JP2880680B2 - Small planing boat - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a personal watercraft, and more particularly to a personal watercraft equipped with a four-cycle engine.

[0002]

2. Description of the Related Art A personal watercraft is a small vehicle that glides on water. Water jet pumps and screws are used as propulsion means, and the driving engine is mounted in the space enclosed by the so-called hull outer panel, such as the hull at the bottom of the ship and the seats, together with the intake and exhaust systems. Have been. In addition, the engine is often arranged in a space inside the hull outer panel, particularly in a portion below a seat on which a person (occupant) straddles and rides. People ride in the middle part of the hull from the rear, but such a part is suitable for mounting an engine because of the weight distribution that affects the hull attitude.

[0003] However, the space in which the engine is provided (ie, the engine room under the seat) in a personal watercraft of one or three persons generally has a considerably limited volume. If the capacity is too large, the personal watercraft itself tends to be large and the specific kinetic characteristics such as speed and turning characteristics tend to decrease, and if the width of the seat is increased, it will be difficult to ride over it. .

Therefore, conventionally, a two-stroke engine has been used as a propulsion engine for a personal watercraft. 2
The cycle engine is compact because it does not have an oil pan, valves and valve trains, and has a high output due to the frequency of combustion, making it suitable for small personal watercraft.

[0005] An example in which a two-stroke engine is mounted on a personal watercraft is described in, for example, Japanese Utility Model Laid-Open Publication No. 3-61152.

[0006]

In recent years, from the viewpoints of noise and environmental improvement, the possibility of using a four-stroke engine for small personal watercraft has begun to be studied.

However, a four-stroke engine is larger than a two-stroke engine having an equivalent output,
In order to mount it on a personal watercraft as a propulsion engine, how to arrange it in the space inside the hull becomes an issue. The problem is difficult to be solved due to the following circumstances. That is, a) The engine room of the personal watercraft is limited in volume as in the case where the two-stroke engine is mounted. In particular, in a personal watercraft of a general type in which a person rides on a seat, the width of the seat is limited due to the physique, so that the width of an engine room corresponding to a lower portion of the seat is extremely narrow.

(B) In addition to the fact that the four-stroke engine is larger than the two-stroke engine, the positional relationship between the intake system devices such as the intake silencer and the carburetor that satisfies certain conditions with respect to the engine and does not leave the engine too far. (The same relationship as in the case of a two-cycle engine). That is, a large four-stroke engine must be accommodated in the engine room as a larger block almost integrally connected to the intake system equipment. The reason why the 4-cycle engine becomes large is that a large space on the cylinder is indispensable because it has intake and exhaust valves (mushroom valves).
As long as a wet sump lubrication system that stores oil in the crankcase follows the example of a general four-cycle engine, a space as an oil pan is required at the bottom, and the combustion frequency is lower than that of a two-cycle engine. The number of cylinders and the displacement must be increased in order to make the output equal since the number is small. In addition, it is necessary to couple the intake system devices almost integrally with the engine because, for efficiency, those devices (especially carburetors) are mounted on cylinders so that fuel particles enter the combustion chamber without opposing gravity. Because they should be on top and they should be located close to the cylinder in the sense of reducing intake resistance.

C) Exhaust system equipment is not so much in relation to the engine as in the intake system.
Only a pipe called an exhaust manifold that connects the engine to a muffler or the like must be directly connected to the exhaust port of each cylinder and arranged near the engine. The exhaust manifold occupies a small space if it is just a convergence pipe, but it uses a special type, such as one in which the pipe length from the exhaust port of each cylinder to the convergence point is equal so that the engine can exhibit high output. To do so, considerable space is required.

D) Since the four-stroke engine also exceeds the weight of the two-stroke engine, sufficient consideration must be given to the weight distribution of the personal watercraft. In other words, for balance and stability of the personal watercraft, the engine must be placed at an appropriate position in both the front, rear, left and right directions of the hull. The space where the engine can be mounted, especially under the seat, is generally narrow in the width direction (left and right), and the installation position of the engine is particularly limited in that direction, so that the weight of the engine is not biased to the left or right of the hull Not easy.

