JP7326589B2 - power unit - Google Patents

Description

The present invention relates to power units.
This application claims priority based on Japanese Patent Application No. 2020-54185 filed in Japan on March 25, 2020, the content of which is incorporated herein.

2. Description of the Related Art Conventionally, in a power unit provided with an internal combustion engine, there is known a technique of configuring a closed crankcase in a crankcase of the internal combustion engine (see, for example, Patent Document 1).

Japanese Patent Application Laid-Open No. 2003-254030

By the way, the above-described conventional technique has the following problems in order to form a closed crank chamber in the crankcase. That is, since the partition wall is provided between the crank chamber in which the crankshaft is accommodated and the transmission chamber in which the transmission is accommodated, the crankshaft and the transmission are separated from each other, which may lead to an increase in the size of the entire power unit.

SUMMARY OF THE INVENTION Accordingly, it is an object of the present invention to suppress an increase in the overall size of a power unit in a power unit having a closed crank chamber within a crankcase.

A first aspect of the present invention provides a cylinder (12) that constitutes a cylinder of an internal combustion engine (10), a piston (13) that reciprocates within the cylinder (12), and the reciprocating motion of the piston (13). A rotationally driven crankshaft (15), a transmission (20) to which the rotational driving force of the crankshaft (15) is transmitted, and a crankcase ( 11), wherein the crankcase (11) is provided between a crank chamber (31) containing the crankshaft (15) and a transmission chamber (32) containing the transmission (20); A partition wall (33) is provided to separate the transmission (20), and the partition wall (33) is arranged so as to at least partially overlap the transmission (20) when viewed in the axial direction of the crankshaft (15). ) is provided, and a breather mechanism (40) is provided on the upper surface of the crankcase (11) for guiding the gas in the crankcase (11) to the outside of the crankcase (11). , the breather mechanism (40) includes a breather arrangement portion (41) on the upper wall (37) of the crankcase (11), and the breather arrangement portion (41) is located on the upper wall (37) of the crankcase (11). 37) is provided with a breather opening (42) having an opening (42a) vertically penetrating through the opening (42a). ), providing a power unit.
According to this configuration, when the crank chamber and the transmission chamber are separated by the partition wall to form a closed crank chamber, the partition wall overlaps the transmission when viewed in the direction of the crankshaft. As a result, the transmission can be brought as close to the partition wall side (crank chamber side) as possible, and the overall size of the power unit can be reduced.
In addition, by providing the partition wall with a cutout portion that avoids the transmission, the partition wall and the transmission can be arranged to overlap each other when viewed in the direction of the crankshaft.
In addition, when forming the cutout portion in the partition wall, the partition wall can be processed by inserting a tool through the opening of the breather arrangement portion. This facilitates manufacture of the crankcase.

In a second aspect of the present invention, in the first aspect, the transmission (20) includes a pair of transmission shafts (25, 26) parallel to the crankshaft (15) and a pair of transmission shafts ( 25, 26), and the pair of transmission shafts (25, 26) are connected to the main shaft (25) on the crankshaft (15) side and the power unit (1). and a counter shaft (26) on the side of the output shaft (26a), wherein the partition wall (33) corresponds to the main shaft (25) in the transmission gear group (27) when viewed in the axial direction of the crankshaft (15). It is arranged so that at least a part of it overlaps with the gear supported by.
According to this configuration, the partition wall and the gear supported by the main shaft overlap when viewed in the direction of the crankshaft. As a result, the main shaft and thus the transmission can be brought as close to the partition wall side (crankshaft side) as possible, and the overall size of the power unit can be reduced.

According to a third aspect of the present invention, in the first or second aspect, a breather mechanism is provided on the upper surface of the crankcase (11) for guiding the gas in the crankcase (11) to the outside of the crankcase (11). (40), the breather mechanism (40) includes a gas-liquid separator (47a) that separates oil contained in gas in the crankcase (11), and a gas-liquid separator (47a) that separates the separated oil from the crankcase (11). an inwardly returning oil return portion (43a), said oil return portion (43a) being located above said transmission (20) and causing said oil to drip into said transmission (20).
According to this configuration, the oil separated from the blow-by gas by the breather mechanism can be dripped onto the transmission and actively used for lubricating the transmission.

