WO2011158268A1

WO2011158268A1 - Lift mast with improved visibility

Info

Publication number: WO2011158268A1
Application number: PCT/IT2011/000189
Authority: WO
Inventors: Paolo Varvara
Original assignee: Paolo Varvara
Priority date: 2010-06-14
Filing date: 2011-06-09
Publication date: 2011-12-22
Also published as: ITMT20100004A1; IT1408595B1

Abstract

Full free lift telescopic mast for fork lift truck comprising a pair of hydraulic two- step cylinders (1; 51) mounted adjacent the outer sides of mast assembly, or rear of this, a frame fixed to the fork lift truck chassis, one or more mobile intermediate frames, a mobile inner frame, a load carriage device, chains and pulleys. The masts are able to perform the so-called "full free lift", i.e. a first lifting of the load without any increment of the overall mast length. During the second lifting stage, the mast assemblies expand increasing their length. The absence of hydraulic cylinders in the middle of the mast assembly improves forward visibility of the fork lift truck operator.

Description

LIFT MAST WITH IMPROVED VISIBILITY

Description FIELD OF THE INVENTION

The invention concerns multistage, in particular three-stage, telescopic lift mast assemblies for fork lift trucks able to perform the full free lift of the load, i.e. the lift of the load without the overall length of mast increases, and then a second lift of the load during which the mast assembly expands longitudinally. The mast assemblies operates by means of hydraulic cylinders.

BACKGROUND ART

Fork lift trucks use various types of telescoping lift masts, hydraulically operated, among which some perform a first lifting of the load, usually positioned on a pair of forks, without any increment of the overall mast length, i.e. without the mast expansion. This is obtained by means of the so-called "full free lift masts", which usually comprise a stationary frame fixed to the fork lift truck chassis and two mobile frames, the "inner" and the "intermediate" sliding one into the other.

Usually, full free lift masts for lift trucks comprise three hydraulic cylinders: one shorter, almost half of the length of the others two, deputed to the full free lifting and arranged in the middle of the mast assembly, and two cylinders, arranged adjacent to the outer sides or rear of the mast assembly, deputed to the second lifting stage during wich the mast expands its length.

Sometimes, in order to improve forward visibility, instead of one shorter cylinder, two shorter cylinders, with smaller cross sectional area and simmetrically arranged on sides within the mast assembly, are preferred and conseguently the cylinders are four.

In any case, the forward visibility through a full free lift mast is hindered because of the presence of the cylinder, or the two cylinders, within the mast assembly. In the past, full free lift mast were assembled with a single hydraulic multistage cylinder arranged in the middle of the mast: these types of masts are disclosed in GB 1 057 140 A (EATON CORPORATION; YALE & TOWNE), GB 2 077 224 A (ASEA AB), US 4 008 648 A (Farmer et al.) with regard to masts comprising two mobile frames, and US 4 261 438 A (D. Olson) with regard to four stage masts comprising three mobile frames. All these masts are equipped with one hydraulic cylinder in the middle of the mast and have the disadvantage of hindering almost completely the operator's visibility.

To meet the market demand for full free lift masts with improved visibility, manufacturers have developed solutions among which the more diffused comprise, as already stated, three or four lifting hydraulic cylinders, of which one or two are shorter and arranged in the middle of the mast.

DISCLOSURE OF THE INVENTION

The purpose of the present invention is to provide full free lift masts for fork lift trucks, with either two or more sliding frames, which are able to operate by means of only a pair of hydraulic two-step cylinders, arranged adjacent the outer sides or rear of the mast assembly, consequently obtaining an improved forward visibility with regard to the prior art.

This invention discloses some different solutions from our previous international application under No. WO 2011/021231.

