US 3255832 A
Description (OCR text may contain errors)
June 14, 1966 Q. LEAVELL VIBRATIONLESS PERCUSSIVE TOOL Filed Nov. 27, 1962 FIG.2
United States Patent 3,255,832 VIBRATIONLESS PERCUSSIVE TOOL Charles Leavell, 206 S. Fair-field Ave., Lombard, Ill. Filed Nov. 27, 1962, Ser. No. 240,316 7 Claims. 01. 173-433 .This invention is concerned with the problem of eliminating vibration in tripartite vibratile structures comprising (1) a first desirably or unavoidably vibrating body, (2) a second body in which the occurrence of vibration is objectionable, and (3) connecting structure accomplishing a necessary transmission of force between such two bodies; and it rel-ates in particular to vibrationless percussive tools of the type disclosed in my issued Patents Nos. 3,028,840 and 3,028,841.
g In Patent No. 3,028,841, I disclosed an inventive concept of fundamental character generally applicable to an exceedingly wide variety of tripartite vibratile structures for substantially eliminating the transmission of vibration between such first and second bodies thereof While maintaining a necessary transmission of force therebetween; and I exemplified such invention in the environment of percussive tools because the problems encountered in eliminating vibration in tools of this class are more difficult of solution than those encountered in most other environments. Within this class of tools, the paving breaker was selected for specific consideration because it presents perhaps the most difiicult challenge for eliminating the transmission of vibration between a first necessarily vibrating body and a second body in which the occurrence of vibration is undesirable.
As set forth in the aforementioned patents in considering the paving breaker as an exemplary percussive tool, the typical paving breaker includes a casing defining an axially extending cylinder, a hammer or piston reciprocable within the cylinder, and a steel spike or work member slidably carried by the casing for limited axial movement with respect thereto and which is adapted to receive impact from the hammer (usually through an anvil or tappet interposed therebetween) at one end of the reciprocatory stroke thereof. The impact transmitted by the hammer to the spike is delivered thereby to a concrete slab or other work material to break or demolish the same, and the hammer is reciprocated within its cylinder by the alternate application of pressure fluid to the opposite ends or faces of the hammer.
In such usual paving breaker, the charges of compressed air alternately admitted into the opposite ends of the cylinder to respectively reciprocate the hammer in directions toward and away from the spike are each reactively applied against transverse surfaces defining the end closures of the cylinder, and as aconsequence thereof, the casing is moved or vibrated in opposite directions along the axis of reciprocation of the hammer. In many tool structures, the hammer is reciprocated through approximately 1,200 cycles each minute, and consequently, the pressure forces reacting alternately against opposite ends of the casing cylinder introduce a violent and objectionable vibration into the casing. Thus, in the usual paving breaker, the compressed air pressure force reacting alternately against opposite ends of'the casing cylinder defines the aforementioned connecting structure accomplishing a necessary transmission of force between the hammer, which is a desirably or unavoidably vibrating body, and the casing, which is a body in which the occurrence of vibration is objectionable.
In Patent No. 3,028,841, the invention disclosed for eliminating the vibration ordinarily introduced into the casing of such a percussive tool by the pressure forces reactively applied against the ends of the casing cylinder in actuating the hammer, includes means for counterbalancing such reactive forces by the simultaneous applica- 3,255,832 Patented June 14, l9fi6 random and irregular recoil forces are fed into the tool structure through the steel spike as a result of the nonhomogeneity of the slab being penetrated thereby, and because such recoil forces tend to cause the oscillator to migrate toward one end of its cylinder and to impact the end closure thereof, which is an undesirable condition in that it would reintroduce vibration into the casing, the invention is also concerned with avoiding such a condition of impact relation between the oscillator and end of its cylinder; and this result is accomplished by stabl-izing the mean position of the oscillator by means of an automatic control system that includes a pneumatic column operative between the oscillator structure and one end of its cylinder. This pneumatic column defines a force-transmitting linkage or connecting structure coupling the necessarily vibrating oscillator and cylinder therefor in which the occurrence of vi ration is objectionable; and the automatic control system also includes an arrangement for maintaining the force defined by such pneumatic column relatively constant during any one cycle of reciprocation of the oscillator, and it further includes feedback control means for regulatively adjusting the value of such relatively constant force during a plurality of reciprocations of the oscillator to positionally stablize the same as aforesaid in order to maintain it in a condition of intermediacy relative to the ends of its cylinder.
In Patent No. 3,028,841, the axis of oscillation or reciprocation of the oscillatory mass member comprised by the pressure-force counterbalancing system is angularly offset from the axis of reciprocation of the blow-striking hammer of the paving breaker which gives rise to the use of a special orientation for such axes identified as a condition of copivotality (see such patent for an explana tion thereof); and in Patent No. 3,028,840, the need for or desirability of using such special condition is obviated by dividing the unitary oscillatory mass member and its assocated system intotwo separate but substantially identical oscillator components each with its own related system and disposing the same symmetrically with respect to the hammer and its axis of reciprocation. Correspondingly, the automatic control system of such twin oscillator tool is divided into two individual systems respectively associated with the two oscillator components.