(E) The propulsion means of a personal watercraft such as a water jet pump and a screw is provided with a drive shaft (drive shaft) near the bottom of the hull, whereas a four-stroke engine has an oil pan. The crankshaft is generally higher than in the case of a two-stroke engine (a position farther upward from the bottom of the engine)
It is in. Therefore, depending on the amount of oil stored in the oil pan and the shape of the oil pan and crankcase,
It is also assumed that the position of the crankshaft is too high to be directly connected to the drive shaft of the propulsion means, or that the drive shaft has to be made useless.

An object of the present invention is to solve the above problems and to provide a personal watercraft equipped with a four-stroke engine in a preferable arrangement.

[0013]

According to a first aspect of the present invention, there is provided a personal watercraft in which a four-stroke engine is mounted in a space below a seat on which a person straddles and rides. the forward and backward directions, and with the crankshaft for mounting the 4-cycle engine so as to be positioned substantially at the center of the hull width, all cylinders of the four-stroke engine, is inclined to the right or left the same side of the hull, b ) At a position adjacent to the part from the lower part of the cylinder head to the cylinder on the inclined side, it extends parallel to the arrangement direction of the cylinders. Arrange exhaust manifolds with exhaust pipe lengths equal (or almost equal) by directing them to c) , and move other exhaust system equipment following the exhaust manifold from the engine out of the space above. Also disposed at the position of the hull rear, d) the intake system equipment opposite the inclined side of all the cylinders
And connect the intake duct upstream of the intake system equipment.
The upstream end (that is, the suction port of the duct)
In the middle of the space above and below and to the left and right (that is,
(In the vicinity of the center when viewed in cross section) .

In this personal watercraft, a four-stroke engine or the like is provided in a small-volume space surrounded by a seat formed so that a person can straddle the vehicle, a bottom hull, and the like. Placed properly.

1) The four-stroke engine and its associated intake system equipment are compactly accommodated in the space, which is limited in width, especially in the width direction, while satisfying the above-mentioned integral relationship. Is done. This is because if a 4-cycle engine with a large height is placed almost in the center of the hull width with the cylinder upright, the space inside the hull will be bisected to the left and right by the cylinder, and only the intake system equipment will be placed. As described in a) above, the cylinder that extends upward from the position of the crankshaft is all on the same side, either left or right, while the crankshaft is positioned almost at the center of the hull width, as described in a) above. This is because, by inclining, the space on the side opposite to the inclined side can be secured as shown in d) , in which the equipment of the intake system can be arranged. As long as the cylinder is tilted and the intake system device is arranged in a space adjacent to the cylinder, the condition of providing a device such as a carburetor above and close to the cylinder is easily satisfied. Since the space inside the hull outer panel, which is the engine room, is usually long in the longitudinal direction of the hull, the position of the engine in that direction is relatively freely determined.

2) Among the exhaust system devices, the exhaust manifold is also appropriately arranged in the vicinity of the engine while being directly connected to the exhaust port of each cylinder. The portion of the seat on which the person straddles the personal watercraft is formed so that the cross section thereof is rectangular or wide and trapezoidal below in consideration of how the legs of the person spread. On the side where the cylinders are inclined, there is a space between the outer wall of those cylinders and the inside of the hull skin such as seats, which is narrow above (that is, near the cylinder head) but widened below (the part closer to the crankcase). Have been. The term “position adjacent to the portion from the lower part of the cylinder head to the cylinder on the inclined side” referred to in the above b) refers to the lower part near the crankcase in the space as described above. In a personal watercraft, the exhaust manifold can be arranged in a relatively large portion of the space near the engine adjacent to the exhaust port. Since that portion is relatively wide, it is also possible to arrange the exhaust manifold in b) above, in which the pipe length from the exhaust port of each cylinder to the junction is equal.

3) Other exhaust system devices following the exhaust manifold, such as a muffler, are rationally arranged in the space inside the hull. The engine, intake system equipment, and exhaust manifold are not located adjacent to the hull right and left, but as shown in c) above, the exhaust system equipment is provided at a position behind the hull, so regardless of the hull shape, It can be arranged without enlarging the width dimension (sheet etc.). Such an arrangement can be made because these devices need not be placed regardless of their positions in relation to the engine or the like, especially in the vicinity of the engine. If the inclination angle of the cylinder in the engine is set appropriately after such arrangement, maintenance and inspection around the cylinder head such as replacement of the spark plug becomes easy. Since the space that can be used as the engine room is usually long in the front-rear direction of the hull and the exhaust of the engine is preferably directed toward the rear of the personal watercraft, the arrangement as in c) is reasonable. It is a target.

