Pallet truck provided with extendable forks with extending equalizer, system and method therefor

Abstract

The invention relates to a pallet truck provided with extendable forks with extending equalizer, and a system and method therefor. The pallet truck according to the invention comprises: a displaceable frame; at least two forks connected to the frame for the purpose of carrying the goods, wherein each of the at least two forks is provided with a fixed fork part and an extendable fork part for adjusting a length of the forks, and a support wheel placed at a distance from the frame; a lengthening drive configured to extend and / or retract the extendable fork part relative to the fixed fork part; and a support wheel drive, provided separately of the lengthening drive, for lowering the support wheel, wherein the separate support wheel drive is arranged between the support wheel and an outer end of the fork.

Description

[0001] PALLET TRUCK PROVIDED WITH EXTENDABLE FORKS WITH EXTENDING

[0002] EQUALIZER, SYSTEM AND METHOD THEREFOR

[0003] The invention relates to a pallet truck for displacing goods over a ground surface, wherein the pallet truck is provided with a displaceable frame on which are arranged two forks, on which goods are placeable for being displaced over the ground surface. Such goods particularly relate to pallets with goods placed thereon.

[0004] Pallet trucks are known in practice and are for instance used in shops, warehouses and factories for the purpose of displacing goods. It is also known to use pallet trucks in combination with trucks for the purpose of loading and unloading for instance pallets into and from the cargo space of such trucks. In a lowered position the forks of such a pallet truck are inserted under the goods and / or engage in a pallet. The forks are then raised by lowering a support wheel so that the goods can be displaced to the desired set-down position. At this set-down position the forks are once again lowered by folding in the support wheel, after which the forks are moved out from under the goods and / or moved out of the pallet.

[0005] Also known in practice are pallet trucks with extendable forks for thereby enabling for instance pallets with different dimensions to be handled. Providing extendable forks enables the length of the forks to be adjusted to the dimensions of, particularly, a pallet. It is hereby for instance prevented that, in the case of a relatively large pallet, the relatively (too) short forks cause an unstable situation wherein goods are able to slide or fall off the pallet. In the case of relatively (too) long forks it is possible that the forks protrude from the pallet on the other side, which can result in damage to other goods and / or can result in unsafe situations. Application of extendable forks therefore contributes to an efficient and safe pallet truck for transport of goods, particularly pallets.

[0006] A problem when providing extendable forks for a pallet truck is that cylinders with a considerable length must usually be provided. This requires considerable installation space, which additionally limits the stroke, i.e. the maximum extension of the forks.

[0007] The invention has for its object to provide a pallet truck whereby the above stated problems are obviated or at least reduced, and goods such as pallets can be displaced in efficient and effective manner.

[0008] The present invention provides for this purpose a pallet truck for displacing goods, wherein the pallet truck comprises: a displaceable frame; at least two forks connected to the frame for the purpose of carrying the goods, wherein each of the at least two forks is provided with a fixed fork part and an extendable fork part for adjusting a length of the forks, and a support wheel placed at a distance from the frame; a lengthening drive configured to extend and / or retract the extendable fork part relative to the fixed fork part; and a support wheel drive, provided separately of the lengthening drive, for lowering the support wheel, wherein the separate support wheel drive is arranged between the support wheel and an outer end of the fork.

[0009] The pallet truck according to the invention is provided with a frame which is displaceable over a ground surface. This frame is provided with one or more wheels and a housing in which the components for the pallet truck can be wholly or partially accommodated. This for instance relates to the hydraulic system. The pallet truck is further provided with at least two forks which are connected with a first outer end to the frame and protrude with a second outer end, and therefore extend therefrom. A support wheel is provided at a distance from the frame, preferably at or close to the other (second) outer end of the extendable fork part. In an embodiment according to the invention more than one support wheel is optionally provided. The forks are composed of a number of parts. In the currently preferred embodiment each fork is provided from a fixed fork part which is connected to the frame at the first outer end, and a fork part which is extendable relative to the fixed fork part and which is extendable for the purpose of thereby adapting the length of the fork to the goods to be picked up, such as one or more pallets. In a currently preferred embodiment the different fork parts are manufactured from folded plate parts or a tube profile, and the extendable fork part is provided with dimensions such that it slides inside the fixed fork part.

