US3613507A

US3613507A - Powerpack unit

Info

Publication number: US3613507A
Application number: US32550A
Authority: US
Inventors: Forrest P Smith Jr
Original assignee: United States Surgical Corp
Current assignee: United States Surgical Corp
Priority date: 1970-04-28
Filing date: 1970-04-28
Publication date: 1971-10-19
Anticipated expiration: 1988-10-19
Also published as: DE2120448A1; GB1344837A

Abstract

A powerpack for converting gas pressure into rectilinear movement of a drive shaft. The powerpack is activated by unseating a spool, releasing a volume of pressurized gas and thereby driving a shaft adapted to be associated with a mechanism requiring an input of rectilinear movement. Differential pressures cause the spool to be reseated, thus allowing the drive shaft, biased toward the spool, to return to its rest position. The operation of the power unit depends upon the formation of pressuretight chambers; and these chambers are defined by a plurality of floating O-rings. The forwardmost journey of the drive shaft is cushioned by the action of an air dashpot.

Description

2,870,749 1/1959. Deitrickson.................. 91/318 3,479,926 11/1969 Hillier 227/130 X FOREIGN PATENTS 525,773 9/1940 Great Britain................ 173/15 Primary Examiner-Martin P. Schwadron Assistant Examiner-Irwin C. Cohen Attorney-Fleit, Gipple 8L Jacobson ABSTRACT: A powerpack for converting gas pressure into 91/398! rectilinear movement of a drive shaft. The powerpack is ac- 91/403, 91/410, 91/433. 92/ tivated by unseating a spool, releasing a volume of pressurized llll. cl....................................................... g and h y i g a shaft adaped to be associated with a mechanism requiring an input of rectilinear movement. Dif ferential pressures cause the spool to be reseated, thus allowing the drive shaft, biased toward the spool, to return to its rest position. The operation of the power unit de formation of pressuretight chambers;

Forrest P.Smlth Northporg NX; 21 Appl. No. 32,550

Apr. 28, 1970 Oct. 19, 1971 United StatesSur lealCmltioI Baltimore, Md.

10 Clair-s, 6 Drawing Fl ..F1Sb 13/04, FOlb 11/02 United States Patent [72] Inventor 22 Filed [45] Patented [73] Assignee [$4] POWERPACK UNIT [50] Field 91/403, 410, 433, 468, 318, 397, 392, 398; 227/130;

173/15, 16,17 pends upon the and these chambers are [56] Rm CM defined by a plurality of floating O-rings. The forwardmost UNITED STATES PATENTS journey of the drive shaft is cushioned by the action of an air 2/1908 dashpot.

PAIENTEUHIZI 1919" SHEET 10F 2 mvsu'ron FORREST P.

SMITH, Jr.

H BY ATTORNEYS PATENTEDUET 19 |97| SHEET 2 BF 2 INVENTOR FORREST P. SMITH, Jr.

TRIGGER rowmumcx UNIT BACKGROUND OF THE INVENTION The concept of a gas-powered driving unit of the typeforming a part of the present invention is not new. See, for example, copending US Pat. application Ser. No. 852,822, filed Aug. 25, I969, and assigned to the present assignee. An advancedgaspowerunitcanalsobefoundincopendingU.S. Pat. application Ser. No. 21,465, filed Mar. 20, I970, and assigned to the same assignee.

The power unit described in each of these above-noted copending patent applications functions relatively well. However, each of the power units suffers from certain disadvantages. For example, in the power unit deacribed'in the first of these patant applications, the gas chambers are defined by a plurality of sliding diaphragms. These diaphragms have been found to be somewhat weak and, in time, oflen developleakalnthepowerunitdisclosedinthesecondof theseapplicatiormthepressurechambersaredefinedbyaseries of O-rings. Again, however, after long periods of wear, leakage between one chamber and the nest often appear.

It is toward the elimination of the above-noted disadvantages and the simplification of known powerpack units that the present invention is directed.

