US3925985A

US3925985A - Impact actuator

Info

Publication number: US3925985A
Application number: US322110A
Authority: US
Inventors: Carl R Peterson
Original assignee: Rapidex Inc
Current assignee: Rapidex Inc
Priority date: 1973-01-09
Filing date: 1973-01-09
Publication date: 1975-12-16
Anticipated expiration: 1992-12-16
Also published as: CA992432A; JPS4998701A; BR7400085D0; FR2325294A7; SE399200B; AU6412074A; DE2400925A1; GB1446096A

Abstract

Actuators capable of repeated impacts in which a hydraulically driven follower follows the expansibly driven impact member. Also shown are constant input and output hydraulic flows valved alternately between an impact member - returning motion which recompresses the expansible drive, and a following motion causing the follower to follow the suddenly accelerated impact member. The follower is shown to control these flows by means of a slave valve operated by changes of pressure attributable to the position of the parts. In the linear actuator embodiments shown a stationary tube between the linear piston and the moving follower sleeve separates the follower drive chamber from the expansible medium in one illustrated embodiment and a follower drive chamber formed along the side of the piston is featured in another illustration.

Description

United States Patent [1 1 Peterson 1 Dec. 16, 1975 [21] Appl. No.: 322,110

[52] U.S. C1. 60/371; 91/165; 91/231;

91/309; 91/313; 91/321; 91/402; 92/134 [51] Int. Cl. FOIL 25/06; FOIB 7/18 [58] Field of Search 91/230, 231, 235, 313,

[56] References Cited UNITED STATES PATENTS 1,429,786 9/1922 Smith 91/231 1,626,087 4/1927 Hultquist 91/231 2,997,849 8/1961 Shimanckas.. 91/402 3,411,592 11/1968 Montabert.... 91/321 3,524,385 3/1970 Ottestad 91/235 3,583,158 6/1971 Foster 91/235 3,595,133 7/1971 Foster 91/390 3,687,008 8/1972 Densmore 91/276 3,735,823 5/1973 Terada 173/119 DISCHARGE Fisk 92/134 Phillips 91/165 Primary Examiner-Paul E. Maslousky 5 7] ABSTRACT Actuators capable of repeated impacts in which a hydraulically driven follower follows the expansibly driven impact member. Also shown are constant input and output hydraulic flows valved alternately between an impact member returning motion which recompresses the expansible drive, and a following motion causing the follower to follow the suddenly accelerated impact member. The follower is shown to control these flows by means of a slave valve operated by changes of pressure attributable to the position of the parts. In the linear actuator embodiments shown a stationary tube between the linear piston and the moving follower sleeve separates the follower drive chamber from the expansible medium in one illustrated embodiment and a follower drive chamber formed along the side of the piston is featured in another illustratron.

19 Claims, 7 Drawing Figures U.S. Patent Dec. 16,1975 Sheet10f4 3,925,985

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FIG. I

US. Patent Dec. 16,1975 Sheet2of4 3,925,985

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US. Patent Dec. 16, 1975 Sheet 3 of4 3,925,985

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US. Patent Dec. 16, 1975 IMPACT ACTUATOR FIELD OF INVENTION The present invention relates to impact delivering devices as might be used for rock drilling, pavement breaking, forging, pile driving, impact wrenches, etc., and in particular to such devices as powered by high pressure hydraulic fluid.

BACKGROUND OF INVENTION Actuators capable of delivering repeated impacts to a variable position, whether in straight or rotary motion, are known. Those to which the present invention relates are of the type in which an elastic or expansible drive, e.g. a trapped volume of pre-compressed air or a spring, is exposed to the impact member to drive it. Countervailing hydraulic pressure controlled by the follower is used in the cycle to return the impact member and recompress the expansible drive prior to initiation of the next impact. It is known to return the follower with the impact member and to employ automatic triggering arrangements. One such known arrangement involves venting of the hydraulic return fluid when the impact member reaches the return position' whereby restraint upon the expansible drive is suddenly removed.

While operable to advantage, such known devices have involved large and expensive components, undesirable limitations on impact rate and design, and other drawbacks which it is the object of the present invention to improve upon.