[0010] The pallet truck according to the invention is further provided with a lengthening drive whereby it is possible to extend and optionally retract the extendable fork part relative to the fixed fork part. The lengthening drive is preferably configured at least to extend the extendable fork part relative to the fixed fork part. The lengthening drive is preferably also suitable for retraction thereof. As alternative to the retraction with the lengthening drive, use can also be made of manual retraction, optionally using the surrounding area. The lengthening drive can be provided with electrical, pneumatic and / or hydraulic operation. In a currently preferred embodiment use is made of a hydraulic system, and extending or retracting of the extendable fork part is controlled hydraulically using the lengthening drive. Operation of the lengthening drive can be embodied in different ways, including for instance using buttons at or in the displaceable frame and / or using a remote control or mobile application. The lengthening drive can function for both forks and / or can also be provided individually per fork. It is optionally also possible also to use the lengthening drive to lower the support wheel.

[0011] The pallet truck according to the invention is further provided with a separate support wheel drive for lowering the support wheel. By providing a separate support wheel drive movement of the support wheel is independent of the lengthening drive and thereby the displacement of the fork parts. This results in a reduced risk of defects or an incomplete operation of the pallet truck according to the invention. It is hereby additionally simpler to lower the support wheel at any desired position, so that more flexibility is obtained for the extending and the dimensioning of the forks. More specifically, the support wheel can be lowered at multiple positions lying between the minimum length and the maximum length of the forks.

[0012] According to the invention, the separate support wheel drive is arranged between the support wheel and an outer end of the fork. The fork extends from the frame of the pallet truck to the (free) outer end of the fork. The support wheel is preferably arranged on the extendable fork part. Providing the support wheel drive, for instance embodied as a lowering cylinder, between the support wheel and the point or outer end of the fork achieves that there is more space for the lengthening drive, for instance embodied as cylinders. In this embodiment the separate support wheel drive is accommodated in the ‘wasted’ space in or close to the point or outer end of the fork(s). This for instance makes it possible to use longer cylinder(s), so that the forks are extendable over a greater distance. It is thus for instance possible in an extended position of the forks to pick up three so-called Europallets from a short side (about 2400 mm in total), while in such an embodiment the fork has a retracted length of about 1200 mm, whereby for instance one Europallet can be picked up from the long side. This results in an effective pallet truck, which can additionally be used flexibly for diverse pallet dimensions.

[0013] According to the invention, the support wheel drive can be provided in different ways, for instance hydraulically, electrically, pneumatically. In a currently preferred embodiment the support wheel drive is provided with a cylinder, preferably a hydraulic cylinder. It has been found that the support wheel can hereby be lowered in desired manner, even with a relatively heavy load resting on the forks.

[0014] In an advantageous embodiment according to the invention the cylinder comprises a cylinder housing arranged at the outer end of the fork, wherein the cylinder comprises a piston movable in the direction of the frame.

[0015] By providing the housing of the cylinder at the outer end of the fork, and preferably moving the piston in the direction of the frame during lowering of the support wheel, a stable configuration for the support wheel drive is obtained.

[0016] The pallet truck preferably comprises a tilting mechanism connected operatively to the support wheel and configured to lower or retract the support wheel in response to the support wheel drive. Providing a tilting mechanism enables an effective transmission between the support wheel drive and the support wheel to be realized. The tilting mechanism is preferably rotatable around a rotation shaft and engages a cylinder of the support wheel drive at an engagement point of the tilting mechanism at a distance from the rotation shaft. This results in an efficient transmission, and also enables the most optimal possible positioning of the different components in the fork.

[0017] In a currently preferred embodiment according to the invention the pallet truck is further provided with an extending equalizer which is connected operatively to the lengthening drive. This extending equalizer is responsible for bringing and / or keeping the forks at substantially the same length so that there is no misalignment between the forks.

