Engine

An engine includes a crank shaft inside a crankcase and an oil pan and penetrates the crankcase and the oil pan in an up-down direction. An oil pump and an oil strainer are provided inside the oil pan. The oil pump is coaxial with the crank shaft and is driven by the crank shaft. The crank shaft includes a first region and a second region respectively supported pivotably by a plate-shaped support and the crankcase. The support is provided in the crankcase such that both surfaces of the support are covered by the crankcase and the oil pan and allows communication between the crankcase and the oil pan.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to engines, and more specifically to vertical engines used in machinery such as mowing equipment.

2. Description of the Related Art

JP-A 2002-242634 discloses an example of an engine of the above type. JP-A 2002-242634 discloses a vertical engine in which a crank shaft axial direction corresponds to an up-down direction, with an oil pan supporting the crank shaft.

In the engine disclosed in JP-A 2002-242634, there is no lid member provided in an upper surface of the oil pan. Therefore, when the engine is tilted, there is a case where, depending on the angle, there is no lubricant oil near a suction inlet of an oil strainer inside the oil pan. If this situation continues, lubricant oil cannot be supplied from the oil strainer to an oil pump, possibly leading to a problem that lubricant oil cannot be circulated inside the engine.

Also, since the crank shaft is supported by the oil pan which is exposed to the outside, vibratory noise from the crank shaft easily leaks to the outside.

SUMMARY OF THE INVENTION

Preferred embodiments of the present invention provide an engine that is able to reliably supply lubricant oil from an oil strainer inside an oil pan to an oil pump while reducing vibratory noise from the crank shaft.

According to a preferred embodiment of the present invention, an engine includes a crankcase including a downward opening; an oil pan provided below the crankcase and including an upward opening; a crank shaft provided inside the crankcase and the oil pan such that a crank shaft axis extends in an up-down direction and the crank shaft penetrates the crankcase and the oil pan; an oil pump coaxial with the crank shaft and driven by the crank shaft; an oil strainer provided inside the oil pan; and a plate-shaped support pivotably supporting a first region of the crank shaft. With the above arrangement, the support is disposed in at least one of the crankcase and the oil pan such that both surfaces of the support are covered by the crankcase and the oil pan and allows communication between the crankcase and the oil pan.

According to a preferred embodiment of the present invention, the support is preferably plate-shaped and therefore, defines and functions as a lid member for the oil pan, and prevents lubricant oil inside the oil pan from moving upward beyond the support. Even if the engine is tilted, for example, causing the lubricant oil to move from below to above the support, the lubricant oil which has moved upward beyond the support returns to the oil pan since the crankcase and the oil pan communicate with each other. Lubricant oil which has circulated inside the engine and flows down from a higher position than the support also returns to the oil pan. Therefore, it is possible to cause the lubricant oil to be near the oil strainer inside the oil pan, and to stably supply lubricant oil from the oil strainer to the oil pump. Also, the support which supports the crank shaft has both of its surfaces covered by the crankcase and the oil pan. This makes it possible to reduce noise, which is caused by vibrations from the crank shaft, from escaping to the outside.

Preferably, the engine further includes a cam shaft parallel or substantially parallel to the crank shaft and located inside the crankcase. With this arrangement, the support pivotably supports the crank shaft and the cam shaft. In this case, it is possible to improve the accuracy in the center-to-center distance between the crank shaft and the cam shaft since the crank shaft and the cam shaft are supported by one support.

Further preferably, the engine further includes a governor shaft parallel or substantially parallel to the crank shaft and located inside the crankcase. With this arrangement, the support supports the crank shaft, the cam shaft and the governor shaft. In this case, it is possible to improve the accuracy in the center-to-center distance between the crank shaft, the cam shaft and the governor shaft since the crank shaft, the cam shaft and the governor shaft are supported by one support.

Further, preferably, the oil pump is disposed inside the oil pan. In this case, a height difference between the oil pump and the oil strainer is small, making it possible to decrease suction resistance in the oil pump.

Preferably, the support includes a perimeter edge region including mounts attached to at least one of the crankcase and the oil pan to mount the support inside the crankcase and the oil pan. In this case, the support is incorporated inside the crankcase and the oil pan, i.e., is not exposed outside of the crankcase or the oil pan. This makes it possible to confine noise, which is caused by vibrations conducted from the crank shaft to the support, within the crankcase and the oil pan and to further decrease noise.

Further preferably, the mounts are attached to the crankcase, and the crankcase pivotably supports a second region of the crank shaft. In this case, the crank shaft is pivotably supported by the support attached to the crankcase, and by the crankcase. This makes it possible to decrease vibrations of the crank shaft than in an arrangement where the support is attached to the oil pan.