According to a fourth aspect of the present invention, in any one of the first to third aspects, a plurality of the cylinders (12) are provided, and the crankcase (11) is arranged between the plurality of cylinders (12). and the crank chamber (31) is divided for each cylinder (12) by the second partition (36).
According to this configuration, a closed crank chamber is formed for each of a plurality of cylinders, so pressure interference between cylinders can be suppressed. Thereby, the pressure in each sealed crank chamber can be stably controlled.

According to a fifth aspect of the present invention, in any one of the first to fourth aspects, the crank chamber (31) is provided between the crank chamber (31) and the transmission chamber (32). A valve mechanism (39b) is provided that opens the valve when the internal pressure rises, and the valve mechanism (39b) is arranged below the crank chamber (31).
According to this configuration, the oil accumulated in the lower portion of the crank chamber can be effectively discharged to the transmission chamber.

Advantageous Effects of Invention According to the present invention, it is possible to suppress an increase in the size of the entire power unit in a power unit that forms a closed crank chamber within a crankcase.

It is a left side view including a partial section of a power unit in an embodiment of the present invention. FIG. 2 is a cross-sectional view taken along the line II-II of FIG. 1; FIG. 3 is a top view showing a main part of the power unit;

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, embodiments of the present invention will be described with reference to the drawings.
A power unit 1 shown in FIG. 1 is used for a prime mover of a saddle type vehicle such as a motorcycle. The power unit 1 integrally includes an engine (internal combustion engine) 10 and a transmission 20 . The power unit 1 includes a crankshaft 15 of the engine 10 and two shafts of the transmission 20 (main shaft 25 and countershaft 26). The crankshaft 15, the main shaft 25, and the counter shaft 26 are arranged along the vehicle left-right direction (vehicle width direction).

Unless otherwise specified, directions such as front, rear, left, and right in the following description are the same as those of the vehicle in which the power unit 1 is mounted. An arrow FR indicating the front of the vehicle, an arrow LH indicating the left of the vehicle, an arrow UP indicating the upper side of the vehicle, and a line CL indicating the center of the left and right of the vehicle body are shown at appropriate locations in the drawings used in the following description.

The engine 10 is a water-cooled 4-stroke parallel 2-cylinder internal combustion engine. The engine 10 is arranged horizontally with two cylinders arranged in the width direction of the vehicle. The crank phase angle between both cylinders is 180 degrees or 270 degrees, etc. instead of 360 degrees. That is, both cylinders reciprocate the pistons 13 at mutually different timings.

The engine 10 has a cylinder 12 standing in a forward tilting posture above the front portion of the crankcase 11 .
A rear portion of the crankcase 11 serves as a transmission case (transmission case) that accommodates a transmission (transmission) 20 .

In the figure, reference character C1 denotes the rotation center axis (crank axis) of the crankshaft 15, reference character C2 denotes the center axis (cylinder axis) of the cylinder bore 12e along the upright direction of the cylinder 12, and reference character C3 denotes the rotation center of the main shaft 25 of the transmission 20. An axis line (main axis line) and reference numeral C4 indicate the rotation center axis line (counter axis line) of the counter shaft 26, respectively.

The cylinder 12 includes, in order from the crankcase 11 side, a cylinder body 12a, a cylinder head 12b, and a head cover 12c. The cylinder 12 is configured by stacking a cylinder body 12a, a cylinder head 12b and a head cover 12c. The cylinder main body 12 a and the cylinder head 12 b are integrally fastened and fixed to the crankcase 11 by stud bolts fixed to the crankcase 11 . Intake system components are connected to the rear portion of the cylinder head 12b, and exhaust system components are connected to the front portion of the cylinder head 12b. An oil pan 14 is attached below the crankcase 11 .

A cylindrical cylinder sleeve 12d along the cylinder axis C2 is provided inside the cylinder body 12a. The cylinder sleeve 12d is integrally inserted into the cylinder body 12a. A cylinder bore 12e is formed along the cylinder axis C2 in the cylinder sleeve 12d. A piston 13 is reciprocally inserted into the cylinder bore 12e. The piston 13 is connected to a crankpin 15a of the crankshaft 15 via a connecting rod 13a. The crank pin 15a is supported by a pair of left and right crank webs 15b. Reciprocating motion of the piston 13 is converted into rotational motion of the crankshaft 15 via the connecting rod 13a. A water jacket 12f is formed around the outer circumference of the cylinder sleeve 12d.

