US3695366A

US3695366A - Hydraulic hammer with back pressure isolation

Info

Publication number: US3695366A
Application number: US87966A
Authority: US
Inventors: Ernst F Klessig
Original assignee: Worthington Corp
Current assignee: Dresser Rand Co; Worthington Corp
Priority date: 1970-11-09
Filing date: 1970-11-09
Publication date: 1972-10-03
Anticipated expiration: 1989-10-03
Also published as: DE2155701A1; GB1360446A; CA935354A; DE2155701C3; DE2155701B2; FR2113667A5; AU3542071A

Abstract

An improved hydraulic hammer constructed to eliminate frequency variations in operation due to fluctuating back pressure. A flow path from a hammer operating piston to a fluid outlet is provided with a venturi to isolate the piston from fluctuation in back pressure downstream of the restriction.

Description

' United States Patent Klessig HYDRAULIC HAMMER WITH BACK PRESSURE ISOLATION Inventor: Ernst F. Klessig, Racine, Wis.

Assignee: Worthington Corporation (Worthington Compressor and Engine International Division), Holyoke, Mass.

Filed: Nov. 9, 1970 Appl. No.: 87,966

[1.8. CI ..l73/l34, 173/17 Int. Cl. ..E2lb 1/00 Field of Search ...l 73/134, 17; 91/404, 407, 394

References Cited UNITED STATES PATENTS 2,881,739 4/1959 l-luppert 173/134 1 1 Oct. 3, 1972 3,213,615 10/1965 Bjiirnberg ..l73/l34 X FOREIGN PATENTS OR APPLICATIONS 819,486 8/1969 Canada 173/1 34 Primary Examiner-David H. Brown Attorney-Hofgren, Wegner, Allen, Stellman & Mc- Cord 5 7] ABSTRACT 6 Claims, 1 Drawing Figure HYDRAULIC HAMMER WITH BACK PRESSURE ISOLATION BACKGROUND OF THE INVENTION Over the years, various forms of demolition work have been accomplished in part through the use of power hammers. In recent years, after extended research and development programs, various concerns have developed, for commercial production, a type of power hammer that is driven by hydraulic fluid under pressure. Such hydraulic hammers perform work as efficiently and more economically than the type of power hammer, specifically an air hammer, previously used most frequently and without the high noise level attendant the operation of an air hammer.

This principal advantage of a hydraulic hammer has resulted in ever increasing use of the same. However, hydraulic hammer constructions still require further improvement of various peripheral facets of their operation. For example,; one difficulty common to many existing commercial hydraulic hammer constructions is the undesirable, uncontrolled variations in the frequency of reciprocation of the hammer element. Specifically, it is quite typical of hydraulic hammers to drive a piston associated with a hammer in one direction within a housing by applying fluid under pressure to one side of the piston and connecting the other side of the piston to a fluid outlet. When variations in back pressure in the fluid flow path extending from the piston to the outlet occur, the resistance opposing the driving of the hammer element varies and the rate at which the hammer element is driven will therefore vary.

One attempted solution to the foregoing problem has been to employ'a check valve in the'outlet line. To the extent that such a valve will open when'the pressure differential across the same exceeds a predetermined value, such a valve has been partially successful in alleviatingfrequency variations due to back pressure. However, because the valve will open only when a predetermined pressure differential exists across it, an increased back pressure downstream from the valve will require a higher pressure upstream of the valve and downstream of the piston before the valve will open. Thus,the back pressure applied to the piston can still vary through a substantial range even with the use of such valves and 'cause variations in operational frequency of the hammer.

