US3159973A - Jack mechanism having an internal locking means - Google Patents

Description

Dec. 8, 1964 F. s. PEARNE 3,159,973

JACK MECHANISM HAVING AN INTERNAL LOCKING MEANS FRANK PEARNE 2f j l my MW ATTORNEYS F. S. PEARNE Dec. 8, 1964 JACK MEcHANIsM HAVING AN INTERNAL LOCKING MEANS 3 Sheets-Sheet 2 Original Filed Dec. 29, 1959 m m 6 |Vl|||o l 3 /M PH w m mmm m f ,LM m u M/VfJ/VWM. m m .m m n 2 u BKM E y S P W Y E S N K R N 0 Ayn m/A Y Fig. 5

DeC 8, 1964 F. s. PEARNE 3,159,973

JACK MECHANISM HAVING AN INTERNAL LOCKING MEANS Original Filed Dec. 29. 1959 3 Sheets-Sheet 3 Fig. 7

lNvENToR FRANK PEARME ATTO RN EYS United States Patent tice 3,159,973 Patented Dec. 8, 1964 3,159,973 JACK MECHABISM HAVING AN IIJ'I'ERNAL I .GCKING MEANS Frank S. Pear-ne, San Gabriel, Calif., assigner to Regent .lack Mfg. Co., Inc., Downey, CM., a corporation of California @riginal application Dec. '2.9, i959, Ser. No. 862,648? now Patent No. 3,094,341, dated .lune 25, 1963. Divided and this application May 7, i963, Ser. No. 278,535

3 Claims. (Cl. 619-52) This invention relates to a jack mechanism having'an internal locking means and, more particularly, to an 1mproved hydraulic jack structure having an extensible ram and an internal locking means for releasably locking the ram in an extended position.

This is a division of my copending application Serial No. 862,648, led December 29, 1959, now Patent No. 3,094,841 granted une 25, 1963.

The invention is particularly concerned with hydraulic jacks which are required to be repeatedly and quickly extended to support a load, locked in the extended position, and then unlocked and retracted. In order to satisfy these requirements, I have devised unique internal locking means for the ram which can be manipulated in a facile manner to quickly lock the ram so that it may support a load, and then to unlock the ram in an equally easy fashion whereby the ram can be retracted. My novel jack mechanism also includes means to automatically retract the ram when the ram has been unlocked.' For illustrative purposes, the invention has been shown and described in conjunction with both a leveling jack and an aircraft tripod jack; however, it is to be understood that the invention may be embodied in many other types of jacks.

Conventional jack constructions commonly employ a locknut which is threaded on the extended portion of the ram into abutment or engagement with the outer shell of the jack to hold the ram in its extended position. This type of construction possesses several disadvantages, the most significant of which is the relatively long time which is required to lock and unlock the ram. Another disadvantage is that, when a jack employing this form of locking means is used out-of-doors, water frequently runs down the threads of the locknut and enters the cylinder, thereby seriously aecting the operation of the jack.

With specific regard to the construction of leveling jacks such as are used on load-supporting vehicles to level the vehicle and to raise the load from the wheels when the vehicle is stationary, the forms of constructions heretofore known possess additional disadvantages over and above the ram locking means. One major objection in the case of leveling jacks permanently mounted on a vehicle is that, commonly, no means are provided for automatically retracting the ram when it is unlocked. As a result, the ram -is often left at least partially extended through inadvertence of the operator when the vehicle is moved, and, hence, the ram is frequently damaged when the vehicle passes over a slight ground rise or the like. Another disadvantage is that the fluid supply or reservoir for the jacks is often separate from the main body or shell, thereby making the entire assembly extremely unwieldy and diicult to install in the available space.

An object of the present invention is to provide a jack mechanism with internal ram locking means which may be operated ina facile manner to lock the ram in an extended position and then to quickly unlock the ram when the latter element is to be retracted.

Another object is to provide a jack mechanism having internal ram locking means of the type described with means for automatically retracting the unlocked ram.

Still another object is to provide a jack mechanism with internal ram locking means whereby water encountered in outdoor use is prevented from entering the cylinder of the jack.

Another more specific object of the invention is to provide a unique hydraulic leveling jack mechanism having internal ram locking means and a self-contained fluid reservoir.