Also referring to FIG. 2 , the rotational power of the crankshaft 15 is transmitted to the main shaft 25 of the transmission 20 via the multi-plate clutch 28 . The multi-plate clutch 28 is arranged on the right side of the crankcase 11 . A primary drive gear 16 is coaxially provided on the right side of the crankshaft 15 . A primary driven gear 17 is coaxially provided behind the primary drive gear 16 and on the right side of the main shaft 25 (on the inner side of the multi-plate clutch 28 in the vehicle width direction). Primary drive gear 16 and primary driven gear 17 mesh with each other to form a primary reduction mechanism of power unit 1 .

The transmission 20 includes a main shaft 25 and a counter shaft 26 that are parallel to the crankshaft 15 and a transmission gear group 27 that is supported across both shafts 25 and 26 . Rotational power of the crankshaft 15 is transmitted to the main shaft 25 and then transmitted to the counter shaft 26 via the transmission gear group 27 . Rotational power of the crankshaft 15 is appropriately reduced through an arbitrary gear pair of the transmission gear group 27 . A left end portion of the counter shaft 26 protrudes to the rear left side of the crankcase 11 and constitutes an output shaft 26 a of the power unit 1 . The rotational power transmitted to the output shaft 26a is transmitted to the rear wheels (driving wheels) of the vehicle via, for example, a chain transmission mechanism.

The transmission gear group 27 is composed of gears corresponding to the number of gear stages supported on both shafts 25 and 26, respectively. The transmission 4 is of a constant mesh type in which corresponding gears of the transmission gear group 27 are always meshed with each other. Each gear supported by both shafts 25 and 26 includes a free gear rotatable about the corresponding shaft and a slide gear (shifter) spline-fitted to the corresponding shaft. One of these gears is provided with an axially convex dog. The other of each gear is provided with an axially concave slot for engaging the dog. Gear change of the transmission 4 (slide of the slide gear) is performed by a change mechanism (not shown). A change mechanism is arranged around the transmission 4 .

The transmission gear group 27 consists of a first gear train 271, a fifth gear train 275, a fourth gear train 274, a third gear train 273, a sixth gear train 276, and a second gear train 272 from the right side. there is The gear trains 271 to 276 for six speeds have reduction ratios that decrease in order from the first speed gear train 271 to the sixth speed gear train 276 . That is, the number of revolutions of the counter shaft 26 with respect to the number of revolutions of the main shaft 25 is increased in order from the first gear train 271 to the sixth gear train 276 . These gear trains 271 to 276 are alternatively selected according to the gear stage of transmission 20 . The selected gear train is used for torque transmission between main shaft 25 and counter shaft 26 .

An axial view of the crankshaft 15 and the shafts 25 and 26 (hereinafter simply referred to as an axial view) will be described with reference to FIG. The axis C<b>3 of the main shaft 25 is arranged above a rearward rising straight line t connecting the axis C<b>1 of the crankshaft 15 and the axis C<b>4 of the counter shaft 26 . The axis C3 of the main shaft 25 is arranged closer to the counter shaft 26 than the central position of the straight line t in the length direction of the straight line t. In other words, in the power unit 1, the three main shafts of the crankshaft 15, the main shaft 25 and the counter shaft 26 are arranged in a triangular shape when viewed in the axial direction. Hereinafter, the direction orthogonal to the straight line t when viewed in the axial direction is referred to as the case up-down direction, and the direction along the straight line t when viewed in the axial direction is referred to as the case front-back direction. The cylinder axis C2 is orthogonal to the straight line t when viewed in the axial direction.

The crankcase 11 is divided vertically into an upper case 11A and a lower case 11B. The straight line t is positioned on the dividing surface 11C between the upper and lower cases 11A and 11B. The crankshaft 15 and the countershaft 26 are sandwiched between the upper and lower cases 11A and 11B and supported on the dividing surface 11C.