Further, preferably, the support includes ribs which are provided at an axial center of the crank shaft and extend radially toward the mounts. In this case, it is possible to improve the strength of the support, making it easy to dissipate loads applied from the crank shaft to the support, to the crankcase or the oil pan along the ribs.

Preferably, the engine further includes a ball bearing disposed between the support and an outer surface of the crank shaft. In this case, by supporting the crank shaft with the ball bearing, the arrangement provides an appropriate solution to receive not only radial loads applied to the crank shaft but also thrust loads applied thereto.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Referring toFIG. 1throughFIG. 6, an engine10according to a preferred embodiment of the present invention is, for example, a vertical, narrow-angle (less than 90 degrees), V-shaped, two-cylinder, OHV engine (Over Head Valve Engine). The engine10includes a crankcase12. Two cylinders14,16are arranged in a V-shape on a side surface of the crankcase12. An oil pan18is provided below the crankcase12. A crank shaft20is provided inside the crankcase12and the oil pan18so that its axial direction extends in an up-down direction (seeFIG. 7). The crank shaft20penetrates the crankcase12and the oil pan18in the up-down direction. Referring toFIG. 7, above the crankcase12, a cooling fan22is arranged coaxially with the crank shaft20. The cooling fan22is driven by the crank shaft20, and introduces cooling air from above the crankcase12. A cover portion24covers the cylinders14,16, the crankcase12, and the cooling fan22from above. The cover portion24includes a first cover26and a second cover28which is attached onto the first cover26. The second cover28includes an air inlet30at a location facing the cooling fan22to introduce air from the outside. Inside the second cover28, a grass screen32is provided to prevent invasion of impurities such as grass. The outside air introduced from the air inlet30by driving the cooling fan22cools the engine10.

Referring toFIG. 7throughFIG. 9, the crankcase12includes a through-hole34that is penetrated by the crank shaft20. The crankcase12includes an upper surface including an upward opening, and a generally gourd-shaped recess36. In the recess36, there are provided a first gas/liquid separating chamber38and a second gas/liquid separating chamber40. The first gas/liquid separating chamber38has a greater capacity than the second gas/liquid separating chamber40. The first gas/liquid separating chamber38and a hollow portion48(which will be described below) of the crankcase12communicate with each other via a through-hole42. The through-hole42is opened/closed by a reed valve44provided in the first gas/liquid separating chamber38. In a central or substantially central region of the first gas/liquid separating chamber38, there is provided a bearing hole46that receives a cam shaft148(which will be described below). In the crankcase12, the hollow portion48includes a downward opening. The hollow portion48defines an oil chamber. In the hollow portion48, a third gas/liquid separating chamber50is provided.

The second gas/liquid separating chamber40and the third gas/liquid separating chamber50communicate with each other via an oil return hole52; the first gas/liquid separating chamber38and the third gas/liquid separating chamber50communicate with each other via an oil return hole54; and the third gas/liquid separating chamber50and the oil pan18communicate with each other via an oil return channel56provided in the crankcase12and an oil return channel58(seeFIG. 16) provided in the oil pan18. The first gas/liquid separating chamber38and the second gas/liquid separating chamber40include a lid60covering their upper surfaces. The third gas/liquid separating chamber50includes a lid62on its lower surface.

The first gas/liquid separating chamber38, the second gas/liquid separating chamber40and the third gas/liquid separating chamber50are located near and/or between the two cylinders14,16(between the V banks) in the crankcase12. The lid60includes a lower surface including a wall64, which reduces gas flow from the first gas/liquid separating chamber38to the second gas/liquid separating chamber40. Blowby gas from the hollow portion48of the crankcase12is separated into gas and liquid in the first gas/liquid separating chamber38and the second gas/liquid separating chamber40, and further in the third gas/liquid separating chamber50. The three gas/liquid separating chambers provided in the crankcase12increase separation efficiency due to the multi-stage expansion. As indicated by white arrows inFIG. 7, blowby gas is sent from the hollow portion48, through the first gas/liquid separating chamber38, the second gas/liquid separating chamber40, the third gas/liquid separating chamber50, a gas tube66, etc., to an upstream location in an air intake system. Lubricant oil separated in the first gas/liquid separating chamber38, the second gas/liquid separating chamber40and the third gas/liquid separating chamber50is returned from the third gas/liquid separating chamber50, through oil return channels56,58, to the oil pan18. The hollow portion48of the crankcase12is surrounded by an end edge68, where there is provided a plurality (for example, eight in the present preferred embodiment) of screw holes72to attach a plate-shaped support70.

