Abstract:
A lubrication and breather system for an engine that is generally adapted for use as either a vertically-oriented crankshaft-type engine or a horizontally-oriented crankshaft-type engine. The crankcase has first and second bearing bosses supporting first and second journal portions of the crankshaft. The second bearing boss lies above the first bearing boss when the engine is of the vertical-type. The system includes a cap that is secured over the second bearing boss and cooperates with the second bearing boss to define an annular chamber for receiving splashed oil produced in the crankcase. The cap has a plurality of ribs formed thereon that reduce an amount of oil, which is entrained in the blow-by gas, sent from the annular chamber to the breather chamber. The second bearing block includes an oil feed hole, a plurality of oil sumps, and a plurality of oil return holes, with the oil return holes being of relatively smaller size. Each of the oil sumps is associated with one oil return hole. A volume of oil ordinarily remains in the oil sump to limit entry of blow-by gases into the annular chamber via the oil return holes.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention generally relates to a lubricating system for use in a horizontal-type engine or a vertical-type engine including a crankcase and a cylinder block and, more specifically, to an improved oil seal and drain structure in such a lubricating system. 
     2. Description of the Related Art 
     Prior art type engines include a horizontal-type in which a crankshaft is disposed horizontally, and a vertical-type in which a crankshaft is disposed vertically. In the conventional engines, the crankcase and the cylinder block are different for each of the types, because of different conditions of the arrangement of a discharge passage for a blow-by gas produced in the crankcase and a return passage for oil separated from the blow-by gas and returned to the crankcase. 
     The different construction of the crankcase and the cylinder block in each of the types is inconvenient for providing a mass-produced engine, resulting in higher cost. 
     U.S. Pat. No. 5,937,836, the disclosure of which is expressly incorporated herein in its entirety, provides a solution to the above referenced problem, and presents an engine that is adapted for both horizontally and vertically-oriented crankshafts. The lubrication system of the &#39;836 patent has been found to work quite well in engines having either horizontally or vertically-oriented crankshafts. However, with the structure of the &#39;836 patent, there is presented a potential problem that, depending upon the engine displacement size and the configuration of the second bearing boss, there may be an excessive amount of oil communicated from the crankcase into the breather chamber when the crankshaft is vertically-oriented. While the breather chamber includes means to filter the oil out of the blow-by gas, the quantity of oil may be so great as to overwhelm the filtering means and therefore cause too much oil to be conveyed with the blow-by gas into the air cleaner of the engine intake system, leading to engine performance issues. 
     Accordingly, there exists a need in the art for an improved lubrication system for an engine having a vertically oriented crankshaft wherein the engine is otherwise generally adapted for use with either a horizontal or vertical crankshaft. There further exists a need in the art for such an engine that is adapted to limit or reduce the amount of oil that is conveyed with the blow-by gas into the breather chamber. 
     SUMMARY OF THE INVENTION 
     The present invention has been accomplished with such circumstance in view, and it is an object of the present invention to provide a lubricating system for a vertically-oriented crankshaft wherein discharge of the blow-by gas, the separation of oil from the blow-by gas, and the return of oil separated from the blow-by gas to the crankcase can be reliably performed. The present invention is therefore directed toward an improved lubrication system for an engine having a vertically oriented crankshaft wherein the engine is otherwise generally adapted for use with either a horizontal or vertical crankshaft. The present invention is further directed toward such an engine that is adapted to limit or reduce the amount of oil that is conveyed with the blow-by gas into the breather chamber. 
     In accordance with the present invention, a lubricating and breather system in an engine having a crankcase and a cylinder block adapted for use in either a horizontal-type or vertical-type engine is provided. The engine includes a crankshaft having first and second journal portions. The crankcase has first and second bearing bosses supporting the first and second journal portions of the crankshaft. The second bearing boss lies above the first bearing boss when the engine is of the vertical-type. 
     In further accordance with the present invention, the lubricating and breather system includes an annular chamber in the second bearing boss for receiving splashed oil produced in the crankcase. A breather chamber, which is in one side of the cylinder block, communicates with the annular chamber to separate blow-by gas and oil. For communication of oil to the crankcase, the breather chamber has a first return bore located at a portion thereof which is a lowermost portion when the engine is a horizontal-type and a second return bore located at a portion thereof which is a lowermost portion when the engine is a vertical-type. 
     In further accordance with the present invention, a breather tube is coupled to an intake system of the engine and connected to a portion of the breather chamber. The breather tube is located above the first return bore when the engine is a horizontal-type and above the second return bore when the engine is a vertical-type. 
     In further accordance with the present invention, a cap is secured over the second bearing boss and cooperates with the second bearing boss to define the annular chamber. The cap has a plurality of ribs formed thereon that serve to reduce the amount of oil that is communicated from the annular chamber to the breather chamber. The ribs include a plurality of radially directed ribs and an annular rib. 