[0018] The extending equalizer makes it possible to eliminate a misalignment of the forks in pallet trucks provided with extendable or lengthenable forks. A misalignment of the forks means that the forks are not extended equally far, and therefore differ in respect of fork length. In the case of unevennesses, for instance when moving into a pallet over the bottom deckboard, a misalignment is prevented by the extending equalizer, whereby it is prevented that the pallet truck is able to start drifting, wherein this drifting can occur in a direction at an angle to the transport direction and preferably substantially at right angles thereto. This therefore avoids the risk that pallets or other goods can fall off the forks, resulting in damage and safety risks.

[0019] An additional effect of preventing a misalignment of the forks with an extending equalizer for instance occurs if one of the support wheels has not fully passed over a bottom deckboard, and one of the support wheels for instance still rests wholly or partially on the deckboard. When lowering the support wheel and picking up a pallet, the pallet truck can shatter this pallet. This is avoided with the extending equalizer, so that the risk of damage to goods and a safety risk are likewise avoided.

[0020] It is particularly the combination of the support wheel drive in an embodiment according to the invention and an extending equalizer that results in a robust lowering mechanism for the support wheel, wherein support wheels of adjacent forks of the pallet truck are positioned at the same distance from the frame. A good support of the load / goods on the forks is realized thereby, also during manoeuvring with the pallet truck through bends and the like, such that damage is avoided.

[0021] The extending equalizer preferably takes active action in the case of a misalignment, so that such a misalignment is avoided and / or is corrected if it were to unexpectedly occur after all. Drifting of the pallet truck in a direction at an angle to the usual transport direction is hereby avoided, so that pallets / goods are prevented from being able to slide off the forks as a result of such drifting in transverse direction. Such drifting for instance occurs when moving over an unevenness in a misaligned position and / or when moving into a pallet and moving over for instance the bottom deckboard. Preventing the misalignment reduces the risk of damage significantly, and also significantly increases the safety of working with the pallet truck according to the invention. In an advantageous embodiment according to the invention the extending equalizer is connected operatively to a controller configured to control the lengthening drive.

[0022] The operative connection of the extending equalizer to a controller enables a misalignment to be avoided and / or to be eliminated in effective manner in that a controller controls the lengthening drive for for instance the lagging fork. Alternatively, it is also possible to control the leading fork and to correct its position. Such a controller can be integrated with the extending equalizer and can alternatively also be provided separately, optionally in combination with a controller of the pallet truck itself. Said operative connection enables the extending equalizer to respond actively to a detected misalignment and / or act proactively in order to prevent misalignment.

[0023] In an advantageous preferred embodiment according to the invention the lengthening drive is provided with a hydraulic system comprising a bypass circuit configured to position the lagging fork.

[0024] In an embodiment wherein the lengthening drive makes use of a hydraulic system a bypass circuit is provided in a currently preferred embodiment. This bypass circuit is continuously active or is switched on as alternative in the case of a detected misalignment and / or expected misalignment. Medium, such as oil, is here preferably conveyed via the bypass circuit to the lagging fork, which can then perform an additional sliding movement in order to eliminate the misalignment. The bypass circuit enables a connection between the hydraulic circuits and / or the cylinders of the individual forks. This makes a mutual coupling / coordination of the movement of the forks possible.

[0025] In a number of the currently preferred embodiments according to the invention the bypass circuit is provided with a synchronizing system. In such a synchronizing system the hydraulic medium, such as the oil, which is pushed out of a first cylinder is fed through to the inlet side of a second cylinder so that a movement of the respective pistons is performed simultaneously. This already avoids or at least largely avoids a misalignment. If a cylinder has reached the maximum stroke, the medium is fed through to the other cylinder, which is there equalized if a misalignment were to have unexpectedly occurred during extension of the cylinders. There is therefore an active extending equalization here during the extending, and optionally retracting, and a passive correction at the maximum stroke of the cylinder. An advantage of such a synchronizing system is that fewer separate conduits and / or hydraulic components such as valves will suffice and, additionally, less control is required. Another advantage of such a synchronizing system is that a smaller hydraulic pump can usually be applied to achieve the same speed when retracting and extending the fork(s). This is advantageous considering, among other factors, the generally limited space for building the components into the pallet truck. This makes a cost-effective and / or a relatively compact system possible. In a further preferred embodiment according to the invention the bypass circuit is provided with a synchronizing valve. In a currently preferred embodiment such a synchronizing valve is activated in the case of a lagging fork / cylinder. At that moment hydraulic medium, such as oil, is diverted via the synchronizing valve to this lagging cylinder / fork, such that an occurring misalignment is avoided and / or is reduced. In a currently preferred embodiment such a synchronizing valve is applied in combination with a so-called flow divider whereby supplied hydraulic medium is distributed over different cylinders of the different forks. This results in an effective system.