Referring toFIG. 8, if the engine10is mounted horizontally, lubricant oil from the first gas/liquid separating chamber38is returned to the oil pan18via a generally V-shaped oil return channel74. Depending on whether the engine18is mounted vertically or horizontally, a different oil return channel is used to return lubricant oil to the oil pan18.

Referring toFIG. 7,FIG. 10,FIG. 11andFIG. 12, the support70includes a through-hole76that receives the crank shaft20, a through-hole78that receives the cam shaft148(which will be described below), and a through-hole80that receives a governor shaft158(which will be described below). Referring toFIG. 13andFIG. 14, the support70has dimensions that define a plurality of gaps S1between an outer circumference of the support70and the end edge68of the crankcase12, and a gap S2between the outer circumference of the support70and an end edge90of the oil pan18. This allows communication between the crankcase12and the oil pan18. The support70includes a perimeter edge region including a plurality (for example, eight in the present preferred embodiment) of mounts82. In the present preferred embodiment, the mounts82are generally hollow and cylindrical and include thick walls. The support70includes a lower surface including a plurality of ribs84. The ribs84extend straight and radially from an axial center (i.e., the through-hole76) of the crank shaft20toward the mounts82; extend radially from an axial center (i.e., the through-hole78) of the cam shaft148toward the mounts82; extend radially from an axial center (i.e., the through-hole80) of the governor shaft158toward the mounts82; extend from the axial center of the crank shaft20toward the axial center of the cam shaft148; extend from the axial center of the crank shaft20toward the axial center of the governor shaft158; and extend from the axial center of the cam shaft148toward the axial center of the governor shaft158. Each of the mounts82in the support70corresponds to one of screw holes72in the end edge68of the crankcase12, and unillustrated fasteners such as bolts, for example, are used to attach the support70to the crankcase12. Then, as shown inFIG. 7, an upper region of the crank shaft20is supported by the crankcase12via a bearing86provided in the through-hole34whereas a lower region of the crank shaft20is supported by the support70via a ball bearing88provided in the through-hole76. In this arrangement, the crank shaft20penetrates the crankcase12and the support70in an up-down direction; the support70pivotably supports one region of the crank shaft20; and the crankcase12pivotably supports another region of the crank shaft20.

Referring toFIG. 9andFIG. 14, the crankcase12and the oil pan18are fastened to each other with unillustrated fasteners, with the end edge68of the lower open surface of the crankcase12and the end edge90of the upper open surface of the oil pan18in contact with each other.

Referring toFIG. 7,FIG. 15andFIG. 16, the upward opening oil pan18includes a through-hole92that the crank shaft20penetrates. An oil seal94is located between the crank shaft20and the through-hole92. Inside the oil pan18, near the through-hole92, there is attached an oil pump96at a lower position of the crank shaft20coaxially with the crank shaft20. The oil pump96is driven as the crank shaft20rotates. The oil pump96is a trochoid pump, for example. Inside the oil pan18, an annular member98surrounds the oil pump96. The annular member98includes a through-hole100. The through-hole100is located on an extended line of an oil path110(which will be described below). Inside the oil pan18, a curved oil strainer102is provided on an outer side of the annular member98, and on an outer side of the oil strainer102, there is provided an oil strainer cover106which is curved and plate-shaped, and includes a suction port104. The oil pump96, the annular member98, the oil strainer102and the oil strainer cover106include a cover108that covers their upper surfaces. Lubricant oil from the oil pump96is sent through the oil path110and an oil hose112, and supplied to an oil cooler114to be cooled. The cooled lubricant oil is supplied to an oil filter118via an oil hose116, filtered there, and then supplied to various portions or elements of the engine10. The oil cooler114and the oil filter118are located outside of the oil pan18. The oil filter118is disposed such that a longitudinal direction of the oil filter118is parallel or substantially parallel to the axial direction of the crank shaft20. This allows for a compact structure. The oil path110is provided with a relief valve120. The relief valve120opens when an oil pressure in the oil path110becomes not smaller than a predetermined value, to return lubricant oil inside the oil path110to the oil pan18. Referring toFIG. 15andFIG. 16, the oil strainer102, the through-hole100, the oil pump96, the oil path110and the relief valve120are disposed on a straight line in a plan view. This makes it possible to decrease the resistance of lubricant oil flowing through the oil path110.

