EP1092848A2

EP1092848A2 - Internal combustion engine

Info

Publication number: EP1092848A2
Application number: EP00122164A
Authority: EP
Inventors: Eiichiro Tsujii
Original assignee: Sanshin Kogyo KK
Current assignee: Yamaha Marine Co Ltd
Priority date: 1999-10-12
Filing date: 2000-10-12
Publication date: 2001-04-18
Anticipated expiration: 2020-10-12
Also published as: EP1092848B1; EP1092848A3

Abstract

Internal combustion engine comprising a cylinder formed in an engine body, a piston disposed for sliding within the cylinder, and a crankshaft connected to the piston by way of a connecting rod, with the axis of the cylinder displaced in the direction opposite the lateral component of the thrust F acting on the piston relative to the line L1 passing the axis of the crankshaft and parallel to the cylinder, characterized in that the center of gravity of a counterweight provided in the crankshaft is positioned near the above-mentioned line L1 parallel to the cylinder.

Description

This invention relates to an internal combustion engine, in particular a reciprocating type of internal combustion engine as indicated in the opening part of claim 1.
In a conventionally known method of making the reciprocating type of internal combustion engine compact, as disclosed for example in a laid open Japanese patent application No. Hei 2-274691, the engine as a whole is displaced relative to the drive shaft to produce a space where various devices of the intake system, fuel supply system, and exhaust system are disposed on both sides of the engine body.
However, the above method has problems: Since the engine as a whole is displaced with respect to the drive shaft by the use of gears, the weight of the engine increases. Moreover, since the rotating direction of the engine is changed by the use of gears, the engine must be modified to cope with the reverse rotation as by providing gears also on the rotating components side. Furthermore, since the entire engine is displaced, the center of gravity is also displaced and the problem of vibration is aggravated.
Accordingly, it is an objective of the present invention to provide an internal combustion engine capable of solving the above problems and rendering the engine compact without increasing the weight and the amount of vibration, and without changing the direction of rotation.
Said objective is performed according to the present invention by an internal combustion engine having the features of claim 1.
Preferred embodiments are laid down in the further subclaims.
Embodiments of the invention will be hereinafter described with reference to the appended drawings. Incidentally, the terms "the front" and "the rear" as used herein are respectively meant with respect to the advancing direction and the reverse direction of a boat.
In the drawings:
FIG. 1 is a side view of a four-stroke cycle engine in which the invention is embodied and which is mounted in an outboard motor as an example;
FIG. 2(A) shows a cross section of the swivel bracket 6 and its vicinity. FIG. 2(B) shows the cross section B-B in FIG. 2(A);
FIG. 3 is a cross-sectional view as seen in the direction of arrows X-X in FIG. 1;
FIG. 4 shows a cross section of an essential part of FIG. 3 in a larger scale with the piston at the top dead center; and
FIG. 5 shows a cross section of an essential part of FIG. 3 in a larger scale with the piston at the bottom dead center.
FIG. 1 is a side view of a four-stroke cycle engine in which the invention is embodied and which is installed in an outboard motor as an example. The outboard motor 1 is provided with; a clamp bracket 3 removably attached to the rear part of a hull 2, a swivel bracket 6 supported for up and down swinging about a tilt shaft 5 on the clamp bracket 3, and a propulsion unit 7 supported for horizontal swiveling on the swivel bracket 6. The propulsion unit 7 has an upper case 9 supported for rotation with the swivel bracket 6, and a lower case 10 attached to the lower part of the upper case 9. The upper and lower cases 9 and 10 constitute a single casing as a whole. A propeller 11 is attached to the lower case 10. A bottom cowling 12 is attached to the top of the upper case 9. A top cowling 13 is removably attached to the bottom cowling 12.
An engine 14 is mounted on the upper case 9. The engine 14 is, for example, of the single cylinder, overhead valve, four-stroke cycle type. An engine body comprises; a head cover 15, a cylinder head 16, a cylinder body 17, and a crankcase 19 serving also as an oil pan. A cylinder 20 and a piston 21 are disposed horizontally, and a crankshaft 22 is disposed vertically. The cylinder head 16 is provided with an intake valve 23, an exhaust valve 24, and an exhaust port 25. A recoil starter 26 is attached to the top of the crankshaft 22. The numeral 18 denotes a drive shaft connected to the crankshaft 22, and the numeral 27 denotes a fuel tank disposed in front of the cylinder body 17.
