Patent Publication Number: US-2016230621-A1

Title: Lubricating device for engine

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     The application claims priority to Japanese Patent Application No. 2015-020886, filed on Feb. 5, 2015, the entire contents of which are incorporated herein by reference. 
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a lubricating device for an engine (internal combustion engine) that can be installed in a portable work machine or the like. 
     2. Description of Related Art 
     An engine installed in a portable work machine, such as a brush/weed cutter, may include a crank chamber, the pressure in which varies as a piston moves up and down, and an oil sump chamber which is disposed beneath the crank chamber and that stores a lubricating oil. Such an engine is disclosed in Japanese Patent Application Laid-open Publication No. 2004-293448. According to the Japanese Patent Application Laid-open Publication No. 2004-293448, a crank chamber and an oil sump chamber are in communication through an opening part, and the mist oil generated in the oil sump chamber is supplied to the crank chamber through the opening part. 
     However, according to the Japanese Patent Application Laid-open Publication No. 2004-293448, the opening area of the opening part, which provides the communication between the crank chamber and the oil sump chamber, is relatively large. Hence, a gas in the crank chamber is supplied extensively in the oil sump chamber through the opening part when the pressure in the crank chamber is a positive pressure, so that a force (pressure) of the gas impacting the surface of the oil is relatively low. Therefore, according to the Japanese Patent Application Laid-open Publication No. 2004-293448, it has been difficult to generate sufficient mist oil in the oil sump chamber. 
     In view of such circumstances, an object of the present invention is to efficiently generate mist oil in an oil sump chamber. 
     SUMMARY OF THE INVENTION 
     According to one aspect of the present invention, a lubricating device for an engine is provided. The lubricating device for an engine includes: a crank chamber, a pressure in which varies as a piston moves up and down; an oil sump chamber which is disposed beneath the crank chamber and that stores a lubricating oil; a valve drive chamber which is disposed on a side of the crank chamber and that accommodates drive components of each valve mechanism for intake and exhaust; a first partition wall that separates the crank chamber and the oil sump chamber; a second partition wall that separates the crank chamber and the valve drive chamber; a first opening part that penetrates the first partition wall and provides communication between the crank chamber and the oil sump chamber; and a second opening part that penetrates the second partition wall and provides communication between the crank chamber and the valve drive chamber. In the lubrication device for an engine, when the pressure in the crank chamber is a positive pressure, a gas in the crank chamber is injected into the oil sump chamber through the first opening part and impacts an oil in the oil sump chamber thereby to generate a mist oil in the oil sump chamber, and a mist oil in the crank chamber passes through the second opening part and is supplied to the valve drive chamber. In the lubricating device for an engine, when the pressure in the crank chamber is a negative pressure, the mist oil in the oil sump chamber passes through the first opening part and is supplied to the crank chamber. 
     Other objects and features of aspects of the present invention will be understood from the following description with reference to the accompanying drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a perspective view of an engine according to an embodiment of the present invention; 
         FIG. 2  is a plan view of the engine according to the embodiment; 
         FIG. 3  is a sectional view taken at line I-I in  FIG. 2 ; 
         FIG. 4  is a partial perspective view of a crank case of the engine according to the embodiment when the crank case is observed from the oil sump chamber side; 
         FIG. 5  is a view illustrating a bearing that rotatably supports a crank shaft of the engine according to the embodiment; and 
         FIG. 6  is a schematic explanatory diagram of a lubricating device of the engine according to the embodiment. 
     
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     The following will describe an embodiment of the present invention with reference to the accompanying drawings. 
       FIG. 1  and  FIG. 2  are a perspective view and a plan view, respectively, of an engine according to an embodiment of the present invention.  FIG. 3  is a sectional view taken at line I-I in  FIG. 2 .  FIG. 3  illustrates the engine when a piston is positioned near a top dead center. Furthermore, as used in the present embodiment, “upper side” approximately coincides with a vertical upper side in a state in which the engine is used over a longest period of time (erect state). 