The present invention is concerned with vi brationless paving breakers of the type disclosed in the aforementioned patents and departs from the teachings thereof in that a single oscillator or oscillatory mass member of unitary annular construction, concentrically related to the hammer-piston and its cylinder, is employed instead of the plurality of oscillators disclosed in Patent No. 3,028,840 and in place of the angularly offset oscillator disclosed in Patent No. 3,028,841. Advantages realized from such construction include, among others, mechanical simplification of the tool, eliminating the duplication of parts in multiple-oscillator tools and thereby reducing manufacturing costs, generally reducing the diameter of the tool and specifically minimizing such dimension by locating the annular oscillator about a reduced diameter portion of the fronthead of the tool, and otherwise providing a conveniently handled and easily manipulated vibrationless percussive tool.
The precussive tool of the present invention also has as an advantage an anvil and hammer-piston arrangement in which a very eflicient and substantially complete transfor of blow-striking energy is eliected from the hammer-piston to the anvil upon impact therebetween. Ad-
3 ditional objects and advantages of the invention will become apparent as the specification develops.
Embodiments of the invention are illustrated in the accompanying drawings in which:
FIGURE 1 is a longitudinal sectional view of a paving breaker embodying the invention taken generally along the axis of reciprocation of the hammer-piston thereof;
FIGURE 2 is a transverse sectional view taken along the plane 22 of FIGURE 1; and
FIGURE 3 is a transverse sectional view generally similar to that of FIGURE 2 but illustrating a slightly modified construction.
The tool structure illustrated in FIGURE 1 is a pneumatically actuated paving breaker comprising a casing composition 11 providing a main cylinder 12 having therein a pneumatically-actuated free-piston hammer or mass member 13. The casing 11 is equipped with handles T, and provides an exhaust composition 14 to atmosphere communicating with the cylinder 12 intermediate the ends thereof. Such exhaust composition 14 includes a plurality of ports 14a opening into the cylinder 12' and communicating through a collection space with passage structure 14b that opens into an outlet 140 provided by the tool casing. The upper end of the cylinder 12 is occupied by a conventional pressure-responsive valve composition 12' operative to direct the flow of gaseous fluid (such as compressed air) alternately to the lower and upper end portions of the cylinder to energize the reciprocatory cycle of the hammer 13 by selectively applying upwardly and downwardly active axial pressure forces alternately to the lower surface 13a and to the upper surface 13b thereof.
Compressed air is supplied to the valve composition 12' from a compressor or other suitable source (not shown) through a hose H coupled to the handle T. A passage 12" in such handle communicates at one end with the hose and at its other end opens into a manifold chamber 120 that connects with a collection space 12d through a plurality of ports 126. A spring-biased trigger or valve 12 is disposed in the passage 12 to control the supply of compressed air to the valve composition 12', and in the position shown, the trigger 12 is depressed so that the passage 12" is open. The valve composition 12' has a pair of separate outlets, one of which is denoted with the numeral 12g and connects with a passage 17a through an annular channel 1211 to supply compressed air to the cylinder space below the hammer 13, and the other of which is denoted with the numeral Hi and communicates directly with the cylinder space above the hammer 13.
The bottom cylinder head area facing the lower surface 13a of the hammer consists only of the upwardly facing surface of the annular shoulder defined around and having a sliding relation with the upper end portion of the anvil element 15. The top cylinder head area facing the surface 13b of the hammer is made up of the downwardly facing surfaces of the valve composition occupying the upper end of the cylinder. For identification, the annular bottom and aggregate top cylinder head surface areas are respectively denoted with the numbers 12a and 12b.
The anvil 15 has an enlarged intermediate portion 15a that sealingly reciprocates within an anvil chamber 16, and the anvil chamber has lower and upper end closures 16a and 16b which respectively engage the lower a plurality of angularly spaced ports 17c, and communicating at its lower end with the anvil chamber through an annular space 210 (the function of which will be described in greater detail hereinafter) and a plurality of flow passages 17d associated therewith. Therefore, the lower end portions of the anvil chamber 16 and cylinder 12 are necessarily pressurized simultaneously to substantially the same value.
The upper end portion of the anvil chamber 16 adjacent the end closure 16b thereof is exhausted to atmosphere through a passage network comprising a plurality of interconnecting passages 18a, 18b and extending through the anvil 15. The passage 18c opens into a chamber 180! that receives therein both the bottom end portion of the lower anvil stem and the upper interior end portion of a steel spike or work member 19 slidably carried by the casing 11 for limited axial movements with respect thereto. Since the spike 19 defines a loose slidable fit with the related walls of the casing, the chamber 18d is maintained at atmospheric pressure and, therefore, the upper end of the anvil chamber 16 is also continuously maintained at atmospheric pressure. The bottom surface of the lower anvil stem (which extends through the surface 16a and is sealingly related thereo) is adapted to rest upon the upper inner end of the spike 19 which may be a conventional hexagonal work member having a pointed lower end and an outwardly extending annular retaining flange 19a adapted to cooperate with a retainer element 19b threadedly mounted upon the casing 11 at the lower end thereof. Thus the spike 19 is removably constrained in the casing by the retainer element 19b for limited axial displacements.
