JP3156276B2 - 4-cycle parallel 4-cylinder engine - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a four-cycle parallel four-cylinder engine, and more particularly to a four-cycle parallel four-cylinder engine in which an exhaust system control device is installed in an exhaust pipe derived from each cylinder.

[0002]

2. Description of the Related Art A conventional four-cycle multi-cylinder engine includes:
Some exhaust pipes are provided with an exhaust system control device in an exhaust pipe derived from each cylinder. In this exhaust system control device, a plurality of exhaust pipes are connected by a connecting pipe, and an exhaust system control valve is installed in the connecting pipe. In this exhaust system control device, the exhaust system control valve is opened and closed according to the engine speed, and when the valve is opened, the output characteristics of the engine are improved by mutual interference of exhaust pressure pulsation waves.

[0003]

However, in a four-cycle multi-cylinder engine provided with the above-described exhaust system control device, the engine output can be improved. The engine output cannot be significantly improved over time.

The present invention has been made in view of the above circumstances, and has as its object to provide a four-cycle multi-cylinder engine capable of greatly improving the engine output over the entire engine speed range. I do.

[0005]

According to the present invention, there is provided an air intake passage for forming an air-fuel mixture by air sucked from an air cleaner, and introducing the air-fuel mixture into a combustion chamber of each cylinder arranged in parallel with a cylinder head. The exhaust pipes arranged in parallel connected to the cylinders of the head are brought closer to each other while lowering and curving the front of the engine, converging in a cross shape below the engine and in front of the collecting pipe, and extending rearward. A four-stroke parallel four-cylinder engine having an exhaust passage connected to a muffler disposed behind a pipe, comprising: an exhaust system control valve that opens and closes according to the engine speed. An exhaust system control device for controlling the flow is provided in the exhaust passage, and the combustion conditions in the combustion chamber are also switched and controlled in accordance with the engine speed. The exhaust pipes connected to the respective cylinders on both outer sides of the engine are defined as the cross-shaped engine side, while the exhaust pipes connected to the respective cylinders at the center of the engine. And the exhaust system control device communicates two cylinders having different exhaust timings connected to each cylinder in accordance with the engine speed by opening and closing the exhaust system control valve. The exhaust system control valve is disposed forward of the collecting pipe disposed below the engine, and the exhaust system control valve is operated when the engine is running at a low speed to connect the two cylinders having different exhaust timings. The exhaust pipes are communicated with each other to cause the exhaust pressure pulsation waves to interfere with each other, and the exhaust is sent to the downstream.The exhaust sent to the downstream is guided into the collecting pipe, and then opened to the atmosphere via the muffler, and furthermore, In the low engine speed, the combustion conditions in the combustion chamber of each cylinder of the cylinder head are controlled by controlling the amount of air-fuel mixture flowing into the combustion chamber, thereby changing other engine speed ranges and combustion conditions. Things. Further, the invention according to claim 2 controls the changing of the combustion condition at the time of low engine rotation in the combustion chamber of each cylinder of the cylinder head from the combustion condition of another engine speed range by controlling the valve characteristic of intake or exhaust. Is controlled by selecting and changing the cam profile of the intake side camshaft or the exhaust side camshaft according to the engine speed.

[0006]

According to the four-stroke parallel four-cylinder engine of the present invention, since the exhaust system control device is disposed in front of the exhaust pipe, the motorcycle can be reduced in weight and size. That is, since the plurality of exhaust pipes are connected by the exhaust system control device, the distance between the exhaust pipes increases as the distance from the exhaust pipe assembly increases,
In addition to increasing the size of the exhaust system control device and dispersing heavy objects, mass concentration cannot be achieved, so by arranging the exhaust system control device ahead of the collecting pipe arranged below the engine, In addition, the size and weight of the motorcycle can be reduced. Regarding the converging shape of the multiple exhaust pipes, the cross-sectional shape of the shaft below the engine has a cross-shaped cross shape, so that the width of the engine and the area under the engine can be kept small to increase the bank angle. become.
The two exhaust pipes from the outer cylinder of the engine are arranged closer to the engine (upper side) in the cross, and both exhaust pipes from the cylinder in the center of the engine are arranged closer to the ground surface (lower side) in the cross. Therefore, each exhaust pipe can be made equal in length. Further, by operating the exhaust system control valve when the engine is running at a low speed, the exhaust pipes connected to the two cylinders having different exhaust timings are communicated with each other, and the exhaust pressure pulsation waves are mutually interfered and the exhaust is sent downstream. In addition, the exhaust pressure pulsation waves interfere with each other, thereby improving the exhaust efficiency and the intake charging efficiency of the engine, and the engine output. Furthermore, when the engine is running at a low speed, the combustion conditions in the combustion chamber of each cylinder of the cylinder head are controlled by controlling the amount of air-fuel mixture flowing into the combustion chamber, thereby changing other engine speed ranges and combustion conditions. , The engine output is improved. According to the second aspect of the present invention, the control for changing the combustion conditions at the time of low engine rotation to the combustion conditions of another engine speed range of medium and high speeds is performed between the low speed cam and the medium and high speed cam having different cam profiles. Therefore, the valve timing and valve lift of the intake and exhaust valves suitable for the whole range of the engine speed are realized, and the engine output is improved.