SUMMARY OF THE INVENTION The present invention relates to a powerpack capable of converting gas pressure into rectilinear movement, efficiently and with a minimum number of moving parts. Freaurized gas is fed to the inventive powerpack and, when the power pack is idle, is held at its source; the pressure source is closed off from the working members of the powerpack when a movable spool is seated against the gas inlet port. The spool is maintained in contact with the inlet port through the action of a driving piston integral with the drive shalt, which assembly is urged against the side of the spool remote from the inlet port by means of a biasing spring. The contact between the spool and the inlet port seals B the supply of pressurind gas.

The powerpack of the present invention is fired when the driving piston and integral drive shaft are moved incrementally against the force of the biasing spring. This movement allows the spool to become unseated from the gas inlet port and is held in its unseated position through the action of the pressurised gas. When the spool is unseated, the source of pressurized gas acts directly on the piston integral with the drive shaft The drive shalt is then driven by the pressurized gas through an entire firing cycle.

During the movement of the drive shaft, the pressure on the side of the spool remote from the inlet port becomes greater than the pressure on the side of the spool adjacent the inlet port. When this occurs, the spool is driven toward the inlet port, seats against same, and thus again isolates the source of pressure from the piston and drive shaft asembly. With the i drive shaft thus isolated from the source ofpressure, its biasingspring returns the integral piston into its contact position with the spool. At this time, the powerpack is ready for another drive cycle.

The operation of the inventive powerpack is dependent upon the definition of a series of pre-uretight chambers. And, these chambers are defined by a series of floating O-rings. Each floating O-ring is seated in a housing having a depth greater than the diameter of the O-ring. A source of pressurized gs is introduced into the O-ring housing at the deepest region thereof, this application of gas forcing the O ring against the surfaces requiring a gastight seal. With such an O-ring arrangement, efficient sealing is ensured notwithstanding severe wear on the O-ring. And, with such an arrangement,

forwardrnost part of the drive shaft stroke. The air dashpot is defined between the wall of the piston chamber and the forward region of the piston. Both the wall ofthe piston chamber and a mating" surface on the piston having chambers defined therein. This mating takes the form of an air mating wherein the exhaust of air forward of the piston is choked when the piston nears the end of its stroke. This choking action exerts a resistive force on the piston, thus tending to quench the for ward thrust thereof.

As constructed above, the powerpaclt forming a part of the present invention has but two major moving parts. As a consequence, the lit'e ofthe powerpack is substantial and so too is the reliability thereof. At the same time, the manufacturing tolerances are relatively loose.

Accordingly, it is the main object of the present invention to provide a powerpack for transforming pressure forces into rectilinear motion and for doing so in an efficient and reliable manner.

It is another object of the present invention to provide a powerpack having a few major moving parts.

It is a further object of the present invention to provide a powerpack unit whose tolerances are relatively loose when compared with similar units known to the prior art.

It is yet another object of the present invention to provide a powerpaclt able to develop a substantial thrust in a drive shaft, efficiently cushion the thrust of this drive shah, and return the moving parts to their prefiring positions by combining the effects of gas pressure and a single biasing spring.

These and other objects of the present invention, as well as many of the attendant advantages thereof, will become more readily apparent when reference is made to the following description taken in conjunction with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a cross section through a powerpack constructed in accordance with the teachings of the present invention;

FIG. 2 is an enlarged cros section of one of the floating 0- ring seals employed in the powerpack of the present invention;

FIG. 3 is a cross section similar to FIG. I but showing the powerpaclt during a power stroke;

FIG. 4 is a cross section through a typical O-ring sealing arrangement;

FIG. 5 is a cross section similar to FIG. 4 but showing the O- ring seal alter substantial use; and

FIG. 6 is an enlarged cross section showing the air dashpot arrangement used in the powerpack of the present invention.

DETAILED DESCRIPTION OF THE DRAWINGS In FIG. I, a cross section through the inventive powerpack is shown generally at 10. The powerpack 10 comprises an outer casing l2 in which is slidably mounted a drive shaft I. The forwardmost end of the drive shaft l4 (not shown) is the output side of the powerpack and serves to operate any device depending upon a rectilinear motion input for its performance.

