GB2192174A - Lifting frame for lifting trucks - Google Patents

Abstract

A lifting frame for lifting trucks, particularly for fork lift trucks, comprises mast sections which are extensible relative to each other and are provided with guide means for guiding each other with a play. At least mast sections (3, 4, 5) which are extensible are provided on end portions thereof with resilient compensating pads (13, 14), which are so arranged that when two adjacent ones of said mast sections (3, 4, 5) have been retracted relative to each other each of said pads mounted on one of said adjacent mast sections engages the other of said adjacent mast sections so as to compensate the play between said two adjacent mast sections. In one embodiment, such compensating pads (13, 14) are mounted on the lower end portions of the mast sections (3, 4) on the front side thereof. It is also possible to provide resilient compensating pads (13, 14) on the upper and bottom end portions of at least one mast section. <IMAGE>

Description

SPECIFICATION Lifting frame for lifting trucks This invention relatesto a lifting frame for lifting trucks, particularly for fork lift trucks, which lifting frame comprises mast sections which are extensible relative to each other and providedwithguiding meansforguiding each otherwith a play.

Such a lifting frame comprises afixed mast section, at leastoneextensibie mastsection and a load carrier, which particularly consists of a load-carrying fork and is mounted on the innermost mast section of the lifting frame and particularly on that mast section which is extensible to the highest level. Drive means for extending the lifting frame and the load carrier are also provided and those mast sections which are movable relative to each other are guided on each other by guide rollers, each ofwhich rolls in a profiled portion of an adjacent mast section, which profiled portions have flanges, which are disposed on opposite sides ofthe guide rollers and parallel to their axes. In a specific embodiment, said guide rollers constitute the guiding means.

E.g.,whereguide rollers are used,the above-mentioned play is necessary because the rollers run on the adjacent mast section only on one side of the roller whereas the other side must be free because otherwise a force opposing the desired movement would be exerted. Such play is required for functional reasons.

A play results also from tolerances although a guide roller can be made exactly to a specified dimension so asto provide the above-mentioned functional play. Itmust be borne in mindthatthe stiles ofthe mast sections ofthe lifting frame are made in the specified profiled shape, which is sometimes complicated. Such mast stiles are hot-rolled and may subsequently be cold-drawn.

The extensible mast sections include the load carrier. Adjacent mast sections are guided on each other by means of guide rollers in such a mannerthat one guide roller is mounted on the top end portion of an outer or lower mast section and another guide roller is mounted on the bottom end portion ofthe adjacent inner mast section, which is upwardly extensible. In that case, tilting moments which are due to a load on the load carrier will be taken up.

Owing to the arrangement on the upper and lower end portions, the distance between the rollers is as large as possible, as is required for a reliable guidance, and the smallest distance between the rollers is determined by the overlap of the mast sections when they have been extended.

In addition to the clearances which are due to the necessa ry tolerances, such clearances are required at rollers because the front and rear portions oftheir periphery move in mutually opposite directions and an engagement is intended only with those flanges which normally constitute a track whereas the opposite flange of the profiled portion defines a small clearance with the roller. In the extended mast, said clearances are substantially eliminated owing to the unilateral load imposed by the load carrier. But when the lifting frame is retracted and particularly when the load carrier is in a lower position, the unilateral load is reduced owing to the large overlap and the clearances permit of a play so thatthe guiding means can oscillate and strike against each other.

This will be particularly undesirable if such lifting frames are designed for a so-called free lift, which meansthatthe load carrier can be moved to the top ofthe lifting frame when the latter has been retracted. This is an important mode of operation because the lifting truck can be operated in that the load carrier is lifted when the lifting frame has been retracted so that the overall height ofthe lifting truck remains constant. In that case the truck can move through doors and the like and can be operated in low spaces, such as in waggons or on board of lorries. But in such cases the clearances between the guiding elements will be undesirable.

