Abstract:
A 4-cycle engine, includes an engine body, having a piston, a crankshaft and a crank chamber, an independent oil reservoir chamber adjacent the crank chamber, the crankshaft extending into the oil reservoir chamber from the crank chamber, an oil mist generator disposed in the independent oil reservoir chamber and being secured to and driven by the crankshaft, and a valve-operating chamber. Further, the engine includes a first passageway connecting the oil reservoir chamber with the crank chamber to provide oil mist communication therebetween, a second passageway connecting the crank chamber with the valve-operating chamber to provide oil mist communication therebetween, and a third passageway connecting the valve-operating chamber with the independent oil reservoir chamber to provide oil communication therebetween, wherein the three chambers and the three passageways form a lubrication oil feed channel to provide one-way circulation of lubrication oil therethrough.

Description:
This application is a division of prior application Ser. No. 09/285,252 filed Apr. 2, 1999, which is a divisional application of U.S. patent application Ser. No. 08/764,813 filed Dec. 12, 1996 now U.S. Pat. No. 5,974,075 issued Sep. 7, 1999. 
    
    
     BACKGROUND OF THE INVENTION 
     Field of the Invention 
     The present invention relates to a system for lubricating a hand-held type 4-cycle engine used as a power source mainly for a trimmer or a chain saw. 
     DESCRIPTION OF THE RELATED ART 
     The conventional hand-held type engine widely used in these applications is a 2-cycle engine capable of exhibiting a lubricating function in any operational attitude of the engine such as inclined and sideways-fallen attitudes. 
     However, as such a hand-held type engine, it is desirable to use a 4-cycle engine from the viewpoint of an exhaust emission control. In the 4-cycle engine, however, it is necessary to store an oil exclusively used for lubrication. Therefore, if the 4-cycle engine is used as the hand-held type engine, it is necessary to reliably lubricate various portion of the engine in any operational attitude of the engine. 
     SUMMARY OF THE INVENTION 
     Accordingly, it is one object of the present invention to provide a 4-cycle engine lubricating system capable of satisfying the above requirements for use in hand-held tools. 
     To achieve the above object, according to a first aspect and feature of the present invention, there is provided a system for lubricating a 4-cycle engine, comprising: an oil reservoir chamber which stores a lubricating oil therein and has an oil mist producing means contained therein for producing an oil mist from the lubricating oil; a crank chamber having a crank portion of a crankshaft contained therein; and a valve-operating chamber having a valve-operating device contained therein, the oil reservoir chamber, the crank chamber and the valve operating chamber being provided in an engine body, the oil reservoir chamber and the crank chamber being in communication with each other through a through-hole above an oil level in the oil reservoir chamber, the crank chamber and the valve operating chamber being in communication with each other through a control valve which is opened upon rising of the pressure in the crank chamber and closed upon reduction of the pressure in the crank chamber, the valve-operating chamber being substantially in communication at its upper portion with the atmosphere and at its bottom portion with the oil reservoir chamber through an orifice, and the following expression is established during operation of the engine; 
     
       
         
           Pc≦Po&lt;Pv 
         
       
     
     wherein Pc is a pressure in the crank chamber; Po is a pressure in the oil reservoir chamber; and Pv is a pressure in the valve-operating chamber. 
     With the first feature of the present invention, in any inclined state of the engine, the oil mist can be constantly circulate to the oil reservoir chamber, the crank chamber, the valve-operating chamber and the oil reservoir chamber and the oil liquified in the valve-operating chamber can be circulated to the oil reservoir chamber by utilizing the magnitude of the differences between the pressures in the chambers, thereby insuring a good lubricating state. Moreover, an expensive oil pump is not required and hence, this lubricating system is convenient even in a respect of cost. 
     According to a second aspect and feature of the present invention, in addition to the above first feature, the system further includes an uppermost chamber which occupies a position above the valve-operating chamber and to communicate with the valve-operating chamber through an orifice end also communicate with the oil reservoir chamber or the crank chamber through an oil passage, and the following expression is established during operation of the engine: 
     
       
         
           Pc≦Po˜≦Pt&lt;Pv 
         
       
     
