CN111365122B

CN111365122B - Piston engine

Info

Publication number: CN111365122B
Application number: CN201910706077.3A
Authority: CN
Inventors: 鹿野达; 石川满; 黑木正宏
Original assignee: Ishikawa Energy Research Co Ltd
Current assignee: Ie Co ltd; Ishikawa Energy Co ltd; Ishikawa Energy Research Co Ltd
Priority date: 2018-12-26
Filing date: 2019-08-01
Publication date: 2022-03-29
Anticipated expiration: 2039-08-01
Also published as: CN111365122A; JP2020105919A; JP6506467B1

Abstract

The invention provides a split piston engine, which realizes size miniaturization, and especially shortens the length of a piston in a reciprocating direction. The opposed piston engine (10) of the present invention has a first engine unit (11) and a second engine unit (21). Further, a valve drive mechanism (30) for driving each valve provided in the first engine unit (11) and the second engine unit (21) is disposed outside the outer edge of the first cylinder (12) of the first engine unit (11) and the second cylinder (22) of the second engine unit (21). With this configuration, the width of the valve drive mechanism (30) can be reduced, and the entire opposed piston engine (10) can be reduced in size.

Description

Piston engine

Technical Field

The present invention relates to a counter piston engine, and more particularly to a counter piston engine in which engine portions arranged to face each other have independent cylinders or the like.

Background

At present, an opposed piston engine having an effect of low vibration or the like is under development. In such a reciprocating piston engine, the two pistons facing each other are configured to reciprocate in a straight line, and the vibration damping effect is exhibited during the operation of the engine.

Patent document 1 describes an example of the above-described opposed piston engine. Specifically, in the twin piston engine, one cylinder is formed in an engine body, and two piston heads reciprocate so as to face each other in the cylinder. Further, a volume space continuous with the cylinder is formed, and an intake valve, an exhaust valve, and a spark plug are disposed in the volume space. Therefore, the cylinder can be easily assembled and processed, and the casting efficiency of the cylinder can be improved.

Patent document 1: japanese patent No. 5508604

However, in the engine described in patent document 1, an intake valve, an exhaust valve, and a drive mechanism for driving these valves are disposed between the pistons that face each other. Therefore, the distance between the pistons is long, which may hinder the downsizing of the entire engine.

In particular, when a counter-piston engine is incorporated in a small-sized vehicle, if the length of the piston in the reciprocating direction is long, the counter-piston engine may become a limiting factor in designing the interior of the vehicle.

Disclosure of Invention

The present invention has been made in view of the above circumstances, and an object thereof is to provide a counter piston engine in which downsizing is achieved, and particularly a counter piston engine in which the length of a piston in the reciprocating direction is shortened.

The opposed piston engine of the present invention is characterized by comprising: a first engine unit having a first cylinder, a first piston reciprocating inside the first cylinder, a first crankshaft converting reciprocating motion of the first piston into rotational motion, a first connecting rod movably connecting the first piston and the first crankshaft, and a first intake valve and a first exhaust valve provided in the first cylinder; a second engine unit having a second cylinder that is separate from and faces the first cylinder, a second piston that reciprocates inside the second cylinder, a second crankshaft that converts the reciprocating motion of the second piston into a rotational motion, a second connecting rod that movably connects the second piston and the second crankshaft, and a second intake valve and a second exhaust valve that are provided in the second cylinder; a valve drive mechanism that drives the first intake valve, the first exhaust valve, the second intake valve, and the second exhaust valve to advance and retreat; when the arrangement direction of the first engine unit and the second engine unit is a first direction and a direction orthogonal to the first direction is a second direction, the valve drive mechanism is disposed outside the outer edges of the first cylinder and the second cylinder in the second direction.

In the opposed-piston engine according to the present invention, the valve drive mechanism includes a first valve drive mechanism disposed on one side along the second direction and a second valve drive mechanism disposed on the other side along the second direction.

In the opposed-piston engine according to the present invention, the first intake valve, the first exhaust valve, the second intake valve, and the second exhaust valve are arranged so as to intersect with each other when viewed from the second direction.

