Exhaust mechanism of pneumatic nailing machine

Abstract: An exhaust mechanism of a pneumatic nailing in which a striking cylinder (3a) is accommodated in a body (1) and a striking piston (3b) in the striking cylinder (3a) is driven to drive a nail (9) when compressed air is supplied to and exhausted from an upper portion of the striking cylinder (3a), comprises: an inner cap (12) arranged in the upper portion of the striking cylinder (3a); a cylinder cap (19) covering the inner cap (17); an exhaust chamber (20) formed along inside the body (1) between the inner cap (17) and the cylinder cap (19); and a throttle hole (21) formed in a lower portion of the exhaust chamber (20), wherein the exhaust air exhausted from the upper portion of the striking cylinder is discharged from the throttle hole (21) via the exhaust chamber (20).

Description: BACKGROUND OF THE INVENTION The present invention relates to an exhaust mechanism of a pneumatic nailing machine for discharging the exhaust air after a nail has been driven by the pneumatic nailing machine. By a pneumatic nailing machine in which compressed air is used, a nail is driven when a driver is activated together with a striking piston incorporated into a striking cylinder into which compressed air is supplied. After the completion of driving a nail, the compressed air is directly discharged outside the nailing machine from an upper end of the striking cylinder. Recently, it is allowed to use compressed air of high pressure for industrial use. Therefore, when compressed air of high pressure is used for a pneumatic nailing machine, it is possible to develop a compact, handy nailing machine, the capacity of which is the same as the capacity of a conventional nailing machine. Although it is possible to obtain a large capacity when compressed air of high pressure is used, the level of exhaust sound is raised. In order to reduce the level of exhaust sound, it is considered to adopt a mechanism in which compressed air is discharged from the striking cylinder via an exhaust chamber. However, even if exhaust air is discharged via the exhaust chamber, when it is directly discharged from the exhaust chamber, the wind pressure generated by the exhaust air is increased. Therefore, a cloud of dust is made, so that the worker feels uneasy and uncomfortable, and the nailing operation is affected. For this reason, it is desired to develop a mechanism capable of reducing the wind pressure caused by exhaust air. However, when a new mechanism is added to the nailing machine, the size of the overall nailing machine is increased. Furthermore, although it is possible to obtain a nailing machine of high capacity by using compressed air of high pressure, the level of exhaust sound is raised. In order to reduce the level of exhaust air sound, several methods are provided, for example, an exhaust hole may be throttled, or a filter is arranged in the exhaust air passage. However, when these methods are adopted, the exhaust of air is delayed. Therefore, the striking piston returning performance is deteriorated when the striking piston returns after the completion of driving a nail. Further, the effect of sound reduction is not so high. Fig. 18 shows a conventional pneumatic nailing machine shown in which a short cylindrical head valve is arranged on the upper outside of a striking cylinder 32. When a head valve 30 is opened, compressed air in an air chamber 31 flows into a clearance between the head valve 30 and the striking cylinder 32. Then, compressed air is suddenly supplied into the striking cylinder 32 from an upper end opening of the striking cylinder 32 as shown by the arrow in the drawing. By the pressure of the compressed air, the driver 34 is actuated together with a striking piston 33 arranged in the striking cylinder 32, so that a nail can be driven. When the head valve 30 is opened and the compressed air of high pressure in the air chamber 31 flows into the clearance between the head valve 30 and the striking cylinder 32 as described above, the compressed air is suddenly expanded. Due to the above adiabatic expansion, the temperature of the compressed air is lowered. Therefore, the moisture contained in the compressed air is frozen on an upper outer circumferential surface "a" of the striking cylinder 31. Due to the foregoing, the head valve to control the supply and discharge of the compressed air is not properly operated, because the head valve can not be sealed properly so that the compressed air leaks out. Therefore, the following problems may be encountered. A striking force is not strong enough to drive a nail, or a lost nailing motion is conducted by the nailing machine. SUMMARY OF THE INVENTION The present invention has been accomplished to solve the above problems. An object of the present invention is to provide an air exhaust mechanism of the pneumatic nailing machine capable of discharging exhaust air of low pressure without increasing the size of the nailing machine. Another object of the present invention is to provide a sound reduction mechanism of a pneumatic nailing machine by arranging an exhaust chamber in the body of the pneumatic nailing machine without deteriorating the returning performance of the striking piston. Still further object of the present invention is to provide a freeze proofing mechanism of the head valve of the pneumatic nailing machine by