[0007]

Embodiments of the present invention will be described below with reference to the drawings.

FIG. 2 is a side view showing one embodiment of a four-cycle multi-cylinder engine according to the present invention.

The engine unit 1 includes a crankcase 2
And a cylinder 3 standing upright on the upper part of the crankcase 2 and extending in the vehicle width direction. The cylinder 3 is configured by sequentially combining a cylinder block 4, a cylinder head 5 and a head cover 6 from below, and one or a plurality of cylinders (not shown) are formed in the cylinder block 4. In this embodiment, upright four cylinders are formed in the cylinder block 4.

In the cylinder head 5, a combustion chamber 7 (FIGS. 3 and 4) is formed for each cylinder, and two intake ports 8 and two exhaust ports 9 are opened in each combustion chamber 7. In the cylinder head 5, an intake passage 10 and an exhaust passage 11 that are respectively connected to the intake port 8 and the exhaust port 9 are formed for each combustion chamber 7, respectively. In the intake passage 10 and the exhaust passage 11, an intake port 8,
Partition walls 12 and 13 are formed in the vicinity of the exhaust port 9, respectively, and the partition walls 12 and 13 constitute a branch passage.

At the upstream ends of the four intake passages 10 formed in the cylinder head 5, via intake pipes 14 shown in FIG.
A carburetor 15 and an air cleaner 16 are sequentially connected, and these 15 and 16 introduce an air-fuel mixture into the combustion chamber 7 through the intake passage 10.

Further, exhaust pipes 17 shown in FIG. 2 are connected to the downstream ends of the four exhaust passages formed in the cylinder head 5, respectively. Each exhaust pipe 17 is connected to the engine unit 1
The engine unit 1 descends from the front and curves rearward.
After connecting to the collecting pipe 18 below the left and right mufflers 19
Divided into open to the rear.

By the way, as shown in FIGS. 3 and 4,
The intake boat 8 and the exhaust port 9 are opened and closed by an intake valve 21 and an exhaust valve 22, respectively. The intake valve 21 and the exhaust valve 22 are slidably inserted into a valve guide 23 installed on the cylinder head 5 and are constantly urged upward by a valve spring 24. The opening and closing of the intake valve 21 and the exhaust valve 22 is controlled by a valve characteristic variable valve device 20 also shown in FIG.

The variable valve characteristic valve operating device 20 is rotatably supported between a camshaft journal portion 25 of a cylinder head 5 and a camshaft journal housing (not shown), and a low-speed cam 27 and a medium-high speed A camshaft 30 provided with cams 28 and 29; a rocker shaft 31 rotatably fitted to a lower portion of the camshaft journal 25 of the cylinder head 5 to form an eccentric large diameter portion; The low-speed rocker arm 32 inserted, the medium- and high-speed rocker arms 33 and 34 inserted on both sides of the low-speed rocker arm 32 on the rocker shaft 31 and at the eccentric large diameter portion, and the rocker for rotating the rocker shaft 31. Hydraulic cylinder 3 as shaft rotation drive source
5 is comprised.

