JPH05213261A - Engine unit for motorcycle - Google Patents

Abstract

PURPOSE:To improve running stability and turn performance and to ensure rigidity and the strength of a crank case by a method wherein a pivot axle is positioned in a level lower than that of the division surface of a crank case, a window having size larger than that of a gear on a main shaft is opened to a side face in such a manner as to have no crossing over the division surface, and the main shaft is pivotally supported on the cover plate of a window. CONSTITUTION:A rear wheel is held to a rear arm pivotally supported to a pivot axle at the rear of an engine. A crank shaft 36 is arranged sideways in a crank case 32c having an engine division surface 34c, and the main shaft 40 and the auxiliary shaft 42 of a transmission 38 are positioned in juxtaposition, in the order named, in the rear thereof. A triangle as seen from a side is formed by a line for interconnecting the centers of the crank shaft 36 and the main and auxiliary shafts 40 and 42. The division surface 24c of a crank case 32c containing the centers of the crank shaft 36 and the auxiliary shaft 42 is inclined such that the front part thereof is lowered and the pivot axle is positioned in a level lower than that of a plane containing the division surface 34c. A window having size slightly larger than that of a maximum gear on the main shaft 40 is opened to the side in such a manner to have no crossing over the division surface 34c, the main shaft 40 is pivotally supported on the cover plate of the window.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an engine unit for a motorcycle in which a transmission is housed in a vertically divided crankcase.

[0002]

2. Description of the Related Art In a motorcycle, an engine unit in which a transmission is housed in a crankcase and the engine and the transmission are integrated is used. This engine unit accounts for a large part of the total body weight. Therefore, by lowering the mounting position of the engine unit, it is possible to lower the center of gravity of the vehicle and improve the steering stability.

However, in a motorcycle, various restrictions are imposed due to the relationship between the rear wheel drive system that transmits power to the rear wheels and the rear wheel suspension system, and it is difficult to lower the mounting position of the engine unit sufficiently. It was

FIG. 1 is a side view showing an example of engine arrangement when a mounting position of a conventional engine unit having a horizontal crankcase split surface is lowered. In this figure, reference numeral 10 is a frame, and a sub-frame 12 made of sheet metal,
The seat pillar tube 14, the seat rail 16, and the back tube 18 are provided.

The seat pillar tube 14, the seat rail 16, and the back tube 18 form a substantially triangular side surface,
The pivot bearing 20 is provided at the apex below the triangle. Reference numeral 22 denotes a rear arm, the front end of which is pivotally attached to the pivot bearing 20 by a pivot shaft 24, and the rear wheel 26 is held at the rear end thereof. The rear arm 22 and the rear wheel 26 are supported by the frame 10 so as to be vertically swingable by a cushion unit (not shown), and a so-called swing arm type rear wheel suspension device is formed.

Reference numeral 30 is an engine unit, and a crankcase 32 thereof has a horizontal split surface 34, and a crankshaft 36 and a main shaft 4 of a transmission 38 are provided laterally on the split surface 34.
0 and the counter shaft 42 are sequentially held. The sprocket 44 fixed to the shaft end of the counter shaft 42 and the rear wheel 26
A chain 48 is wound between the sprocket 46 and the sprocket 46 to form a chain type rear wheel drive system.

When the mounting position of such a conventional engine unit 30 is lowered so that the split surface 34 is lower than the pivot shaft 24 by h, the angle formed by the line connecting the auxiliary shaft 42 and the pivot shaft 24 and the horizontal line. θ increases. Therefore, as the rear wheel 26 moves up and down, the chain 48 moves toward the pivot shaft 24.
However, it is impossible to increase h.

That is, the height of the engine unit 30 needs to be substantially equal to the height of the pivot shaft 24, and the position of the pivot shaft 24 is the outer diameter of the rear wheel 26 and the frame 1.
Since it is determined by the structure of 0, etc., the unit 30 could not be mounted sufficiently low. When the shaft drive mechanism is used for the rear wheel drive system, if the angle θ becomes excessively large, the transmission efficiency of the universal joint sharply decreases, so that the position of the unit 30 cannot be sufficiently lowered.

