JP3359747B2 - Power unit for vehicles - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a power unit mounted on a vehicle such as a three-wheeled vehicle or a four-wheeled vehicle, and more particularly, to an integrated internal combustion engine and transmission suitable for a saddle type vehicle for traveling on rough terrain, which is called a buggy vehicle. And a power unit for a vehicle.

[0002]

2. Description of the Related Art In most of conventional straddle-type vehicles 01, FIG.
(See JP-A-63-137087)
The power unit 02 was mounted with the crankshaft and the transmission shaft oriented in the vehicle width direction perpendicular to the traveling direction of the vehicle.

[0003]

[Problem to be Solved] The power unit shown in FIG.
In the case 02, mounting bosses 04, 05, 06 and 07 are respectively formed on the front upper portion, the front upper and lower middle portions, and the rear upper and lower portions of the case 03 in which the crankcase and the transmission case are integrated. 05, 06, and 07 are detachably mounted on the body frame 08 via the brackets 09, so that the power unit 02 is mounted on the body frame 08 of the straddle-type vehicle 01.
When assembling the power unit 02, the power unit 02 was lifted by inserting a jig (not shown) into the hole of the mounting boss 06 and engaging the front end claw (not shown) of the hanging fitting with the front lower step portion 011 of the cylinder head 010.

Normally, a saddle-ride type vehicle 01 has a power unit
Since the body frame 08 also exists above the vehicle body 02, the power unit 02 suspended by the jig and the hanging bracket cannot be lowered from above and assembled to the body frame 08, and the side of the saddle type vehicle 01 The power unit 02 must be moved in the vehicle width direction while supporting the power unit 02 in a cantilever shape with the two types of jigs and hanging brackets oriented in the vehicle width direction from the side, and inserted into the power unit 02. The assembly work of 02 was not easy.

When a power unit in which the crankshaft and the transmission shaft are oriented in the vehicle traveling direction is mounted on a saddle-ride vehicle, the tips of the jigs and the suspension fittings are bent at a right angle, and the bent ends are bent. Since the vehicle must be moved in the vehicle traveling direction while being moved in the vehicle traveling direction while being supported in a cantilever manner by engaging with the mounting boss and moving in the vehicle direction, a horizontal saddle-ride vehicle in which the crankshaft and the transmission shaft are perpendicular to the vehicle traveling direction. The assembling work was more difficult than in 01.

[0006]

SUMMARY OF THE INVENTION The present invention relates to an improvement of a power unit for a vehicle which overcomes the above-mentioned drawbacks, and in which a crankcase and a transmission case of an internal combustion engine are integrated, and the case rotates. In a vehicle power unit in which a crankshaft and a transmission shaft group freely supported are mounted in a substantially central portion of a vehicle in a vehicle traveling direction, mounting bosses are protruded on both lower sides of the case. An engaging notch is formed on one side of the upper part from the side of the case toward the center of the case and the front end thereof is directed upward of the case.

[0007] Since the present invention is configured as described above, the engaging projection of the supporting jig is engaged with the engaging notch of the power unit for a vehicle, and then the lower part of the supporting jig below the engaging projection is engaged. The vehicle power unit is mounted integrally with a mounting boss of the vehicle power unit, and the support jig is used to support the vehicle power unit in a cantilever manner and inserted into the vehicle body from the side of the vehicle body. Power unit can be very easily assembled to the vehicle.

In the present invention, since it is sufficient to provide the mounting bosses on both lower sides of the case, when the power unit of the present invention is mounted on a saddle type vehicle, the mounting boss protrudes from the upper portion of the power unit. The power unit does not approach the inner thighs of the driver straddling the straddle-type vehicle.

[0009]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention shown in FIGS. 1 to 14 will be described below.

[0010] In rough terrain traveling straddle type is called a illustrated buggy 1 vehicle A, channel-shaped main frame B ₁ is a bridging directed to the longitudinal direction on the vehicle body upward without right and left pair, the channel-shaped main pipe-shaped frame B ₂ under the frame B ₁ is provided integrally, mounting a pair of left and right balloon-type low-pressure tires, respectively front and rear of the body frame B consisting of these channel-shaped main frame B ₁ and the pipe-shaped frame B ₂ The front wheel Wf and the rear wheel Wr are suspended.