Other objects and advantages of the invention will become more readily apparent when the -same is considered in connection with the following detailed description and the accompanying drawings wherein:

FIGURE 1 is a schematic side elevation of a dolly having attached leveling jacks constructed in accordance with my invention;

FIGURE 2 is aside view of my novel leveling jack construction;

FIGURE 3 is a vertical section ofthe leveling jack shown in FIG. 2;

FIGURE 4 is a horizontal sectional view taken through the jack near the .top thereof along the line 4 4 of FIG. 3;

FIGURE 5 is an enlarged vertical sectional view of a portion of the jack showing the piston in an upstroke and showing a fluid lay-pass opening for retracting the jack;

FIGURE 6 is a side view of an aircraft tripod jack embodying the locking mechanism;

FIGURE 7 is a vertical sectional view of the jack shown in FIG. 6;

FIGURE 8 is a horizontal sectional view taken through the jack of FIG. 6 near the top thereof along theY line 8 8 of FIG. 7.

Referring now to the drawings, the apparatus embodying my invention may be in the form of a leveling jack 20 which is used to stabilize and level a load relative to the ground or other supporting surface. `As shown diagrammatically in FIG. 1, four such jacks 20 may be arranged at the corners of a missile dolly D adjacent each wheel. When the dolly is being moved, the jacks are maintained above the lower wheel surfaces, and when the dolly is stationary, as in a tiring position or a storage position, the jacks are lowered or extended to raise the weight of the loaded dolly from the wheels. As will hereinafter be discussed in more detail, the construction of the jacks is such that they are automatically fully retracted from their extended, load-bearing position, thereby eliminating the hazard of the jacks being inadvertently left in a partially extended position and damaged when the dolly is moved over a slight ground rise. My novel leveling jack is not limited, of course, to use on vehicles since it is equally well adapted to be used in conjunction with any support equipment.

Referring next to FIGS. 2 through 5, there is shown in detail a leveling jack construction embodying my invention. The principal components of the illustrated leveling jack include an outer shell 21 having a load carrying ring 22 welded or otherwise secured thereto, a ram 23, a main shaft 24, a pump cylinder 25, and a piston 26, the latter four components being concentrically nested within the shell. A foot pad 2'7 is connected to the ram and is adapted to be pushed by the foot of the operator into initial Contact with the ground, as shown in dot-dash outline in FIG. 2, while a handle 2S, operatively connected to the piston 26, is adapted to be actuated by the hand of the operator to apply hydraulic pressure to the extended ram.

The outer shell 2l preferably is in the form of an elongated, hollow, open-ended cylinder, and includes a a locking ring 36. The load ring 22 may be fastened to the outer periphery of the shell 21 approximately one-third of the distance from the bottom toward the top of the shell.

The ram 23 is also in the form of a hollow cylinder, and has a diameter such that it may be concentrically nested in a position contiguous to the inner surface of coll'ar 33 with the wall of `the ram spaced inwardly from the shell 21. A helical compression spring 40, positioned inthe space between the ram and shell, constantly urges the ram to a retracted position wherein the upper end of the ram 23 is spaced below the upper end of the shell. The lower end of the 'ram Ais plugged by a ram base 41 which has a lthreaded recess 42 in its bottom, and the foot pad 27 is secured to this ram base by means of a bolt 43 which is threaded into the recess 42. The head of the bolt 43 is pivotally anchored within the pad by a washer 44, the pivotal connection serving to permit the pad to Y engage uneven supporting surfaces.

As shown most clearly in FIG. 3, the main shaft 24 is a hollow cylinder, there being a shaft base 50 and a shaft head 45 integrally joined to the bottom and top, respectively, of the main shaft. The diameter of the shaft base 50 is equal to that of the `ram base 41 and is greater than the width of 4the main shaft, whereby the walls of the shaft are spaced inwardly from the cylindrical wall of the ram. The diameter of the main shaftV head is equal to the inner diameter of shell 21 so that, in its assembled position, the main shaft head 45 and attached shaft will be locked against upward movement by the lock ring 36 which is seated in -a circular seat 51 cut in the head. The outer shell 21,V shaft head 45 and shaft base 50 define a fluid yreservoir 49 from which fluid is drawn during operation ofthe jack.

In order that the ram 23 can be locked in an extended position as indicated in FIG. 2, the jack is provided with an internal ra-m locking means or ratchetmechanism. This mechanism includes downwardly sloped, circumferential ratchet teeth 55 formed on the periphery of the shaft 24.1 The teeth, which extend along a major portion of the length of the shaft, are -shaped to cooperate with ratchet arms 56 and 57.