The crankshaft 36, the main shaft 40, and the auxiliary shaft 42
Are arranged in order between the split surfaces 34, the front-rear dimension of the engine unit 30 becomes large and the pivot shaft 24
The position of also retreats. As a result, the distance between the front and rear wheels (wheel base) becomes large, making it difficult to improve turning performance.

Therefore, the inventor considered the configuration of FIG. 2 as an improved example. That is, the split surface 34A of the crankcase 32A of the engine unit 30A is inclined so that its front portion is lowered, and the crankshaft 36, the main shaft 40, and the sub shaft 42 are held on the split surface 34A, while the sub shaft 42 is pivoted. The height is substantially the same as that of the shaft 24. In this figure, the same parts as those in FIG. 1 are designated by the same reference numerals.

However, even if the split surface 34A is inclined as described above, the dimension of the engine unit 30 in the front-rear direction is still large, and it is difficult to make the wheel base sufficiently small.

Therefore, the inventor further considered the configuration of FIG. 3 as a second improved example. That is, the engine unit 30
Level the split surface 34B of the B crankcase 32B,
While holding the crankshaft 36 and the main shaft 40 on the split surface, the auxiliary shaft 42 is connected to the upper case 50 of the crankcase 32B.
And the auxiliary shaft 42 is made substantially flush with the pivot shaft 24.

However, in this case, the auxiliary shaft 42 must be mounted so as to be inserted into the upper case half body 50 from the side. The diameter of the speed change gear provided on the auxiliary shaft 42 is generally larger than the diameter of the gear provided on the main shaft 40. Therefore, it is necessary to form a large-diameter opening in the upper case half body 50, which is very disadvantageous when considering the strength of the crankcase 32B.

[0014]

SUMMARY OF THE INVENTION The present invention has been made in view of the above circumstances, and lowers the mounting position of the engine unit to lower the center of gravity of the vehicle, thereby improving the running stability and the engine. Provides a motorcycle engine unit that reduces the size of the unit in the front-rear direction, reduces the wheelbase, improves vehicle turning performance and mountability on the vehicle body, and is also preferable in terms of securing the strength of the crankcase. The purpose is to do.

[0015]

According to the present invention, the object is to hold a rear wheel on a rear arm pivotally supported on a pivot shaft located at the rear of the engine, and to mount the crankshaft in a crankcase having a split surface of the engine. In the case where the main shaft and the sub shaft of the transmission are arranged side by side behind the crank shaft, the line connecting the centers of the crank shaft and the main and sub shafts forms a triangle in a side view, While inclining the split surface of the crankcase including the center and the center of the auxiliary shaft so that the front portion thereof becomes low, the pivot shaft is positioned below the plane including the split surface, and the maximum diameter on the main shaft is determined. An engine of a motorcycle characterized in that a window having a diameter slightly larger than that of the gear is opened on a side surface of the crankcase so as not to cover the split surface, and the main shaft is pivotally supported by a cover plate closing the window. Knit, it is achieved by. Hereinafter, the present invention will be described in detail based on the illustrated embodiments.

[0016]

FIG. 4 is a side view showing an embodiment of the present invention, and FIG. 5 is a sectional view taken along line VV thereof. In this embodiment, front and rear V
A four-cylinder engine unit 30C is used, and a shaft drive type rear wheel drive system is adopted.

The split surface 34C of the vertically split crankcase 32C is inclined so that its front portion is lowered, and the crankshaft 36 and the auxiliary shaft 42 are held between the split surfaces 32C. 52 and 54 are the front bank and the rear bank,
Each of the banks 52 and 54 is provided with an overhead cam shaft 56 (only one is shown in FIG. 5). Reference numeral 58 is a flywheel magneto attached to the left end of the crankshaft 36.

The main shaft 40 is held by the lower case half body 60 of the crankcase 32C. Lower case half 60
Has a circular window 62 formed on the right side wall 60a (FIG. 5). The diameter of the window 62 is slightly larger than the gear 64 having the largest diameter among the speed change gears provided on the main shaft 40.
The main shaft 40 is inserted through the window 62 in a state in which the speed change gear is assembled, and its tip (left end) is held by the side wall 60b of the lower case half body 60. In this state, the window 62 has a cover plate 66.
Is attached, and the main shaft 40 is held in a state of penetrating the cover plate 66.

