Internal combustion engine with decompression device
BACKGROUND OF THE INVENTION 
     The present invention generally relates to an internal combustion engine with a decompression device, such as a small air-cooled two-cycle gasoline engine, especially adapted for a portable or conveyable working machine, such as a chain saw, trimmer, etc. and more particularly, to an automatic decompression device which is mounted to a cylinder portion of the internal combustion engine. 
     Generally, in such portable or conveyable working machines, an air-cooled two cycle gasoline engine with a recoil starter is used as a power source, which provides reduction in size and weight thereof, and in many cases, the decompression device is mounted to the engine so that the start-up of the engine is facilitated. The foregoing decompression device basically includes a perforation passage which allows a combustion chamber, defined by an inner wall of a cylinder of an engine body, to communicate with the outside, a pressure reducing valve for closing the passage mounted therewithin, and a valve operating member for opening the pressure reducing valve responsive to the start-up operation (cranking period). 
     Various attempts have been made to provide decompression devices which reduce the pressure inside the cylinder of the engine when starting the engine. In such engines for conveyable working machines, such as a chain saw, a manually operated decompression device, which is to be manually operated every time the engine is started, is normally used. This is because it is necessary for the construction thereof to be simple, compact and sturdy in order to easily operate. 
     Further, other various attempts have been made to come up with an automatic decompression device which is interconnected to a recoil starter device of the engine. For example, Japanese Utility Model Laid-Open Publication No. Hei 2-139366 teaches an automatic decompression device wherein the swing motion of a swinging lever, responsive to the rotation of a recoil starter, operates an exhaust valve of the decompression device to open so that the air-fuel mixture in a cylinder is released to the outside and the pressure of the combustion chamber can be reduced. Other references, such as Japanese Utility Model Laid-Open Publication No. Hei 2-144665, discloses an automatic decompression device which includes a swinging lever, the tip portion thereof being swung upon contact with a recoil rope of the recoil starter when the recoil rope is drawn, and a push rod reciprocating in accordance with the swing motion of the swinging lever, wherein a pressure reducing valve of the decompression device is made to open by the reciprocation of the push rod so that a gas within the cylinder is released to the outside thereby reducing the pressure of the combustion chamber. 
     In a conventional decompression device, as described above, if the operating mechanism portion of the pressure reducing valve thereof is exposed and, especially in the case of being adapted for an engine of conveyable working machines, such as a chain saw, it is likely that the operating mechanism portion of the pressure reducing valve of the decompression device will contact external obstacles, such as for example, trees, during operation. This results in the operating mechanism portion of the pressure reducing valve being damaged thereby causing a malfunction thereof. In the manually operated decompression device, because the pressure reducing valve is kept closed before the start-up thereof, it is necessary to push in the pressure reducing valve by hand every time the engine is started so that the gas within the cylinder of the engine can be released. Further, the foregoing conventional automatic decompression device, interconnected to the recoil starter of the engine, has problems in that the structure thereof is complicated and that enough room is needed to allow large displacement of the moving member, such as the swinging lever. 
     In view of the foregoing disadvantages inherent in the known types of prior art, the present invention solves the above-mentioned problems. Thus, it is an object of the present invention to provide an automatic decompression device, which can be adapted for the internal combustion engine for conveyable working machines, such as a chain saw, wherein the operating mechanism portion of the pressure reducing valve of the decompression device cannot be damaged by contacting external obstacles, such as for example, trees while at work, and to provide the same which is capable of automatically reducing the pressure of the combustion chamber within the cylinder in association with the start-up of the engine, wherein the structure is simplified and compactly made. 
     SUMMARY OF THE INVENTION 
     To attain the foregoing objects, an internal combustion engine with a decompression device, according to the present invention basically includes: a decompression member including a pressure reducing valve; a recoil starter member; and a decompression working mechanism, in association with the motion of the recoil starter member, for opening and closing the pressure reducing valve, wherein the decompression working mechanism includes a rotatable recoil reel with at least one abutting jut disposed on the outer periphery thereof; a decompression lever, swingably mounted to a fixed member of the internal combustion engine, which is swung upon abutting against the abutting jut of the recoil reel; and a decompression rod, which is formed as a crooked-rod and which is pivotally supported by the fixed member, the decompression rod being rotated upon abutment against the decompression lever. Further, the decompression lever and the decompression rod are disposed between the fixed member and a recoil cover which covers the recoil starter member, and are covered with a cylinder cover of the internal combustion engine at the upper portion thereof. 
