Impact tool
O United States Patent 1191 1111 3,878,902  
 Matsuo Apr. 22, 1975 1 IMPACT TOOL 1.319.975 10/1919 Smith 173/116 1.829.609 10/1931 Robinson 173/116 [761 Invent Susum&#34; Mats, 196 3.568.780 3 1971 Matsuo 173/116 Minami-Isshiki, Nagaizumi-cho, sumo&#39;guni shlzuoka&#39;ken&#39; Japan Primary Examiner-Ernest R. Purser 22 Filed; Man 22 1973 Assistant Examiner-William IF. Pate, Ill  
 Attorney, Agent, or FirmKurt Kelman [57] ABSTRACT [30] Foreign Application Priority Data Disclosed is a free-piston type, pneumatically operated Apr. 3, 1972 Japan 47-33357 mPaC 100 comprising a tool cylinder and a pump cylinder both pneumatically and integrally connected. [52] U.S. Cl. 173/14; 173/1 16; 173/122 e eciprocation of the pump piston in the pump cyl- [51] Int. Cl 825d 9/08 inder ll cause the massive free-piston to rise and de- 158] Field of Search 173/116, 118, 122, 14; scend in the i001 cylinder, nd th fr -pist n will 60/531 538, 542, 543; 91/396; 92/8, 85 hammer the shank of the chisel at the end of the down stroke. The unique design of&#39; the pneumatic connec- [56] R f n Cit d tion between the top spaces of the tool and pump pis- UNITED STATES PATENTS tons permits the use of a heavier free-piston. and 964.875 7/1910 Nathorst 60 537 hence the &#39;mpact power be accordmgly mcreased&#39; 974.267 11/1910 Hennessy et a1 173/116 5 Claims, 10 Drawing Figures 2 I 10 s S 2 8 1 l3 PATENTEU APR 2 21975 sum 2 m PATENTEUAPRZZIHYS HEET 3 UF 3 BHOHLS NOlSld IMPACT TOOL This invention relates to a free-piston type. pneumatically operated impact tool, and more particularly to an improvement of the impact tool invented by the same inventor and patented as Japanese Pat. No. 656,654.  
 BACKGROUND OF THE INVENTION:  
  The inventor proposed a pneumatically operated impact tool comprising an air pump cylinder having a pump piston slidably mounted therein. both the cylinders pneumatically communicating with each other, thus causing the normal reciprocation of the pump pis ton in the pump cylinder to induce an anomalousreciprocation of the free-piston in the tool cylinder. More specifically, in the impact tool above mentioned the normal reciprocation of the pump piston in the pump cylinder controls the movement of the free-piston in the tool cylinder in such a way that it uses as much time as possible to reach the top of the tool cylinder, but uses as little time as possible to reach the bottom of the tool cylinder.  
  The impact tool proposed in the Japanese Patent above works satisfactorily. However, if a free-piston of large mass is used in the hope of increasing the impact power generated thereby, it is difficult to retain such a heavy free-piston at the top dead point. and the use of a heavy free-piston results in abnormal timing between the pistons and a consequent loss of efficiency.  
 SUMMARY OF THE INVENTION The object of this invention is to provide a pneumatically operated impact tool in which a massive freepiston is controlled so as to generate an increased impact power.  
 . To attain this object the pneumatically operated impact tool according to this invention comprises an air pump cylinder having a pump piston slidably mounted therein; a tool cylinder having a free-piston slidably mounted therein; the head portion of said tool cylinder having an aperture and a uni-directional exhaust port, said free-piston having a male portion which is adapted to fit in and close said aperture of the head portion; both said pump and tool cylinders being integrally connected and pneumatically communicating through a side opening made on the adjacent side walls of the cylinder housings and at the same time through said aperture and uni-directional exhaust port and through an, upper tube whose opposite ends open at the upper spaces of said cylinders; a chisel slidably mounted to the bottom of said tool cylinder and protruding therefrom into:said tool cylinder; and a crank mechanism operatively connected to said pump piston.  
 BRIEF DESCRIPTION OF THE DRAWINGS The above and still further objects, features and advantages of this invention will be more apparent from the following description when considered in connection with the accompanying drawings in which:  
  FIG. I is a longitudinal sectional view of an embodiment of the pneumatically operated impact tool according to this invention in which the free-piston is at the bottom dead point whereas the pump piston is at the top dead point.  
  FIGS. 2-1 to 2-7 are the sequential operations of the pump piston and the free-piston of this invention.  
  FIG. 3 is a graphic representation of the periodical movements of the free-piston of the impact tool of this invention (solid line), the pumppiston of the same (broken line) and the free-piston of the Japanese Patent (chain line).  