<Sealed crankcase>
1 and 2, the engine 10 has a partition wall 33 that separates a crank chamber 31 that houses the crankshaft 15 from a transmission chamber 32 that houses the transmission 20 . As a result, the engine 10 substantially seals the crank chamber 31 . As a result, the pressure in the crank chamber 31 can be forcibly reduced to negative pressure by the reciprocating motion of the piston 13 or the driving of the oil pump. This contributes to reducing the pumping loss associated with the reciprocating motion of the piston 13 . The engine oil in the crank chamber 31 is discharged to the transmission chamber 32 due to the pressure increase when the piston 13 descends. By discharging excess engine oil in the crank chamber 31, the following effects are obtained. That is, the crankshaft 15 contributes to the reduction of friction loss due to agitation of the engine oil. When the pressure fluctuation in the crankcase 11 is suppressed by sealing the crank chamber 31, the following effects are obtained. That is, it contributes to miniaturization of the breather mechanism 40, which will be described later, by reducing the amount of blow-by gas discharged.

The crankcase 11 has a partition wall 33 separating the crank chamber 31 and the transmission chamber 32 . Substantially sealing the crank chamber 31 with the partition wall 33 has the following effects. That is, the internal pressure of the crank chamber 31 can be increased or decreased as the piston 13 reciprocates.
Referring to FIG. 1 , partition wall 33 extends downward from the lower surface of upper wall 37 forming the upper surface of crankcase 11 . The partition wall 33 extends downward inside the crankcase 11 to a position below the crank axis C1. The partition wall 33 includes an upper extension portion 34 that extends from the upper wall 37 in parallel with the cylinder axis C2, and a lower extension portion 35 that extends in an arc shape around the crank axis C1 below the upper extension portion 34. ing.

The upwardly extending portion 34 extends linearly parallel to the cylinder axis C2 when viewed in the axial direction. The upper extending portion 34 is positioned between the lower portion of the cylinder sleeve 12d and the main shaft 25 in the longitudinal direction of the case. In the vertical direction of the case, the lower end of the upper extending portion 34 is located below the lower end of the cylinder sleeve 12d and below the main axis C3. In the vertical direction of the case, the lower end of the upper extending portion 34 is located above the straight line t. The lower end of the upper extension 34 is connected to the upper end of the lower extension 35 .

The lower extending portion 35 is formed to bulge rearward in the case front-rear direction more than the upper extending portion 34 . The downward extending portion 35 is formed in an arc shape when viewed in the axial direction. The downward extending portion 35 is curved so as to extend downward from the rear of the crankshaft 15 . The lower extending portion 35 has a lower end portion below the crankshaft 15 . A front lower wall 38 of the crankcase 11 is positioned forwardly and downwardly of the crankshaft 15 . The front lower wall 38 extends toward the lower side of the crankshaft 15 while being inclined rearwardly downward. The front lower wall 38 extends the rear end portion below the lower end portion of the downward extending portion 35 .

The rear end portion of the front lower wall 38 and the lower end portion of the downward extending portion 35 are connected to each other in a stepped manner via the standing wall 39 . The standing wall 39 is provided with a communication port 39a for communicating the closed crank chamber 31 and the transmission chamber 32 with each other. A lead valve (valve mechanism) 39b is connected to the communication port 39a. When the internal pressure of the closed crank chamber 31 rises, the reed valve 39b is opened by this internal pressure. The reed valve 39 b allows gas (including blow-by gas) in the closed crank chamber 31 to escape to the transmission chamber 32 . At this time, the reed valve 39b discharges the engine oil that has dripped to the lower end of the crank chamber 31 into the transmission chamber 32 together with the gas. Gas containing oil (oil mist) in the transmission chamber 32 is led to a breather mechanism 40 provided on the upper surface of the crankcase 11 .

Also referring to FIG. 3 , the breather mechanism 40 includes a breather placement portion 41 provided on the upper wall 37 of the crankcase 11 and a breather cover 45 attached to the breather placement portion 41 .
The breather placement portion 41 has a breather opening 42 in the upper wall 37 of the crankcase 11 . For example, a pair of left and right breather openings 42 are provided.
The left and right breather openings 42 each form an opening 42a. The opening 42a is formed in a substantially rectangular shape in which the lateral width is larger than the front-rear width when viewed from above in FIG. The left and right breather openings 42 are separated from each other in the left-right direction. The openings 42a of the left and right breather openings 42 penetrate the upper wall 37 of the crankcase 11 along the direction of the cylinder axis C2.