4) Despite the cylinders being gathered on either one of the left and right sides of the hull by tilting,
The deviation of the weight of the engine to that side is small and can be corrected by the arrangement of the intake system equipment and the like. This is because, in order to collect the cylinders on one side, the whole engine together with the crankshaft is not brought to that side, but the position of the crankshaft is almost at the center of the hull width as in a) above. Even if the crankshaft is arranged at such a position, as long as the cylinder above it is shifted to the left or right, there is no problem in arranging the intake system equipment above. Since the space for the engine room is usually long in the front-rear direction of the hull as described above, it is relatively heavy to select the position in that direction and arrange the engine appropriately. it can. 5) As described in b ) above, since the lengths of the exhaust pipes in the exhaust manifold are all equal, high output can be obtained even if the engine is small. Therefore, the four-stroke engine can be easily arranged in the personal watercraft.

[0019]

Since the personal watercraft is a vehicle on water,
Some water may enter the hull during gliding from the air intake part, etc., and may also flood when rolling over. Claim
Considering this point, the personal watercraft ( 1) is configured so that even if water enters the space under the seat, which is the engine room, it does not enter the engine via the intake system. .

6) Since the intake duct is connected to the equipment of the intake system as in d) and its upstream end is opened near the center of the space, there is water in the space, and Regardless of the attitude of the personal watercraft, the water can hardly enter from there because the water can be kept at a considerable distance from the surface of the water due to flooding to the opening of the intake duct. As described above, the intake system equipment is located in a tight space between the engine (the side opposite to the inclined side of the cylinder) and the outer skin of the hull, such as seats, so that water enters the hull. If the hull tilts or rolls over with the intake system equipment down, water may enter from the intake port of the equipment to the equipment, engine, etc. if the above intake duct is not connected However, there is no such disadvantage as long as the configuration of d) is adopted.

According to a second aspect of the present invention, e) an output shaft provided via a pair of gears at a position closer to the bottom of the engine with respect to the crankshaft; The connection may be made via an elastic joint provided at the first position.

According to the personal watercraft of the second aspect , the crankshaft of the mounted four-cycle engine can always be connected to the drive shaft of the propulsion means in a favorable state. Height difference between these crankshafts and drive shafts (displacement of the shaft center)
This is because, when there is a gear pair, the gear pair provided as described above e) connects the two so as to eliminate the difference. As described above, the drive shaft of the propulsion means is generally provided near the bottom of the hull, whereas the crankshaft of a four-stroke engine having an oil pan is slightly above that of a two-stroke engine, Depending on the amount of oil and the shape of the oil pan / crankcase, the position of the crankshaft may be so high that it cannot be directly connected to the drive shaft.
In such a case, if the upper crankshaft and the output shaft near the bottom are connected via the gear pair as described above, and the output shaft and the drive shaft of the propulsion means are connected via the elastic joint, Regardless of the position of the crankshaft (and without greatly tilting the shaft), the drive shaft of the propulsion means can be arranged near the bottom of the hull. Even if there is no height difference between the two, if the positions of the shafts are properly determined and the two are connected via a gear pair with an appropriate gear ratio, the rotation speed of the crankshaft at the maximum output of the engine Is transmitted to the drive shaft of the propulsion means after being converted into a rotational speed that is preferable in terms of efficiency.
As a power transmission means between the crankshaft and the drive shaft, a belt or a chain can be considered in addition to the gear pair. However, considering that the torque to be transmitted is large and the number of rotations is high, the gear pair is optimal.

[0024]

1 to 5 show an embodiment of the present invention. This example relates to a personal watercraft 1 on which a four-cycle engine 20 is mounted. FIG. 1 is a cross-sectional view of the personal watercraft 1 and the engine 20 as viewed from the rear of the hull, and FIG. FIG. 3 is a vertical cross-sectional view of the engine 20 (II in FIG. 1).
FIG. 4 is a rear view (FIG. 4A) and a side view (FIG. 4B) showing the exhaust manifold 51, and FIG. 5 is a partial view showing the engine 20 and the like. It is a side view of the personal watercraft 1 seen through.

