restricting the piston movement speed.

[0011] In total, this makes the cylinders and the hydraulic system costly and also slow in operation.

[0012] A solution to address this problem may be to control the cylinders separately and independently, by use of electric valves. However, even if this may increase the lifting and lowering speed of the free-lift movement, this solution would make the system still more complicated and costly. Further, the increased lifting and lowering speed hereby obtained is only related to the free-lifts, since it does not address the deformation / buckling problem, which is setting the required dimensions for the mast lift cylinders.

[0013] There is therefore a need for an improved extendable mast arrangement for an industrial truck addressing these problems in the prior art. In particular, there is a need for an extendable mast arrangement which can be operated at a higher speed, which is more cost-effective and / or with higher resistance against damages, such as buckling and other forms of deformation.SUMMARY OF THE INVENTION

[0014] It is therefore an object to provide an industrial truck which alleviates all, or at least some, of the above-discussed drawbacks and problems of the prior art.

[0015] This object is achieved with an industrial truck as defined in the appended claims.

[0016] According to a first aspect of the invention there is provided an industrial truck comprising: a stationary mast frame; a first moveable mast frame, the first moveable mast frame being moveable in a vertical direction in relation to the stationary mast frame; a load handling arrangement displaceably connected to the first moveable mast frame, the load handling arrangement being moveable in a vertical direction; at least one mast lift cylinder arranged to move the first moveable mast frame in relation to the stationary mast frame, the mast lift cylinder comprising a piston; a moveable support slidably arranged around the piston of the mast lift cylinder; and a receiver fixedly arranged on the first moveable mast frame, wherein the moveable support and the receiver comprise complementary engagement parts arranged to releasably engage the moveable support and the receiver when brought together as the first moveable mast frame is moved upwards.

[0017] The piston may also be referred to as a rod. The piston may be tubular, i.e. tube-shaped, but may alternatively be solid. The piston preferably has a circular cross-section, but other cross-sectional shapes are also feasible.

[0018] The new solution enables use of essentially the same set-up as has been used previously, with an outer, stationary mast frame and an inner displaceable mast frame, and optionally one or more additional mast frames in between. Further, the displaceable mast frame(s) is moved by one or more mast lift cylinder, and a load handling arrangement, such as a fork, is displaceable along the inner mast frame, e.g. by use of a free-lift cylinder.

[0019] The new solution provides an additional support and stabilization for the piston(s) of the mast lift cylinder(s), thereby protecting the cylinder(s), and in particular the piston(s), against buckling, deforming and other types of related damage.

[0020] Due to the moveable support it becomes possible to use smaller and less costly mast lift cylinders, and consequently also a smaller and less costly free-lift cylinder(s). The smaller cylinders also increase the operational speed for lifting and lowering the mast frames and forks.

[0021] The moveable support is relatively loosely arranged around the piston of the mast lift cylinder, thereby allowing it to slide axially along the length of the piston.

[0022] In a retracted position, the movable support may be arranged on top of the outer sleeve of the mast lift cylinder.

[0023] The moveable support preferably has a base plate with an opening loosely holding the moveable support on the piston, allowing the moveable support to glide over the piston.

[0024] As the receiver is moved upwards when the first moveable mast frame is lifted, it is brought into contact with the movable support. Upon contact, the complementary engagement parts are releasably engaged, whereby the movable support is lifted together with the receiver upon continued lifting of the first moveable mast frame. Hereby, the moveable support will slide along the piston. Since the receiver is fixedly connected to the first moveable mast frame the moveable support it connects the piston to the first moveable mast frame in lateral directions, thereby providing support to the piston in horizontal directions.

[0025] Thus, differently put, the operation may be described as follows. When the cylinder is in a retracted position, the moveable support is preferably in contact with, or in the vicinity of, the upper end of the outer sleeve / tube of the first mast lift cylinder. In an embodiment, the moveable support rests on the outer sleeve of the mast lift cylinder. At the same time, when the first moveable mast frame is in a retracted position, the receiver block is at a distance from the moveable support.