Returning toFIG. 2andFIG. 4, the cylinder14includes a cylinder body122, a cylinder head124and a cylinder head cover126. The cylinder16includes a cylinder body128, a cylinder head130and a cylinder head cover132. Referring toFIG. 8andFIG. 9, the cylinder bodies122,128are preferably formed integrally with the crankcase12. Each of the cylinder bodies122,128includes fins134,136on its outer circumference.

Referring toFIG. 8,FIG. 9,FIG. 17andFIG. 18, pistons140,142are slidably provided inside the cylinder bodies122,128, respectively. Each of the pistons140,142is connected by a corresponding one of connecting rods144,146to the crank shaft20inside the crankcase12. In the present preferred embodiment, the connecting rods144,146include diagonally split connecting rods (seeFIG. 20). Also in the present preferred embodiment, large end portions of the connecting rods144,146are not coaxial with each other (seeFIG. 17). Thus, crank pins on the crank shaft20are not coaxial with each other (seeFIG. 7). Reciprocating movement of the pistons140,142is converted into rotating movement by the crank shaft20. Referring toFIG. 9, an arc-shaped cutout138is provided, near an end region of the crank shaft20, in an inner circumferential surface in each of the cylinder bodies122,128. In the present preferred embodiment, the cutout138is coaxial with the through-hole34in order to avoid interference with the large end portions of the connecting rods144,146. The crankcase12incorporates the cam shaft148which moves together with the crank shaft20. Referring toFIG. 7, the cam shaft148includes an end region supported pivotably in the bearing hole46by the crankcase12via a film of oil. Another end region of the cam shaft148is supported pivotably by the support70via a ball bearing150in the through-hole78. The crank shaft20is provided with a driving gear152, whereas the cam shaft148is provided with a driven gear154which rotates as the driving gear152rotates. Referring toFIG. 17andFIG. 18, a governor156is provided inside the crankcase12. The governor156is a structure or system that maintains the number of rotations of the engine10within a predetermined range even if there is load fluctuation. The governor156includes the governor shaft158, which is pressed into the through-hole80of the support70. The governor156includes a governor gear160, which is attached pivotably to the governor shaft158, engaged with the driven gear154, and is rotated as the driven gear154rotates. The crank shaft20, the cam shaft148and the governor shaft158which are supported by the support70are parallel or substantially parallel to each other.

In the respective cylinders14,16, from the cylinder bodies122,128to the cylinder heads124,130, communication paths (not illustrated) provide communication between the inside of the crankcase12and rocker arm chambers (not illustrated) inside the cylinder head covers126,132.

Referring toFIG. 17andFIG. 18, in the cylinder14, a push rod162and a tappet164provided in an end region of the push rod162are inserted into the communication path. The tappet164includes a tip portion in contact with an air intake cam166of the cam shaft148inside the crankcase12. The push rod162includes another end region, which is connected to a rocker arm168, provided inside the rocker arm chamber. Air intake valves174,176, which are constantly urged by valve springs170,172in a closing direction, are driven by the rocker arm168. The air intake valves174,176open/close two air intake ports (not illustrated). Also, a push rod178and a tappet180provided at an end region of the push rod178are inserted into the communication path. The tappet180includes a tip portion in contact with an exhaust cam182of the cam shaft148inside the crankcase12. The push rod178includes another end region, which is connected to a rocker arm184, provided inside the rocker arm chamber. An exhaust valve188, which is constantly urged by a valve spring186in a closing direction, is driven by the rocker arm184. The exhaust valve188opens/closes an exhaust port190(seeFIG. 4,FIG. 13).

Likewise, in the cylinder16, a push rod192and a tappet194provided at an end region of the push rod192are inserted into the communication path. The tappet194includes a tip portion in contact with an air intake cam196of the cam shaft148inside the crankcase12. The push rod192includes another end region, which is connected to a rocker arm198, provided inside the rocker arm chamber. Air intake valves204,206, which are constantly urged by valve springs200,202in a closing direction, are driven by the rocker arm198. The air intake valves204,206open/close two air intake ports (not illustrated). Also, a push rod208and a tappet210provided at an end region of the push rod208are inserted into the communication path. The tappet210includes a tip portion in contact with an exhaust cam212of the cam shaft148inside the crankcase12. The push rod208includes another end region, which is connected to a rocker arm214, inside the rocker arm chamber. An exhaust valve218, which is constantly urged by a valve spring216in a closing direction, is driven by the rocker arm214. The exhaust valve218opens/closes an exhaust port220(seeFIG. 4,FIG. 13).