The breather placement portion 41 includes breather recesses 43 behind the left and right breather openings 42 . The breather recess 43 is recessed below the general portion of the upper wall 37 of the crankcase 11 . The breather recess 43 has a tray shape that opens upward. The breather recess 43 has a generally rectangular shape with a lateral width larger than a front-rear width when viewed from above in FIG. 3 . The front-to-rear width of the breather recess 43 is wider than the front-to-rear width of the left and right breather openings 42 . The lateral width of the breather recess 43 is narrower than the lateral width of the left and right breather openings 42 over the left and right outer ends. The left end of the breather recess 43 is at the same horizontal position as the left end of the left breather opening 42 . The right end of the breather recess 43 is located at the same horizontal position as the right-left middle portion (not limited to the left-right center) of the right breather opening 42 .

Referring to FIG. 1, breather cover 45 is attached to cover breather arrangement portion 41 from above. The breather cover 45 is provided integrally over the left and right breather openings 42 and the breather recesses 43 . The breather cover 45 has a box shape that opens downward. The breather cover 45 includes a cover front portion 46 that covers the left and right breather openings 42 and a cover rear portion 47 that covers the breather concave portion 43 . A gas introduction chamber 46a is formed in the cover front portion 46 so that the left and right breather openings 42 face each other. A labyrinth flow passage 47 a is formed in the cover rear portion 47 so as to face the breather recess 43 . The labyrinth flow path 47a is formed, for example, by erecting a plurality of ribs inside the cover rear portion 47. As shown in FIG. The gas that has reached the inside of the breather cover 45 from the left and right breather openings 42 passes through the labyrinth flow path 47a and undergoes gas-liquid separation. That is, the cover rear portion 47 constitutes a gas-liquid separating portion for the gas reaching the inside of the breather cover 45 .

The oil separated from the gas through the labyrinth flow path 47 a accumulates in the breather recess 43 . An oil return portion 43 a is provided at, for example, the lowest end portion of the breather recess portion 43 . The oil return portion 43 a returns the oil accumulated in the breather concave portion 43 to the transmission chamber 32 . The oil return portion 43a is a through hole that opens into the transmission chamber 32, for example. Oil return portion 43 a (breather recess 43 ) is positioned vertically above transmission 20 . The oil returned into the transmission chamber 32 from the oil return portion 43 a drips onto the transmission 20 and is directly used for lubricating the transmission 20 . The gas from which the oil has been separated is sent to, for example, an intake passage and taken into the cylinder 12 together with fresh air.

Referring to FIG. 2, the partition wall 33 is arranged so as to overlap the front end portion of the large-diameter gear supported by the main shaft 25 of the transmission 20 when viewed in the axial direction. The large-diameter gears are the gears of the fifth-speed gear train 275 and sixth-speed gear train 276 . By arranging the gear supported by the main shaft 25 near the crankshaft 15 in the transmission 20 and the partition wall 33 to overlap each other, the following effects can be obtained. That is, it is possible to bring the transmission 20 as close to the partition wall 33 side (crank chamber 31 side) as possible.

The upper extending portion 34 of the partition wall 33 is formed with a notch portion 34a for avoiding the front end portion of the gear. The notch portion 34a is formed at a position overlapping each opening 42a of the left and right breather openings 42 when viewed from the top and bottom direction of the case. By forming the notch portion 34a in the partition wall 33, the thickness of the left and right breather opening portions 42 can be removed. Further, when forming the notch portion 34a in the partition wall 33, it is generally possible to correspond by simply removing the crankcase 11 at the time of casting. When forming the notch portion 34a, it is possible to insert a processing tool from each opening 42a and perform processing such as cutting on the partition wall 33. As shown in FIG.