The device according to the aim of the invention relates to lift mast assemblies comprising three or more frames, one of which fixed to the fork lift truck chassis and two or more sliding frames, a pair of hydraulic two-step cylinders wich are able, by means of a transmission device comprising chains and pulleys, to transmit the motion to the mobile parts of the mast assembly in such a way to perform a first lifting of the fork carriage without any increment of the overall mast length, that is the full free lift, and then a second lifting of the fork carriage up to the maximum lifting heigth, during which the mobile frames slide reciprocally and the masts expand longitudinally. There are various ways to transmit motion, by means of chains and pulleys, from the hydraulic two-step cylinders to the mobile parts of the mast assembly.

BRIEF DESCRIPTION OF DRAWINGS

The invention will be disclosed hereinafter with reference to the annexed drawings wherein:

- Fig. 1 is a sectional view of a hydraulic two-step cylinder;

- Figs. 2, 3, 4 show the cylinder of Fig. 1 , respectively, in retracted position, after first stage and after second stage;

- Fig. 5 shows a partial sectional view of a hydraulic two-step cylinder different from that of Fig. 1.

- Figs. 6, 7, 8 show the cylinder of Fig. 5, respectively, in retracted position, after first stage and after second stage;

- Figs. 9, 10, 11 are schematic side views of a pattern of chain drive at various stages of lifting of a full free lift mast, according to the invention, comprising one fixed frame and two mobile frames, operating by two hydraulic two-step cylinders shown in Fig. 1;

- Figs. 12, 3, 14 show a schematic side view of a pattern of chain drive at various stages of lifting of a full free lift mast, according to the invention, comprising one fixed frame and two mobile frames, operating by two hydraulic two-step cylinders shown in Fig. 5;

- Fig. 5 is a schematic side view of a pattern of chain drive different from that shown in Fig. 9, operating by two hydraulic two-step cylinders shown in Fig. 1 , according to the invention;

- Fig. 16 is a schematic side view of a pattern of chain drive different from that shown in Fig. 12, operating by two hydraulic two-step cylinders shown in Fig. 5, according to the invention;

- Fig. 17 shows the rear view of a three stage mast with full free lift, operating in accordance to the pattern of chain drive illustrated in Figs. 9, 10, 11 and according to the invention; - Fig. 18 is the sectional view of the mast in Fig. 17;

- Figs. 19 and 20 show the rear view, in a reduced scale, of the mast of Fig.

17, after the first, the free lift, and the second lifting stage, respectively;

- Figs. 21 , 22 and 23 are schematic side views of a pattern of chain drive at various stages of lifting of a full free lift mast, according to the invention, comprising one fixed frame and three mobile frames, operating by a pair of hydraulic two-step cylinders 51 shown in Fig.1 ;

- Figs. 24, 25 and 26 are drawings showing the extension of the invention to a full free lift multistage mast with more than three mobile frames: it is an example of a mast comprising one fixed frame and five mobile frames and operating by a pair of hydraulic two-step cylinders 51 shown in Fig. 1.

BEST MODE FOR CARRYING OUT THE INVENTION

Fig. 1 is a longitudinal section through the hydraulic two-step cylinder 51 in its neutral position. The cylinder assembly 51 comprises an outer mobile tube 52 whose length is about half that of the cylinder assembly 51. An upper threaded cap 3 and a bottom welded cap 5 are fixed to the ends of the outer tube 52.

Both caps are axially drilled and have peripheral sealing gaskets 4.

A mobile intermediate tube 56 is mounted inside the tube 52, which is characterized by two different wall thicknesses 57 and 58 in order to differentiate the longitudinal hydraulic thrusts in the two sliding directions, because of the cylinder 51 is an "immersion" type cylinder, that is the annular chambers above and below the piston 54 are communicating one with the other. The intermediate tube 56 has a threaded cap 60 at the upper end and, at the other end, a welded cap 63 provided with the inlet/outlet hydraulic port. At the top, a stop collar 12 is housed inside of the intermediate tube 56. At about half of the length of the tube 56 the piston 54 is welded to the outer surface of the tube 56.