The arms 56 and 57 are pivotally mounted in a scissors-type arrangement by pivot 58 on a lock base 59, the lock base being integrally joined ,to the top of the ram 23. As most clearly shown in FIG. 4, the arms-56 and 57 encompass the main shaft 24,. and when closed by 4 96 which permits hydraulic uid tovilow down through the passageway but prevents uid from owing' in the opposite direction.

The pump piston 26 is slidably received within the pump Vcylinder and extends through and above the plate 90 at the upper end thereof. The bottom end of the piston 26 is hollowed out to form a uid feeding chamber 190 having an enlarged lower end 1M in which is positioned a ball 162 held by a perforate retaining washer 193. The ball 102 constitutes another check valve which, when seated against a shoulder 104 during a downstroke of the piston, prevents fluid from entering chamber 100 through the open lower end of the piston. The outer surface of the piston is relieved at 107 in the region of chamber 100 to form, in conjunction with ports 105 and 106 in the main shaft and cylinder, respectively, and ports 108 in the piston, a fluid ow path whereby fluid contained within the outer shell 21 is at all times in communication with fluid in the fluid feeding chamber 10G and is permitted to llow through the chamber 190 while the piston is being raised. O-rings 109 mounted in grooves in the sides of the piston 26 prevent fluid from leaking from the relieved area.

The piston 26 is raised and lowered by actuation of the pump handle 2S. As indicated in FIGS. 2 and 3, the handle 28.is channel-shaped and has one end rotatably connected to yan end of a link 121, the other end of the link being pivotally connected to a colla-r 122 surrounding the outer shell 21. The legs 123 of the channelshaped handle may be crimped inwardly in an areagenerally designated by reference numeral 124, and fitted into engagement with a neck 125 on lthe top end of piston 26. When assembled in the manner illustrated in FIG. 2, the handle may be moved laterally with respect to the yaxis of the piston, thereby providing a lever arrangement having a mechanical advantage that can be varied as desi-red. Also, the collar 122 can be rotated with respect to the shell 21 by loosening bolt 126 in order to change the pumping position of the handle. When not in use, the crimped area of the anges 123 may be disengaged from the piston neck and the handle thrown over the top of the jack so that it depends vertically along the side of the shell, this position being shown in FIG. 2

springs 60, which are fastened to the free end of each of-square cross-section between the shaft head 45 and the collar 33.l It may have various other shapes as long as they have unequal radial dimensions for camming the arms 56 and 57 apart against the action of the springs 60 when the release rod is rotated through an langle about its axis.

The pump cylinder 25 isreceived within the bore of the main shaft and extends through the shaft head 45 as indicated in FIG. 3. The top of the pump cylinderl is connected to a plate 90 while a hollow valve seat 92 is joined to the bottom of the cylinder. The upper end of the cylinder isV additionally surrounded by a sleeve 93 which is threadedly engaged at one end with the shaft head 45 and integrally joined to plate 90 at the other end. When assembled, the valve seat 92 is normally received in the mouth of a Huid passageway 54 which extends through the shaft ybase 50. The hollow valve seat together with a spring-pressed ball 94, held in passageway 54 by a perforate retaining washer 95, constitute a check valve in dot-dash outline.

When it is desired to operate the jack, the operator iir-st pushes down the foot pad 27 yuntil it contacts the ground, thereby drawing the ram 23 downward in the shell 21. As the ram is extended below the shell, there is formed between the ram base 41 and the shaft base. 50 the pressure area 67. This area is promptly ooded by hydraulic uid which passes through the 4uid ports 105 and 106 into the cylinder area 107, and then into the feeding chamber 10h through ports 10S. Check valves 102 and 96 permit fluid in the chamber 10h to llow through passageway 54 into the pressure area. It is possible, of course, to initially extend the ram by reciprocating the piston 26; however, this procedure requires more time than to simply push down on the foot pad.

The ram is automatically locked in the extended position by the arms 56 and 57 which engage the teeth 55 on the main shaft 24. This locking engagement is permitted when the rod 63 is in the position indicated in FIG. 4,

with thek arms 56 and 57 biased into ratcheting engagement with the teeth 55 by the springs 6).

