A FORKLIFT TRUCK

Abstract: A forklift truck (1) having a wheeled chassis (2), a lifting mast (4) and lifting forks (5) carried by said mast. The mast is arranged for movement between a first position in which at least a major portion of the mast (4) is located substantially horizontally beneath said chassis (2), and a second position in which at least a part of said mast extends vertically in the form of a rigid column. The mast (4) comprises a plurality of individual, elongate sections (6) which are pivotally connected together in a manner such that when the sections form a straight line said sections are able to pivot in only one direction. A means is provided for preventing pivotal movement of said sections (6) in said one direction when the mast is raised, thereby to form a column which is rigid in all directions.

Description: A for lift truck The present invention relates to a forklift truck hav¬ ing a wheeled chassis, a lifting mast and a lifting fork carried by said mast. Many differing variants of such forklift trucks are known to the art. In all lifting operations using a fork¬ lift truck for transporting and stacking purposes , it is important that the load is lifted fully vertically and lowered in the same way. To this end the lifting masts of some known forklift trucks are guided in vertical guides whose vertical dimensions are commensurate with the ceiling heights in those locales in which the truck is expected to work. As will be understood, the forward vision of the truck driver is an aspect of safe working which must be given the greatest of attention. For example, the thickness of the vertical guides must not be of such a nature as to unduly obstruct the vision of the driver. In realization of this fact, attempts have been made to slenderize the said vertical guides , in order to provide the truck driver with the clearest possible forward view. Although the provision of slender guides has improved the forward view of such fork¬ lift trucks to some extent, it has resulted in an unfavour¬ able wheel-pressure distribution. In order to overcome the obstructiveness of the afore- mentioned guides and to improve the balance of pressure on the wheels of the truck, it has been proposed that fork¬ lift trucks intended for use in locales of differing ceiling heights shall be provided with telescopic lifting masts , such that when taking a load the forks of the truck can be lowered to a desired low level and then elevated by the mast to a desired higher level. The inherent nature of a telescopic mast, however, requires that the first, or lower¬ most section of the mast must be relatively thick or stout. Thus , these lowermost sections of the masts are also liable to obstruct the forward vision of the driver, even with the OMPI mast in a totally collapsed position. It will be understood that there is need of a fork¬ lift truck which is able to be driven to a load without the forward vision of the driver being obstructed, and which can be operated satisfactorily in locales of varying ceil¬ ing heights, so that loads can be safely collected from one level and stacked to a further desired level. Consequently, one object of this invention is to pro¬ vide a forklift truck of the said kind in which the afore- mentioned disadvantages are substantially eliminated in a simple and economic manner. To this end there is proposed a forklift truck having a wheeled chassis, a lifting mast, and a load-carrying fork arrangement carried by said mast, characterized in that said mast is arranged for movement between a first position in which at least a major part of the mast is located sub¬ stantially horizontally beneath said chassis, and a second position in which at least a major part of said mast extends rigidly vertically. Conveniently, the mast comprises a plurality of indi¬ vidual, elongate sections which are pivotally connected to¬ gether in a manner such that when the sections form a straight line said sections are able to pivot in only one direction; and in that a means is provided for preventing pivotal movement of said sections in said one direction when the mast is raised, thereby to form a column which is rigid in all directions. The sections are preferably of substantially U-shaped cross-section, exhibiting a web portion and two leg por- tions extending at right angles from a respective end of said web portion; and mounted on the free ends of each of said leg portions are pairs of mutually spaced apart lugs, the spaces between said lugs being effective to receive a respective portion of an adjacent section, such as to lock said section against pivotal movement in three directions. According to one embodiment of the invention the means for preventing pivotal movement of said sections in said one direction comprises a plunger mechanism carried by individual sections and arranged to engage an opening located in an adjacent section. The plunger mechanism pre¬ ferably includes a plunger having at least one wheel or roller which is guided in a curved guide means extending from a vertical position in front of the truck to a hori¬ zontal position beneath said truck. The arrangement of' the guide means is such that respective plungers are moved axially, into and out of the openings of respective adja- cent sections, as the mast is raised and lowered respec¬ tively. Movement of the mast sections between said first and said second positions is effected through rollers mounted on respective mast sections and arranged to run in the guide means, said guide means extending in a curved manner from a substantially vertical position in front of the truck to a substantially horizontal position beneath the chassis thereof. It will be understood that the extent of the guide