JPH0243886B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to an engine unit for a motorcycle in which a transmission is housed in a crankcase.

(Background of the Invention) In motorcycles, an engine unit is generally used in which a transmission is housed in a crankcase and the engine and transmission are integrated. This engine unit occupies a large portion of the total weight of the vehicle. Therefore, by lowering the mounting position of this engine unit, it is possible to lower the center of gravity of the vehicle and improve handling stability.

However, motorcycles are subject to various limitations due to the relationship between the rear wheel drive system that transmits power to the rear wheels and the rear wheel suspension system, so it has been difficult to lower the mounting position of the engine unit sufficiently.

FIG. 1 is a side view showing an example of the engine arrangement when the mounting position of a conventional engine unit having a horizontal crankcase split surface is lowered. In this figure, the reference numeral 10 is a frame, which includes a sub-frame 12 made of sheet metal, a seat pillar tube 14,
It includes a seat rail 16 and a back tube 18. The seat pillar tube 14, the seat rail 16, and the back tube 18 form a substantially triangular side surface, and a pivot bearing 20 is installed at the lower apex of this triangle.
is provided. Reference numeral 22 denotes a rear arm, the front end of which is pivotally attached to a pivot bearing 20 by a pivot shaft 24, and a rear wheel 26 is held at the rear wheel. The rear arm 22 and the rear wheel 26 are supported by the frame 10 so as to be able to swing up and down by a cushion unit (not shown), forming a so-called swing arm type rear wheel suspension system.

30 is an engine unit, and its crankcase 32 has a horizontal split surface 34, and a crankshaft 36 and a transmission 38 are mounted horizontally on this split surface 34.
A main shaft 40 and a sub-shaft 42 are held in sequence. A chain 48 is wound between a sprocket 44 fixed to the shaft end of the subshaft 42 and a sprocket 46 of the rear wheel 26, forming a chain type rear wheel drive system.

The mounting position of such a conventional engine unit 30 is lowered so that the dividing surface 34 is h higher than the pivot shaft 24.
If the angle .theta. is made lower, the angle .theta. between the line connecting the sub-shaft 42 and the pivot shaft 24 and the horizontal line increases. Therefore, as the rear wheel 26 moves up and down, the chain 48 interferes with the pivot shaft 24, which makes it impossible to increase h. That is, the height of the engine unit 30 needs to be approximately the same as the pivot shaft 24, and the position of the pivot shaft 24 is at the outer diameter of the rear wheel 26 and the frame 10.
It was not possible to mount the unit 30 sufficiently low. When a shaft drive mechanism is used in the rear wheel drive system, if the angle θ becomes excessively large, the transmission efficiency of the universal joint will drop sharply, so the position of the unit 30 cannot be made sufficiently low.

Further, since the crankshaft 36, the main shaft 40, and the subshaft 42 are arranged side by side in order between the split surfaces 34, the front and rear dimensions of the engine unit 30 become large, and the position of the pivot shaft 24 is also moved backward. This caused the problem that the distance between the front and rear wheels (wheelbase) became large, making it difficult to improve turning performance.

Therefore, the inventor considered the configuration shown in 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 part is lower, and the crankshaft 36, main shaft 40, and subshaft 42 are held on this split surface 34A, while the subshaft 42 is pivoted. It is designed to be approximately at the same height as the shaft 24. Note that in this figure, the first
The same parts as those in the figure are given the same reference numerals.

However, even if the dividing surface 34A is inclined in this manner, the longitudinal dimension of the engine unit 30 is still large, and it has been difficult to sufficiently reduce the wheel base.

(Object of the Invention) The present invention has been made in view of the above circumstances, and aims to lower the mounting position of the engine unit to lower the center of gravity of the vehicle, thereby improving running stability. An object of the present invention is to provide an engine unit for a motorcycle, which makes it possible to reduce the front and rear dimensions of the engine unit to reduce the wheelbase, thereby improving the turning performance of the vehicle.

(Structure of the Invention) According to the present invention, this 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 hold a rear wheel on a rear arm that is pivotally supported on a pivot shaft located at the rear of the engine. In a transmission in which a main shaft and a subshaft are sequentially arranged side by side, a line connecting the crankshaft and the centers of the main and subshafts forms a triangle in side view, and the plane including the center of the crankshaft and the center of the subshaft is defined as a triangle. This is achieved by an engine unit for a motorcycle, characterized in that the front part is inclined so as to be lower, and the pivot shaft is located below the plane.