The drive means which have been mentioned are known. They comprise at least one hydraulic cylinder-piston device for extending either only the load carrierfor a free lift orfor extending an extensible mast section. In the latter case, chain or rope drives are provided for connection to the other mast sections. In the design providing for a free lift, the cylinder-piston device may be so designed that the other extensible mast sections will be carried along by the load carrier as the latter is raised further, e.g., when a stop has engaged an extensible mast section.

Within the scope of the invention, lifting frames are included which are designed for a free liftor which do not provide for a free lift and said lifting frame may comprise two, three or more telescopic mast sections. During a travel ofthe lifting truck with the lifting frame in a retracted position, the lifting frame sections which are guided each other may move relative to each other owing to the above-mentioned clearances. Such a movementwill particularly be due to impulses which occur as the lifting truck is started or braked. This will result in a noise. A similar result will be produced by shocks which are due to irregularities ofthe runway.

The noise is undesirable in itself It will resultwhen guiding means, particularly guide rollers and mast section flanges, strike on each other and will result in a wear thereof.

Besides, vibration will be generated when loads are picked up and such vibrations will result in a rapid wearofthe guiding means, particularly in damageto guide rollers and their tracks, and if an unforeseen resonance occurs this will result in a morefar-reaching destruction and may adversely affectthe position control means of a lifting truck.

It is an object of the invention to provide an extensible lifting frame which is of the kind described first hereinbefore and which is so designed that when retracted it constitutes a unit which is virtually free of backlash and in which the known noises and vibrations are avoided so that the interacting guiding means, particularly interengaging guiding elements, will be protected from a rapid wear.

That object is accomplished in accordance with the invention in that at least mast sections which are extensible are provided on end portions thereof with resilient compensating pads, which are so arranged that when two adjacent ones of said mast sections have been retracted relative to each other each of said pads mounted on one of said adjacent mast sections engages the other of said adjacent mast sections 50 as to compensate the play between said two adjacent mast sections. Because the play is thus compensated, a generation of noise and vibration will be avoided and the interengaging guiding means will be preserved from wear. The resilient compensating pads may have such a compliance that they can be compressed as the mast sections are retracted orthatthe pads can properly adapt themselves as the lifting frame is extended or retracted.This is desirable because an appreciable inhibition of the retracting movement should be avoided. The compliance is so selected that the mast sections will not clamp each other. The compliance will be selected in consideration on the mass of the sections of the lifting frame and on the mass of the loads to be picked up.

That mast section which can be extended to the uppermost level may be constituted by the load carrier.

In a desirable embodiment, resilient compensating pads are mounted on the lower end portion of each extensible mast section on the inside of a profiled portion which embraces the next lower mast section and is provided with the guide means.

Inthatcasea damping wiii be effected not only in a lower position but throughout the extending movement until the lifting frame has been fully extended and this is accomplished bytheprovision of only one compensating pad on each extensible mast section. That design will afford the additional advantage that the compensating pad will be effective when the lifting frame has been retracted and that there will be no abrupt changes as the lifting frame is extended. In thatcase the compensating pad consisting particularly of a spring will oppose the load imposed by the load carrier. That arrangement is particularly desirable in comparison with other compensating means.

In a particularly preferred other embodiment, resilient compensating pads are mounted on the lower end portions ofthe mast sections on the front side thereof and are so arranged that as the mast sections which are extensible to a higher level are lowered they will engage said compensating pads.

Asaresult,thecompensating pads will become effective when the lifting frame has been lowered and/orshortlybeforea given mastsection reaches its lowermost position.

Within the scope of the invention, resilient compensating pads may be mounted on the upper and lower end portions of at least one mast section and in that case the pad provided on the upper end portion is particularly disposed on the front side and at such a distance from the top end that that mast section which can be raised relative to said mast section can be raised to an uppermost position in which the residual overlap is such thatthe upper mast section still covers the compensating pad mounted on the upper end portion ofthe next lower mast section and the compensating pad mounted on the lower end portion may constitute a buffer pad.