     An engine  1  is an overhead valve (OHV) 4-stroke, air-cooled engine. The engine  1  has a cylinder block  2 , a crank case  4 , and a cylinder head  6 . The crank case  4  is disposed on one end (the lower end) in the longitudinal direction of the cylinder block  2  and constitutes a crank chamber  3 . The cylinder head  6  is disposed on the other end (the upper end) in the longitudinal direction of the cylinder block  2  and constitutes, together with the cylinder block  2 , a combustion chamber  5 . 
     In the present embodiment, the cylinder block  2 , the crank case  4 , and the cylinder head  6 , which are all provided separately, are connected by bolts. An oil case  7  for storing a lubricating oil is connected to the lower end of the crank case  4 . 
     The crank case  4  is provided at the lower end of the cylinder block  2 . The cylinder block  2  and the crank case  4  rotatably support a crank shaft  9 . More specifically, both ends of the crank shaft  9  are disposed so that the ends project out of the crank chamber  3  formed inside the crank case  4 . In the present embodiment, both ends of the crank shaft  9  projecting out of the crank chamber  3  are held between the cylinder block  2  and the crank case  4 , and are rotatably supported thereby. Furthermore, in the present embodiment, one end of the crank shaft  9  (namely, the end adjacent to a valve drive chamber  30 , which will be described below) is rotatably supported by the cylinder block  2  and the crank case  4  via a bearing  40 , which will be described below. This will be described below in more detail with reference to  FIG. 5 . 
     A cylinder  10  having a columnar space is provided in the cylinder block  2 . A piston  11  is inserted in the cylinder  10  such that the piston  11  can reciprocate in the vertical direction. The piston  11  is connected to the crank shaft  9  of the crank chamber  3  via a crank web  12  and a connecting rod  13 . Thus, the reciprocating motion of the piston  11  is converted into the rotational motion of the crank shaft  9 . Furthermore, the reciprocation of the piston  11  also changes the pressure (air pressure) in the crank chamber  3 . 
     The cylinder head  6  is provided with an intake port  15  and an exhaust port  16 . The intake port  15  is in communication with a carburetor (not illustrated). The exhaust port  16  is in communication with a muffler  17 . Furthermore, the cylinder head  6  is provided with an intake valve  18 , which opens and closes the intake port  15 , and an exhaust valve  19 , which opens and closes the exhaust port  16 . 
     Furthermore, the cylinder head  6  includes a valve system chamber  20 , which accommodates the intake valve  18  and the exhaust valve  19 . The valve system chamber  20  is formed of the cylinder head  6  and a valve system chamber cover  21 . 
     The intake valve  18  and the exhaust valve  19  are provided with a valve mechanism  25  (refer to  FIG. 6 ) for driving the intake valve  18  and the exhaust valve  19 . The valve mechanism  25  includes a valve drive gear  26 , a cam gear  27 , a cam  28 , a pair of cam followers (not illustrated), a pair of pushrods (not illustrated), and valve springs (not illustrated). The valve drive gear  26  is fixed to the crank shaft  9 . The cam gear  27  is driven by the valve drive gear  26 . The cam  28  is provided on one end of the cam gear  27 . The pair of cam followers is swung by the cam  28  and rotatably supported by the cylinder block  2 . The pair of pushrods is supported by a rocker shaft (not illustrated) provided on the head of the cylinder block  2 , one ends thereof being in contact with the valve heads of the intake valve  18  and the exhaust valve  19 . The valve springs urge the intake valve  18  and the exhaust valve  19  in a valve closing direction. 
     Among the sections constituting the valve mechanism  25 , the valve drive gear  26 , the cam gear  27 , and the cam  28  are accommodated in the valve drive chamber  30 . The valve drive chamber  30  is disposed on a side of the crank chamber  3 . The valve drive chamber  30  is composed of the cylinder block  2 , the crank case  4 , and a valve drive chamber cover (not illustrated). Among the sections constituting the valve mechanism  25 , the pushrods and the valve springs are accommodated in the valve system chamber  20 . The valve system chamber  20  is disposed above the combustion chamber  5 . 