     wherein Pt is a pressure in the uppermost chamber. 
     With the above second feature of the present invention, not only the circulation of the oil mist but also the circulation of the oil liquified and accumulated in the uppermost chamber can be reliably performed, and a good lubricating state can be insured. 
     According to a third aspect and feature of the present invention, in addition to the above first feature, the oil mist producing means comprises an oil slinger which is rotated by the crankshaft to agitate and scatter the lubricating oil in the oil reservoir chamber at all times irrespective of the inclined state of the. 
     With the third feature of the present invention, the oil mist can be reliably produced in the oil reservoir chamber by the rotation of the oil slinger in any operational attitude of the engine and moreover, the structure of the oil slinger is relatively simple. 
     According to a fourth aspect and feature of the present invention, in addition to the first or second feature, the control valve comprises a one-way valve of a pressure responsive type. 
     With the fourth feature, the one-way valve can be opened and closed in operative association with the pressure pulsation in the crank chamber to transfer the oil mist from the crank chamber into the valve-operating chamber and to maintain the crank chamber in an averagely negative pressure state. Particularly, the sealing is good during closing of the one-way valve and hence, the lubricating system is effective for an engine rotating at relatively lower speeds. 
     According to a fifth aspect and feature of the present invention, in addition to the first or second feature, the control valve comprises a rotary valve which is opened upon the lowering movement of a piston operatively associated with the rotation of the crankshaft and closed upon the elevating movement of the piston. 
     With the fifth feature, the rotary valve can be opened and closed in mechanically operative association with the rotation of the crankshaft to transfer the oil mist from the crank chamber into the valve-operating chamber and to maintain the crank chamber in an averagely negative pressure state. Particularly, a deviation in timing of opening and closing of the rotary valve cannot be produced and hence, the lubricating system is effective for a relatively lower-speed rotated type engine. 
     According to a sixth aspect and feature of the present invention, in addition to the fifth feature, the opening duration of the rotary valve is approximately 180° in terms of a crank angle, and the start point of opening of the rotary valve is set in a range of from a middle point between top and bottom dead centers of the piston to a lowering-piston position of 45° of the piston in terms of the crank angle. 
     With the sixth feature of the present invention, the discharge of a positive pressure from the crank chamber into the valve-operating chamber can be effectively performed by utilizing an inertial effect of a gas during rotation of the engine at a high speed. Therefore, the transferring of the oil mist and insuring of the negative pressure state of the crank chamber can be more reliable. 
     The above and other objects, features and advantages of the invention will become apparent from the following description of preferred embodiments taken in conjunction with be accompanying drawings. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIGS. 1 to  10  show a first embodiment of the present invention, wherein FIG. 1 is an illustration for explaining the service state of a power trimmer equipped with an engine including one lubricating system according to the invention; 
     FIG. 2 is a vertical sectional front view of the engine; 
     FIG. 3 is a sectional view along the line  3 — 3  in FIG. 2; 
     FIG. 4 is a sectional view taken along the line  4 — 4  in FIG. 2; 
     FIG. 5 is a sectional view taken along the line  5 — 5  in FIG. 2; 
     FIG. 6 is a sectional view taken along the line  6 — 6  in FIG. 2; 
     FIG. 7 is a sectional view taken along the line  7 — 7  in FIG. 2; 
     FIG. 8 is a sectional view taken along the line  8 — 8  in FIG. 2; 
     FIG. 9 is a sectional view taken along the line  9 — 9  in FIG. 2; and 
     FIGS. 10A and 10B are sectional views illustrating the position between a level of oil stored in an oil reservoir chamber and a circulating passage in a sideways fallen state ( 10 A) and a turned upside-down or inverted state ( 10 B) of the engine; 
     FIGS. 11 to  14  show a modification of the engine, wherein FIG. 11 is a vertical sectional view of an engine; 
     FIG. 12 is a sectional view taken along the line  12 — 12  in FIG. 11; 
     FIG. 13 is a sectional view showing an opened state of the rotary valve; and 
     FIG. 14 is a diagram illustrating the opening and closing timing of the rotary valve; 
     FIGS. 15 to  25  show a second embodiment of the present invention, wherein 
     FIG. 15 is a side view of an engine including a lubricating system; 
     FIG. 16 is a vertical sectional front view of the engine; 
     FIG. 17 is an enlarged view of an essential portion shown in FIG. 16; 
     FIG. 18 is a sectional view similar to FIG. 17, but illustrating a different operational state of the rotary valve; 
     FIG. 19 is a sectional view taken along the line  13 - 19  in FIG. 16; 
     FIG. 20 is a sectional view taken along the line  20 — 20  in FIG. 16; 
     FIG. 21 is a sectional view taken along the line  21 — 21  in FIG. 16; 
     FIG. 22 is a sectional view taken along the line  22 — 22  in FIG. 16; 
     FIG. 23 is a sectional view taken along the line  23 — 23  in FIG. 17; 
     FIG. 24 is a sectional view showing the state of a lubricating oil in a crank chamber when the engine is fallen sideways; and 
     FIG. 25 is a sectional view showing the state of the lubricating oil in the crank chamber when the engine is inverted or turned upside down. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     The present invention will now be described by way of preferred embodiments with reference to the accompanying drawings. 
     A first embodiment of the present invention shown in FIGS. 1 to  10  will be first described. Referring to FIG. 1, a hand-held type cycle engine E is mounted, for example, as a power source for a power trimmer T, to a drive section of the power trimmer T. The power trimmer T is used with its cutter turned in each of various directions depending upon its working state and hence, is largely inclined or turned upside down, wherein its working state is not constant. 