which the moisture contained in compressed air is prevented from freezing so that the head valve can be operated in a good condition at all times. According to the present invention, there is provided an exhaust mechanism of a pneumatic nailing machine in which a striking cylinder is accommodated in a body and a striking piston in the striking cylinder is driven to drive a nail when compressed air is supplied to and exhausted from an upper portion of the striking cylinder, the exhaust mechanism comprising: an inner cap arranged in the upper portion of the striking cylinder; a cylinder cap covering the inner cap; an exhaust chamber formed along inside the body between the inner cap and the cylinder cap; and a throttle hole formed in a lower portion of the exhaust chamber, wherein the exhaust air exhausted from the upper portion of the striking cylinder is discharged from the throttle hole via the exhaust chamber. It is preferable that the size of the throttle hole is adjustable. It is further preferable to add to the subject-matter of the independent claim a freeze proofing mechanism of the head valve of the pneumatic nailing machine comprising: a striking piston for driving a nail; a cylindrical striking cylinder into which the striking piston is slidably incorporated; an annular protruding edge arranged on an upper outside of the striking cylinder; a short cylindrical head valve arranged in an upper portion of the protruding edge on the same axis as that of the striking cylinder, the short cylindrical head valve capable of sliding upward and downward; and an air chamber for storing compressed air arranged outside the head valve, the improvement which comprises a cover integrally made of rubber for covering the protruding edge and the upper portion of the outer wall surface of the striking cylinder, wherein the air chamber is opened to the striking cylinder when the lower end of the head valve is separated from the protruding edge, and the air chamber is closed to the striking cylinder when the lower end of the head valve is contacted with the protruding edge. According to the present invention, the exhaust air discharged from an upper portion of the striking cylinder after the completion of driving a nail is diffused into the exhaust chamber at a stroke, and then the exhaust air in the exhaust chamber is diffused and discharged from the throttle hole. Accordingly, compared with a case in which exhaust air is directly discharged outside, the level of exhaust sound is remarkably reduced. Since the exhaust chamber is formed along the side of the body, it is possible to form the exhaust chamber without increasing the total height of the nailing machine. Therefore, an increase in the size of the nailing machine can be avoided. The upper end surface of the cylindrical body is preferably butted to the lower end surface of the cylinder cap, and both of them are integrally connected with each other by fixing bolts. Preferably, The exhaust cover is arranged outside the thin recess formed between the protrusions on the circumferential surface of the body. Since the body is preferably formed to be cylindrical , the pressure proof property can be ensured. In the body, the attaching hole for attaching the fixing bolt is formed in the protrusion, the wall thickness of which is large. However, the wall thickness of other portions is reduced. The recess formed in this way between the protrusions adjacent to each other is used as an attaching portion for attaching the exhaust cover. Due to the above arrangement, the total size of the body is not increased more than the needed size. In a preferred embodiment there are formed a large number of exhaust holes on the exhaust cover. Accordingly, the exhaust air discharged from the throttle hole is sent into the exhaust cover. Then it passes through the exhaust passage and diffuses from a large number of exhaust holes. Accordingly, the reduction of the sound level can be more enhanced, and the wind pressure of exhaust air can be reduced. Therefore, no dust is made during the operation of the nailing machine, and the operation can be smoothly conducted. According to the invention, when compressed air is supplied to the striking cylinder, the striking piston is moved so that a nail can be driven. After the completion of driving the nail, the compressed air supplied to the striking cylinder is discharged from an upper portion of the striking cylinder. This exhaust air is diffused into the exhaust chamber and passes through the throttle hole. Then the exhaust air is diffused and discharged outside from the exhaust port of the exhaust cover. As described above, the exhaust air exhausted from the striking cylinder is discharged into the exhaust chamber at a stroke and diffused outside from the throttle hole. Therefore, the exhaust time can be extended. Accordingly, as compared with a conventional structure in which the exhaust air is directly discharged outside, the level of sound of the exhaust air is remarkably reduced according to the structure of the invention. Especially when compressed air of high pressure is used, it is possible to obtain the same capacity as that of the conventional structure, by a striking piston, the size of which is smaller than the striking piston of the conventional structure. Accordingly, it is possible to form a sufficiently large exhaust chamber. Therefore, the