     In further accordance with the present invention, the second bearing boss includes an oil feed hole through which oil and blow-by gases flow from the crankcase to the annular chamber. A plurality of oil return holes, through which oil is returned from the annular chamber to the crankcase, are formed in the second bearing boss. The oil return holes have a smaller diameter than that of the oil feed hole. The second bearing boss further includes a plurality of oil sumps, each of the oil sumps being associated with one of the oil return holes and being adapted to retain an amount of oil therein. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     These and further features of the invention will be apparent with reference to the following description and drawings, wherein: 
     FIG. 1 is a vertical sectional side view of an embodiment of the present invention applied to a vertical-type engine; 
     FIG. 2 is a vertical sectional view taken along a line  2 — 2  in FIG. 1; 
     FIG. 3 is a view taken in a direction of an arrow  3 — 3  in FIG. 1 with the cap for the annular chamber being removed; 
     FIG. 4 is a sectional view taken along a line  4 — 4  in FIG. 1; 
     FIG. 5 is a sectional view taken along a line  5 — 5  in FIG. 4; 
     FIG. 6 is a sectional view taken along a line  6 — 6  in FIG. 3; 
     FIG. 7 is an inner side view of a lid for a breather chamber; 
     FIG. 8 is a cross-sectional view through the second bearing boss of the crankcase as seen along line  8 — 8  of FIG. 3; 
     FIG. 9 is a partial plan view of an inside surface of a cap; and, 
     FIG. 10 is a partial cross-sectional view of the cap of FIG.  9 . 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     Referring to FIGS. 1 and 2, an engine body  1  is comprised of a crankcase  3  that supports a crankshaft  2  disposed vertically. A cylinder block  5  has a cylinder bore  5   a  in which a piston  4  slides, and a cylinder head  8  in which intake and exhaust valves  6  and  7  are supported. The crankshaft  2  and the piston  4  are interconnected by a connecting rod  9 . The crankcase  3  is divided into an upper case half  3   a  and a lower case half  3   b  along a diagonal line on the case  3 , which obliquely intersects an axis of the crankshaft  2 . The upper case half  3   a , the cylinder block  5 , and the cylinder head  8  are integrally formed. In this way, the engine body  1  is formed of two parts and, moreover, is applicable to a vertical-type engine. The upper and lower case halves  3   a  and  3   b  are releasably coupled to each other by one or more bolts. 
     A flat valve-operating transmitting chamber  10  is defined in one side of the cylinder block  5  adjacent the cylinder bore  5   a . A timing transmitting device  12  is disposed in the chamber  10  and interconnects the crankshaft  2  and a valve-operating camshaft  11  supported on the cylinder head  8 . The timing transmitting device  12  is comprised of a toothed driving pulley  13   1  secured to the crankshaft  2 , a toothed driven pulley  13   2  secured to the valve-operating cam shaft  11 , and a toothed belt  14  reeved around both the pulleys  13   1  and  13   2 , so that the rotation of the crankshaft  2  is reduced to one half and transmitted to the valve-operating cam shaft  11 . The valve-operating cam shaft  11  is adapted to open and close the intake and exhaust valves  6  and  7  through a rocker arm  15  by the rotation thereof. Portions of the timing transmitting device  12  and the rocker arm  15  are covered by a head cover  16 , which is coupled to the cylinder head  8  by bolts. 
     The engine body  1  is disposed so that the second bearing boss  3   2  occupies a position above the first bearing boss  3   1 , in order to support the crankshaft  2  vertically. An oil reservoir chamber  26 , which is a level that is lower than that of the chamber  10 , is defined in the lower case half  3   b  of the crankcase  3 . The amount of lubricating oil  27  stored in the oil reservoir chamber  26  is set such that the timing transmitting device  12  is not immersed in the oil. 
     The support shaft  20  of a speed-adjusting centrifugal governor  19  is horizontally secured to a bracket  50  secured to the inner wall of the lower case half  3   b . The centrifugal governor  19  is formed by the rotary table  21 , a tubular slider  23  slidably supported on the support shaft  20 , and a plurality of swinging pendulum-type centrifugal weights  24 , which are swingably supported on the rotary table  21  to sandwich the slider  23 . Each of the centrifugal weights  24  includes an operating arm  24   a  that allows the slider  23  to slide in one direction when the weight  24  is swung radially outwards by centrifugal force. When the slider  23  slides in the one direction, a throttle valve in the intake system is operated to a closed position through a link mechanism (not shown) and the number of revolutions of the engine is controlled to a preset value, in a conventional manner. 