BRIEF DESCRIPTION OF FEATURES AND ADVANTAGES OF THE INVENTION The invention features use of hydraulic drive for the follower as it follows the impact member, and use of a hydraulic system including a positive displacement constant flow rate source of hydraulic fluid, which alternately is caused to drive the impact member in its return direction and the follower in its following direction.

Preferred embodiments of the invention feature: a trigger effective to release the impact member and actuate the separate motion of the follower, preferably the trigger in the form of a hydraulic vent; use of return drive pressure to hold a directional slave valve to vent the follower drive while causing the return of the impact member; and employing the trigger vent-reduced pressure to reverse the valves, to apply pressure to the follower while venting the impact member return system. Preferred embodiments feature a linear actuator construction of simple design. Other features are mentioned in the Abstract.

Regarding advantages of the present invention it is noted that certain prior through-flow hydraulic impacting devices, including one invented previously by the present inventor, have had very unsteady flow, particularly in the discharge line where flow rate may vary between zero and double or more the average value. Such devices use expansible means (e.g., compressed gas) to restore a follower or sleeve to a downward position to begin a subsequent cycle. According to the present invention I have realized that such construction are un-needfully limited in efficiency (energy expended by the elastic member in moving the follower sleeve is wasted) and in descent rates and, hence, blow frequency. A gas chamber, used as an energy storage device, must remain at pressure below hydraulic fluid pressure in such devices.

In contrast the present invention can achieve nominally constant flow rates in both inlet and discharge lines at all times. Its sleeve or valving unit, being positively driven in both directions, permits higher frequency operation. It may utilize gas or other energy storage mechanisms at pressures higher than hydraulic fluid pressure, thus allowing a smaller energy storage device or chamber.

These and other objects, features and advantages will be understood from a description of a preferred embodiment taken in conjunction with the drawings wherein:

FIG. 1 is a cross section of the presently preferred embodiment of the invention.

FIGS. 2a-d are similar cross-sections at different times in the operating cycle.

FIG. 3 is a similar cross-section for the special case of piston overtravel.

FIG. 4 is a partial view of an alternate construction of the top of the unit of FIG. 1.

DESCRIPTION OF A PREFERRED EMBODIMENT OF THE INVENTION Referring to FIG. 1, the device consists of a housing 11, a piston 10, and a sleeve 12. As shown the piston is generally rod-like and of constant diameter except for an enlargement 10a in the center. A relatively thinwalled tube 13, extends from the housing and its inner surface makes a sliding seal with the upper portion of the piston. Gas is stored in chamber 14 defined by this tube 13, the housing 11, and the top of the piston 10. Gas charging valve is shown at 15, where gas is injected into chamber 14 at intervals to make up for leakage from chamber 14. The movable sleeve 12, slidingly seals on the outer surface of tube 13 and the inner surface of housing 11. The sleeve 12 is flared at 12a at its lower end and shaped to seal against the piston enlargement at 16. The sleeve contains a number of longitudinal internal holes 17, communicating radially through short holes 17a with its outer surface at 18. A number of external short, axially extending slots, 19, are provided in the sleeve in such position as not to communicate with holes 17. The piston 10, piston enlargement 10a, sleeve 12, and tube 13, define an annu lar volume of fluid at 20.

The housing 11 includes an upper bore 11a, sized to seal slidingly with the sleeve 12 and a second, next lower bore 11b of enlarged diameter making no seals with any moving parts. A third, next lower bore 110, of short axial dimension, again is sized to seal slidingly with the sleeve and defines with the outer surface of sleeve 12 and upper parts of the housing an annular volume 22.

Below bore the housing has a bore lle of larger dimension than those above, defining a region for free axial movement of the enlargement 10a of the piston, and of the flared end 12a of piston 12, with ample space S for displacementof fluid about the periphery of these members when they move.

The lower-most bore 11f of the housing slidingly seals against the piston.

The housing contains a lower port, 23, communicat ing with the enlarged lower housing volume 23", a vent, 24, communicating with the volume 22, and an upper port 25, communicating with volume 15'', the volume above the sleeve 12.

The volume 14 is filled with gas to the desired pressure. Except for leakage, this operation is not repeated.