With the ram extended, the operator then engages the pump handle 28 with the piston 26, and adjusts the handle and the collar 122 to-obtain the optimum mechanical advantage and pumping position. As the handle is oscillated to actuate the piston, fluid between the check valves 162 and 94 will be forced by downward movement of theV piston past the check valve 94 into the pressure area 67 to further extend and pressurize the ram.

It will be apparent that, during the upstroke of the piston,

the check valve 94 will seat to prevent hydraulic fluid from 5. Teavi'ng the pressure' area 67 and valve 102 will open to fill the space between the valves 94 and 102.

When the ram is to be retracted, the operator first turns the release handle 64 on the rod 63. The twisting of the release rod 63 serves to cam the ears 61 and 62 apart and to thereby separate the arms 56 and 57 and move them radially out of contact with the teeth 55.

With the internal locking mechanism thus disengaged, the operator next turns the plate 9G to raise the attached cylinder 25 and the valve seat 92 away from the shaft base tothe position shown in FIG. 6. In this position, the check valves 94 and 102 are by-passed and fluid is free to pass from the pressure area 67 into the space between the pump cylinder and the main shaft 24, and thence through the ports 105. At the same time, the ram is automatically fully retracted under the action of the spring 40.

After the ram has been retracted, the rod 63 may again be turned to its first position so that the arms 56 and 57 will re-engage the teeth under the action of the springs 613. The valve seat 92 may then be moved back into the mouth of the passageway 54 by reverse rotation of the plate 90. Alternately, the by-pass may be kept open until the pressure area is again flooded, and then reseated.

The scissors-type internal locking mechanism is particularly suitable to be incorporated into an aircraft tripod jack, and this arrangement is shown in FIGS. 6, 7, and 8. In the illustrated embodiment, Vreference numeral 150 designates the legs of the jack, the legs being attached at their upper ends to a collar 151 which is connected to an outer shell 152 of the lifting mechanism. The bottom of the shell 152 and a hand pump assembly 153 are mounted on .a bottom plate 154, which is attached to each leg 150 as shown.

A. ram 160 is reciprocally mounted within the outer shell, and is spaced a short distance inwardly from the inner'wall thereof by internal rings 161 and 162. The ring 161 is secured to the inner surface of shell 152, while ring 162 is carried by the ram.

A cylindrical main shaft 164, having an annular shaft head 165 and a shaft base 166, is positioned within the ram and is secured to the ram for movement therewith by means of a locking ring 167 which locks the ange 16S of the shaft head 165 to the upper end of the ram. As indicated in FIG. 7, the ram and main shaft are spaced apart by a flange 168 on the shaft head 165, and this space constitutes a fluid reservoir 169 which may be filled with hydraulic fluid through the filler plug 170. The main shaft assembly further includes a screw extension shaft 181 which is received within the main shaft and which is threadedly engaged with the interior bore of the shaft head 165.

The shaft base 166 abuts a pedestal 171 when the ram is retracted, and is separated therefrom to form a pressure zone when the ram is extended. Hydraulic fluid is drawn from the reservoir 169 by the hand pump assembly 153 through a passageway (not shown) in the bottom plate 154 and is injected by the pump into the pressure zone through a bore 172 in the plate 154 and a port 173 in the pedestal 171.

A sleeve 182 is fixedly mounted in the reservoir area 169, the bottom of the sleeve being fastened to the sides of pedestal 171. The scissors-type locking mechanism comprising arms 174 and 175 on a lock base 183 is mounted on the top of the sleeve for cooperation with teeth 176 formed on the main shaft 164. As in the previously described jack, the scissors arms are biased inwardly by springs 177 attached to the free ends of the arms, While ears 179 and 178 on arms 174 and 175, respectively, cooperate with a release rod 186. The release rod projects downwardly through the bottom plate 154 and has a release handle secured thereto.

The jack may be operatively extended by pumping hydraulic fluid, by means of the hand pump assembly 153, from the reservoir through the bore 172 and port 173 vto cause the shaft base and pedestal to separate. Continued expression of fluid into' the pressure zone therebetween continues to lift the main shaft and rto extend the attached ram. The arms 174 and 175 will grip the teeth on the main shaft to hold the same in a raised position, thus locking the ram in an extended position, as shown in dotdash outline in FIG. 6. The screw extension may also be threaded upwardly to provide increased height if such is desired.