In operation of the structural arrangement thus far described, and assuming initially a parts configuration in which the hammer 13 is in abutment with the upper surface 15b of the anvil, a charge of compressed air will be directed by the valve composition 12' into the lower end portion of the cylinder 12 through the passage 17a in the tool casing. Such charge of air acting upwardly upon the bottom surface 131: of the hammer will reciprocate the hammer upwardly through the return stroke thereof. Simultaneously, however, a reactive pressure force acting downwardly upon the lower reaction surface (the terms lower reaction surface and upper reaction surface respectively designating the total upwardly facing and total downwardly facing surface areas reactively pressurized by the charges of air reciprocating the hammer, and which respectively transmit downwardly directed and upwardly directed axial forces to the casing; and which in the subject structure respectively comprise the aforesaid surfaces 12a and 16a, and the aforesaid surface 12b) will tend to cause the casing 11 to vibrate downwardly as the hammer 13 is reciprocated through its return stroke, and such reactive pressure force is applied to the casing until the upwardly moving hammer passes the port 14a of the exhaust composition 14, at which time the lower end portion of the cylinder 12 as well as the lower end portion of the anvil chamber 16 will be exhausted to atmosphere.
As the hammer 13 approaches the upper end closure of the cylinder 12, the valve composition 12' directs a charge of compressed air into the upper end portion of the cylinder, and the resulting pressure force acting downwardly uponthe hammer reciprocates it into impact with the surface 15b of the anvil which transmits such impact to the spike 19. Simultaneously, however, such charge of compressed air exerts an upwardly directed reactive force against the upper reaction surface of the casing or of the cylinder defined thereby which tends to vibrate the casing upwardly, and such reaction force is applied to the casing until the downwardly moving hammer 13 passes the exhaust port 14a, at which time the upper end portion of the cylinder 12 is exhausted to atmosphere.
Since the reciprocatory frequency of the hammer in a conventional vibratory tool may approach and exceed 1,200 cycles per minute, the casing thereof would objectionably vibrate longitudinally at the same rapid rate; but with reference to the present invention, the aforementioned counterbalancing system is effective to nullify the reactive pressure forces that normally cause such casing vibration; and the structural arrangement accomplishing this counterbalancing in the tool of FIGURE 1 will now be described.
Operative in the main tool casing 11 is an annular oscillator 20 reciprocable in its own cylinder 21. This oscillator element 20 comprises a massive body or piston portion having annular shoulders or piston surfaces 20d and 2% which are reciprocable relative to and in coaxial relation with the respectively opposing annular cylinder head surfaces 21a and 21b carried by the casing (respectively denoted hereinafter as upper and lower counterbalancing surfaces).
It will be observed in the drawings that the oscillator cylinder 21, and more particularly the variable-volume annular space 21c thereof defined between the upper piston and cylinder head surfaces 20d and 21a, connects by the tube or passageway 17, annular space 17b and ports 170 to the variable-volume space under the hammer 13 in the main cylinder 12. Similarly, the lower variablevolume space 21d in the oscillator cylinder and the variable-volume space above the hammer 13 in the main cylinder 12 are connected by a tube or passageway 22.
Before describing the operation of the tool with reference to the pressure-force counter-balancing system, it should be noted that the axially projected areas of the upper reaction surface 125 in the main cylinder 12 and the lower counter-balancing surface 21b in the oscillator cylinder 21 are substantially equal, and similarly, that the axially projected areas of the lower reaction surface (12a plus 16a) in the main cylinder 12 and the upper counterbalancing surface 21a of the oscillator cylinder 21 are substantially equal, for such conditions of equality provide the most ideal functioning of the pressure-force counterbalancing system. In the specific tool structure considered, an additional equality is present in that the axially projected areas of the lower and upper surfaces 13a and 13b of the hammer are substantially equal, and approximately equal thereto are the axially projected areas of the lower and upper reaction surfaces.
Considering again the operation of the tool, and assuming the same initial condition thereof, the admission of a charge of compressed air beneath the hammer to reciprocate the same upwardly, and which necessarily applies a downwardly directed reactive pressure force against the casing, will simultaneously apply an upwardly directed pressure force against the casing or, more specifically, against the upper counterbalancing surface 21a thereof, because of the interconnection of the upper end portion 210 of the oscillator cylinder with the lower end of the cylinder 12 through the passage 17, chamber 171) and ports 170. Since the axially projected areas of the upper counterbalancing surface 21a and the lower reaction surface are approximately equal, the upwardly and downwardly directed pressure forces applied simultaneously to the casing are substantially equal and, therefore, counterbalance and effectively eliminate downward vibratory movement of the casing which would otherwise result f-rom the admission of compressed air into the lower end portion of the cylinder 12 to reciprocate the hammer 13 upwardly.
correspondingly, when a charge of air is introduced into the upper end portion of the cylinder 12 to reciprocate the hammer 13 downwardly, the reactive force acting against the upper reaction surface of the casing and which tends to vibrate the same upwardly is counterbalanced by the simultaneous application of a downwardly directed pressure force upon the casing or, more specifically, against the lower counterbalancing surface 21b because of the interconnection of the lower end portion 21d of the oscillator cylinder with the upper end portion of the cylinder 12 through the passage 22. Since the axially projected areas of the upper reaction surface of the cylinder 12 and the lower counterbalancing 21b of the oscillator are substantially equal, the reactive pressure force which would otherwise vibrate the casing 11 upwardly is effectively counterbalanced.
It will be apparent that the counterbalancing action requires phases of operation during which each of the surfaces 21a and 21b is pressurized without the other of these surfaces being simultaneously pressurized; and in terms of structure, this requirement defines the condition that the oscillator 20 be a hermetic barrier interposed between the surfaces 21a and 21b to maintain pneumatic isolation therebetween. It is further evident that the oscillator 20 in this environment is necessarily subjected to reversing forces of a substantial order of magnitude, and must be supported within its cylinder with a positional stability such that it is maintained intermediate the ends of the cylinder in a non-impacting relation therewith so as not to transmit any uncounterbalanced variable forces to the casing.