The personal watercraft 1 is a water vehicle mainly for leisure. As shown in FIG. 5, a hood 3, a seat 4, a handle 5 and the like are mounted on a hull 2 at the bottom of the boat.
Three people can board. As a propulsion means, a water jet pump 45 is provided in the lower rear of the hull, and the water jet pump 45 pressurizes the water jet and jets on the water surface with a thrust by a jet jet. A pump 45 for forming a water jet is driven by an engine 20. The engine 20 is a ship surrounded by a hull 2, a hood 3 and a seat 4 at substantially the center of the hull along with the intake system equipment 10. It is installed in the space inside the body (engine room). The output of the engine 20 is transmitted to a drive shaft 44 via an elastic joint 43, and the drive shaft 44
5 (the impeller) is rotated.

As the engine 20, a four-cycle, in-line four-cylinder engine configured as shown in FIG. 1 is mounted. A cylinder head 21 is provided above the engine 20, and a cylinder 25, a crankcase 29, and an oil pan 34 are provided below the cylinder head 21. The cylinder head 21 has an intake port 22 and an exhaust port 23.
A valve mechanism 24, such as a cam 24b and a timing chain 24c (FIG. 3), together with a valve 24a for opening and closing 23.
And a spark plug 21a (FIG. 3) is also attached. An intake system device 10 including an intake silencer 11 and a carburetor 12 is connected upstream of the intake port 22, and an exhaust manifold 51 is located downstream of the exhaust port 23.
An exhaust system device 50 such as a muffler 52 is connected thereto.
A piston 26 connected to a crankshaft 28 is disposed inside the cylinder 25 so as to be slidable up and down. The crankshaft 28 is moved by a crankcase 29 via a bearing 29f (FIG. 3). Supported. At the lowest part of the crankcase 29, an oil pan 34 for storing oil is densely mounted, and a cylindrical strainer 35 is arranged at the recessed lower part, which is connected to an oil supply pump (not shown). Have been. For mounting on the hull, two rod-shaped frames 7a are integrated at the front and rear near the bottom of the engine 20, and the frames 7a
Are fixed on an iron plate support plate 7c fixed in the bottom hull 2 or the hood 3. A rubber damper 7b is provided in a corresponding portion of the plate 7c, and a frame 7a is mounted thereon. Further, since the plate 7c itself has elasticity, the vibration of the engine 20 can be prevented by the damper 7b.
b and the plate 7c, and are not easily transmitted to the hull.
As shown in FIG. 3, a generator 36 and the like are connected to the crankshaft 28. Since the valve mechanism 24 and the like are provided in the upper part and the oil pan 34 is also provided in the lower part,
The height of the cycle engine 20 is considerably larger than that of the two-cycle engine, and the cycle engine 20 is considerably large in the horizontal direction due to the four cylinders and the width of the oil pan 34.

The personal watercraft 1 is characterized in that the large and heavy four-cycle engine 20 is mounted on the hull as a propulsion engine as shown in FIG. When the four-stroke engine 20 is mounted in the hull of the personal watercraft 1 having a limited capacity, it is necessary to solve the following problems. That is, a) Since the four-cycle engine 20 is considerably large in comparison with the two-cycle engine which is conventionally generally mounted, the four-stroke engine 20 is appropriately disposed in the hull together with the intake system equipment 10 and the like which should be disposed in a close upper position. It is difficult, b) Because the 4-cycle engine 20 is heavy,
It is necessary to pay attention to the weight distribution in the personal watercraft 1, especially the weight of the engine 20 should not be biased to the left or right of the hull. C) From the circumstances a) and b) above, the four-cycle engine 20 is compact. Although it is unavoidable that some water will enter the hull, even if the small planing boat rolls over, such water will not enter the intake system or engine. E) The lubrication system should be a wet sump type lubrication system like a normal four-stroke engine (rather than a dry sump as in a two-stroke engine) because of its structurally simple and preferable structure. Oil rolls over cylinder 25
(FIGS. 1 and 3), which makes it difficult to continue and restart the operation. F) Since the crankshaft 28 (FIG. 1) is generally at a higher position than in the case of a two-stroke engine, the hull Water jet pump 4 that needs to be installed near the bottom
It is difficult to connect the crankshaft 28 to the fifth drive shaft 44. In this regard, the personal watercraft 1 solves the problem by adopting the following configuration.

