The invention relates to a motion mechanism for obtaining several movements from a single power unit. It has been developed particularly in connection with fork trucks to make possible that a single hydraulic cylinder provides the lateral movement operation as well as the expanding operation and preferably also the rotating operation. The lateral movement operation comprises displacement of the two forks laterally in parallel and at a uniform mutual spacing of the forks, and the expanding operation comprises displacement of the forks towards and away from each other. The additional pivoting operation, if any, comprises rotation of the forks as a unit on the fork frame about a substantially horizontal axis. The systems for generating these motions, which are available on the market today, comprise two hydraulic cylinders connected one to each fork for effecting the lateral movement and the expanding operations. If the fork truck shall perform also a rotating operation, a third hydraulic cylinder is required. The prior art system makes some problems. At the expanding operation an accurate distribution of the oil flow to the two hydraulic cylinders cannot be obtained at reasonable costs. When the forks are slowly adjusted it thus happens that one fork moves away, which considerably obstructs the insertion of the forks e.g. under a container or a pallet. Moreover, dirt in the system and existing leakage, if any, unfavourably affect the properties of the system.

The related problems are eliminated by the invention which relates to a motion mechanism for obtaining several movements from a single power unit of the kind and with

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the characteristics appearing from claim 1.

Except that the. related problems are overcome it is achieved by the invention that no larger hydraulic cylinder is required, because a single hydraulic cylinder serves the purpose of displacing the two forks and it is not necessary as in the prior art system to dimension each hydraulic cylinder with regard to the case wherein the centre of gravity of the load is located on one of the forks. In the motion mechanism of the invention the hydraulic cylinder can be dimensioned independently of the location of the centre of gravity of the load. More¬ over, the motion mechanism of the invention can be manufactured and maintained at considerably lower costs, said motion mechanism at the same time being superior to the prior art system as far as reliability and operational accuracy are concerned.

Although the invention has been made particularly in connection with fork trucks and similar implements it should already now be indicated that the invention in principle is not limited to said application but can be utilized also in other connections where several different movements have to be obtained from a single power unit. However, in order to explain the invention in more detail the invention will be described with reference to the application on a fork truck, reference being made to the accompanying drawings, in which FIG. 1 is a perspective view of a fork system provided with the motion mechanism of the invention, FIG. 2 is a diagrammatic vertical sectional view and side view of the motion mechanism,

FIG. 3 is a cross-sectional view of the motion mechanism perpendicular to the view of FIG. 2, FIGS. 4 to 6 illustrate diagrammatically in elevational view the several functions of the fork system,

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FIG. 7 is a front, view of the motion, mechanism of the invention in a constructive embodiment thereof, and

FIG. 8 is a cross-sectional view along line 5 VIII - VIII in FIG. 7.

Referring to FIG. 1, there are displaceably guided on a fork frame 10 intended to be mounted on a fork truck by means of conventional attachments 11, two forks 12A and 12B for linear parallel displacement on the 10. fork frame. Referring also to FIGS. 2 and 3, each fork 12A and 12B, respectively, is rigidly connected to a rack 13A and 13B, respectively, said racks being received by a runner box 14. Inside said box, a gear wheel 13 is rotatably mounted, the two racks 13A and 13B engaging 5 said wheel diametrically opposite to each other. Necess¬ ary guides are provided in the runner box 14 to maintain the racks in engagement with the gear wheel, and in FIG. 3 such guides are shown as slide bearings 15 of a suitable bearing material. The runner box 14 is mounted for 0 longitudinal displacement in a box girder 16 and is guided in the girder by means of slide bearings 17 of a suitable bearing material. The box girder 16 can be mounted directly to the fork frame 10, but in this case said girder is pivotally mounted by means of a pivot 18, 5 forming an end flange 19, in a bearing 20 on the fork frame 10 for pivotal movement about a substantially horizontal axis.

A double-acting hydraulic cylinder 21 is anchored at one end thereof to the fork frame 10 at 22, the 0 piston rod 23 thereof being connected to one fork, viz. the fork 12A, by means of a connection 24. The hydraulic cylinder 21 is connected to a conventional hydraulic system by means of inlet and outlet conduits for pressurized fluid at opposite sides of the. piston, but 5 these details can be of conventional construction and

therefore are not shown in detail here.