SUMMARY OF THE INVENTION application of hydraulic fluid under pressure to one side thereof and through successive return strokes by the continuous application of hydraulic fluid under pressure to an opposed surface on the piston having a lesser size than the first mentioned surface. During return stroke, the first mentioned surface is connected to a fluid outlet. Sequencing is provided by a control valve shiftable within the hammer casing to connect the first surface to a fluid inlet at the beginning of each power stroke and to connect .the first surface of the piston to the outlet at the beginning of each return stroke. v

The means for isolating the first surface of the piston from back pressure variations comprises a venturi located downstream of the first surface and in the flow path established therebetween and the outlet during the return stroke of the hammer. In the most advantageous form, the venturi is defined by'an annular projector on a spool serving as the control valve, which land is of lesser diameter than a bore in which the spool reciprocates. When the spool is in a position to connect the first-mentioned piston surface to the outlet, the projection, in conjunction with the bore in which the spool is received, defines an annular venturi between the first piston surface and the outlet and isolates back pressure variations downstream of the venturi from the flow path connecting with the piston first surface upstream of the venturi.

Other objects and advantages of the invention will become apparent from the following specification taken in conjunction with the accompanying drawing.

DESCRIPTION OF THE DRAWING The FIGURE illustrates a preferred form of a hydraulic hammer embodying the invention.

DESCRIPTION OF THE PREFERRED EMBODIMENT An exemplary embodiment of a hydraulic hammer made according to the invention is illustrated in the FIGURE and is seen to include a casing, generally designated 10, having a central bore 12 therein. Disposed within the bore 12 for reciprocation therein is a hammer element, generally designated 14, having an upper end including an annular reduced diameter portion 16 and a pressure responsive piston 18. The hammer element 14 also includes a lower, enlarged hammer 20 which is disposed within an enlarged diameter portion 22 of the bore 12.

Secured to the lower end of the casing 10 is a tool mount 24 having a central bore 26 receiving a movable tool 28 which is disposed to be struck by the hammer 20 and which has a lower, work performing end (not shown). Alternatively, that portion of the tool 28 illustrated could be an anvil having its lower end operatively associated with a selected tool to be used in conjunction with the hammer. For example, the lowerend of such an anvil may ride on the upper end of the tool. The tool 28 includes a key way 30 and a key 32 which extends through the tool mount 24 and the key way 30 to restrict the movement of the tool 28 within the tool mount 24 to the length of the key way 30.

The casing 10 includes an inlet 34 which may be connected to any suitable source of hydraulic fluid under pressure to serve as 'a source of energy for reciprocating the hammer 20 within the casing 10 to impart energy to the tool 28. In fluid communication with the inlet is a conventional accumulator 36. The casing 10 further includes an outlet 38 and a second accumulator 40 in fluid communication with the outlet 38.

A port 42 transverse to the bore 12 in the casing and in fluid communication with the inlet 34 is arranged to permit the application of fluid under pressure to a lowermost surface 44 of the piston 18 of the hammer element 14. As will be seen, this application of fluid under pressure serves to move the hammer element l4 upwardly in the bore 12 for its return stroke. A series of small grooves 45 extend upwardly partially to the port 46 from the port 42 for purposes to be seen.

A port 46 normally in fluid communication with the port 42 through the bore 12 and reduced diameter portion 16 provides fluid under pressure to a hydraulically operated control valve spool, generally designated 50, which is operative to control the reciprocation of the hammer element 14 within the bore [2. The spool 50 includes a reduced diameter portion 52. The spool 50 is shiftable within a bore 54 to a first position (illustrated in the FlGURE) wherein fluid under pressure from the inlet 34 passing through the port 42 and the port 46 is fed along the reduced diameter portion 52 to the upper end of the bore 12 via a conduit 56 in communication with both the bore 54 and the bore 12 and applied to an upper surface 58 on the piston 18 of the hammer element 14. The surface 58 is larger than the surface 44 so that when fluid under pressure is applied to the former, notwithstanding the fact that fluid under pressure is also applied to the latter, the hammer element 14 will be driven downwardly to strike the tool 28. a