     Referring to FIGS. 2 and 3, a carburetor  2  and an exhaust muffler  3  are mounted in front and rear portions of an engine body  1  of the engine E, and an air cleaner  4  is mounted in an inlet of an intake passage in the carburetor  2 . A fuel tank  5  is mounted to a lower surface of the engine body  1 . The carburetor  2  includes a diaphragm pump for pumping fuel from the fuel tank  5  by utilizing a pressure pulsation in a crank chamber (which will be described hereinafter) of the engine E to circulate the surplus fuel to the tank  5 , so that the fuel can be supplied to an intake port in the engine E in any attitude. 
     As shown in FIGS. 2 and 3, the engine body  1  includes a cylinder block integral with a head, and a crankcase  7  bonded to a lower end face of the cylinder block  6 . The cylinder block  6  includes a single cylinder  9  having a piston  8  received therein, and a large number of cooling fins  10  around its outer periphery. 
     The crankcase  7  includes a pair of upper and lower case halves  7   a  and  7   b  coupled to each other by a plurality of bolts  11  arranged in their peripheral edges. A crankshaft  13  is connected to the piston  8  through a connecting rod  12  and supported between the case halves  7   a  and  7   b  in the following manner: 
     The upper case half  7   a  is integrally provided with a pair of left and right upper journal support walls  14  and  14 ′ depending from a ceiling wall, and the lower case half  7   b  is integrally provided with a pair of left and right lower journal support walls  15  and  15 ′ rising from its bottom wall and opposed to the upper journal walls  14  and  14 ′. A left journal portion of the crankshaft  13  is clamped between the left upper and right journal support walls  14  and  15  with a plane bearing  16  interposed therebetween, and a right journal portion of the crankshaft  13  is clamped between the right upper and lower journal support walls  14 ′ and  15 ′ with a ball bearing  17  interposed therebetween. A total of four bolt bores  18  are made in each of the upper and lower journal support walls  14 ′ and  15 ′ in an arrangement on opposite sides of the plane bearing  16  or the ball bearing  17 , and vertically passed through the crankcase  7 . Four stud bolts  19  are embedded in a lower end face of the cylinder block  6  and passed through the bolt bores  18 . A nut  20  is threadedly fitted over a lower end of each of the stud bolts  19  protruding from a lower surface of the crankcase  7 . In this manner, the upper and lower journal support walls  14 ,  14 ′, and  15 ,  15 ′ are coupled to each other, and the cylinder block  6  and the crankcase  7  are also coupled to each other. 
     Such coupling structure does not interfere with the cooling fins  10  provided around the outer periphery of the cylinder block  6  and hence, the number, the extent and the like of the cooling fins  10  can be freely selected, and the cooling effect for the engine can be enhanced sufficiently. The support rigidity of the crankcase  7  to the crankshaft  13  can be also enhanced. 
     Oil seals  21  and  21 ′ are mounted at opposite end walls of the crankcase  7  at portions through which the crankshaft  13  is passed. 
     The inside of the crankcase  7  is divided into a left oil reservoir chamber  22 , a central crank chamber  23  and a right valve-operating chamber  24 , as viewed in FIG. 2. A crank portion  13   a  of the crankshaft  13  is disposed in the crank chamber  23 . A defined amount of lubricating oil  0  is stored in the oil reservoir chamber  22 , and an oil slinger  25  (which is an oil mist generating means) for agitating and scattering the lubricating oil  0  is secured to the crankshaft  13 . 
     As shown in FIGS. 2 and 4, the oil slinger  25  includes a boss  25   a  fitted over the crankshaft  13 , a plurality of longer-arm blades  25   b  and a plurality of shorter-arm blades  25   c  both protruding from an outer periphery of the boss  25   a.  Tip ends of the blades  25   b  and  25   c  are bent in axially opposite directions. 
     The oil slinger  25  having such structure is capable of agitating the oil stored in the oil reservoir chamber  22  by the rotation of both the blades  25   b  and  25   c  in any operational attitude of the engine E to produce an oil mist at all times. 
     The valve-operating chamber  24  extends through one side of the cylinder block  6  to the head of the cylinder block  6 . An upper portion or the valve-operating chamber  24  is capable of being opened and closed by a head cover  26  coupled to the head of the cylinder block  6 . 
     As shown in FIGS. 2 and 5, the head of the cylinder block  6  is provided with exhaust ports  27  and  28  connected to the carburetor  2  and the exhaust muffler  3 , and intake and exhaust valves  29  and  30  for opening and closing the intake and exhaust ports  27  and  28 . A valve-operating device  31  for opening and closing the intake and exhaust valves  29  and  30  is disposed in the valve-operating chamber  24 . 
     The valve-operating device  31  includes a follower timing gear  33  which is rotatably carried on a support shaft  34  supported between coupled surfaces of the cylinder block and the crankcase  7  and which is driven at a speed-reduction ratio of 2/1 from a driving timing gear  32 , a cam  35  integrally connected to one end of the follower timing gear  33 , a pair of cam followers  37  and  38  carried on a cam follower shaft  36  mounted in the cylinder block  6 , so that they are swung by the cam  35 , a pair of rocker arms  40  and  41  carried on a rocker shaft  39  mounted in the head of the cylinder block  6  with their one ends abutting against valve heads of the intake and exhaust valves  29  and  30 , a pair of push rods  42  and  43  connecting the can followers  37  and  38  to the other ends of the rocker arms  40  and  41 , and valve springs  44  and  45  for biasing the intake end exhaust valves  29  and  30  in closing directions. During an intake stroke of the piston  8 , the intake valve  29  can be opened, and during an exhaust stroke of the piston  8 , the exhaust valve  30  can be opened. 
     The oil reservoir chamber  22  and the crank chamber  23  communicate with each other through a through-hole  46  provided in the crank shaft  13 . In this case, an opening of the through-hole into the oil reservoir chamber  22  is disposed at a center portion of the oil reservoir chamber  22 . The amount of lubricating oil  0  stored in the oil reservoir chamber  22  is set so that the opening is submerged into the oil even in any inclined or inverted state of the engine. Alternatively, the through-hole  46  may be provided in the plane bearing  16  or a partition wall between the oil reservoir chamber  22  and the crank chamber  23 . 