On the upper part of the saddle riding type vehicle A for traveling on wasteland,
A steering wheel H, a fuel tank T, and a seat S are sequentially disposed from the front to the rear. A front wheel Wf and a rear wheel Wr are provided below the fuel tank T and the seat S in the center of the body frame B. A power unit P to be driven is mounted.

A saddle-ride type vehicle A for traveling on rough terrain has fenders F covering substantially upper portions of front wheels Wf and rear wheels Wr, respectively.
And a carrier C located on the upper surface thereof.

Further, a step D for supporting both feet of the driver straddling the seat S is disposed in the lower center part of the body frame B, and a brake pedal (not shown) is disposed near the step D on the right side. A change pedal (not shown) is arranged near the left step D.

Further, the power unit P is constituted by integrating a crankcase of the internal combustion engine E and a transmission case of the transmission M. The internal combustion engine E includes a cylinder head 1, a cylinder block 2, a front crankcase 3, Rear crankcase 4, front case cover 5, and rear case cover 6
The front crankcase 3 and the rear crankcase 4, which are integrated with each other by connecting bolts (not shown), are mounted on mounting bosses 8 on both lower sides thereof as shown in FIGS. to, and it is coupled to the pipe-shaped frame B ₂ of the right and left via the elastic mount member 9.

Further, as shown in FIGS. 6 to 9, the cylinder block 2 is superimposed on the front crankcase 3 and the rear crankcase 4 which are integrally connected to each other, and the cylinder block 2 and the front crankcase 3, Cylinder / case coupling bolts 11 are inserted and screwed into two bolt holes 10 provided in the rear crankcase 4 and screwed tightly. A holder-head-cylinder coupling bolt 13 is inserted into one bolt hole 12 provided in the rocker arm holder 19, the cylinder head 1 and the cylinder block 2, and screwed and tightened. A head / cylinder coupling bolt 15 is inserted into one bolt hole 14 provided in the cylinder block 2 and screwed tightly. And two bolts 16 provided on the cylinder head 1, cylinder block 2, front crankcase 3 and rear crankcase 4.
Then, a head / cylinder / case connecting bolt 17 is fitted and screwed and tightened.
A coupling bolt (not shown) is screwed into a bolt hole 18 provided in the cylinder head 1, the cylinder block 2, the front crankcase 3, and the rear crankcase 4, and screwed tight. 1, cylinder block 2, front crankcase 3, rear crankcase 4
And the rocker arm holder 19 are integrally connected.

The crankshaft 20, which is rotatably supported by the front crankcase 3 and the rear crankcase 4 of the internal combustion engine E in the traveling direction of the saddle riding type vehicle A for traveling over rough terrain,
As shown in FIG. 5, the cylinder block 2 is disposed slightly rightward from the center of the front crankcase 3 and the rear crankcase 4, and is directed obliquely upward and leftward from the crankshaft 20. And a piston 22 whose cylinder head 1 is tilted leftward and slidably fitted to the cylinder 21.
Is connected to a crankpin 23 of the crankshaft 20 via a connecting rod 24, and the crankshaft 20 is driven to rotate by raising and lowering the piston 22.

Further, a main shaft 25 and a sub-shaft 26 of the transmission M are sequentially disposed to the left of the crankshaft 20, and a reverse shaft 27 is disposed midway above the main shaft 25 and the sub-shaft 26;
With the drive shaft 28 arranged below the main shaft 25 and the sub shaft 2
6, the reverse shaft 27 and the drive shaft 28 are rotatably supported by the front crankcase 3 and the rear crankcase 4 in parallel with the crankshaft 20.

Further, a camshaft 29 is provided on the upper right of the
While the balancer shaft 30 is disposed therebelow, and the shift drum 31 is disposed below the main shaft 25 to the right of the drive shaft 28, and the cam shaft 29, the balancer shaft 30, The shift drum 31 is rotatably supported by the front crankcase 3 and the rear crankcase 4.

Further, as shown in FIG. 4, a sprocket 32, 33 is provided on the crankshaft 20 and the camshaft 29, respectively, and an endless chain 34 is bridged over the sprockets 32, 33. When 20 rotates, the camshaft 29
It is driven to rotate at a rotation speed of / 2.