In the opposed-piston engine according to the present invention, the valve drive mechanism includes: a first intake rocker arm disposed between a first intake cam and the first intake valve; a first exhaust rocker arm disposed between a first exhaust cam and the first exhaust valve; a second intake rocker arm disposed between a second intake cam and the second intake valve; a second exhaust rocker arm disposed between a second exhaust cam and the second exhaust valve; the first intake rocker arm abuts against the first intake cam from a side where the second engine section is disposed, the first exhaust rocker arm abuts against the first exhaust cam from a side where the second engine section is disposed, the second intake rocker arm abuts against the second intake cam from a side where the first engine section is disposed, and the second exhaust rocker arm abuts against the second exhaust cam from a side where the first engine section is disposed.

According to the above aspect of the present invention, an opposed-piston engine according to the present invention includes: a first engine unit having a first cylinder, a first piston reciprocating inside the first cylinder, a first crankshaft converting reciprocating motion of the first piston into rotational motion, a first connecting rod movably connecting the first piston and the first crankshaft, and a first intake valve and a first exhaust valve provided in the first cylinder; a second engine unit having a second cylinder that is separate from and faces the first cylinder, a second piston that reciprocates inside the second cylinder, a second crankshaft that converts the reciprocating motion of the second piston into a rotational motion, a second connecting rod that movably connects the second piston and the second crankshaft, and a second intake valve and a second exhaust valve that are provided in the second cylinder; a valve drive mechanism that drives the first intake valve, the first exhaust valve, the second intake valve, and the second exhaust valve to advance and retreat; when the arrangement direction of the first engine unit and the second engine unit is a first direction and a direction orthogonal to the first direction is a second direction, the valve drive mechanism is disposed outside the outer edges of the first cylinder and the second cylinder in the second direction. Thus, according to the opposed piston engine of the present invention, the valve drive mechanism is disposed outside the outer edges of the first cylinder and the second cylinder in the second direction, so that the first cylinder and the second cylinder can be brought close to each other in the first direction, and the entire opposed piston engine can be downsized.

In the opposed-piston engine according to the present invention, the valve drive mechanism includes a first valve drive mechanism disposed on one side along the second direction and a second valve drive mechanism disposed on the other side along the second direction. Thus, according to the opposed-piston engine of the present invention, the lengths of the first valve drive mechanism and the second valve drive mechanism in the first direction can be shortened, and the entire opposed-piston engine can be downsized.

In the opposed-piston engine according to the present invention, the first intake valve, the first exhaust valve, the second intake valve, and the second exhaust valve are arranged so as to intersect with each other when viewed from the second direction. Thus, according to the opposed piston engine of the present invention, the length occupied by each valve can be shortened in the first direction, and the entire opposed piston engine can be downsized.

In the opposed-piston engine according to the present invention, the valve drive mechanism includes: a first intake rocker arm disposed between a first intake cam and the first intake valve; a first exhaust rocker arm disposed between a first exhaust cam and the first exhaust valve; a second intake rocker arm disposed between a second intake cam and the second intake valve; a second exhaust rocker arm disposed between a second exhaust cam and the second exhaust valve; the first intake rocker arm abuts against the first intake cam from a side where the second engine section is disposed, the first exhaust rocker arm abuts against the first exhaust cam from a side where the second engine section is disposed, the second intake rocker arm abuts against the second intake cam from a side where the first engine section is disposed, and the second exhaust rocker arm abuts against the second exhaust cam from a side where the first engine section is disposed. Thus, according to the opposed piston engine of the present invention, the space enclosed by the valve drive mechanism can be reduced in the first direction, and the entire opposed piston engine can be downsized.

Drawings

Fig. 1 is a diagram showing a counter-piston engine according to an embodiment of the present invention, in which (a) is a side view and (B) is a plan view;

fig. 2 is a side view showing a valve drive mechanism of a counter piston engine according to an embodiment of the present invention;

fig. 3 is a plan view showing each port of the opposed piston engine according to the embodiment of the present invention.

Description of the reference numerals

10: a split piston engine; 11: a first engine section; 12: a first cylinder; 13: a first piston; 14: a first crankshaft; 15: a first link; 17: a first intake valve; 18: a first exhaust valve; 21: a second engine section; 22: a second cylinder; 23: a second piston; 24: a second crankshaft; 25: a second link; 27: a second intake valve; 28: a second exhaust valve; 30: a valve drive mechanism; 301: a first valve actuation mechanism; 302: a second valve drive mechanism; 31: a drive mechanism housing section; 36: a first intake cam; 37: a first exhaust cam; 38: a second intake cam; 39: a second exhaust cam; 40: a first intake valve spring; 41: a first exhaust valve spring; 42: a second intake valve spring; 43: a second exhaust valve spring; 44: a camshaft; 45: a camshaft; 46: a first intake rocker arm; 47: a first exhaust rocker arm; 48: a second intake rocker arm; 49: a second exhaust rocker arm; 50: a first air inlet; 51: a first exhaust port; 52: a second air inlet; 53: a second exhaust port; 55: a flow path; 56: a flow path; 57: a virtual line; 58: a virtual line.

