US2992812A

US2992812A - Jacking mechanism and controls

Info

Publication number: US2992812A
Application number: US732307A
Authority: US
Inventors: David H Rasmussen; George E Suderow
Original assignee: De Long Corp
Current assignee: De Long Corp
Priority date: 1958-05-01
Filing date: 1958-05-01
Publication date: 1961-07-18
Anticipated expiration: 1978-07-18

Description

July 18', 1961 D. H. RASMUSISEN ETAL 2,992,812

JACKING MECHANISM AND CONTROLS Filed May 1, 1958 6 Sheets-Sheet 1 l :4 h! In 1.. 1W

l h! I ll! 5 In H h] Ill h I n I Dar/d ll. Rasmqssen Geo/9e E. Sud 00W ATTORNEYS i July 18, 1961 D. H. RASMUSSEN ETAL 2,992,812

* JACKING MECHANISM AND CONTROLS Filed May 1, 1958 6 Sheets-Sheet 2 INVENTORS Oar/d Rasmussen George E 506/6/0W ATTORNEYS July 18, 1961 D. H. RASMUSSEN ETAL I 2,992,812 JACKING MECHANISM AND CONTROLS Filed May 1, 1958 6 Sheets-Sheet 5 INVENTORS Dar/a Rasmussen q George E. fiuderon/ w ATTORNEYS July 18, 1961 D. H. RASMUSSEN ETAL 2,992,812

JACKING MECHANISM AND CONTROLS S eeg Sheet 4 Filed May 1, 1958 ATTORNEYS kill r-l R-L J ly 8, 19 1 D. H. RASMUSSEN ETAL 2,992,812

JACKING MECHANISM AND CONTROLS Filed May 1, 1958 IIHII E9 III II \IIIIIIII 6 Sheets-Sheet 6 I illlll I will lzllll I I III in II IN VENTOR5 0a wa/ A. Rasmussen 24 George E fiua eron 7M flail MW ATTORNEYS United States Patent 2,992,812 JACKING MECHANISM AND CONTROLS David H. Rasmussen, Staten Island, and George E.

Suderow, New York, N.Y., assignors to De Long Corporation, New York, N.Y., a corporation of Delaware Filed May 1, 1958, Ser. No. 732,307 8 Claims. (Cl. 254-407) This invention relates to improvements in jacking mechanisms, and, more particularly, to improvements in mechanisms of the type disclosed in the patent to Pointer No. 2,775,869, the patent to Suderow No. 2,822,670, and in the copending application of Suderow Serial No. 523,323 now Patent No, 2,932,486. The jacking mechanisms disclosed in those patents and in that application find their primary usage in mobile marine platforms wherein a platform-like body is raised or lowered on supporting legs, or such are raised or lowered relative to the body.

While the jacking mechanism disclosed in the aforementioned Pointer patent, and the improved jacking mechanism disclosed in the aforementioned Suderow application have met with considerable commercial success and have proved to be more than adequate for their intended purpose, such mechanisms are susceptible of improvements. In particular, those jacking mechanisms operate on a step-by-step principle and for that purpose have a pair of upper and lower holding or locking means, each releasably engageable with a supporting leg. The mechanisms also have power-operated means for moving one of the holding means vertically relative to both the other holding means and the body in order to efiect relative movement between the supporting leg and the body when the one holding means is locked to the leg and the other is unlocked therefrom. The other holding means is employed to support the body on the leg, or the leg on the body, while the first-mentioned one holding means is recycled in preparation for another lifting or lowering stroke. Such recycling of the movement-effecting holding means is relatively time-consuming.

Accordingly, it is an object of this invention to provide an improved jacking mechanism of the type under consideration that eliminates the aforedescribed time-consuming recycling action and effects a jacking stroke with both holding means.

It is another object of this invention to provide an improved jacking mechanism of the type under consideration that wil effect a substantially continuous step by-step jacking movement, interrupted only by the time required to transfer the jacking load from one holding means to the other.

It is a further object of this invention to provide a novel control system for a fluid-pressurcpperated jacking mechanism embodying this invention.