When the ram is to be retracted, the operator twists the release rod 180 to separate and disengage the arms 174 and 175 from the teeth. The ram and main shaft will then fall back into the cylinder until the shaft base again abuts the pedestal.

Obviously, many other modications and variations of the specific forms of the invention shown and described herein are possible in the light of the above teachings. It is therefore to be understood that, within the scope of the appended claims, the invention may be practiced otherwise than as specifically shown and described.

What is claimed is: l

1. A jack mechanism comprising an outer shell, an extensible hollow ram telescopically mounted within said shell, a main shaft mounted within said ram, said main shaft being fixedly secured to said shell, pressure means for extending said ram, internal locking means for locking said ram in an extended position, said internal locking means including teeth formed on the peripheral surface of said main shaft, a pair of arms pivotally mounted in a scissors-type .arrangement on said ram, said arms having their free ends surrounding said main shaft, spring means connected to the free end of each arm, said spring means serving to bias said arms into locking engagement with said teeth, a rearwardly extending ear formed on the pivoted end of each arm, a release rod positioned between said ears and extending longitudinally of said shell,

said release rod having a radial dimension in one direction greater than a radial dimension in another direction so that rotation of said rod will cause said ears and arms to separate, thereby releasing said ram for retraction, and spring means connected to said ram for automatically retracting it when the ram has been released.

2. A hydraulic jack mechanism comprising an ou-ter shell, an extensible hollow ram reciprocally telescoped in one end of said shell, said ram being closed at one end by a ram base, a hollow shaft mounted in said ram, an annular shaft head fastened to the shaft and to the shell at the other end of the shell, a shaft base on said shaft, said outer shell, shaft head and shaft base defining a fluid reservoir, said shaft base being slidably received against the inner wall surface of said ram, a fluid passageway through said shaft base, a cylinder within said main shaft, a piston reciprocally mounted in said cylinder, the top of said piston extending through the center of said shaft head, a pump handle on the top of the piston, a fluid feeding chamber in the bottom of said piston, an open iiuid path between said feeding chamber and reservoir, an outlet from said feeding chamber, a rst one-way check valve in said outlet, said first check valve permitting huid to ow through said feeding chamber and iicod said cylinder during the upstroke of the pis-ton, a fluid outlet from said cylinder communicating with said Huid-passageway of the shaft base, a second one-way check valve in said liuid outlet from said cylinder, said second check valve permitting fluid to be expressed from said cylinder during the downstroke of said piston to force said ram base away from said shaft base and thereby extend said ram, a fluid bypass around said check valves whereby fluid can be expressed from between said shaft base and ram base into said reservoir so that said ram can be retracted, internal locking means for locking said ram in an extended position, said internal locking mean-s including teeth formed on the peripheral surface of said main shaft, a pair of arms pivotally mounted in a scissors-type arrangement on said ram, said arms having their free ends surrounding said main shaft, spring means connected to the free end il? of each arm, said spring means serving to bias said arms into locking engagement with said teeth, a rearwardly extending ear formed on the pivoted end of each arm, a release rod positioned between said ears and extending longitudinally of said shell, said'release rod having a radial dimension in one direction greater than a radial dimension in another direction whereby rotation of said rod will cause said ears and arms to separate, thereby releasing said ramtfor retraction, and a spring positioned between said main shaft and rarn for automatically retracting said ram when the arms are out of engagement with said teeth.

3. A jack mechanism comprising an outer shell, an extensible hollow ram mounted within said shell, a main shaft mounted within said ram and connected to ksaid ram for movement therewith, pressure means for extending said ram and main shaft, internal locking means for locking said ram in an extended position, said internal locking means comprising a sleeve ixedly mounted in said shell between the ram and main shaft, a pair of arms pivotally mounted in a scissors-type arrangement on the top of 20 said sleeve, said arms surrounding said main shaft, teeth formed on the periphery of the main shaft, spring means connected to the free ends of said arms to yieldably urge said arms -into engagement with said Iteeth to lock the ram in an extended position, a rearwardly extending ear formed on the pivoted end of each arm, a release rod positioned lbetween said ears and extending longitudinally of said shell, said release rod having a radial dimension in one direction greater than a radial dimension in a-nother direction whereby rotation of said release rod will force said ears and arms apart to release said ram for retraction, and spring means connected to said ram for automatically retracting it when the ram has been re-` leased.

