US1918934A - Lifting jack - Google Patents

Description

July 18, 1933. F. H. SCHWERIN LIFTING JACK Filed Feb. 24. 1933 2 Sheets-Sheet l INVENTOR 7M4 X/ 424M;

' ATTORNEY July 18., sc w l LIFTING JACK Filed Feb. 24, 1933 2 Sheets-Sheet 2 w m INVENTOR ATTORNEY Patented July 18, 1933 FRANK H. SCHWELRIN, Cab" BELLEVUE,

"EGRATZUN OF PENEISYLVANIA than PENNSYLVANIA, ASSIG-N OR TO DUFF- NGRZION MANUFACTURING COMPANY, OF PITTSBURGH,

rn'nnsvnvamn. A con- LIFTENG JACK Application filed This invention relates to lifting jacks of the ratchet type, in which a load is raised or lowered with a step-by-step movement.v

Lifting jacks of this type have two pawls which are movable into and out of engage ment with a ratchet or rack bar. One pawl, known as the lifting pawl, is connected to and operated by a handle which is fulcrumed on the ack frame as a lever of the first class. The other pawl holds the bar against movement by the load during the periods in a raising or lowering operation when the lifting pawl is out of engagement with the rack teeth and returning to eng'agem a new position. r

In the raising operation both pawls re.

main in contact with the rack. "When the load is to be lowered, it is necessary for the lifting'pawl to move upwardly clear of the rack teeth while the holding pawl supports the load. Near the end of its upward movepawl must engage the rack ment, the lifting and raise it slightly to lift the load from the holding pawl.

then move clear of the rack while thelifting pawl moves down and lowers the rackbar and load, but the holding pawl must again engage the rack teeth during the last'part of the lowering movement so that the lifting pawl is relieved of the load and free to'move clear of the rack in preparation for another upward movement.

The invention has for'its object to provide an improved ack of this type, and comprises novel features and combinations-of elements by which the pawls are operated in proper sequence with simplified mechanism, which economical to manufacture, durable, and convenient and advantageous in use, and which can be adjusted readily.

Other objects, features and advantages of the invention will appear or be pointed out as the description proceeds;

In the accompanying drawings, forming a part hereof: v

Fig. 1 is a side elevation of a lifting jack made in accordance with this. invention, the

cover plate being removed to expose the mechanism within the case and the reversing lever set for a lowering operation.

The holding pawl mustsp'ective trunnion projections.

- washers retain February at, 1933. Serial 1%. 658,459.

one position of the parts when the reversing lever is set to raise a load.

Fig. A is a sectional view on the line l4 of Fig. 3, with the cover'platein place and the upper part of therack bar broken away to expose the pawls. I Y

The jack has a case 11 and a rack bar 12 vertically slidable in the case. An. operating lever i l is pivotally supported bythe case for oscillation about an axis 16. A lifting pawl 18 is pivoted'ina notch 20 of the operating'lev'er and retained in the notch by a bearing "pin 19. "A holding pawl 22 is pivotallyconnectedwith the'case by a pin 24. gothof the pawls engage teeth 25 of the rack The pawls 18 and 22 have trunnion projec tions 27 and 28, respectively, extending from one side,-and best shown in F 4. The trun nion projection 28 has a shoulder, and a washerf3O abuts against this shoulder. A bearing block 32 fits over the trunnion projection 28, between the washer and another washer 3 l-which is retained onthe trunnionon the trunnion projection 27 Both of the bearing blocks are free to turn on their re- A frame 38 has upper and lower slots 10 and 41, respectively, infwhich the bearing blocks are retainedgforsliding movement lengthwise of the slots; The dimensions of the bearing blocks axially of the trunnions are substantially equal to the thickness of the frame" 38, and the. diameters of the washers on both sides of the bearing blocks are greater than the width of the slots so that the V the bearing blocks" within the frame: i I

A compression spring 43 in the slot 40 be tween the block 32 and the upper end of the slot urges the block against the bottom end of the slot. A similar spring 45 in the slotv 41 urges the block 36 against the lower end of'tha-t slot. A screw 47 threads through the bottom end of the spring frame 38,- and this screw can be moved into position so that its end projects into theslot 41 and limits the sliding movement of the block 36. The screw 47 is set to limit the sliding movement of the block 36 to regulate the operation of the pawls and compensate for wear of the pawls, as will be more fully explained in describing the operation of the jack.

A reversing lever 50 is pivotally supported by a stud 52 projecting from a wall of the case 11. One end of the reversing lever 50 has an enlarged grip 54 for convenient hand operation of the reversing lever. The other end of the reversing lever is pivotally connected to a link 56 by a pin 58. The upper end of the link 56 hasv a slot 60 throughwhich a pin 62 extends. The pin 62 is a drive fit in the spring frame 38, but fits'freely in the slot 60. The link 56 is retained in position on the pin 62 by a collar 64 on one side of the link and a washer and cotter-pin 66 on the other side of the link.