A second position of the spool 50 within-the bore 54 is one wherein the spool 50 is shifted upwardly from the position shown in the FIGURE and wherein an enlarged lower end 60 blocks off the path of fluid under pressure from the inlet 34 to the upper end of the bore 12 while an enlarged upper end 62, in conjunction with the reduced diameter portion 52 permits fluid in the upper end of the bore above the surface 58 to exit to the outlet 38 via a conduit 64. lnterposed between the conduit 64 and the outlet 38 and hydraulically prior to the point of connection of the accumulator 40 to the outlet 38 is a restriction or orifice 65 for purposes to be seen. When the spool 50 is in the just-mentioned position, the fact that the pressure sensitive surface 58 is subjected to outlet pressure while the pressure sensitive surface 44 is subjected to inlet pressure will cause the hammer to move upwardly for its return stroke.

Positioning of the spool 50 is controlled by a differential pin device including pins 66 at the lowermost end of the spool 50 and pins 68 at the opposite end thereof. The pins 66 have a lesser efi'ective area than the pins 68 and are continuously subjected to inlet pressure. The pins 68 are intermittently subjected to inlet pressure dependent upon the position of the hammer 14 within the bore 12 and when such is the case, the spool 50 will be driven by the pins 68 to the position shown. When such is not the case, the pins 66 will drive the spool 50 upwardly to the second mentioned position above. For a more detailed statement of the operation and specific construction of the differential pin device, reference may be had to US. Letters Patent No. 3,399,602 to Klessig et al., the details of which are herein incorporated by reference.

As mentioned previously, one of the difficulties encountered in the operation of hydraulic hammers is variations in the frequency of operation principally due to varying back pressure. Specifically, the rate of return of the hammer element during the return stroke will be generally dependent upon the ratio of the area of the smaller surface 44 and the pressure applied thereto to the area of the larger surface 58 and the pressure applied thereto. And since, during return, the latter surface is subjected only to outlet pressure, an increased back pressure will cause a slower rate of return than would be the case with little or no back pressure present. Accordingly, the exemplary embodiment of the invention includes means by which the back pressure against the surface 58 during the return stroke of the hammer element 14 is maintained constant so that cycling frequency will be constant.

Specifically, a venturi, generally designated 70, is located in the flow path from the upper endof the bore 12 to the outlet 38 and which is established when the valve 50 is in the second position mentioned above. The venturi 70 is carried on the upper end of the reduced diameter portion 52 of the spool 50. The venturi 70 is generally defined by an annular projection having a diameter less than the diameter of the bore 54 and greater than that of the reduced diameter portion 52; an upstream tapered short side 74; and a downstream tapered long side 76. That is, the longitudinal extent of the upstream side 74 of the projection 72 is less than the longitudinal extent of the downstream side 76.

When the spool 50 is moved upwardly to the second mentioned position, the same, in conjunction with a portion 78 of the bore 54 interposed between the conduit 56 and the conduit 64 define an annular venturi. The annular venturi effectively isolates the pressure in the conduit 56 from pressure variations normally encountered in the return conduit 64.

It should be specifically noted that while the exemplary embodiment employs a venturi on the spool 50, the same could be located at any one of a variety of downstream points in fluid communication with the outlet 38. However, because the casing 10 is generally fonned as a casting and the various conduits contained therein are frequently defined by bores, the forming of a restriction in one of the conduits would require a rather complex machining or casting operation. In contrast, the formation of the venturi 70 on the spool 50 may be accomplished relatively easily during the formation of the reduced diameter portion 52 thereon.

The exemplary embodiment further includes a bypass conduit 80 which extends between the inlet 34 and the outlet 38 and which is normally closed by a bypass valve, generally designated 82. The bypass valve 82 is mounted for reciprocation within a bore 84 in the casing 10. One end of the bore 84 is closed by a plug 86 which serves to position a spring 88 in a recess 90 formed in the body of the valve member 82 to bias the valve member 82 against a seat 92 surrounding the bypass conduit 80.

