US3032998A - Ram catcher for piston-ram assembly - Google Patents

Description

y 1962 G. E. ATKINSON 3,032,998

RAM CATCHER FOR PISTON-RAM ASSEMBLY Filed May 5, 1961 2 SneetsSheet 1 FIG. I

INVENTOR GEORGE E. ATKINSON ATTORNEY y 1962 cs. E. ATKINSON 3,032,998

RAM CATCHER FOR PISTON-RAM ASSEMBLY Filed May 5, 1961 2 Sheets-Sheet 2 20 FIG. 3

M 22 MENTOR "IIIQ I QQAL l8 GEORGE E. ATKINSON \T Kw BY ZMM%M ATTORNEY United States Patent 3,032,998 RAM CATCHER FOR PISTON-RAM ASSEMBLY George E. Atkinson, Linthicum Heights, Md., assignor to The Black and Decker Manufacturing Company, Towson, Md., a corporation of Maryland Filed May 5, 1961, Ser. No. 108,180 11 Claims. (Cl. 60-625) The present invention relates to a ram catcher for a piston-ram assembly, and more particularly, to such a ram catcher that is actuated upon an initial impact between the piston and ram, thereby coupling the piston and ram together for movement in unison and preventing any further impacting therebetween.

One specific embodiment, wherein the present invention may find particular utility, is a portable electric hammer of the type which is provided with a hollow cylindrical ram having a closed forward end, a piston reciprocating within the ram, a resilient sealing ring carried by the piston, an entrapped air chamber between the piston and ram, and momentary venting means to allow the entrapped air to vent at certain times during the operating cycle of the tool. The function of the entrapped air is twofold: one, to drive the ram ahead of the piston by a compression of the entrapped air; and two, to retract the ram away from the tool bit by means of a suction effect. Thus, the ram will reciprocate in response to, and relatively With respect to, the reciprocating piston; and it will be appreciated that although the volume of the entrapped air chamber will change during the operating cycle, still, the sealing eifect of the resilient ring is such as to preclude the piston from bottoming against the ram.

However, at various times at or near the normal life of the tool, usually when the sealing ring has become worn or frayed, the compression of air in the entrapped air chamber decreases appreciably, with the result that the piston will bottom against, or initially impact against, the closed forward end of the ram. If this bottoming of the piston with respect to the ram is allowed to continue, then the physical shocks of the repeated impacts will be transmitted, via the piston, to the cross-head, and thence to the connecting rod, gearing, and ultimately to the motor of the tool; and thus, the basic components of the tool will be impaired, and quite often, irreparably damaged. Nor can the operator anticipate or determine the instant of initial bottoming of the piston, inasmuch as the ram will continue to strike a blow against the tool bit, even though the magnitude of the blow is diminished.

Thus the failure of the mere sealing ring will usually be undetected, until serious damage to one or more of the basic components of the tool is encountered; and then, the repair of the tool-will be time-consuming and quite expensive. Moreover, even though the tool may be disconnected, immediately subsequent to failure of the sealing ring and initial bottoming of the piston, nevertheless, prior designs have necessitated an indirect, and hence expensive, disassembly of the tool in order to replace the resilient sealing ring.

Accordingly, it is an object of the present invention to provide a ram catcher for a piston-ram assembly that will alleviate the aforementioned defects.

It is another object of the present invention to provide a ram catcher for a piston-ram assembly, which, upon initial bottoming of the piston, will couple the piston and ram together for reciprocation in unison, thus preventing any further bottoming or impacting between the piston will be responsive to appreciable wear of the sealing ring to prevent relative movement of the piston and ram.

It is yet still another object of the present invention to provide a ram catcher, wherein the press-fit acquired between the piston and ram is suflicient to allow the piston and ram to reciprocate in unison, but insuflicient to preclude the piston and ram from being disengaged by a mere manual pulling.

It is a further object of the present invention to provide a power-operated percussive tool having a pistonram assembly and further having a ram catcher means, wherein, subsequent to actuation of the ram catcher, the barrel of the tool may be quickly detached, the piston and ram separated by a manual pull, and a new sealing ring easily installed on the piston.