Since the sprockets 32 and 33 are disposed at positions protruding forward from the front crankcase 3, the chain tensioner 36 swings up and down on the bearing holder 35 of the main shaft 25 as shown in FIG. A slipper 37 is provided on the lower surface of the distal end of the bearing holder 35 so as to be freely movably supported, and a pressure lower portion of an adjusting device 38 fitted from above the front crankcase 3 and attached by bolts (not shown) is shown in FIG. As shown in the figure, the endless chain 34 is brought into contact with a receiving portion 39 protruding forward from the chain tensioner 36, and is urged inward by the additional force of the pressing portion of the adjusting device 38. It is set to a moderate tension.

As shown in FIG. 11, a hydraulic pump 40 is disposed in front of the balancer shaft 30, and the rotary shaft of the hydraulic pump 40 is directly connected to the balancer shaft 30, and the internal combustion engine E Is in an operating state, the hydraulic pump 40 is rotationally driven integrally with the balancer shaft 30, and lubricating oil is supplied to the lubricating portions of the internal combustion engine E and the transmission M.

As shown in FIGS. 11 and 13,
An intake cam 41 and an exhaust cam 42 are integrally formed on the cam shaft 29,
A decompression cam 43 is attached adjacent to the front of the exhaust cam 42, and a rib 44 is formed rearward on the intake cam 41,
Moreover, the front crankcase 3 has the same diameter as the outer circumferential surface of the ball bearing 45 supporting the front portion of the camshaft 29, and
A cylindrical surface portion 46 having a diameter larger than the base circle diameter of the base 29 and a locking step portion 47 are formed behind the cylindrical surface portion 46, and the intake cam 41, the exhaust cam 42, and the decompression cam 43 are positioned as shown in FIG. In the state described above, notches 48 and 49 are formed in the locking step 47 so that the cam shaft 29 can be pulled out forward.

Further, a tappet 50 is fitted to the front crankcase 3 and the rear crankcase 4 so as to be able to move up and down, and is located above the intake cam 41 and the exhaust cam 42. As shown in FIG. A push rod 53 is interposed at the right end of the rocker arm 52 pivotally supported by the rocker shaft 19 via the rocker shaft 51 and the tappet 50, and the rocker arm 52 moves up and down in response to the rotation of the cam shaft 29. The intake valve 54 and the exhaust valve 55 that are oscillated and located on the right side of the center of the cylinder 21 and in contact with the left end of the rocker shaft 51 are driven to open and close.

Further, an ignition plug 56 is mounted on the left side of the center line of the cylinder 21 and further inclined leftward with respect to the center line of the cylinder 21.

An intake passage 57 in which an intake valve 54 is provided.
Is connected to an exhaust pipe (not shown) connected to an exhaust passage 58 provided with an exhaust valve 55.

Further, a rotor 60r of the ACG 60 is mounted on a rear portion of the crankshaft 20, and an ACG cover 7 is detachably mounted on the rear case cover 6 mounted on the rear crankcase 4, and the ACG 60 is mounted on the ACG cover 7. Stator 60s
Is attached, and as shown in FIG.
The ACG 60 and other electrical components are mounted on the CG cover 7, and when the ACG cover 7 is removed, the stator 60s, the pulsar 61, and other electrical components of the ACG 60 are simultaneously AC-mounted.
It can be taken out together with the G cover 7.

Further, a starting wheel 62 is provided at the rear end of the crankshaft 20.
The recoil starter 63 is provided opposite to this, and the internal combustion engine E can be started by manually operating the recoil starter 63.

As shown in FIG. 11, a starting gear 65 is loosely fitted to the crankshaft 20 via a one-way clutch 64 and is mounted on the rear crankcase 4 in front of the rotor 60r of the ACG 60. An output shaft 66a of the starter motor 66 is connected to a starting gear 65 via a reduction gear device 67,
When the starter motor 66 rotates, the crankshaft 20 is rotationally driven via the reduction gear device 67, the starting gear 65, and the one-way clutch 64, and the internal combustion engine E is automatically started.

Further, a centrifugal start clutch 70 is provided at the front end of the crankshaft 20, and a multi-plate transmission clutch 71 is provided at the front end of the main shaft 25. The output gear 70a of the centrifugal start clutch 70 is a multi-plate transmission clutch 71. When the crankshaft 20 is stopped or rotating at or below a predetermined rotation speed, the centrifugal start clutch 70 is in a disengaged state, and when the rotation speed exceeds the predetermined rotation speed, the centrifugal start clutch 70 is engaged. The centrifugal start clutch 70 is configured so that the start clutch 70 is in the connected state.