That design will permit a particularly strong damping to be effected when the upper mast section has been lowered but will also permit a compensation ofthe play atthetop end of the lifting frame and a damping throughout the extending movement. In accordance with the teachings furnished herein before, each of the compensating pads mounted on the upper and lower end portions may be provided on the inside of an extensible mast section and in that case the adjacent mast sections may beso designed thatthe compensating pads, particularly springs, will be disposed one below the other and will not contact each other even when the lifting frame has been fully extended.

In that embodiment which has been described hereinbefore and in which the relatively movable mast sections are guided on each other by guide rollers, a resilient compensating pad consisting particularly of a spring is desirably mounted at least onthefixed mastsection and on the lowermost extensible mast section and said compensating pads extend along a length portion near the bottom end of the respective mast section and at least when the lifting frame has been retracted each of said compensating pads is in pressure contact with a stile of an adjacent mast section and eliminates any play between the stiles of adjacent mast sections or between a profiled portion and a guide roller contained in said profiled portion. The resilient compensating pad desirably consists of a spring.In an embodiment in which the springs are provided on the front side ofthe mast sections, the springs mounted on the lower end portions of the fixed mast section and of extensible mast sections consist of buffer springs and each of said springs has a side face which is upwardly inclined and faces the associated mast section to which the spring or compensating pad has been secured.

In that embodiment the engagement ofthe compensating pads will be facilitated and a clamping action will be avoided as the sections are moved apart.

In a desirable embodiment the same aspects are applicableto a lifting frame designedfora free lift; in that case the load carrier is resiliently held in a similar manner when it is in its lower position.

In a preferred embodiment, resilient compensating pads preferably consisting of springs are provided also on that mast section which is extensible to the uppermost level and which is provided with a load carrier, which is guided on said uppermost mast section by means of rollers and are engaged by said pads when said load carriers are in their uppermost position.

In that casethe load carrier can also be resiliently held in a predetermined lower position. That predetermined lower position of the load carrier is not the lowermost position to which the load carrier consisting of a load-carrying fork can be lowered when a load isto be picked up from the ground but the position which is assumed by the load carrier as the load is transported on the retracted lifting frame.

In that case the resilient compensating pads, particularly springs, which are provided on the mast section on which the load carrier is guided, are preferably provided with a run-up surface also at the lower end.

In another desirable embodiment compensating pads are mounted on the lower end portions of mast sections on the inside thereof and each ofthe extensible mast sections is provided on its lower end portion with a compensating pad that preferably consists of a spring and is engageable with the fixed mastsection orwiththatextensiblemastsection which is the next lower mast section when the lifting frame has been extended. In that case a damping action will be obtained in any position to which the mast has been extended.

In a suitable embodimentthesprings consistof leaf springs, each of which has a leg that is secured to the underside of a stile of one mast section and the spring has an arcuate portion which rises in a profiled portion of the stile of the mast section on the front side thereof and adjacenttothetopendforms an inclined run-up surface. That embodiment is simple and can easily be installed in an existing lifting frame and can be adapted to given loading conditions by its design and by the properties ofthe material.

The rising portion is desirably substantially S-shaped and with its upper curved portion bears on that mast section to which the spring is secured, and the spring is bentbackto an extent which is smaller than the overhang of the protruding arch ofthe spring near the fixing end. This will result in a particularly desirable design.

Each spring may have a horizontal leg, which is secured to the underside of a stile of a given mast section.

In another desirable embodiment the springs are particularly provided on the inside ofthe extensible mast sections orthe constantly engaging springs have a protruding intermediate portion and movably mounted supporting ends so that a compliance in both directions will be ensured.

In that embodimentthe springs are suitably substantially W-shaped and at their bent-back ends are movably held by pins.