FIG. 2(A) shows a cross section of the swivel bracket 6 and its vicinity in FIG. 1. FIG. 2(B) shows the cross section B-B in FIG. 2(A). An upper tube 8 for supporting the engine 14 is formed in tubular shape with an internal exhaust passage 8a. In the exhaust passage 8a are disposed; the drive shaft 18, a shift rod 62, and a cooling water pipe 61 in the vertical direction. An oil pan connecting portion 8b flaring like a dish is formed in the upper part of the upper tube 8. A small diameter tubular portion 8c is formed in the lower part of the upper tube 8. The swivel bracket 6 is formed in tubular shape and its inside circumference is formed with support flanges 6a extending horizontally in two, upper and lower positions. When the swivel bracket 6 is installed around the upper tube 8, mounts 28 made of an elastic material such as rubber are disposed between the tubular portion 8c of the upper tube 8 and the support flanges 6a of the swivel bracket 6 in two, upper and lower positions. In this way, a full pivot type of outboard motor is constituted in which the upper tube 8 is supported for 360 degree rotation on the swivel bracket 6 through the mounts 28. Incidentally, a bush 28a is interposed between the upper tube 8 and the mounts 28.
FIG. 3 is a cross-sectional view as seen in the direction of arrows X-X in FIG. 1. Incidentally, the same parts are provided with the same reference numerals and their explanations are sometimes omitted in the following description. The crankshaft 22 is provided with a crank pin 29 and counterweights 30. The crank pin 29 is connected through a connecting rod 31 to the piston 21. A camshaft 32 is disposed in the cylinder body 17 parallel to the crankshaft 22 so that the rotation of the crankshaft 22 is transmitted to the camshaft 32 through gears 33 and 34. In the drawing is shown a carburetor 43 and an ignition plug 44.
A valve drive chamber 35 is formed in the cylinder head 16 and the head cover 15. The exhaust valve 24 (also the intake valve 23) extends through the cylinder head 16 into the valve drive chamber 35 and comes into contact with one end of a rocker arm 39 through a valve spring 36 and a retainer 37. A lifter 40 is slidably disposed in the cylinder body 17. One end of the lifter 40 is in contact with a cam of the camshaft 32. The other end of the lifter 40 is in contact with the other end of the rocker arm 39 through a push rod 41. The plunger of a fuel pump 42 is also in contact with the cam of the camshaft 32. With the above constitution, when the camshaft 32 rotates, the lifter 40 and the push rod 41 slide to rock the rocker arm 39, and to drive the intake valve 23 and the exhaust valve 24 to be opened and closed against the valve spring 36, and the fuel pump 42 is driven.
Next will be described the features of this invention in reference to FIG. 4. FIG. 4 shows a cross section of an essential part of FIG. 3 in a larger scale. One end of the connecting rod 31 is rotatably connected to the crank pin 29 using bolts 46. The other end of the connecting rod 31 is connected to the piston 21 through a piston pin 45. When the piston 21 is thrust down to rotate the crankshaft 22 in the direction of the arrow R as shown, a lateral component Fs of the thrust exists (the direction of the lateral component is hereinafter simply referred to as the thrust direction). As a result, operation efficiency is lowered and durability becomes poor.
Therefore, in this embodiment, the axis L2 of the cylinder 20 is displaced by a distance D1 in the direction opposite the direction of the lateral component Fs of the thrust acting on the piston 21 with respect to the line L1 that is parallel to the cylinder 20 and passes the axis of the crankshaft 22. Also, the axis of the piston pin 45 is displaced by a distance D2 in the direction of the lateral component of the thrust with respect to the axis L2 of the cylinder 20. In this way, the moment acting on the piston pin 45 is reduced, operation efficiency and durability are improved, and slap noise is reduced. This arrangement also makes it possible as shown in FIG. 3 to displace the cylinder 20 and the cylinder head 16 toward the right to produce a space where engine components such as the camshaft 32, the fuel pump 42, and the carburetor 43 are disposed. Thus, the engine is made compact without increasing the weight and without changing the direction of rotation. Moreover, since the crankshaft 22 made of a heavy, iron-based material is not displaced, the amount of displacement of center of gravity is held small, so that the amount of vibration is held to a minimum.