First, with respect to the above problems a) and b), the four-stroke engine 20 and the intake system equipment 10 are installed in the hull of FIG.
It is assumed to be arranged as follows. That is, the four-cylinder engine 20 is so-called vertically installed (the crankshaft 28 is oriented in the front-rear direction of the hull, and the cylinders 25 are arranged along the same), and the crankshaft 28 is positioned at the center of the hull width. All the cylinders 25 are tilted to the right of the hull (to the right in the traveling direction), and the intake system device 10 is arranged on the left side of the hull, which is the opposite side of the hull. As for the exhaust system device 50, an exhaust manifold 51 is provided on the inclined side (the right side of the hull) immediately to the right of the portion extending from the lower portion of the cylinder head 21 to the cylinder 25,
The muffler 52 and the like downstream therefrom are arranged behind the position of the engine 20 in the hull, as shown in FIG.

By adopting such a layout,
The four-stroke engine 20 and the like can be appropriately arranged in a narrow space inside the hull while solving the problems of the above (a) and (b).
The reason is as follows. As shown in FIG. 1, by inclining all four cylinders 25 extending upward from the position of the crankshaft 28 to the right, a space in which the intake system device 10 can be arranged is secured on the anti-inclination side. Cylinder 2
The arrangement of the carburetor 12 and the like above and close to the cylinder 25 is easy as long as the intake system device 10 is arranged in the space on the opposite side of the slope corresponding to the oblique upper side of the cylinder 5. Even though the cylinders 25 are collected on the right side of the hull, the position of the crankshaft 28 is set at the center of the hull width, so that the deviation of the weight of the engine 20 to the right side of the hull is small. The center of gravity can be centered in the width of the hull. In view of the fact that the cross section of the seat 4 and the portion under the seat 4 are trapezoidal in consideration of a person straddling, the cylinder 4 is moved from the lower side of the cylinder head 21 on the inclined side of the cylinder 25 as described above. In the part immediately to the right of the part up to 25, there is a long open space with a considerable cross-sectional area (the lower part is slightly wider), and a slightly larger exhaust manifold 51 can be provided there. it can. As shown in FIG. 5, the exhaust system device 50 regardless of the relative position with respect to the engine 20 is provided at a position behind the hull where the engine 20 and the intake system device 10 are separated from the portions adjacent to the hull left and right. It can be arranged even with a narrow hull. Since the space in the hull is long in the front-rear direction, the engine 20 and the like can be easily arranged in an appropriate position in that direction in consideration of the installation space and weight distribution.

As a means for solving the problem (c), which is also related to the above (a) and (b), this personal watercraft uses an exhaust manifold 51 shown in FIG. The exhaust manifold 51 is a so-called merging connection pipe that merges exhaust gas from the four exhaust ports 23 of the engine 20 into one and sends it to a muffler 52 (see FIG. 5).
In particular, the connection port 51a with each exhaust port 23 (FIG. 1)
Exhaust pipes 51 from the rear (after merging) to the outlet 51c
The lengths of b are configured to be almost equal. In order to make the length equal, each exhaust pipe 51
4B, as shown in FIG. 4B, the pipe is once advanced forward (to the left in the figure) from the discharge port 51a and then bent to form a rear discharge port 51a.
c. Since there is no difference in the length of the exhaust pipe 51b, the output of the engine 20 can be drawn out, and high output can be obtained even with a small engine 20, which is convenient for solving the problem (c). It is.
The exhaust manifold 51 is relatively compact by integrally molding the four exhaust pipes 51b by aluminum casting so that the exhaust pipes 51b are densely arranged. Since it also has the cooling water jacket 51d, it is considerably larger than a simple merging pipe consisting of a main pipe and a branch pipe. However, according to the above-described layout, a large empty space is provided on the inclined side of the cylinder 25 immediately to the right of the portion from the lower portion of the cylinder head 21 to the cylinder 25 as shown in FIG. Even though they could be properly arranged.

In order to prevent water from entering the intake system or the like as described in (d), as shown in FIGS. 1 and 2, the intake duct 1 is located at the upstream opening (two front and rear positions) of the intake silencer 11.
1a, and connect its end (the intake end at the upstream end)
It was located in the center of the engine room below the seat 4 (in the middle of the vertical and horizontal directions as shown in FIG. 1). This position where the end of the duct 11a is provided is a position where the water can be maintained at a considerable distance from the surface of the water, regardless of the attitude of the personal watercraft, regardless of the position of the watercraft in the engine room. Therefore, water is prevented from entering the intake system by such a configuration.