     In operation, the internal combustion engine with a decompression device of the present invention when constructed as described above operates as follows. The operator manipulates (pulls out) the recoil rope of the recoil starter in order to start-up the engine. The recoil reel rotates while moving the abutting jut to abut against the end portion of the decompression lever, which, in turn, is made to swing. The swinging of the decompression lever rotates the decompression rod, and then the end portion of the decompression rod makes the pressure reducing valve open so that a part of the air-fuel mixture within the combustion chamber of the cylinder of the engine is released, through the discharge aperture, to the outside of the cylinder block, thereby reducing the pressure in the combustion chamber. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The instant invention will be more fully described and better understood from the following description, taken with the appended drawings, as follows. 
     FIG. 1 is a side view of one embodiment of the internal combustion engine with a decompression device according to the present invention, wherein the recoil starter portion and the cylinder head cover are removed therefrom. 
     FIG. 2 is an enlarged cross sectional view of the internal combustion engine with a decompression device taken along lines II--II of FIG. 1. 
     FIG. 3 is a plan view of the internal combustion engine with a decompression device of FIG. 1. 
     FIG. 4 is a fragmentary side view of the fan cover of the present invention. 
     FIG. 5 is a fragmentary plan view of the fan cover of the present invention. 
     FIG. 6 is a perspective view of the decompression rod of the present invention. 
     FIG. 7 is a perspective view of a recoil reel of the present invention. 
     FIG. 8 is an exploded perspective view of the pressure reducing valve of the present invention. 
     FIG. 9 is an enlarged cross sectional view of the decompression device of the present invention. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     The preferred embodiment of the present invention will now be described, in detail, with reference to the accompanying drawings. 
     Referring to FIG. 1 and FIG. 2, the internal combustion engine of the illustrated example is a well-known, small air-cooled two-cycle gasoline engine 10, adapted for a chain saw. The gasoline engine 10 includes a cylinder block 12 mounted thereon at the upper portion thereof and a piston 13 slidably reciprocating within the cylinder block 12. The cylinder block 12 includes a spark plug 50 and a decompression device 11 attached thereto at the top portion thereof. The entire upper portion of the cylinder block 12 is covered with a cylinder head cover 14 which is integrally formed of such materials as synthetic resin. A crankcase 16 is attached to the cylinder block 12 at a bottom portion thereof, wherein a crankshaft 17 is rotatably supported by the crankcase 16. A cooling fan 18 is mounted to the crankshaft 17 at one end thereof by means of a nut 19. A fan cover 15 is a fixed stationary member of the engine 10 mounted so that the cooling fan 18 is covered therewith. A recoil starter device 20 is mounted outside the cooling fan 18, in axial alignment with the crankshaft 17. The recoil starter device 20 includes a starter body 21 having a recoil cover 21a at the outer periphery thereof, a starter cover plate 24 for fitting into the starter body 21, a recoil spring 22 disposed within the starter cover plate 24 for recoiling a recoil rope 23g, and a recoil reel 23 rotatably fitted around a shaft body 21b which is formed at the central portion of the starter body 21, wherein the recoil rope 23g is wound around the recoil reel 23. The tail end portion (not shown) of the recoil rope 23g is guided, passing through the recoil cover 21a of the starter body 21 to the outside, to form an operating portion of the recoil starter device 20. 
     As shown in FIGS. 2 and 7, the recoil reel 23 includes a hub portion 23a, rotatably fitted around the shaft body 21b of the starter body 21, and two collar portions 23b, 23c, radially extending from the hub portion 23a, wherein the recoil rope 23g is wound up between the collar portions 23b and 23c. Four abutting juts 23d are formed, at regular intervals along the outer periphery of the collar portion 23c on the side of the cooling fan 18. Further, a ratchet wheel 23e, being in axial alignment with the hub portion 23a, is formed integrally on the outer surface of the collar portion 23c, wherein four ratchets 23f are formed on the ratchet wheel 23e, at regular intervals along the outer periphery thereof. 
     The recoil spring 22 is mounted such that the outer peripheral surface thereof is engaged with the starter cover plate 24 while the inner peripheral surface thereof is engaged with the end portion of the hub portion 23a of the recoil reel 23. When the tip portion of the recoil rope 23g is operated (drawn), the recoil reel 23 rotates in a direction of the arrow shown in FIG. 1, so that this rotation winds up the recoil spring 22 and reserves the restoring power, which, in turn, would work on the recoil rope 23g to be wound up when stopping to draw the recoil rope 23g. 
     A centrifugal ratchet 25 is rotatably mounted on the cooling fan 18 at the outer surface thereof through a washer 26 by a hexagon socket head cap screw 27. The centrifugal ratchet 25 is slightly urged into pushing on the ratchet wheel 23e of the recoil reel 23 by a spring (not shown). 
