US2823551A - Lifting jack - Google Patents

Description

Feb. 18, 1958 H. u'rz LIFTING JACK Filed Nov. 9, 1953 FLPM INVENTOR )VW 25 .WJM HTTORN E Y United States Pate nt LIFllNG JACK Hans'Utzystegen, Ammerseeyfiermany Application November 9, 1953, Serial No. 391,015 Claims priority, application Germany November 11, 1952 1 Claim. (Cl. 74-141.5)

Among the various types of jacks for lifting heavy objects, vehicles, etc., the jacks with a self-locking plate mechanism are especially simple and inexpensive. Such jacks lift a heavy body by means of two plates, i. e., an elevating-plate and a locking-plate, which are alternatingly caused to be locked to a column or shaft, the elevating plate being moved by a lever relatively to a load carrying-body that is slidable along the shaft. The return movement from a lifted position back to the starting position is usually brought about by releasing the locking-plate from its locked lifted position, i. e. by inserting a lever between the locking-plate and the carrying-body and tilting the locking-plate so that its clamping engagement with the shaft is nullified. Following this operation, the carrying-body under and with its load usually drops down suddenly and all the way down along the shaft, because in most cases the operator does not succeed in reacting fast enough and with a sensitiveness necesary for a gradual lowering.

It is an object of this invention to prevent the load from falling down all of a sudden and to avoid other ditficulties by allowing the locking plate to move only a limited way and in steps by means of a special return-movement device. With this object in view this invention provides in a lifting jack, besides the elevating-plate and the locking plate of the conventional mechanism, an additonal self-locking plate which in the following text is called "return-movement-plate. This additional plate temporarily assumes the function of the locking-plate, while the return-movement is going on, that is while the locking-plate is unlocked. Due to this device the locking-plate and with it the asociated carrying-body will move at each operation thereof only a limited distance towards the return-movement-plate. A suitable operative connection between the locking-plate and the returnmovement-plate causes the return-movement-plate to be safely locked before the locking-plate is unlocked. The forementioned connection, which is an important part of this invention, is brought about by a system of levers, consisting of a lever with two arms and a lever with one arm (called guide lever in the following text). The short arm of the two-arm lever is attached to the returnmovement-plate, while the long lever serves as a controlhandle for the return movement. The one-arm lever is attached to the locking-plate and bears at its free end the fulcrum for the two-arm lever. n the short arm of the twoarm lever there is a stop device, which limits the movement of the locking-plate with the carrying-body towards the return-movement-plate, i. c. it determines the length of the step down during one returnmovement stroke. A spring, arranged between the locking-plate and the return-movement-plate, takes the returnmovement-plate back to its resting position between two operations of the control-handle. A full and detailed description of the operation as well as of the main elements of an embodiment of the invention is given by reference to the accompanying drawing which is a diagrammatic elevation, partly in section, in which: A designates the plate E on the shaft A is brought about.

6 2,823,551 Patented Feb. 18,1958

the locking-plate. "Thecarrying-body 'Bfis shown insect'ioniso that therseIf-locking.mechanism can. be seen.

The mode ,o'floperationo'f-the conventional part of this arrangement is known. After the load has beenlifted by tilting lever C relatively to self-locking lifting plate C, the locking-plate D is tilted against the shaft A so that the necessary locking-effect is brought about. This effect is due to the engagement of inner edges K1 and K2 in a position of the locking-plate D relative to the shaft A at a certain inclination. E designates the return-movement-plate, provided by the inventor. H1 and H2 mark the two springs: one of them is located between the locking-plate D and the lifting-plate C, the other between the locking-plate D and a portion of body B above the return-movement-plate E. Pivoted at P to the returnmovement-plate E is the two-arm lever F with its short arm; the long arm serves as the operating-handle for the return-movement mechanism. Pivoted to the lockingplate D is the one-arm lever or guide G, which at its free end bears the fulcrum of a the two-arm lever P. On the short arm of the two-arm lever F the stop M is to be seen, which, on the return-movement presses against the guide G and thus stops the further operation as well as the drop of the load. For dropping the load, the long (right arm of the lever) of the two-arm lever P, which is the operating-handle, must be tilted down. Then it turns about the fulcrum L and tilts the return-movement-plate E against the shaft A, a position in which the shaft is engaged by the inner edges N1 and N2. By such an operation the desired locking effect of the return-movement- While moving the right arm of the lever F farther down, the latter one starts turning around the fulcrum P, since the returnmovement-plate E is now in locked position. While increasing the locking effect on E, the guide G is pulled down and nullifies the locking effect between the lockingplate D and the shaft A by tilting the locking-plate D back. Thus, the locking-plate D can move down along the shaft A and the spring H2 is compressed. With the locking-plate D the carrying-body B and the load (not indicated in the drawing) moves down the same distance. This return-movement is stopped by the return-movementplate E which is now locked and serves as an auxiliary locking-plate. Through subsequent moving up of the operating-handle or lever F, the return-movement-plate E is unlocked by means of the short arm of this lever, while the load over the carrying-body B causes the locking-plate D to lock itself again and cannot drop any farther. By moving the operating-handle still farther up, the returnmovement-plate E is again moved away from the locked (tilted) locking-plate D, until the above described position is reachedand then the whole procedure may be repeated.

The diagram is only schematic. The scale as well as the kinematic correlations (especially the distance of the fulcrums and the lengths of the levers respectively the arms) do not correspond to the requirements for undisturbed operation.

What is claimed is:

A lifting jack comprising, in combination, a rigid shaft; a subsantially C-shaped carrying body havin top and bottom walls respectively formed with openings through which said shaft freely extends; a lifting plate formed with an opening through which said shaft freely extends, said lifting plate being located between said top and bottom walls and adjacent said top wall of'said carrying body; a return movement plate formed with an opening through which said shaft freely extends, said return movement plate being located between said top and bottom walls and adjacent said bottom wall of said carrying body; a

locking plate formed with an opening through which said shaft freely extends and located between said lifting plate and return movement plate-{first spring means located between said lifting plate and locking plate for urging the same apart from each other; second spring means located between said locking plate and return movement plate and abutting against a portion of said body for urging said locking plate away from said return movement plate; a first lever turnably connected at one end to said return movement plate and extending freely therefrom so that 4 the operator may turn said first lever; and a second lever pivotally connected at one end to said locking plate and at its opposite end to said first lever at a part thereof adjacent said one end of said first lever connected to said 5 return movement plate.

References Cited in the file of this patent UNITED STATES PATENTS Gunn Sept. 26, 1939 2,537,839 Lord Jan. 9, 1951

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