In accordance with the teachings of the present invention, there is provided, in combination, a first member (such as a piston) together with means to reciprocate the first member; and there is further provided a second member (such as a ram) having relative reciprocating movement with respect to, and in response to, the first member, a chamber being formed between the members for the trapping of a compressive gas therein. Means are further provided to prevent the members from conv tinually impacting against one another, such means heing operative after a certain critical amount of gas has leaked from the chamber, and comprising a male element and a cooperating female element. Each of these elements are on a respective one of the members, and the elements are normally out of engagement. Thus, when the first member initially impacts against the second member, the male and female elements acquire a press fit therebetween, thereby coupling the members together for movement in unison and preventing any further impacting between the members.

These and other objects of the present invention will become apparent from a reading of the following specification, taken in conjunction with the enclosed drawings, in which:

FIGURE 1 is a longitudinal elevational view of the complete power-operated percussive tool, with parts broken away and sectioned to show the reciprocating piston, the reciprocating ram, and the ram catcher means;

FIGURE 2 is an enlarged portion of FIGURE 1, showing the ram catcher means;

FIGURE 3 shows the piston-ram assembly in its normal function during the life of the sealing ring;

FIGURE 4 shows the initial bottoming of the piston with respect to the ram, the ram catcher means then being actuated to couple the piston and ram together;

FIGURE 5 shows the piston and ram coupled together by the ram catcher for reciprocation in unison, further bottoming of the piston being precluded; and

FIGURE 6 is an enlarged portion of a sealing ring that has experienced appreciable wearing, thus actuating the ram catcher.

With reference to FIGURE 1, there is illustrated a power-operated percussive tool, such as a portable electric hammer 10, having a motor 11, switch handle 12, gear case 13, connecting rod '14, cross-head 15, piston 16, piston rod 16a, detachable barrel 17, ram 18, tool bit 19, and tool bit retaining means, the latter being denoted generally as at 20. Such a hammer, in one specific embodiment thereof, is capable of drilling a 2 inch diameter hole, 3 inches deep, in concrete in one-minute; and it will be understood that the percussive shocks and impacts normally generated, or encountered, by the hammer 10 "are fairly appreciable.

With reference to FIGURE 2, there is illustrated a relatively-short disc-shaped piston 16, which reciprocates within the hollow cylindrical ram 18, the space therebetween defining a chamber 21 whereby a compressive gas, such as air, may be entrapped therein. The piston 16 has an external annular groove 22, and a suitable resilient sealing ring 23 is loosely disposed within the groove 22. Moreover, momentary venting means, hereinafter to be described, is provided so as to allow the entrapped air in chamber 21 to momentarily vent, at certain times, during the operating cycle, thus providing for an equalization of the mass of entrapped air in chamber 21 to a substantially constant working level. Hence, as the piston 16 is reciprocated by the cross-head 1S and connecting rod '14, the entrapped air in chamber 21 will exhibit alternate compression and suction effects, with the result that the ram 18 will be reciprocated by a compression of entrapped air in chamber 21 to strike a blow upon tool bit 19, and further, that the ram 18 will be retracted from the tool bit 19 by a suction effect created by the rapid withdrawal of the piston 16 and the consequent sub-atmospheric pressure created in the chamber 21; and hence, the ram 18 will be in position for again being driven by the piston 16 by compression of air in chamber 21, and of course, further striking another blow upon the tool bit 19'. In no case during the normal life of the tool, however, will'the piston 16 strike the ram 18 an actual physical blow, inasmuch as this is precluded by the compression of entrapped air in chamber 2 1, Moreover, at or near the normal life of the tool, as when the sealing ring 23 wears appreciably so as to lose a good sealing effect between the respective mating walls of the piston 16 and ram 18, the piston 16 will initially bottom against or impact against the ram 13; and in order to prevent the continued bottoming of the piston 16 against the ram 18, a ram catcher means is provided.

With reference, again, to FIGURE 2, the ram catcher means comprises a male element, such as cylindrical protrusion 24 formed on the forward face 25 of piston 16, and a cooperating female element, such as cylindrical recess 26, formed in the closed forward end 27 of ram 18 and aligned with protrusion 14. Preferably, but not necessarily, the forward portion of protrusion 24- is tapered at an angle denoted by X, which angle X may be in the order of 15, while the depth B of the recess 26 is slightly greater than the height A of the protrusion 24. Thus, when the piston 16 initially bottoms against the ram 18, the protrusion 24- is received within and acquires a press lit with respect to the cooperating recess 26, thereby coupling the piston 16 and ram 18 together for non-relative movement in unison, the purpose of the tapered portion of protrusion 24 being to pilot the protrusion 24 within the recess 26.

