JPH0122457B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention relates to a power unit for a motorcycle that integrates an engine and a transmission.

Prior Art In conventional power units for motorcycles, the crankshaft, the main transmission shaft, and the transmission counter shaft are arranged along approximately the same horizontal plane, and the crankcase is arranged vertically on the plane that connects the center lines of these axes. Since it was divided into two parts, it was easy to assemble and divide.

However, since the gear chain sprocket etc. fitted to each of these shafts are arranged on the same plane, the front and rear length of the crankcase becomes longer.
It has been difficult to make the crankcase lighter and more compact.

In order to shorten the longitudinal length of the crankcase, as shown in Japanese Utility Model Application Publication No. 56-55735,
2. Description of the Related Art Power units for motorcycles have long been available in which the upper and lower dividing surfaces of a crankcase that clamps and supports a crankshaft and a transmission main shaft are inclined.

In the power unit shown in FIG. 2 of the above-mentioned Japanese Utility Model Publication No. 56-55735, the engine cylinder is connected to the down tube of the vehicle body frame (from the lower part of the head pipe that supports the front wheel rotatably via the front fork). The upper vertical dividing surface of the crankcase is inclined forward to follow the vehicle body members disposed diagonally rearward and downward, and the upper vertical dividing surface of the crankcase is tilted diagonally rearward and upward.

Further, in the power unit shown in FIG. 5 of the above-mentioned publication, the engine is composed of cylinders arranged in a V-shape in the front and rear, and the upper vertical dividing plane of the crankcase is inclined backwardly and downwardly.

Problems to be Solved In the power unit shown in Figure 2 of the above publication,
Since the upper and lower dividing planes of the crankcase are slanted backwards and upwards, the space between the rear of the cylinder and the upper part of the crankcase becomes narrower, allowing space for the fuel tank and seat that are normally installed above the power unit. It is difficult to arrange auxiliary equipment such as a starter motor and carburetor without getting in the way.

In addition, in the power unit shown in Figure 5 of the above publication, the cylinders are arranged in a V-shape in the front and rear, so the space between the rear part of the rear cylinder and the upper part of the crankcase is narrow, and the space between the starter motor, carburetor, etc. auxiliary equipment cannot be placed.

Moreover, in the power units shown in FIGS. 2 and 5, the lower dividing surface of the lower crankcase is horizontal, although the upper dividing surface of the lower crankcase is inclined with respect to the horizontal plane. Since the upper and lower dividing surfaces are not parallel, various machining processes are required, such as machining bolt holes for aligning the upper and lower crankcases, and lubrication formed within the crankcase wall to send lubrication to each sliding part of the power unit. When machining oil passages, etc. on the lower crankcase, the lower crankcase must be installed on the machining table of the machine tool via a jig in order to keep the upper dividing surface, which is the normal machining reference plane, horizontal. , the number of man-hours increases and it is difficult to maintain machining accuracy at a high level.

Means and Effects for Solving the Problems The present invention relates to an improvement of a power unit for a motorcycle that overcomes the above-mentioned difficulties, and the crankcase is formed into three parts, upper, middle and lower. A crankshaft and a transmission main shaft are pivotally supported between the split surfaces of the crank, and a transmission counter shaft is pivotally supported on the upper crankcase at an angle above and behind the transmission main shaft. The lower crankcase is formed and the upper part of the cylinder of the engine is formed to tilt forward so that the dividing plane with the lower crankcase below and the dividing plane between the lower crankcase and the crankcase below it are parallel. At the same time, in a state where the dividing surface of the crankcase is inclined rearward and downward with respect to the horizontal plane of the vehicle body,
The crankcase is attached to the vehicle body, and the bottom crankcase is formed such that the vertical width of the bottom crankcase gradually becomes narrower toward the rear.

In the present invention, the crankcase is formed into three parts, upper, middle and lower, and the crankshaft and the transmission main shaft are pivotally supported between the divided surfaces of the upper crankcase and the lower crank, and the transmission counter shaft is supported between the divided surfaces of the upper crankcase and the lower crank. The engine cylinder is pivoted to the upper crankcase at an angle rearwardly upper than the main shaft, and the upper part of the cylinder of the engine is tilted forward, and the splitting surface of the crankcase is tilted backwardly and downwardly with respect to the horizontal plane of the vehicle body. Since the crankcase is attached to the vehicle body, the distance between the crankshaft and the transmission counter axis can be shortened, making it possible to shorten the length of the crankcase from front to back.