     As shown in FIGS. 2 and 7, a valve chamber  47  is defined under a lower surface of the crankcase  7  and connected to the valve-operating chamber  24 . The valve chamber  47  communicates with a bottom of the crank chamber  23  through a valve bore  48 . A one-way valve  49  is mounted in the valve chamber  47  as a control valve for opening and closing valve bore  48  and is moved in response to the pressure pulsation in the crank chamber  23 , so that the valve bore  48  is closed upon a reduction in pressure and opened upon a pressure rise. 
     A U-shaped oil return chamber SO is defined under the lower surface of the crankcase  7  to surround the valve chamber  47 . The oil return chamber  50  communicates with the bottom of the valve-operating chamber  24  through a pair of orifices  51  disposed spaced apart from each other to the utmost, and also communicates with the oil reservoir chamber  22  through the pair of through-hole  46 . The total sectional area of the through holes  46  is set sufficiently larger than the total sectional area of the orifices  51 . 
     The valve chamber  47  and the oil return chamber  50  are defined by closing a recess defined in the lower surface of the crankcase  7  by a bottom plate  53 . The bottom plate  53  is clamped to the crankcase  7  by the stud bolts  19  and the nuts  20 . 
     An upper portion of the valve-operating chamber  24  communicates with an inside of the air cleaner  4  through a breather tube  54  made of rubber and mounted through one-side wall of the head cover  26 . In this case, that end of the breather tube  54  which is opened into the valve-operating chamber  24  is disposed to protrude into the valve-operating chamber  24  over a predetermined length. Therefore, the oil somewhat accumulated in the valve-operating chamber  24  can be prevented from flowing out of the chamber  24  into the breather tube  54  in any operational attitude of the engine E. 
     As shown in FIGS. 2,  8  and  9 , an outer cover  55  is coupled to the head cover  26 , so that it is fitted over an outer periphery of the head cover  26 . A flat uppermost chamber  56  is defined between ceiling walls of the covers  26  and  55  and communicates with the valve-operating chamber  24  through a pair of orifices  57  provided in the ceiling wall of the head cover  26  at diagonal locations (desirably at four corners). The uppermost chamber  56  also communicates with the oil return chamber  50  through a single oil passage  58  provided in the cylinder block  6  and the crankcase  7 . The oil passage  58  has a sectional area larger than the total sectional area of the pair of orifices  57 . 
     The orifices  51  and  57 , the uppermost chamber  56 , the oil passage  58 , the oil return chamber  50  and the through-holes  46  constitute a circulating passageway L for returning the lubricating oil from the valve-operating chamber  24  to the oil reservoir chamber  22 . An opening  52  of the circulating passageway into the oil reservoir chamber  22 , i.e. an outlet end of the through-hole  52  is located at a longitudinally and laterally central portion of the oil reservoir chamber  22  and below a vertically central portion of the oil reservoir chamber  2  and below a vertically central portion of the chamber  22 . Thus, as shown in FIGS. 10A and 10B, such opening is exposed above the stored oil level in the oil reservoir chamber  22  in a sideways-fallen or inverted state of the engine E in which the valve-operating chamber  24  is located below the oil reservoir chamber  22 . 
     If the rotation of the crankshaft  13  causes the lubricating oil O to be agitated in the oil reservoir chamber by the oil slinger  25  during operation of the engine E to produce an oil mist, when the pressure in the crank chamber is reduced by the elevating movement of the piston  8 , the oil mist is drawn through the through-holes  46  into the crank chamber  23  to lubricate portions around the crank portion  13   a  and the piston  8 . Then, when the pressure in the crank chamber  23  increases by the lowering movement of the piston  8 , the one-way valve  49  is opened to permit the oil mist to be supplied along with blow-by gas generated in the crank chamber  23  from the valve bore  48  into the valve chamber  47  and thus into the valve operating chamber  24 , where the oil mist and the blow-by gas are separated from each other. Thus, the oil mist lubricates the various portions of the valve-operating device  31 , while the blow-by gas is discharged through the breather tube  54  into the air cleaner  4 . 
     The pressure in the crank chamber  23  is pulsated by the elevating and lowering movements of the piston  5  between positive and negative pressures alternately repeated. Under the positive pressure, the one-way valve  49  is opened to permit the positive pressure to be released toward the valve chamber  47 . Under the negative pressure, the one-way valve  49  is closed to inhibit the back-flow of the positive pressure from the valve chamber  47  and hence, the pressure in the crank chamber  23  is kept negative on an average. 
     On the other hand, the valve-operating chamber  24  and the valve chamber  47  connected to each other communicate with the inside of the air cleaner  4  which is in an atmospheric pressure state, through the breather tube  54  and hence, the pressures in both the chambers  24  and  47  are substantially equal to atmospheric pressure. 
     The oil reservoir chamber  22  communicates with the crank chamber  23  through the through-holes  46  and hence, the pressure in the oil reservoir chamber  22  is equal to or slightly higher than the pressure in the crank chamber  23 . 
     The oil return chamber  50  communicates with the oil reservoir chamber  22  through the through-hole  52  and also with the valve-operating chamber  24  through the orifices  51  and hence, the pressure in the oil return chamber  50  is equal to or slightly higher than the pressure in the oil reservoir chamber  22 . 
     The uppermost chamber  56  communicates with the oil return chamber  50  through the oil passage  58  and also with the valve-operating chamber  24  through the orifices  57  and hence, the pressure in the uppermost chamber  56  is equal to or slightly higher than the pressure in the oil return chamber  50 . 
     The magnitude relationship between the pressures in the chambers can be represented by the following expression: 
     