FIG. 4 shows the state of the piston 21 at the top dead center, with the axis P1 of the FIG. 4 shows the state of the piston 21 at the top dead center, with the axis P1 of the crankshaft 22, the axis P2 of the crank pin 29, and the axis P3 of the piston pin 45 aligned in that order on the line L3. The symbol G' denotes the center of gravity of a conventional counterweight 30'. At this time, the direction of the centrifugal force Fe' acting on the center of gravity G' of the counterweight 30' is deviated by an angle α from the line L1, or from the direction of the vibration inducing force Fv of the piston 21. As a result, unwanted vibration is induced. To cope with this, the shape of the counterweight 30 is changed so that the center of gravity of the counterweight falls on the position G on the line L1 and that the centrifugal force Fe acting on the center of gravity G is approximately in agreement with the direction opposite the vibration inducing force Fv.
FIG. 5 shows the state of the piston 21 at the bottom dead center, with the axis P2 of the crank pin 29, the axis P1 of the crankshaft 22, and the axis P3 of the piston pin 45 aligned in that order on the line L3. At this time, the direction of the centrifugal force Fe' acting on the center of gravity G' of the counterweight 30' is deviated by an angle β from the line L1, or from the direction of the vibration inducing force Fv of the piston 21. As a result, unwanted vibration is induced. To cope with this, the shape of the counterweight 30 is changed so that the center of gravity of the counterweight falls on the position G on the line L1 and that the centrifugal force Fe acting on the center of gravity G is approximately in agreement with the direction opposite the vibration inducing force Fv.
As described above, the amount of deviation, α or β, in the position of center of gravity undesirably varies depending on the position of the piston; at the top dead center or bottom dead center. Therefore, if the amount of the center of gravity deviation γ from the line L3 is set to be 0 < γ ≤ (α + β)/2 so that the center of gravity is as close as possible to the line L1 parallel to the cylinder, the amount of vibration may be held to a minimum. Incidentally, the deviation of the center of gravity may be made not only by changing the shape of the counterweight 30 but also by boring a hole in, or adding a weight to the counterweight 30.
As shown in Figures 4 and 5 providing the counterweight 30 with a longitudinal recess (hole) being designed symmetrically to the line L3 when the piston is in either one of its top and bottom dead center positions is most suitable for performing the deviation of the center of gravity G.
While the invention is described above by way of an embodiment, the invention is not limited to the embodiment but may be modified in various ways. For example, while the above embodiment uses the outboard motor as the subject of applying the invention, the invention may also be applied to engines of vehicles. Moreover, while the engine used in the above embodiment is of a single cylinder four-stroke cycle type, the engine may also be of a single cylinder two-stroke cycle type, or two cylinder four-stroke cycle type. For, the two cylinder two-stroke cycle engine and the four cylinder four-stroke cycle engine have the state in which pistons are at both the top and bottom dead centers in which different phases of vibration offset each other.
As is clear from the above description, with the invention it is possible to weaken the lateral component of the thrust acting on the piston, improve operation efficiency and durability, and make the engine compact without increasing the weight and without changing the direction of revolution. Moreover, since the crankshaft made of an iron-based material and so having a heavy weight need not be displaced, the amount of displacing the center of gravity is reduced. Displacing the center of gravity of the counterweight reduces the amount of engine vibration to a minimum and the lateral thrust acting on the cylinder. This makes it possible to disuse an iron sleeve, to use an aluminium cylinder, and so reduce cost and weight.
The invention may be favorably employed in engines with a single cylinder, or two cylinder four-stroke cycle type in which piston vibration is a problem.
The invention, when employed in outboard motors used at high revolutions with a wide variation in revolution, is especially effective in holding down the amount of engine vibration.