Further, in the present invention, the upper part of the cylinder of the engine is formed to be inclined forward, and the dividing surface between the upper crankcase and the lower crankcase below it, and the dividing surface between the lower crankcase and the bottom crankcase below it. The lower crankcase is formed so that the lower crankcases are parallel to each other,
Since the bottom crankcase is formed so that the vertical width of the bottom crankcase gradually narrows toward the rear, the bottom surface of the crankcase can be oriented approximately parallel to the horizontal plane of the vehicle body, and An increase in the height of the lower crankcase due to the inclination is absorbed by the rearwardly tapered shape of the bottom crankcase, and even with the forward inclination of the cylinder, the height of the power unit can be reduced.

Embodiment An embodiment of the present invention illustrated in the drawings will be described below.

The power unit 1 consists of a gasoline engine 2 and a transmission 3, and the crankcase 4 of the gasoline engine 2 is connected to the transmission 3.
It also serves as a casing.

Therefore, the bottom surface of the crankcase 4 is formed parallel to the horizontal plane of the vehicle body, and the crankcase 4 has a dividing surface 5 inclined rearward and downward with respect to the horizontal axis L of the vehicle body.
It is divided vertically into two parts 6 and 7, and
The bottom part 9 is divided into the lower crankcase 7 by a dividing plane 8 parallel to the dividing plane 5, and the upper crankcase 6, lower crankcase 7, and bottom crankcase 9 are separated from the dividing planes 5 and 8. They are connected to each other by bolts 10 oriented at right angles so that they can be moved toward and away from each other.

Further, the cylinder 11 of the engine 2 is tilted forward so that its upper part is located forward, and the center line of the crankshaft 12 is aligned with the crankcase 4.
The crankshaft 12 is rotatably supported by the upper and lower crankcases 6 and 7 via bearings (not shown) so that the crankshaft 12 coincides with the dividing surface 5 of the crankcase.

Furthermore, the main shaft 1 of the transmission 3
3 also connects the upper and lower crankcases 6 and 7 with their center lines aligned with the dividing surface 5 of the crankcase 4.
The transmission counter shaft 14 is rotatably supported on the upper crankcase 6 at a position adjacent to the vehicle horizontal axis L passing through the center line of the crankshaft 12. has been done.

Furthermore, the drive sprocket 15 integrated with the crankshaft 12 is connected to the transmission main shaft 13.
Chain 1 is integrated with transmission sprocket 17.
They are connected via 6.

In addition, several gears 18 are fitted to the main shaft 13 so that they do not rotate relative to each other but are movable in the axial direction, and several gears 19 are also fitted to the mission counter shaft 14 so that they do not rotate relative to each other. are fitted to be movable in the axial direction, a gear fork 21 is fitted to the gear shift fork guide shaft 20 to be movable in the axial direction, and a gear fork 21 is fitted to the gear shift fork guide shaft 22 to be movable in the axial direction. Gear fork 23 is gear shift drum 2
The gears 18 and 19 are guided by guide grooves 4 (not shown) and moved appropriately in the axial direction, and the gears 18 and 19 are selectively engaged to obtain a required speed ratio.

Further, a starter motor 26 is disposed above the crankcase 4 and located between the engine 2 and the transmission 3, and is connected to the crankshaft 12 via a transmission mechanism (not shown). The rotational force of crankshaft 1
2 and the engine 2 is started.

Furthermore, a carburetor 27 is disposed at the rear of the engine 2 above the starter motor 26, and the air-fuel mixture mixed with gasoline and air is supplied to the engine 2 by the carburetor 27.

Since the illustrated embodiment is configured as described above, when the engine 2 is in operation, rotational force is transmitted from the drive sprocket 15 to the sprocket 17 of the transmission 3 via the chain 16, and the transmission The speed is reduced to an appropriate gear ratio in the transmission 3, and the rotational force is transmitted to a rear wheel (not shown) via the chain 25.