     The valve mechanism  25  corresponds to “each valve mechanism for intake and exhaust” in the present invention. Furthermore, the valve drive gear  26 , the cam gear  27 , and the cam  28  correspond to “the drive components of each valve mechanism for intake and exhaust” in the present invention. 
     The oil case  7  is formed of a casing surrounding all sides and the bottom. By attaching the oil case  7  to the crank case  4 , an oil sump chamber  32  is formed by the cases  4  and  7 . A lubricating oil is stored in the oil sump chamber  32 . A semi-cylindrical part of the crank case  4  rotatably accommodates the crank shaft  9 , and the semi-cylindrical part provides a first partition wall  33 , which separates the crank chamber  3  and the oil sump chamber  32 . 
       FIG. 4  is a partial perspective view of the crank case  4  of the engine  1  according to the present embodiment when the crank case  4  is observed from the oil sump chamber  32  side. 
     As illustrated in  FIG. 3  and  FIG. 4 , the crank chamber  3  and the oil sump chamber  32  are separated by the first partition wall  33 . The first partition wall  33  has a semi-cylindrical shape. More specifically, the first partition wall  33  functions to rotatably accommodate the crank web  12 , which is accommodated in the crank chamber  3 , on the crank chamber  3  side, thus providing a curved surface part bulging toward the oil sump chamber  32 . A central portion  34  of the curved surface part bulges most toward the oil sump chamber  32 . 
     A first opening part  35 , which provides communication between the crank chamber  3  and the oil sump chamber  32  is penetratingly formed in the central portion  34  of the semi-cylindrical first partition wall  33 . The first opening part  35  is positioned within a projection plane of the piston  11  in the first partition wall  33 . In other words, the first opening part  35  is penetratingly formed in an area hidden by the piston  11  when the first partition wall  33  is observed from the combustion chamber  5  side. 
     The first opening part  35  is preferably positioned right below the central portion of the piston  11 . In other words, the central axis of the first opening part  35  and the central axis of the piston  11  are preferably positioned on the same axial line. 
     The opening area of the first opening part  35  is preferably within a range of from 3% up to 40% of the cross-sectional area of the piston  11 , and more preferably within a range of from 5% up to 35% of the cross-sectional area of the piston  11 . The cross-sectional area of the piston  11  refers to the cross-sectional area of the piston  11  in a plane that is orthogonal to the direction of the reciprocation of the piston  11  (i.e., the central axis of the piston  11 ). 
     Although the shape of the cross-section of the first opening part  35  is rectangular in the present embodiment, the shape of the cross-section of the first opening part  35  is not limited thereto, and may be, for example, circular. Furthermore, the first opening part  35  in the present embodiment is composed of the single through hole; however, the first opening part  35  may alternatively be composed of two or more through holes. If the first opening part  35  is composed of two or more through holes, then the total sum of the opening areas of the two or more through holes, i.e. the total opening area, is preferably within a range of from 3% up to 40% of the cross-sectional area of the piston  11 , and more preferably within a range of from 5% up to 35% of the cross-sectional area of the piston  11 . 
     A tubular section  36  is provided, surrounding the first opening part  35 , at the lower surface of the semi-cylindrical first partition wall  33 . The tubular section  36  projects downward from the lower surface of the first partition wall  33 . In the present embodiment, the tubular section  36  has a rectangular cross-sectional shape. Alternatively, however, the cross-section of the tubular section  36  is not limited to the rectangular shape, and may be, for example, a circular shape. 
       FIG. 5  illustrates the bearing  40  that rotatably supports the crank shaft  9  of the engine  1  according to the present embodiment. The crank chamber  3  and the valve drive chamber  30  are separated by a second partition wall  42 . The second partition wall  42  is composed of the cylinder block  2  and the crank case  4 . 
     In the second partition wall  42 , an upper opening part  43  having a semicircular cross-section is formed in the lower end of the cylinder block  2 . In the second partition wall  42 , a lower opening part  44  having a semicircular cross-section is formed in the upper end of the crank case  4 . 