[0026] When the first mast cylinder is operated, the piston is expelled out from the outer sleeve. However, the moveable support maintains its position at the end of the outer sleeve. At the same time, the inner mast frame moves upwards in conjunction with the piston, and, consequently, the receiver block is moved closer to the moveable support.

[0027] At a certain height, e.g. when the first moveable mast frame has been lifted a distance corresponding to the height when the support becomes positioned close to the middle of the piston, the receiver block reaches the moveable support, and the complementary engagement parts of the moveable support and the receiver engage.

[0028] Upon continued lifting, the moveable support is moved together with the receiver and the inner mast frame. Hereby, the moveable support maintains its position relative to the piston, whereas the distance from the outer sleeve increases.

[0029] At the fully extended position, the moveable support is preferably at a height corresponding to 20-80% of the length of the fully extended piston, e.g. about 50% of the length of the fully extended piston. At this position, and also previously during the entire lifting operation, the moveable support stabilizes the piston to the inner frame. This significantly reduces the risk of kinking, deformation, bending and other damages occurring to the piston.

[0030] A lift height corresponding to 50% of the length of the fully extended piston represents the most effective support position from a buckling prevention point of view, since it minimizes the bending of the cylinder rod and minimizes the horizontal counteracting forces in the most critical cylinder rod position.

[0031] However, it also feasible to use other maximum heights, within the range from 20-80% of the length of the fully extended piston. The position can be varied quite freely since the moveable support constitutes a "third hand" when placed somewhere at the free length of the cylinder rod when the rod extends. It may be activated earlier or later during the staging by selecting the position of the receiver. If load limitations are applied against height, another, lower critical height position than at 50% may exist where it is favorable to activate the moveable support earlier. Other cases may occur where it is favorable to activate the moveable support later due to practical circumstances.

[0032] When the first moveable mast is again lowered, the same steps are repeated in a reverse order.

[0033] In embodiments, it is possible to move the load handling arrangement, such as forks, in various ways, such as by electric motors, by chains, etc. However, preferably, the load handling arrangement is moved by a hydraulic cylinder, i.e. a free-lift cylinder.

[0034] Thus, in an embodiment, the industrial truck further comprises a free-lift cylinder arranged to move the forks in relation to the moveable mast frame.

[0035] In embodiments, the mast lift cylinder(s) and the free-lift cylinder are hydraulic cylinders actuated by the same hydraulic system. Preferably, the internal cross-sectional areas of the at least one mast lift cylinder(s) and the free-lift cylinder are such that the free-lift cylinder is moved before the mast lift cylinder(s) upon operation of the hydraulic system. In such embodiments the support of the piston of the first mast cylinder(s), as discussed in the foregoing, is of particular importance and advantage.

[0036] In an embodiment, the first moveable mast frame is arranged as an inner mast frame in relation to the stationary mast frame, and wherein a second moveable mast frame is arranged as an intermediate mast frame, arranged between the stationary mast frame and the first moveable mast frame. Thus, in such an embodiment the telescopic mast arrangement comprises three mast sections - one stationary and two moveable masts frames. The second moveable mast frame may be moved by one or several additional second mast lift cylinder(s). Such additional piston(s) of such second mast lift cylinder(s) may be stabilized in the same way as for the piston(s) of the first mast lift cylinder, by use of additional moveable support(s) and receiver(s). Alternatively, the second moveable mast, and even a possible third moveable mast, fourth moveable mast, etc., will be connected, e.g via chains to move together with the first moveable mast in a way where all the moveable masts telescope the complete mast simultaneously, in one joint movement. In such embodiments, only one cylinder, or one set of cylinders, connected to the moveable mast closest to the stationary mast is / are needed to move all moveable masts frames.

[0037] In an embodiment, the first moveable mast frame is arranged as an inner mast frame in relation to the stationary mast frame, and wherein a second moveable mast frame is arranged as an intermediate mast frame, arranged between the stationary mast frame and the first moveable mast frame, wherein at least one of said mast lift cylinder(s) is connected to the moveable mast frame closest to the stationary mast.

[0038] In an embodiment, the moveable support, in a retracted position, is arranged at, or in the vicinity of, a top end of an outer sleeve of the mast lift cylinder.