The rearwardmost end of the drive shafl 14 takes the form of a piston 16 slidably mounted in a piston chamber 18 defined by an inner casing member 20. The inner casing 20 is maintained in a fixed position within the outer casing 12, sandwiched between a plug 22 and a series of stainless steel shims 24. The shims 24 are, in turn, wedged between the body of the outer casing 12 and the body of the inner casing 20 and serve, basically, as a means for adjusting the stroke of the drive shaft 14. A cap 26, threadably mounted in the rear of the outer casing l2, holds the plug 22, the inner casing 20 and the shims 24 in fixed positions within the outer casing 12.

The only other major movable element in the powerpack ltl, besides the piston I6 and its integral drive shalt I4, is a spool 28. The spool 28 is positioned intermediate the drive shaft 14 and the plug 22 and is held, under conditions of rest, in contact both with the piston I6 ofthe drive shah 14 and the plug 22 through the action of a biasing spring 30.

Carved into the outer casing 12 is a path 32 through which the source of pressurized gas (not shown) feeds the working mechanisms of the powerpack 10. The pressurized gas leaves thecasing l2at34andentersaring36carvedintothebodyof the plug 22. A sintered steel gas filter 38 is set into the plug 22, is held in position by a spacing block 40 and filters the gas leaving the ring 36 and passing through a gas inlet port 42.

Surrounding the gas inlet port 42 is a projecting ring-shaped seal 44; and embedded in the spool 28, adjacent the seal 44, is a disc, as of nylon, adapted to seat against the seal 44 thus preventing the pmage of pressurized gas out of the gas inlet port 42. As seen in FIG. I, the biasing spring 30 urges the piston 16 against the spool 28 which, in turn, seats the nylon disc 46 against the seal 44.

Centrally located in the spool 28 is a threaded bore 48. An orificediscSOisseated atthebaseofthebore48andismaintained in position by a plug 52 threaded into the threads of the bore 48. In the center of the orifice disc 50 is a restrictive opening 54. A gas transfer port 56 leads from the rearwardmost portion of the spool 28 to the rear of the orifice disc 50.

In the rear end of the spool 28, a floating O-ring 58 is housed in a ring-shaped seat 60; and in the forward end of the spool 28, a floating O-ring 62 is housed in a ring-shaped seat 64. FIG. 2 shows an enlarged section of the portion of the plug 22 and spool 28 associated with the O-ring 58.

As best seen in FIG. 2, the gas transfer port 56 communicates with the seat 60 at the deepest region thereof. Similarly, a passage 66 is carved into the spool 28 and leads from the forwardmost surface of the spool 28 into the ringshaped seat 64. A gas bypass 68 is carved into the body of the spool 28 and leads from the forwardmost surface of the spool into an exit chamber 70 which is defined between the floating O-rings 58 and 62.

As noted previously, the drive shaft 14, with its associated piston 16, is mounted for rectilinear motion. The rearwardmost stroke of the drive shaft 14 is defined at the point when the rear of the piston 16 comes into contact with the seated spool 28; and the forwardmost stroke of the drive shaft 14 is defined when a forward face 78 of the piston 16 comes in contact with a shoulder 80 carved into the body of the inner casing 20. Because of the force on the piston 16, the impact between the face 78 and the shoulder 80 could be substantial. Naturally, it is best to avoid substantial impacts between these elements.

For the above reason, the powerpack is provided with two damping mechanisms. The first damping mechanism is in the form of a biasing spring 30 which, at all times, urges the piston 16 toward the spool 28. The second damping mechanism takes the fon'n of a gas dashpot which depends, for its operation, upon the interaction between a chamfer 82 in the rear of the drive shah l4 and a chamfer 84 defined in the inner casing 20, near the shoulders 80. FIG. 5 shows an enlarged cross section of the gas dashpot just described. A complete explanation of the dashpot operation is given below.