[0026] In an advantageous preferred embodiment according to the invention the extending equalizer is provided with at least one length detector configured to determine a fork length directly or indirectly.

[0027] By providing a length detector a misalignment can be detected in time and be equalized using the extending equalizer. Such a length detector can determine the length of the respective fork directly or indirectly. Use can for this purpose be made of different types of sensor, for instance an ultrasonic sensor, a contact sensor, a sensor combination with a stop detection, and / or other suitable detectors. The at least one length detector is preferably connected operatively to the above stated controller in one of the currently preferred embodiments according to the invention. This enables an active control of the lengthening drive on the basis of the length detector. This makes an active control possible, so that misalignment remains limited to maximum extent.

[0028] In an advantageous embodiment according to the invention the pallet truck comprises an activatable pallet stop.

[0029] Providing an activatable pallet stop makes it possible to adapt the effective (usable) length of the forks to the dimensions of the goods to be displaced. Such an activatable pallet stop is preferably a hydraulic pallet stop and is preferably arranged in or on the frame. This is for instance advantageous when handling so-called Europallets. In an extended position of the forks, these forks are for instance 2400 mm long in order to enable three Europallets (each of 800 mm) to be picked up in transverse direction. In a practical embodiment of the pallet truck according to the invention the fork length is for instance 1400 mm in a retracted position. A Europallet in longitudinal direction is typically 1200 mm long. By activation of the activatable pallet stop, the pallet stop is extended about 200 mm, as seen from the frame, and slides / moves over or otherwise relative to the forks over this distance. This makes the effective usable fork length 1200 mm. When the Europallet is picked up in this example, the forks then do not protrude beyond the Europallet. This further increases the safety of working with extendable forks. In a currently preferred embodiment such a system can operate hydraulically and can for instance be controlled via a sequence valve with the existing hydraulic diagrams. In a further advantageous embodiment according to the invention the pallet truck comprises a guide strip.

[0030] By providing a guide strip a better confinement of the extendable fork part relative to the fixed fork part is realized. Such an improved confinement reduces the risk of the pallet truck drifting, for instance when moving into a pallet with misaligned forks, to further extent. By making use of a guide strip the resistance in a relative displacement of the extendable fork part relative to the fixed fork part is substantially equal between the different forks, and therefore contributes to the equal extension or retraction of the fork parts. Such a guide strip is therefore preferably applied in combination with the extending equalizer, so that the shared objective of avoiding and reducing a misalignment is realized.

[0031] An additional advantage of applying a guide strip, and the improved confinement between the individual fork parts realized thereby, is that less clearance remains between the fork parts, whereby wear as a result of extension of the fork parts is limited and is also concentrated in the guide strip. In such a situation the guide strip functions as a type of wear strip, whereby maintenance becomes simpler and more cost-effective. For this purpose the guide strip is preferably arranged between the extendable fork part and the fixed fork part. More preferably, the guide strip is here provided releasably so that it can be removed from the fork parts in simple manner and, if desired, can be replaced with a new one. This makes maintenance simpler and also cheaper. The risk of wear to other parts is also avoided.

[0032] A second guide strip is preferably also provided in addition to a first guide strip. This further improves the confinement of the fixed fork part and extendable fork part. The first guide strip is here preferably provided at the second outer end of the fixed fork part, and the second guide strip is preferably provided at an outer end of the extendable fork part directed toward the frame of the pallet truck. It will be apparent that other configurations of guide strips according to the invention are also possible.

[0033] In a further alternative preferred embodiment according to the invention the lengthening drive is provided with a cylinder comprising a cylinder housing and piston, wherein the cylinder housing is configured as support construction.