With reference to FIGURES 3, 4, and 5 the sequential operation of the ram catcher means may be more clearly understood. In FIGURE 3, which represents the normal operation of the hammer 10, the piston 16 is reciprocated within the hollow cylindrical ram 18, which, at certain times, then strikes a blow against the tool bit 19. In this situation, there is a good sealing of the entrapped air in chamber 21, and the ram catcher means is, in a sense, dormant. At or near the normal life of the hammer 10 say the normal life of the sealing ring 23 (which incidentally, is usually in the order of at least several hundred hours) the piston 16 will initially bottom against the ram 18; and the ram catcher means is, in a sense, actuated to create a physical coupling between the piston 16 and ram 18, as shown in FIGURE 4. Naturally, it will be understood by those skilled in the art that the axial position of the piston 16 and ram 18 (with respect to barrel 17) at the instant of lock up of the piston 16 and ram 18, may vary and that the position shown in FIGURE 4 is only a typical illustration. Moreover, it will be further understood that the teachings of the present invention are equally applicable to other forms of piston-ram assemblies, and that the particular form of piston 16 and ram 18, herein illustrated, represents a typical embodiment of the present invention.

It will be further appreciated that, in the usual operation of the hammer 10, that the piston 16 and ram 18 reciprocate relatively to each other, that is to say, the

piston 16 and ram 18 do not ordinarily reciprocate in unison with each other; and there is a portion in the operating cycle of the mechanism where in the piston 16 is being driven forwardly (by means of the connecting rod 14 and cross-head 15) at the very instant when the ram 18 is still being retracted rearwardly by the suction effect previously exhibited by the retracting piston 16. Moreover, there is a point during the normal operating cycle wherein the piston 16 and ram 18 are fairly close to each other, although not physically contacting one another. Then, as the sealing ring 23 wears appreciably over the life of the hammer 10, the alternate compression and suction etfects exhibited by the entrapped air in chamber 21 will diminish, but nevertheless, there is still a residual or modicum of suction effect sufiicient to cause the ram 18 to be retracted somewhat, and that, in combination with the normal rebound of the ram 18 from striking the tool bit 19, causes the ram '18 to be retracted sufiiciently to physically engage the moving piston 16; and the initial physical contact of the piston 16 and ram 18 will actuate the ram catcher means, in the manner hereinbefore explained. Thereafter, the piston 16 and ram 18 will no longer move relatively with respect to each other, but rather, will now reciprocate in unison, preventing any further bottoming of the piston 16 with respect to the ram 18, and preventing any further striking of the ram 18 against the tool bit 19. In an actual test of the teachings of the present invention, a new sealing ring 23 was deliberately ground down and then installed in the hammer 1d; and as soon as the hammer 10 was actuated, the ram catcher means of the present invention caused the piston 16 to immediately engage and hold the ram 18 without any continuous bottoming or impacting therebetween.

Thus, when the ram catcher means is actuated, the piston 16 and ram 18 will reciprocate together, in unison, so as to preclude any further and repeated bottoming or impacting therebetween; and naturally, the ram 18 is preeluded from impacting against the tool bit 19. Hence, no repeated blows are developed by the hammer 10, and no harmful repeated impacts are related or transmitted back to the major components of the hammer 11); and the operator is automatically informed of the failure of the sealing ring 23 and the consequent actuation of the ram catcher means, inasmuch as the ram 18 is precluded from impacting against the tool bit 19, and inasmuch as the weight of the ram 18 added to the piston 16 creates a noticeable unbalance in the hammer 10. A typical case of appreciable wear of the sealing ring 23 is illustrated in FIGURE 6, wherein theclearance between the mating walls of the piston 16 and ram 18 is deliberately exaggerated for purposes of illustration. Sealing ring 23 is of the resilient type, but of course, it is understood that the present invention may be practiced with various forms of sealing rings made of various materials. Also, in FIGURES 3, 4, and 5, sealing ring 23 is illustrated as being in the forward portion of groove 22 on piston 16, as when the piston 16 is moving rearwardly; naturally, it will be appreciated that when piston 16 is moving forwardly of barrel 17, that the sealing ring 23 will probably be in the rearward portion of groove 22. However, in

the drawings, the sealing ring 23 is illustrated in the forward portion of groove 22 for sake of convenience.