Other objects and advantages of the invention will become apparent from the following description and ac companying drawings in which:

FIGURE 1 is a fragmentary elevational view of a jacking mechanism embodying this invention and showing such mechanism mounted on a platform-like body in operative relationship to a supporting leg for the latter. Certain parts are broken away and others shown in section in order to illustrate details.

FIGURE 2 is a side elevational view of the jacking mechanism shown in FIGURE 1, and taken from the left-hand side of the latter figure. Parts are broken away and other parts shown in section in order to better illustrate details.

FIGURE 3 is a horizontal sectional view taken substantially on line 3--3 0f FIGURE 1.

FIGURE 4 is a horizontal sectional view taken substantially on line 4--4 of FIGURE 1.

FIGURE 5 is a schematic view of a hydraulic control system embodying this invention for the jacking mechanism shown in FIGURES 1 and 2.

FIGURE 6 is a diagrammatic showing of sequential views to illustrate the steps in the operation of jacking mechanism embodying this invention in order to lower a body on a supporting leg or to raise a supporting leg relative to the body.

FIGURE 7 is a diagrammatic showing of sequential views to illustrate the steps in the operation of jacking mechanism embodying this invention in order to raise a body on a supporting leg or lower a supporting leg relative to the body;

FIGURE 8 is a view corresponding to FIGURE 1 but illustrating a modified form of jacking mechanism embodying this invention.

FIGURE 9 is a side elevational view, with parts broken away and other parts shown in section, of the jacking mechanism shown in FIGURE 8 and taken from the left hand side of the latter figure.

FIGURE 10 is a horizontal sectional view taken on line 10--10 of FIGURE 8.

FIGURE 11 is a horizontal sectional view taken on line 11-11 of FIGURE 8.

FIGURE 12 is a horizontal sectional view taken on line 12--12 of FIGURE 8.

Referring now to FIGURES l and 2 of the drawings, there is shown a portion of a platform-like body 20, which may be in the form of a barge, having a guiding well 22 extending vertically therethrough. Extending through the well 22 and guided for substantially vertical movement thereby is a supporting leg 24 for the body 20, such leg being here illustrated as being in the form of an elongated cylinder or caisson. It will be realized, how'- ever, that the supporting leg may take other forms, such as an open work tower (not shown). The leg 24 is provided with at least two (only one of which is shown here) uniformly-circumferentially-spaced, longitudinally extending rows of rectangular apertures or holes 26 for the reception of substantially complementary locln'ng bolts or pins 28 on a jacking mechanism mounted on the body 20. In the embodiment here illustrated, these holes 26 are formed in the web of a channel member 30, which may be termed a pin rail, having the edges of the side flanges thereof securely fastened to the leg 24, as by welding. For reasons later described, the web of the member 30 projects outwardly, as at 32, beyond both of its side flanges, as best shown in FIGURES 3 and 4.

Preferably, the caisson well 22 is of somewhat greater diameter than that of the leg 24 so that the latter has a somewhat loose guiding fit within the well. In order to further this object, the side of the well 22 is recessed to provide a longitudinal groove 34, as shown in FIGURES 3 and 4, for the somewhat loose accommodation of the pin rail 30.

A jacking mechanism is provided for each row of holes 26, only one such mechanism being shown in the drawings. Each jacking-mechanism includes an upper horizontal thrust beam 36 and a lower horizontal thrust beam 33, each somewhat U-shaped in plan view, as shown in FIGURE 3, with widely divergent arms in order to relatively closely embrace the leg 24. The base of each beam is provided with a cut-out portion 46} for the accommodation of the. pin rail 30. Fingers or claws 42 (FIGURE 3) which extend behind the web extensions 32 on the pin rail 30 are provided on each

beam

36 and 38 in order to provide a relatively loose dovetailed engagement between each thrust beam and the pin rail. This engagement serves to hold the jack mechanism in proper relation to the supporting leg 24.