[0034] By combining the support construction and the cylinder for extending the extendable fork part into a construction element the number of different components of the pallet truck is reduced in this embodiment according to the invention. This results in a cost-effective construction for such a pallet truck. In such an embodiment the fork part forms the cylinder housing inside which a piston or piston element can be moved if extending or retracting of the slidable fork part is desired.

[0035] In a further embodiment the lengthening drive is provided with at least one double-action cylinder. Providing a double-action cylinder makes it possible to realize both retraction and extension via the lengthening drive in effective manner. This provides a robust and easily operated system for a pallet truck in such an embodiment. In a further embodiment of the pallet truck according to the invention the cylinder housing is provided with an integrated oil throughfeed and / or bores for so-called cartridge valves and / or a guide for hydraulic hoses. A compact and protected embodiment for hydraulic components is hereby provided.

[0036] In an embodiment according to the invention the pallet truck is further provided with a separate support wheel drive for lowering the support wheel. By providing a separate support wheel drive movement of the support wheel is independent of the lengthening drive and thereby the displacement of the fork parts. This results in a reduced risk of defects or an incomplete operation of the pallet truck according to the invention. It is hereby additionally simpler to lower the support wheel at any desired position, so that more flexibility is obtained for the extending and the dimensioning of the forks. More specifically, the support wheel can be lowered at multiple positions lying between the minimum length and the maximum length of the forks.

[0037] In one of the currently preferred embodiments according to the invention, the separate support wheel drive is arranged between the support wheel and an outer end of the fork.

[0038] Providing the support wheel drive, for instance embodied as a lowering cylinder, between the support wheel and the point or outer end of the fork achieves that there is more space for the lengthening drive, for instance embodied as cylinders. In this embodiment the separate support wheel drive is accommodated in the ‘wasted’ space in or close to the point or outer end of the fork(s). This for instance makes it possible to use longer cylinder(s), so that the forks are extendable over a greater distance. It is thus for instance possible in an extended position of the forks to pick up three so-called Europallets from a short side (about 2400 mm in total), while in such an embodiment the fork has a retracted length of about 1200 mm, whereby for instance one Europallet can be picked up from the long side. This results in an effective pallet truck, which can additionally be used flexibly for diverse pallet dimensions.

[0039] In an advantageous embodiment of the pallet truck according to the invention the forks have in a retracted position a retracted length in the range of 800 mm- 1400 mm, preferably a minimum length of 800 mm, and more preferably at least 1000 mm. The maximum (extended) length of the forks in an extended state preferably lies in the range of 1200 mm-2400 mm, more preferably amounts to at least 1800 mm, still more preferably at least 1900 mm, and is most preferably at least 1950 mm. A good range of lengths for the forks is hereby realized, whereby a wide range of loads, including pallets, can in practice be handled with the pallet truck in an embodiment according to the invention.

[0040] The invention further also relates to a system for lengthening a carrying part of a pallet truck in an embodiment according to the invention, wherein the system comprises: coupling means for operatively connecting the system to a frame of the pallet truck; at least two forks connected to the frame for the purpose of carrying the goods, wherein each of the at least two forks is provided with a fixed fork part and an extendable fork part for adjusting a length of the forks, and a support wheel placed at a distance from the frame; a lengthening drive configured to extend and / or retract the extendable fork part relative to the fixed fork part; and a support wheel drive, provided separately of the lengthening drive, for lowering the support wheel, wherein the separate support wheel drive is arranged between the support wheel and an outer end of the fork.

[0041] Such a system provides similar advantages and effects as described for the pallet truck. The system is particularly effective for converting existing pallet trucks and providing them with extendable forks.

[0042] The invention further also relates to a method for using and / or controlling pallet trucks and / or system in an embodiment according to the invention.

[0043] Such a method provides similar effects and advantages as described for the pallet truck and / or the system.

[0044] Further advantages, features and details of the invention are elucidated on the basis of preferred embodiments thereof, wherein reference is made to the accompanying drawings, in which:

[0045] Figure 1 shows a view of a pallet truck in an embodiment according to the invention;

[0046] Figures 2 and 3 show views with forks in different positions of the pallet truck of figures 1;

[0047] Figures 4A-B show views of an embodiment of the pallet truck according to the invention with lifting cylinder for the support wheel.