Referring to FIG. 2a, the unit is combined with an ordinary two-position reversing valve shown schematically at 26. It contains an internal shuttling member or spool 27 that is biased upwardly by springs at 28. The valve is connected to a pump 29 of the positive displacement, constant flow type, through line 30, and to a return reservoir (not shown) through line 31. Opposite ends of the valve spool 27 are pressurized from these two lines through lines 30' and 31'. The valve is connected to the hammer as shown with line 23 to port 23 and volume 23", line 25 to port 25 and volume 25". Vent 24 is connected through line 24' to the reservoir line 31.

In operation, starting with the position of FIG. 2a, similar to FIG. 1, inflow from the pump is entering volume 23". Volume 20, between sleeve and piston, is at low pressure, sealed from 23" at 16 (FIG. 1) and vented through

holes

17, 17a, 18, volume 22, port 24 and line 24 to the reservoir. Volume 25 is also vented to the reservoir. The outer diameter of the main body of sleeve 12 is less than the diameter of the seal at 16, hence there is a net downward force acting upon the upper surface of the flare 12a, holding the sleeve to the piston as suggested by arrows at 32. High pressure inflow at 23' to volume 23" then pushes the piston and sleeve combination upward as a unit, venting fluid to discharge from volume 25" and from annular volume 20. This same high pressure of the pump fluid (determined by the resistance of the gas pressure in volume 14 and the appropriate piston areas) acts through line 30' to keep valve 26 in the down position shown, with spring 28 compressed. Upward motion of piston continues until the position shown in FIG. 2 b is reached. Here, slots 19 short circuit the sea] at the bottom of volume 22 allowing flow from main volume 23" into volume 22 and thence into volume and out vent line 24'. The net effect is a reduction in pressure in volume 23" and an increase in pressure in volume 20 until the net force acting across piston enlargement 10a is no longer sufficient to hold the piston 10 upward against gas pressure in volume 14, albeit sleeve 12 still moves upwardly due to pressure differential across it caused by continued inflow to volume 23". The seal at 16 is thus broken and the pressure differential across enlargement 10a is completely destroyed. The piston is thus triggered" and free to move downward rapidly under the influence of compressed gas in volume 14, here without any displacement of hydraulic fluid from volume 23" because the two ends of the piston are of equal diameter. Once seal 16 is broken, pressures in

volumes

23 and 25" tend to equalize across the equal area ends of sleeve 12. Thus pressures in lines and 31 become equal, at vent pressure, as do pressures in

lines

30 and 31, so that the valve spool 27 switches to the position shown in FIG. 2b under the influence of spring 28. Then as in FIG. 20, inflow is directed into volume 25", pushing sleeve 12 downward (the piston 10 having already descended rapidly and delivered its blow). Downward motion of sleeve 12 pushes fluid out of volume 23 through line 23' (some will also exit through holes 17 and line 24' Outflow through line 31 will equal inflow through line 30. Because the frontal area of sleeve 12 is less than the effective upstroke piston area in this embodiment (by the frontal area of tube 13), the downward velocity of sleeve 12 will, using the same flow rate in the two different phases, be

greater than the upward velocity of the piston-sleeve combination. Pressures in volumes 23" and 25 during downstroke of sleeve 12 will be about equal and valve 26 will remain as shown in FIG. 20 for the entire downstroke.

When the sleeve 12 seats downwardly against the piston as in FIG. 2d it can descend no further (e.g. a bit at the lower end of the piston being firmly in contact with the rock by virtue of hold-down force on the entire unit). Fluid can no longer enter volume 25 and having no place else to go, it will flow through line 30, rising in pressure as necessary to displace the spool 27 and compress spring 28. The sleeve is thus firmly seated on the piston, sealing at 16, with volume 20 returned to low pressure. With the valve switched as in FIG. 2d, then, flow enters volume 23" where, because of resistance to upward movement of piston and sleeve by residual gas pressure in 14, it immediately assumes a relatively high pressure thus keeping valve 26 in the position shown for the upward stroke. The cycle then repeats.

FIG. 3 illustrates the special case when the bit 50 at the end of the piston has dropped away and the piston overtravels to the position shown, stopped by a mechanical stop (with snubbing action) shown schematically at 40. In most applications it is desirable to have the piston stop cycling when this occurs. This can be provided as shown by having the top of sleeve 12 travel below the top of volume 22, as at 41, before it travels sufficiently downward to make a seal at 16 with the now depressed piston. Inflow at 25 will now flow out vent 24 and also through holes 17, volume 20, the open seal 16, volume 23", and line 23. There will thus be no pressure build up in volume 25" and the valve 26 will not switch. To restart, the bit 50 must be pushed relatively back up against the piston (i.e., the housing lowered) sufficiently to make a seal at 16 and close the gap at 41. Pressure in volume 25" will then build up and the valve 26 will switch, starting a new cycle.