The crankcase 11 has a second partition wall 36 that separates the left and right cylinders 12 . The second partition wall 36 divides the crank chamber 31 into the left and right cylinders 12 . Forming the closed crank chamber 31 for each of the left and right cylinders 12 has the following effects. That is, pressure interference is suppressed when the pistons 13 in the left and right cylinders 12 reciprocate at different timings. Thereby, in the multi-cylinder engine 10, the sealed crank chamber 31 can be easily configured for each cylinder.

As described above, the power unit 1 in the above embodiment includes a cylinder 12 that constitutes a cylinder of the engine 10, a piston 13 that reciprocates within the cylinder 12, and a crankshaft that is rotationally driven by the reciprocation of the piston 13. 15, a transmission 20 to which the rotational driving force of the crankshaft 15 is transmitted, and a crankcase 11 that houses the crankshaft 15 and the transmission 20. The crankcase 11 accommodates the crankshaft 15. A partition wall 33 separates a crank chamber 31 and a transmission chamber 32 that accommodates the transmission 20 . are arranged so that they partially overlap.
According to this configuration, when the closed crank chamber 31 is formed by separating the crank chamber 31 and the transmission chamber 32 with the partition wall 33, the partition wall 33 and the transmission 20 overlap each other when viewed in the crankshaft direction. . As a result, the transmission 20 can be brought as close to the partition wall 33 side (crank chamber 31 side) as possible, and the overall size of the power unit 1 can be reduced.

In the power unit 1, the transmission 20 includes a pair of transmission shafts (main shaft 25 and counter shaft 26) parallel to the crankshaft 15, and a transmission gear group 27 straddling the pair of transmission shafts. The pair of transmission shafts includes a main shaft 25 on the side of the crankshaft 15 and a counter shaft 26 on the side of the output shaft 26a of the power unit 1. It is arranged so as to overlap at least a part of gears supported on the main shaft 25 in the transmission gear group 27 .
According to this configuration, the partition wall 33 and the gear supported by the main shaft 25 overlap each other when viewed in the direction of the crankshaft. As a result, the main shaft 25 and thus the transmission 20 can be brought as close to the partition wall 33 side (crankshaft 15 side) as possible, and the size of the power unit 1 as a whole can be reduced.

In the power unit 1, the upper surface of the crankcase 11 is provided with a breather mechanism 40 for guiding the gas inside the crankcase 11 to the outside of the crankcase 11, and the breather mechanism 40 is included in the gas inside the crankcase 11. A gas-liquid separation portion (labyrinth flow path 47a) for separating oil and an oil return portion 43a for returning the separated oil to the crankcase 11 are provided. , causing the oil to drip into the transmission 20 .
According to this configuration, the oil separated from the blow-by gas by the breather mechanism 40 can be dripped onto the transmission 20 and actively used for lubricating the transmission 20 .

In the power unit 1 , the breather mechanism 40 includes a breather arrangement portion 41 on the upper wall 37 of the crankcase 11 , and the breather arrangement portion 41 has an opening 42 a penetrating through the upper wall 37 of the crankcase 11 in the vertical direction. and the partition wall 33 is provided with a notch 34a for avoiding the gear at a position overlapping with the opening 42a when viewed in the vertical direction.
According to this configuration, the partition wall 33 is provided with the notch portion 34a that avoids the gear of the main shaft 25, so that the partition wall 33 and the transmission 20 can be arranged to overlap each other when viewed in the crankshaft direction. When forming the notch portion 34 a in the partition wall 33 , the partition wall 33 can be processed by inserting a tool through the opening 42 a of the breather arrangement portion 41 . Thereby, the manufacture of the crankcase 11 can be facilitated.

The power unit 1 includes a plurality of cylinders 12, the crankcase 11 includes a second partition 36 that separates the plurality of cylinders 12, and the crank chamber 31 is separated by the second partition 36 for each cylinder 12. is divided into
According to this configuration, since the closed crank chamber 31 is formed for each of the plurality of cylinders, pressure interference between the cylinders can be suppressed. Thereby, the pressure in each sealed crank chamber 31 can be stably controlled.

In the power unit 1, a reed valve 39b is provided between the crank chamber 31 and the transmission chamber 32. The reed valve 39b is opened by the internal pressure of the crank chamber 31 when the internal pressure of the crank chamber 31 increases. is placed at the bottom of the
With this configuration, the oil accumulated in the lower portion of the crank chamber 31 can be effectively discharged to the transmission chamber 32 .