The piston 54 has an inner circular hollow 1 and some longitudinal slots 16 on the periphery, through which and through the radial holes 17, provided on the wall of the tube 56, pressurized oil can flow into the upper and lower annular chambers, delimited by the tubes 52 and 56 and separated by the piston 54. Inside the tube 56 is the piston-rod 68, at the bottom of which is screwed the threaded piston 19.

The piston 19 is drilled axially and has some radial holes 21 which allow the oil passage towards the annular chamber delimited by the rod 68 and the tube 56. The piston 19 mounts externally the guide collar 20 and internally the hollow valve 24 on which acts the spring 23. The valve 24 has radial orifices 25 and has the function of reducing the rate of speed of the piston-rod 68 in the last lowering sector. In Fig. 1 the valve 24 is completely retracted because of the contact pressure of the cap 63 when the tube 56 is closed upon the piston 19. Fig. 2 represents, in a different scale, the hydraulic two-step cylinder 51 in its neutral position. Fig. 3 shows the cylinder 51 when the tube 52 has completed the first downward stroke, the first step, due to the oil pressure provided by a hydraulic pump, shown in dashed lines. In this condition, the outer tube 52 is at the end of the stroke. Pressurized oil enters from the lower cap 63, passes through the valve 24, the holes 21 of piston 19, the annular chamber between the rod .68 and the tube 56, passes through the radial holes 17 and the hollows 15, 16 of the piston 54 and reaches the outer cylinder 52.

Fig. 4, finally, represents the cylinder assembly 51 at the end of second stage, during which the piston rod 68 slides out of the tube 56. At the end of the second stage, the cylinder 51 has reached its maximum extension as the stop collar 12 is in contact with the piston 19.

When the hydraulic fluid within the cylinder 51 is discharged through the cap 63 towards the reservoir, shown in dashed lines, which is at atmospheric pressure, the reverse sequence of lowering is obtained, so that the piston rod 68 moves downward relatively to the tube 56 and the cylinder 51 returns in the position shown in Fig. 3.

After the downward run of the piston rod 68, the outer tube 52 begins to slide upward because of gravity forces of the fork carriage, the forks and the load, if there, to which the tube 52 is linked by chains and pulleys (see, for example, Fig. 9 and Fig. 15). At the end of second stage, the hydraulic cylinder 51 returns to its neutral position shown in Fig. 2.

Fig. 5 represents the two-step cylinder assembly 1 partially sectioned longitudinally in its neutral state. The hydraulic cylinder 1 is obtained by rotating of 180° the previously described cylinder 51 shown in Fig. 1 and modifying the piston-rod and the inlet port: infact, the piston rod 18 of the cylinder 1 is completely hollow and the inlet/outlet port is arranged in the cap 22 of the piston rod 18, while the upper cap 13 of the intermediate tube 6 is closed.

When, by means of a hydraulic pump as in the case of the cylinder 51, pressurized oil flows through the bottom cap 22 and the tubular rod 18, the radial holes 21 of the piston 19, the radial holes 17 in the wall of the intermediate tube 6 and through the hollows 15 and 16 of the piston 9, the outer tube 2 moves upward.

The sequence of movements is described, in a smaller scale, in Figs. 6, 7 and 8 which show, respectively, the cylinder 1 in neutral state, at the end of the first stage and at the end of the second stage. Fig. 7 represents the cylinder assembly 1 when the outer tube 2 has completed its upward stroke, first stage, and Fig. 8 shows the cylinder 1 at the end of the second stage, when the collar 12 comes in contact with the piston 19, and the intermediate tube 6 has moved up to its uppermost position dragging simultaneously the outer tube 2.

When hydraulic oil within the cylinder assembly 1 is discharged, by means of a hydraulic valve, towards the fluid reservoir at the atmosphere pressure, the reverse sequence occurs. Firstly, the intermediate tube 6 moves downward jointly to the outer tube 2, so that the cylinder assembly 1 returns to the position shown in Fig. 7; secondly, the outer tube 2 moves downward and the cylinder 1 returns to its neutral position shown in Fig. 6.