       
         
           Pc≦Po≦Pr≦Pt&lt;Pv 
         
       
     
     wherein, 
     Pc represents pressure in the crank chamber  23 , 
     Po represents pressure in the oil reservoir chamber  22 , 
     Pr represents pressure in the oil return chamber  50 , 
     Pt represents pressure in the upper most chamber  56 , and 
     Pv represents pressure in the valve-operating chamber  24 . 
     As a result, during operation of the engine, the pressure flows through a path which will be shown below:                           
     Therefore, the oil mist fed to the valve-operating chamber  24  is circulated via the pressure path to the oil reservoir chamber  22 , and the oil liquefied in the valve-operating chamber  24  is circulated via the orifices  51  to the oil return chamber  50  and the oil reservoir chamber  22 . Such circulation of the oil mist and the liquefied oil is performed without hindrance even when the engine E is inclined in any attitude. 
     In the inverted operational state of the engine E, the upper most chamber  56  is located below the valve-operating chamber  24  and hence, the oil liquefied in the valve-operating chamber  24  flows through the orifices  57  into the uppermost chamber  24  and is drawn upwards through the oil passage  58  into the oil return chamber  50  and circulated into the oil reservoir chamber  22 . 
     Even in any operational attitude such as inclined and inverted attitudes of the engine E, the circulation of the lubricating oil can be conducted without interruption to insure a good lubricating state at all times. Therefore, it is possible for the engine to resist the working of the power trimmer T in all directions. Moreover, since the pressure pulsation in the crank chamber  23  is utilized for the circulation of the lubricating oil, the expense of an oil pump is not required. 
     After completion of the working, the operation of the engine E is stopped to leave the power trimmer to stand, the engine E may be fallen sideways or inverted in some cases, as shown in FIGS. 10A and 10B. However, in such a state, the opening of the circulating path L connected to the valve-operating chamber  24  into the oil reservoir chamber  22 , i.e., the outlet end of the through-hole  52  is exposed above the oil level of the lubricating oil O stored in the oil reservoir chamber  22  and hence, the lubricating oil  0  in the oil reservoir chamber  22  can be prevented from flowing backwards through the circulating path L into the valve-operating chamber  24 . Therefore, it is possible to avoid the leakage of the lubricating oil from the valve-operating chamber  24  into the breather tube  54 . 
     Referring again to FIG. 2, a rotor  61  of a flywheel magneto  59  with a cooling blade  60  is secured to an outer end of the crankshaft  13  adjacent the valve-operating chamber  24 , and an ignition coil  62  cooperating with the rotor  61  is secured to the cylinder block  6 . A centrifugal clutch  64  is interposed between the rotor  61  and a working machine driving shaft  63 . The centrifugal clutch  64  includes a plurality of clutch shoes  65  expandably carried on the rotor  61 , a clutch spring  66  for biasing the clutch shoes  65  in a contracting direction, and a clutch drum  67  secured to the driving shaft  63  to surround the clutch shoes  65 . When the rotor  61  is rotated in a predetermined number of rotations or more, the clutch shoes  65  are expanded to come into pressure contact with an inner peripheral surface of the clutch drum  67 , thereby transmitting an output torque from the crankshaft  13  to the driving shaft  63 . 
     A shroud  69  is mounted to the engine body  1  to cover the head portion of the engine body  1  and the flywheel magneto  59  and to define a cooling air passage  68  between the shroud and the head portion of the engine body  1  and the flywheel magneto  59 . An inlet  68 I into the cooling air passage  68  is mounted in an annular configuration between the centrifugal clutch  64  and the shroud  69 , and an outlet  68   o  is mounted in the shroud  69  on the opposite side from the inlet  68 I. 
     Thus, during rotation of the rotor  61 , wind produced by the cooling blade  60  flows through the cooling air passage  68  to cool the various portions of the engine E. 
     The oil reservoir chamber  22  adjoining one side of the crank chamber  23  is disposed to protrude from the outer surface of the cylinder block  6  to face the cooling air passage  68 , and a known coil starter  70  capable of cranking the crankshaft  13  is mounted to the outer surface of the crankcase  7  adjacent the oil reservoir chamber  22 . The starter  70  is disposed to protrude to the outside of the shroud  69 , so that the shroud  69  does not interfere with operation of a starter rope of the start  70 . 
     When the rotor  61  is rotated along with the crankshaft  13 , wind produced by the cooling blade  60  flows through the cooling air passage  68  to cool the various portions of the engine E, but particularly, since the oil reservoir chamber  22  faces the cooling air passage  68 , the oil reservoir chamber  22  is also cooled by the cooling air, whereby the cooling of the lubricating oil O can be effectively performed. Moreover, the oil reservoir chamber  22  is disposed in a space between the crank chamber  23  and the recoil-type starter  70 , which is conventionally a dead space, and hence, the size of the engine E is not increased by the presence of the oil reservoir chamber  72 . 
     FIGS. 11 to  14  show a modification to tie engine, which employs a rotary valve  71  in place of the one-way valve  49 . In FIGS. 11 to  13 , the rotary valve  71  includes a pair of fan-shaped valve members  72  formed in a bulged manner on an opposite side of the follower ting gear  33  of the valve-operating devise  31  from the cam  35  and arranged on a diametrical line, and a pair of recesses  73  circumferentially located between the valve members  72 . The rotary valve  71  is opposed to a valve bore  74  provided in a partition wall between the crankshaft chamber  23  and the valve-operating chamber  24  to open and close the valve bore  74  by the rotation of the follower timing gear  33 . 