The bypass valve 82, intermediate its ends, includes a reduced diameter portion 93 which normally permits fluid under pressure to flow from the inlet 34 to the port 42 for use in driving the hammer in the manner mentioned previously. The bypass valve 82 further includes a pair of pressure

responsive surfaces

94 and 96 with the surface 94 being larger than the surface 96. The recess 90 terminates in a third pressure sensitive surface 98 on the valve 82. The arrangement is such that the combined areas of the

surfaces

96 and 98 is greater than the area of the surface 94 but the surface 94 is greater in size than the surface 96 alone. More particularly, the

surfaces

94, 96 and 98 and the spring 88 act such that when'inletpressure is applied against the surface 96 and the surface 94 (as will always be the case) and is applied to the surface 98 (as will usually be the case) the valve 82 will be in the position shown. However, when inlet pressure is not applied to the surface 98, the valve will shift downwardly from the position shown to open the bypass 80 whereupon fluid under pressure from the inlet 34 will flow directly to the outlet 38 bypassing entirely the control valve 50. As

a result, reciprocation of the hammer element will cease.

the surface 98 via the port 42 and a section 100 of the bore 12 interconnectingthe port 42 and a port 102. The bore section 100 is of slightly greater diameter than the shank of thehammer element 14 but, for-purposes to be seen, is of the same diameter as the diameter of the piston 18. a

The relief of fluid pressure against the surface 98 so as to permit the valve 82 to open for bypass purposes is accomplished by means ofa port 104 in the bottom of a stationary sleeve 1106 embracing the shank of the hammer element 14. Also-included are a series of small grooves 105 extending upwardly a short distance from the port 104 to permit the establishment of fluid communication to the port 104 through the bore section 100 slightly before the reduced diameter portion moves to the upper boundary of the port 104. A channel 108 is in fluid communication with the port 104 and a bore 110 which empties into the hollow center 112 of the spool 50. From the hollow center 112, fluid may flow through a radial bore 114 in the uppermost end of the spool 50 to the conduit 64 to the outlet 38. The arrangement is such that when the hammer element 14 has been driven downwardly past a position wherein it would normally encounter the tool 28 and not yet has encountered the tool, the side of the piston 18 will enter the bore portion 100 thereby blocking fluid communication between the inlet 34 via the port 42 to the surface 98. Simultaneously, the reduced diameter portion 16 on the hammer element 14 will establish fluid communication between the port 102 and the port 104 thereby permitting the fluid under pressure bearing against the surface 98 to flow to the outlet 38 via the path mentioned previously.

This relieving of the pressure against the surface 98 will cause the inlet pressure to shift the valve 82 downwardly thereby permitting fluid from the inlet 34 to flow directly to the outlet 38 via the bypass 80 without operating the control valve thereby ceasing the reciprocation of the hammer 14. As a result, it will be seen that whenever the tool is at a predetermined position within its bore 26 and lower than the desired position, as for example, when a tool associated with the anvil 28 is not bearing against the work, the hammer will automatically cease to operate.

From the foregoing, it will be seen that a hydraulic hammer made according to the invention employing the venturi can be used in a hydraulic system wherein there are large variations in back pressure without affecting the rate of reciprocation of the hammer element during operation thereof. The flow characteristics Fluid under pressure from the inlet 34 is applied to i of the hydraulic fluid around the venturi are such that pressure variations downstream of the same are effectively isolated from the flow path above the venturi so that a constant back pressure will be applied to the piston during the return stroke thereof resulting in a constant rate of operation.

1 claim 1. A hydraulic hammer comprising:

a. a casing having a bore;

b. a hammer received within said bore for reciprocating movement therein;

c. a work performing member operatively associated with said casing to be struck by said hammer during reciprocation of said hammer;

(1. means for reciprocating said hammer within said bore including l. means within said bore having opposed first and second pressure surfaces, said first surface being of greater size than said second surface,

2. first means establishing constant fluid communication between said second surface and a source of hydraulic fluid under pressure, and

3. second means alternately establishing fluid communication between said first surface and said source or a hydraulic fluid outlet; and

. means associated with one of said second means and said fluid outlet defining a venturi to maintain back pressure against said first surface at a relatively constant level when said second means establishes fluid communication between said first surface and said fluid outlet.