Detailed Description

Hereinafter, the structure and operation of the opposed piston engine 10 according to the present embodiment will be described with reference to the drawings.

In the following description, the front, rear, up, down, left, and right directions are used as appropriate. Here, the front direction means an arrangement direction of the first engine portion 11 in the entire opposed piston engine 10; the rear direction means a direction opposite to the front direction. The front-back direction is a first direction, and the up-down direction is a second direction.

Referring to fig. 1, a basic structure of a reciprocating piston engine 10 is described. In fig. 1, (a) is a side view of the opposed piston engine 10, and (B) is a plan view of the opposed piston engine 10.

Referring to fig. 1 (a) and (B), the opposed piston engine 10 includes a first engine portion 11 disposed on the front side and a second engine portion 21 disposed on the rear side. The first engine unit 11 and the second engine unit 21 are arranged line-symmetrically with respect to a virtual line 58, and the virtual line 58 is a symmetrical line extending in the vertical direction at the center between the first engine unit 11 and the second engine unit 21.

The first engine unit 11 includes: a first cylinder 12; a first piston 13 reciprocating inside the first cylinder 12; a first crankshaft 14 that converts reciprocating motion of the first piston 13 into rotational motion; a first connecting rod 15 that movably connects the first piston 13 and the first crankshaft 14; the first intake valve 17; a first exhaust valve 18. The first intake valve 17 and the first exhaust valve 18 are shown in fig. 2.

The second engine section 21 includes: a second cylinder 22; a second piston 23 reciprocating inside the second cylinder 22; a second crankshaft 24 that converts reciprocating motion of the second piston 23 into rotational motion; a second connecting rod 25 that movably connects the second piston 23 and the second crankshaft 24; a second intake valve 27; and a second exhaust valve 28. The second intake valve 27 and the second exhaust valve 28 are shown in fig. 2.

Further, a valve drive mechanism 30 that drives the advancing and retreating operations of the respective valves included in the first engine portion 11 and the second engine portion 21 is disposed between the first engine portion 11 and the second engine portion 21. The structure of the valve drive mechanism 30 will be described later with reference to fig. 2. The valve drive mechanism 30 is incorporated in the drive mechanism housing portion 31. The drive mechanism housing section 31 is a frame member, and is disposed between the first engine section 11 and the second engine section 21.

The structure of the valve drive mechanism 30 provided in the opposed piston engine 10 will be described with reference to fig. 2. Fig. 2 is an enlarged side view of the valve drive mechanism 30.

The valve drive mechanism 30 has a first valve drive mechanism 301 and a second valve drive mechanism 302. The first valve drive mechanism 301 is disposed in an upper portion, and the second valve drive mechanism 302 is disposed in a lower portion.

The first valve drive mechanism 301 has the first intake valve spring 40, the first intake rocker arm 46, and the first intake cam 36 as a mechanism for driving the first intake valve 17. The first intake valve spring 40 applies a force to the first intake valve 17 in the closing direction of the first intake valve 17. One end of the first intake rocker arm 46 contacts the rear end of the first intake valve 17, and the other end contacts the outer surface of the first intake cam 36. Further, the shaft rotatably penetrates the vicinity of the center portion of the first intake rocker arm 46. This structure is also the same for other rocker arms described later. The first intake cam 36 is substantially oval-shaped and is connected to the camshaft 44 so as to be incapable of relative rotation.

Further, the first valve drive mechanism 301 has the second intake valve spring 42, the second intake rocker arm 48, and the second intake cam 38 as a mechanism for driving the second intake valve 27. The first intake cam 36 and the second intake cam 38 are connected to a camshaft 44 with a prescribed phase difference. The second intake valve spring 42 applies a force to the second intake valve 27 in the closing direction of the second intake valve 27. One end of the second intake rocker arm 48 contacts the rear end of the second intake valve 27, and the other end contacts the outer surface of the second intake cam 38. The second intake cam 38 is substantially oval-shaped and is connected to the camshaft 44 so as to be incapable of relative rotation.