A first illustrative embodiment of the present invention is a full free lift, triple stage, mast 100 actuated by two hydraulic cylinders 51 shown in Fig. 1. The mast 100 is schematically depicted at rest, Fig. 9, at the end of the first stage, the full free lift, Fig. 10, and at the end of the second lifting stage, Fig. 11.

The mast 100 comprises the fork carriage 141 sliding in the mobile inner frame 131 which is also sliding in the intermediate frame 121 , sliding in the stationary outer frame 111 , and two hydraulic two-step cylinder 51 of Fig. 1.

The lower part of the intermediate tube 56 is joined to the intermediate frame 121 at the bottom, in order to prevent reciprocal relative longitudinal motion. The upper part of the piston rod 68 of the cylinder 51 is anchored, in both longitudinal directions, to the upper tie-bar 133 of the mobile inner frame 131. The outer tube 52 is joined with the pulley 153. The lift chains 151 is secured at one end to the load carriage 141 and at the opposite end to the stationary frame 111 , and extends up around the pulleys 152, fixed to the inner frame 131 , and 153. When pressurized oil flows into the cylinder 51, Fig. 10, the first lifting stage, i.e. the free lift, occurs. The pressurized oil pushes downward the outer tube 52, which lifts the load carriage 141, by means of the pulley 153 and the chain 151 , at twice the speed of the tube 52. At the end of the first stage, the load carriage 141 contacts stop member 132 secured to the inner frame 131. At this point, oil pressure increases and the second stage occurs, in which the piston-rod 68 slides out the tube 56 and drags firmly the inner frame 131 and the pulley 152. The upward movement of the inner frame 131 and the pulley 152, causes, by means of the chain 151, the lifting of the pulley 153 secured to the tube 52 which drags upward the whole cylinder 51 and therefore the intermediate frame 121 which is secured to the tube 56. At the end of the second stage the mast 100 reaches its maximum extension, shown in Fig. 11. According to the aim of the invention, i.e. improving visibility through the mast assembly, Fig. 7 shows the rear view of a full free lift mast 100 operating according to the drawings of Figs. 9, 10 and 11. Fig. 18 is the sectional view of the mast 100 shown in Fig. 17. There are shown the stationary outer frame 111 , the mobile intermediate frame 121, the mobile inner frame 131, the fork carriage 141 , the two hydraulic two-step cylinders 51 arranged rear of the mast assembly 100, the two chains 151 , the two pulleys 153 secured to the outer tubes 52 by means of the tie-bar 98, the two pulleys 152 secured to the mobile inner frame 131 , a stop member 132 mounted on the mobile inner frame 131 , Fig. 18, the nuts 99 which secure the intermediate tubes 56 to the intermediate frame 121 , the bottom caps 63 and the upper part of the rod 68 secured to the upper tie- bar 133 of the mobile inner frame 131.

Figs. 19 and 20 represent, in a smaller scale, the mast 100 of Fig. 17 and are equivalent to the schematic Figs. 10 and 11. The mast 100 has performed the first stage, the full free lift, in Fig. 19 and the second stage, at the maximum elevation, in Fig. 20.

The above embodiment of the present invention is for illustrative purposes and obviously you could use other configurations without departing from the functional scheme.

Another example of the invention relates to a three stage mast with full free lift operating by means of a pair of hydraulic two-step cylinders 1 shown in Fig. 5. Schematic drawings of the mast 200 are shown in the lowered position in Fig.12, at the end of the first stage, the full free lift stage, in Fig. 13, and at the end of the second lifting stage in Fig. 14, i.e. at the maximun extension.