The jacking mechanism, in a sense, floats between upper and lower abutments on the body 20 in order to :be seen that each exert upward or downward jacking forces through such abutments. The upper abutment is formed by the undersurface of a beam 44, which is of substantially the same plan configuration as the

thrust beams

36 and 38 and is rigidly secured to the body 20 by upstanding tensioned elements, here shown in the form of four channel-shaped beams 46 welded to the beam 44 and to the deck 48 of the body. The lower abutment may be formed by the deck 48 itself. Preferably, cushioning members 50, which may be in the form of resilient blocks of rubber or the like, are interposed between the upper thrust beam 36 and the abutment beam 44, and between the lower thrust beam 38 and the deck 48. Since, as has been previously mentioned, each leg 24 is operated upon by at least two jacking mechanisms arranged symmetrically about the leg, the cushioning members 50 serve to equalize the jacking forces between the several mechanisms operating on each leg. Additionally, the

cushioning members 50 will absorb any shocks which may be imparted to the mechanism by abrupt engage- .ment of the leg 24 with the marine bottom.

Secured to, as by welding, and extending between the upper and

lower thrust beams

36 and 38 are a plurality of parallel tie and guide rods 52. An upper lifting beam 54 and a lower lifting beam 56 are slidably mounted on the rods 52, i.e., the latter extend through guiding apertures in the lifting beams, so as to be movable substantially vertically, that is, in directions parallel to the axis of the leg 24. Preferably, the intermediate portions of the guide rods 52 are connected together by an intermediate bracing beam 58, through which the guide rods extend and to which they are secured as by welding, as "shown in FIGURE 1.

All of the

beams

54, 56, and '58 preferably are of substantially the same configuration, in plan view, as the thrust beams 36 and 38, except that there are no fingers 42 on the lifting and brace beams.

Vertical movement of the upper and lower lifting beams 54 and 56, in either direction along the guide rods, is effected by means of two pairs of double-acting upper and lower

fluid jacking motors

60 and 62, respectively, the motors of each pair being disposed symmetrically with respect to the pin rail 30 and each '

ing lifting beam

54 or 56, as by being disposed in an aperture therein and welded thereto, as shown in FIG- URE 1. Additionally, the

motors

60 and 62 on the two

beams

54 and 56 are vertically aligned and a com mon piston rod 66 is employed for each pair of

motors

60 and 62 in vertical alignment. The opposite ends of the piston rods 66 are secured to the upper and lower thrust beams 36 and 38, as by welding, and the intermediate portions of the piston rods may pass through and be secured to the brace beam 58, as by welding. By appropriate operation of the

motors

60 and 62, it will lifting

beam

54 or 56 can be moved selectively upwardly or downwardly along its guide rods 52 or restrained against any movement therealong.

Reciprocable on each

lifting beam

54 or 56, in a guideway 68 which may be integral therewith as shown in FIGURE 2, is a locking bolt or pin 28 adapted to project into an aperture 26 in the pin rail 30, when aligned with such aperture, in order to lock the respective lifting beam to the supporting leg 24 against movement longitudinally therealong. Each locking pin 28 may be reciprocated by a double-acting fluid motor 70 that may have one end of the cylinder thereof detachably secured to the

corresponding lifting beam

54 or 56, as by screws 72, and have the end of its piston rod 74 secured to the outer end of the corresponding pin, as shown in FIGURE 2. The operation of each motor 70 FIGURE 5 of the drawings.

may be controlled by an appropriate manually-operable control valve (not shown) connected between the motor and a suitable supply (not shown) of fluid under pressure.

In order to achieve the objects of this invention, the jacking

motors

60 and 62 are so operated that when one

lifting beam

54 or 56 is locked, by its pin 28, to the supporting leg 24 and the jacking motors of that beam are being operated to efiect relative movement, i.e., a jacking step, in one direction between the supporting leg and the body 20 while the other lifting beam is unlocked from the leg, the jacking motors of such other or unlocked lifting beam are operated to move that beam in a direction relative to the body opposite that in which the locked and active or jacking lifting beam is being moved relative to the body. The effect of such operation of the jacking

motors

60 and 6 2 is to move the unlocked or inactive beam into a position where it can be locked to the leg 24 and take over and immediately commence another jacking step after the other or active beam has reached the end of its jacking stroke and has been unlocked.