     Each of the valve members  72  and the recesses  73  has a center angle of approximately 90°, but because the follower timing gear  33  is driven with a reduction ratio of 1/2 from the driving gear  32  rotated in unison with the crankshaft  13 , each of the durations of closing and opening of the valve bore  74  by the valve members  72  and the recesses  73  is of approximately 180° in terms of a crank angle. 
     Moreover, as shown in FIG. 14, the valve member  72  and the recess  73  are disposed so that they cause the valve to be opened (see FIG. 13) during the lowering stroke of the piston  8  and to be closed (see FIG. 11) during the elevating stroke of the piston  8 . Particularly, a desirable disposition is such that the valve bore  74  is opened in a range of from the middle point P between top and bottom dead points of the piston  8  to a lowering-piston position corresponding to 45° in terms of the crank angle, and closed in a range of from such middle point P to an elevating-piston position of 45° in terms of the crank angle. 
     Other arrangements are similar to those in the above described embodiment, except that the valve chamber  47  is eliminated, and in FIGS. 11-14, portions or components corresponding to those in the above-described first embodiment are designated by like reference characters. 
     The rotary valve  71  opens and closes the valve bore  74  in mechanically operative association with the rotation of the crankshaft  13  and hence, even during rotation of the engine E at a high speed, a deviation in a predetermined timing for opening and closing the valve bore  74  cannot be produced, and by effectively utilizing in inertial effect of the flowing gas, the oil mist can be efficiently supplied from the crank chamber  23  into the valve-operating chamber  24  and at the same time, an average negative pressure state of the crank chamber  23  can be insured. 
     A second embodiment of the present invention will now be described with reference to FIGS. 15 to  25 . 
     Referring to FIG. 15, a carburetor  102  and an exhaust muffler  103  are mounted to front and rear portions of an engine body  101  of a hand-held type 4-cycle engine  10 E, respectively, and an air cleaner  104  is mounted at an intake inlet of the carburetor  102 . A fuel tank  105  is mounted to a lower surface of the engine body  101 . The carburetor  102  includes a diaphragm pump for pumping fuel from the fuel tank  105  by utilizing a pressure pulsation in a crank chamber which will be described and for circulating the surplus fuel to the fuel tank, so that the fuel can be supplied to an intake port of the engine  10 E in any attitude of the engine. 
     Referring to FIGS. 16,  17 ,  19  and  20 , the engine body  101  includes a crankcase  106  comprised of a pair of left and right case halves  106   a  and  106   b  coupled to each other by bolts, and an integral head-type cylinder block  107  bolted to an upper end face of the crank case  106 . The case halves  106   a  and  106   b  carry a crankshaft  108  horizontally, and a piston  110  is connected to a crank pin of the crankshaft  108  through a connecting rod  109  and slidably received in a cylinder  107   a  which is defined in the cylinder block  107 . 
     A top wall of the cylinder  107   a  includes intake port  111  and an exhaust port  112  defined therein and connected to the carburetor  102  and the exhaust muffler  103 , and intake and exhaust valves  113  and  114  provided therein for opening and closing the intake and exhaust ports  111  and  112 . A valve-operating device  115  for driving the intake and exhaust valves  113  and  114  is disposed in a valve-operating chamber  116  which is defined to extend from the crankcase  106  and the side of the cylinder block  107  to the top of the cylinder block  107 . The valve-operating chamber  116  is capable of being opened and closed by a head cover  121  coupled to the head of the cylinder block  107 . 
     The valve-operating device  115  includes a driving timing gear  117  secured to the crankshaft  108 , a follower driving gear  118  which is carried on a support shaft  119  mounted to the crankcase  106  at an intermediate portion of the valve-operating chamber  116  and which is driven at a reduction ratio of 1/2 from the driving timing gear  117 , a cam  120  integrally connected to one end of the follower timing gear  118 , a pair of cam followers  123  and  124  carried on a cam follower shaft  122  mounted in the cylinder head  107 , a pair of rocker arms  126  and  127  supported by a rocker shaft  125  mounted in the head of the cylinder block  107  with their one ends abutting against valve heads of the intake and exhaust valves  113  and  114 , a pair of push rods  128  and  129  which connect the cam followers  123  and  124  to the other ends of the rocker arms  126  and  127 , and valve springs  130  and  131  for biasing the intake and exhaust valves  113  and  114  in a closing direction, so that the intake is opened during an intake stroke of the piston  110  and the exhaust valve  114  is opened during an exhaust stroke of the piston  114 . 
     A crankcase  132  is defined in the crankcase  106  and includes a cylindrical inner chamber  132   a  in which a crank portion  108   a  of the crankshaft  108  is disposed, and an outer chamber  132   b  having a U-shape in section and surrounding the inner chamber  132  over from its bottom to its circumferentially opposite sides. An opening  133  is provided in a partition wall  134  between the inner and outer chambers  132   a  and  132   b  at the bottom of the crank chamber  132  and permits the inner and outer chambers  132   a  and  132   b  to communicate with each other. 