[0039] The moveable support preferably comprises a base plate with an opening therein, the opening having an internal diameter exceeding an outer diameter of the piston of the mast-lift cylinder, and wherein at least one of the engagement parts is arranged at, or in the vicinity of, an end side of the base plate. The opening of the base plate may consequently be arranged to closely encircle the piston, thereby providing lateral support in all horizontal directions.

[0040] The complementary engagement parts may comprise at least one vertically protruding element, arranged on the moveable support or the receiver, and at least one hole dimensioned to receive the vertically protruding element, the at least one hole being arranged on the other of the moveable support and the receiver.

[0041] In an embodiment, the moveable support comprises the at least one vertically protruding element, the vertically protruding element(s) having a downwardly directed free end, and wherein the receiver comprises the at least one hole arranged to engage with the vertically protruding element(s).

[0042] In an embodiment, the vertically protruding element(s) have over at least a part of the length a tapered, conical shape, thereby having a smaller cross-sectional area at a free end and a greater cross-sectional area at a base or at an intermediate position. This presents a smaller, more pointed forward end, which facilitates insertion of the vertically protruding element(s) into the corresponding holes.

[0043] For example, in embodiments where the moveable support comprises a base plate, engagement parts may be arranged as a a side of the base plate, e.g. in the form of one or more downwardly extending fingers or pins. In a preferred embodiment, two such downwardly extending fingers are provided. The fingers preferably have a tapering, conical shape, at least towards the lowermost end, with a gradually decreasing cross-sectional area in the downward direction. A corresponding receiver block may be fixedly arranged on the first moveable mast frame. The receiver block is here provided with openings corresponding to the fingers of the moveable support.

[0044] The receiver is preferably arranged at a height position on the first moveable mast frame so that the moveable support is lifted to a position between 25% and 75% of the length of the fully extended piston, i.e. when the length of the piston protruding out from the cylinder when the piston is maximally extended, and preferably to a position at about the middle of the piston. The receiver block is hereby arranged at a height so that the support is provided close to the middle of the piston when in a maximally extended state, thereby offering maximum support.

[0045] The receiver is preferably arranged at a height position on the first moveable mast frame which is closer to a top end than a bottom end of the first moveable mast frame. Preferably, the receiver is arranged at a height position of the first moveable mast frame corresponding to 50-90% of the height of the first moveable mast frame, and preferably 60-80%, and most preferably about 75%. Thus, the receiver may be arranged at an intermediate height, between the far ends of the first moveable mast, such as at height corresponding to at least half the height of the inner mast, and preferably at about ¾ of the height of the inner mast.

[0046] According to another aspect of the invention there is provided a method for operating the industrial truck of the type discussed in the foregoing, comprising: moving the first moveable mast frame, together with the fixedly arranged receiver, upwards in relation to the stationary mast frame; bringing the receiver into engagement with the moveable support when in a retracted position; moving the moveable support upwards together with the receiver upon continued movement of the first moveable mast frame, the moveable support thereby sliding along the piston of the mast lift cylinder to an extended position.

[0047] The industrial truck is preferably of a type referable to as a reach truck. The truck is preferably arranged to enable loading and off-loading at great heights. However, the novel solution could also be used for other types of trucks having one or more masts which carry the forks and which are telescopically displaceable in relation to the main body of the truck.

[0048] Other aspects, benefits and advantageous features of the invention will be apparent from the following description and claims.BRIEF DESCRIPTION OF THE DRAWINGS

[0049] The present invention will be described in more detail with reference to the appended drawings, showing currently preferred embodiments of the invention. Fig. 1 illustrates an overview of an exemplifying industrial truck in accordance with a first embodiment of the present disclosure; Fig. 2 is a block diagram illustrating the control system of the industrial truck of Fig. 1; Figs. 3A and 3B are views of the telescopic lifting arrangement of an industrial truck in accordance with an embodiment of the present disclosure; and Fig. 4 is a schematic illustration of a part of the telescopic lifting arrangement of Figs. 3A and 3B. DETAILED DESCRIPTION OF CURRENTLY PREFERRED EMBODIMENTS

[0050] The present invention will now be described more fully hereinafter with reference to the accompanying drawings, in which currently preferred embodiments of the invention are shown. This invention may, however, be embodied in many different forms and should not be construed as limited to the embodiments set forth herein; rather, these embodiments are provided for thoroughness and completeness, and fully convey the scope of the invention to the skilled addressee. Like reference characters refer to like elements throughout.