exhaust air discharging mechanism of the present invention is effective when it is used for a nailing machine in which compressed air of high pressure is used. Since the exhaust air is quickly discharged from the striking cylinder into the exhaust chamber at a stroke, the exhaust of air from the striking cylinder is not delayed. Accordingly, the returning performance of the striking piston is not deteriorated even when the level of exhaust sound is reduced. In the present invention, the exhaust chamber is not provided in such a manner that a cover is simply attached to the outer circumference of the cylinder cap while a space is provided between the cylinder cap and the cover, but the exhaust chamber is formed along the side of the body. Accordingly, even if the height of the overall nailing machine is not increased, the exhaust air chamber can be positively formed in the nailing machine. From this viewpoint, the nailing machine can be made compact. Preferably, the size of the throttle hole of the exhaust chamber is adjustable. Accordingly, in a packing work in which they attach importance to the speed of driving nails even if the level of sound is raised, the size of the throttle hole may be increased. In a conventional architectural method in which they attach importance to the effect of sound reduction rather than the speed of driving nails, the size of the throttle hole may be decreased so as to enhance the effect of sound reduction. It is preferable to arrange the head valve in such a manner that the head valve surrounds an upper outside of the striking cylinder, and that the head valve slides upward and downward in the opening and closing operation. When the head valve is opened, a lower end of the head valve is separated from the protruding edge of the striking cylinder, so that an air passage between the striking cylinder and the head valve can be opened. Then, the compressed air of high pressure is supplied into the striking cylinder, and a nail is driven . When the head valve is opened and the compressed air of high pressure is supplied into the striking cylinder as described above, the compressed air is suddenly expanded. Due to this adiabatic expansion, temperatures of the protruding edge of the striking cylinder and the upper outer wall surface are lowered. However, these portions are covered with the cover made of rubber. Accordingly, even if the moisture contained in the compressed air is frozen and ice is generated, it is difficult for the ice to adhere to the cover made of elastic rubber, the heat insulating property of which is high. Even if the ice adheres to the cover, it can be easily removed. Therefore, the removed ice is easily blown off by the compressed air. Accordingly, the compressed air passage can be effectively prevented from freezing. As a result, the head valve can be sealed in a good condition and no air leaks out. Accordingly, the head valve can be always operated properly. BRIEF DESCRIPTION OF THE DRAWINGS Fig. 1 is a side view of the nailing machine according to the present invention; Fig. 2 is a longitudinal cross-sectional view of the above nailing machine; Fig. 3 is a longitudinal cross-sectional view of the primary portion of the body of the above nailing machine, wherein the view is taken on the cross section perpendicular to Fig. 2; Fig. 4 is a longitudinal cross-sectional view of the primary portion of the body of the above nailing machine in the case of driving a nail; Fig. 5 is a schematic illustration showing a connecting condition of the main body with the cylinder cap; Fig. 6 is a transverse cross-sectional view of the portion in which the exhaust cover is attached; Fig. 7 is an exploded perspective view of the upper portion of the main body of the nailing machine; Fig. 8 is a side view of another nailing machine according to the present invention; Fig. 9 is a longitudinal cross-sectional view of the above nailing machine; Fig. 10 is a longitudinal cross-sectional view of the primary portion of the body of the above nailing machine, wherein the view is taken on a cross section perpendicular to Fig. 9; Fig. 11 is a longitudinal cross-sectional view of the primary portion of the body of the above nailing machine in the case of driving a nail; Fig. 12 is a cross-sectional view of the primary portion of another example of the exhaust chamber; Fig. 13 is a plan view of the baffle member; Fig. 14 is a side view of still further nailing machine according to the present invention; Fig. 15 is a longitudinal cross-sectional view of the above nailing machine; Fig. 16 is a longitudinal cross-sectional view of the primary portion of the body of the above nailing machine taken on the section perpendicular to Fig. 15; Fig. 17 is a longitudinal cross-sectional view of the primary portion in the case of driving a nail; and Fig. 18 is a cross-sectional view of the head valve portion of a conventional nailing machine. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Figs. 1, 2 and 3 are views showing a nailing machine of the present invention. In a body 1 of the nailing machine, there are provided an air chamber 2 to store compressed air supplied from a compressed air source (not shown), and a striking cylinder and piston mechanism 3. When a trigger lever 4 is pulled by an operator, compressed air is supplied to and discharged from a striking cylinder 3a by the operation of a start valve 5 and a head valve 6 which are interlocked with the trigger lever 4. By the action of the compressed air, a striking piston 3b is reciprocated in the striking cylinder 3a. Therefore, a driver 7 integrally connected with the striking piston 3b is shot to a nose portion 8 arranged at an end of the body 1, so that a nail 9 supplied to an outlet of the nose portion 8 is struck by the driver 7. In this way, the nail 9 is driven into an object to be nailed. As shown in Fig. 4, the trigger lever 4 pushes a stem 10 of the start valve 5, so that a pilot valve 11 is moved downward and an air passage 12 is open to an exhaust port 13. Due to the foregoing, compressed air in an upper chamber 14 of the head valve 6 is exhausted from an exhaust port 13, so that the head valve 6 is opened, and compressed air in the air chamber 2 is suddenly supplied into the striking cylinder 3a, and the striking piston 3b is driven so as to drive a nail. After the nail has been driven, the trigger lever 4 is returned. Then the valve stem 10 of the start valve 5 is moved downward by the action of a spring 15. At the same time, the pilot valve 11 is moved upward, and compressed air is supplied again from the air passage 12 to the upper chamber 14 of the head valve, so that the head valve 6 is closed, and at the same time, the discharge port is opened and the compressed air supplied into the striking cylinder 3a is discharged outside. At the same time, the striking piston 3b is moved upward by the compressed air, which was compressed in the process of striking, stored in the block chamber 16 arranged around the striking cylinder 3a. Therefore, the striking piston 3b returns to the initial uppermost point so as to prepare the next nail driving operation. In this connection, the exhaust air discharged from the striking cylinder 3b after the completion of driving a nail is discharged outside by the exhaust mechanism shown as follows. In the upper portion of the striking cylinder 3a, there is provided a cylindrical inner cap 17 having a bottom, in which a drive valve mechanism (head valve 6) is accommodated. By the drive valve mechanism, the striking cylinder 3a is changed over between the air supply source and the atmosphere. In the inner cap 17, there is provided an exhaust hole 18 for the exhaust air discharged from the striking cylinder 3a. The circumference of the inner cap 17 is covered with a cylinder cap 19. Between the inner cap 17 and the cylinder cap 19, there is provided an exhaust chamber 20 that is formed along the inside of the body 1. The exhaust chamber 20 is a space for diffusing the exhaust air sent from the striking cylinder and piston mechanism. Inside the cylinder cap at the lower end portion, there is formed a throttle hole 21 for discharging the exhaust air sent from the exhaust chamber 20. In this connection, as shown in Figs. 5 to 7, the body 1 is arranged as follows. The lower end surface of the cylinder cap 19 is butted to the upper end surface of the main body 1a having the striking cylinder-piston mechanism, and both of them are integrally connected with each other by the fixing bolts 24. Although the wall thickness of the main body 1a is small, it is formed to be cylindrical, so that the pressure proof property can be ensured. At the upper end of the main body 1a, both sides are formed into the same cylindrical shape, the wall thickness of which is small, as that of the outside of the inner cap 17. At the upper end of the main body 1a, on the sides perpendicular to both sides described above, four protrusions 25, the wall thickness of which is large, are formed, and a portion of the exhaust chamber 20 is formed when the outside of the protrusions 25 are connected with each other by a large arc. The lower portion of the main body 1a is formed to be cylindrical, and the air chamber 2 and the blow-back chamber 16 are defined between the main body 1a and the outer circumferential surface of the striking cylinder 3a. Between the protrusions 25 which are adjacent to each other, there is formed a recess 26, the wall thickness of which is small. In the protrusion 25, there is formed an attaching hole 27. The attaching hole 27 is open to the upper end surface of the main body 1a. The reason why the protrusions 25 are formed on the main body 1a by means of padding is that the portions around the attaching holes 27 are weakest in the mechanical strength when pressure is applied. In the cylinder cap 19, there are provided insertion holes, into which the fixing bolts 24 are inserted, corresponding to the protrusions 25 of the main body 1a. The fixing bolts 24 inserted into these insertion holes are screwed into the attaching holes 27 open to the upper end surface of the main body 1a. Inside the cylinder cap 19 at the lower end portion, there is formed a throttle hole 21 for discharging the exhaust air sent from the exhaust chamber 20. Next, as shown in Figs. 1, 3, 5, 6 and 7, at the lower portion of the exhaust chamber 20 inside the cylinder cap 19, there is provided an exhaust cover 23. The exhaust cover 23 has a large number of exhaust holes 22 and covers the outside of the recess 26, the wall thickness of which is small, formed between the protrusions 25 which are adjacent to each other. Due to the foregoing arrangement, an exhaust passage 28 is formed between the exhaust cover 23 and the recess 26. The upper end of