2. The hydraulic hammer of claim 1 wherein said second means comprises a control valve and said venturi defining means is carried thereon.

3. The hydraulic hammer of claim 1 wherein said second means comprises a bore and a reciprocably movable valve spool having a reduced diameter portion received in the bore, and said venturi defining means comprises a land on said spool reduced diameter portion and having a diameter less than the diameter of said bore.

4. A hydraulic hammer comprising:

a. a casing having a bore;

b. a hammer received within said bore for reciprocating movement therein;

d. means for reciprocating said hammer within said bore including 1. means for driving said hammer in one direction within said bore,

2. means, including a surface to be subjected to hydraulic fluid under pressure, for driving said hammer within said bore in a direction opposite said one direction, and

3. means for. alternately establishing a first fluid flow path between said surface and a source of hydraulic fluid under pressure and a second flow path between said surface and a hydraulic fluid outlet; and

e. means defining a venturi in said second flow path for isolating pressure fluctuations downstream of the isolating means from fluid in said second flow path and upstream of the isolating means whereby bore in the casing adjacent said first surface and with 10 said fluid outlet, and a valve spool having a reduced diameter portion received within said second bore for reciprocal movement therein to interconnect said fluid outlet and said casing bore end in one position of movement within said second bore; and said venturi defining means comprises an annular projection on said reduced diameter portion having a lesser diameter than the diameter of said second bore.

6. A hydraulic hammer according to claim 5 wherein the sides of said projection are tapered with the side of said projection adjacent said outlet having a greater longitudinal extent than the opposite side of said land.

Claims

1. A hydraulic hammer comprising: a. a casing having a bore; b. a hammer received within said bore for reciprocating movement therein; c. a work performing member operatively associated with said casing to be struck by said hammer during reciprocation of said hammer; d. means for reciprocating said hammer within said bore including 1. means within said bore having opposed first and second pressure surfaces, said first surface being of greater size than said second surface, 2. first means establishing constant fluid communication between said second surface and a source of hydraulic fluid under pressure, and 3. second means alternately establishing fluid communication between said first surface and said source or a hydraulic fluid outlet; and e. means associated with one of said second means and said fluid outlet defining a venturi to maintain back pressure against said first surface at a relatively constant level when said second means establishes fluid communication between said first surface and said fluid outlet.

3. means for alternately establishing a first fluid flow path between said sUrface and a source of hydraulic fluid under pressure and a second flow path between said surface and a hydraulic fluid outlet; and e. means defining a venturi in said second flow path for isolating pressure fluctuations downstream of the isolating means from fluid in said second flow path and upstream of the isolating means whereby pressure against said surface is maintained constant when said second flow path is established to eliminate variations of operational frequency due to said pressure fluctuations.

3. second means alternately establishing fluid communication between said first surface and said source or a hydraulic fluid outlet; and e. means associated with one of said second means and said fluid outlet defining a venturi to maintain back pressure against said first surface at a relatively constant level when said second means establishes fluid communication between said first surface and said fluid outlet.

4. A hydraulic hammer comprising: a. a casing having a bore; b. a hammer received within said bore for reciprocating movement therein; c. a work performing member operatively associated with said casing to be struck by said hammer during reciprocation of said hammer; d. means for reciprocating said hammer within said bore including

5. A hydraulic hammer according to claim 4 wherein said hammer is arranged to be driven against said member when said first surface is in fluid communication with said source; said second means includes a second bore in fluid communication with the end of the bore in the casing adjacent said first surface and with said fluid outlet, and a valve spool having a reduced diameter portion received within said second bore for reciprocal movement therein to interconnect said fluid outlet and said casing bore end in one position of movement within said second bore; and said venturi defining means comprises an annular projection on said reduced diameter portion having a lesser diameter than the diameter of said second bore.