Holloway Dec. 4, 1917 Powers et al Feb. 17, 1925,

Claims (1)

1. 2. A HYDRAULIC JACK MECHANISM COMPRISING AN OUTER SHELL, AN EXTENSIBLE HOLLOW RAM RECIPROCALLY TELESCOPED IN ONE END OF SAID SHELL, SAID RAM BEING CLOSED AT ONE END BY A RAM BASE, A HOLLOW SHAFT MOUNTED IN SAID RAM, AN ANNULAR SHAFT HEAD FASTENED TO THE SHAFT AND TO THE SHELL AT THE OTHER END OF THE SHELL, A SHAFT BASE ON SAID SHAFT, SAID OUTER SHELL, SHAFT HEAD AND SHAFT BASE DEFINING A FLUID RESERVOIR, SAID SHAFT BASE BEING SLIDABLY RECEIVED AGAINST THE INNER WALL SURFACE OF SAID RAM, A FLUID PASSAGEWAY THROUGH SAID SHAFT BASE, A CYLINDER WITHIN SAID MAIN SHAFT, A PISTON RECIPROCALLY MOUNTED IN SAID CYLINDER, THE TOP OF SAID PISTON EXTENDING THROUGH THE CENTER OF SAID SHAFT HEAD, A PUMP HANDLE ON THE TOP OF THE PISTON, A FLUID FEEDING CHAMBER IN THE BOTTOM OF SAID PISTON, AN OPEN FLUID PATH BETWEEN SAID FEEDING CHAMBER AND RESERVOIR, AN OUTLET FROM SAID FEEDING CHAMBER, A FIRST ONE-WAY CHECK VALVE IN SAID OUTLET, SAID FIRST CHECK VALVE PERMITTING FLUID TO FLOW THROUGH SAID FEEDING CHAMBER AND FLOOD SAID CYLINDER DURING THE UPSTROKE OF THE PISTON, A FLUID OUTLET FROM SAID CYLINDER COMMUNICATING WITH SAID FLUID PASSAGEWAY OF THE SHAFT BASE, A SECOND ONE-WAY CHECK VALVE IN SAID FLUID OUTLET FROM SAID CYLINDER, SAID SECOND CHECK VALVE PERMITTING FLUID TO BE EXPRESSED FROM SAID CYLINDER DURING THE DOWNSTROKE OF SAID PISTON TO FORCE SAID RAM BASE AWAY FROM SAID SHAFT BASE AND THEREBY EXTEND SAID RAM, A FLUID BYPASS AROUND SAID CHECK VALVES WHEREBY FLUID CAN BE EXPRESSED FROM BETWEEN SAID SHAFT BASE AND RAM BASE INTO SAID RESERVOIR SO THAT SAID RAM CAN BE RETRACTED, INTERNAL LOCKING MEANS FOR LOCKING SAID RAM IN AN EXTENDED POSITION, SAID INTERNAL LOCKING MEANS INCLUDING TEETH FORMED ON THE PERIPHERAL SURFACE OF SAID MAIN SHAFT, A PAIR OF ARMS PIVOTALLY MOUNTED IN A SCICCORS-TYPE ARRANGEMENT ON SAID RAM, SAID ARMS HAVING THEIR FREE ENDS SURROUNDING SAID MAIN SHAFT, SPRING MEANS CONNECTED TO THE FREE END OF EACH ARM, SAID SPRING MEANS SERVING TO BIAS SAID ARMS INTO LOCKING ENGAGEMENT WITH SAID TEETH, A REARWARDLY EXTENDING EAR FORMED ON THE PIVOTED END OF EACH ARM, A RELEASE ROD POSITIONED BETWEEN SAID EARS AND EXTENDING LONGITUDINALLY OF SAID SHELL, SAID RELEASE ROD HAVING A RADIAL DIMENSION IN ONE DIRECTION GREATER THAN A RADIAL DIMENSION IN ANOTHER DIRECTION WHEREBY ROTATION OF SAID ROD WILL CAUSE SAID EARS AND ARMS TO SEPARATE, THEREBY RELEASING SAID RAM FOR RETRACTION, AND A SPRING POSITIONED BETWEEN SAID MAIN SHAFT AND RAM FOR AUTOMATICALLY RETRACTING SAID RAM WHEN THE ARMS ARE OUT OF ENGAGEMENT WITH SAID TEETH.

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