this exhaust passage 28 is open to the throttle hole 21. When the head valve 6 is closed as shown in Fig. 2 in the above arrangement, the exhaust port 18 of the inner cap 17 is opened. Accordingly, the striking piston 3b is moved upward, that is, the striking piston 3b is returned. Therefore, the exhaust air discharged from the upper portion of the striking cylinder 3a is diffused from the exhaust port 18 into the exhaust chamber 20. Further, the exhaust air in the exhaust chamber 20 passes through the throttle hole 21 and is discharged outside from the exhaust port 22 of the exhaust cover 23. As described above, the exhaust air discharged from the striking cylinder 3a is diffused from the exhaust port 18 into the exhaust chamber 20 at a stroke. Further, the exhaust air in the exhaust chamber 20 is diffused and discharged from the throttle hole 21. Therefore, compared with a case in which the exhaust air is directly discharged outside from the exhaust port 18, the level of exhaust sound of the nailing machine of this embodiment is remarkably reduced. In this case, the exhaust chamber 20 is formed along the side of the body 1. Accordingly, the exhaust chamber 20 can be ensured without increasing the total height of the nailing machine. From this viewpoint, it is possible to avoid the increase in the size of the nailing machine. In the above nailing machine, the wall thickness of a portion in which padding is not required is reduced. Due to the foregoing, the recess 26 is formed between the protrusions 25 adjacent to each other. This recess 26 is used as an attaching portion in which the exhaust cover 23 is attached. Therefore, the size of the overall body is not increased more than the needed size. Since a large number of exhaust holes 22 are formed on the exhaust cover 23, the exhaust air that has been once discharged from the throttle hole 21 into the exhaust cover 23 is diffused and discharged from the large number of exhaust holes 22. Accordingly, the effect of sound reduction can be more enhanced, and at the same time the wind pressure of the exhaust air can be reduced. Therefore, no dust is raised during the work. Consequently, the nailing operation can be smoothly conducted. Figs. 8, 9 and 10 are views showing another nailing machine of the present invention. This nailing machine is similar to the nailing machine of the first embodiment as follows. In the body 101, there are provided an air chamber 102 to store compressed air supplied from a compressed air source (not shown), and a striking cylinder-piston mechanism 103. When a trigger lever 104 is pulled by an operator, compressed air is supplied to and discharged from a striking cylinder 103a by the operation of a start valve 105 and a head valve 106 which are interlocked with the trigger lever 104. By the action of the compressed air, a striking piston 103b is reciprocated in the striking cylinder 103a. Therefore, a driver 107 integrally connected with the striking piston 103b is shot to a nose portion 108 arranged at an end of the body 101, so that a nail 109 supplied to an outlet of the nose portion 108 is struck by the driver 107. In this way, the nail 109 is driven into an object to be nailed. As shown in Fig. 11, the trigger lever 104 pushes a stem 110 of the start valve 105, so that a pilot valve 111 is moved downward and an air passage 112 is open to an exhaust port 113. Due to the foregoing, compressed air in an upper chamber 114 of the head valve 106 is exhausted from an exhaust port 113, so that the head valve 106 is opened, and compressed air in the air chamber 102 is suddenly supplied into the striking cylinder 103a, and the striking piston 103b is driven so as to drive a nail. After the nail has been driven, the trigger lever 104 is returned. Then the valve stem 110 of the start valve 105 is moved downward by the action of a spring 115. At the same time, the pilot valve 111 is moved upward, and compressed air is supplied again from the air passage 112 to the upper chamber 114 of the head valve, so that the head valve 106 is closed, and at the same time, the discharge port is opened and the compressed air supplied into the striking cylinder 103a is discharged outside. At the same time, the striking piston 103b is moved upward by the compressed air, which was compressed in the process of striking, stored in the blow-back chamber 116 arranged around the striking cylinder 103a. Therefore, the striking piston 103b returns to the initial uppermost point so as to prepare the next nail driving operation. In this connection, when the compressed air is discharged from the striking cylinder 103a after the striking piston 103b has been driven, exhaust sound is generated. The level of this exhaust sound is reduced by the following sound level reduction mechanism. In an upper portion of the above striking cylinder 103a, there is provided an inner cap 117 in which the head valve 106 is accommodated. In the inner cap 117, there is provided an exhaust hole 118 for the exhaust air discharged from the striking cylinder 103a. The circumference of the inner cap 117 is covered with a cylinder cap 119. Between the inner cap 117 and the cylinder cap 119, an exhaust chamber 120 is formed along the inside of the body 101. In the lower portion of the exhaust chamber 120, there is provided a throttle hole 121. In the lower portion of the throttle hole 121, there is