  FIG. 4 is a longitudinal sectional view of another embodiment of pneumatically operated impact tool according to this invention.  
 DESCRIPTION OF THE PREFERRED EMBODIMENTS:  
  Referring to FIG. 1, l is a free-piston; 2 a tool cylinder whose head portion has an aperture 2&#39; at the center thereof; 3 a pump piston; and 4 a pump cylinder whose head portion has an aperture 4&#39; at the center thereof.  
  Both the cylinders 2 and 4 are parallel-arranged and integrally connected, communicating with each other by an upper tube 5 whose opposite ends open at the apertures 2&#39; and 4&#39;, and by a lower side opening 6 which is provided to the lower portions of the adjacent inner walls of the cylinders. The pump cylinder 4 has a crank casing 7 at the bottom end of the cylinder housing. A crank 8 contained in the crank casing is connected to a piston 3 by a piston rod. Crank 8 is driven by motor 14 through belt 15 and pulley 13. The chamber space defined by the crank casing and by the pump cylinder is closed in air-tight fashion except for the top aperture 4&#39; and the side opening 6.  
  The free-piston 1 has a male portion 10 which is adapted to fit in and close the aperture 2 of the head portion when the free-piston reaches the top level of the tool cylinder, and the head portion of the tool cylinder head a port 12, which is positioned in parallel relation with the aperture 2 and contains a non-return valve means 11.  
  The free-piston 1 when driven downward. will strike against the end ofa chisel 9 with a strong force before the free-piston reaches the bottom dead point.  
  Referring to FIGS. 2-1 to 2-7, FIG. 12-] shows the state of the tool before the start of the operation. and in this case the upper remaining space 4a of the pump cylinder communicates with the upper remaining space 2a of the tool cylinder through the upper tube 5 and the lower remaining space 4b of the pump cylinder communicates with the upper remaining space 2a through the upper part of the opening 6 which is open when the free-piston l is at the bottom dead point. The freepiston 1 thus is not influenced by the motion of the pump piston 3 which free to reciprocate in an idle state.  
  To start the free-piston 1, the chisel 9 is brought in contact with the material to be crushed to push the free-piston l upward to a position where the bottom thereof is somewhat above the bottom of the side opening 6 thus communicating thelower remaining space 2b of the tool cylinder with the lower remaining space 4b of the pump cylinder. (See FIG. 2-2) As the pump piston 3 moves downward it compresses the air in both the lower remaining spaces 2b and 4b and reduces the pressure of the air in both the upper remaining spaces 20 and 4a. The positive pressure of the air thus compressed and the negative pressure of the air thus expanded cause the free-piston I to move upward. (See FIGS. 2-3) The free-piston 1 moves to the vicinity of the top dead point (See FIGS. 2-4). and then the male portion 10 of the freepiston enters and closes the aperture 2&#39; of the head portion in an air-tight fashion, thus preventing the air from passing to the upper space of the pump cylinder through the. upper tube 5. (At the same moment as the pump-piston is in the vicinity of the bottom dead point.) As a result, the free-piston rises at a reduced speed, compressing the air which is confined in the remaining space between the free-piston and the head portion of the tool cylinder. The pressure of the air confined and compressed in the remaining space 2a is so increased that it overcomes the counter spring force of the non-return valve 1 l, and then the valve 11 is opened, allowing the trapped air to flow from the remaining space 2a of the tool cylinder to the upper space 4a of the pump cylinder through the port 12.  
  While the trapped air is being released, the freepiston is still rising, purging the remaining air to the upper space 4a of the pump cylinder, and at the same time the free-piston is being cushioned until it reaches the top dead point.  
  The free-piston 1 reaches its highest point at the time the pump piston 3 reaches the bottom dead point. The pressure of the air trapped in the upper remaining space 2a is then reduced under the weight of the free piston l.  
  The negative pressure due to this air will apply to the upper surface of the free-piston, and hence the freepiston is kept still at the top dead point, while the pump piston is rising to the top dead point (See FIGS. 2-5).  