The tubular piston-rod 8 of the cylinder 1 rests at the bottom on the bracket 222 which is secured to the mobile intermediate frame 221 , while at the top the intermediate tube 6 is secured to the upper tie-bar 233 of the mobile inner frame 231. The chain 251 is anchored to the stationary frame 211 at one end and to the fork carriage 241 at the other end, and is guided by the pulley 252 which is joined to the outer tube 2 and by the pulley 253 secured to the intermediate frame 221.

When oil pressure is acting in the cylinder 1 , Fig. 13, the outer tube 2 and the pulley 252 move up, lifting the fork carriage 241. The upward speed of the fork carnage 241 is at twice the speed of the tube 2 and the pulley 252. At the end of the first stage, the fork carriage 241 contacts the stop member 232 of the inner frame 231 , so that at this point the fork carriage 241 and the inner frame 231 are elevated as a unit. In Fig. 14 the mast 200 has completed also the second stage. In the second stage, the tube 6 slides up on the tubular piston-rod 18, dragging the outer tube 2, therefore also the pulley 252, and the mobile inner frame 231. By means of the pulley 253, secured to the mobile intermediate frame 221, and of the chain 251 , the movement is transmitted to the intermediate frame 221 and therefore also to the cylinder 1. As a consequence, the upward speed of the fork carriage 241 , and of the mobile inner frame 231 , is at twice the speed of the intermediate frame 221 which moves at the same speed of the tube 6.

Fig. 15 represents a chain drive functionally equivalent to that shown in Fig. 9. in this case, the transmission of motion from the two-stage cylinder 51 to the fork carriage 141 is by means of two pairs of chains 161 and 162. The first pair 161 is anchored to the fork carriage 141 and to the mobile inner frame 131, and is guided by a pair of pulleys 152, secured to the inner frame 131 , and a pair of pulleys 153 secured to the outer tube 52, while the pair of chains 162 is anchored to the inner frame 131 and to the stationary frame 111 being guided by a pair of pulleys 154 secured to the intermediate frame 121.

Fig. 16 shows a drive chain functionally equivalent to that represented in Fig. 12. In this case, the transmission of motion from the two-stage cylinder 1 to the fork carriage 241 is by means of two pairs of chains 261 and 262. The pair of chains 261 is anchored to the fork carriage 241 and to the mobile inner frame 231 , and is guided by a pair of pulleys 252, secured to the outer tube 2, while the pair of chains 262 is anchored to the inner frame 231 and to the stationary frame 211 being guided by a pair of pulleys 253 which is secured to the intermediate frame 221.

The present invention is applicable to a generic multistage full free lift mast comprising more than one mobile intermediate frame: two illustrative embodiments of this application are represented in Figs. 21, 22 and 23, relating to a four-stage mast, i.e. comprising two mobile intermediate frames, and the 2011/000189

other is represented in Figs. 24, 25 and 26, relating to a six-stage mast, i.e. comprising four mobile intermediate frames.

Figs. 21 , 22 and 23 are schematic drawings showing sequential extensions of a four-stage mast 300 constructed in accordance with the present invention. The mast 300 comprises the fork carriage 341 sliding in the mobile inner frame 331 , two mobile intermediate frames 321, 322, the stationary outer frame 311 and a pair of hydraulic two-step cylinder 51 of Fig. 1. Two pairs of chains 351 and 352 are involved in lifting the fork carriage and in extending the mast 300. The first pair of chains 351 is guided by two pairs of pulleys 361, fixed to the mobile inner frame 331, and 362, fixed to the mobile outer tubes 52 of the cylinders 51 , and is fixed at one end to the fork carriage and at the other end to the second intermediate frame 321. The other pair of chains 352, guided by a pair of pulleys 363, fixed to the second mobile intermediate frame 321 , is secured to the first intermediate frame 322 at one end, and to the stationary frame 311 at the other end. In the first step, oil pressure pushes downward the outer tube 52 of the cylinder 51 and the pulley 362, so that the chain 351 lifts the fork carriage 341 which comes in contact with the stop member 332 on the inner frame. At this point, the fork carriage 341 has completed the full free lift stage shown in Fig. 22.