In order to solve the problem (e), the crankcase 29 of the four-stroke engine 20 shown in FIG.
The following contrivances are applied to the components such as the oil pan 34 and the like. That is, in addition to the outer shell portion 29a, a bag-shaped inner portion 29b is formed as the crankcase 29, and the bottom of the inner portion 29b is located on the oil pan 34. However, a communication hole 31 is provided at the bottom of the inner portion 29b so that oil forcibly supplied to the crankshaft 28 or the like drops on the oil pan 34 and is collected. Outer part 29 which can be said to be the side wall of oil pan 34
Since a large distance is provided between each surface of the outer peripheral portion 29a and the communication hole 31 and a considerable vertical dimension is provided between the upper end portion of the outer portion 29a and the communication hole 31.
9 and an outer portion 29a (oil pan 34).
(The side wall) has a space S having a sufficient volume in any direction.

If the oil pan 34 and the like are configured in this manner, the four-stroke engine 20 is of the wet sump type, but the personal watercraft 1 rolls over and the engine 20 rolls over or turns over (180 ° turnover). 3) There is no danger that the oil in the oil pan 34 will flow into the cylinder 25 even when the state is reached. When the engine 20 turns over or reverses, the oil stored in the oil pan 34
The oil pan 34 moves inside or above the side wall (outer shell portion 29a) of the oil pan 34. Since the large space S exists between the side wall and the communication hole 31 as described above, oil accumulates there. . That is, it hardly enters the inside of the crankcase 29 (the inner portion 29b) through the communication hole 31, and therefore, there is no inconvenience in the operation of the engine 20. In particular, a detection switch (not shown) that automatically stops the engine 20 when the vehicle rolls over.
Is preferably mounted on the personal watercraft 1, since the forced refueling of the crankshaft 28 and the like is stopped when the vehicle rolls over or reverses. The oil pan 34 has a water jacket 34a through which cooling water passes, like the cylinder 25 and the cylinder head 21, and allows water taken out from the water jet outlet 6 shown in FIG. To cool down. For this reason, engine 20 can receive appropriate cooling despite being arranged in the almost enclosed space of personal watercraft 1.

Since the crankcase 29 (29b) and the oil pan 34 have a double structure as described above, the height from the bottom (installation surface) of the engine 20 to the crankshaft 28 is particularly large. In this personal watercraft 1, as shown in FIG.
By providing the output shaft 42 connected to 8 in the engine 20, the above-mentioned problem (f) is solved. That is, the output shaft 42 is rotatably supported by the crankcase 29 and attached below the crankshaft 28, and the pinion 41a on the crankshaft 28 and the gear 41b on the output shaft 42
As the gear pair 41 described above. And, as shown in FIG.
3, the drive shaft 44 of the water jet pump 45 was connected. Since the output shaft 42 is provided at a position closer to the bottom of the engine 20 separately from the crankshaft 28,
The connection with the drive shaft 44 of the water jet pump 45 which needs to be arranged near the bottom of the hull can be made well (that is, the drive shaft 44 is hardly tilted).
The lubrication of the gear pair 41 is performed by a simple method of immersing a part of the gear 41b in the oil on the oil pan 34 in the engine 20 (see FIG. 3) of the wet sump type.

In addition, the gear pair 41 has an appropriate gear ratio for converting the rotation speed of the crankshaft 28 into a rotation speed that is efficient for the water jet pump 45, so that the personal watercraft 1 has good results in terms of propulsion efficiency. It was brought. That is, the output characteristics of the engine 20 and the propulsion efficiency of the water jet pump 45 could be suitably matched by the gear ratio of the gear pair 41. This means that by using the appropriate gear pair 41, the same type of four-stroke engine 20 can be mounted on other types of personal watercraft equipped with other water jet pumps having different propulsion performances, It is also possible to reduce the cost of small planing boats by promoting common use of engines. It is needless to say that the same operation and effect can be obtained even when the same gear pair is provided outside the engine 20.

[0036]

According to the personal watercraft of the present invention, a four-cycle engine which is considerably larger than a two-cycle engine is used.
It can be properly arranged in the narrow space below the seat as follows.