The structural arrangement for accomplishing this condition of positional stability includes a piston 23 extending upwardly from the top of the oscillator 20. A cylinder 24 that slidably receives the piston 23 is provided with escape holes 25a permitting the cylinder to exhaust to atmosphere, and the uncapped upper end 24a of the cylinder opens into an annular tank 26 defining a constant pressure space 2'7 therein. Each of the escape holes 25a leads into an annular space 25b defined about the cylinder 24 and such annular space is loosely covered by a dust seal but is maintained at atmospheric pressure. Each of the escape holes 25a is equipped with a spring biased valve 250 which, along with the annular space and dust shield, are optional features and function to prevent the pressure in the cylinder 24 and constant pressure space 27 from dropping below arelatively low predetermined value (for example, 3 pounds per square inch gauge) sufficient to hold the oscillator 20 in its downmost position when the tool is not running, which prevents the first upward oscillations of the oscillator from carrying it into impact with its own upper cylinder head 21a.
Air is supplied to the constant pressure space 27 through a restricted passage or inlet orifice 29 that communicates through a passage 30, recess 39a, annular channel 36b and passage Site with the passage 12" in the handle T upstream of the trigger valve 12 Thus, the constant pressure space 27 is continuously supplied with compressed air (substantially reduced beolw line pressure because of the restriction 29) irrespective of whether the tool is running. Preferably a valve (not shown) located along the conduit H, or at the compressor or other source, is used to terminate the flow of air to the constant pressure space during periods of relatively long inactivity of the tool.
The escape holes 25a, collection space 25b and valve 25c together comprise the exhaust system for the space 27, and this exhaust system, together with the restricted infeed orifice 29 and piston 23 acting cooperatively therewith in a manner described hereinafter, comprises the aforementioned automatic control system whereby the aforesaid condition of positional stability is imposed upon the oscillator 20.
This composite automatic control system is pneumatically energized by a high pressure inflow through the restricted orifice 29, which generally effects a substantial pressure drop, and into and through the composite space consisting of the constant pressure space 27 and space in the upper portion of the cylinder 24, to commence its escape therefrom to atmosphere, whenever the position of the piston seal 231: permits, through the small ports 25a which collectively comprise a considerably greater cross-sectional area than that of the inflow orifice 29. It may be noted that the cylinder 24 need not necessarily have an open upper end as shown, which is the ideal condition, but any lesser opening connecting the cylinder and constant pressure space 27 should be sufficiently large so that substantially no pressure gradients will develop in the reciprocating air flow between the uper end portion of the cylinder and the constant pressure space.
The composite automatic control system is utilized to keep the oscillator from striking the cylinder heads 21a and 21b, and the principal tendency of the oscillator in this respect is to rise during its oscillatory motion toward a condition of impact with the upper cyinder head 21a which may be explained in terms of the forces acting on the hammer 13 as follows: First, the only forces acting downwardly upon the hammer are the intermittently effective pneumatic forces (omitting the force of gravity which is negligible and ineffective when the tool is operated in a horizontal position). Secondly, intermittently effective pneumatic forces act upwardly upon the hammer, but in addition there is a mechanical force which assists such upwardly acting pneumatic forces in urging the hammer upwardly. Such mechanical force is caused by the impact relation of the hammer and anvil for when the hammer strikes the anvil, the anvil is urged downwardly for an extremely brief interval by an extremely large force which may approach a value of 50,000 pounds. Action and reaction being equal, the hammer is urged upwardly by this very large force.
These considerations establish that the average value of the pneumatic forces acting upwardly on the hammer must be less than the average value of the pneumatic forces acting downwardly thereon inasmuch as the mean position of the hammer remains fairly fixed during operation of the tool; for, since the hammer does not migrate beyond the limits of its cylinder during operation of the tool, it is necessarily implied that the respective average values of all of the forces acting downwardly on the hammer and of all of the forces acting upwardly thereagainst are very closely equal; whence, more specifically, the average value of the total pneumatic and mechanical force acting upwardly upon the hammer must be almost exactly equal to the average value of the pneumatic force acting downwardly thereagainst; so that it follows that the average value of the pneumatic forces acting upwradly against the hammer must be substantially less than the average value of the pneumatic forces acting downwardly thereon.
Since the space 21c above the oscillator is in open communication with the space in the cylinder 12 below the hammer, and the space 21d below the oscillator is in open communication with the space in the cylinder above the hammer, the average values of the pressures in these oscillator spaces are substantially equal respectively to the average values of the pressures in the cylinder spaces below and above the hammer. Therefore, in consequence of the foregoing argument, there is an effective preponderance of the average value of the pneumatic force acting upwardly upon the oscillator over the average value of the pneumatic force acting downwardly thereon, which imposes upon the oscillator a continuous tendency to rise which, if not arrested, would reintroduce vibration into the casing 11 since the oscillator would pound against the upper cylinder head surface 211:.
To prevent this, an additional surface is employed on the oscillator against which sufficient pressure can be developed to hold the oscillator down whereby it can be made to operate over a reciprocatory range intermediate the ends of its maximum stroke so that it will not strike the cylinder heads 21a and 21b respectively above and below the oscillator, and such additional surface is the top surface of the piston 23 in the automatic control system comprising the previously specified elements 29, 25a, 25b, 25c and 23a, together with the piston 23 and the continuous space within the tank 26 and cylinder 24.