At the end of the first stage, oil pressure increases and the second stage occurs: the piston-rod 68 extends and lifts the inner frame 331 and the pulley 361. The upward movement of the mobile inner frame 331 and the pulley 361 , causes, by means of the chain 351, the lifting of the pulley 362 secured to the tube 52 which drags upward the whole cylinder 51 and therefore the first intermediate frame 322 which is secured to the outer tube 56. As a result, also the second intermediate frame 321 moves up because of the chain 352 and the pulley 363. At the end of the second stage, the mast 300 is fully extended to the maximum elevation as shown in Fig. 23.

In the case of the four-stage mast 300, the speed of the fork carriage 341 is at a ratio of 2:1 relative to the downward speed of the outer tube 52 during the first 1 000189

step, while the speed during the second step is at a ratio of 3:1 relative to the speed of extention of the cylinder assembly 51, i.e. the upward speed of the rod 68 relative to the tubes 56 and 52, which are elevated toghether with the first intermediate frame 322. The reduction of the speed of the fork carriage during the second stage, i.e. the extension of the mast, could be obtained reducing the volumetric oil flow into the cylinders: for example, reducing the rotation speed of the oil pump of 1/3, the speed in the second stage will be almost equal to that in the first stage.

The next example is intended merely to show how the present invention can be extended to a generic multi-stage mast comprising more than four frames.

Figs. 24, 25 and 26 are schematic drawings showing the sequential extensions of a six-stage mast 400 comprising the fork carriage 441 sliding in the mobile inner frame 431 , four mobile intermediate frames 421 , 422, 423, 424 sliding one into the other, the stationary outer frame 411 and a pair of hydraulic two-step cylinder 51 of Fig. 1. The arrangement of the six-stage mast 400 is very similar to the four-stage mast 300 of Fig 21 : in the case of the six-stage mast 400, four pairs of chains 451, 452,453, 454 and five pairs of pulleys 461, 462, 463, 464, 465 are involved in lifting the fork carriage and in extending the mast. The pair of chains 451 is secured at one end to the fork carriage 441 and at the other end to the second mobile intermediate frame 423. All the other pairs of chains extend up around a pair of pulleys, which is fixed to an intermediate frame, and is secured to the previous and next frames: for example, the pair of chains 453 estends up the pulleys 464, fixed to the intermediate frame 422, and is secured to the previous 423 and the next 421 frames. Fig. 25 shows the six-stage mast 400 at the end of the first step, i.e. when the fork carriage 441 has completed the full free lift stage. The speed of the fork carriage 441 is at a ratio 2:1 relative to the downward speed of the outer tube 52. During the second step, the piston- rod 68 moves out of the tube 56 and the four chains 451, 452, 453, 454 lift the four mobile intermediate frames 421 , 422, 423, 424 as shown in Fig. 26 at the end of the second stage, i.e. the expansion of the mast 400. The speed of the fork carriage is at a ratio of 5:1 relative to the speed of extention of the cylinder 51, i.e. the speed of the piston-rod 68 relative to the tube 56. The reduction of the speed of the fork carriage during the second stage, i.e. the extension of the mast, could be obtained reducing the volumetric oil flow into the cylinders: for example, reducing the rotation speed of the oil pump of 3/5, the speed in the second stage will be almost equal to that in the first stage.

Claims

Multistage, at least three-stage, telescopic mast for fork lift truck, that is able to perform a first lifting stage of the fork carriage without any increment of the overall mast length, that is a full free lift stage, hydraulicaily operated, comprising a stationary outer frame, at least one mobile intermediate frame, a mobile inner frame, a fork carriage, or an equivalent load device, characterized by a lifting device comprising:

• a pair of hyraulic two-step cylinders (51 ; 1) simmetrically mounted on both, left and rigth, outer sides of mast assembly, or rear of the mast;

• a fixing means of the cylinders (51; 1) to the first mobile intermediate frame, i.e. the adjacent one to the mobile inner frame, at the bottom, and to the mobile inner frame, at the top;

• a transmission device comprising chains and guiding pulleys.