     FIGS. 4 and 5 show enlarged fragmentary views of the fan cover 15 which includes a hole 29a for screwing a supporting pin 29 of a decompression lever 28 (described later) and holes 30a and 30b for fixing a cover plate 30 (described later). Further, the fan cover 15 includes a groove 31d with a U-shaped cross section, which serves as a guiding holder for rotatably supporting a decompression rod 31 (described later) with respect to the axis thereof between the groove 31d and the cover plate 30. 
     The decompression lever 28 is pivotally mounted to the supporting pin 29 at the upper portion of the fan cover 15. The decompression lever 28 integrally includes a swinging rod 28a elongated downwardly, an abutting jut 28b elongated upwardly, and a short pin 28c for mounting a coil spring 28d which urges the lower end of the swinging rod 28a in an opposite direction of the arrow shown in FIG. 1. 
     It should be noted that a springy strip, instead of the coil spring 28d, may be integrally pre-formed on the decompression lever 28 itself. 
     FIG. 6 is a perspective view of the decompression rod 31 which includes a lower end portion 31b elongated outwardly and parallel to the crankshaft 17, an intermediate portion 31a elongated upwardly from the lower end portion 31b vertical thereto, and an upper end portion 31c elongated rearwardly from the intermediate portion 31a and upturned parallel thereto at the rear end, to form a crooked bar made of steel. The lower end portion 31b of the decompression rod 31 is disposed to abut the abutting jut 28b of the decompression lever 28. The intermediate portion 31a is disposed within the groove 31d of the fan cover 15 and is covered with the cover plate 30 so that the decompression rod 31 is rotatably supported about the axis of the intermediate portion 31a . While the upper end portion 31c of the decompression rod 31 is disposed to abut the thrust case 41 of the pressure reducing valve 40. 
     FIG. 8 and FIG. 9 show, in detail, the pressure reducing valve 40 of the decompression device 11. The pressure reducing valve 40 of the decompression device 11 leaves a passage 12b, formed at a wall portion of a combustion chamber 12a of the cylinder block 12 open to the outside, thereby reducing the compressive pressure therewithin. The pressure reducing valve 40 comprises the thrust case 41, a valve body 42, a valve shaft 43, a set pin 44, a U-shaped spring clip 41a and a coil spring 45. 
     The valve body 42 includes a bore 42a axially elongated therethrough, a screw portion 42b for screwing the valve body 42 through a washer 4Oa, on the screw hole which is in axial alignment with the passage 12b of the cylinder block 12 at one end thereof, and an engaging portion 42c for loosely fitting the thrust case 41 therearound at the other end thereof. Further, the engaging portion 42c includes two positioning grooves 42f, 42g, parallel to each other in a direction perpendicular to the axis thereof, at the outer periphery thereof, for engaging with a U-shaped clip 41a that is inserted in the thrust case 41. Furthermore, the bore 42a includes a valve seat 42d formed at the end portion thereof on the side of the screw portion 42b and a gas discharge aperture 42e, extending downwardly to communicate between the bore 42a and the outside, at the central portion thereof. 
     The valve shaft 43 includes a sliding shaft body 43a guided by the bore 42a of the valve body 42 and slidably reciprocating therewithin, a small diameter shaft body 43b having a smaller outer diameter than that of the sliding shaft body 43a and being disposed within the bore 42a to form a discharge passage for a gas therebetween, and a conical valve body 43d mounted at the tip portion of the small diameter shaft body 43b for being seated at the valve seat 42d. 
     The thrust case 41 is connected to the valve shaft 43 by a set pin 44. The coil spring 45, biasing the conical valve body 43d of the valve shaft 43 to its closed position, is interposed between one end of the valve body 42 and the thrust case 41. The U-shaped clip 41a is inserted from above into a pair of slotted grooves 41b, 41b formed on both sides of the thrust case 41, and thereafter is engaged with either of the two grooves 42f or 42g. 
     Next, the operation of the decompression device according to the disclosed embodiment of the present invention will now be described. 
     When the recoil rope 23g of the recoil starter device 20 is pulled out forcibly in order to start the engine 10, the recoil reel 23 rotates in the direction of the arrow in FIG. 1. The rotational torque generated by the rotation of the recoil reel 23 is imparted to the centrifugal ratchet 25 of the cooling fan 18 press-abutting on the ratchet 23f of the recoil reel 23 to rotate the cooling fan 18, and the crankshaft 17 rotates so that the engine 10 is made to start. 