In order to operate the jacking

motors

60 and 62 in the aforedescribed manner, this invention makes use of the fluid being exhausted from the active jacking motors to operate the-inactive jacking motors in the aforedescribed opposite direction, that is, to recycle the latter in preparation for another jacking stroke. A control arrangement for accomplishing this function is shown in Of course, in actual practice the supply and exhaust connections of the pair of

motors

60 or 62 on each

lifting beam

54 or 56 are connected in parallel for simultaneous operation of the motors of each pair. Likewise, the jacking motors on the corresponding lifting beams of all of the jacking mechanisms operable on each leg are connected together for simultaneous operation. For purposes of illustration, however. FIGURE 5 includes a showing of only one upper and one lower jacking motor.

The fluid control system includes a source of fluid under pressure, such as a pump 76, which withdraws fluid from a sump 78, via a conduit 80, and discharges the fluid under pressure into a supply conduit 82 that leads to a four-way motor-control valve '84. An exhaust conduit 86 is connected between the control valve 84 and the sump 78 and, preferably, a pressure relief valve 88 is connected between the supply and

exhaust conduits

82 and 86 to limit the effective operating pressure of the system to a predetermined amount, such as 3000 psi. Also connected to the control valve 84, for selective reversible connection thereby to the supply and

exhaust conduits

82 and 86, respectively, are two supply and exhaust conduits 90 and 92 for supplying or exhausting pressure fluid to or from one of the jacking

motors

60 or 62 while respectively exhausting or supplying pressure fluid from or to the other jacking motor. The motor-control valve 84 may be of the solenoid type having two operating coils 94 and 96 alternatively energizea-ble, for selectively moving the valve to either of its two open positions, by a manually-operable single-pole double-throw switch 98 which connects the coils with a source of electric power, e.g., 110 V. AC. When the switch 98 is open, the valve 84 is closed, i.e., positioned midway between its two open positions.

The conduits 90 and 92 are connected to their

respective motors

60 and 62 through two four-way motordirection-control valves 100 and 102 that are ganged, such as by a mechanical connection 104, for simultaneous manual operation. The opposite ends of the motors 6G and 62 are connected to their respective valves 100 and 102 by the

conduits

106 and 108, and 110 and 112, respectively, so that by appropriate operation of the valves 100 and 102 the conduits 90 and 92 can be connected selectively to one or the other ends of their respective motors, The valves 100 and 102 are also connected together by a conduit 114 having a back-flow-preventing check valve 116 interposed therein. All of these connections are such that when pressure fluid is being supplied to one end of a

motor

60 or 62 by the conduits 90 or 92, respectively, the exhaust from that motor flows, via the conduit 114, into the opposite end of the

other motor

62 or 60 and operates the latter motor in the opposite direction while such latter motor is exhausted through the other conduit 92 or 90.

Since the direction of flow through conduit 114 depends on which

motor

60 or 62 is performing a jacking stroke, provision must be made for reversing the opening direction of the check valve 116 in the conduit 166. This can be done by a four-way reversing valve 118 connected into the conduit 114 on both sides of the check valve 116. The reversing valve 118 preferably is operated automatically by a double-acting hydraulic motor 120, the opposite ends of which are connected, via

branch conduits

122 and 124, to the supply and exhaust conduits 9t) and 92, respectively. From the construction described it will be seen that, as illustrated in FIGURE 5, when pressure fluid is supplied to the conduit 92, and to the lower end of the motor 62, the motor 120 is operated to properly position the reversing valve 115 to correctly connect the check valve 116 into the line 114 for the flow of exhaust fluid therethrough from the motor 62 to the motor 69. Similarly, if pressure fluid is supplied to the conduit 90, instead of to the conduit 92, the pressure in the conduit 96 will operate the motor 120 to reverse the connections to the check valve 116 so that the exhaust fluid from the motor 66 will flow through the conduit 114- into the upper end of the motor 62.