A brake 25 is arranged inside the runner box 14 and can be engaged with the rack 13A for locking said rack to the runner box, and in a corresponding manner a brake 26 is arranged inside the box girder 16 and can be engaged with the runner box 14 to lock said box to the box girder 16. Finally, a brake 27 is arranged on the fork frame 10, which can be engaged with the end flange 19 of the pivot 18 of the box girder 16. These brakes can be constructed to be engaged hydraul ically, but they can of course be of any other type. Considering the fact that the fork truck has a hydraulic system, the hydrau- 1 cally operated brake is, however, the preferred type in the present case. However, it is conceivable to arrange other means for locking the rack 13A to the runner box 14, for locking the runner box 14 to the box girder 16, and for locking the box girder 16 to the fork frame 10.

For explanation of the function of the motion mechanism described reference is now made also to FIGS. 4 to 6. It is assumed that the brake 27 is engaged with the flange 19 such that the box girder 16 initially can be considered a part fixedly connected to the fork frame. Moreover, it is assumed that the box girder is in a substantially horizontal position. In order to effect the expanding operation when the forks 12A and 12B are to be displaced towards or away from each other, the brake 26 is engaged with the runner box 14 such that also said box can be considered a part fixedly connected to the fork frame 10. Now that the hydraulic cylinder 21 is pressurized for displacement of the fork 12A to the left or to the right, the movement of this fork will be transmitted to the gear wheel 13 by the intermediary of the rack 13A and accordingly the fork 12B will be dis- placed through the rack 13B in opposite direction to

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that of the displacement of the fork 12A. This is illustrated in FIG. 4 wherein the two forks may have been displaced in this manner from the position indicated by dot and dash lines, to the position indicated by solid lines.

In order to effect the lateral displacement operation the brake 26 is now disengaged and the brake 25 is instead engaged with the rack 13A. This means that the runner box 14 is now no longer to be considered a part fixedly connected to the fork frame 10 but can be displaced horizontally to the left or to the right. How¬ ever, the rack 13A is now a part fixedly connected to the runner box 14 and not only this rack but also the rack 13B because said latter rack is locked to the runner box 14 through the gear wheel 13 located between the racks and engaging therewith. When the hydraulic cylinder 21 is now pressurized to displace the fork 12A in one direction or the other, the fork 12B will follow slavishly the fork 12A at a unitary spacing between the two forks. This is illustrated in FIG. 5 wherein it may be imagined that the forks have been displaced from the position indicated by dot and dash lines to the position indicated by solid lines.

In order to rotate or tilt the forks the two brakes 25 and 26 are maintained engaged such that the box girder 16, the runner box 14 and the two racks 13A and 13B with the forks 12A and 12B form a rigid unit. How¬ ever, the brake 27 is now disengaged such that the pivot 18 can rotate freely in the bearing 20. This means that said unit will be rotated clockwise or anticlockwise when the hydraulic cylinder 21 is pressurized. This operation is illustrated in FIG. 6 wherein the pivoted unit with the forks 12A and 12B may be assumed to have been rotated clockwise from the position indicated by dot and dash lines to the position indicated by solid lines.

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In addition to this, the motion mechanism described provides a fourth motion operation which is obtained by the brakes 25 and 26 being disengaged .simul¬ taneously while the brake 27 is engaged. This function can be used when handling goods lifted by the forks being pressed against opposite sides of the goods, e.g. a pulp bale. If the fork 12B is first engaged with one side of the goods and the hydraulic cylinder 21 is then pressurized to displace the fork 12A towards the other side of the goods, the fork 12A as well as the runner box 14 will be able to move; thus a combina¬ tion of the operations in FIGS. 4 and 5 is obtained. When the fork 12A is engaged with said other side of the goods, the runner box 14 is then locked to the box girder 16 by engaging the brake 26, the two forks then being pressed against opposite sides of the goods by means of the hydraulic cylinder 21.