A total of two camshafts 30 are arranged in the vehicle width direction, one each at the front and rear of the cylinder head 5 in the vehicle. A front camshaft 30 is used for driving the exhaust valve 22 and a rear camshaft 30 is used. Are for driving the intake valve 21. Each camshaft 30 is formed with a set of cam units in which middle and high speed cams 28 and 29 are arranged on both sides of the low speed cam 27, by the number of cylinders (that is, the number of combustion chambers 7). In this embodiment, four sets are formed. Each camshaft 30 is rotated by a crankshaft (not shown) housed in the crankcase 2 of the engine unit 1 via a cam chain (not shown).

The medium and high speed cams 28 and 29 are formed in the same cam profile. Further, the low speed cam 27 is formed in a cam profile different from the cam profiles of the middle and high speed cams 28 and 29. In other words, the cam profile of the low-speed cam 27 is formed such that an appropriate valve lift amount and valve lift timing are obtained when the engine is operated in a low rotation speed range.
Also, the cams 28 and 29 for middle and high speed
The cam profile is formed such that an appropriate valve lift amount and valve lift timing are obtained when the engine is operated in a high rotation speed range.

A total of four rocker shafts 31 are arranged on the left and right sides of the cylinder head 5 in the vehicle width direction, respectively, in the front and rear direction of the vehicle, and extend immediately below the camshaft 30 in the same direction as the camshaft 30. There is provided. Two sets of the low-speed rocker arm 32 and the medium-high speed rocker arms 33 and 34 are installed on one rocker shaft 31. The positions of the low-speed rocker arms 32 and the medium- and high-speed rocker arms 33 and 34 of each set are regulated together with the rocker shaft 31 by a positioning spring (not shown) interposed in the rocker shaft 31.

As shown in FIGS. 5 and 6, the distal end of the low-speed rocker arm 32 branches into two, and these two branch distal ends 32b abut on the intake valve 21 or the exhaust valve 22 via a shim 37. You. The support portion 32a of the low-speed rocker arm 32 is directly inserted into the rocker shaft 31, and the low-speed rocker arm 32 has a cam floor surface 32c formed between the branch distal end portion 32b and the support portion 32a.

The support portion 33a of the medium-high speed rocker arm 33
Is an eccentric bush 38 having a larger diameter than the rocker shaft 31.
Is rotatably fitted to the rocker shaft 31 via the. As shown in FIGS. 3 and 4, the eccentric bush 38 has an outer peripheral surface whose axis is eccentric from the center of the rocker shaft 31, and is detachably fixed to the rocker shaft 31 by a positioning fixing pin 40. Therefore, the eccentric bush 38 functions as an eccentric large diameter portion in the rocker shaft 31.

As shown in FIG. 6, the supporting portion 34a of the medium / high speed rocker arm 34 also has the same shape as the eccentric bush 38 and is eccentric in the same direction.
Is rotatably fitted to the rocker shaft 31 via the. This eccentric bush 39 also has a positioning fixing pin 40.
It is detachably fixed to the rocker shaft 31 by (FIGS. 3 and 4) and functions as an eccentric large diameter portion.

The lower surfaces of the distal ends 33b and 34b of the medium and high speed rocker arms 33 and 34 are connected to one or the other of the branch distal end 32b of the low speed rocker arm 32.
They are brought into contact with each other via shims 41. Medium-high speed cam 3
3 and 34, the cam floor surfaces 33c and 34c are provided between the tip portions 33b and 34b and the support portions 33a and 34a, respectively.
Is formed. The contact point between the branch tip 32b of the low-speed rocker arm 32 and the tips 33b and 34b of the medium- and high-speed rocker arms 33 and 34 is determined by the intake valve 21.
Alternatively, it is set substantially on the axis of the exhaust valve 22.

Therefore, as shown in FIG. 3, the low-speed cam 27 is mounted on the cam floor surface 32c of the low-speed rocker arm 32.
When the low-speed cam 27 in which the branch end portions 32b are lowered by operating the rocker arms 33 and 3
The tip portions 33b and 34b of No. 4 follow the branch tip portion 32b by gravity and descend. On the other hand, as shown in FIG. 4, the cams 28 and 29 for medium and high speeds are cam floor surfaces 33c and 34 of the rocker arms 33 and 34 for medium and high speeds.
When the middle and high speed cams 28 and 29 are actuated by pressing down the respective forward end portions 33b and 34b of the middle and high speed rocker arms 33 and 34, the branch end portions 32b of the low speed rocker arm 32 are pushed down. The part 32b is forcibly lowered.