Further, as shown in FIG.
A multi-speed gear train 72 is interposed between 25 and the counter shaft 26,
Output gear 26a is meshed with an input gear 28a of the drive shaft 28,
As shown in FIG. 12, the output gear 25a of the main shaft 25 is meshed with the input gear 27a of the reverse shaft 27, and the output gear 27b of the reverse shaft 27 is connected to the reverse input gear 26 of the sub shaft 26.
When the change pedal near the left step D is operated to the required shift position or reverse position, the multi-plate type transmission clutch 71 is disengaged only at the time of the operation, and the multi-stage transmission gear train 72 and the auxiliary gear are engaged. The reverse input gear 26b of the shaft 26 is switched, so that the sub shaft 26 is set to a required speed ratio or a forward / reverse rotation state and is driven to rotate.

As shown in FIG. 15, the front ends 73 of the front crankcase 3 and the rear crankcase 4 are directed to the center of the case, to the upper side of the case, and to the top of the case.
An engagement notch 73 whose a is directed upward is formed.

Further, the case upper surface 7 on the left side of the cylinder opening 74 of the front crankcase 3 and the rear crankcase 4
The clutch upper portion 77 adjacent to the front of the case upper surface portion 75 rises upward by the ACG 60 on the inside thereof, and the transmission upper portion 7 on the left side of the case upper surface portions 75 and 76.
8 and 79 also rise upward, and the case upper surfaces 75 and 76 surrounded by the clutch upper portion 77 and the transmission upper portions 78 and 79 are gently inclined downward from the clutch upper portion 77 toward the rear. It is formed so that.

Since the embodiment shown in FIGS. 1 to 14 is constructed as described above, the driver sits on the seat S, puts his foot on the step D, and uses the starter motor 66 or the recoil starter 63. When the internal combustion engine E is started and the right grip of the steering handle H is grasped and an operation lever (not shown) disposed below is operated, the carburetor 59 is opened, When the internal combustion engine E is accelerated and the crankshaft 20 exceeds a predetermined number of revolutions, the centrifugal start clutch 70 is automatically connected and the saddle riding type vehicle A
Can start running.

The crankshaft 20, the main shaft 25, the sub shaft 26, the reverse shaft 27, and the drive shaft 28 are all oriented in the traveling direction of the saddle riding type vehicle A for traveling on rough terrain, so that the bevel gear device is minimized. The power of the internal combustion engine E can be transmitted to the front wheels Wf and the rear wheels W
r can be transmitted to the front wheel differential device Gf and the rear wheel drive gear device Gr, and the weight of the power transmission system can be reduced.

Further, in the power unit P, the upper part of the crankshaft 20 is inclined leftward, and the lower part of the crankshaft 20 is arranged slightly rightward from the center of the left and right widths of the front crankcase 3 and the rear crankcase 4. Main shaft 25, sub shaft 26, reverse shaft 27, drive shaft of transmission M
28 and a shift drum 31 are arranged, and a cam shaft 29, a balancer shaft 30, a hydraulic pump 40, a starter motor 66, a valve train tappet 50, a rocker shaft 51, a rocker arm 52, and a push rod 53 are arranged to the right of the crankshaft 20. As a result, the height of the front crankcase 3 and the rear crankcase 4 can be reduced while the left and right widths of the front crankcase 3 and the rear crankcase 4 are kept small, and the power unit P can be reduced in size. In addition, the front shape of the power unit P can be substantially isosceles triangular to lower the center of gravity of the power unit P, and the driver can easily straddle the seat S above the power unit P without the power unit approaching the inner thigh. be able to.

Further, since the cylinder 21 is tilted to the left and the ignition plug 56 is tilted to the left from the center of the cylinder 21 to the left, the fuel tank T and the seat S above the cylinder 21 The replacement of the spark plug 56 can be easily performed without any hindrance.