This composite structure operates so that if the oscillator 20 starts to oscillate about a mean position which is too high, thereby causing a danger of impact with the cylinder head 21a, the piston 23 will rise upwardly with the oscillator and will close the escape holes 25a, as seen in FIGURE 1. The establishment of this condition prevents escape of air from the total space above the piston 23, and the compressed air continuously fed into this space through the restricted inlet orifice 29 will cause the pressure therein to increase in value and, as a consequence, the oscillator 20 will be urged downwardly with a steadily increasing pressure force until it reaches a position in which the escape holes 25a are uncovered during at least part of reciprocatory cycle of the oscillator. If the oscillator is forced downwardly until the escape holes remain uncovered during the entire reciprocatory cycle of the oscillator, the pressure within the space above the piston 23 will drop rapidly. The pressure will then continue to decrease until it no longer gives sufiicient assistance to the pressure force acting on the surface 20d of the oscillator to hold it in such lower position, and the oscillator will then start to rise toward its stable intermediate location in which the escape holes are covered during a part of each cycle of reciprocation.
Experience has shown that migration of the oscillator such that the escape holes are either closed or open during the entire reciprocatory cycle of the oscillator is held to brief durations, and there is therefore a strong tendency for the oscillator to remain stabilized in an intermediate location wherein the escape holes are closed during only a part of each reciprocatory cycle of the oscillator. It should be understood that successful operation of the automatic control in this particular structural design requires compensatory changes in the pressure acting downwardly on the surface of the piston 23 to be effected quickly since the average value of the mechanical impact force reactively delivered during any relatively short interval by the anvil 15 upwardly against the bottom of the hammer 13 is related to the strength and elastic properties of the concrete being encountered by the spike 19 during that same interval, and such qualities of the concrete are subject to rapid variations. It will be apparent that the purpose of the relatively large pressurized space comprising the space 27 and space within the cylinder 24 in communication therewith, as compared to the cyclic displacements of the piston 23, is to assure that the value of the force present in the force-transmitting linkage defined by the air column connecting the casing structure and oscillator will remain substantially constant during each cyclic displacement of the oscillator so as to invest such force-transmitting linkage with the valuable incapacity to transmit vibration between two bodies necessarily interconnected thereby, being respectively an unavoidably vibrating body-namely, the oscillator 20and a body in which the occurrence of vibration is objectionable namely, the oscillator cylinder and other elements of the composite casing structure.
As heretofore indicated, the axially projected area of the upwardly-facing lower pressurizable surface 16a of the anvil chamber 16 is substantially equal to the area of the upwardly-facing, impact-receiving surface 15b of the anvil 15. Evidently, then, the downwardly-facing pressurizable surface at the lower end of the enlarged intermediate section 15a of the anvil has substantially the same axially projected area as that of the surface 16a; and, therefore, the upwardly-facing surface 15b of the anvil and the downwardly-facing surface at the lower end of the anvil section 15a are substantially equal to area. Consequently, and because the lower end portion of the cylinder 12 and lower end portion of the anvil chamber 16 are connected to each other by the passage 17, chambers 17b and 21c, and ports 17c and 17d, such lower end portions of the cylinder 12 and anvil chamber 16 are simultaneously pressurized and the respective pressures therein are necessarily of substantially equal value. This interrelationship defines a compensated anvil and the function and advantages thereof are described in detail in the aforementioned Patent No. 3,028,841, to which reference may be made for a complete description of such feature.
For convenience herein, however, it may be stated in general terms that a compensated anvil has the advantage of eliminating the waste of downpush momentum supplied to the tool (and delivered through the spike thereof to the concrete slab) that results from the conventionally employed expedient of attempting to firmly seat the anvil of the tool upon the upper end of the spike thereof at the moment of the delivery of impact to the anvil by the downwardly accelerating hammer-pistonsuch expedient being pressurization of the upwardly-facing, impact-receiving surface of the anvil to develop a downwardly-acting force thereon tending to move the anvil downwardly relative to the tool casing and into abutment with the upper end of the spike. The downpush momentum wasted by pressurizing the anvil to create a downwardly-acting force thereon between the intervals of impact is obviated in the compensated anvil structure by pressurizing the downwardly facing surface of the intermediate section 15a of the anvil simultaneously with the pressurization of the upwardly-facing surface 151) thereof. Therefore the simultaneously-applied, equal-valued pressure forces acting downwardly upon and upwardly against the anvil substantially cancel each other since they are of equal value and no net downward force, and no waste of downpush momentum, are then wastefully transmitted tothe concrete slab.
The desirability of having the anvil firmly seated upon the upper end of the spike at the moment of impact is to avoid what can be termed rattling or bouncing degeneration of the blow energy. More particularly, it has been found in the demolition of concrete that any specific amount of blow energy delivered to the spike is much more effective for driving the spike into the concrete if concentrated into a single blow than if subdivided into a great number of weaker blows totaling the same amount of energy. In view of the almost perfect elasticity of the steel anvil and hammer-piston components, the action which follows the delivery of a blow by the typically much heavier hammer to the relatively light-weight anvil when the anvil is caught by the hammer in a midair position (i.e., not sea-ted upon the spike but spaced upwardly therefrom) is as follows:
First, the anvil will bounce downwardly from such rnidair position off of the bottom surface of the hammer with a velocity considerably higher than the hammer velocity (just as a highly elastic golf ball bounces with greater velocity off the advancing face of a golf club).