It should be noted that the present invention is not limited to the above embodiments. For example, although a reed valve is used to form a closed crankcase, the invention is not limited to this. For example, not only a reed valve but also a scavengeing pump may be used.
The saddle type vehicle includes all types of vehicles in which the driver straddles the vehicle body, not only motorcycles (including motorized bicycles and scooter type vehicles), but also three-wheeled vehicles (one front wheel and two rear wheels). , including vehicles with two front wheels and one rear wheel) or vehicles with four wheels.
The configuration in the above embodiment is an example of the present invention, and various modifications, such as replacing the constituent elements of the embodiment with known constituent elements, are possible without departing from the gist of the present invention.

1 power unit 10 engine (internal combustion engine)
11 crankcase 12 cylinder 13 piston 15 crankshaft 20 transmission 25 main shaft (transmission shaft)
26 counter shaft (transmission shaft)
26a output shaft 27 transmission gear group 31 crank chamber 32 transmission chamber 33 partition wall 34a notch portion 36 second partition wall 39b reed valve (valve mechanism)
40 breather mechanism 41 breather placement portion 42 breather opening 42a opening 43a oil return portion 47a labyrinth flow path (gas-liquid separation portion)

Claims (5)

a cylinder (12) forming a cylinder of an internal combustion engine (10);
a piston (13) reciprocating within the cylinder (12);
a crankshaft (15) rotationally driven by the reciprocating motion of the piston (13);
a transmission (20) to which the rotational driving force of the crankshaft (15) is transmitted;
a crankcase (11) housing the crankshaft (15) and the transmission (20);
The crankcase (11) has a partition wall (33) separating a crank chamber (31) containing the crankshaft (15) and a transmission chamber (32) containing the transmission (20). prepared,
The partition wall (33) is arranged so as to overlap at least a part of the transmission (20) when viewed in the axial direction of the crankshaft (15), and has a cutout portion (34a) that avoids the transmission (20). ) and
A breather mechanism (40) for guiding gas in the crankcase (11) to the outside of the crankcase (11) is provided on the upper surface of the crankcase (11),
The breather mechanism (40) includes a breather arrangement portion (41) on the upper wall (37) of the crankcase (11),
The breather placement portion (41) includes a breather opening (42) having an opening (42a) vertically penetrating the upper wall (37) of the crankcase (11),
A power unit, wherein the partition wall (33) includes the notch (34a) at a position overlapping the opening (42a) when viewed in the vertical direction. The transmission (20) is
a pair of transmission shafts (25, 26) parallel to the crankshaft (15);
A transmission gear group (27) spanning the pair of transmission shafts (25, 26),
The pair of transmission shafts (25, 26) are
a main shaft (25) on the crankshaft (15) side;
a counter shaft (26) on the output shaft (26a) side of the power unit (1),
The partition wall (33) is arranged so as to at least partially overlap gears supported by the main shaft (25) in the transmission gear group (27) when viewed in the axial direction of the crankshaft (15). A power unit according to claim 1 . A breather mechanism (40) for guiding gas in the crankcase (11) to the outside of the crankcase (11) is provided on the upper surface of the crankcase (11),
The breather mechanism (40) is
a gas-liquid separator (47a) for separating oil contained in the gas in the crankcase (11);
an oil return part (43a) for returning the separated oil into the crankcase (11);
The power unit according to claim 1 or 2, wherein said oil return portion (43a) is positioned above said transmission (20) and drips said oil onto said transmission (20). A plurality of the cylinders (12) are provided,
The crankcase (11) comprises a second partition (36) separating the plurality of cylinders (12),
The power unit according to any one of claims 1 to 3 , wherein the crank chamber (31) is divided for each cylinder (12) by the second partition wall (36). provided between the crank chamber (31) and the transmission chamber (32) is a valve mechanism (39b) that opens a valve when the internal pressure of the crank chamber (31) rises, and
The power unit according to any one of claims 1 to 4 , wherein the valve mechanism (39b) is arranged below the crank chamber (31).

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