     A second opening part  45  is composed of the semicircular upper opening part  43  and the semicircular lower opening part  44  and has a circular cross-sectional shape. The second opening part  45  penetrates the second partition wall  42 , providing communication between the crank chamber  3  and the valve drive chamber  30 . 
     The bearing  40  is inserted in the second opening part  45  of the second partition wall  42 . In other words, the bearing  40  is provided in the second opening part  45  of the second partition wall  42 . The bearing  40  is an open ball bearing, which has a gap between the inner ring and the outer ring thereof and has gaps among a plurality of balls thereof. Thus, the bearing  40  allows the passage of a mist oil, which is a mist-like oil. 
     The bearing  40  has one end of the crank shaft  9  (the end on the valve drive chamber  30  side) inserted in the inner ring thereof to rotatably support the crank shaft  9 . Hence, the one end of the crank shaft  9  (the end on the valve drive chamber  30  side) is rotatably supported by the cylinder block  2  and the crank case  4  via the bearing  40 . A valve drive gear  26  is fixed to a portion of the one end of the crank shaft  9  that is positioned in the valve drive chamber  30 .  FIG. 5  does not illustrate the cam gear  27  driven by the valve drive gear  26 . 
     Referring now to  FIG. 6 , a description will be given of a lubricating device  50  of the engine  1  according to the present embodiment.  FIG. 6  is a schematic explanatory diagram of the lubricating device  50  of the engine  1  according to the present embodiment. The lubricating device  50  of the engine  1  utilizes the changes in the pressure in the crank chamber  3  caused by the reciprocation of the piston  11  to circulate the oil stored in the oil sump chamber  32 , thereby lubricating each section of the engine  1 . 
     A circulation path  61  for circulating the oil is provided between the oil sump chamber  32  and the valve system chamber  20 . The circulation path  61  includes the first opening part  35 , the second opening part  45 , the valve drive chamber  30 , the valve system chamber  20 , an oil feed passage  62 , and the crank chamber  3 . 
     If the piston  11  moves toward the top dead center, causing the pressure in the crank chamber  3  to become a negative pressure, then the mist oil in the oil sump chamber  32  passes through the first opening part  35  and is supplied to the crank chamber  3 . Thereafter, if the piston  11  moves toward a bottom dead center, causing the pressure in the crank chamber  3  to become a positive pressure, then the mist oil in the crank chamber  3  passes through the second opening part  45  and is supplied to the valve drive chamber  30  and the valve system chamber  20 . 
     The bearing  40  is provided in the second opening part  45  (refer to  FIG. 5 ). With this arrangement, mist oil droplets having relatively large diameters among the mist oil droplets in the crank chamber  3  are blocked by the bearing  40 , thus restricting their passage to the valve drive chamber  30  from the crank chamber  3 . Meanwhile, among the mist oil droplets in the crank chamber  3 , mist oil droplets having relatively small diameters pass through the gap between the inner ring and the outer ring of the bearing  40  and through the gaps among the plurality of balls of the bearing  40 , and are supplied to the valve drive chamber  30 . Thus, the valve drive gear  26 , the cam gear  27 , the cam  28 , the pushrods, and the valve springs constituting the valve mechanism  25  are lubricated by the mist oil flowing through the circulation path  61 . 
     A suction passage  64  through which the oil in the valve system chamber  20  is drawn in is provided inside the valve system chamber  20 . The oil feed passage  62  is provided between the suction passage  64  and the crank chamber  3 . The oil feed passage  62  has the open end on one side thereof connected to the suction passage  64  and the open end on the other side thereof connected to the crank chamber  3 . The open end on the other side of the oil feed passage  62  is positioned such that the open end is fully opened when the piston  11  reaches the top dead center. 
     When the pressure in the crank chamber  3  becomes a negative pressure due to the movement of the piston  11  to the top dead center, the mist oil in the valve system chamber  20  is drawn in through the opening of the oil feed passage  62  and fed into the crank chamber  3  through the suction passage  64  and the oil feed passage  62 . The oil fed into the crank chamber  3  is returned into the oil sump chamber  32  through the first opening part  35 . 