1) By sloping all cylinders of the engine to the same side on either the left or right side of the hull, a space for arranging the intake system equipment is secured. Therefore, the four-stroke engine and the intake system equipment attached thereto are preferably integrated. While satisfying the basic positional relationship, it can be compactly accommodated in the above space.

2) Since the cylinder is inclined as described above, a relatively large space is secured in a portion adjacent to the exhaust port of the engine, so that a desirable exhaust manifold can be appropriately arranged.

3) Other exhaust system devices following the exhaust manifold, such as a muffler, can be rationally arranged in the hull. Since the engine is disposed behind the engine by utilizing the fact that the space in which the engine is disposed is long in the longitudinal direction of the hull, it is not necessary to increase the width of the hull.

4) Since the four-stroke engine is arranged so that the position of the crankshaft is substantially at the center of the hull width, the weight of the engine is not extremely deviated to one of the right and left sides, and a good weight balance as a whole is achieved. realizable. 5) Make sure that each exhaust pipe in the exhaust manifold is
4 cycle engine into the personal watercraft in connection with
Arrangement of the components becomes easy.

[0041] Further, 6) the upstream end or inlet of the air intake of the air intake duct, since there is provided in the vicinity of the center of the space for arranging the engine, there is flooded to the space, and in what posture personal watercraft Even if it does, water hardly enters the intake system.

According to the personal watercraft of claim 2 , 7) the gear pair eliminates the inconvenience caused by the height difference between the crankshaft of the four-cycle engine and the drive shaft of the propulsion means, At the same time, the number of revolutions between the engine and the propulsion means is matched, so that the above-described crankshaft and drive shaft can always be connected in a favorable state.

[Brief description of the drawings]

FIG. 1 is a transverse cross-sectional view (view from the rear) showing a hull, a four-stroke engine 20, and the like of a personal watercraft 1 according to an embodiment of the present invention.

FIG. 2 is a perspective view showing an engine 20 and devices arranged on the right and left sides of the engine 20.

FIG. 3 shows a four-stroke engine 2 mounted on the personal watercraft 1.
FIG. 1 is a vertical sectional view taken along line III-III in FIG.

4 (a) is a rear view showing the exhaust manifold 51, and FIG. 4 (b) is a side view thereof (a bb arrow view in FIG. 4 (a)).

FIG. 5 shows the personal watercraft 1 with a four-cycle engine 2
It is a side view which shows a part transparently so that 0 etc. can be seen.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Small personal watercraft 10 Intake system equipment 11a Intake duct 20 4 cycle engine 25 Cylinder 28 Crankshaft 41 Gear pair 42 Output shaft 44 Drive shaft 45 Water jet pump (propulsion means) 50 Exhaust system equipment 51 Exhaust manifold

──────────────────────────────────────────────────続 き Continuation of the front page (51) Int.Cl. ⁶ Identification symbol FI B63H 21/14 B63H 21/24 (56) References JP-A-7-237588 (JP, A) JP-A-5-10122 (JP) JP-A-3-9027 (JP, A) JP-A-5-34100 (JP, U) JP-A-58-56110 (JP, U) (58) Fields investigated (Int. Cl. ⁶ , DB Name) F02B 67/00 B63H 21/00 B63H 21/14

Claims (2)

(57) [Claims] An engine for driving a propulsion means is a personal watercraft mounted in a space below a seat on which a person straddles and rides, wherein the engine is a four-stroke engine, and the crankshaft is a hull. And the cylinders of the four-stroke engine are tilted to the same side on either the left or right side of the hull. An exhaust manifold extending parallel to the cylinder arrangement direction is disposed at a position adjacent to a portion from the lower part of the head to the cylinder, and each exhaust pipe in the manifold is bent forward once and then bent. And the exhaust is directed to the rear exhaust so that the length is equal, and other exhaust system equipment following the exhaust manifold is It is also disposed at the position of the hull rear, the intake system equipment of distribution opposite the inclined side of all the cylinders
And an intake duct is connected to the upstream of the intake system.
The upstream end of the
A small planing boat characterized by being open to the throat. 2. A drive shaft of the propulsion means, wherein the drive shaft is a crankshaft.
In contrast, a gear pair located closer to the bottom of the engine
Output shaft and the elastic joint
The personal watercraft according to claim 1, wherein the personal watercraft is connected via a hand.