It will be seen that if any leakage occurs past the piston of the

motor

60 or 62 which is being operated by the exhaust fluid from the other or

power motor

62 or 6%, the exhaust-fluid-operated motor will not effect a full stroke unless the same quantity of fluid leaks past the piston of such other motor. Obviously, this is a highly undesirable condition because the locking bolt 28 on the lifting beam being moved by the exhaust-fluid-operated motor possibly will not become aligned with a hole 26 in the pin rail St? at the end of the power motors stroke. Any such leakage in the exhaust-fluid-operated motor can be compensated for, however, by making provision for admitting fluid under system pressure, e.g., 3000 p.s.i., into the conduit 114 on the downstream side of the check valve 116 therein at the end of the power motors stroke. Thus, the conduits 9i? and 92 are interconnected by a conduit 126 which has a branch conduit 128 connected thereto and to the conduit 114 downstream of the check valve 116. The branch conduit 128 has a pressure relief valve interposed therein and set to open at slightly less than system pressure, e.g., 3000 p.s.i. Check valves 132 and 134 are interposed in the conduit 126 on both sides of the connection of the conduit 128 thereto to prevent flow from either conduit 94 or 92 t the other.

Accordingly, when the

motor

60 or 62 that is effecting a jacking stroke reaches the end of such stroke, full system pressure will be developed in the conduit 90 or 92 supplying pressure fluid to such motor. This full system pressure will open the pressure relief valve 130 to admit fluid under system pressure into the conduit 114 onthe downstream side of the check valve 116 so that full system pressure will be supplied to the

motor

60 or 62 that is being operated by exhaust fluid from the jacking motor. The admission of such system pressure to the recycling motor will serve, if necessary, to move the latter to the limit of its recycling stroke and, at the same time, serve to rigidly restrainsuch motor against any reverse movement while the jacking load is being transferred thereto.

In operation of the foregoing control system in order, for example, to lift the body 20 on the leg 24, or to lower the leg relative to the body, the motor-reversing valves 100 and 102 are placed in the position shown in FIGURE 5, i.e., wherein the upper ends of the jacking

motors

60 and 62 are connected together, via the conduit 114, and the lower ends of these two motors are connected to the supply and exhaust lines and 92, respectively. If then the lifting beams 54 and 56 are in a position wherein they are separated vertically to their full extent with the upper beam 54 locked to the leg 24 and the lower beam 56 unlocked from the leg as shown in FIGURES 5 and 7A, the switch 98 may be operated to energize the coil 94 and thereby supply pressure fluid through the conduit 90 to the lower end of the upper motor 60. Hence, the piston rod 66 will move up and raise the body 20 through a full lifting step to the leg 24 :to the position shown in FIGURE 73, as best observed by inspection of the reference line 136 on the leg 24.

At the same time, it will be seen that the fluid being exhausted from the upper end of the upper motor 60 will flow through the conduit 114 into the upper end of the lower motor 62. In this connection, it will be noted that the supply pressure in the conduit 90 operates the motor to position the reversing valve 118 so that the check valve 116 is connected into the line 114 in such a manner that flow can take place therein from the upper motor 63 to the lower motor 62. The supply of exhaust fluid to the upper end of the lower motor 62 causes the lower lifting beam 56 to move up relative to the body 20, i.e., toward the upper beam 54. This movement of the beam 56 causes a discharge or exhaust of fluid from the lower end of the lower motor 62, this exhaust can take place through the conduit 92, valve 84, and conduit 86 back to the sump 76.

When the upper motor 60 reaches the end of its bodylifting stroke, as shown in FIGURE 73, it will be seen that maximum system pressure will then be developed in the conduit 90. This full system pressure will open the relief valve 13% so that the maximum system pressure will be supplied to the conduit 114, downstream of the check valve 116, and, thence, to the upper end of the lower motor 62. Consequently, the lower motor 62 will move through its full recycling stroke, even though there might possibly have been some leakage between the piston and cylinder of the lower motor during its operation by exhaust fluid from the upper motor 60.

As soon as the upper motor 6% commences its bodylifting stroke, the pin motor 70 of the lower lifting beam 56 is operated to project its pin 28. The latter then will engage against the web of the pin rail 3t) and slide therealong, with the upward movement of the beam 5-6 by the lower motor 62, until at the end of the recycling stroke of the lower motor 62 the pin becomes aligned with the next higher opening 26 in the pin rail. At this time, the pin 28 on the lower beam 56 will be projected into such opening and lock the lower lifting beam to the leg 24, as shown in FIGURE 7B. The pin motor 76 for the upper lifting beam 54 is then operated to withdraw or retract its locking pin 28 from the pin rail 39. Such retraction will not occur, however, until the j acking load has been transferred to the lower lifting beam 56.