(Embodiment) FIG. 3 is a side view showing a first embodiment of the present invention. In this embodiment, the split surface 34B of the crankcase 32B of the engine unit 30B is horizontal, and the crankshaft 36 and the main shaft 4 are placed on the split surface 34B.
0, while rotating the subshaft 42 to the crankcase 3.
It is held in the upper case 50 of 2B, and the countershaft 42 is at approximately the same height as the pivot shaft 24. As a result, the center of the crankshaft 36, the center of the main shaft 40, and the center of the subshaft 42 form a triangle in side view, and the center of the crankshaft 36 and the center of the subshaft 42 form a triangle in side view.
The plane containing the center of 2 is inclined so that its front part is lower.

According to this embodiment, the crankshaft 36 and the main shaft 4
0 and the center of the countershaft 42 form a triangle, the front and rear dimensions of the engine unit 30B are reduced,
Wheelbase decreases. Furthermore, since the crankshaft 36 and the main shaft 40 can be lowered while making the subshaft 42 higher, the center of gravity can be lowered.

FIG. 4 is a side view showing the second embodiment, and FIG. 5 is a cross-sectional view taken along the line --. In this example, the front and rear V
It uses a type 4-cylinder engine unit 30C and a shaft drive type rear wheel drive system. The split surface 34C of the upper and lower split crankcase 32C is inclined so that its front part is lower.
A crankshaft 36 and a subshaft 42 are held between C. 52 and 54 are a front bank and a rear bank, respectively, and each bank 52 and 54 is provided with an overhead camshaft 56 (only one is shown in FIG. 5). 58 is a flyhole magneto attached to the left end of the crankshaft 36.

The main shaft 40 is held in a lower case 60 of the crankcase 32C. The lower case 60 includes
A circular window 62 is provided on the right side wall 60a (FIG. 5).
is formed. The diameter of this window 62 is the same as that of the main axis 40.
It is slightly larger than the largest diameter gear 64 among the gears for speed change provided in the gear. The main shaft 40 is inserted through the window 62 with the transmission gear assembled, and its tip (left end) is held by the left side wall 60b of the lower case 60. In this state, a cover plate 66 is attached to the window 62, and the main shaft 40 is held in a state passing through the cover plate 66.

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

Of the speed change gears provided on the subshaft 42, the largest diameter gear 72 is larger than the largest diameter gear 64 of the main shaft 40, as is clear from FIG. The rotation of the countershaft 42 is transmitted from the left end of the countershaft 42 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 being further changed in speed by the transmission 38, the rotation is transmitted to the subshaft 42, the output shaft 76, and the known shaft drive type rear shaft. Power is transmitted to the rear wheels via the wheel drive system.

Also, in the case of a V-type engine like this example,
Since the main shaft 40 is lowered, the rear bank 54 can be strongly tilted rearward, which is suitable for downsizing the entire unit 30C.

FIG. 6 is a side view showing a third embodiment of the present invention. In this embodiment, a transverse in-line multi-cylinder engine unit 30D is used, and the split surface 34D of the vertically split crankcase 32D is inclined so that the front part thereof is lower. and crankshaft 36
and the sub-shaft 42 are held between this split surface 34D,
The main shaft 40 is the lower case 7 of the crankcase 32D.
It is held at 8. Further, the counter shaft 42 is arranged at substantially the same height as the pivot shaft 24. In this figure, the same parts as in the above-mentioned Figs. 1 to 3 are given the same reference numerals, so their description will not be repeated.

(Effects of the Invention) As described above, the present invention allows lines connecting the centers of the crankshaft, the main shaft and the subshaft to form a triangle in side view, and a plane including the crankshaft and the subshaft. Since the front part of the engine unit is inclined so that it is lower, the center of gravity of the engine unit can be lowered, and running stability can be improved. In addition, the front and rear dimensions of the engine unit can be reduced, and the pivot shaft located at the rear of the engine unit can be placed close to the bottom of this plane, making it possible to shorten the wheelbase and improve the vehicle's turning performance. It becomes possible to improve.

[Brief explanation of the drawing]

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 an improved example thereof, and Fig. 3 is a side view showing a first embodiment of the present invention. FIG. 4 is a side view showing the second embodiment, FIG. 5 is a cross-sectional view taken along the line ``--'', and FIG. 6 is a side view showing the third embodiment. 30, 30A to 30D...Engine unit,
32, 32A to 32D...Crank case, 3
4, 34A to 34D... split surface, 36... crankshaft, 38... transmission, 40... main shaft, 42...
Minor axis.

Claims (1)

[Scope of Claims] 1. A rear wheel is held on a rear arm pivotally supported on a pivot shaft located at the rear of the engine, and a main shaft and a sub-shaft of a transmission are mounted behind the crankshaft, which is disposed laterally within the crankcase of the engine. In the case where the shafts are sequentially arranged side by side, the line connecting the crankshaft and the centers of the main and subshafts forms a triangle in side view, and the plane containing the crankshaft center and the subshaft center is drawn so that the front part is lower. An engine unit for a motorcycle, characterized in that the pivot shaft is tilted and positioned below the plane.