Second, by virtue of this greater downward velocity of the anvil, it will arrive at and bounce upwardly off of the upper end of the spike while the more slowly descending hammer, further reduced in speed by having thus elastically transmitted aportion of its energy to the anvil, is still at a relatievly considerable distance above it.
Third, the anvil, in consequence of thus bouncing upwardly off the spike, will return to meet and again impact with the hammer in a somewhat lower new midair position, after where there will be several repetitions of such sequential bouncing action between the hammer and anvil to define a number of successively lower midair positions of this sort.
Inasmuch as each repetition of such sequential bouncing action entails the delivery by the thus rapidly vibrating anvil of one impact upon the spike, transmitting thereto a parcel of energy obtained from the total amount of kinetic energy contained in the descending hammer before its initial impact with the anvil in its first-mentioned midair position, it is obvious that the described repetitive bouncing process causes that specific amount of blow energy to be subdivided into a number of weaker blows totaling the same amount of energythus, as hereinbefore stated, re-
it) ducing the effectiveness of the total blow energy so subdivided for driving the spike into the concrete.
In the conventional vibratory tool structure, the aforementioned expedient of pressurizing the anvil to seat the same upon the upper end of the spike is extensively employed because it is virtually impossible to utilize the violently vibrating casing for this purpose by bringing the same (or a downwardly-facing surface of the anvil block provided therein) into firm abutment with an upwardlyfacing, associated surface defined by the anvil for the purpose of pressing the anvil downwardly and into such seating engagement with the spike. In the tool structure being considered herein, the casing is substantially vibrationless, and, as a result, a workman can continuously control the casing 11 and the anvil 15, and can seat the latter upon the upper end of the spike 19.
in addition to this advantageous compensated anvil feature, the tool structure illustrated in FIGURE 1 comprises an anvil and hammer-piston relationship that maximizes the transfer of energy from the hammer-piston to the anvil by what may be termed a billiard ball effect. More specifically, the anvil 15 and hammer-piston 13 have the characteristic of effecting a substantially complete transfer of all of the kinetic energy of the downwardly-accelerating hamer-piston to the relatively stationary anvil upon impact of the hammer-piston with the anvil. The proper design of such components to effect this result resides in assigning proper mass-distribution relationship thereto.
More particularly, such relationship comprises two terms; namely, weight and shape, and of the two weight is ordinarily by far the dominant term. Therefore, in the tool shown in FIGURE 1 the anvil and the hammer-piston have substantially equal weights, and the shapes thereof have the same general order of similitude although the anvil is somewhat greater in axial length than the hammer-piston and is also somewhat smaller in average diameter. Both dimensions are of the same general order and for the purpose of the aforementioned relationship, are well within the permissible range of variation. Therefore, since the weights of the hammer-piston 13 and anvil 15 are substantially the same, the shapes thereof are sufficiently similar, and both are almost perfectly elastic elements, impact of the hammer-piston against the anvil will result in a substantially complete transfer of the blow energy from the hammer to the anvil with the result that the anvil will be almost instantaneously accelerated downwardly and the acceleration of the hammer will be correspondingly reduced to zero, i.e., it will be essentially stopped upon impact.
Such energy transfer will be effected irrespective of Whether the anvil 15 is firmly seated upon the upper end of the spike 19 and, therefore, the energy transfer from the hammer to the anvil will be much greater than in prior structures even if the anvil is in a midair position. In this latter instance, the anvil, in effect, becomes the hammer element after impact thereof with the hammer 13 and delivers the blow energy transferred thereto to the spike 19 by impact therewith. However, the transmission of impact energy from the hammer-piston 13 to the spike 19 will, in general, be more complete and perfect if the anvil 15 is seated upon the spike at the moment of its impact with the hammer-piston. In some instances it may be desirable to have the weight of the hammerpiston 13 slightly less than the weight of the anvil 15 in order to prevent the anvil from rebounding upwardly and into impact engagement with the casing which could introduce an undesirable vibratory motion thereto.
More particularly, it has been found that the spike 19 sometimes tends to be accelerated upwardly as a consequence of recoil forces operative thereagainst which, at least in part, are belived to be caused by the composition of certain concretes. For example, it is known that a considerable portion of the impact energy delivered to the spike 19 appears as heat developed between the spike and the concrete slab resisting penetration by the spike. It is postulated that the moisture content of certain concrete compositions is such that pockets of steam are caused under the spike by the heat developed between it and the concrete slab, and upon occasion, conditions are such that the resulting steam pressure causes the spike to recoil upwardly. When this condition occurs, the spike jumps upwardly and transmits such motion to the anvil which in turn is propelled upwardly and into impact engagement with the casing.
If the weight of the hammer 13 is slightly less than that of the anvil 15, it will tend to be accelerated upwardly at a very slow rate by impact thereof with the anvil; and if such upward acceleration of the hammer is sufiiciently slow, the anvil 15 which has been accelerated upwardly by the aforementioned recoil force will then strike the upwardly-moving hammer and most of the energy then contained by the anvil will be transmitted to the hammerpiston further tending to accelerate it upwardly. As a consequence, the upward motion of the anvil will be terminated or slowed sufficiently so that any subsequent impact thereof with the casing will transmit a negligible force thereto.