As will be understood from alternate long and short dash lines X, Y1, Y2, Y3, Y4shown inFIG. 18, the cam shaft148is perpendicular or substantially perpendicular to rocker shafts222,224,226,228of the rocker arms168,184,198,214in a side view. This makes it possible to reduce an increase in friction in a valve driving mechanism, which includes a plurality of air intake valves174,176, and in a valve driving mechanism, which includes a plurality of air intake valves204,206, caused by an increase in the number of valves.

Referring toFIG. 19, the air intake ports of the cylinder14and the air intake ports of the cylinder16are connected to each other by an air intake manifold230. The air intake manifold230is connected to a throttle body232. The throttle body232is disposed between the cylinders14,16which are arranged in a narrow-angle, two-cylinder, V-shape style. To the throttle body232, an air filter236is attached via an air intake pipe234(seeFIG. 1,FIG. 2). A pressure/temperature sensor238is provided at a branch section where the air intake manifold230branches toward the two cylinders14,16. In other words, the pressure/temperature sensor238is disposed at a center portion of a cylinder-to-cylinder region of the air intake manifold230which connects the air intake ports of the cylinder14and the air intake ports of the cylinder16(i.e., between the air intake ports of the two cylinders). The pressure/temperature sensor238detects pressures and temperatures of intake air for fuel injection control. Based on outputs from the pressure/temperature sensor238, it is possible to detect an amount of air flow.

Referring toFIG. 20, the exhaust ports190,220of the cylinders14,16are connected to a muffler244via exhaust pipes240,242respectively. Exhaust gas from the engine10is discharged outside via the muffler244. The engine10is supplied with fuel from an unillustrated fuel tank. A starter motor246rotates the crank shaft20to start the engine10.

In the engine10, the support70preferably has a plate-shape and therefore defines a lid member for the oil pan18and prevents lubricant oil inside the oil pan18from moving upward beyond the support70. Even if the engine10is tilted, for example, causing the lubricant oil to move from below to above the support70, the lubricant oil which has moved upward beyond the support70returns to the oil pan18since the crankcase12and the oil pan18communicate with each other. Lubricant oil which has circulated inside the engine10and flows down from a higher position than the support70also returns to the oil pan18. Therefore, it is possible to cause the lubricant oil to be near the oil strainer102inside the oil pan18, and to stably supply lubricant oil from the oil strainer102to the oil pump96. Also, the support70which supports the crank shaft12has its both surfaces covered by the crankcase12and the oil pan18. This makes it possible to reduce noise, which is caused by vibrations from the crank shaft20, from escaping to the outside.

Since one support70supports the crank shaft20, the cam shaft148and the governor shaft158, it is possible to improve the accuracy in the center-to-center distance between the crank shaft20, the cam shaft148and the governor shaft158.

Since the oil pump96is inside the oil pan18, a height difference between the oil pump96and the oil strainer102is small (approximately zero in the present preferred embodiment). This makes it possible to decrease suction resistance in the oil pump96.

The support70is incorporated inside the crankcase12and the oil pan18, i.e., is not exposed outside of the crankcase12or the oil pan18. This makes it possible to confine noise, which is caused by vibrations conducted from the crank shaft20to the support70, within the crankcase12and the oil pan18, and to further decrease noise.

The crank shaft20is supported pivotably by the support70which is attached to the crankcase12, and by the crankcase12. This makes it possible to decrease vibrations of the crank shaft20compared to an arrangement where the support70is attached to the oil pan18.

The support70includes the ribs84which are provided at the axial center of the crank shaft20and radially extend toward the mounts82. This makes it possible to improve the strength of the support70, making it easy to dissipate loads applied from the crank shaft20to the support70, to the crankcase12or the oil pan18along the ribs84.

The ball bearing88is provided between the support70and an outer surface of the crank shaft20. By supporting the crank shaft20with the ball bearing88, the arrangement provides an appropriate solution to receive not only radial loads applied to the crank shaft20but also thrust loads applied thereto.

The connecting rods144,146include diagonally split connecting rods (seeFIG. 20), and each of the cylinder bodies122,128includes the cutout138(seeFIG. 9). This makes it possible to decrease a dimension of the crankcase12, and consequently a dimension of the engine10in its fore-aft direction (in the direction indicated by Arrow F inFIG. 20).

It should be noted here that the support70may be positioned in the oil pan18inside the crankcase12and the oil pan18, with a gap provided between the outer circumference of the support70and the end edge90of the oil pan18. In this arrangement, the mounts82of the support70are attached to the oil pan18.

Also, a carburetor may be disposed between the cylinders14,16of the narrow-angle V-shaped two-cylinder engine.