When the reversing lever 50 is in the position shown in Fig. 2, the spring frame 38 is free to move without restraint from the link 56. The slot 60 is long enough so that the pin 62 does not strike either end of the slot.

during the movement of the spring frame 38 while lowering the rack bar.. If thereversing lever 50 is rotated in a counter-clockwise direction from the position shown in Fig. 2

to the position shown in Fig. 3, the link 56'is drawn down and pulls the pin 62 and'spring frame 38 down so that the springs 43 and 45 are compressed. w 1 V Vi/hen moving into the position shown in Fig. 3, the center line ofthe link 56 crosses the axis of the stud 52 and the compression of the spri holds thereversing lever 50 in the F i 3 iosition with one arm a ainst an r; l a

abutment 68 at one end of a recess through which the grip end of, the reversing lever projects from the case. The reversing lever is shown against the otherend of the recess in Fig. 2. A cover plate 70,,shown in Fig.4, encloses the mechanism plate 70 is removed in Figs. 1, 3 to expose the mechanism. i f I The operation of the ack is as follows:

hen a load is to be raised, the reversing lever 50 is moved into thepositionshown in Fig.3. The link 56* is held down and this link holds the pin'6'2 and spring frame 38 down so that the bottom ends ofthe slots 40 and 41 are away from the blocks 7 32 and 36, and the springs 43 and 45 are compressed.

' l'Vith the parts in these positions, the Springs 43 and 45 urge the pawls and 18 against the rack bar. lVhen the operating handle 14 is moved to raise the lifting pawl 18, this pawl raises the rack bar. During thisrising movement of the rack bar the teeth of the rack bar ratchet past the holding pawl 22.

" E- When the operatinghandle 14 moves the of the frame 38 of, the jack. This pression of "the spring 43 will be extent and bring the holdingzpawl into en-' therack at an earlier-point in pawl 18 downwardly preparatory to another raising stroke, the holding pawl 22 prevents the rack bar from descending, and the lifting pawl 18 ratchets past the rack teeth.

lVhen the jack is to be lowered, the reversing lever 50 is moved from the position shown in Fig. 3 to that of Fig. 2. Thelink 56 is raised to a position in which the lost mos tion of its pin and slot connection with the spring frame 38 permits the frame to move without restraint from the link 56. If the lifting pawl 18 is in a raised position when the reversing lever is shifted into lowering position, the spring 43 will expand and push the frame 38 slot 40 strikes the block 32.

The spring 45 will also expand as the frame 38 is pushed up,'but since the lifting pawl 18 is in raised position the bottom end of the slot 41 will not'rise far enoughto contact with the block 36.. Thus, the spring 45 is still under compression and the block 36 away from the bottom end of the slot 41 (or screw 47) when the end of the slot 40strikes the block 32. Thiscompressionofthe spring 45 urges the frame 38 upward, and the bottom end of the slot 40 urges the holding pawl 22 out of engagement with the rack. The teeth of the holdingpawl and rack are so shaped that the pawl can not move out of, en} gag-ement with therack teeth without raising therack'bar slightly. 7 Thus, the load on the jack prevents the holding pawl from moving out of engagement with the rack until the lifting-pawl is raised slightly to take the load off the holding pawl. lVhen the load on the holding pawl is thus released, the spring 45 expands and pushes the frame38 up until the bottom end of the slot '41 (or the screw 47) strikes the block moves the block rocks the holding pawl clear of the rack.-

Thev operating handle 14 is then moved to lower the lifting pawl and rack bar, as shown inFig 2. Asthe' lifting pawl. moves down, the block 36 draws the spring frame 38 down so that the bottom end of the slot40 moves away from the block 32 and the spring 43 above the block 32 iscompressed. As the lifting pawl 18 continues t-o-move down, the comspring 43 increases until it rocks the holding pawl 22 into engagement with the rack. The parts are so proportioned that this engagement of the'holding pawl with the rack occurs shortly before the lifting pawl reaches the downward -imit of its travel. If the screw 47 is set so that it projects a substantial distanceintothe slot 41, the spring frame will occupy a lower position for any given position of the lifting l compressed to "a greater 32 up an d gagement with the stroke. I V

The final downward movement of the liftup until the bottom end of the 1 36. This upward movement pawl and the 1 ing pawl relieves it of the load which is assumed by the holding pawl 22, moves the spring frame 38 down, and continues to compress the spring 43. During this final movement, after the load is transferred to v the holding pawl, the lifting pawl is pull'eddown by the pin 19, and this pull tends to move the block 36 into a straight line with the block 32 and pin 19. The lifting pawl 18 is thus rocked away from .the rack, the frame 38 moving about the trunnion projection 28 as a pivot. The lifting pawl is then free of the rack and ready to return for another lowering stroke.