Since the crankshaft 20 is tilted to the left, the camshaft 29 is arranged to the upper right of the crankshaft 20, and the push rod 53 is arranged to the right of the cylinder 21,
Compared with the push rod provided above the crankshaft, the dimension of the internal combustion engine E in the crankshaft direction can be reduced, and the front-rear length of the entire power unit P can be shortened.
Moreover, the length of the push rod 53 can be reduced, and the weight of the reciprocating portion of the valve train can be reduced.

Further, since the balancer shaft 30 is located below the camshaft 29 and the hydraulic pump 40 is disposed on the axis of the balancer shaft 30, the height of the hydraulic pump 40 with respect to the lubricating oil level O in the power unit P Can be reduced, the suction height of the hydraulic pump 40 can be reduced, and lubricating oil suction can be performed smoothly.

Further, the cylinder head 1, the cylinder block 2, the front crankcase 3, and the rear crankcase 4
6 and 9, the cylinder head 1, the cylinder block 2, the front crankcase 3, the rear crankcase 4, and the rocker arm holder 19 are firmly integrated with each other. The cylinder head 1, the cylinder block 2, and the cylinder / case coupling bolt 11, the head / cylinder / case coupling bolt 17, and the bolts (not shown) screwed into the bolt holes 18 are tightened.
And the rocker arm holder 19 can be easily removed from the front crankcase 3 and the rear crankcase 4 while being connected to each other.

Further, when the camshaft 29 is replaced by removing the cylinder head 1 and the cylinder block 2 from the front crankcase 3 and the rear crankcase 4, as shown in FIG. When the bolt 33a connecting the sprocket 33 and the sprocket 33 is removed and the sprocket 33 is removed from the camshaft 29, the tappet 50 is removed upward from the front crankcase 3 and the rear crankcase 4, and then the intake cam 41 is removed. Unless the exhaust cam 42 and the decompression cam 43 are aligned with the notch 49, the intake cam 41
The rib 44 is locked to the tappet 50 that has fallen on the base circle, or the intake cam 41, the exhaust cam 42, and the decompression cam 43 are locked to the locking step 47, so that the cam shaft 29 cannot be pulled out. As a result, the tappet 50 falls into the front crankcase 3 and the rear crankcase 4 by mistake, and if the front crankcase 3 and the rear crankcase 4 are not disassembled, the tappet 50 in the front crankcase 3 and the rear crankcase 4 will not be disassembled. The trouble that the tappet 50 cannot be taken out can be prevented beforehand.

As shown in FIG. 15, the distance between the connecting projection 81 of the supporting jig 80 and the lower hole 82 is adjusted to the distance between the tip 73a of the notch 73 and the mounting boss 8l. Ingredient
After the connecting projection 81 of the support jig 80 is engaged with the engagement notch 73 and locked at the tip 73 a thereof, the support jig 80 is used.
By inserting a pin (not shown) into the hole 82 and the mounting boss 8l, the support jig 80 is moved to the front crankcase 3 of the internal combustion engine E.
It can be integrally connected to the rear crankcase 4, and in that state,
The power unit P can be supported in a cantilever manner by pulling it upward while giving a counterclockwise moment to the support jig 80.

[0042] Therefore, the vehicle body frame B wasteland traveling straddle-type vehicle A is formed in a loop shape in a side view, even if there is channel-shaped main frame B ₁ above the power unit P, the channel-shaped main without being obstructed by the frame B _1, a power unit P is carried into rough terrain traveling straddle-type vehicle in a from the side of wasteland traveling straddle-type vehicle a,
A pipe-shaped frame B _2, it is possible to mount the power unit P easily through the mounting bosses 8 and the elastic mount member 9.

Further, even if the upper case portions 75 and 76 on the left side of the cylinder opening 74 are surrounded by the clutch upper portion 77 and the transmission upper portions 78 and 79 which rise upward, the case upper portion 75 and the case Since the upper surface 76 is gently inclined downward from the front to the rear, rainwater and the like can be naturally discharged without collecting on the case upper surfaces 75 and 76.

[Brief description of the drawings]

FIG. 1 is a schematic perspective view of a saddle riding type vehicle for traveling on rough terrain, on which a vehicle power unit of the present invention is mounted.

FIG. 2 is an enlarged side view of a main part of FIG.

FIG. 3 is a view taken in the direction of arrows III-III in FIG. 2;

FIG. 4 is a front view of the power unit with a front case cover removed.

FIG. 5 is a partially longitudinal rear view in which a rear case cover is removed and a center of a cylinder head and a cylinder block is cut off.