[0051] Fig. 1 illustrates an overview of an exemplifying industrial truck 1 in accordance with a first embodiment of the present disclosure. In a preferred embodiment, the industrial truck is a reach truck. The industrial truck 1 comprises a body frame 11, to which are mounted the major operating components of the vehicle 1, such as a telescoping mast arrangement 2, for lifting of a load handling arrangement, such as forks 3, an operator compartment 4, two non-steerable wheels 51, and a drive wheel 52 (not visible in fig 1). The drive wheel 52 may be arranged generally underneath the operator compartment. The dive wheel may also function as the steered wheel, for steering the truck. The two non-steerable wheels 51 may be arranged on a pair of outriggers 24 that extend from the body of the truck in a direction opposite the driving direction, so as to flank either side of the load handling arrangement and the forks. The operator compartment 4 may be open at the side positioned opposite to the load handling arrangement, to provide easy access thereto for the operator.

[0052] The truck may be adapted such that a user operating the vehicle 1 is seated transversely to a driving direction D. For seating, an operator's seat 6 is provided comprising an essentially horizontal seat section 61 for supporting the seated user's buttocks, along with a backrest 62 for supporting the seated operator's vertebral column.

[0053] As best seen in Fig. 2, the lift truck may comprise a vehicle controller 12 which receives operator input signals from operator controls 13, such as handles, key switches, pedals, stick controllers, steer wheels, control buttons etc. Based on the received signals, the controller provides command signals to electric motors, such as a lift motor 14 and a traction motor 15, as is per se known in the art. The drive motor provides a force for driving the truck in a selected direction, through the drive wheel 52, while the lift motor drives forks 3 along the mast 2 to raise or lower a load. The lift truck 1, including the vehicle controller 12 and the motors, may be powered by an electric energy source in the form of one or more battery.

[0054] The vehicle controller 12 may be a separate unit, possibly integrating several controller functions, or be arranged as a distributed controller system, including a plurality of connected controller units.

[0055] The speed of the traction motor 15 and associated wheels is selected by the operator by a speed control 131, such as an operator control handle, a pedal or the like. The drive wheel 52 may also be connected to a friction brake through the drive motor, providing both a service and parking brake function for the lift truck 1. The traction motor 15 is typically an electric motor. A speed detector 17 may be provided to estimate a current speed of the truck.

[0056] Steering of the steerable wheel, here the drive wheel 52, can be made through a steering control 132, such as a steering wheel or a steering tiller. The steering control may be arranged in front of the operator, but may alternatively be arranged towards one of the sides, such as on the lefthand side of the operator. The steering can be made manually, i.e. by a direct mechanical connection between the drive wheel 52 and the steering control 132, or by a steer motor, to steer the wheel in a direction selected by the operator. A steering angle detector 16 or other feedback device may be coupled to the steer motor or the steering wheel, to detect the current steering direction. This may be used by the controller to maintain the direction of travel of the lift truck 1 within a predetermined range of the selected direction of motion. The steerable wheel and the drive wheel need not be the same, but may also be arranged as different wheels.

[0057] A lift motor control 133 provides command signals to control the lift motor 14. The lift motor is connected to a hydraulic circuit including a pump for driving hydraulic cylinders for movement of the load handling arrangement and telescopic mast arrangement to be discussed in the following.

[0058] As illustrated in more detail in Figs. 3A and 3B, the telescopic mast arrangement 2 comprises a stationary mast frame 21, fixedly connected to the body of the industrial truck, and a first moveable mast frame 22. The first moveable mast frame 22 is moveable in a vertical direction in relation to the stationary mast frame 21. More than one moveable mast frame may also be provided, such as a second moveable mast frame (not shown).