     A discharge passage  65  for discharging the blow-by gas in the oil circulation path to the combustion chamber  5  is provided inside the valve system chamber  20 . One end  66  of the discharge passage  65  is provided in the valve system chamber  20 , while the other end thereof is connected to an air cleaner  67 . The air cleaner  67  is provided on the upstream side of the above-mentioned carburetor and functions to remove dust and the like in the air. 
     The blow-by gas containing oil, which has been sent to the air cleaner  67 , is subjected to the gas-liquid separation to be separated to the blow-by gas and oil by an oil separator  68  provided in the air cleaner  67 . The separated oil passes through a reflux passage  70 , which provides communication between the air cleaner  67  and the crank chamber  3 , to be sent to the crank chamber  3 . The open end of the reflux passage  70  on the crank chamber  3  side is positioned such that the open end is fully opened when the piston  11  reaches the top dead center. Hence, when the pressure in the crank chamber  3  becomes a negative pressure due to the movement of the piston  11  to the top dead center, the oil separated by the oil separator  68  is drawn through the reflux passage  70  and fed into the crank chamber  3 . Meanwhile, the blow-by gas separated by the oil separator  68  is burnt in the combustion chamber  5  and then discharged to the outside through the muffler  17 . 
     When the pressure in the crank chamber  3  becomes a positive pressure due to the movement of the piston  11  to the bottom dead center, a high-pressure gas in the crank chamber  3  is injected into the oil sump chamber  32  through the first opening part  35 . In other words, the gas in the crank chamber  3  that is pushed out as the piston  11  moves to the bottom dead center is injected into the oil sump chamber  32  through the first opening part  35 . The injected gas impacts the oil in the oil sump chamber  32 . The high-pressure gas from the crank chamber  3  blown onto the oil surface in the oil sump chamber  32  in the manner described above expedites the misting of the oil in the oil sump chamber  32 , thus efficiently generating a mist oil in the oil sump chamber  32 . 
     If the opening area of the first opening part  35  is unduly large, then it becomes difficult to cause the gas in the crank chamber  3  to vigorously impact the surface of the oil in the oil sump chamber  32  through the first opening part  35 . This may lead to unsuccessful generation of a mist oil. Meanwhile, if the opening area of the first opening part  35  is unduly small, then the crank chamber  3  functions like a pump, and the output of the engine  1  may be reduced. Thus, the upper limit value of the opening area of the first opening part  35  can be set, considering the efficiency of the generation of the mist oil in the oil sump chamber  32 . Furthermore, the lower limit value of the opening area of the first opening part  35  can be set, considering the output required of the engine  1 . Taking these into account, the opening area of the first opening part  35  is preferably within a range of from 3% up to 40% of the cross-sectional area of the piston  11 , and more preferably within a range of from 5% up to 35% of the cross-sectional area of the piston  11 . 
     According to the present embodiment, the lubricating device  50  of the engine  1  includes: the crank chamber  3 , the pressure inside which varies as the piston  11  moves up and down; the oil sump chamber  32  which is disposed below the crank chamber  3  and that stores a lubricating oil; the valve drive chamber  30  which is disposed on the side of the crank chamber  3  and that accommodates the drive components of each valve mechanism for the intake and the exhaust; the first partition wall  33  that separates the crank chamber  3  and the oil sump chamber  32 ; the second partition wall  42  that separates the crank chamber  3  and the valve drive chamber  30 ; the first opening part  35  that penetrates the first partition wall  33  and provides communication between the crank chamber  3  and the oil sump chamber  32 ; and the second opening part  45  that penetrates the second partition wall  42  and provides communication between the crank chamber  3  and the valve drive chamber  30 . In the lubricating device  50  of the engine  1 , when the pressure in the crank chamber  3  is a positive pressure, the gas in the crank chamber  3  is injected through the first opening part  35  into the oil sump chamber  32  and impacts the oil in the oil sump chamber  32  thereby to generate the mist oil in the oil sump chamber  32 , and the mist oil in the crank chamber  3  passes through the second opening part  45  and is supplied to the valve drive chamber  30 . In the lubricating device  50  of the engine  1 , when the pressure in the crank chamber  3  is a negative pressure, the mist oil in the oil sump chamber  32  passes through the first opening part  35  and is supplied to the crank chamber  3 . Thus, the high-pressure gas from the crank chamber  3  is blown onto the oil surface in the oil sump chamber  32  so as to disturb the oil surface. This makes it possible to expedite the misting of the oil in the oil sump chamber  32 , thus efficiently generating a mist oil in the oil sump chamber  32 . 