To ensure that the pressurized gas is able to properly exit from the power pack 10, the exit chamber 70 is made to communicate with a bore 86 and a ring-shaped groove 88 cut into the body of the plug 22. And, communicating with the groove 88 is a bore 90 through the wall of the casing 12, thereby allowing direct communication between the exit chamber 70 and the atmosphere. A second bore 92 is defined in the body of the casing 12 and serves as a gas communication port between the chamber forward of the piston 16 and the atmosphere.

With reference now to FIG. 2, the operation of each of the floating O-rings will be explained. As seen in FIGS. 2 and 3, provision is made, during the operation of the inventive powerpack 10, for the spool 28 to become unseated from the seal 44. At this occurrence, an inlet chamber 94 is defined and this chamber becomes filled with pressurized gas. The gas then passes through the transfer port 56 and, in so doing, passes into the O-ring seat 60. Simultaneously, the pressurized gas flows from the inlet chamber 94 into the small opening defined between the spool 28 and the plug 22. The arrows 96 represent each of these gas flows.

As seen in FIG. 2, the pressurized gas entering the seat 60, acting with the gas passing between the spool 28 and the plug 22, lodges the O-ring 58 against the wall of the plug 22 and also against the wall of the seat 600a the low-pressure side thereof. This lodging of the O-ring forms an extremely efficient gas seal. Naturally, the O-rings 62 and 72 function in a manner similar to the functioning of the O-ring 58 explained above.

By using floating O-rings, a substantial disadvantage of the known tightly seated O-rings (such as O-

rings

98 and 100 forming seals between the plug 22 and the casing I2) is avoided. This will become readily apparent when reference is directed to FIGS. 4 and 5, taken in conjunction with what has been explained above with reference to FIG. 2.

In FIG. 4, a conventional tightly seated O-ring 102 is shown housed in a seat 104. The seat 104 is carved into a moving piston 106 sliding along a piston wall defined by an external housing 108. Assuming that the high-pressure side of the piston 106 is to the right, there is attempted gas flow in the direction of arrow I10. When the O-ring 102 is new, a tight seal is defined, and, therefore, no gas leakage occurs.

However, after a large number of thrusts of the piston 106, the O-ring 102 becomes worn at the region of frictional contact with the wall of the casing 108. Such wear is illustrated in FIG. 5. In this Figure, it is readily apparent that the worn O- ring 102' is unable to seal, in a gastight manner, the region between the casing 108' and the sliding piston 106'. Instead, when the pressurized gas attempts to flow in the direction of arrow I10, the worn area 112 of the O-ring 102' allows gas leakage past the O-ring 102' as indicated at I 14.

It should be evident from the operation of the floating O- ring illustrated in FIG. 2, that O-ring wear does not adversely affect the seal developed by the O-ring. Since gas pressure is always used to urge the O-ring toward the wall of the piston chamber, an efficient seal is always defined. Therefore, unlike the O-ring shown in FIG. 5, the floating O-ring interrupts the attempted longitudinal flow of gas; and this is the case even after severe O-ring wear.

With reference now to FIGS. 1 and 3, the operation of the inventive powerpack will be described. To initiate the firing operation, the drive shah 14 is moved, in the direction of arrow 116, by any conventional triggering device. As noted previously, a constant source of pressurized gas feeds the inlet ring 36 and, therefore, a constant force is exerted against the nylon disc 46. As a consequence of the above, when the drive shaft 14 is moved in the direction of arrow 1 16, the spool 28 is driven, by pressurized gas pouring through the inlet port 42, toward the left. And, when this occurs, the inlet chamber 94 fills with gas and forces the spool 28 into abuttment with the rear wall of the inner casing 20. This position is shown in FIG. 3.

During the forward movement of the spool 28, the pressurized gas flows through the transfer port 56 and, consequently, into the seat 60. The gas entering the seat urges the floating O-ring 58 toward the wall of the plug 22 and, in

this way, forms a gastight seal between the spool 28 and the plug 22. And, during the forward movement of the spool 28, pressurized gas trapped between the rear of the piston 16 and the front of the spool 28 enters the bore 66, thus filling the seat 64 and forcing the O ring into gastight contact with the inner wall of the plug 22.