[0059] A load handling arrangement, such as forks 3, is displaceably connected to the first moveable mast frame 22. Hereby, the load handling arrangement 3 is moveable in a vertical direction.

[0060] For movement of the load handling arrangement 3 and the one or more moveable mast frames, one or more hydraulic cylinders are provided.

[0061] The load handling arrangement 3 may be moved by a free-lift cylinder 24. However, other ways of moving the load handling arrangement 3 are feasible, as would be known by the skilled reader.

[0062] At least one mast lift cylinder 23 is arranged to move the first moveable mast frame 22 in relation to the stationary mast frame 21. The mast lift cylinder 23 comprises a cylinder tube or outer tube 232 and a piston 231. Preferably, two mast lift cylinders 23 are provided, arranged on opposite sides of the frame. Further, in case more than one moveable mast frame is used, one or more additional mast lift cylinders may be used to operate such additional mast frames. Alternatively, the second moveable mast, and even a possible third moveable mast, fourth moveable mast, etc., will be connected, e.g via chains to move together with the first moveable mast in a way where all the moveable masts telescope the complete mast simultaneously, in one joint movement. In such embodiments, only one cylinder, or one set of cylinders, connected to the moveable mast closest to the stationary mast is / are needed to move all moveable masts frames.

[0063] The free-lift cylinder 24 and the mast lift cylinder(s) 23 are preferably operated by the same hydraulic system, and connected to the same hydraulic pump 27. Hereby, the hydraulic pressure provided by the hydraulic pump 27 is distributed to all cylinders simultaneously, which means that the hydraulic cylinders with the lowest resistance, i.e. with the greatest cross-sectional area, will move first. Preferably, the internal cross-sectional areas of the at least one mast lift cylinder(s) 23 and the free-lift cylinder 24 are such that the free-lift cylinder 24 is moved before the mast lift cylinder(s) 23 upon operation of the hydraulic pump 27.

[0064] A moveable support 25 is slidably arranged around the piston 231 of the mast lift cylinder 23. Correspondingly, a receiver 26 is fixedly arranged on the first moveable mast frame 22.

[0065] The moveable support 25 and the receiver 26 comprise complementary engagement parts arranged to releasably engage the moveable support 25 and the receiver 26 when brought together as the first moveable mast frame 22 is moved upwards.

[0066] The moveable support 25 closely encircles the piston 231 of the first mast cylinder 23. Thus, the moveable support 25 preferably has an inner diameter which is essentially the same as, or only slightly larger, than an outer diameter of the piston 231. Hereby, the moveable support 25 may offer support to the piston 231 in all horizontal directions, and at the same time be easily moveable along the piston 231. To facilitate sliding of the moveable support 25 over the piston 231, the moveable support may, at an internal surface facing the piston, be provided with a low friction surface.

[0067] In the exemplary embodiment, the moveable support comprises a base plate 253, providing an opening or hole 254 closely surrounding the exterior surface of the piston 231 of the first mast lift cylinder 23. However, other realizations of the moveable support are also feasible. For example, the moveable support may have a flexible structure surrounding the piston 231, such as a chain or the like.

[0068] In the illustrative embodiment, the engagement parts of the moveable support 25 comprises one or more vertically protruding elements 251, in the form of taps, pins, fingers or the like. The vertically protruding elements are preferably generally cylindrical in shape, and preferably have a tapered, conical shape, at least towards the free, downwardly directed ends. In the illustrative example, the vertically protruding elements 251 have generally pointed, conical ends directed downwardly, i.e. at the free ends, followed by a generally cylindrical base part.

[0069] In the illustrative example, two parallel vertically protruding elements 251 are provided. However, in alternative embodiments, only one vertically protruding element 251 may be used. It is also feasible to use more than two vertically protruding elements 251.

[0070] In the illustrative example, where the moveable support is realized as a base plate, the engagement parts, i.e. here the vertically protruding elements 251, may be arranged at a side of the base plate. In the illustrative example, the vertically protruding elements 251 are arranged as one or more downwardly extending fingers or pins, directed vertically downwardly from a part of the base plate extending out from the enclosed piston 231.