Furthermore, since the dividing surface 5 that divides the upper and lower crankcases 6 and 7 and supports the crankshaft 12 and the transmission main shaft 13 is inclined, the horizontal distance between the crankshaft 12 and the main shaft 13 is shortened. Moreover, since the mission counter shaft 14 is located at an angle of about 45° diagonally upward and backward with respect to the mission main shaft 13, the mission shaft 13
The horizontal distance between the shaft and the transmission counter shaft 14 is significantly shortened, and the longitudinal length of the crankcase 4 is therefore shortened. Even if the cylinder 11 is tilted forward and the longitudinal length of the power unit as a whole becomes longer, the longitudinal length of the crankcase 4 is short, and the cylinder 11 is moved along a down tube (not shown), so that there is a gap between the down tube and the power unit. are held substantially uniformly in the vertical direction, so the rear end of the crankcase 4 is located at the front of the vehicle body, and the pivot point of the rear fork (not shown) is located at the front, so that the vehicle length of the motorcycle can be shortened.

Furthermore, the cylinder 11 of the engine 2 is tilted forward,
The lower crankcase 7 is formed so that the upper and lower dividing surfaces 5 and 8 of the lower crankcase 7 are parallel, and the bottom crankcase 7 is formed so that the vertical width of the rear end of the bottom crankcase 9 gradually narrows toward the rear. Since the case 9 is formed, most of the bottom surface of the crankcase 4 can be aligned with the horizontal plane of the vehicle body, and the increase in height of the lower crankcase 7 due to the inclination of the lower crankcase 7 is due to the rear taper of the bottom crankcase 9. This is absorbed by the shape, and even if the cylinder 11 is tilted forward, the vertical height of the power unit 1 is reduced.

Therefore, the power unit 1 as a whole is made more compact and lighter.

Further, since the height of the power unit 1 is reduced, there is a larger space for the frame and the gasoline tank (not shown), and the assembly, removal, and maintenance of the power unit 1 can be easily performed.

Furthermore, since the female threads for screwing together the bolts 10 are oriented at right angles to the dividing surfaces 5 and 8, the lower crankcase 7 can be simply placed and fixed on the processing table of the machine tool, making the work easier. High performance and high processing accuracy.

Effects of the Invention As described above, in the present invention, the distance between the crankshaft and the transmission counter shaft is shortened, the front and rear length of the crankcase is shortened, and the height of the power unit is reduced. A large space is secured above to store engine accessories such as the starter motor and carburetor, making it easy to install and maintain the power unit. By shifting the pivot point of the motorcycle forward, it is possible to make the motorcycle more compact.

Further, in the present invention, the lower crankcase is formed so that the dividing plane between the upper crankcase and the lower crankcase below it and the dividing plane between the lower crankcase and the bottom crankcase below it are parallel. When performing the required machining on the lower crankcase, simply placing and fixing the crankcase on the machining table of the machine tool allows the upper dividing plane, which is the normal machining reference plane, to be set horizontally. This reduces man-hours and makes it easy to maintain a high level of machining accuracy.

[Brief explanation of drawings]

The drawing is a partially cutaway side view illustrating an embodiment of a power unit for a motorcycle according to the present invention. 1...Power unit, 2...Gasoline engine, 3...Transmission, 4...Crankcase, 5...Divided surface, 6...Upper crankcase, 7...Lower crankcase, 8...Divided surface ,
9...Bottom crankcase, 10...Bolt, 1
1...Cylinder, 12...Crankshaft, 13...
Mission main shaft, 14...Mission counter shaft, 15...Drive sprocket, 16...
...Chain, 17...Mission sprocket, 1
8... Gear, 19... Gear, 20... Gear shift fork guide shaft, 21... Gear shift fork, 22... Gear shift fork guide shaft, 23... Gear fork, 24... Gear shift drum, 25... Chain, 26... Starter motor, 27... carburetor.

Claims (1)

[Claims] 1 The crankcase is divided into three parts, top, middle, and bottom, and the crankshaft and the transmission main shaft are supported between the divided surfaces of the upper crankcase and the lower crank, and the transmission counter shaft is supported between the transmission main shaft and the transmission main shaft. It is pivotally supported on the upper crankcase at a more oblique rearward upper position, so that the dividing plane between the upper crankcase and the lower crankcase below it and the dividing plane between the lower crankcase and the bottom crankcase below it are parallel. The lower crankcase is formed so that the upper part of the cylinder of the engine is tilted forward, and the crankcase is attached to the vehicle body with the dividing surface of the crankcase tilted backward and downward with respect to the horizontal plane of the vehicle body. A motorcycle power unit characterized in that the bottom crankcase is formed such that the vertical width of the bottom crankcase gradually narrows toward the rear.