provided an exhaust cover 123 on which a large number of exhaust holes 122 are formed. In this connection, when the head valve 106 is closed, the exhaust port 118 of the inner cap 117 is opened. When the head valve 106 is opened, the exhaust port 118 of the inner cap 117 is closed. In the above arrangement, when the head valve 102 is closed as shown in Fig. 9, the exhaust port 118 of the inner cap 117 is opened. Accordingly, the striking piston 103b is moved upward, that is, the striking piston 103b is returned, and the exhaust air discharged from the upper portion of the striking cylinder 103a is discharged from the exhaust port 118 into the exhaust chamber 120. Further, the exhaust air in the exhaust chamber 120 passes through the throttle hole 121 and diffuses from the exhaust port 122 on the exhaust cover 123. In this way, the exhaust air is discharged outside. As described above, the exhaust air discharged from the striking cylinder 103a is sent from the exhaust port 118 of the inner cap 117 into the exhaust chamber 120 at a stroke. Further, the exhaust air in the exhaust chamber 120 is diffused and discharged from the throttle port 121. Therefore, the level of exhaust sound is remarkably reduced as compared with an arrangement in which the exhaust air is directly discharged outside from the exhaust port 118. Further, the exhaust air discharged from the striking cylinder 103a is quickly sent into the exhaust chamber 120. Accordingly, the exhaust of air from the striking cylinder 103a is not delayed. Therefore, the returning performance of the striking piston 103b is not deteriorated even if the sound of exhaust air is reduced as described above. In the present invention, the exhaust chamber 120 is not provided in such a manner that a cover is simply attached to the outer circumference of the cylinder cap 119 while a space is provided between the cylinder cap 119 and the cover, but the exhaust chamber 120 is formed along the side of the body 101. Accordingly, even if the height of the overall nailing machine is not increased, the exhaust air chamber 120 can be positively formed. From this viewpoint, the nailing machine can be made compact. In this connection, the size of the throttle hole 121 may be adjusted to be small as follows. As shown in Fig. 12, an attaching space 124 is formed in the upper portion of the throttle hole 121 of the exhaust chamber 120. In this attaching space 124, there is provided an arcuate baffle member 125 shown in Fig. 13. Due to this baffle member 125, the size of the throttle hole 121 can be more reduced. The size of the throttle hole 121 of the exhaust chamber 120 is adjustable as described above. Accordingly, in a packing work in which they attach importance to the speed of driving nails even if the level of sound is raised, the above baffle member 125 is not attached. In a conventional architectural method in which they attach importance to the effect of sound reduction rather than the speed of driving nails, the above baffle member 125 is attached so as to enhance the effect of sound reduction. Figs. 14, 15 and 16 are views showing still further nailing machine of the present invention. This nailing machine is arranged as follows. In the body 201, there are provided an air chamber 202 to store compressed air of high pressure supplied from a compressed air source (not shown), and a cylindrical striking cylinder-piston mechanism 203. When a trigger lever 204 is pulled by an operator, compressed air is supplied to and discharged from a striking cylinder 203a by the operation of a start valve 205 and a head valve 206 which are interlocked with the trigger lever 204. By the action of the compressed air, a striking piston 203b is reciprocated in the striking cylinder 203a. Therefore, a driver 207 integrally connected with the striking piston 203b is shot to a nose portion 209 arranged at an end of the body 201, so that a nail 208 supplied to an outlet of the nose portion 209 is struck by the driver 207. In this way, the nail 208 is driven into an object to be nailed. The start valve 205 includes a cylindrical pilot valve 211 slidably arranged in the valve housing 210, and a valve stem 212 slidably arranged in the pilot valve 211. Usually, the compressed air sent from the air chamber 202 is supplied between the pilot valve 211 and the lower bottom portion of the valve housing 210, so that the pilot valve 211 can be pushed upward. By the pilot valve 211 moved upward, the air passage 214 communicated with the upper chamber 213 of the head valve 206 is opened to the air chamber 202, and the exhaust port 215 of the upper end of the valve housing 210 is closed. When the valve stem 212 is pushed, resisting the spring force, by the operation of the trigger lever 204 as shown in Fig. 17, the compressed air, which has been supplied, is discharged from the stem guide hole 217 at the lower end of the valve housing 210. Due to the foregoing, the pilot valve 211 is moved downward, so that the air passage 214 is closed to the air chamber 202 and opened to the exhaust port 215 arranged at the upper end of the valve housing 210. On the upper outside of the striking cylinder 203a, there is provided an annular protruding edge 218. In the upper portion of the protruding edge 218, a short cylindrical head valve 206 is arranged on the same axis as that of the striking cylinder 203a, and this head valve 