The second valve drive mechanism 302 has the first exhaust valve spring 41, the first exhaust rocker arm 47, and the first exhaust cam 37 as mechanisms for driving the first exhaust valve 18. The first exhaust valve spring 41 applies a force to the first exhaust valve 18 in the closing direction of the first exhaust valve 18. One end of the first exhaust rocker arm 47 contacts the rear end of the first exhaust valve 18, and the other end contacts the outer surface of the first exhaust cam 37. The first exhaust cam 37 is substantially oval-shaped and is connected in a relatively non-rotatable manner with respect to the camshaft 45.

Further, the second valve drive mechanism 302 has the second exhaust valve spring 43, the second exhaust rocker arm 49, and the second exhaust cam 39 as a mechanism for driving the second exhaust valve 28. The first exhaust cam 37 and the second exhaust cam 39 are connected to a camshaft 45 with a predetermined phase difference. The second exhaust valve spring 43 applies a force to the second exhaust valve 28 in the closing direction of the second exhaust valve 28. One end of the second exhaust rocker arm 49 contacts the rear end of the second exhaust valve 28, and the other end contacts the outer surface of the second exhaust cam 39. The second exhaust cam 39 is substantially oval-shaped and is connected in a relatively non-rotatable manner with respect to the camshaft 45.

Referring to fig. 3, the structure of each port for exhaust and intake of the opposed-piston engine 10 will be described. Fig. 3 is a plan view of a portion of the opposed-piston engine 10 where the ports are arranged. In this figure, the flow path of the mixture gas or the exhaust gas is shown by a broken-line arrow.

A first intake port 50 and a first exhaust port 51 are connected to the first cylinder 12. The first intake port 50 is a path through which the mixture gas flowing into the first cylinder 12 passes. The first exhaust port 51 is a path through which exhaust gas discharged from the first cylinder 12 passes.

A second intake port 52 and a second exhaust port 53 are connected to the second cylinder 22. The second intake port 52 is a path through which the mixture gas flowing into the second cylinder 22 passes. The second exhaust port 53 is a path through which exhaust gas discharged from the second cylinder 22 passes.

Although not shown in fig. 1 and 2, the opposed-piston engine 10 includes a camshaft drive mechanism, not shown, that rotates the camshaft 44 and the camshaft 45 by the rotational force of the first crankshaft 14 and the second crankshaft 24. Further, the opposed-piston engine 10 includes a reverse mechanism, not shown, that reverses the rotational direction of the first crankshaft 14 and the rotational direction of the second crankshaft 24.

Here, the operation of the opposed piston engine 10 will be described with reference to the above-described drawings. The first engine unit 11 and the second engine unit 21 constituting the opposed piston engine 10 are four-stroke engines, and therefore, an intake stroke, a compression stroke, a combustion stroke, and an exhaust stroke are repeated. As a result, the first crankshaft 14 and the second crankshaft 24 are rotated to drive a load such as a generator, and further, a driving force is given to a mechanical structure such as a vehicle. Here, the first engine unit 11 and the second engine unit 21 simultaneously perform an intake stroke, a compression stroke, a combustion stroke, and an exhaust stroke.

Referring to fig. 2 and (a) of fig. 1, the operation of the first engine unit 11 in each stroke is as follows.

In the intake stroke, the first intake cam 36 rotates the first intake rocker arm 46, the first intake rocker arm 46 extends the first intake valve 17, and the first exhaust valve 18 not pushed by the first exhaust rocker arm 47 is retracted, and in this state, the first piston 13 moves forward inside the first cylinder 12. Thereby, a mixture gas, which is a mixture of fuel (e.g., gasoline) and air, is introduced into the first cylinder 12 through the first exhaust port 51 shown in fig. 3.

In the compression stroke, the first intake valve 17 not pushed by the first intake rocker arm 46 is in a retracted state, and further, the first exhaust valve 18 not pushed by the first exhaust rocker arm 47 is also in a retracted state. In this state, the first piston 13 is pushed out rearward by the inertia of the rotating first crankshaft 14, and the mixed gas is compressed in the first cylinder 12.

In the combustion stroke, a spark plug, not shown, ignites inside the first cylinder 12, and the mixture is combusted inside the first cylinder 12, whereby the first piston 13 is pushed out to the front end, which is the bottom dead center.

