US2258827A - Lifting jack - Google Patents

Description

I. TRACHT LIFTING JACK Oct. 14, 1941.

Filed May 23, 1940 H In FIG.6.

INVENTOR. IRWIN RACH :1 TORN S fatented Oct. 14, 1941 UNrrso STATES PATENT orrics LIFTING JACK Irwin Tracht, Pontiac, Mich, assignor to The American Forging & Socket Company, Pontiac, Mich., a corporation of Michigan Application May 23, 1940, Serial No. 336,780

1 Claim.

This invention relates to lifting jacks, and particularly to improvements in screw-type jacks of the variety having a stationary screw shaft and means for rotating a traveler nut, threaded thereupon, to cause the nut, together with a cage or the like carried thereby, to travel up and down the screw shaft.

More partiicularly the invention is directed to improvement of the jack construction disclosed in the copending application of Walter S. Saunders, Serial No. 312,030, filed January 2, 1940, patented August 5, 1941, as Patent 2,251,759.

In the manufacture of jacks of the indicated variety, designed to be furnished as a part of the tool equipment of motorcars, simplicity and inexpensiveness of construction are important considerations, yet strength and reliability of operation under all conditions are vital. necessary, in jacks of the indicated variety, to provide some form of ratchet mechanism permitting operation of the jack by means of a reciprocatory handle. Difficulty has been encountered with such ratchet mechanisms by reason of the fact that under some conditions the ratchet mechanism tends to cause the traveler nut to back down the shaft at undesired times, during efforts to raise the load. The present invention aims to provide improved means, of very simple -and inexpensive character, adapted to prevent such unwanted reverse movement of the traveler, without, however, interfering with normal operation of the jack, or requiring any special manipulation, and without appreciably increasing the cost of construction or assembly of the jack.

Other objects and advantages will be apparent from the following description, wherein reference is made to the accompanying drawing illustrating a preferred embodiment of my invention and wherein similar reference numerals designate similar parts throughout the several views.

In the drawing:

Figure l is a side elevational view of a lifting jack constructed in accordance with the present invention, a portion of the screw shaft being broken away.

Figure 2 is a view, partly in vertical section and partly in side elevation, of the traveler operating and ratchet mechanism, on a somewhat larger scale.

Figure 3 is a horizontal section taken substantially on the line 3-3 of Figure 2, and looking in the direction of the arrows.

It is- Figure 4 is an enlarged substantially diametric section of the traveler, traveler cage and screw shaft assembly.

Figure 5 is a horizontal section taken substantially on the line 5-5 of Figure 4 and look ing in the direction of the arrows.

Figure 6 is a side elevational view of the friction brake for the traveler nut.

Referring now to the drawing: Reference character It designates a sheet metal base, provided with a substantially vertical tubular socket portionJZ, into which the lower end of the screw shaft M is adapted to be fitted and whereby the screw shaft is held in substantially vertical position. A key portion l I carried by the base projects into a keyway IS in the shaft to hold I the latter against turning.

The load is adapted to be lifted and supported by an arm, l5, formed integrally with and projecting laterally from a cage ll, these parts being formed of a metal sheet wrapped to substantially cylindrical form, to encircle and slide freely along the screw shaft, the end portions being contoured to define the supporting arm l5. Between the arm portions 15 is a reenforcing and keying plate l6 which projects into the keyway 13 to hold the cage against turning, portions 44 and the interposed plate being riveted or otherwise secured together.

Threaded upon the screw shaft is a traveler nut 20, from whose periphery project a plurality of ratchet teeth 2i. A sheet metal cage 25 encircles the ratchet toothed portion of the nut, and is rotatable relatively thereto. The cage projects laterally from the shaft, its outer extremity being socketed to receive the handle 21, while between the socket portion and the nut it houses a pawl 28 and a pawl spring 29 The pawl will be seen to be provided with two spaced nose portions, each adapted to engage the ratchet teeth 2|, the nose portions being operative, when the handle is reciprocated about the axis of the shaft, to turn the nut in opposite directions. The pawl is pivoted on a pin 36, and a pointed rear extremity 32 of the pawl is adapted to be so engaged by the central convolutions of the spring 29 that the spring yieldably maintains either nose of the pawl in engagement with the teeth, yet the pointed extremity may be thrown over center to cause the spring to maintain the other nose of the pawl in yieldable engagement with the ratchet. The spring will be seen to be of double-ended helico-spiral form the center turns being of larger diameter than those nearer its ends, the smaller end turns 10- An undercut slot 46 in the lower end of the.

traveler 20 houses a flat leaf spring, 42, which is so shaped as to frictionally engage both the screw shaft and the interior of the traveler, thereby imposing a predetermined minimumlfrica tion upon the traveler. The stressed condition of the spring when the shaft extends therethrough is clearly shown in Figure 5, and its relaxed shape is shown in Figure 7. The friction imposed by the spring 42 is greater than the friction between the pawl 28 and the ratchet teeth during return movement of the handle, so that after the traveler has been advanced along the screw shaft, the friction imposed by the spring is sufiicient, even when the jack is heavily loaded, to prevent the traveler from backing down the shaft, when the pawl is set to advance the traveler, and vice versa.

I am aware that the invention may be embodied in other specific forms without departing from the spirit or essential attributes thereof. and I therefore desire the present embodiment to be considered in all respects as illustrative and not restrictive; reference being had to the ap pended claim rather than to the foregoing description to indicate the scope of the invention.

I claim:

In a lifting jack, in combination with a standard and a screw shaft supported thereby in upstanding position, a traveler threaded upon said screw shaft means for turning said traveler to move the same along the screw shaft, comprising a handle rotatable with relation to said traveler, pawl and ratchet means providing a one directional drive between said handle and traveler and permitting rotation of the latter in response to reciprocatory actuation of said handle, spring means maintaining the pawl means and ratchet means in operative engagement with predetermined'force and exerting a drag upon said traveler during return movement of said handle, a load-supporting element actuable along said screw shaft bysaid traveler, and friction spring meanshoused within said traveler and engaging the screw shaft and imposing frictional resistancetorotation of the traveler which exceeds the drag exerted upon the traveler by said first mentioned spring means, the threads of said screw shaft are fiat-topped in cross section, said friction spring means. comprising a flat band wide enough to bridge aplurality of threads, engaging the tops of said threads and the interior of said traveler, and trapped Within aninternal slot in the latter.

IRWIN TRACHT.

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