The hydraulic cylinder 35 shown in FIG. 5 is installed in a cam chain chamber (not shown) in the cylinder head 5. The hydraulic cylinder 35 accommodates the same number of pistons (not shown) as the rocker shaft 31, and a rack 43 is connected to each piston. These racks 43
Is engaged with a pinion 44 formed at one end of the rocker shaft 31. The hydraulic cylinder 35 is provided with a low-speed hydraulic port 45 and a medium-high-speed hydraulic port 46, and the hydraulic pressure from the engine is selectively guided to the respective ports 45, 46, and each piston or rack 43 is provided. Reciprocates.

When the engine speed is in the low speed range, hydraulic pressure is supplied to the low-speed hydraulic port 45 and the rack 4
3, the pinion 44 is rotated in the direction of the arrow O (FIG. 5), and the eccentric bushes 38 and 39 have their thick tops 38a and 39a located at the center in the front-rear direction of the engine as shown in FIG. To rotate. Thereby, the cam floor surfaces 33 of the medium and high speed rocker arms 33 and 34 are formed.
c and 34c move downward relative to the cam floor surface 33c of the low-speed rocker arm 33,
A gap is formed between the peripheral surfaces of the camshafts 8 and 29 and the cam floor surfaces 33c and 34c of the medium and high speed rocker arms 33 and 34. As a result, the middle and high speed cams 4 and 5 run idle, and only the low speed cam 27 comes into contact with the cam floor surface 32c of the low speed rocker arm 32 and rotates. For this reason, the intake valve 21 and the exhaust valve 22 operate the intake port 8 and the exhaust port 9 at a valve lift timing and a valve lift amount suitable for the low engine speed range by the operation of the low speed cam 27 and the low speed rocker arm 32. Open and close each.

When the engine speed is in the middle / high speed range, hydraulic pressure is supplied to the middle / high speed hydraulic port 46 (FIG. 5), the rack 43 is pushed out, and the pinion 44 is moved in the direction of arrow P (FIG. 5). As shown in FIG. 4, the eccentric bushes 38 and 39 rotate so that their thick tops 38a and 39a are located outward in the front-rear direction of the engine. Thereby, the medium and high speed rocker arms 33 and 3
No. 4 cam floor surfaces 33c and 34c move relatively upward or to the same position relative to the cam floor surface 32c of the low-speed rocker arm 32, and the cam floor surfaces 33c and 34c contact the peripheral surfaces of the middle and high speed cams 28 and 29, respectively. Touch Here, since the cam lifts of the middle and high speed cams 28 and 29 are formed larger than the low speed cam 27, the low speed cam 27 idles in the above state,
Medium and high speed cams 28 and 29
3 and 34 respectively rotate in contact with the cam floor surfaces 33c and 34c. As a result, the intake valve 21 and the exhaust valve 22 actuate the medium and high speed cams 28 and 29 and the medium and high speed rocker arms 33 and 34 to operate the valve at the valve lift timing and valve lift amount suitable for the medium and high speed range of the engine. The port 8 and the exhaust port 9 are respectively opened and closed.

As shown in FIG. 7, the exhaust pipes 17 are # 1, # 2, # 3, and # 4 from one side to the other side in accordance with the parallel arrangement of the cylinders in the cylinder 3. This # 2 and #
The exhaust pipe 17 of No. 3 is connected by a connecting pipe 51, and the exhaust pipes of # 1 and # 4 are connected by a connecting pipe 52, and an exhaust system control valve mechanism 52A (FIG. 1) is installed in the connecting pipe 52. The exhaust system control device 50 includes the connection pipe 51, the connection pipe 52, and the exhaust system control valve mechanism 52A. Then, as shown in FIG.
The exhaust pipe 17 is converged in a cross shape below the engine unit 1 and in front of the collecting pipe 18 and extends rearward, and is connected to a muffler 19 behind this collecting pipe 18. Moreover, the exhaust pipes 17, 17 on both sides of the engine unit 1 on the outer sides # 1, # 4 are connected to the engine unit 1 having the cross-shaped convergence.
On the other hand, the exhaust pipes 17 and 17 of # 2 and # 3 inside the engine unit 1 are disposed on the ground surface side of the cross-shaped convergence, that is, on the lower side. The pipe 17 is made equal in length, and the width of the engine unit 1 and the lower region of the engine unit 1 in the width direction is reduced to increase the bank angle.