In a preferred embodiment, an extensible mast section or the fixed mast section is provided with spring-mounting bearing brackets and ata distance from said bearing brackets is provided with laterally protruding pins, which are adapted to be stressed in shears and engaged from behind by end legs of the springs, which end legs are defined by longitudinal slits and embrace the bearing brackets. In such an arrangementthecompliance at the ends is maintained and a lateral guidance is provided and simple means are provided for holding the springs against a movement along the mast section.

The provision of such a spring, which is particularlyW-shaped, in such an arrangement will beparticularlysuitableforacompensation pad which in the manner described hereinbefore is mounted on the upper end portion of a mast section on the front side thereof.

In the embodiments which comprise springs, the S-shaped springs having a rising portion orthe W-shaped springs desirably consist of straight portions and in the S-shaped spring both bent back upper portion and in the W-shaped spring both bent-back portions are short. In that case an embodiment in which the compliance can be adjusted with high accuracy can be manufactured in a simple manner.

Each of the compensating pads or springs which are mounted on the lower end portion of an associated mast section preferably rise from the lower end of a mast section above a guide roller mounted on the lower end portion of an extensible mast section. This means thatthe compensating pads or springs have only a small length relative to the mast section and are intended to engage the adjacent mast section only when the lifting frame has been retracted. Itwill be understood that the fixed mast section and the extensible mast sections of the lifting frame comprise side stiles and that each stile is provided with a compensating pad or spring.

The invention will now be explained with reference to illustrative embodiments which are shown in the drawing, in which Figure 1 is a diagrammatic side elevation showing a lifting truck having an extended lifting frame. That figure serves to explain the principle ofthe mutual guidance.

Figure2 is a fragmentary elevation showing the lower portion of a retracted lifting frame and illustrates an embodiment of the invention.

Figure 3shows an individual spring.

Figure 4 is a diagrammaticfragmentary top plan view showing a partofa lifting frame having a plurality of extensible mast sections and springs used as compensating means.

Figure 5is a diagrammatic side elevation which is similarto Figure 1 but shows a different embodiment.

Figure 6 is a diagrammatic side elevation which is similar two Figure 1 but shows a further embodiment.

Figure 7is a fragmentary elevation showing a part of a mast section with a special design and arrangement of a compensating spring shown in a top plan view.

Figure 8 is a side elevation related to Figure 7.

Figure 1 shows a lifting truck 1 with an extended lifting frame 2. The latterconsists of a plurality of mast sections which can be telescppically extended relative to each other and comprise a fixed mast section 3, the next inner extensible mast section 4 and the innermost mast section 5, which is adapted to be extended to the highest level. A load carrier 6, which is illustrated asa load-carrying fork, is vertically movably guided on the innermost mast section 5, which can be extended to the highest level.

ltisapparentthata guide roller 7,8 or9 is mounted on the upper end portion of each mast section and is arranged to engage and guide an adjacent mast section, and that guide rollers 10 and 12 are respectiveiy mounted onthe lower end portions of such adjacent extensible mast sections. As a result, tilting moments, particularly forwardly directed tilting moments, can be taken up because the guide rollers are disposed in and run in profiled portions.

In a three-section mast as shown in Figure 1 the load carrier6 is not stabilized &commat;nd and compensating pads consisting of springs 13,14 are respectively mounted on the lower end portions of the fixed mast section 3 and of the extensible mast section 4. As the lifting frame is retracted, each inner mast section, which can be extended to a higher level, runs up on said springs 13, 14to eliminate the play between the guide rollers 7 to 10 and the profiled guiding portions associated with said springs. It will be understood that similar springs may be mounted on the lower end portion of each stile ofthe mast section sand will cooperate with surfaces provided on the load carrier 6.

With that design, all sections ofthe mast can be clamped together in such a mannerthatvilbration will substantially be precluded and particularly a generation of noise will be avoided.