[0048] Figures 5 and 6 show views of the outer end of the forks with the support wheel in different positions,

[0049] Figure 7 shows a detail with the guide strip of the pallet truck according to figure 1;

[0050] Figure 8 shows a hydraulic diagram of a master-slave configuration applicable in a pallet truck according to figure 1 ; and

[0051] Figure 9 shows a hydraulic diagram with a flow divider applicable in a pallet truck according to figure 1. Pallet truck 2 (figure 1) is provided with a frame with housing 4 on which or at which handle or arm 6 with handgrip 8 is arranged. Pallet truck 2 is further provided with a set or pair of forks 10 comprising a first fork 12 and second fork 14. Each of the forks 12, 14 consists of a respective fixed part 16, 18 and extendable part 20, 22 with points or outer ends 11. In the shown embodiment extendable part 20, 22 is provided with support wheel 24. Forks 12, 14 are provided with length L, wherein fixed fork part 16, 18 is provided with length Li. Extendable fork part 20, 22 is extendable in direction A for adjusting length L thereby. Shown schematically for pallet truck 2 are lengthening drive 26, extending equalizer 28 and controller 30. These components are optionally accommodated for the most part in housing 4 and / or in the forks themselves. This latter is particularly advantageous when an existing pallet truck is converted. In the shown embodiment an activatable pallet stop 31, which is preferably controlled hydraulically, is provided in or on housing 4. In this shown embodiment pallet stop 31 is extendable from housing 4 over a stop distance 31a of about 200 mm using one or more extending cylinders 31b (shown schematically). It will be apparent that other embodiments and distances according to the invention are likewise possible. Is thus for instance possible to provide a single stop 31 for both forks collectively or to provide separate stops 31 per fork.

[0052] In a retracted position forks 12, 14 are provided with length Lmin(figure 2). In a fully extended position of extendable fork parts 20, 22 a length Lmaxfor forks 12, 14 (figure 3) is achieved. Pallet truck 2 can be used here to move into pallet 32, and then lift this pallet by lowering support wheel 24 and displace it to a desired set-down location. The extendable character of pallet truck 2 enables pallets 32 of different dimensions to be picked up and displaced in effective manner.

[0053] Lengthening drive 26 makes use of cylinder(s) 34, 36 with cylinder housing 38 and piston rod 40 (figures 5 and 6). Piston rod 40 is connected at the outer end to push plate 42 of the respective extendable fork parts 20, 22. Due to extension of piston rod 40, extendable fork parts 20, 22 are extended and forks 12, 14 are lengthened. When piston rod 40 retracts, a reverse movement takes place, and thereby a retraction of extendable fork parts 20, 22.

[0054] In an alternative embodiment fixed fork part 16, 18 also forms cylinder housing 38. Cylinder housing 38 hereby forms part of the support construction of forks 12, 14.

[0055] In an embodiment of pallet truck 2 according to the invention (figures 4A-B) pallet truck 2 is provided with the same or similar components discussed / shown above, including housing 4, forks, 10, 12, 14, points / outer ends 11, and support wheel 24. Also provided are lowering cylinder 44 and tilting mechanism 48. In the shown embodiment of pallet truck 2 lowering cylinder 44 is provided in or close to point / outer end 11 of forks 12, 14. Lowering cylinder 44 is therefore provided between support wheel 24 and point / outer end 11. An advantage of the positioning of lowering cylinder 44 is that there is more space for cylinders 34, 36, while lowering cylinder 44 is accommodated in the ‘wasted’ space in or close to point / outer end 11. This makes it possible to use longer cylinder(s) 34, 36, so that forks 12, 14 are extendable over a greater distance.