Once the ram catcher means has thus been actuated, the operator may then easily disassemble the barrel 17 from the hammer 10 by removing a plurality of mounting screws 28 (shown in FIGURE 1) between the barrel 17 and gear case 13; and thereafter the ram 18 may be removed from the piston 16 by a manual pulling, it being recalled that the press fit acquired between protrusion 24 and recess 26 is sufficient to preclude relative movement of the piston 16 and ram 18, but insufficient to preclude a separation by. a normal manual pulling, and especially, by a combined pulling and twisting that may be exerted to a substantially constant working level.

' pairment, even if and when the sealing ring 23 fails; and imoreover, the operator is instantly informed of the failure of the sealing ring 23, and the replacement of the sealing ring 23 is simple, easy, and direct.

The momentary venting means (hereinbefore mentioned) for the entrapped air in chamber 21, comprises the relatively-short disc-shaped piston 16 in combination with an internal annular recess 29 in the ram 18, wherein the axial width of the recess 29 is greater than the axial height of the piston 16. Therefore, the entrapped air in chamber 21 is allowed to vent, at certain times during the operating cycle of the mechanism (as when the piston 16 passes by the recess 29), thus enabling the entrapped air to compensate for slight, but inherent, leakages in the mechanism, and thus enabling the entrapped air to adjust Such momentary venting means is described more particularly in the co-pending Akerman application S.N. 18,178 filed March :28, 1960, and assigned to the same assignee as the present invention. However, it will be appreciated that the present invention may be practiced with various forms of ventin'g" means.

Obviously, many modifications may be made without departing from the basic spirit of the present invention; and therefore, within the scope of the appended claims, the invention may be practiced other than has been specifically described.

I claim:

1. In combination, a first member, means to reciprocate said first member, a second member having relative reciprocating movement with respect to and in response to said first member, a chamber between said members, whereby a compressive gas may be trapped therein, and means to prevent said members from continually impacting against each other, said means being operative after a certain critical amount of gas has leaked from said chamber and comprising a male element and a cooperating female element, each of said elements on a respective one of said members, said elements being normally out of engagement, whereby when said first member initially impacts against said second member, said male and female elements will acquire a press fit therebetween, thereby coupling said members together for movement in unison and preventing any further impacting between said members.

2.. In combination, a reciprocating piston, a reciprocating ram having relative movement with respect to and in response to said piston, a chamber between said piston and said ram, whereby a compressive gas may be trapped therein, and means to prevent said piston from continually bottoming against said ram, said means comprising a protrusion formed on said piston, and said ram having a cooperating recess, said protrusion and said recess being normally out of engagement, whereby when a suificient quantity of said compressive gas leaks from said chamber and said piston initially bottoms against said ram, said protrusion will acquire a press fit with respect to said recess, thereby coupling said piston and ram together for movement in unison and preventing any further bottoming of said ram and piston.

3. In combination, a cylindrical ram having a blind axial bore, a cylindrical piston telescoped within said ram, said piston and said ram having a chamber therebetween, whereby air may be trapped therein, poweroperated means to reciprocate said piston, whereby said ram will reciprocate relatively with respect to and in response to said piston, momentary venting means for the entrapped air in said chamber, and means to prevent said when said piston initially bottoms against said ram, said piston from continually bottoming against said ram, said means being operative after a certain critical mass of air has leaked from said chamber and comprising a protrusion formed on said piston, and said ram having a cooperating recess, said protrusion and said recess being normally out of engagement, whereby when said piston initially bottoms against said ram, said protrusion and said recess will acquire a press fit therebetween, thereby coupling said piston and ram together for non-relative movement in unison and preventing any further impacting between said piston and ram.

4. In a percussive tool, the combination of a hollow cylindrical ram having a closed forward end including an interior wall transverse to the axis of said cylindrical ram, a disc-shaped relatively-short piston telescoped within said ram and having a flat forward face parallel to said interior wall of said ram, said wall and said face and the walls of said cylindrical ram forming a cylindrical chamber therebetween, whereby air may be trapped therein, power-operated means to reciprocate said piston,

means for the entrapped air in said chamber, and means to prevent said piston from continually bottoming against said ram, said means being operative after a certain critical mass of air has leaked from said chamber and comprising a protrusion projecting from said forward face of said piston, and said ram having a cooperating aligned recess in said interior wall thereof, said protrusion and said recess being normally out of engagement, whereby protrusion and said recess will acquire a press fit therebetween, thereby coupling said piston and ram together for non-relative movement in unison and preventing any further impacting between said piston and ram.