     A driven gear  22  is formed at an end face of a rotary table  21  rotatably carried on the support shaft  20  and is meshed with a governor driving gear  18  secured to the crankshaft  2 . The rotary table  21  has a plurality of vanes  25   a  projecting from an outer peripheral surface thereof to form an impeller  25 , and a lower half of the rotary table  21  is immersed in the lubricating oil  27 . 
     A guide wall  51  is integrally formed on an inner wall of the crankcase  3  to cover a path extending from the driving pulley  13   1  to the valve-operating transmitting chamber  10  toward the driven pulley  13   2 . A recess  52 , which functions as an oil reservoir, is provided in an upper end face of the valve-operating cam shaft  11 . 
     In the crankshaft  2 , a journal portion  2   1  on the side of the timing transmitting device  12  is called a first journal portion, and a journal portion  2   2  on the opposite side is called a second journal portion. In the crankcase  3 , bearing bosses  3   1  and  3   2  carrying the first and second journal portions  2   1  and  2   2  are called first and second bearing bosses, respectively. When the engine body  1  is used as a vertical engine, as illustrated, the second bearing boss  3   2  lies above the first bearing boss  3   1 . 
     In FIGS. 3 to  5 , a circular recess  33  is defined in an outer end face of the second bearing boss  3   2  of the crankcase  3  and is formed as an annular chamber  33  by closing it with a cap  35 . The cap  35 , which is preferably formed from metal, carries an oil seal  34  that sealingly engages an outer peripheral surface of the crankshaft  2 . The oil seal  34  is surrounded by an annular metal spring  34   a  (FIG.  10 ), which presses the seal  34  against the crankshaft  2 . 
     The cap  35  preferably has an elastomeric or flexible rubber-like structure molded or otherwise attached thereto. In addition to the oil seal  34 , the elastomeric structure includes a plurality of ribs  35   a ,  35   b  formed on an inner surface of the cap  35 , as shown best in FIGS.  5  and  9 - 10 . Although the ribs are preferably flexible and integrally formed with the oil seal  34 , it is contemplated that the ribs, instead, could be formed from the metal body of the cap  35  by suitable forming operations. 
     The ribs include a plurality of radially directed ribs  35   a  and an annular rib  35   b , which is concentric with the crankshaft  2 . The annular rib  35   b  is formed by a series of arcuate rib sections that extend between the radially directed ribs  35   a  at a location generally midway along the length of the radially directed ribs  35   a , as illustrated. The ribs  35   a ,  35   b  present an obstacle to the fluid stream, which consists of blow-by gas and entrained oil, flowing into the annular chamber  33 , and thereby permit the entrained oil to fall out of the blow-by gas, as described hereinafter. Naturally, the elastomeric ribs  35   a ,  35   b  and oil seal  34  may be molded over the metal body of the cap  35 , or may be attached by suitable adhesive bonding techniques. 
     With respect to FIGS. 3,  4  and  8 , an oil feed hole  36 , which permits the annular chamber  33  to communicate with the inside of the crankcase  3 , is provided in the second bearing boss  3   2 . A plurality of oil sumps  36 ′ are also formed in the outer face of the second bearing boss  3   2 . Each of the oil sumps  36 ′ have an oil return hole  36 ″ formed therein through which oil flows back to the crankcase  3 . As will be appreciated, the oil feed hole  36  has a relatively large and, preferably, constant diameter so as to provide free or uninhibited communication between the interior of the crankcase  3  and the annular chamber  33 . On the other hand, the oil return holes  36 ″ are substantially smaller in diameter than the oil feed hole  36  and thereby substantially prevent or inhibit the flowing-through of blow-by gas into the annular chamber  33  via the oil return holes  36 ″. Moreover, the oil return holes  36 ″ are sized such that, in use, the oil sumps  36 ′ retain a volume of oil, which further inhibits the flow of blow-by gas through the oil return holes  36 ″. 
     A cone-shaped oil reservoir  37  is partially or entirely defined in the end face of the second bearing boss  3   2  that faces the annular chamber  33 . An opening to a breather passage  40 , described hereinafter, is preferably formed in the second bearing boss  3   2  at a location that is radially opposite the oil feed hole  36 , as illustrated. 
     A polygonal recess  38  is defined in one side of the cylinder block  5  and is formed as a breather chamber by closing its opened surface with a lid  39 . A breather passage  40 , through which the breather chamber  38  communicates with the interior of the crankcase  3 , extends from the breather chamber  38  to the annular chamber  33 . 
     As shown in FIGS. 3,  6  and  7 , the end face of an opening of the breather passage  40  into the breather chamber  38  is formed on valve seat  41 , and a plurality of support pieces  43  are welded to the lid  39  for supporting the valve plate  42  opposed to the valve seat  41  for opening and closing movements. The valve seat  41  and the valve plate  42  form a check valve  44  that is adapted to be opened upon increasing of the pressure in the crankcase  3  and to be closed upon decreasing of the pressure in the crankcase  3 . The lid  39  is secured to the cylinder block  5  by a bolt  45 . 