As shown in FIG. 8, the connecting pipe 51 is fixed to the side faces of the exhaust pipe 17 opposite to # 2 and # 3, and openings 53 are formed on both side faces thereof. Exhaust pipe 17 # 2
And # 3 are communicated by the opening 53 and the connecting pipe 51.

The connecting pipe 52 is, as shown in FIG.
The exhaust pipe 17 is fixed to opposing side surfaces of # 1 and # 4, and openings 54 are formed on both side surfaces. Exhaust pipe 17
# 1 and # 4 are the openings 54 and the connecting pipes 5
2 communicates.

The exhaust system control valve mechanism 52A includes a servomotor 55 and a disk-shaped exhaust system control valve 57 fixed to a rotating shaft 56 of the servomotor 55. The servomotor 55 is bolted to a mounting seat 58 fixed to the connecting pipe 52 via a heat insulating material 59, and opens and closes the exhaust system control valve 57 by the rotation of the rotation shaft 56. The tip of the rotating shaft 56 is supported by the connecting pipe 52.

The rotation of the servo motor 55 is controlled by an igniter 60 which is a control means of the exhaust system controller 50 shown in FIG.
This is done by the servo motor control signal d from The igniter 60 receives the engine speed signal a from the pickup coil 61 and the carburetor opening signal b from the carburetor sensor 62 to output an engine ignition signal e, and outputs the servo motor control signal d and the cam switching signal c. Output to the hydraulic cylinder 35. The switching of the hydraulic pressure to the low-speed hydraulic port 45 (FIG. 5) or the middle-high speed hydraulic port 46 of the hydraulic cylinder 35 is controlled by the cam switching signal c, and the operation of the low-speed cam 27 or the middle-high speed cams 28 and 29 is performed. Operation switches. Further, the forward / reverse rotation of the servo motor 55 and the amount of rotation thereof are controlled by the servo motor control signal d, and the opening and closing of the exhaust system control valve 57 (FIG. 1) is controlled.

That is, as shown in FIG. 10, when the engine speed increases, the igniter 60
The opening and closing of the exhaust system control valve 57 is controlled from the open state to the closed state at a rpm, and the operation of the low speed cam 27 to the medium and high speed cam is performed at an engine speed Nb (Nb> Na) rpm. The switching of the cam to the operation of 28 and 29 is controlled. In addition, the igniter 60
When the engine speed drops, the engine speed Nbrpm
The cam is switched from the operation of the medium and high speed cams 28 and 29 to the operation of the low speed cam 27 at a slightly lower rotation speed, and the exhaust system control valve 57 is opened from a closed state at a rotation speed slightly lower than the engine rotation speed Narpm. Control to the valve state,
Hunting is prevented.

In FIG. 10, a broken line 63 indicates the engine output characteristic when the low speed cam 27 is operating and the exhaust system control valve 57 is opened, and a dashed line 64 indicates the exhaust gas when the low speed cam 27 is operating. This is an engine output characteristic when the system control valve 57 is closed. The two-dot chain line 65 is
The engine output characteristics when the middle and high speed cams 28 and 29 are operating and the exhaust system control valve 57 is open, and the solid line 66 is when the middle and high speed cams 28 and 29 are operating and the exhaust system control valve 57 is closed. It is an engine output characteristic at the time.

Therefore, as described above, the igniter 60 opens and closes the exhaust system control valve 57 and operates the cams 27, 28,
When the switching of the engine speed 29 is controlled, the engine output characteristics are indicated by a broken line 63 below the engine speed Narpm, the output characteristics indicated by a one-dot chain line 64 from the engine speed Narpm to Nbrpm, and indicated by a solid line 66 above the engine speed Nbrpm. Exhibits engine output characteristics. As described above, since the igniter 60 is controlled to select the best output characteristics from the low speed range to the high speed range, the engine output can be largely improved as a whole.

The reason why the engine output characteristics are improved by opening and closing the exhaust system control valve 57 will be described below.