[0056] For lowering of support wheel 24 use is in the shown embodiment made of lowering cylinder 44 (figures 4-6). Piston 46 (also referred to as piston 44b in figure 4B, which together with housing 44a forms cylinder 44) of cylinder 44 is in this embodiment connected at the outer end to tilting mechanism 48, such that tilting mechanism 48 rotates relative to rotation shaft 50. A movement of outer end / engagement point 52, to which piston 46 is connected, is thereby converted into a lifting movement of wheel axle 54 in direction B. Due to the lowering of support wheel 24, forks 12, 14 are here moved over a height of for instance about 120 mm in order to enable transport of goods. Supply of hydraulic medium, such as oil, to cylinder 44 for instance takes place with a flexible tube in order to be able to accommodate the change in length of forks 12, 14.

[0057] In the shown embodiment of pallet truck 2 guide strip 56 (figure 7) is provided between fixed fork part 18 and extendable fork part 22. A number of openings 58 and mounting openings 60 are also provided in the shown embodiment. Guide strip 56 extends in direction A over a distance Lg. Second guide strip 61 is also provided in the shown embodiment. In this embodiment first guide strip 56 is provided at or close to the (second) outer end of fixed fork part 16, 18, and second guide strip 61 is provided at or close to an outer end of slidable fork part 20, 22 which is directed toward housing 4 of pallet truck 2.

[0058] Hydraulic circuit 102 (figure 8) is provided with lengthening drive 26, whereby the extending or retracting of extendable fork parts 20, 22 is controlled using respective cylinders 36, 38 of hydraulic part 26a. For this purpose motor 106 is connected to pump 108 whereby hydraulic medium, such as oil, can be conveyed via valve 110 to cylinder 36 and is carried via synchronizing system 112 from the outlet of cylinder 36 to the inlet of cylinder 38, and then back again. The volume, determined by diameter Di of cylinder 36, is here smaller than the volume determined by for instance diameter Dj of cylinder 38 in order to realize an identical extending movement of extendable fork parts 20, 22. Valve 104 (shown schematically) is provided in pistons 36a, 38a of the cylinders, such that when the cylinders are fully retracted, hydraulic medium such as oil can flow through piston 36a, 38a in order to synchronize the (lagging) cylinder, and thereby functions as extending equalizer 28. Optional detector 105 is preferably connected operatively to the likewise optional controller 30 (shown schematically). Hydraulic part 26b of diagram 102 relates to the lowering of support part 24. In the shown embodiment use is once again made here of motor 106 and pump 108 from lengthening drive 26. Hydraulic medium such as oil is conveyed via respective valves 114, 116, 118 to cylinders 44 in extendable fork parts 20, 22 and to cylinders 44a in the housing of frame 4.

[0059] In an alternative embodiment hydraulic part 26b for lowering of support wheel 24 (figure 9) is the same as in diagram 102 (figure 8). The hydraulic part 26a of diagram 202 (figure 9) is however represented in an alternative embodiment. Use is made here of detectors 204 and diameters Dcof cylinders 36, 38 are the same. Detectors 204 are preferably likewise connected operatively to extending equalizer 28 and / or controller 30 (shown schematically). For controlling cylinders 36, 38 use is made of flow divider 206. In the shown embodiment with flow divider 206 hydraulic sub-system 26a is provided with bypass circuit 208 in which synchronizing valve 210 is arranged. This makes it possible to convey a greater proportion of hydraulic medium to cylinder 36 or to cylinder 38, depending on a possible misalignment of the respective extendable fork parts 20, 22.

[0060] For the purpose of displacing goods with pallet truck 2 extendable fork parts 20, 22 are first brought to the correct length L. Pallet truck 2 is then moved into pallet 32. For extension use can be made of hydraulic systems 102, 202. It is also possible to use an alternative hydraulic system or even to apply a pneumatic or electric drive. After pallet truck 2 has been positioned relative to the goods to be picked up and displaced, support wheel 24 is lowered using sub-system 26b. After the goods have been lifted they can be displaced to the set-down location, where a reverse process then takes place and support wheel 24 is retracted, after which pallet truck 2 can be removed from under the goods. Extendable fork parts 20, 22 can then be retracted in order to for instance reduce the turning circle of pallet truck 2.

[0061] Pallet truck 2 was shown in the above with extendable forks. If an existing pallet truck must be converted with extendable forks, fork assembly 10 can be provided together with drive 26, extending equalizer 28 and controller 30. A modular assembly 302 is hereby obtained.