The switch 98 then is operated to energize the coil 96 and reverse the control valve 84 so that it will supply fluid under pressure to the conduit 92 and connect the conduit 90 with the exhaust conduit 86. This supply of fluid under pressure to the conduit 92 will cause the lower motor 62 to operate to lower the lower lifting beam 56 until its pin 28 takes the load from the pin on the upper beam 54. At this time, this latter pin will retract, as shown in FIGURE 7C. Continued operation of the lower motor 62 lifts the piston rod 66, and, thereby, lifts the body 20. At the same time, the pressure in the conduit 92 will operate the motor 120 to reverse the connections to the check valve 116 so that the exhaust from the lower motor 62 will flow through the conduit 114- and serve to move the upper motor 66 in the opposite direction while the exhaust from the latter motor returns to the sump 78 via the

conduits

108, 90 and 86.

' As soon as the upper motor 60 has moved suficiently for the pin 28 on the upper lifting beam 54 to move out of alignment with the hole in the pin rail 30 in which it was previously engaged, the motor for such pin is operated to extend it back into engagement with the pin rail 30. Consequently, the pin 28 on the upper lifting beam 54 will slide upwardly along the web of the pin rail 30 because of the upward movement of the beam 54. When this pin 23 comes into alignment with the next higher pin hole 26 in the pin rail 30, such pin will be projected thereinto to thereby lock the upper lifting beam 54 to the pin rail, as shown in FIGURE 7D. This action will occur at the end of the body-lifting stroke of the lower motor 62, so that the load can then be transferred from the lower to the upper lifting beam, and the upper motor 60 operated to lift the body 20 through another step.

In the event that it is desired to lift the leg 24 relative to the body 20, or lower the latter relative to the leg, sequential operation of the upper and lower motors 6t) and 62 and the locking pins 28 on the upper and lower lifting beams 54 and 56 will take place as shown in FIGURE 6A to FIGURE 6D, respectively. For this purpose, the motor-direction-control valves 160 and 162 are moved into a position wherein the conduits 90 and 92 are connected, respectively, to the upper ends of the jacking

motors

60 and 62, while the lower ends of such motors are connected together by the conduit 1.14.

Assuming then, for example, that the upper and lower lifting beams are separated to their full extent and that the lower lifting beam 56 is locked to the leg 24, and the upper beam 54 is unlocked from such leg, as shown in FIGURE 6A, the switch 98 then is operated in a manner to energize the coil 96 so that fluid pressure will be supplied to conduit 92. This pressure fluid will then flow into the upper end of the lower motor 62 to thereby raise the lower lifting beam '56 which will carry therewith the leg 24, as will be seen from an inspection of the reference line 138 in FIGURE 68. During the upward movement of the lower lifting beam 56 it will be seen that the exhaust from the lower motor 62 will fiow through the

conduits

112, 114 and 108, into the lower end of the upper motor 60, to thereby operate such motor in the opposite direction from the lower motor 62. In this connection, it will be noted that pressure fluid in the conduit 92 operates the motor 12% to connect the check valve 116 into the conduit 114 in such a manner that flow can take place therein from the lower motor 62 to the upper motor 60. It also will be noted that the exhaust from the upper motor 6% will flow back to the sump through the

conduits

106, 90 and 86.

During the foregoing movements of the upper and

lower beams

54 and 56, the pin motor for the pin 28 on the upper lifting beam 54 is operated to project such pin into sliding engagement with the web on the pin rail 36, so that when such pin comes into alignment with the next lower pin hole 26, substantially at the end of the leg-lifting stroke of the motor 62, such pin will be projected into the pin hole in the manner shown in FIGURE 6B. Hence, the load can then be transferred to the upper lifting beam 54, and the lower lifting beam 56 unlocked from the leg, as shown in FIGURE 6C, by operation of the motor-control valve 84 to connect conduit 90 with the pressure fluid supply conduit 82 and connect conduit 92 with the exhaust conduit 86. The upper motor 62 will then operate to lift the leg 24 through another elevating step, as shown in FIGURE 6D, while at the same time the pressure in conduit 90 operates the motor 120 to reverse the connections to the check valve 116 so that the exhaust from the upper motor 60 can flow through the conduit 114 and into the lower motor 62 to recycle such latter motor in preparation for another lifting stroke thereof, again as shown in FIGURE 6D.