In the exhaust stroke, the first intake valve 17 not pushed by the first intake rocker arm 46 is retracted, and the first exhaust valve 18 pushed by the first exhaust rocker arm 47 is extended, and in this state, the first piston 13 is pushed rearward by the inertia of the rotating first crankshaft 14, and the burned gas present in the first cylinder 12 is discharged to the outside through the first exhaust port 51 shown in fig. 3.

The operation of the second engine section 21 in each stroke is as follows.

In the intake stroke, the second intake cam 38 rotates the second intake rocker arm 48, the second intake rocker arm 48 extends the second intake valve 27, and the second exhaust valve 28, which is not pushed by the second exhaust rocker arm 49, is retracted, and in this state, the second piston 23 moves rearward inside the second cylinder 22. Thereby, a mixture of fuel (e.g., gasoline) and air, i.e., a mixed gas, is introduced into the second cylinder 22 through the second intake port 52 shown in fig. 3.

In the compression stroke, the second intake valve 27, which is not pushed by the second intake rocker arm 48, is in a retracted state, and the second exhaust valve 28, which is not pushed by the second exhaust rocker arm 49, is also in a retracted state. In this state, the second piston 23 is pushed forward by the inertia of the rotating second crankshaft 24, and the gas mixture is compressed inside the second cylinder 22.

In the combustion stroke, the spark plug, not shown, ignites inside the second cylinder 22, and the air-fuel mixture is combusted inside the second cylinder 22, whereby the second piston 23 is pushed out to the rear end, which is the bottom dead center.

In the exhaust stroke, the second intake valve 27 not pushed by the second intake rocker arm 48 is retracted, and the second exhaust valve 28 pushed by the second exhaust rocker arm 49 is extended, and in this state, the second piston 23 is pushed forward by the inertia of the rotating second crankshaft 24, and the burned gas present in the second cylinder 22 is discharged to the outside via the second exhaust port 53 shown in fig. 3.

In the opposed piston engine 10 according to the present embodiment, the components constituting the valve drive mechanism 30 are disposed outside the outer edges of the first cylinder 12 and the first piston 13 in the vertical direction.

Referring to fig. 2 and 1 (a), specifically, the first intake valve spring 40, the first intake rocker arm 46, and the first intake cam 36 that drive the first intake valve 17 are disposed above the upper edge portions of the first cylinder 12 and the second cylinder 22. Further, the second intake valve spring 42, the second intake rocker arm 48, and the second intake cam 38 that drive the second intake valve 27 are disposed above the upper edge portions of the first cylinder 12 and the second cylinder 22.

The first exhaust valve spring 41, the first exhaust rocker arm 47, and the first exhaust cam 37 that drive the first exhaust valve 18 are disposed below the lower edge portions of the first cylinder 12 and the second cylinder 22. Further, the second exhaust valve spring 43, the second exhaust rocker arm 49, and the second exhaust cam 39 that drive the second exhaust valve 28 are disposed below the lower edge portions of the first cylinder 12 and the second cylinder 22.

With this configuration, the members constituting the valve drive mechanism 30 are not disposed between the first cylinder 12 and the second cylinder 22 in the front-rear direction, and therefore the width of the valve drive mechanism 30 can be shortened. Further, the overall length of the opposed piston engine 10 can be shortened. Thus, when the opposed-piston engine 10 is incorporated in a vehicle, the volume occupied by the opposed-piston engine 10 in the vehicle can be reduced, and the degree of freedom in designing the vehicle can be improved.

Further, referring to fig. 2 and fig. 1 (a), the first intake rocker arm 46 included in the first engine section 11 disposed on the left side of the opposed piston engine 10 abuts on the first intake cam 36 from the right side. That is, the arrangement direction of the first engine section 11 in the entire opposed piston engine 10 is opposite to the arrangement direction of the first intake rocker arm 46 with respect to the first intake cam 36. The same is true for the first exhaust rocker arm 47, the second intake rocker arm 48, and the second exhaust rocker arm 49. With this configuration, the width of the valve drive mechanism 30 can be further reduced.

Further, referring to fig. 1 (a), in the opposed piston engine 10 according to the present embodiment, main constituent components constituting the first engine unit 11 and the second engine unit 21 are arranged on a predetermined virtual line 57 along the front-rear direction. Specifically, the first cylinder 12, the first piston 13, the first crankshaft 14, and the first connecting rod 15 of the first engine unit 11 are arranged on the virtual line 57. Further, the second cylinder 22, the second piston 23, the second crankshaft 24, and the second connecting rod 25 of the second engine unit 21 are also arranged on the virtual line 57. By disposing the components of each engine unit on the virtual line 57 in this manner, vibrations generated by the operation of each engine unit are cancelled out, and the vibration damping effect can be improved.