206 can be slid upward and downward. The protruding edge 218 and the outer wall surface of the striking cylinder 203a are covered with a cover 219 integrally made of rubber. In the initial condition shown in Figs. 15 and 16, the lower end of the head valve 206 comes into contact with the protruding edge 218 and receives a force generated by the compressed air introduced from the air chamber 202. There is provided an upper chamber 213 in the upper portion of the head valve 206. This upper chamber 213 is communicated with the start valve 205 via the air passage 214. When the compressed air is supplied to the upper chamber 213, the head valve 206 is located at a lower position, and the lower end of the head valve 206 comes into contact with the protruding edge 218, so that the air chamber 202 is closed to the striking cylinder 203a. When the compressed air is discharged from the upper chamber 213 as shown in Fig. 17, the head valve 206 is slid upward, and the lower end of the head valve 206 is separated from the protruding edge 218, so that the air passage between the striking cylinder 203a and the head valve 206 is opened, and the air chamber 202 is connected with the striking cylinder 203a. In the upper portion of the striking cylinder 203a, there is provided an inner cap 221 having an exhaust port 220. There is provided a cylinder cap 222 around the inner cap 221. As shown in Figs. 15 and 16, there is provided an exhaust chamber 223 between the cylinder cap 222 and the inner cap 221. In the lower portion of the exhaust chamber 223, there is provided a throttle hole 224. In the lower portion of the throttle hole 224, there is provided an exhaust cover 226 having an exhaust port 225. As described above, the exhaust air discharged from the exhaust hole 220 of the inner cap 221 is discharged outside via the exhaust chamber 223 formed along the inside of the body 201. When the head valve 206 is closed, the exhaust hole 220 of the inner cap 221 is opened. When the head valve 206 is opened, the exhaust hole 220 of the inner cap 221 is closed. In the case of driving a nail in the above arrangement, the trigger lever 204 is pulled as shown in Fig. 17 so that the valve stem 212 of the start valve 205 is pushed. Then the pilot valve 211 is moved downward, and the air passage 214 is opened to the exhaust port 215, so that the compressed air in the upper chamber 213 is discharged from the exhaust port 215, and the head valve 206 is opened. Therefore, the compressed air in the air chamber 202 is suddenly supplied into the striking cylinder 203a via the air passage formed between the striking cylinder 203a and the head valve 206. When the compressed air in the air chamber 202 is suddenly supplied into the striking cylinder 203a, the striking piston 203b is driven. After a nail has been driven, the trigger lever 204 is returned. Then, as shown in Fig. 15, the valve stem 212 of the start valve 205 is moved downward by the action of a spring. At the same time, the pilot valve 211 is moved upward, and compressed air is supplied again from the air passage 214 to the upper chamber 213 of the head valve, so that the head valve 206 is closed, and at the same time, the discharge port 220 of the inner cap 221 is opened and the compressed air supplied into the striking cylinder 203a is discharged outside from the exhaust chamber 223 via the exhaust port 215. At the same time, the striking piston 203b is moved upward by the compressed air, which was compressed by the striking piston 203b in the process of striking, stored in the block chamber 227 arranged around the striking cylinder 203a. Therefore, the striking piston 203b moves upward and returns to the initial uppermost point so as to prepare the next nail driving operation. Next, as described above, when the head valve 206 is operated, the air passage is formed between the striking cylinder 203a and the head valve 206 as shown in Fig. 17. When the head valve 206 is opened and the compressed air of high pressure is supplied into the striking cylinder 203a, the inner pressure of which has been reduced in the previous exhaust operation, the compressed air is suddenly expanded. Due to this adiabatic expansion, temperatures of the protruding edge 218 of the striking cylinder 203a and the upper outer wall surface are lowered. However, these portions are covered with the cover 219 made of rubber. Accordingly, even if the moisture contained in the compressed air is frozen and ice is generated, it is difficult for the generated ice to adhere to the cover 219 made of elastic rubber, the heat insulating property of which is high. Even if the ice adheres to the cover 219, it can be easily removed. Therefore, the removed ice is easily blown off by the compressed air. Accordingly, the compressed air passage can be effectively prevented from freezing when the head valve 206 is opened. As a result, the head valve 206 can be sealed in a good condition and no air leaks out. Accordingly, the head valve 206 can be always operated properly. In this connection, when the head valve 206 is made of synthetic resin, the heat insulating property of which is high, the freeze of moisture contained in the compressed air can be further prevented. It should be noted that the head valve of the present invention is not limited to the above example. For example, the head valve may be arranged as shown in Fig. 18.