The exhaust gas flowing through the exhaust pipe 17 shown in FIG.
The processing is performed in the order of # 1 → # 2 → # 4 → # 3 at 80 ° intervals. Accordingly, the # 2 and # 3 exhaust pipes 17 communicated by the connecting pipe 51 are also the # 1 and # 4 exhaust pipes 17 communicated by the connecting pipe 52 and the exhaust system control valve 57.
In both cases, the ignition orders are not adjacent to each other, and the exhaust timing is shifted by 360 ° of the crankshaft rotation angle. Therefore, when the engine speed is low (the engine speed N
When the exhaust pipes # 2 and # 3 communicate with the exhaust pipe 17 of # 1 and # 4 through the coupling pipe 52 and the exhaust system control valve 57 is fully opened, the exhaust pressure increases. Since the exhaust efficiency and the charging efficiency are increased by the mutual interference of the pulsating waves, the output of the engine is improved.
On the other hand, when the engine is running at medium to high speeds (the engine speed Narpm
When the exhaust system control valve 57 is fully closed as described above and the communication between the # 1 and # 4 exhaust pipes 17 is interrupted, the # 1 and # 4 exhaust pipes 17 become independent and the exhaust gas flows smoothly. Therefore, it is possible to cope with an increase in the exhaust flow velocity, and the engine output is greatly improved.

According to the above embodiment, as described above, the cam 2
By switching between 7, 28, and 29 and opening and closing the exhaust system control valve 57 to open and close the connection pipe 52, the output characteristics of the engine can be significantly improved over the entire rotation speed range.

In the above embodiment, the connecting pipe 52 is connected to the # 2.
And hidden in the # 3 exhaust pipe,
Even if the exhaust system control valve mechanism 52A is installed behind the connecting pipe 52, there is no problem in design.

In the above embodiment, the engine speed Narpm for changing the opening and closing of the exhaust system control valve 57 and
Engine speed Nb for switching cams 27, 28, 29
rpm is different from the engine speed Na.
The rotation speed of the cams 27, 28 and 29 and the opening and closing of the exhaust system control valve 57 may be simultaneously performed at the engine speed Nbrpm. In this case, although the engine output characteristics are slightly lowered, the apparatus can be simplified because only one signal is output to the hydraulic cylinder 35 and the servomotor 55, and the exhaust system control valve mechanism 52A is additionally provided as an option. it can.

In the above embodiment, the exhaust system control valve mechanism 52A is installed only in the connecting pipe 52.
An exhaust system control valve mechanism similar to the exhaust system control valve mechanism 52A may be provided in the connecting pipe 51 to further improve the engine output.

[0040]

As described above, according to the present invention, the 4
According to the cycle-parallel four-cylinder engine, the weight and size of the motorcycle can be reduced because the exhaust system control device is disposed in front of the exhaust pipe collecting pipe provided below the engine. That is, since the plurality of exhaust pipes are connected to each other by the exhaust system control device, the distance between the exhaust pipes increases as the distance from the exhaust pipe assembly increases, leading to an increase in the size of the exhaust system control device and weight. Since the objects cannot be concentrated because mass is scattered, the size and weight of the motorcycle can be reduced by arranging the exhaust system control device in front. Also, regarding the converging shape of the exhaust pipe, the cross-sectional shape of the shaft below the engine is formed in a cross-shape, so that the width of the engine and the area under the engine in the width direction can be suppressed to increase the bank angle. . The two exhaust pipes from the outer cylinder of the engine are arranged closer to the engine (upper side) in the cross, and both exhaust pipes from the cylinder in the center of the engine are arranged closer to the ground surface (lower side) in the cross. Therefore, each exhaust pipe can be made equal in length. Further, by operating the exhaust system control valve when the engine is running at a low speed, the exhaust pipes connected to the two cylinders having different exhaust timings are communicated with each other, and the exhaust pressure pulsation waves are mutually interfered and the exhaust is sent downstream. In addition, the exhaust pressure pulsation waves interfere with each other, thereby improving the exhaust efficiency and the intake charging efficiency of the engine, and the engine output. Further, when the engine is running at a low speed, the combustion conditions in the combustion chamber of each cylinder of the cylinder head are controlled by controlling the amount of air-fuel mixture flowing into the combustion chamber, thereby changing other engine speed ranges and the combustion conditions. Output is improved. According to the second aspect of the present invention, the control for changing the combustion condition at the time of low engine rotation to the combustion condition of another engine speed range of middle and high speed is performed.
It is performed by switching the intake and exhaust valves between low-speed cam and medium-high speed cam with different cam profiles,
The valve timing and valve lift of the intake and exhaust valves suitable for the entire engine speed range are realized, and the engine output is improved.