Referring to FIGURES 8 to 12 of the drawings, there is shown a modification of this invention wherein jacking movement of the lifting beams 54 and 56 is effected 8 through a different instrumentality than the fluid pressure-operated

motors

60 and 62 of the embodiment shown in FIGURES l and 2. In this modification, the upper and lower lifting beams 54 and 56 are connected together by two groups of jackscrews which threadedly extend through these beams. Two such groups disposed symmetrically on opposite sides of the pin rail 30 are shown in the drawing, with three jackscrews 140 in each group. The threaded engagement of the jackscrews 140 with the upper lifting beam 54 is of an opposite direction from their engagement with the lower lifting beam 56 so that appropriate rotation of the jackscrews will move the

beams

54 and 56 toward or away from each other along the guide rods 52. The opposite ends of each jackscrew 140 may be appropriately jou-rnalled in thrust bearings 142 in the upper and lower thrust beams 36 and 38, and the threads of the jackscrews in each group are so related that all the screws in each group may be interconnected adjacent their opposite ends by appropriate gears 144, so that rotation of one jackscrew of a group will rotate all of the other jackscrews of that group in the correct direction to effect opposite movement of the upper and lower lifting beams 54 and 56 toward or away from each other.

A jackscrew 140 in each group may be rotated by any appropriate type of motor, but for illustrative purposes there is shown, in FIGURES 8 and 9, a reversible electric motor 146 directly driving a worm gear 148 that meshes with a pinion gear 150 fixed to an intermediate portion of a jackscrew of each group. The motor 146 may be secured on a shelf-like bracket 152 that is mounted on the frame of the jack, constituted by the upper and lower thrust beams 36 and 38 and the guide rods 52, by appropriate supporting arms 154 that are secured to the upper and lower thrust beams.

From the foregoing construction it will be seen that operation of the motor 146 in one direction will serve to move the upper and lower lifting beams 54 and 56 apart, while operation of the motor in the other direction will serve to move the upper and lower lifting beams together. Consequently, the jack mechanism illustrated in FIGURES 8 and 9 may be operated to effect substantially continuous step-by-step movement in either direction between the leg 24 and the body 20. In this connection it will be particularly noted that because of the threaded engagement between the jack screws 140 and the lifting beams '54 and 56 and the engagement between the worm and

pinion gear

148 and 150, a static load can be imposed on either lifting beam, such load being either the partial Weight of the body or the partial weight of the leg, without providing means for positively restraining rotation of the jack screws. Thus, power failure of the motor 146 will not result in the dropping of a load. In other words, the jackscrews 140 afford a substantially fail-safe construction.

It thus will be seen that the objects of this invention have been fully and effectively accomplished. It will be realized, however, that the foregoing specific embodiments have been shown and described only for the purpose of illustrating the principles of this invention and are subject to extensive change without departure from such principles. Therefore, this invention includes all modifications encompassed within the spirit and scope of the following claims. 1

We claim:

1. Jack mechanism for selectively effecting or restraining relative movement in either direction between a platform-like body and a supporting leg for the body that is guided thereon for movement in directions extending substantially longitudinally of the leg, the combination comprising: a pair of spaced holding means each releasably engageable with the leg against movement relative thereto longitudinally thereof, each of said means being movable longitudinally of the leg when disengaged therefrom; and power-operated means connected to said holding means and to the body for selectively efiecting relative movement between one of said holding means and the body in one direction extending longitudinally of the leg and at the same time eflecting relative movement between the other holding means and the body in the opposite direction extending longitudinally of the leg or restraining relative movement in either of said directions between both of said holding means and the body, said power-operated means including a double-acting reciprocating hydraulic motor for each of said holding means with the cylinder of each motor secured to the corresponding holding means, a piston in each cylinder, and a common piston rod connecting said pistons.