Claims: An exhaust mechanism of a pneumatic nailing machine in which a striking cylinder (3a,103a,203a) is accommodated in a body (1,101,201) and a striking piston (3b,103b,203b) in the striking cylinder is driven to drive a nail (9,109,208) when compressed air is supplied to and exhausted from an upper portion of the striking cylinder, characterised in that the exhaust mechanism comprises: an inner cap (17,117,221) arranged in the upper portion of the striking cylinder; a cylinder cap (19,119,222) covering the inner cap; an exhaust chamber (20,120,223) formed along inside the body (1,101,201) between the inner cap (17,117,221) and the cylinder cap (19,119,222); and a throttle hole (21,121,224) formed in a lower portion of the exhaust chamber (20,120,223), wherein the exhaust air exhausted from the upper portion of the striking cylinder (3a,103a,203a) is discharged from the throttle hole (21,121,224) via the exhaust chamber. The exhaust mechanism according to claim 1, wherein the size of the throttle hole (21,121,224) is adjustable. The exhaust mechanism according to claim 1 or 2, further comprising: a cover (219) made of rubber attached outside the upper portion of the striking cylinder (3a,103a,203a). An exhaust mechanism of a pneumatic nailing machine according to any one of the preceding claims, wherein a striking cylinder-piston mechanism (3,103,203) having the striking cylinder (3a,103a,203a) and the striking piston (3b,103b,203b) accommodated therein is accommodated in a cylindrical main body (la); the cylinder cap (19,119,222) is cylindrical and has a bottom to cover an upper portion of the striking cylinder-piston mechanism (3,103,203), the lower end surface of the cylinder cap (19,119,222) being butted to an upper end surface of the main body (la); the exhaust mechanism further comprises a fixing bolt (24) implanted in the cylinder cap, screwed into an attaching hole (27) open onto the upper end surface of the main body (la); the inner cap (17,117,221) is arranged inside the cylinder cap (19,119,222) and accommodates a drive valve mechanism (6,106,206) for changing over the connection of the striking cylinder between an air supply source and the atmosphere; the exhaust chamber (20,120,223) formed between the inner cap (17,117,221) and the cylinder cap (19,119,222) diffuses exhaust air sent from the striking cylinder-piston mechanism (3,103,203); the throttle hole (21,121,224) for discharging exhaust air sent from the exhaust chamber is formed inside at a lower end of the cylinder cap; the exhaust mechanism comprises a plurality of protrusions (25), the wall thickness of which is larger than other portions, arranged on the circumferential surface of the main body (la), the attaching hole (27) being formed in each protrusion (25) at predetermined intervals; and the exhaust mechanism further comprises an exhaust cover (23,123,226) having a large number of exhaust ports (22,122,225), the exhaust cover (23,123,226) covering the outside of at least one thin recess (26) formed between the protrusions (25) adjacent to each other, wherein an exhaust passage (28) is formed between the exhaust cover(23,123) and the recess (26), and an upper end of the exhaust passage (28) is open to the throttle hole (21,121,224).

Inventors: ADACHI MICHIAKI, AIHARA YASUNORI, HAGIWARA MOTOMITSU, KISHI NOBUO, KOSUGE MAKOTO, NAITO YASUHIRO, OGAWA TATSUSHI, TAKEZAKI MITSUGU, ADACHI, MICHIAKI, AIHARA, YASUNORI, HAGIWARA, MOTOMITSU, KISHI, NOBUO, KOSUGE, MAKOTO, NAITO, YASUHIRO, OGAWA, TATSUSHI, TAKEZAKI, MITSUGU, Adachi, Michiaki, c/o Max Co., Ltd., Aihara, Yasunori, c/o Max Co., Ltd., Hagiwara, Motomitsu, c/o Max Co., Ltd., Kishi, Nobuo, c/o Max Co., Ltd., Kosuge, Makoto, c/o Max Co., Ltd., Naito, Yasuhiro, c/o Max Co., Ltd., Ogawa, Tatsushi, c/o Max Co., Ltd., Takezaki, Mitsugu, c/o Max Co., Ltd.
Applicants: MAX CO LTD, MAX CO., LTD.
Application year: 1996
Main classification: B25C1
IPC codes: B25C1