The operating lever 14 is moved to raise the lifting pawl, while clear of the rack, and this movement of the lifting pawl raises the block 36 and compresses the spring 415. The frame 38 can not rise because the bottom end of the slot 40 is against the block 32, which can not rise while the holding pawl is under load. As the lifting pawl 18 continues to rise, the compression of the spring increases until it is of sulficient strength to rock the lifting pawl into engagement with the rack. This occurs near the end of the upward travel of the lifting pawl. During its final upward movement the lifting pawl assumes the load and the holding pawl is rocked away from and clear of the rack, as already described.

The movement of the screw 47 to extend different distances into the slot 45 has the effect of changing the length of this slot.

his changes the travel of the block 36 and affects the point in the stroke at which movements of the pawls occur. Wear of the pawl teeth afiects the point of the stroke at which they engage with the teeth of the rack bar. Such wear can be compensated for by changing the setting of the screw 47. No other adjusting means besides the screw 47 are necessary with this invention.

The preferred embodiment of the invention has been described, but changes and modifications can be made, and various features of the invention can be used alone or in combination with other features without departing from the invention as defined in the claims.

I claim:

1. In a ratchet lifting jack, a lifting pawl; a holding pawl; a frame in which are two slots; a projection on the side of each pawl,

each projection extending into one of the slots in the frame; and a spring between each projection and one end of the corresponding slot for urging the projection. against the other end of the slot.

2. A ratchet lifting jack including in combination a lifting pawl; a holding pawl; a trunnion projection on the side of each pawl; a bearing block on each trunnion projection; a frame having slots in which the blocks slide; and spring means for holding the blocks against the corresponding ends of the respective slots in which they slide.

3, A ratchet lifting-j ack including in combination a lifting pawl; a holding pawl; a trunnion projection on the side of eachpawl; a frame having two slots a block slidable in each slot; and a compression'spring -between each block and one end of the corresponding slot, each of the blocks having a bearing opening for receiving the trunnion projection of axpawl. l 4:. In a ratchet lifting jack, alifting pawl; a holding pawl; aframe having twoslots; a bearing block slidablein each slot; and a compression spring between one end of each.

slot and the associated block; a trunnion projection ,on each pawl. extending into one of the bearing blocks; and screw means carried by the frame and movable to regulate the extent of the sliding movement of one of the blocks.

5. A lifting jack comprising a toothed lifting element; a lifting pawl for moving said element; a holding pawl; a trunnion projection extending from the side of each pawl; a frame; and blocks slidable on the frame,'and supported by the respective trunnion projections as bearings, for operatively connecting the frame with the pawls.

6. A lifting jack comprising a toothed lifting element; a lifting pawl for moving said element; lever means for operating the I lifting pawl; a holding pawl; a trunnion projection on'the side of each pawl; a frame; two blocks slidable on the frame, each block having a bearing opening for receiving the trunnion projection of one of the pawls; and movable means for limiting the sliding movement of one of the blocks on the frame.

7 In a ratchet lifting jack, the combination of a toothed liftinp'element; a lifting pawl; a lever for operating the lifting pawl; a holding pawl; a frame operatively connected toboth pawls and slidable with respect to the pawls; springs in position to resist sliding movement of the frame in one direction; and reversing lever mechanism having a lost motion connection with the frame and operable in one position to hold the frame in position to compress both springs and hold both pawls against the toothed lifting element.

ion

s. In a ratchet lifting jack, the combination of a toothed lifting element; a lifting pawl; a lever for operating the lifting pawl; a holding pawl; a frame operatively connected to both pawls and slidable with respect to thepawls; springs to urge the frame in one direction with respect to the pawls; and reversing lever mechanism for moving the frame in another direction to compress the springs so that they hold the pawls against the toothed lifting element, said reversing le-- ver mechanism including a pivoted lever which moves beyond dead center in compressing the springs and is held in such position by the force of said springs.

9. A ratchet lifting jack comprising a case; a rack bar slidable in the case; an opto both pawls by the blocks which are re tained in the slots; a compression spring in each slot between one end of the slot and the corresponding block; a reversing lever pivoted'to the case; a link connecting the reversinglever with the frame by a pin and slot connection which in one position holds the frame in position to compress the springs and urge the pawlsagainst the rack bar and in another position allows free movement of the framewith the pawls by virtue of the lost motion of the pin andslot;connection.,

FRANK H. soHWERINfI

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