     First and second return bores  46   1 ,  46   2  are formed in the breather chamber  38 . The first return bore  46   1  is provided at a portion which is a lowermost portion when the engine body  1  is a horizontal-type engine while the second return bore  46   2  is provided at a portion which is a lowermost portion when the engine body  1  is a vertical-type engine. Both of the return bores  46   1  and  46   2  lead to the inside of the crankcase  3 . Moreover, each of the return bores  46   1  and  46   2  have a diameter far smaller than that of the breather passage  40  to inhibit, as much as possible, the flowing-through of the blow-by gas. 
     A connecting bore  47  is provided in the lid  39  and opens into the breather chamber  38 . A breather tube  48  connected to an air cleaner (not shown) in the intake system of the engine is connected to the connecting bore  47 . The connecting bore  47  is located above the first return bore  46   1  when the engine body  1  is applied to a horizontal-type engine, and at a location above the second return bore  46   2  when the engine body  1  is applied to a vertical-type engine. In the breather chamber  38 , a partition wall  49  is integrally formed on the sidewall of the cylinder block  5  to separate the valve seat  41  and the connecting bore  47  from each other. 
     During rotation of the crankshaft  2 , the lubricating oil in the oil reservoir chamber  26  is splashed by the rotation of the impeller  25 . A portion of the splashed oil is guided by the guide wall  51  in the vicinity of the impeller  25 , toward the chamber  10  and lubricates the timing transmitting device  12 , the other valve-operating mechanism elements, and the first journal portion  2   1 . The other portion of the splashed oil passes through the oil feed hole  36  in the second bearing boss  3   2  into the annular chamber  33 . Simultaneously, the pressure in the crankcase  3  is repeatedly increased and decreased with the reciprocating movement of the piston  4 . When the pressure in the crankcase  3  is increased, the check valve  44  is opened, so that the pressure is transferred along with the blow-by gas via the annular chamber  33  and the breather passage  40  into the breather chamber  38 . When the pressure in the crankcase  3  is decreased, the check valve  44  is closed, whereby the back flow of the blow-by gas is prevented. 
     Upon entering the annular chamber, the fluid stream (blow-by gas and oil) confronts the ribs  35   a ,  35   b  extending from the inner surface of the cap  35 , which causes the velocity of the fluid stream to slow and thereby allows at least some of the oil entrained in the fluid stream to drop out of the blow-by gas. Accordingly, the amount of oil that is entrained in the blow-by gas that enters the breather passage  40  and, ultimately, the breather chamber  38  is reduced. The splashed oil is accumulated in the cone-shaped oil reservoir  37  in the upper surface of the second bearing boss  3   2  and can effectively lubricate the second journal portion  2   2  at a location above the first journal portion  2   1 . Further, splashed oil is accumulated in the oil sumps  36 ′, and slowly drains back into the crankcase via the oil return holes  36 ″. The diameter of the oil return holes  36 ″ is preferably selected to provide sufficient drainage flow to prevent the sumps  36 ′ from overflowing, while retaining a small volume of oil in the sumps  36 ′. The small diameter of the oil return holes  36 ″ coupled with the oil retained in the sumps  36 ′ serves to prevent or limit blow-by gas from entering the annular chamber  33  through the oil return holes  36 ″. 
     Blow-by gas produced in the crankcase  3  is passed via the annular chamber  33  (wherein a first portion of the oil entrained in the blow-by gas is removed) and the breather passage  40  into the breather chamber  38 . The fluid stream (blow-by gas and oil (reduced)) enters the breather chamber  38  and traverses the partition wall  49 , which causes further oil to fall out of the blow-by gas. This further oil drains from the breather chamber  38  to the crankcase  3  via the second return bore  46   2 . The blow-by gas, now substantially free of oil, is guided through the breather tube  48  to the air cleaner (not shown) and discharged. 
     After stopping of the engine, the oil droplets are accumulated in the recess  52  in the upper end face of the valve-operating camshaft  11  from above the recess  52 . Upon restart of the engine, such oil is shaken off by the rotation of the valve-operating cam shaft  11  and is used in the lubrication of the valve-operating mechanism elements around the valve-operating cam shaft  11 . Therefore, particularly even upon the start of the engine which has hitherto been in its stopped state, the valve-operating mechanism can be prevented from being out of oil. 
     Although the embodiment of the present invention has been described in detail, it will be understood that the present invention is not limited to the above-described embodiment, and various modifications in design may be made without departing from the spirit and scope of the invention defined in claims.