5. The combination according to claim 4, wherein said protrusion and said recess are cylindrically-formed and are aligned with the axis of said cylindrical ram.

6. The combination according to claim 5, wherein said recess has an axial length which is slightly greater than the axial length of said protrusion.

7. The combination according to claim 5, wherein said protrusion has a beveled forward portion to pilot said protrusion in said recess.

8. In a percussive tool, the combination of a hollow cylindrical floating ram having a closed forward end, a piston telescoped for reciprocation within said ram, a sealing ring carried by said piston, means to reciprocate said piston, a chamber between said piston and ram, whereby air may be trapped in said chamber, and whereby the alternate compression and suction efiects of the entrapped air in said chamber will cause said ram to reciprocate relatively with respect to said piston, momentary venting means for the entrapped air in said chamber, and means to prevent relative movement of said piston and ram, said means being responsive to appreciable wear of said sealing ring and the consequent loss of compression in said chamber and comprising a pair of elements, one on said piston and the other on said ram, said elements being physically coupled together upon the physical engagement of said piston with said ram, whereby said piston and said ram will thereafter reciprocate in unison.

9. The combination according to claim 8, wherein said responsive means causes said elements to acquire a press fit therebetween, said fit being suflicient to prevent relative movement between said piston and ram in the percussive tool, but insufficient to prevent said piston and ram from being manually pulled apart.

It). A power-operated percussive tool comprising a motor housing, a motor in said motor housing, a gear case secured to said motor housing, a longitudinal barrel having a cylindrical bore, means to detachably secure said barrel forwardly of gear case, a cross-head reciprocating in said bore of said barrel, motion-translating means in said gear case and coupled between said cross-head and said IIIOtOIyB. cylindrical ram guided for reciprocation in said here of said barrel, 'said ram having a blind axial bore, a disc-shaped piston telescoped within said ram, a

sealing ring carried by said piston, a piston rod between entrapped air in said chamber Will exhibit alternate compression and suction efiects, thereby reciprocating said ram relatively to said piston, said barrel having a forward portion, a tool bit disposed in said forward portion of said barrel, retaining means for said tool bit, whereby said ram will deliver a 'blow against said tool bit, a protrusion formed on said piston, and said ram having a cooperating recess, whereby as said sealing ring wears appreciably and the alternate compression and suction eifects of the entrapped air in said chamber become insuflicient to reciprocate said ram, said piston will initially bottom against said ram, thereby causing said protrusion to acquire a press fit with respectto said recess to mechanically couple said ram to said piston, and whereby said piston and ram will thereafter reciprocate in unison and said ram will be precluded'from thereafter delivering a blow against said'tool bit.

ll. A power-operated percussive tool comprising a motor housing, a motor in said motor housing, a gear case secnredto said motor housing, a longitudinal barrel having a cylindrical bore, means to detachably secure said barrel forwardly of said gear case, a cross#head reciprocating in said bore of said barrel, motion-translating m'eans'insaid ,gear case and coupled between said crosshead and said motor, a cylindrical ram guided for reciprocation in said bore of said barrel, saidtram having a blind axial bore, a disc-shapedpiston telescoped Within said ram, a sealing ring carried by said piston, a piston rod between said piston and cross-head, a chamber between said ram and said piston, whereby air may be entrapped in said chamber, momentary venting meansfor the entrapped air in said chamber, whereby as said piston reciprocates, the entrapped air in said chamber will exhibit alternate compression and suction effects, thereby reciprocating said ram relatively to said :piston, said barrel having a forward portion, a tool bit disposed in said forward portion of said barrel, retaining means for said tool bit, whereby said ram will deliver a blow against said tool bit, means to prevent said piston from continually bottoming against said ram, said means being responsive to appreciable wear of said sealing ring and the consequent loss of compression in said chamber and comprising a pair of elements, one on said piston and the other on said ram, said elements acquiring a press fit therebetween upon the bottoming of said piston with respect to said ram, said piston and said ram thereafter reciprocating in unison and said ram being precluded from delivering a blow against said tool bit, and said press fit between said elements being insufficient to preclude a manual disengagement of said piston and said ram, whereby said barrel may be detached from said lgear'case, and whereby said ram may be manually disengaged from said piston, thereby allowing a replacement of said sealing ring.

References Cited in the file of this patent UNITED STATES PATENTS 2,880,585 Badcock Apr. 7, 1959

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