Reference numeral 68 denotes a wet multi-plate clutch mounted on the right end portion of the main shaft 40, and the rotation of the crankshaft 36 is transmitted to the clutch housing by a silent chain 70.

Of the speed change gears provided on the auxiliary shaft 42, the maximum diameter gear 72 is, as is apparent from FIG. 5, the main shaft 40.
Is larger than the maximum diameter gear 64. From the left end of the counter shaft 42,
The rotation of the counter shaft 42 is transmitted to the output shaft 76 via the bevel gear 74.

According to this embodiment, the rotation of the crankshaft 36 is transmitted to the main shaft 40 via the chain 70 and the clutch 68, and after the speed is changed by the transmission 38, the auxiliary shaft 42, the output shaft 76, and a known shaft. It is transmitted to the rear wheels via the drive type rear wheel drive system. Further, in the case of the V-type engine as in this embodiment, since the main shaft 40 is lowered, the rear bank 54 can be strongly tilted backward, which is suitable for downsizing the entire unit 30C.

FIG. 6 is a side view showing another embodiment of the present invention. In this embodiment, a horizontal in-line multi-cylinder engine unit 30D is used, and the crankcase 32 is divided into upper and lower parts.
The split surface 34D of D is inclined so that the front portion thereof becomes low. The crank shaft 36 and the sub shaft 42 are held between the split surfaces 34D, and the main shaft 40 is attached to the crank case 32.
It is held by the lower case half 78 of D. In addition, counter shaft 4
2 is disposed at substantially the same height as the pivot shaft 24.
In this figure, the same parts as those in FIGS. 1 to 3 are designated by the same reference numerals, and the description thereof will not be repeated.

[0023]

As described above, according to the present invention, the crankshaft and
A line connecting the centers of the main shaft and the sub shaft forms a triangle in a side view, and a crankcase split surface including the crank shaft and the sub shaft is inclined so that its front portion is lowered. Therefore, the center of gravity of the engine unit can be lowered, and the running stability can be improved.

Further, since the front-rear dimension of the engine unit can be made smaller, the mountability on the vehicle body is improved, and the pivot shaft located at the rear of the engine unit is arranged close to the lower part of the front lower split surface. As a result, the wheel base can be shortened and the turning performance of the vehicle can be improved.

Further, a window is provided in the crankcase so that the crankcase splitting surface does not come into contact with the crankcase, and a spindle equipped with a gear is inserted into the crankcase from the side through the window,
Although the main shaft is pivotally supported by the cover plate that closes this window, the speed change gear with the maximum diameter of the main shaft is smaller than the gear with the maximum diameter of the counter shaft, so a window for inserting the main shaft into the case half is used. Can be small. Therefore, it is convenient to secure the rigidity and strength of the crankcase.

[Brief description of drawings]

FIG. 1 is a side view showing an example of engine arrangement when a conventional engine unit is used.

FIG. 2 is a side view showing a second improved example.

FIG. 3 is a side view showing a third improved example.

FIG. 4 is a side view showing an embodiment of the present invention.

FIG. 5 is a sectional view taken along line VV.

FIG. 6 is a side view of another embodiment.

[Explanation of symbols]

 30, 30A to 30D Engine unit 32, 32A to 32D Crankcase 34, 34A to 34D Split surface 36 Crankshaft 38 Transmission 40 Main shaft 42 Secondary shaft 60, 78 Lower case 62 Window 66 Cover plate

Claims (1)

[Claims] 1. A rear arm supported on a pivot shaft located at the rear of the engine holds a rear wheel, and the crank shaft is laterally arranged in a crankcase having a split surface for splitting the engine vertically. A main shaft and a sub-shaft of the transmission are arranged side by side in the rear of the above, the line connecting the centers of the crank shaft and the main and sub-shafts forms a triangle in a side view, and includes a crank shaft center and a sub-shaft center. While inclining the split surface of the crankcase so that its front part becomes lower, the pivot shaft is located below the plane including the split surface, and a window having a diameter slightly larger than that of the gear with the largest diameter on the main shaft is provided. An engine unit for a motorcycle, wherein the main shaft is pivotally supported by a cover plate that is opened on a side surface of the crankcase so as not to cover the split surface and closes the window.