2. Jack mechanism for selectively effecting or restraining relative movement between a platform-like body, and a supporting leg for the body that is guided thereon for movement in directions extending substantially longitudinally of the leg, the combination comprising: elongated guide means adapted to be disposed adjacent and parallel to the leg; a pair of thrust beams carried on the opposite ends of said guide means; a pair of movable holding means engaged with said guide means and guided thereby for linear movement parallel to the leg, each of said holding means being releasably engageable with the leg against movement relative thereto longitudinally thereof; and power-operated means connected to said thrust beams and to said holding means for selectively simultaneously eflecting relative movement in opposite directions between each of said holding means and said thrust beams or restraining relative movement between both of said holding means and said thrust beams.

3. The structure defined in claim 2 in which there are a plurality of jack mechanisms spaced uniformly about the leg and including a mounting for each mechanism comprising a pair of opposed abutments spaced along the length of the leg and secured to the body for alternatively receiving the opposite thrusts of the beams of the corresponding mechanism, and resilient force-transmitting means interposed between each abutment and the corresponding beam for equalizing the jacking forces of the mechanisms.

4. Jack mechanism for selectively effecting or restraining relative movement between a platform-like body and a supporting leg for the body that is guided thereon for movement in directions extending substantially longitudinally of the leg, the combination comprising: a pair of spaced holding means each releasably engageable with the leg against movement relative thereto longitudinally thereof; a pair of double-acting hydraulic motors connected to said holding means and to the body for selectively eflecting relative movement between each of said holding means and the body in directions extending longitudinally of the leg or restraining relative movement between each of said holding means and the body; control means for supplying pressure fluid alternatively to one or the other of said motors while exhausting pressure fluid alternatively from said other or said one motor, respectively; a fluid connection between said motors whereby the exhaust from the motor being supplied with pressure fluid is supplied to the other motor to eflect operation thereof in a direction opposite to that of the motor being supplied with pressure fluid; a check valve; means selectively connecting said check valve in said fluid connection to permit flow of fluid therethrough in the proper direction on operation of said motors; and means for supplying said fluid connection, downstream of said check valve, with fluid under pressure at the end of each operating stroke of said motors, said supply being at a pressure greater than that of the fluid supplied to the motors during their operating strokes.

5. Jack mechanism for selectively effecting or restraining relative movement between a platform-like body and a supporting leg for the body that is guided thereon for movement in directions extending substantially longitudinally of the leg, the combination comprising: a pair of spaced holding means each releasably engageable with the leg against movement relative thereto longitudinally thereof; a pair of double-acting hydraulic motors connected to said holding means and to the body for selectively effecting relative movement between each of said holding means and the body in directions extending longitudinally of the leg or restraining relative movement between each of said holding means and the body; control means for supplying pressure fluid alternatively to one or the other of said motors while exhausting pressure fluid alternatively from said other or said one motor; a fluid connection between said motors whereby the exhaust from the motor being supplied with pressure fluid is supplied to the other motor to effect operation thereof in a direction opposite to that of the motor being supplied with pressure fluid; a check valve in said fluid connection; valve means for reversing the connections to said check valve; and means responsive to the alternative supply of pressure fluid by said control means for operating said valve means to permit the flow of fluid through said fluid connection.

6. The structure defined in claim 5 including means for supplying the fluid connection, downstream of the check valve, with fluid under pressure at the end of each operating stroke of the motors, said supply being at a pressure greater than that of the fluid supplied to the motors during their operating strokes.

7. The structure defined in claim 2 in which the poweroperated means includes a pair of double-acting hydraulic motors one connected to one of the holding means and to the thrust beams and the other connected to the other holding means and to the thrust beams for selectively effecting or restraining relative movement between each of said holding means and said thrust beams, and control means for supplying and exhausting pressure fluid to and from said motors in a manner to efiect their operation to cause simultaneous relative movement in opposite directions between each of said holding means and said thrust beams.

8. The construction defined in claim 2 in which the power-operated means includes a jack screw having two sets of threads of opposite direction each engaging with one of the holding means.

References Cited in the file of this patent UNITED STATES PATENTS 2,558,401 Voigt June 26, 1951 2,822,670 Suderow Feb. 11, 1958 2,947,148 Young Aug. 2, 1960 FOREIGN PATENTS 478,297 Great Britain Jan. 17, 1938