  As the pump piston 3 is moving to the vicinity of the top dead point (See FIGS. 2-6), the air is being compressed in the upper space 4a of the pump cylinder and in the upper tube 5 communicating therewith. As shown in FIG. 1, the port 12 is closed by the ball 11, and therefore the pressure of the air thus compressed both in the upper space 40 and in the tube 5 will apply to, the small surface of the male portion only. Because of the small surface area of the male portion 10, the pressure of air applied to each unit area of the whole upper surface of the free-piston is ofa small fraction of the pressure of air applied to each unit area of the male portion, and therefore the free-piston remains at the top dead point under a state of suction, or sometimes the freepiston is allowed to descend somewhat, but the male portion thereof still does not leave the aperture 2&#39; (See FIG. 2-7). When the pump piston reaches the top dead point, and when the pressure of the air in the remaining upper space 4a is increased to the maximum, the free-piston starts descending, the male portion leaves the apperture 2&#39;. Thus, the maximum positive pressure of air will apply to the whole upper surface of the free-piston, and at the same time the maximum negative&#39;pressure of the air in the remaining lower space of the pump cylinder will apply to the whole lower surface of the free-piston through the side opening 6. The free-piston thus subjected to the push-pull action will be jerked, pulling the male portion clear of the aperture 2. The free-piston descends at an increased speed until it strikes against the chisel 9 (See FIG. 2-1), and then the upper space 2a of the tool cylinder communicates with the lower space 417 of the pump cylinder, thus allowing the positive pressure of air to flow from the tool cylinder to the lower space of the pump cylinder through the side opening 6.  
  The side opening 6 is somewhat shorter than the height of the free-piston 1 and can be divided into two side openings as shown in FIG. 4.  
  After hammering the chisel 9, the free-piston l is pushed upward by the chisel 9 which is still in contact with the material and by the reaction resulting from its impact with the chisel 9 (See FIG. 2-2). The bottom of the free-piston I thus passes above the bottom of side opening 6 so that negative pressure is generated in the upper remaining space 2a and the positive pressure is generated in the lower remaining space 4b causing the free-piston l to rise as the pump piston 3 moves downward. (See FIGS. 2-3 to 2-4) Thus the impact motion repeats smoothly and continuously. The impact motion of the free-piston 1&#39; can be stopped only by removing the chisel 9 from the material.  
  The central features of this invention as mentioned above can be reduced to:  
 i. the free-piston 1 has a male portion 10, which is adapted to fit in and close the aperture 2&#39; of the head portion of the tool cylinder 2 in the vicinity of the termination of the upward stroke of the freepiston I, thus closing the gas passage from the tool cylinder 2 to the pump cylinder 4;  
  the head portion of the tool cylinder has an exhaust part 12 positioned adjacent to the aperture 2&#39; of the head portion thus allowing, after the closure by the male portion of the aperture 2, the freepiston to rise and compress the air confined in the upper remaining space 2a of the tool cylinder 2 until the pressure of the air thus compressed causes the associated non-return valve to open, and at the same time thus allowing the free-piston to rise and purge the remaining air into the gas passage to the upper space of the piston cylinder until it reaches the top dead point and is held there under suction;  
 iii. the free-piston 1 will not start descending before the pump piston 3 has compressed the air confined in the remaining upper space of the piston cylinder 4 to the maximum because the pressure of the compressed air is applied to the large upper surface of the free-piston only via the small top surface of the male portion.  
  The result attained thereby is shown in FIG. 3, particularly, around the top dead point of the stroke of the free-piston. The ramps B, H of the curve (solid line) around the top dead point in FIG. 3 indicates that this invention permits the use of a freepiston which is heavier than that of the conventional machine, and hence the impact or smashing power of the chisel is substantially increased.  
 What is claimed is:  
  1. A pneumatic impact tool comprising in combination:  
 A. an air pump cylinder having a pump piston slidably disposed therein, and crank mechanism means for slidably moving said pump piston;  
 B. a tool cylinder having a free-piston slidably disposed therein, said tool cylinder having an aperture on the head portion thereof and a unidirectional port means which allows air to pass from said tool cylinder to said pump cylinder through said upper tube housing, but prevents air from otherwise passing, said free-piston having a male member disposed to pneumatically close the aperture;  
 C. an upper tube housing pneumatically connecting the upper portion of the air pump cylinder and, the aperture and unidirectional exhaust port of the tool cylinder; 3  
 D. a common side wall opening joining the lower portion of the air pump cylinder and the lower portion of the tool cylinder said opening having a height less than the height of the free-piston and disposed to permit a free pneumatic opening when the freepiston is at the bottom dead point within the tool cylinder; and  
 E. a chisel slidably mounted into the bottom of said tool cylinder and protruding therefrom, said chisel contacting the free-piston and movable thereagainst for placing the free-piston in position to top thereof when the free-piston reaches the bottom dead point and is closed when the free-piston is elevated by the chisel, the pump piston being permitted to slidably operate in idle state when the free-piston is at the bottom dead point without effecting pneumatic movement of the free-piston.  
  4. A pneumatic impact tool according to claim 1 wherein the bottom surface of said free-piston has a counter sunk recess to accomodate the end of said chisel when said free-piston strikes against said chisel.  
  5. A pneumatic impact tool according to claim 1 wherein said common side wall opening is formed of two sections, one of which openings is sealed when the free-piston is at the bottom dead point.