Referring to the embodiment of FIG. 4, an integral housing casting 11' which forms the bores 11a and 1 lb, etc., has an uppermost bore 11g above and of smaller diameter than bore 11a. A constant diameter portion of piston extends entirely through sleeve 12 into sealing contact with bore 11g throughout the operating range, forming compressed gas chamber 14. By this construction the necessity of sleeve 13 of FIG. 1 is avoided.

The dashed lines of FIG. 4 illustrate an automatic filling arrangement useful when volume 14 is sized to receive hydraulic fluid to provide a hydraulic spring for driving the impact member. For filling or for refilling to make up for loss, the upper dashed line receives fluid from the pump (line 30) through check valve 14. The lower dashed line leads to vented discharge. This vent is positioned just below the piston top edge when the piston is at its normal impact point. This will enable volume 14 to be vented as the piston returns from an abnormally low position (as in FIG. 3), and thereby sets the maximum amount of hydraulic fluid trapped in volume 14, and thus avoids build-up of excess pressure in volume 14 during operation. The construction shown in FIG. 4, in which volume 14 is formed by the housing, can be made very ruggedly and is suitable for the pressures associated with use of hydraulic fluid as the spring for driving the impact member.

Instead of these constructions for instance: a radially floating separately formed stationary tube 13 could be employed; instead of compressed gas other compressible material or mechanism could act upon the piston or hydraulic fluid as just mentioned; the ends of the piston could be of different area with provision for flow of displaced fluids; the entire reciprocating structure could be of rotary rather than linear arrangement; all fluid can be made to exit chamber 23 through hole 17 and port 24, etc.

These and other variations in the specific details shown are within the spirit and scope of the following claims.

What is claimed is:

1. In an actuator capable of delivering repeated impacts to a variable, stopped position comprising the combination of an impact member movable back and forth relative to said position, an expansible drive for driving said member toward said position while expanding, and a return for returning said impact member and recompressing said drive, said return including a follower which follows said impact member to its variable stopped position and a hydraulic system enabled by said position of said follower to apply return force to said impact member, the improvement wherein said hydraulic system includes a hydraulic drive for said follower in the following direction, a valve separate from said follower and impact member effective to direct said flow alternately to drive said follower in following direction and drive said impact member in its return direction and a control for actuating said follower drive upon said driving of said impact member.

2. The actuator of claim 1 wherein said hydraulic system includes a source of hydraulic fluid which comprises a positive displacement constant flow pump and said impact member has a constant cross-section at its opposite end regions whereby movement of said impact member does not displace hydraulic fluid.

3. The actuator of claim 1 including a trigger, said follower being returnable by said hydraulic fluid with said impact member, and said trigger being effective both to release said impact member to be driven by said expansible drive and to actuate said control for separate following motion of said follower drive.

4. The actuator of claim 3 wherein said trigger comprises a vent opened by said impact member and follower reaching said return position, said vent operable both to relieve the net hydraulic return pressure upon said impact member to the point where it is overcome by said expansible drive and to actuate said control.

5. The actuator of claim 4 wherein said valve is held in a first position by pressure returning said impact member, the valve effective to admit return fluid to said impact member and to vent said follower drive, and said vent effective, through relief of return pressure, to operate said valve to a second position to apply hydraulic pressure to and control said follower drive.

6. The actuator of claim 5 wherein said vent is also effective to open a further vent of said impact member return.

7. The actuator of claim 5 wherein said valve is operative in said second position to apply the pressure of said follower drive to said valve upon buildup of pressure in said follower drive associated with said follower reaching said impact member, said pressure operative to reverse said valve to said first position.

8. The actuator of claim 4 wherein said trigger is formed by mating portions of said follower and impact member providing a seal when seated and creating pressure conditions whereby said impact member and follower are returned as a unit, and in the return position said vent operative to break said seal and expose a surface of said impact member to forces concelling return forces.