Each hydraulic two-step cylinder (1; 51) is characterized by:

• an inner piston-rod (68; 18);

• a hollow piston (19) equipped with radial holes (21) and a guiding collar (20), fixed on the piston-rod (68; 18);

• an intermediate tube (56; 6) with radial holes (17) for oil passage, equipped with a welded cap (63; 13) at one end, and a hollow threaded cap (60; 10) at the other end;

• an annular piston (54; 9) welded, or anyway fixed, to the outer surface of the intermediate tube (56; 6), equipped with a circular hollow (15) and longitudinal slots (16) on the periphery;

• a stop collar (12) secured on the intermediate tube (56;6);

• an outer tube (52; 2), sliding on the intermediate tube (56; 6), equipped at its ends with a welded hollow cap (5) and a threaded hollow cap (3).

Full free lift, three-stage, telescopic mast (100; 101) (Figs. 9; 15) as claimed in claim 1, characterized in that: • said lifting device comprises a pair of two-step cylinders (51), wherein the bottom caps (63) of the intermediate tubes (56) are axially drilled and connected to the hydraulic oil supply pipe;

• said fixing means of the cylinders (51) comprises, at the bottom, the brackets (122) secured to the mobile intermediate frame (121) on which the intermediate tubes (56) rest, and, at the top, the upper tie-bar (133) of the mobile inner frame (131) to which the upper ends (72) of the rods (68) are anchored.

Full free lift, three stage, telescopic mast (100) (Fig. 9) as claimed in claim 2, characterized in that:

• said lifting device comprises: a stop member (132), secured on the upper side of the mobile inner frame (131), able to engage the fork carriage (141); a pair of chains (151) anchored to the fork carriage (141), at one end, and to the stationary frame (111), at the other end, guided by two pairs of pulleys, of which a pair (152) is fixed to the upper side of the mobile inner frame (131) and the other pair (153) is fixed to the mobile outer tubes (52) of the cylinders (51);

• said fixing means of the hydraulic cylinders (51) to the bracket (122) comprises the nuts (99), or an equivalent fixing device, fastened to the lower caps (63) of the intermediate tubes (56) because the two-step cylinder assemblies (51) are able to carry the intermediate frame (121).

Full free lift, three stage, telescopic mast (101) (Fig. 15) as claimed in claim 2, characterized in that:

• said lifting device comprises two pairs of chains: one pair (161), anchored to to the fork carriage (141), at one end, and to the mobile inner frame ( 31), at the other end, is guided by two pairs of pulleys, of which a pair (152) is fixed to the upper side of the mobile inner frame (131) and the other pair (153) is fixed to the outer tubes (52) of the cylinders (51); the other pair of chains (162), anchored to the mobile inner frame (131), at one end, and to the stationary frame (111), at the other end, is guided by a pair of pulleys (154) fixed to the lower side of the mobile intermediate frame (121).

Full free lift, three stage, telescopic mast (200; 201) (Figs. 12; 16) as claimed in claim 1 , characterized in that:

• said lifting device comprises two hydraulic two-step cylinders (1), wherein the lower caps (22) and the rods (18) are axially drilled and connected to the hydraulic oil supply pipe;

• said fixing means of the cylinders (1) comprises, at the bottom, the brackets (222), stationary to the mobile intermediate frame (221), on which the lower caps (22) of the tubular rods (18) of the two cylinders (1) rest, and, at the top, the upper tie-bar (233), of the mobile inner frame (231), to which the upper caps (13) of the intermediate tubes (6) of the cylinders (1) are anchored.