The initial movement of the spool 28 brings about slight movement of the drive shaft 14. When, however, the spool 28 is in the position shown in FIG. 3, with the front end of the spool in contact with the wall of the inner casing 20, a large pressure is developed on the rear surface of the piston 16. This will be readily apparent when one notes that the spool, in its forwardrnost position, contacts the wall of the inner casing 20 thus sealing off the gas bypass 68. When this occurs, the gas entering the gas inlet port 42, passes through the transfer port 56 and exerts a pressure on the rear wall of the piston 16. It will be noted that when the pressurized gas reaches the rear wall of the piston 16, the bore 76 and thus the seat 74 fills with gas causing the O-ring 72 to go into gastight contact with the inner wall of the inner casing 20. The substantial pressure exerted on the rear of the piston 16 forces the piston, and thus the drive shaft 14, in the direction of arrow 1 16.

When the drive shaft and piston assembly approach the forwardmost portion of their stroke, the air dashpot, illustrated in FIG. 6, exerts a cushioning force on the movement of the piston. More particularly, the operation of the air dashpot is as follows.

In FIG. 3, the drive shaft 14 is shown somewhere during the intennediate stages of its forward stroke. Here, because of the direct communication between the forward side of the piston 16 and the atmosphere, through bore 92, air is forced from the front of the piston 16 as shown by the arrow l 18. There is little restriction to the flow of air. But, due to the communication between

chamfers

82 and 84, the passage through which the air is allowed to flow rapidly decreases in area as the chamfer surfaces approach one another. In FIG. 5, the relative positions of the chamfers are illustrated shortly before the passage for air is virtually closed 08.

As the chamfer 82 on the piston 16 approaches the chamfer 84 on the inner casing 20, the rapid decrease in flow area through which the air forward of the piston 16 passes, brings about a dashpot action. That is, the flow resistance to the forward thrust of the piston 16, with its integral drive shaft 14, is rapidly quenched due to the restrictive dashpot action. In this manner, the stroke of the piston is quietly yet emciently damped without the necessity for complex damping mechanslms.

Now, with continuing reference to FIG. 3, the remainder of the operation of the powerpack will be described. At a time before the drive shalt l4 and its associated piston 16 have reached their forwardmost positions, the spool 28 reseats itself against the seal 44. This movement of the spool 28 is the result of pressure differentials acting on the two faces of the spool. Just after the spool 28 becomes unseated from the seal 44, the gas pressure exerted against the spool wall defining one wall of the inlet chamber 94 is less than the gas pressure exerted against the spool wall defining one side of what may be termed a piston chamber 120. Therefore, the gas pressure maintains the spool 28 in the position shown in FIG. 3. However, once the pressure in the piston chamber 120 rises, the force exerted on the wall of the spool 28 defining one wall of the piston chamber 120 becomes greater than the force exerted on the wall of the spool 28 defining one wall of the inlet chamber 94. Actually, there is a pressure equalization between the pressure in the inlet chamber 94 and the pressure in the piston chamber 120; however, the area of the spool wall in the piston chamber is larger than the area of the spool wall in the inlet chamber and, as a consequence, the spool is urged in a direction tending to close the gas inlet port 42.

Once the gas inlet port is closed, the piston 16 is acted upon only by inertia and the force exerted by its biasing spring 30. Accordingly, the piston 16, with its integral drive shaft 14, begins its return stroke. The gas filling the piston chamber 120 is expelled from the bore 90 after passing through the gas bypass 68, the exit chamber 70, the bore 86 and the ring shaped groove 88. Once the piston 16 reseats itself on the spool 28, the powerpack lflis ready for another drive operation.

Above there has been described a single embodiment of the present invention. It should be appreciated, however, that this embodiment is described for the purpose of illustration only and that numerous alterations and modifications may be practiced by those skilled in the art without departing from the spirit and scope of the invention. Accordingly, it is the intent that the invention not be limited by the above but be limited only as defined in the appended claims.