means in its vertical direction is such as not to obstruct the forward view of the driver. So that the invention will be more readily understood and further features thereof made apparent , an exemplary embodiment of the invention will now be described with reference to the accompanying schematic drawings, in which Fig. 1 illustrates in side view a forklift truck according to the invention with its mast in a raised posi¬ tion, Fig. 2 is a view similar to Fig. 1 with the mast in a lowered position, in which a greater part of the mast is located beneath the truck, Fig. 3 is* an end view of a mast section seen on the line III-III in Fig. 6, Fig. 4 is a side view of the mast section illustrated in Fig. 3, Fig- 5 is a sectional view taken on the line V-V in Fig- 4, Fig. 6 illustrates a section seen on the line VII-VII in Fig. 5 and discloses the manner in which mutually adjacent mast sections are interconnected, and Fig. 7 illustrates the action of the plunger mecha¬ nisms as the mast is raised and lowered. In Figs. 1 and 2 there is shown a forklift truck, generally referenced 1, having a chassis 2, wheels 3, a lifting mast, generally shown at 4, and lifting forks 5. In the illustrated embodiment, the mast 4 comprises a plurality of interconnected, pivotable sections 6 arranged for movement from a first position in which at least a major part of the mast is located substantially horizon¬ tally beneath the chassis 2 (Fig. 2), to a second position in which at least a major part of the mast is located substantially vertically in front of the truck (Fig. 1). As will be understood, the sections are also arranged for movement between positions intermediate of said first and second positions. The extent to which the mast is moved between these positions will, of course, depend on the ceiling height of the locale in which the truck is to work or the height to which goods to be transported are stacked. The sections 6 are pivotable relative to one another in a plane such that in one direction they can be swung to form a straight mast, while in another direction they can swing in a manner to permit them to be guided along a curved guide path, from beneath the chassis 2 to a vertical position in front of the truck, in a manner hereinafter described. As will be seen from Fig. 6, and also from Figs. 3 and 4, the mast sections 6 are pivotally connected by lugs 7. These lugs -are mounted on each end of a respective section, so as to be located at the four corners thereof as shown in Fig. 3. The lugs 7 comprise pairs of spaced apart plates (not referenced). It will be understood from this that, when the mast is being raised, the lugs 7 are pivoted to a straight line, i.e. to an angle of 180 , which is their maximum angle of pivot.' Contacting sur- faces 8 at the leading edge of each section 6 are then acted upon by vertically acting compression forces, and the raised mast is prevented from pivoting in three directions and when carrying a useful load will remain vertical and straight unless subjected to a force acting in the fourth direction, i.e. the direction of the arrow P in Fig. 1. To ensure that the mast, when raised, is completely rigid in all directions, each section 6 of the mast illu- strated in Figs. 3,4,5 and 7 is provided at one end there¬ of with a locking means generally shown at 9. The locking means 9 comprises a plunger 10 which extends from a shaft 11 at right angles thereto. Mounted for rotation on each end of the shaft 11 is a roller 12 which is guided for movement in a guide 13. It should be mentioned here that although the illustrated embodiment prefers the provision of two rollers 12, as shown, only one roller need be pro- vided j with the plunger 10 located in the vicinity of said roller. The guide 13 of the illustrated embodiment is formed integrally with a further guide 14 which extends in a curved path from a vertical position in front of the truck 1 to a horizontal position beneath the chassis 2. * As before mentioned, the height to which the guide 14 ex¬ tends in front of the truck 1 should not be such as to obstruct the forward view of the driver. Arranged for rotation in the guides 14 are rollers 15 mounted on shafts 16 extending through respective lugs 7. The plunger 10 of the locking means extends through a casing 17 having an end wall 18 and an intermediate wall 19, and is biassed by a spring 20 arranged between the walls 18 and 19. The plunger 10 is intended to engage an opening 21 arranged in or on a respective section 6, at the end thereof opposite the locking means 9, as shown in Fig. 3. As will be seen from Fig. 7, the arrangement of the guide means 14 is such that as the sections 2 are moved around the curve of said guide means to take a vertical position, the plungers 10 are progressively displaced axially by the guide means 14 until said plungers enter their respective openings 21 of adjacent sections 6, the springs 20 serving to assist in holding the plungers in said openings. It is desirable that no play exists between the outer surfaces of the plungers and the walls of the respective openings. To this end, the plungers are con- veniently tapered at the ends thereof adjacent the open¬ ings, and said openings suitably have a conforming inter¬ nal shape. As will be seen from Fig. 6, the mast elements 6 of the illustrated embodiment are provided along one side thereof with teeth 22, as are also the lugs 7. The teeth 22 are arranged to mesh with the toothed drive wheel 23, for raising and lowering the mast 4. In practice, the mast 4 is lowered until the upper¬ most section 26, i.e. the section carrying the forks 5, is located at the top of the guide 14, such that the drive wheel 23 is constantly in driving engagement with the teeth 22 of a