FIG. 6 is a longitudinal section of the internal combustion engine taken along the line VI-VI of FIG. 7;

FIG. 7 is a plan view of a cylinder head.

FIG. 8 is a plan view of a cylinder block.

FIG. 9 is a plan view of a main part of a front crankcase and a rear crankcase.

FIG. 10 is a longitudinal sectional view of the power unit taken along line XX of FIG. 4;

FIG. 11 is a longitudinal sectional view of the power unit cut along the line XI-XI in FIG. 5;

12 is a longitudinal sectional view of the power unit, taken along line XII-XII of FIG.

FIG. 13 is an enlarged vertical sectional view of a main part of FIG. 11;

FIG. 14 is a view taken in the direction of arrows XIV-XIV in FIG. 13;

FIG. 15 is an essential part perspective view of 3 and 4 as viewed obliquely from the rear upper left.

FIG. 16 is a side view of a conventional vehicle.

[Explanation of symbols]

A: saddle riding type vehicle for traveling on rough terrain, B: body frame, C: carrier, D: step, E: internal combustion engine, F: fender,
Gf: front wheel differential, Gr: rear wheel drive gear, H: steering wheel, M: transmission, O: lubricating oil level, P: power unit, S: seat, T: fuel tank, Wf: front wheel,
Wr: rear wheel, 1 ... cylinder head, 2 ... cylinder block, 3 ... front crankcase, 4 ... rear crankcase,
5 front case cover, 6 rear case cover, 7 ACG
Cover, 8… Mounting boss, 9… Elastic mount member, 10…
Bolt hole, 11… Cylinder / case connecting bolt, 12… Bolt hole, 13… Holder head / cylinder connecting bolt, 14…
Bolt hole, 15… Head / cylinder connection bolt, 16… Bolt, 17… Head / cylinder / case connection bolt, 18… Bolt hole, 19… Rocker arm holder, 20… Crank shaft, 21
... Cylinder, 22 ... Piston, 23 ... Crank pin, 24 ... Connecting rod, 25 ... Main shaft, 26 ... Sub shaft, 27 ... Reverse shaft, 28 ... Drive shaft, 29 ... Cam shaft, 30 ... Balancer shaft, 31 ...
Shift drum, 32, 33… Sprocket, 34… Endless chain, 35… Bearing holder, 36… Chain tensioner,
37 ... Slipper, 38 ... Adjusting device, 39 ... Receiving part, 40 ... Hydraulic pump, 41 ... Intake cam, 42 ... Exhaust cam, 43 ... Decomp cam, 44 ... Rib, 45 ... Ball bearing, 46 ... Cylinder surface part, 47 ... Stop, 48, 49… Notch, 50… Tapet, 51
... rocker shaft, 52 ... rocker arm, 53 ... push rod, 54 ... intake valve, 55 ... exhaust valve, 56 ... spark plug, 57 ... intake passage, 58 ... exhaust passage, 59 ... carburetor, 60 ... ACG, 61 ... pulser , 62 ... Starting wheel, 63 ... Recoil starter, 64 ... One-way clutch, 65 ... Starting gear, 66 ... Starter motor, 67 ...
Reduction gear device, 68, 69 gear, 70 centrifugal start clutch, 71 multi-plate transmission clutch, 72 multi-stage transmission gear train, 73
... Coupling notch, 74 ... Cylinder opening, 75, 76 ... Case upper part, 77 ... Clutch upper part, 78,79 ... Transmission upper part, 80 ...
Supporting jig, 81: engagement projection, 82: hole.

──────────────────────────────────────────────────続 き Continued on the front page (58) Field surveyed (Int. Cl. ⁷ , DB name) B60K 5/00-5/12 B60K 17/08 B62K 5/00

Claims (1)

(57) [Claims] 1. A crankcase and a transmission case of an internal combustion engine are integrated, and a crankshaft and a transmission shaft group rotatably supported by the case are directed substantially in the center of the vehicle in a vehicle traveling direction. In the vehicle power unit to be mounted, mounting bosses are protruded on both sides of a lower portion of the case, and an engagement notch is formed on one upper side of the case from the side of the case toward the center of the case and the front end thereof is directed upward of the case. A power unit for a vehicle, wherein the power unit is formed.