I claim:

1. A gas-powered driving unit for converting gas pressure into rectilinear motion in a drive shafi, the unit comprising: a main caing, a hollow defined in the body of said main casing; inlet means for injecting gas under pressure into the hollow of said main casingg: spool slidably mounted within said hollow and, In one post It sealing the inlet means for said gas under pressure; a first ring-shaped seat carved into the periphery of said spool; a first O-ring housed within said seat, the depth of said first seat being larger than the diameter of said first O- ring; a gas transfer port extending from one end of said spool to the other, said gas transfer port communicating with said first seat on the side of said first O-ring remote from the main casing; said first O-ring serving, when pressurized gas flows through said gas transfer port, to provide a gastight seal between the side of said spool adjacent the gas inlet port and the side of said spool remote from the gas inlet port; piston means slidably mounted within said main casing and in one position seating against said spool to efiect saidsealing of the inlet means; a ring-shaped seat defined in the periphery of said piston means; a second O-ring housed within said seat, the depth of said seat being larger than the diameter of said second O-ring; a bore passing from the side of said piston adjacent said spool into said seat on the side of said second 0- ring remote from the main casing; said bore, said seat and said second O-ring associated in such a manner that when pressurized gas is injected into said seat from said bore, the second O-ring forms a gastight seal between the forward and the rearward sides of said piston; means for biasing said piston toward said spool; and means for triggering said unit.

2. The unit defined in claim 1, wherein the face of said spool adjacent said inlet port has an area smaller than the area of the face of said spool remote from said inlet port.

3. The unit defined in claim 2, and further comprising means for filtering the gas entering said inlet port.

4. The unit defined in claim 2, and further comprising means for cushioning the forward thrust of said piston at the forwardmost portion thereof.

5. The unit defined in claim 4, wherein said cushioning means is in the form of an air dashpot.

6. The invention recited in claim 5, wherein said dashpot is defined by a chamfer on the forward face of said piston and a mating chamfer on the sidewall of said main casing.

7. The unit recited in claim 6, wherein the largest diameter of said chamfer on said piston is smaller than the smallest diameter of said chamfer on said main casing.

8. The unit defined in claim 2, and further comprising: a second ring-shaped seat carved into the periphery of said spool; a third O-ring housed within said second seat; and a bore passing from the side of said spool adjacent said piston into the second seat on the side of said third O-ring remote from the main casing.

9. The unit defined in claim 8, and further comprising a gas bypass between the area defined intennediate said first and third O-rings and the area defined intermediate said spool and said piston.

10. The unit defined in claim 9, and further comprising means for ejecting the pressurized gas from the main casing to the atmosphere.

Claims

1. A gas-powered driving unit for converting gas pressure into rectilinear motion in a drive shaft, the unit comprising: a main casing, a hollow defined in the body of said main casing; inlet means for injecting gas under pressure into the hollow of said main casing; a spool slidably mounted within said hollow and, in one position sealing the inlet means for said gas under pressure; a first ring-shaped seat carved into the periphery of said spool; a first O-ring housed within said seat, the depth of said first seat being larger than the diameter of said first O-ring; a gas transfer port extending from one end of said spool to the other, said gas transfer port communicating with said first seat on the side of said first O-ring remote from the main casing; said first O-ring serving, when pressurized gas flows through said gas transfer port, to provide a gastight seal between the side of said spool adjacent the gas inlet port and the side of said spool remote from the gas inlet port; piston means slidably mounted within said main casing and in one position seating against said spool to effect said sealing of the inlet means; a ring-shaped seat defined in the periphery of said piston means; a second Oring housed within said seat, the depth of said seat being larger than the diameter of said second O-ring; a bore passing from the side of said piston adjacent said spool into said seat on the side of said second O-ring remote from the main casing; said bore, said seat and sAid second O-ring associated in such a manner that when pressurized gas is injected into said seat from said bore, the second O-ring forms a gastight seal between the forward and the rearward sides of said piston; means for biasing said piston toward said spool; and means for triggering said unit.

9. The unit defined in claim 8, and further comprising a gas bypass between the area defined intermediate said first and third O-rings and the area defined intermediate said spool and said piston.