     Furthermore, according to the present embodiment, the first opening part  35  is positioned in the projection plane of the piston  11  in the first partition wall  33 . Therefore, the high-pressure gas generated in the crank chamber  3  by the reciprocation of the piston  11  can be vigorously blown, through the first opening part  35 , onto the oil surface in the oil sump chamber  32  to disturb the oil surface, thus permitting more efficient generation of the mist oil in the oil sump chamber  32 . 
     Furthermore, according to the present embodiment, the opening area of the first opening part  35  is within a range of from 3% up to 40% of the cross-sectional area of the piston  11 . This allows the mist oil to be efficiently generated in the oil sump chamber  32  and also allows the output required of the engine  1  to be ensured. 
     Furthermore, according to the present embodiment, the first partition wall  33  has the tubular section  36 , which projects downward from the lower surface of the first partition wall  33  and which surrounds the first opening part  35 . This makes it possible to restrain the oil in the oil sump chamber  32  from excessively flowing into the crank chamber  3  through the first opening part  35  during, for example, an inverted operation of the engine  1 . 
     Furthermore, according to the present embodiment, the bearing  40  rotatably supporting the crank shaft  9  is provided in the second opening part  45 . The bearing  40  is an open ball bearing, which permits the passage of the mist oil. Hence, mist oil droplets having relatively small diameters among the mist oil droplets in the crank chamber  3  pass through the gap between the inner ring and the outer ring of the bearing  40  and through the gaps among the plurality of balls of the bearing  40 , and are supplied to the valve drive chamber  30 , thus making it possible to restrain oversupply of the oil to the valve drive chamber  30  and the valve system chamber  20 . 
     In the present embodiment, the dimensions, the opening area, the shape and the like of the first opening part  35  may be set based on the volume of the stroke of the vertical movement of the piston  11  in the cylinder  10  (cylinder capacity) of the engine  1 . 
     Furthermore, in the present embodiment, the flow velocity of the gas injected through the first opening part  35  into the oil sump chamber  32  and blown onto the surface of the oil in the oil sump chamber  32  (i.e. the blowoff velocity of the gas at the first opening part  35 ) is preferably within a range of from 1,000 cm/s up to 10,000 cm/s, and more preferably within a range of from 1,500 cm/s up to 8,000 cm/s. Setting the blowoff velocity of the gas at the first opening part  35  to the ranges mentioned above permits efficient generation of the mist oil in the oil sump chamber  32 . 
     Furthermore, the engine  1  in the present embodiment can be installed, as a drive source, in a portable work machine, such as a brush/weed cutter, a hole digging machine, or a concrete cutter. Furthermore, the engine  1  can be installed, as a drive source, in a backpack work machine, such as a backpack blower, a sprayer, a duster, or a backpack brush/weed cutter. 
     In the lubricating device for an engine according to the present invention, the mist oil is generated in the oil sump chamber by a gas in the crank chamber being injected into the oil sump chamber through the first opening part and impacting the oil in the oil sump chamber when the pressure in the crank chamber is a positive pressure. This makes it possible to expedite the generation of the mist oil (misting) in the oil sump chamber by blowing the high-pressure gas from the crank chamber onto the surface of the oil in the oil sump chamber, so that the mist oil can be efficiently generated in the oil sump chamber. 
     Although the embodiment of the present invention has been described, the present invention is not limited to the foregoing embodiment, and it is obvious that more modifications, changes and the like can be made on the basis of the technical idea of the present invention.