     A lubricating oil  0  is stored in the bottom of the crank chamber  132 , and the amount of lubricating oil stored is set at a value such that the oil surface slightly contacts with an outer periphery of the crank portion  108   a.  An oil dipper  135  is formed at an enlarged end of the connecting rod  109  as an oil mist producing mans for producing an oil mist by agitating and scattering the lubricating oil O during rotation of the crankshaft  108 . 
     As shown in FIGS. 17 and 23, the crank chamber  132  and the valve-operating chamber  116  communicate with each other through first and second oil supply passages  136  and  137  provided in the crankshaft  108  and the crankcase  106  above the oil level in the crank chamber  132 , respectively. The valve-operating chamber  116  also communicates at its bottom with the crank chamber  132  through an orifice  138 . 
     A rotary valve  139  is mounted between the first and second oil supply passage  136  and  137  as a control valve. The rotary valve  139  includes an arcuate groove  160  of approximately 180° made in an outer periphery of a journal portion  108   b  at one side of the crankshaft  108 , and a valve bore  162  which is provided in a bearing portion  161  of the crankcase  106  for bearing the journal portion  108   b  to communicate with the arcuate groove  160 . The first oil supply passage  136  in the crankshaft  108  is connected to the arcuate groove  160 , and the second oil supply passage  137  in the crankcase  106  is connected to the valve bore  162 . Thus, every time the crankshaft is rotated through approximately 180° the arcuate groove  160  and the valve bore  162  are brought alternately repeatedly into and out of communication with each other, but the rotary valve is disposed, so that it is opened (see FIG. 18) during a lowering stroke of the piston  110  and closed (see FIG. 17) during a elevating stroke of the piston  110 . Particularly, a desirable disposition is such that the opening of the rotary valve is started in a range of from a middle point P between top and bottom dead points of the piston  8  to a lowering-piston position corresponding to 45° in terms of the crank angle, and the opening of the rotary valve is completed in a range of from such middle point P to an elevating-piston position of 45° in terms of the crank angle, as in the above-describe modification (see FIG.  14 ). 
     As shown in FIG. 20, an upper portion of the valve operating chamber  124  communicates with the inside of the air cleaner  104  through a breather tube  142  made of a rubber and mounted through one side wall of the head cover  121 . In this case, that end of the breather tube  142  which is opened into the valve-operating chamber  16  is disposed to protrude into the valve-operating chamber  116  over a predetermined length. Therefore, the oil somewhat accumulated in the valve-operating chamber  116  can be prevented from flowing out of the chamber  116  into the breather tube  142  in any operational attitude of the engine  10 E. 
     As shown in FIGS. 16,  21  and  22 , an outer cover  163  is coupled the head cover  121 , so that it is fitted over an outer periphery of the head cover  121 . A flat uppermost chamber  164  is defined between ceiling walls of the covers  121  and  163  and communicates with the valve-operating chamber  116  through a pair of orifices  165  provided in the ceiling wall of the head cover  121  at diagonal locations (desirably at four comers). The upper most chamber  164  also communicates with the inner chamber  132   a  of the crank chamber  132  through a series of circulating oil passages  166  provided in the cylinder block  107  and the crankcase  106 . The circulating oil passages  166  have a sectional area larger than the total sectional area of the pair of orifices  165 . 
     Thus, by allowing the oil dipper  135  at the enlarged end of the connecting rod  109  to be swung while being vertically moved through the opening  133  between the inner and outer chambers  132   a  and  132   b  of the crank chamber  132  with the rotation of the crankshaft  108  during operation of the engine  10 E the lubricating oil is agitated and scattered to produce an oil mist in the crank chamber  132 . This oil mist first lubricates the peripheral portions of the crank portions  108   a  and the piston  110 , and upon opening of the rotary valve  139 , is then supplied along with a blow-by gas through the first and second oil supply passages  136  and  137  into the valve-operating chamber  116 , where the oil mist, and the blow-by gas are separated from each other. The oil mist lubricates the various portions of the valve operating device  115 , and the blow-by gas is discharged through the breather tube  142  into the air cleaner  104 . 
     The pressure in the crank chamber  132  is pulsated between positive and negative pressures alternatively repeated by elevating and lowering movements of the piston  110 . When the positive pressure is generated, the rotary valve  139  is opened to permit the positive pressure to be released via the first end second oil supply passages  136  and  137  into the valve-operating chamber  116 . When the negative pressure is generated, the rotary valve  139  is closed to inhibit the back-flow of the positive pressure from the valve-operating chamber  116  and hence, the pressure in the crank chamber  23  is kept negative on an average. 
     On the other hand, the valving chamber  116  communicates with the inside of the air cleaner  104  which is in an atmospheric pressure state, through the breather tube  142  and hence, the pressure in the valve-operating chamber  116  is substantially equal to atmospheric pressure. 
     The uppermost chamber  164  communicates with the crank chamber  132  through the oil circulating passage  166  and also with the valve-operating chamber  116  through the orifices  165  and hence, the pressure in the uppermost chamber  164  is equal to or slightly higher than the pressure in the crank chamber  132 . 
     The magnitude relationship between the pressures in the chambers can be represented by the following expression: 
     