     In the process for starting the engine 10, the rotation, in the direction of the arrow in, FIG. 1, of the recoil reel 23 makes the abutting juts 23d repeatedly abut against the lower end portion of the swinging rod 28a of the decompression lever 28 to rotate the swinging rod 28a in a clockwise direction as viewed in FIG. 1. Because the abutting jut 28b, the upper end portion of the decompression lever 28, is moved rearward by the swing of the swinging rod 28a, the decompression rod 31 is made to rotate in a counterclockwise direction as viewed in FIG. 3. By rotational motion of the decompression rod 31, the upper end portion 31c of the decompression rod 31 thrusts the thrust case 41, moving the valve shaft 43 rightward, as viewed in FIGS. 2 and 9, and releasing the conical valve body 43d from the valve seat 42d to open the pressure reducing valve 40, so that the air-fuel mixture within the combustion chamber 12a of the cylinder block 12 is discharged to the outside through the bore 42a and the gas discharge aperture 42e. This discharge of the air-fuel mixture enables the compressive pressure of the combustion chamber 12a to be reduced, thereby allowing the piston 13 to smoothly reciprocate and facilitating the start-up of the engine. 
     As will be apparent, because the recoil reel 23 includes plural abutting juts 23d, the process of opening the pressure reducing valve 40 is performed many times during one operation of the drawing of the recoil rope 23g, thereby assuring the working of the decompression device 11. 
     The U-shaped clip 41a, mounted on the thrust case 41, is engaged with the outer groove 42f of the engaging portion 42c of the valve body 42 before the thrust imposed by the decompression rod 31 so that the valve shaft 43 is kept in its closed position, as shown in FIG. 2 and FIG. 9, while the U-shaped clip 41a is switched to engagement with the inner groove 42g as the thrust case 41 moves rightward, as viewed in FIG. 8, so that the valve shaft 43 is kept in its open position. 
     When operated as described above, the pulling of the recoil rope 23g of the recoil starter device 20 is performed to provide the crankshaft 17 of the engine 1O with some degree of rotational speed known as, the restoring power. The restoring power is reserved in the recoil spring 22 which has been wound during the pulling of the recoil rope 23g to rotate the recoil reel 23 in a reverse direction so that the recoil rope 23g is wound to restore it to its start-up position. 
     With the above mentioned operation, the thrust pressure on the thrust case 41 of the decompression rod 31 disappears, and the engine 10 begins a self-rotation while the crankshaft 17 is rotating by means of the inertia force of the cooling fan 18 and the like. This results in a completion of the start-up operation. When the engine 10 rotates by itself and an explosion occurs within the combustion chamber 12a, the explosion makes the valve body 43 of the pressure reducing valve 40 automatically move toward its closed position, in a leftward direction as viewed in FIG. 2 and FIG. 9, so that the conical valve body 43d is seated at the valve seat 42d. With the movement of the thrust case 41, the U-shaped clip 41a, mounted on the thrust case 41, resumes its pre-thrust position to be engaged with the outer groove 42f so that the pressure reducing valve 40 is assured to remain in its closed position. 
     It should be noted that a member for positioning the valve shaft 43, which includes of the U-shaped clip 41a, the slotted grooves 41b, 41b, and two rows of grooves 42f, 42g, is provided in order for the decompression device to work more assuredly. Thus, the omission of such positioning member would not cause any practical trouble because the operation of the decompression device 11 is reiterated during the rotation of the recoil reel 23. 
     It should be noted that the decompression device 11 according to the present invention, is not limited to be adapted for a portable or conveyable working machine, such as a chain saw or trimmer, but may be adapted for other internal combustion engines in general. 
     Further, the decompression device 11 including the pressure reducing valve 40 or the recoil starter device 20, is not limited to the embodiment described above, but the present invention can employ various constructions thereof. 
     As hereinbefore pointed out, in an engine with a decompression device, because a decompression working mechanism including at least one abutting jut of a recoil reel, a decompression lever and a decompression rod is disposed between the fan cover and the recoil cover, in addition to the decompression device itself being housed within the cylinder head cover, it is possible to simplify and downsize the construction of the decompression working mechanism, for easy manipulation and assemblage, and to prevent the working mechanism from being damaged by bumping against external obstacles, such as for example, trees and grasses, during operation. 
     The terms and expressions which have been employed herein are used as terms of description and not of limitation, and there is no intent, in the use of such terms and expressions, of excluding any of the equivalents of the features shown and described or portions thereof, but it is recognized that various modifications are possible within the scope of the invention claimed.