Such a design with compensation pads 13,14 consisting of springs is shown on a larger scale in Figure 4. Figure 2 indicates the fixed mast section 3, which is provided with the spring 13, the extensible mast section 4 and the load carrier 6, which is guided on the mast section 4.

The spring comprises a lower horizontal leg 15, from which the leaf spring proper, designated 13, rises substantially in S shape. An upper arch 16 bears on the mast section 3, to which the leg 15 ofthe spring 13 is connected by screw means 17. The overhang ofthelowerarch 18 exceedsthe extentto which the spring is bent back at 16 above the upper arch 19 so that a bearing surface 20 is provided, which is accessible from above.

Such springs may be provided on all mast sections, particularly also on the mast section 4, in a manner not shown in Figure 2, so that the meansfor guiding the load carrier on the mast section 4 will be correspondingly strengthened.

The height 21 of a spring 13may be so selected that a sufficiently flat run-up surface is ensured as well as a stable supportforthe lower end ofthe retracted mast section. The spring may rise, e.g., as far as to the level ofthe periphery ofthe running wheel 22 ofthe lifting truckor,with reference to Figure 1, overthe height ofthe respective lower guide roller 10 or 11. The running wheel 22 is disposed on the runway 30.

Aspecially designed spring 13 is shown in Figure 3. The spring portions 23 to 25 are straight and extend at an angle to each other. The free upper leg 25 is short.

In connection with the remarks made hereinbefore on the vertical extent ofthe springs, reference is made also to Figure 1,which shows a spring 14 rising above the guide roller 10. This will also be the case with springs disposed adjacent to other guide rollers 11 and 12.

Run-up surfaces are suitably provided atthetop and bottom.

It may be suitable for the guide means or guide rollers ofthe load carrier to run up from below on the compensating pad or spring. For this purpose it is possible, e.g., to provide a leaf spring with a leaf portion 23 as shown in Figure3.

Figure 4 is a top plan view showing parts wop a lifting frame 2, in which each of the extensible mast sections 31,32 comprises profiled side stiles 33,34; 35, 36 and the flxed mast section comprises stiles 38, 39, which are fixed at the bottom. The stiles comprise profiled portions L38, 40,41; 42,43; 44, 45, which are in rolling contactwith guide rollers46,47; 48,49; 50,51 of adjacent mast sections. The last adjacent mast section is constituted by the load carrier 6, which is provided with the guide rollers 50, 51.

The profiled portions 40 to 45 comprise flanges 61, 62; 63,64; 65,66; 67,68; 71, 72,which are parallel to the roller axles 55, 56; 57, 58; 59, 6O. The guide rollers 46 to 51 move between said flanges and there is a play on one side ofthetread.

That play is to be eliminated.

In Figure 4, the play on both sides ofthe guide rollers is apparent as well as a special profiled shape.

The springs 13,13' (see also Figure 1) are mounted on the stiles 38,39 of the fixed mast section (see also Figure 1). The springs 14,14' are mounted on the lower end portions ofthe stiles 36, 37 ofthe mast section 4 (Figure 1). Said springs eliminate the play indicated in the drawing. In accordance with the description, corresponding springs may be provided for the load carrier 6 adjacentto its guide rollers.

in the em bodiment shown, drive means 52,53,54 are shown at least in cross-section by the contours of hydraulic cylinder-piston assemblies for extending the load carrier 6 and for extending the extensible lifting frame.

In Figure 5, parts shown also in Figure 1 are designated with the same reference characters.

In the embodiment shown in Figure 5 the springs 13, 14 of Figure 1 have been replaced by compensating pads on the lower end portions ofthe mast sections 4,5 on the inside, i.e., on the rear ofthe profiled portions which embrace the nextiower mast section 3 or4. Thatdesign will affordthe above-described advantages of a permanently damping compensation effected in any extended position of the lifting frame.