mast section 6. When wishing to raise the mast, the wheel 23.is rotated by means (not shown), so as to move the sections from their horizontal position to a vertical one. As the sections 6 move along the curved guide 14, the lugs 7 pivot to their maximum angle of pivot, i.e. to an angle of 180 , and the contacting surfaces 8 at the leading edge are acted upon by compression forces, and the sections are locked against pivotal movement in three directions. As the sections 6 con¬ tinue to move along the guide 14, the plungers 7 are displaced axially until they enter respective openings 21, thereby locking the sections 6 against pivotal movement in the fourth direction, i.e. against movement resulting from a force acting in the direction of arrow P in Fig. 1. When lowering the mast, the reverse sequence of operations takes place, so that the sections 6 are free to swing beneath the chassis 2. As indicated in Fig. 2, the* guide means 14 may be arranged to extend up behind the truck 1, thereby enabling a longer mast to be provided. As will be understood, the described and illustrated forklift truck offers many advantages over those trucks at present known to the art. For example, not only does the driver have a completely free view when manouvering his vehicle to pick up a load, but can also, work efficiently in locales of greatly differing ceiling heights with one and the same truck. An example of this is the removal of goods from inside a container to a large warehouse. Although the invention has been described with reference to a preferred embodiment thereof, this embodi- ment is not limitive of the invention, but can be modified within the scope of the claims . For example , any pivotal movement of the sections 6 when subjected to a force acting in the direction of arrow P of Fig. 1 may be prevented or the force counteracted by means of a line or chain 24 wound on a drum 25 and extend¬ ing along the pressured side of the mast parallel thereto, said line or chain being held in tension by means not shown, such as a spring. The line or chain may be used instead of the locking means 9 or may be used in con- junction therewith as an additional safety factor. Further, two or more masts may be arranged side by side, and the sections 6 may be connected together by means other than those illustrated, e.g. by links or latches. Also, the curved part of the mast may be guided along different paths or rolled up.

Claims: C L A I S : 1. A forklift truck (1) having a wheeled chassis (2) a lifting mast (4) and lifting forks (5) carried by said mast, characterized in that the mast is arranged for move¬ ment between a first position in which at least a major portion of the mast is located substantially horizontally beneath said chassis (2), and a second position in which at least a part of said mast extends vertically in the form of a rigid column. • 2. A forklift truck according to claim 1 , characterized in that the mast (4) comprises a plurality of individual, elongate sections (6) which are pivotally connected together in a manner such that when the sections form a straight line said sections are able to pivot in only one direction, and in that a means (9;24) is provided for preventing pivotal movement of said sections (6) in said one direction when the mast is raised, thereby to form a column which is rigid in all directions. 3. A forklift truck according to claim 2, characterized in that said sections (6) are of substan- tially U-shaped cross-section, exhibiting a web portion (30) and two leg portions (31) extending at right angles from a respective end of said web portion; and in that mounted on the free ends of each of said leg portions are pairs of mutually spaced apart lugs (7), the spaces between said lugs being effective to receive a respective portion (8) of an adjacent section (6), such as to lock said section against pivotal movement in three directions. 4. A forklift truck according to claim 2 , characterized in that the means (9;24) for preventing pivotal movement of the sections (6) in said one direction comprises a plunger mechanism (10,17,18,19 and 20) carried by individual sections and arranged to engage an opening (21) located in an adjacent section (6). 5. A forklift truck according to claim , characterized in that the plunger mechanism (10,17,18,19 and 20) includes a plunger 10 having at least one wheel (12) which is guided in curved guide means (13,14) extend¬ ing from a vertical position in front of the truck to a horizontal position beneath said truck, the arrangement of said guide means being such that respective plungers (10) are moved axially, into and out of the openings (21) of respective adjacent sections (6) as the mast (4) is raised and lowered respectively. 6. A forklift truck according to claim 5 , characterized in that each of said sections (6) exhibits a multiplicity of drive teeth (22) arranged to cooperate with a toothed drive wheel (23), for raising and lowering the mast (4). 7. A forklift truck according to claim 2 , characterized in that said means (9;24), for preventing pivoting of said sections (6) in said one direction com¬ prises a tensioned line or chain (24) extending parallel with the raised sections (6) of the mast (4) on the pressured side thereof. 8. A forklift truck according to claim 4, characterized in that a tensioned line or chain (24) ex¬ tending parallel with the mast sections (6) in the raised position thereof on. the pressured side of said sections is arranged to cooperate with said plunger mechanism (10,17, 18,19 and 20) in preventing said pivotal movement of said sections (6) in said one direction.

Inventors: ENERUS T
Applicants: ENERUS T
Application year: 1980
Main classification: B66F9
IPC codes: B66F3, B66F9