Full free lift, three stage, telescopic mast (200) (Fig.12) as claimed in claim 5, characterized in that:

• said lifting device comprises: a stop member (232) fixed to the upper side of the mobile inner frame (231), able to engage the fork carriage (241);

• said lifting device comprises a pair of chains (251) anchored to the fork carriage (241), at one end, and to the stationary frame (211 ), at the other end, guided by two pairs of pulleys, of which a pair (252) is fixed to the mobile outer tubes (2) of the cylinders (1) and the other pair (253) is fixed to the lower side of the mobile intermediate frame (221).

Full free lift, three stage, telescopic mast (201) (Fig. 16) as claimed in claim 5, characterized in that:

• said lifting device comprises two pairs of chains: one pair (261), anchored to to the fork carriage (241), at one end, and to the mobile inner frame (231), at the other end, is guided by a pair of pulleys (252) fixed to the mobile outer tubes (2) of the cylinders (1); the other pair of chains (262), anchored to the mobile inner frame (231 ), at one end, and to the stationary frame (211), at the other end, is guided by a pair of pulleys (253) fixed to the lower side of the mobile intermediate frame (221).

- Full free lift, four-stage, telescopic mast (300) (Fig. 21) comprising two mobile intermediate frames as claimed in claim 1, characterized in that:

• said lifting device comprises a pair of two-step cylinders (51), wherein the bottom caps (63) of the intermediate tubes (56) are connected to the hydraulic oil supply pipe and are fixed to the first intermediate frame;

• said lifting device comprises a stop member (332), secured to the upper side of the mobile inner frame (331), able to engage the fork carriage (341);

• said transmission device comprises two pairs of chains (351; 352); the first pair (351) is anchored to the fork carriage (341), at one end, and to the second mobile intermediate frame (321), at the other end, and is guided by two pairs of pulleys, a pair (361) of which is stationary to the upper side of the mobile inner frame (331) and the other pair (362) is stationary to the mobile outer tubes (52) of the cylinders (51); the other pair of chains (352), is anchored to the first intermediate frame (322), at one end, and to the stationary frame (311), at the other end, and is guided by a pair of pulleys (363) fixed to the lower side of the second intermediate frame (321);

• said fixing means of the cylinders (51) comprises, at the bottom, brackets (323), fixed to the first intermediate frame (322), to which the lower caps (63) of the intermediate tubes (56) are fixed by means of the nuts (99) or by an equivalent means and, at the top, the upper tie-bar (333) of the mobile inner frame (331) to which the upper ends (72) of the rods (68) are anchored.

- Full free lift telescopic mast (400) (Fig. 24) comprising more than two mobile intermediate frames as claimed in claim 1, characterized in that: • said lifting device comprises a pair of two-step cylinders (51), wherein the bottom caps (63) of the intermediate tubes (56) are connected to the hydraulic oil supply pipe;

• said lifting device comprises a stop member (432), fixed to the upper side of the mobile inner frame (431), able to engage the fork carriage (441);

• said fixing means of the cylinders (51) comprises, at the bottom, brackets (425), fixed to the first intermediate frame (424), to which the lower caps (63) of the intermediate tubes (56) are fixed by means of the nuts (99) or by equivalent means, and, at the top, the upper tie-bar (433) of the mobile inner frame (431) to which the upper ends (72) of the piston-rods (68) are anchored;

• said transmission device comprises:

o a pair of chains (451) anchored to the fork carriage (441), at one end, and to the second mobile intermediate frame (423), at the other end, guided by two pairs of pulleys, a pair (461) of pulleys is fixed to the upper side of the mobile inner frame (431) and the other pair (462) is fixed to the outer tubes (52) of the cylinders (51);

o as many pairs of pulleys as the number of the intermediate frames beyond the first; every pair of pulleys is mounted on an intermediate frame, excluding the first, and guides a pair of chains which is anchored to the previous and to the next intermediate frames.

- Full free lift telescopic mast as claimed in one of claims 1 to 9, characterized in that at least one of the two-step cylinder assemblies is equipped with a braking valve (24) arranged within the piston (19).