In Figure 6 the lifting truck i is shown, which is provided with the lifting frame in accordance with Figures 1 and 5. In the embodiment shown in Figure 6 the springs which constitute compensating pads 13, 14 are arranged as described and additional compensating pads are provided,which consist of the springs 75,76, which are mounted on the same mast section as the springs 13, 14 but on its upper end portion. The spring 75 is provided on the fixed mast section 3 and the spring 76 is provided on the extensible mast secTion 4. Each of said springs 75, 76 is spaced such a distance from the top extremity of the fixed mast section 3 and ofthe extensible mast section 4thatthe springs are overlapped by the next adjacent mast section which is upwardly extensible therefrom. In that embodiment, springs are mounted on the lower and upper end portions of a mast section.

The springs 73 to 76 are specially designed, as is apparent from Figures 7 and 8 showing by way of example the spring 75. The spring 75 is mounted on the fixed mast section 3 and comprises a protruding intermediate portion 77, which is contained in and in pressure contact with a profiled portion of the extensible mast section 4, for instance, with a flange of a profiled portion of a stile of the mast section, as isapparentfrom Figure 4.

It is apparent that the spring 75, just as the springs 73,74 and 76, is substantially W-shaped. The end portions 78,79 are bent back and are shiftably held behind pins 80,81. In the selected embodiment, the lateral alignment and the holding in position in the longitudinal direction are ensured in spite of the freedom of movement The mounting means comprise, e.g., three bearing brackets 82,83, which are mounted on the stile ofthe fixed mast section and pins 80,81, which extend through the facing end portions of said bearing brackets. Said pins are spaced a distance from that surface of the stile ofthe mast section to which the bearing brackets have been secured, e.g., by welding. That distance is so large that the bent-back ends 78,79 can pass under the pins 80,81.

Each ofthe end portions 78 and 79 of the spring 75 is divided by longitudinal slots 84,85 into parallel legs 86,87 or 88,89, which extend on both sides of the bearing brackets 82,83 and serve for a lateral guidance. The longitudinal slots 84,85 are sufficiently long to ensure the compliance, on the one hand, and to hold the spring in position on the associated mast section, on the other hand.

It will be understood that the bearing brackets 82, 83 associated with the springs 73,74 in Figure are mounted on the stiles of the mastsections4,5, respectively, so thatthe generally W-shaped spring has an orientation which is opposite to that shown in Figure 6.

Claims (17)

1. A lifting frame for lifting trucks, particularly for forklifttrucks,which lifting frame comprises mast sections which are extensible relative to each other and provided with guiding meansforguiding each other with a play, characterized in that at least mast sections which are extensible are provided on end portions thereof with resilient compensating pads, which are so arranged that when two adjacent ones of said mast sections have been retracted relative to each other each of said pads mounted on one of said adjacent mast sections engages the other of said adjacent mast sections so as to compensate the play between said two adjacent mast sections.

2. A lifting frame according to claim 1, characterized inthat resilientcompensating pads are mounted on the lower end portion of each extensible mast section on the inside of a profiled portion which embraces the next lower mast section and is provided with the guide means.

3. A lifting frame according to claim 1, characterized in that resilient compensating pads are mounted on the lower end portions ofthe mast sections on the front side thereof and are so arranged that asthe mast sections which are extensible to a higher level are lowered they will engage said compensating pads.

4. A lifting frame according to claim 1, characterized in that resilientcompensating pads are mounted on the upper and lower end portions of at least one mast section and in that case the pad provided on the upper end portion is particularly disposed on thefront side and atsuch a distance from the top end that that mast section which can be raised relative to said mast section can be raised to an uppermost position in which the residual overlap is such that the upper mast section still covers the compensating pad mounted on the upper end portion of the next lower mast section and the compensating pad mounted on the lower end portion may constitute a buffer pad.