[0071] The receiver 26 may be arranged as a receiver block, fixedly arranged on the first moveable mast frame. The receiver block is here, in the illustrative example, provided with openings or holes 261 corresponding to the vertically protruding elements, such as fingers / taps / pins, of the moveable support 25. However, the receiver need not be rectangular, and other shapes are also feasible. For example, the receiver may have the shape of a plate, a cylinder, a wedge, or the like. Any shape capable of forming the openings to receive the vertically protruding elements could be used.

[0072] However, other types of engagement parts are also feasible. For example, the receiver may be provided with vertically protruding elements, directly upwardly, and the moveable support may be provided with corresponding holes or openings. Further, other types of engagement elements, such as wedge-shaped engagement parts, are also feasible, as would be appreciated by the skilled reader.

[0073] In the illustrative embodiment, the moveable support 25, in its retracted position, is arranged at, or in the vicinity of, a top end 233 of an outer sleeve 232 of the mast lift cylinder 23.

[0074] Upon use, the receiver 26 is moved upwards when the first moveable mast frame 22 is lifted. At a certain point, the receiver 26 is brought into contact with the movable support 25. Upon contact, the complementary engagement parts are releasably engaged, whereby the movable support 25 is lifted, together with the receiver 26, upon continued lifting of the first moveable mast frame 22. Hereby, the moveable support 25 will slide along the piston 231. Since the receiver 25 is fixedly connected to the first moveable mast frame 22 the moveable support 25 connects the piston 231 to the first moveable mast frame 22 in all lateral. horizontal directions, thereby providing support to the piston 231.

[0075] Thus, differently put, the operation may be described as follows. When the cylinder 231 is in a retracted position, the moveable support 25 is preferably in contact with, or in the vicinity of, the upper end 233 of the outer sleeve / tube 232 of the first mast lift cylinder 23. Preferably, the moveable support 25 in this state rests on the outer sleeve 232 of the mast lift cylinder 23. At the same time, when the first moveable mast frame 22 is in a retracted position, the receiver block 26 is at a distance from the moveable support 25.

[0076] When the first mast cylinder 23 is operated, the piston 231 is expelled out from the outer sleeve 232. However, the moveable support 25 maintains its position at the end 233 of the outer sleeve 232. At the same time, the inner mast frame 22 moves upwards in conjunction with the piston 231, and, consequently, the receiver 26 is moved closer to the moveable support 25.

[0077] At a certain height, e.g. when the first moveable mast frame 22 has been lifted a distance corresponding to the height when the support becomes positioned close to the middle of the piston 231, the receiver 26 reaches the moveable support 25, and the complementary engagement parts 251, 261 of the moveable support 25 and the receiver 26 engage.

[0078] Upon continued lifting, the moveable support 25 is moved together with the receiver 26 and the inner mast frame 22. Hereby, the moveable support 25 maintains its position relative to the piston 231, whereas the distance from the outer sleeve 232 increases.

[0079] At the fully extended position, the moveable support 25 is at a height corresponding to e.g. ½ or ¾ of the height of the piston 231. At this position, and also previously during the entire lifting operation, the moveable support stabilizes the piston to the inner frame. This significantly reduces the risk of kinking, deformation, bending and other damages occurring to the piston.

[0080] When the first moveable mast 22 is again lowered, the same steps are repeated in a reverse order.

[0081] In an embodiment, the first moveable mast frame 22 is arranged as an inner mast frame in relation to the stationary mast frame 21. A second moveable mast frame (not shown) may be arranged as an intermediate mast frame, arranged between the stationary mast frame 21 and the first moveable mast frame 22. Thus, in such an embodiment the telescopic mast arrangement comprises three mast sections - one stationary and two moveable masts frames. The second moveable mast frame may be moved by one or several additional second mast lift cylinder(s). Such additional piston(s) of such second mast lift cylinder(s) may be stabilized in the same way as for the piston(s) of the first mast lift cylinder, by use of additional moveable support(s) and receiver(s). Alternatively, the second moveable mast, and even a possible additional moveable mast(s), may be operated by the first mast lift cylinder, e.g. by being connected via chains to move together with the first moveable mast in a way where all the moveable masts telescope the complete mast simultaneously, in one joint movement.