9. The actuator of claim 8 wherein said follower and said impact member when seated together define a fluid volume, said fluid volume vented through a passage in said follower to a low pressure region, said follower having a surface portion exposed to hydraulic pressure effective to press said follower and impact member together and prevent relief through said passage of pressure acting upon said impact member, and said vent operative to introduce hydraulic pressure to said fluid volume tending to break said seal.

10. The actuator of claim 1 wherein said follower telescopes upon said impact member in response to said follower drive.

11. The actuator of claim 10 in the form of a linear actuator wherein said impact member comprises a reciprocable piston having an enlarged middle portion, said follower comprises a sleeve linearly telescopically fitted about the exterior of said piston, having a flared end engageable upon said enlarged middle portion of said piston and having an oppositely directed surface exposed to said hydraulic follower drive.

12. The actuator of claim 11 including a housing forming a first chamber into which said piston and flared end of said sleeve extend, a first hydraulic line connected thereto for said hydraulic return, a second chamber to which said oppositely directed surface of said follower is exposed, a second hydraulic line connected thereto for said follower drive, a third chamber intermediate said first and second chambers and normally sealed therefrom, a third hydraulic line connected thereto for venting, a passage extending from said third chamber to the space between said flared end of said sleeve and said enlarged portion of said piston, and a vent passage in the exterior of said sleeve positioned so that when the sleeve is in its return position, said first chamber is vented to said third chamber.

13. The actuator of claim 12 including a positive displacement, constant flow hydraulic pump and a valve effective alternately to direct flow to said second line and exhaust from said first line and vice versa.

14. The actuator of claim 13 wherein a branch from the outlet of said pump is connected so that pressure therefrom urges said valve toward a first position directing said flow to said first line and exhaust from said second line, said valve constructed so that relief of said pressure on said branch line causes said flows to be reversed.

15. The actuator of claim 1 in the form of a linear actuator wherein said impact member comprises a linear piston, a stationary tube in which the inner end of said piston is fitted, the inner end of said piston and the interior of said tube cooperating to form a volume for an expansible gas drive and said follower comprising a sleeve slidably engaged upon the exterior of said tube and forming therewith a hydraulic chamber for said follower drive.

16. The actuator of claim 1 in the form of a linear actuator wherein said impact member comprises a linear piston, said follower comprising a sleeve slidably engaged upon the exterior of said piston, said housing and a portion of the side of said piston forming a hydraulic chamber for said follower drive, said piston extending beyond said chamber in sealed relation into a further chamber, the end of said piston disposed in said further chamber and exposed therein to an expansible fluid drive.

17. The actuator of claim 1 in the form of a linear actuator wherein said impact member comprises a linear piston including a housing defining a bottoming position for said impact member in the absence of a workpiece at the impactreceiving position, said follower and housing cooperatively constructed to vent said follower drive prior to said follower reaching said impact member in said bottoming position, thereby preventing said follower from reaching the position for enabling application of return forces to said piston.

18. The actuator of claim 16 wherein said further chamber is connected to a supply of makeup fluid through a check valve that permits inflow but not outflow to said further chamber, and a'vent line from said further chamber that is exposed when said impact member travels beyond a position predetermined to limit the maximum fluid trapped in said further chamber.

19. An actuator capable of delivering repeated impacts to a variable position comprising the combination of an impact member movable back and forth relative to said position, an expansible fluid drive for driving said member toward said position while expanding, and a return for returning said impact member and recompressing said drive, said drive consisting of a volume of fluid connected through a check valve to a supply of makeup fluid to allow inflow to said volume of fluid but not outflow from said volume of fluid, and a vent from said volume of fluid opened by said impact member upon overtravel beyond a predetermined position and closed by said impact member upon return travel back to said predetermined position said vent thereby being adapted to vent excess fluid at low pressure before it is recompressed by return motion of said impact member whereby said vent is effective to limit the maximum quantity of fluid trapped as said volume of fluid.

Claims

7. The actuator of claim 5 wherein said valve is operative in said second position to apply the pressure of said follower drive to said valve upon build-up of pressure in said follower drive associated with said follower reaching said impact member, said pressure operative to reverse said valve to said first position.

18. The actuator of claim 16 wherein said further chamber is connected to a supply of makeup fluid through a check valve that permits inflow but not outflow to said further chamber, and a vent line from said further chamber that is exposed when said impact member travels beyond a position predetermined to limit the maximum fluid trapped in said further chamber.