       
         
           Pc≦Pt≦Pv 
         
       
     
     wherein, 
     Pc represents pressure in the crank chamber  132 , 
     Pt represents pressure in the uppermost chamber  164 , and 
     Pv pressure in the valve-operating chamber  116 . 
     As a result, during operation of the engine  10 E, the pressure flows through a path which will be shown below:                           
     Therefore, the oil mist fed from the crank chamber  132  to the valve-operating chamber  116  is circulated via the path back to the crank chamber  132 . The circulation of such oil mist and the liquefied oil is performed without hindrance even when the engine E is inclined in any attitude. 
     When the engine  10 E is fallen sideways or inverted during operation of the engine  10 E, as shown in FIGS. 24 and 25, much of the lubricating oil O in the crank chamber  132  flows in a direction to close the outer chamber  132   b,  and the lubricating oil  0  remains in a smaller amount in the inner chamber  132   a.  Thus, it is possible to prevent the piston  110  from being dipped in the oil end to avoid the entering of the oil into a combustion chamber. 
     In the operational state of the engine  10 E in the sideways-fallen or inverted attitude, the oil liquefied in the valve-operating chamber  116  flows through the orifices  165  into the uppermost chamber  164 . However, the pressure relationship between the chambers is maintained and hence, the oil accumulated in the uppermost chamber  164  is drawn through the oil circulating passage  166  into the inner chamber  132   a  in the crank chamber  132 . 
     On the other hand, the oil dipper  135  of the connecting rod  109  is incapable of agitating the lubricating oil in such case, but the oil returned through the oil circulating passage  166  into the inner chamber  132   a  strikes the crank portion  108   a  of the crankshaft  108  and the piston  110  and as a result, such oil is scattered to produce an oil mist again. Therefore, the lubrication of the various portions of the engine  10 E cannot be impeded. 
     Even in any operational attitude such as inclined and inverted attitudes of the engine E, the circulation of the lubricating oil can be conducted without interruption to insure a good lubricating state at all times. 
     Referring again to FIG. 16, a recoil type starter  143  capable of cranking the crankshaft,  108  is mounted to an outer surface of the crankcase  106  on the opposite side from the valve-operating chamber  116 . A rotor  146  of a flywheel magneto  144  with a cooling blade  145  is secured to an outer end of the crankshaft  108  adjacent the valve-operating chamber  116 , and an ignition coil  147  cooperating with the rotor  146  is secured to the cylinder block  107 . A centrifugal clutch  149  is interposed between the rotor  146  and a working machine driving shaft  148 . The centrifugal clutch  149  includes a plurality of clutch shoes  150  expandably carried on the rotor  146 , a clutch spring  151  for biasing the clutch shoes  150  in a contracting direction, and a clutch drum  152  secured to the driving shaft  148  to surround the clutch shoes  150 . When the rotor  146  is rotated in a predetermined number of rotations or more, the clutch shoes  150  are expanded to come into pressure contact with an inner peripheral surface of the crutch drum  152 , thereby transmitting an output torque from the crankshaft  108  to the driving shaft  148 . 
     A shroud  153  is mounted to the engine body  101  to cover the head portion of the engine body  101  and the flywheel magneto  144  and to define a cooling air passage  154  between the shroud and the head portion of the engine body  1  and the flywheel magneto  59 . An inlet  154   a  into the cooling air passage  154  is mounted in an annular configuration between the centrifugal clutch  149  and the shroud  153 , and an outlet  154   b  is mounted in the shroud  153  on the opposite side from the inlet  154   a.    
     Thus, during rotation of the rotor  146 , wind produced by the cooling blade  145  flows through the cooling air passage  154  to cool the various portions of the engine  10 E. 
     Although the embodiments of the present invention have been described in detail, it will be understood that the present invention is not limited to the above-described embodiments, and various modifications may made without departing from the spirit and scope of the invention as defined in the claims.