[0082] As best seen in Fig. 4, the receiver 26 is preferably arranged at a height position on the first moveable mast frame 22 so that the moveable support 25 is lifted to a position between 20-80%, and preferably 25-75%, of the length of the piston 231 when maximally extended, and preferably to a position at about the middle of the piston 231. The receiver 26 is hereby arranged at a height so that the support is provided close to the middle of the piston 231 when in a maximally extended state, thereby offering maximum support.

[0083] The length of the fully extended piston, i.e. the length protruding out from the cylinder when maximally extended, may be denominated L1, and the height of the receiver 26 and the moveable support 25, i.e. the length from the top end of the cylinder to the moveable support 25 and the receiver 26, at the fully extended position may be denominated L2. Thus, in a preferred embodiment L2 = L1 * 0.5 when the cylinder is fully extended. This represents the most effective support position from buckling prevention point of view, since it minimizes the bending of the cylinder rod and minimizes the horizontal counteract forces in the most critical cylinder rod position.

[0084] However, in embodiments, the length L2 could also assume other values within the range L2 = L1 * 0.2 .. L1 * 0.8 when the cylinder is fully extended. The position can be varied quite freely since the moveable support constitutes a "third hand" when placed somewhere at the free length of the cylinder rod when the rod extends. It may be activated earlier or later during the staging by selecting the position of the receiver. If load limitations are applied against height, another, lower critical height position L1 * 0.5 may exist where it is favorable to activate the moveable support earlier. Other cases may occur where it is favorable to activate the moveable support later due to practical circumstances.

[0085] Further, the receiver 26 is preferably arranged at a height position on the first moveable mast frame 22 which is closer to a top end than a bottom end of the first moveable mast frame 22. Preferably, the receiver 26 is arranged at a height position of the first moveable mast frame 22 corresponding to 50-90% of the height of the first moveable mast frame 22, and preferably 60-80%, and most preferably about 75%. Thus, the receiver 26 may be arranged at an intermediate height, between the far ends of the first moveable mast 22, such as at height corresponding to at least half the height of the first moveable mast 22, and preferably at about ¾ of the height of the first moveable mast 22.

[0086] The person skilled in the art realizes that the present invention by no means is limited to the preferred embodiments described above. On the contrary, many modifications and variations are possible within the scope of the appended claims. For example, many types of engagement parts are possible to releasably connect the receiver and the moveable support. Further, the industrial truck may comprise only one moveable mast frame, or two or even more moveable mast frames. In such embodiments, the solution with a movable support may be used only to support the cylinder operating the outermost, first moveable mast frame, but may also be used to support cylinders operating one or more intermediate mast frames.

[0087] Such and other obvious modifications must be considered to be within the scope of the present invention, as it is defined by the appended claims. It should be noted that the above-mentioned embodiments illustrate rather than limit the invention, and that those skilled in the art will be able to design many alternative embodiments without departing from the scope of the appended claims. In the claims, any reference signs placed between parentheses shall not be construed as limiting to the claim. The word "comprising" does not exclude the presence of other elements or steps than those listed in the claim. The word "a" or "an" preceding an element does not exclude the presence of a plurality of such elements. Further, a single unit may perform the functions of several means recited in the claims.

Examples

Embodiment Construction

[0050]The present invention will now be described more fully hereinafter with reference to the accompanying drawings, in which currently preferred embodiments of the invention are shown. This invention may, however, be embodied in many different forms and should not be construed as limited to the embodiments set forth herein; rather, these embodiments are provided for thoroughness and completeness, and fully convey the scope of the invention to the skilled addressee. Like reference characters refer to like elements throughout.

[0051]Fig. 1 illustrates an overview of an exemplifying industrial truck 1 in accordance with a first embodiment of the present disclosure. In a preferred embodiment, the industrial truck is a reach truck. The industrial truck 1 comprises a body frame 11, to which are mounted the major operating components of the vehicle 1, such as a telescoping mast arrangement 2, for lifting of a load handling arrangement, such as forks 3, an operator compartment 4, two non-s...