Further, the first engine unit 11 and the second engine unit 21 are arranged line-symmetrically with respect to a predetermined virtual line 58 in the left-right direction. With this configuration, vibrations generated by the operation of the respective engine units are also cancelled out, and the vibration damping effect can be improved.

Referring to (a) of fig. 1, the first cylinder 12 of the first engine part 11 and the second cylinder 22 of the second engine part 21 are formed in the form of separate combustion chambers rather than a continuous space. Accordingly, since the first cylinder 12 and the second cylinder 22 are formed as substantially cylindrical spaces, the shape of the combustion chamber is simplified, and the output can be increased by improving the intake efficiency and the exhaust efficiency. Further, since the first cylinder 12 and the second cylinder 22 have a substantially cylindrical shape, heat transfer in the first cylinder 12 and the second cylinder 22 is substantially the same when the opposed piston engine 10 is operated, and therefore, deformation of the first cylinder 12 and the second cylinder 22 during operation is suppressed.

Further, in the present embodiment, the first cylinder 12 of the first engine section 11 and the second cylinder 22 of the second engine section 21 each have an intake valve and an exhaust valve. Specifically, a first intake valve 17 is disposed at a rear end portion of the first cylinder 12 of the first engine unit 11, and a first exhaust valve 18 is disposed at a rear end portion of the first cylinder 12. Therefore, during engine operation, the flow path 55 for the mixture gas and the exhaust gas flowing through the first cylinder 12 is simplified, and the combustion toughness can be improved by simplifying the shape of the combustion chamber. Similarly, a second intake valve 27 is disposed at a front end portion of the second cylinder 22 of the second engine unit 21, and a second exhaust valve 28 is disposed at a front end portion of the second cylinder 22. Therefore, during engine operation, the flow path 56 for the mixture gas and the exhaust gas flowing through the second cylinder 22 is simplified, and the combustion toughness can be improved as in the case of the first cylinder 12.

The embodiments of the present invention have been described above, but the present invention is not limited to the above embodiments.

Claims

1. An opposed piston engine, comprising:

a first engine unit having a first cylinder, a first piston reciprocating inside the first cylinder, a first crankshaft converting reciprocating motion of the first piston into rotational motion, a first connecting rod movably connecting the first piston and the first crankshaft, and a first intake valve and a first exhaust valve provided in the first cylinder;

a second engine unit having a second cylinder that is separate from and faces the first cylinder, a second piston that reciprocates inside the second cylinder, a second crankshaft that converts the reciprocating motion of the second piston into a rotational motion, a second connecting rod that movably connects the second piston and the second crankshaft, and a second intake valve and a second exhaust valve that are provided in the second cylinder;

a valve drive mechanism that drives the first intake valve, the first exhaust valve, the second intake valve, and the second exhaust valve to advance and retreat;

when the arrangement direction of the first engine unit and the second engine unit is set as a first direction and a direction orthogonal to the first direction is set as a second direction,

the valve drive mechanism is disposed further outward than outer edges of the first cylinder and the second cylinder in the second direction,

the first intake valve, the first exhaust valve, the second intake valve, and the second exhaust valve are arranged to intersect with each other when viewed from the second direction.

2. Opposed piston engine according to claim 1,

the valve drive mechanism includes a first valve drive mechanism disposed on one side along the second direction and a second valve drive mechanism disposed on the other side along the second direction.

3. Opposed piston engine according to claim 1 or 2,

the valve drive mechanism includes:

a first intake rocker arm disposed between a first intake cam and the first intake valve;

a first exhaust rocker arm disposed between a first exhaust cam and the first exhaust valve;

a second intake rocker arm disposed between a second intake cam and the second intake valve;

a second exhaust rocker arm disposed between a second exhaust cam and the second exhaust valve;

the first intake rocker arm abuts against the first intake cam from a side where the second engine section is disposed,

the first exhaust rocker arm abuts against the first exhaust cam from a side where the second engine section is disposed,

the second intake rocker arm abuts against the second intake cam from a side where the first engine section is disposed,

the second exhaust rocker arm abuts against the second exhaust cam from a side where the first engine unit is disposed.