Claims

Internal combustion engine, in particular four-stroke cycle engine, comprising at least one cylinder formed in an engine body, a piston slidingly disposed in said cylinder and a crankshaft connected to the piston through a connecting rod, wherein a cylinder axis (L2) of the cylinder is displaced laterally offset with respect to a parallel line (L1) intersecting the axis of the crankshaft (22), wherein a center of gravity (G) of a counterweight (30) associated to the crankshaft (22) is positioned on or close to said parallel line (L1) intersecting the axis of the crankshaft (22) when the piston is in one of its top or bottom dead center positions.
Internal combustion engine according to claim 1, wherein the cylinder axis (L2) is displaced in a direction opposite to the direction of a lateral component of thrust (F) acting on the piston (21) relative to said line (L1) extending in parallel to the cylinder axis (L2) and intersecting the axis of the crankshaft (22).
Internal combustion engine as claimed in claim 1 or 2, wherein a line (L3) interconnecting the axis (P2) of a crank pin (29) which is rotatably connected to one end of a connecting rod (31), the other end of which is connected to the piston (21) through a piston pin (45), the axis (P1) of the crankshaft (22) and the axis (P3) of the piston pin (45) when said piston is in either one of a top or bottom dead center position defining an angle (α, β) with the line (L1) intersecting the axis (P1) of the crankshaft (22) and extending in parallel to the cylinder axis (L2).
Internal combustion engine according to claim 3, wherein the amount of displacement γ of the center of gravity (G) relative to the line (L3) interconnecting the axis (P2) of the crank pin (29), the axis (P1) of the crankshaft (22) and the axis (P3) of the piston pin (45) is set to be 0 < γ ≤ (α + β)/2 wherein α is assumed to be the angle between the line (L3) connecting the axes (P2,P1,P3) of the crank pin (29), the crankshaft (22) and the piston pin (45) and the line (L1) extending in parallel to the cylinder axis (L2) and intersecting the axis of the crankshaft (22) with the piston (21) being at its top dead center position while β is assumed to define the same geometrical relationship between the afore-indicated lines (L3,L1) when the piston is in its bottom dead center position.
Internal combustion engine according to at least one of the preceding claims 1 to 4, wherein the position of the center of gravity (G) when the piston (21) assumes its top or bottom dead center positions is adjusted by adapting the counterweight (30) in shape, providing a recess therein or adding a weight thereto.
Internal combustion engine according to at least one of the preceding claims 1 to 5, wherein the axis of a piston pin (45) is displaced by a distance (D2) in the direction of a lateral component of the thrust (F) with respect to the axis (L2) of the cylinder (20).
Internal combustion engine according to one of the preceding claims 1 to 6, wherein engine components, in particular a camshaft (32), a fuel pump (42), and a carburetor (43) are disposed in the area of a side surface of the engine that is opposite to the direction of displacement of the cylinder axis (L2).
Internal combustion engine according to at least one of the preceding claims 1 to 7, wherein some engine components, in particular a carburetor (43) and a fuel tank (27), are disposed in the area of a side surface of the engine that is opposite to the direction of displacement of the cylinder axis (L2), some of the engine components such as the camshaft (32) are disposed in the area on a side surface of the engine that complies with the displacement direction of the cylinder axis (L2) with respect to the line (L1) extending in parallel and intersecting the axis of the crankshaft (22) and some of the engine components, in particular the fuel pump (42) are disposed outside of a cylinder block body (17) of the engine.
Internal combustion engine according to at least one of the preceding claims 1 to 8, wherein the engine forms part of an outboard motor and the crankshaft (22) is disposed substantially vertically.
Internal combustion engine according to at least one of the preceding claims 1 to 9, wherein mounts (28) are provided to support the engine, said mounts (28) having a variable wall thickness such that the wall thickness of parts of each of the mounts (28) on the side opposite to the displacement direction of the cylinder axis (L2) is increased compared to the side extending towards the direction of displacement of the cylinder axis (L2).
Internal combustion engine according to at least one of the preceding claims 1 to 10, wherein a valve drive chamber (35) is formed in a cylinder head (16) and a head cover (15) of the engine wherein the valves (23,24) are driven via a rocker arm mechanism (39) and a lifter (40), said lifter (40) being in contact with an end of the rocker arm (39) through a push rod (41) and, on the other hand, being slidably disposed in the cylinder body (17), is operated by a cam of the camshaft (32) which is in contact with said end of the lifter (40).
Internal combustion engine according to at least one of the preceding claims 1 to 11, wherein the camshaft (42) is driven from the crankshaft (22) by means of gears (33,34) being in mesh with each other.
Internal combustion engine according to at least one of the preceding claims 1 to 12, wherein the crankshaft (22) is made of iron-based material while the cylinder can be made of an aluminium based alloy including aluminium.
Internal combustion engine according to at least one of the preceding claims 1 to 13, wherein the engine is of the four-stroke cycle type with one or two cylinders.