Claims

1. An industrial truck comprising: a stationary mast frame; a first moveable mast frame, the first moveable mast frame being moveable in a vertical direction in relation to the stationary mast frame; a load handling arrangement displaceably connected to the first moveable mast frame, the load handling arrangement being moveable in a vertical direction; at least one mast lift cylinder arranged to move the first moveable mast frame in relation to the stationary mast frame, the mast lift cylinder comprising a piston; a moveable support slidably arranged around the piston of the mast lift cylinder; and a receiver fixedly arranged on the first moveable mast frame, wherein the moveable support and the receiver comprise complementary engagement parts arranged to releasably engage the moveable support and the receiver when brought together as the first moveable mast frame is moved upwards.

2. The industrial truck of claim 1, further comprising a free-lift cylinder arranged to move the load handling arrangement, such as forks, in relation to the moveable mast frame.

3. The industrial truck of claim 2, wherein the mast lift cylinder and the free-lift cylinder are hydraulic cylinders actuated by the same hydraulic system.

4. The industrial truck of claim 3, wherein internal cross-sectional areas of the at least one mast lift cylinder(s) and the free-lift cylinder are such that the free-lift cylinder is moved before the mast lift cylinder(s) upon operation of the hydraulic system.

5. The industrial truck of any one of the preceding claims, wherein the first moveable mast frame is arranged as an inner mast frame in relation to the stationary mast frame, and wherein a second moveable mast frame is arranged as an intermediate mast frame, arranged between the stationary mast frame and the first moveable mast frame, wherein at least one of said mast lift cylinder(s) is connected to the moveable mast frame closest to the stationary mast.

6. The industrial truck of any one of the preceding claims, wherein the moveable support, in a retracted position, is arranged at, or in the vicinity of, a top end of an outer sleeve of the mast lift cylinder.

7. The industrial truck of any one of the preceding claims, wherein the moveable support comprises a base plate with an opening therein, the opening having an internal diameter exceeding an outer diameter of the piston of the mast-lift cylinder, and wherein at least one of the engagement parts is arranged at, or in the vicinity of, an end side of the base plate.

8. The industrial truck of any one of the preceding claims, wherein the complementary engagement parts comprise at least one vertically protruding element, arranged on the moveable support or the receiver, and at least one hole dimensioned to receive the vertically protruding element, the at least one hole being arranged on the other of the moveable support and the receiver.

9. The industrial truck of claim 8, wherein the moveable support comprises the at least one vertically protruding element, the vertically protruding element(s) having a downwardly directed free end, and wherein the receiver comprises the at least one hole arranged to engage with the vertically protruding element(s).

10. The industrial truck of claim 8 or 9, wherein the vertically protruding element(s) have over at least a part of the length a tapered, conical shape, thereby having a smaller cross-sectional area at a free end and a greater cross-sectional area at a base or at an intermediate position.

11. The industrial truck of any one of the preceding claims, wherein the receiver is arranged at a height position on the first moveable mast frame so that the moveable support is lifted to a position between 20% and 8075%, and preferably 25-75%, of the length of the piston when maximally extended, and preferably to a position at about the middle of the piston.

12. The industrial truck of any one of the preceding claims, wherein the receiver is arranged at a height position on the first moveable mast frame which is closer to a top end than a bottom end of the first moveable mast frame.

13. The industrial truck of claim 12, wherein the receiver is arranged at a height position of the first moveable mast frame corresponding to 50-90% of the height of the first moveable mast frame, and preferably 60-80%, and most preferably about 75%.

14. A method for operating the industrial truck of any one of the preceding claims, comprising: moving the first moveable mast frame, together with the fixedly arranged receiver, upwards in relation to the stationary mast frame; bringing the receiver into engagement with the moveable support when in a retracted position; moving the moveable support upwards together with the receiver upon continued movement of the first moveable mast frame, the moveable support thereby sliding along the piston of the mast lift cylinder to an extended position.

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