The description so far is related to the principle embodiment of the motion mechanism of the invention, applied to the fork system of a fork truck. However, the principle embodiment can be modified within the scope of the accompanying claims. Thus, the connection between the two forks 12A and 12B can be obtained by means of other transmission members than racks and gear wheel. A possible modification is to replace these elements by two links each of said links connecting one of the forks with a crank of a shaft rotatably mounted in the runner box 14. Then, the brake 25 acts e.g. on this shaft. In a further conceivable embodiment, the gear wheel 13 is replaced by a sprocket which engages with a chain in an endless path, said chain having an upper and a lower run which are parallel to each other and to the runner box 14. The sprocket engages with one of these runs, and the two forks 12A and 12B are connected each to one of the runs.

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A constructive practical embodiment of the motion mechanism of the invention will be described with refer¬ ence to FIGS. 7 and 8. In these figures, elements which correspond directly to the elements of FIGS. 1 to 3 are provided with the same references as in FIGS. 1 to 3 but with the addition of 100.

The runner box 114 in this case is displaceably guided in a manner not shown in detail on a frame 110. Inside the runner box, two racks 113A and 113B are displaceably guided by means of slide bushings 115. They engage a gear wheel 113 which is rotatably mounted by means of flange bearings on a shaft 131 which extends with clearance through the runner box and is guided for axial displacement in the flange bearings 130. The shaft 131 is fixedly connected to an attachment 132 for a hydraulic clamp cylinder 133, a passage 134 being formed in the shaft for connecting pressure fluid to and from the clamp cylinder 133. Between the cylinder attachment 132 and the runner box 114 two conical spring washers 135 are provided, which maintain the cylinder attachment 132 and the box 114 in the position shown when the clamp cylinder 133 is not pressurized. Between the cylinder attachment 132 and the racks 113A and 113B brake linings 136A and 136B are provided, and between the racks and the runner box brake linings 125A and 125B are provided. These brake linings are not engaged with the racks when the clamp cylinder is not pressurized. A bracket 137 is fixedly connected to the cylinder attach¬ ment 132 and supports a brake lining 126 which can be engaged with one side of an angle-iron 138 fixedly connected to the frame 110. The bracket 137 projects from a cylindrical socket 139 arranged on the runner box 114, through a slot 140 formed in said socket which is provided with a cover 141 covering the clamp cylinder 133. Two abutments 142 are attached to the socket 139,

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which engage with the side of the angle-iron 138 which is opposite to the brake lining 126. Under the bias of the spring washers 135 the cylinder attachment 132 and the runner box 114 are pressed away from each other to the position shown in FIG. 8, the brake lining 126 and the abutment 142 being engaged with opposite sides of the angle-iron 138 to lock the runner box 114 to the frame 110.

The two racks 113A and 113B are provided at the ends thereof with lugs 143A and 143B, respectively, to be connected at said lugs e.g. each to a fork of a fork system in the manner described above, one of said forks being connected with a hydraulic cylinder to be displaced along the frame 110. With the motion mechanism in the condition shown, the expanding operation of FIG. 4 will be obtained, because the movement of the fork operated directly by the hydraulic cylinder will be transmitted to the other fork.

Now, if the clamp cylinder 133 is pressurized by the supply of pressurized fluid through the passage 134, the cylinder attachment 132 and the runner box 114 will be pressed against each other against the bias of the spring washers 135, the brake linings 125A and 125B as well as 130A and 130B being engaged with the associated racks as a consequence thereof. Thus, the racks will be locked to the runner box 114 while the brake lining 126 and the abutment 142 thereof will be moved away from the angle-iron 138 fixedly connected to the frame 110. The runner box 114 will now be free for movement along the frame 110 such that the transverse movement operation of FIG. 5 can be obtained in the manner previously described.

In the illustrative embodiment, the power unit and the operating means have been said to be of the hydraulic type, but they can also be of the pneumatic type or

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comprise electrical operational means with linear move¬ ment.. Particularly on electrical fork trucks, electrical operating means are preferred.

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