[0062] The present invention is by no means limited to the above described preferred embodiments thereof. The rights sought are defined by the following claims, within the scope of which many modifications can be envisaged.

Claims

CLAIMS1. Pallet truck for displacing goods, comprising: a displaceable frame; at least two forks connected to the frame for the purpose of carrying the goods, wherein each of the at least two forks is provided with a fixed fork part and an extendable fork part for adjusting a length of the forks, and a support wheel placed at a distance from the frame; a lengthening drive configured to extend and / or retract the extendable fork part relative to the fixed fork part; and a support wheel drive, provided separately of the lengthening drive, for lowering the support wheel, wherein the separate support wheel drive is arranged between the support wheel and an outer end of the fork.

2. Pallet truck according to the foregoing claim, wherein the support wheel drive is provided with a cylinder.

3. Pallet truck according to the foregoing claim, wherein the cylinder comprises a cylinder housing arranged at the outer end of the fork, and wherein the cylinder comprises a piston movable in the direction of the frame.

4. Pallet truck according to any one of the foregoing claims, further comprising a tilting mechanism connected operatively to the support wheel and configured to lower or retract the support wheel in response to the support wheel drive.

5. Pallet truck according to any one of the foregoing claims, further comprising an extending equalizer connected operatively to the lengthening drive and configured to bring and / or keep the at least two forks at substantially the same length.

6. Pallet truck according to the foregoing claim, wherein the extending equalizer is connected operatively to a controller configured to control the lengthening drive.

7. Pallet truck according to any one of the foregoing claims, wherein the lengthening drive is provided with a hydraulic system comprising a bypass circuit configured to position the lagging fork.

8. Pallet truck according to the foregoing claim, wherein the bypass circuit comprises a synchronizing system.

9. Pallet truck according to claim 7 or 8, wherein the bypass circuit comprises a synchronizing valve.

10. Pallet truck according to any one of the foregoing claims, wherein the extending equalizer is provided with at least one length detector configured to determine a fork length directly or indirectly.

11. Pallet truck according to any one of the foregoing claims, further comprising an activatable pallet stop.

12. Pallet truck according to any one of the foregoing claims, further comprising a guide strip.

13. Pallet truck according to the foregoing claim, wherein the guide strip is arranged between the extendable fork part and the fixed fork part.

14. Pallet truck according to any one of the two foregoing claims, wherein the guide strip is provided releasably.

15. Pallet truck according to any one of the foregoing claims 12-14, further comprising a second guide strip, wherein a first guide strip is provided at or close to an outer end of the fixed fork part, and the second guide strip is arranged on the extendable fork part.

16. Pallet truck according to any one of the foregoing claims, wherein the lengthening drive is provided with a cylinder comprising a cylinder housing and piston, wherein the cylinder housing is configured as support construction.

17. Pallet truck according to any one of the foregoing claims, wherein the lengthening drive is provided with at least one double-action cylinder.

18. Pallet truck according to any one of the foregoing claims, wherein in a retracted position the length of the forks lies in the range of 800 mm- 1400 mm, is preferably a minimum length of at least 1250 mm, and more preferably at least 1500 mm.

19. Pallet truck according to any one of the foregoing claims, wherein in an extended position the length of the forks lies in the range of 1200 mm-2400 mm, is preferably a minimum length of at least 1800 mm, more preferably at least 1900 mm, and most preferably at least 1950 mm.

20. System for lengthening a carrying part of a pallet truck according to any one of the foregoing claims, comprising: coupling means for operatively connecting the system to a frame of the pallet truck; at least two forks connected to the frame for the purpose of carrying the goods, wherein each of the at least two forks is provided with a fixed fork part and an extendable fork part for adjusting a length of the forks, and a support wheel placed at a distance from the frame; a lengthening drive configured to extend and / or retract the extendable fork part relative to the fixed fork part; and an extending equalizer connected operatively to the lengthening drive and configured to bring and / or keep the at least two forks at substantially the same length.

21. Method for using and / or controlling a pallet truck and / or system according to any one of the foregoing claims.

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