[Brief description of the drawings]

FIG. 1 is a sectional view taken along the line II of FIG. 7;

FIG. 2 is a side view showing one embodiment of a four-cycle multi-cylinder engine according to the present invention.

FIG. 3 is a cross-sectional view of the cylinder head of FIG. 2, showing an operation state of the valve train at the time of low engine rotation.

FIG. 4 is a cross-sectional view of the cylinder head of FIG. 2, illustrating an operation state of the valve train when the engine is running at a high engine speed.

FIG. 5 is a perspective view of the valve train shown in FIGS. 3 and 4;

FIG. 6 is a plan view of the valve gear of FIG. 5;

FIG. 7 is a view taken in the direction of arrow VII in FIG. 2;

FIG. 8 is a sectional view taken along the line VIII-VIII in FIG. 7;

FIG. 9 is a block diagram of a control system that controls the exhaust system control valve mechanism of FIG. 1 and the valve gear of FIG. 5;

10 is a graph showing the engine output shown in FIG. 2 together with the engine speed.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Engine unit 17 Exhaust pipe 20 Valve characteristic variable valve device 21 Intake valve 22 Exhaust valve 27 Low speed cam 28,29 Medium / high speed cam 31 Rocker shaft 32 Low speed rocker arm 33,34 Medium / high speed rocker arm 35 Hydraulic cylinder 38,39 Eccentric bush 50 Exhaust system control device 51, 52 Connecting pipe 52A Exhaust system control valve mechanism 57 Exhaust system control valve 60 Igniter a Engine speed signal

Claims (2)

(57) [Claims] 1. An air-fuel mixture is formed by air taken from an air cleaner, and the air-fuel mixture is connected to an intake passage for introducing the air-fuel mixture into a combustion chamber of each cylinder arranged in parallel with a cylinder head, and to each cylinder of the cylinder head. The exhaust pipes arranged in parallel are brought closer to each other while lowering and curving the front of the engine, converging in a cross shape below the engine and in front of the collecting pipe, and extending rearward, and disposed behind the collecting pipe. What is claimed is: 1. A four-stroke parallel four-cylinder engine having an exhaust passage connected to a muffler, comprising: an exhaust system control valve that opens and closes in accordance with the engine speed, wherein the exhaust system control valve controls the flow of exhaust gas. Is provided in the exhaust passage, and the combustion conditions in the combustion chamber are also switched and controlled according to the engine speed. The exhaust pipe connected to each of the cylinders on both sides of the engine is defined as the cross-shaped engine side, while the exhaust pipe connected to each cylinder at the center of the engine is defined as the cross-shaped side of the cross. The exhaust system control device is configured to open and close the exhaust system control valve to communicate two cylinders having different exhaust timings connected to the respective cylinders according to the engine speed. An exhaust pipe connected to two cylinders having different exhaust timings is provided by operating the exhaust system control valve when the engine is running at a low speed so that the exhaust pipes are disposed forward of the collecting pipe disposed below the engine. Exhaust pressure pulsation waves are caused to interfere with each other to send exhaust gas downstream, and the exhaust gas sent downstream is guided into the collecting pipe, and then opened to the atmosphere via a muffler,
Further, at low engine speeds, the combustion conditions in the combustion chamber of each cylinder of the cylinder head are controlled by controlling the amount of air-fuel mixture flowing into the combustion chamber, thereby changing other engine speed ranges and combustion conditions. 4 cycle parallel 4-cylinder engine. 2. A control for changing a combustion condition at the time of low engine rotation in a combustion chamber of each cylinder of the cylinder head to a combustion condition at another engine speed range by controlling a valve characteristic of intake or exhaust by an intake cam. The four-stroke parallel four-cylinder engine according to claim 1, wherein the control is performed by selecting and changing a cam profile of a shaft or an exhaust-side camshaft according to an engine speed.