The casing composition 11 comprises an inner casing element 11a and an outer casing element 11b coaxially circumjacent thereto. The outer casing elements is equipped with the handles T at its upper end, carries the retainer element 19b at its lower end, and is of generally tubular or cylindrical configuration having an axially extending hollow interior. At its upper end the outer casing element is provided with internal threads 11c that matingly engage external threads provided by a closure cap or plug 11d.
The plug 11d bears downwardly upon the upper end of the inner casing element 11a to seat the lower end thereof upon an inwardly stepped annular shoulder He provided by the outer casing element adjacent the lower end portion thereof. For convenience in machining the inner casing element, it is divided into two sections, as shown at 11), and such sections are maintained in the position shown, and the entire interior casing element maintained in a condition of compression, by the compressional force applied to the opposite ends thereof by the outer casing through the shoulder He and plug 11d. Quite apparently then, the outer casing element 11b is necessarily in a condition of tension and it is, in effect, a spring element maintaining the upper and lower sections of the inner casing component in a unitary state.
The tool is assembled by inserting the inner casing element 1111 into the hollow interior of the outer casing element 11b through the open upper end thereof; and the anvil 15, anvil block surrounding the upper stem of the anvil, hammer piston 13, and valve composition 12a are inserted into the interior of the inner casing element 11a, in the order stated, through the open upper end thereof which is occupied by the valve composition 12a in the illustration of FIGURE 1. The anvil block surrounding the upper stem of the anvil 15 is rigidly constrained in the position shown by a tubular sleeve 11g telescopically received within the inner casing element and forming the annular wall of the cylinder 12. The sleeve, or cylinder liner 11g, is pressed downwardly and into engagement with the anvil block by the cap 11d which resiliently bears downwardly upon the valve composition 12a through the helical spring shown, and the valve composition seats upon the upper end of the sleeve 11g to urge the same downwardly. At its lower end the valve block seats upon an annular shoulder 1111 provided by the inner casing element adjacent the upper end portion of the anvil chamber 12; and, therefore, the anvil block and sleeve are both constrained within the inner casing element.
The exhaust system 14 for the main cylinder 12 includes a plurality of angularly spaced ports 140 provided in the sleeve 11g and such ports respectively communicate with a plurality of angular spaced, axially extending grooves 14b cut in the inner casing element 11a, and each such groove opens into a pair registering ports 14c extending transversely through the inner and outer casing elements. The grooves 1411 are closed interiorly by the circumjacent sleeve 11g.
The constant pressure space 27 is defined by a pair of axially-elongated annular channels respectively out along the inner surface of the outer casing element 11b and the outer surface of the inner casing element 11a. Such channels are disposed in facing relation when the casing elements are assembled to form the constant pressure space. It will be apparent that the oscillator or oscillatory mass member 20, which is a continuous, unitary annular component may be formed integrally with the control piston 23, as shown, and that such component must be inserted into the outer casing element either prior to or at the same time that the inner casing element is inserted thereinto. Quite evidently, the piston 23 as well as the oscillatory mass member may be equipped with rings or other seal elements to effect a good sealing relation with the slidably engaged surfaces of the inner and outer casing elementsif such seals are either necessary or desirable.
The various flow passages formed in the inner and outer casing elements may be drilled or otherwise provided by conventional techniques, and plugs are used where necessary to close access openings formed by such boring operations. Such plugs have been largely omitted in the drawing for the purpose of simplifying the same. As shown most clearly in FIGURE 2, the flow passage 22 is formed in an axially extending boss or enlargement provided by the outer casing element 11b along one side thereof; and in the structure of FIGURES 1 and 2, such lateral enlargement is located below the laterally extending handles T which in some instances may be inconvenient or undesirable. Since the angular location of the passage 22 and easing enlargement containing the same is in no sense critical, both may be located wherever convenient such, for example, as shown in FIGURE 3 wherein both the enlargement and bore are offset by approximately from the position thereof shown in FIGURE 2. In other respects the modified structure shown in FIGURE 3 is identical and for this reason the primed form of the same numerals are employed to designate the respectively corresponding parts.
Wherever appropriate enlarged ports, 30a for example, and annular channels such as 12h and 30b may be used to facilitate registration of the various interconnecting ports, passages and other air-flow spaces; and appropriate registration of the upper and lower sections of the inner casing element, of the sleeve 12g with the inner casing element, and of the inner and outer casing elements may be determined and enforced in any convenient and conventional manner as, for example, by indexing or polarizing pins and recesses.
It is evident that a number of pressurizable ports, passages, cylinders and other chambers or spaces are -defined between the circumjacent inner and outer casing of other contiguous surfaces where the occurrence of leakage is undesirable are finished to close tolerances and may be coated with a thin layer of a suitable sealing or gasket compound (a conventional silicone-rubber gasket material, for example) prior to the assembly of the tool. As is customary in percussive tools, positive air cushions are provided where necessary to prevent metal-to-metal impact, except as between the hammer 13 and anvil 15 and as between the anvil 15 and spike 19. An example of the provision for the establishment of one such air cushion is at the lower end of the cylinder 12 where the inlet ports 17c are seen to be located a substantial distance above the cylinder end closure 12a.