5. A lifting frame according to any of claims 1,3 and 4, comprising a fixed mast section, at least one extensible mast section and a load carrier,which particularly consists of a load-carrying fork and is mounted on the innermost mast section ofthe lifting frame and particularly on that mast section which is extensible to the highest level, and further comprising drive means for extending the lifting frame and the load carrier, wherein those mast sections which are movable relative to each other are guided on each other by guide rollers, each of which rolls in a profiled portion of an adjacent mast section, which profiled portions have flanges, which are disposed on opposite sides of the guide rollers and parallel to their axes, characterized in that a resilient compensating pad consisting particularly of a spring is provided at least on the fixed mast section and on the lowermost extensible mast section and said compensating pads extend along a length portion nearthe bottom end of the respective mast section and at least when the lifting frame has been retracted each of said compensating pads is in pressure contact with a stile of an adjacent mast section and eliminates any play between the stiles of adjacent mast sections or between a profiled portion and a guide roller contained in said profiled portion.

6. A lifting frame according to any of claims 1 to 4, characterized in that the springs mounted on the lower end portions of the fixed mast section and of extensible mast sections consist of buffersprings and each of said springs has a side face which is upwardly inclined and faces the associated mast section to which the spring or compensating pad has been secured.

7. A lifting frame according to any of claims 1 to 6, characterized in that resilient compensating pads preferably consisting of springs are provided also on that mast section which is extensible to the uppermost level and which is provided with a load carrier, which is guided on said uppermost mast section by means of rollers and are engaged by said pads when said load carriers are in their uppermost position.

8. A lifting frame according to any of claims 1 and 3 to 7, characterized in that each of the extensible mast sections is provided on its lower end portion with a compensating pad that preferably consists of a spring and in any position of the lifting frame engages the fixed mast section orthatextensible mast section which is the next lower mast section when the lifting frame has been extended.

9. A lifting frame according to any of claims 1 to 7, characterized in that the springs consist of leaf springs, each of which has a leg that is secured to the underside of a stile of one mast section and the spring has an arcuate portion which rises in a profiled portion ofthe stile of the mast section on the front side thereof and adjacent to the top end forms an inclined run-up surface.

10. A lifting frame according to claim 9, characterized inthatthe rising portion is substantially S-shaped and with its uppercurved portion bears on that mast section to which the spring is secured, and the spring is bent backto an extent which is smallerthan the overhang of the protruding arch of the spring near the fixing end.

11. A lifting frame according to claim 9 or 10, characterized in that each spring has a horizontal leg, which is secured to the underside of a stile of a mast section.

12. A lifting frame according to any of claims 1 to 4, characterized in that the springs are particularly provided on the inside ofthe extensible mast sections or the constantly engaging springs have a protruding intermediate portion and movably mounted supporting ends.

13. A lifting frame according to claim 12, characterized in thatthe springs are substantially W-shaped and their bent-back end portions are movably held by pins.

14. A lifting frame according to claim 13, characterized in that an extensible mast section or the fixed mast section is provided with spring-mounting bearing brackets and at a distance from said bearing brackets is provided with laterally protruding pins, which are adapted to be stressed in shears and engaged from behind by end legs of the springs, which end legs are defined by longitudinal slits and embrace the bearing brackets.

15. A lifting frame according to claims 10 and 13, characterized in thatthe S-shaped springs having a rising portion orthe W-shaped springs consist of straight portions and in the S-shaped spring the bent back upper portion and in the W-shaped spring both bent-back portions are short.

16. A lifting frame according to any of claims 7 to 10, 12, 13, characterized in that each ofthe compensating pads, which preferably consist of springs and are provided on that mast section on which the load carrier is guided, is provided with a run-up surface also at the lower end of said pad.

17. A lifting frame according to any of claims 1 to 16, wherein the fixed mast section and the extensible mast sections ofthe lifting frame comprise side stiles, characterized in that each stile is provided with a compensating pad, which preferably consists of a spring.

18; A lifting frame for a lifting truck, substantially as described hereinbefore with reference to or as shown on the drawings.