It should be noted that the oscillator 20, which is a rather massive component, is located about a restricted portion of reduced outer diameter of the inner casing element 11a and, consequently, the external diameter of the outer casing element 11b has not been increased to accommodate the oscillator component. Therefore, the tool structure is relatively small and compact, yet it may have a generally uniform dimension from the upper to the lower end thereof which is provided without having to arbitrarily increase the exterior diametral dimension of the tool simply for the purpose of attaining such uniformity. The oscillator cylinder is defined between the inner and outer casing elements, and the reciprocatory axis of the oscillatory mass member is substantially coincident with the axis of reciprocation of the hammer 13; and, therefore, the reciprocatory axes of the center of gravity of the oscillator mass is coincident with that of the hammer and no angular or torsional vibration is introduced into the tool structure by the reciprocatory motions of the oscillator.
While in the foregoing specification embodiments of the invention have been described in considerable detail for purposes of making a complete disclosure, it will be apparent to those skilled in the art that numerous changes may be made in those details without departing from the principles or spiritof theinvention.
I claim: v
1. In combination with a percussive tool having a casing provided with a main cylinder, work member structure carried by said casing for limited axial displacements with respect thereto, a hammer-piston axially reciprocable within said cylinder for the successive intermittent delivery of impact force to said Work member structure, and means for reciprocating said hammer-piston by application of a reversing force thereto reactively applied against said casing and tending to vibrate the same: said casing providing an oscillator cylinder therein coaxially circumjacent said main cylinder, an oscillatory mass member of annular configuration within said oscillator cylinder, means for applying to said oscillatory mass member to efiect reciprocation thereof a reversing force which is reactively applied to said casing in opposition to the aforesaid reversing force whereby said casing does not vibrate as a consequence of the reactive application of such reversing forces thereto, means for developing a substantially continuous force operative against said oscillatory mass member urging the same generally in the direction of motion of said hammer-piston immediately prior to the delivery of impact force thereby to said work member structure, and automatic control structure responsive to the relative position of said casing and oscillatory mass member for varying the value of said continuous force over a plurality of impact cycles of said hammer-piston to maintain the range of reciprocatory movement of said oscillatory mass member relative to said casing within predetermined limits.
2. The percussive tool of claim 1 in which means are provided to maintain said continuous force substantially constant during any one impact cycle of said tool.
3. The percussive tool of claim 1 in which the force tending to reciprocate said hammer-piston in a direction away from its impact relation with said work member structure being in part impact reaction force developed against said hammer-piston during the actual interval of impact thereof with said work member structure, said automatic control structure being operative to vary the valve of said continuous force in accordance with changes in the average value of said impact reaction force intermittently operatively against said hammer-piston to maintain the aforesaid relation between said casing and oscillatory mass member.
4. The percussive tool of claim 3 in which means are provided to maintain said continuous force substantially constant during any one impact cycle of said tool.
5. In a pneumatic percussive tool having a casing in which the occurrence of vibration is undesirable and providing a main cylinder, work member structure carried by said casing for limited axial displacements with respect thereto, a hammer-piston axially reciprocable Within said cylinder for the successive intermittent delivery of impact force to said Work member structure, and means for reciprocating said hammer-piston by the application of pneumatic pressures alternately against the opposite faces thereof whereby corresponding pneumatic reaction forces are alternately developed in opposite directions against said casing tending to vibrate the same: said casing providing an oscillator cylinder therein coaxially circumjacent said main cylinder, an oscillatory mass member of annular configuration within said oscillator cylinder and having oppositely oriented pressurizable faces having axially projected areas approximately equal to the similarly projected areas of the faces of said hammer-piston,means for applying to said oscillatory mass member for reciprocating the same pneumatic pressures alternately against the opposite faces thereof and coordinately operative with said means for reciprocating said hammer-piston so as to maintain a condition of substantially simultaneous equality between the values of the pressures respectively acting against the oppositely oriented faces of said hammer-piston and oscillatory mass member to continuously provide counteractive pneumatic reaction forces substantially nullifying the pneumatic reaction forces tending to vibrate said casing as a consequence of reciprocating said hammerpiston, means for developing a substantially constant force operative against said oscillatory mass member urging the same generally in the direction of motion of said hammerpiston immediately prior to the delivery of impact force thereby to said work member structure, and automatic control structure responsive to the relative position of said casing and oscillatory mass member for varying the valve of said constant force over a plurality of impact cycles of said hammer-piston to maintain the range of reciprocatory movement of said oscillatory mass member relative to said casing within predetermined limits.
1 6. The percussive tool of claim 5 in which said means for developing said substantially constant force includes a pair of relatively reciprocable opposed surfaces respectively provided by said casing and oscillatory mass member, a pressurizable enclosure defined about said surfaces, and means for establishing a gaseous column within said enclosure operative between said opposed surfaces, and in which said automatic control structure includes means for admitting gas under pressure to said enclosure, means for permitting the escape of gas therefrom, and means for regulating the relative rates of such supply of gas to and escape of gas from said enclosure.
7. The apparatus of claim 5 in which the weights of said hammer-piston and work member structures are substantially equal so that substantially the entire kinetic energy content of said hammer-piston is delivered to said work member structure upon impact of said hammerpiston therewith.
References Cited by the Examiner UNITED STATES PATENTS 534,812 2/1895 Carlinet l73l28 X 1,802,987 4/1931 Shook 173l03 3,028,841 4/1962 Leavell 173l39 X 3,060,894 10/1962 Dean et al 173139 X BROUGHTON G. DURHAM, Primary Examiner.
L. P. KESSLER, Assistane Examiner.