JP3451638B2 - Scavenging device for engine with mechanical supercharger - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a scavenging device for scavenging exhaust gas in a combustion chamber in a cylinder with fresh air in an engine equipped with a mechanical supercharger.

[0002]

2. Description of the Related Art Conventionally, as a scavenging device for an engine of this type, as shown in, for example, Japanese Patent Laid-Open No. 61-58920, two intake valves and an exhaust valve are provided in a cylinder combustion chamber of the engine on both sides of the cylinder center. And one of the intake / exhaust valves diagonally opposed to the cylinder center is made larger in diameter than the other set, and the opening overlap period of these large intake / exhaust valves is By making it shorter than the other small-diameter intake / exhaust valves, it is possible to obtain a scavenging effect while preventing a portion of the fresh air supplied to the combustion chamber from blowing through to the exhaust port at low engine speeds. It has been known.

By the way, in an engine having a mechanical supercharger driven by the engine, intake air is pressurized and supplied by the supercharger, so that the intake / exhaust valve opening overlap period is set to a normal engine. By setting the value to be larger than that of the above, the scavenging effect of the combustion chamber can be enhanced. For example, in the engine disclosed in Japanese Patent Application Laid-Open No. 2-119641, in an engine with a supercharger, a valve timing variable mechanism is provided in one of intake / exhaust valves, and the valve timing variable mechanism controls the engine in a high load range. The scavenging property is improved by increasing the valve opening overlap period of the intake / exhaust valve, and the knocking resistance and the intake air charging efficiency are improved.

[0004]

[Problems to be Solved by the Invention] However, on the other hand,
Since the valve opening overlap period of the intake / exhaust valve is large, it is impossible to effectively prevent the above-mentioned blow-through of fresh air to the exhaust port. Especially in the low speed and high load range of the engine,
This is remarkable because the valve opening overlap period per unit time is relatively longer than in the high speed range.

The present invention has been made in view of the above points, and an object thereof is to improve the profile of a cam for opening and closing an intake / exhaust valve so that two intake / exhaust valves can be provided as in the former prior art. The present invention is not limited to the structure of a combustion chamber that requires an exhaust valve, but aims to achieve both reduction of fresh air blow-through and improvement of scavenging property.

[0006]

In order to achieve the above object, in the invention of claim 1 or 2, the intake / exhaust valve opening periods are overlapped at least in the high load region of the engine, and the overlap is caused. In the lap period, the period during which the opening area of the exhaust valve is larger than the opening area of the intake valve is shortened.

That is, according to the first aspect of the invention, the intake port opened and closed by the intake valve and the exhaust port opened and closed by the exhaust valve are arranged so that the openings to the cylinders face each other with the center of the cylinder in between. In a mechanical supercharged engine in which the center lines of the openings of the intake / exhaust ports are set in the same direction as each other, the valve opening periods are overlapped so that the valve opening periods overlap at least when the engine is in a high load range. Set the opening / closing timing of the intake / exhaust valve.

Further, the lift characteristics of the intake / exhaust valve due to the cam are set so that the lift amount of the intake valve at the closing timing of the exhaust valve is larger than the lift amount of the exhaust valve at the opening timing of the intake valve. In addition, the lift characteristics of the above exhaust valve should be set near the valve close.
The lift amount of
In the high speed range, the lift of the exhaust valve is reduced, and in the high speed range
Switching control that switches to increase the exhaust valve lift amount
Provide means.

On the other hand, in the second aspect of the present invention, the period during which the lift amount of the intake valve is larger than the lift amount of the exhaust valve is set to half or more of the entire valve opening overlap period of the intake / exhaust valve.

According to the third aspect of the present invention, the lift amount of the intake valve is changed to be larger than the lift amount of the exhaust valve during the ramp portion near the valve closing in the cam lift characteristic of the exhaust valve. .

[0011]

According to the fourth aspect of the invention, when the engine is in the low load region, the start timing of the ramp portion near the valve closing in the cam lift characteristic of the exhaust valve is before the top dead center of the piston.

According to the fifth aspect of the present invention, a mask portion having a predetermined height is provided on the periphery of the opening of the exhaust port and on the opening side of the intake port.

[0014]

With the above construction, in the invention of claim 1 or 2, the intake / exhaust valve opening periods overlap at least when the engine is in the high load region. Therefore, during this overlap period, the supercharger The supercharged fresh air can be supplied to the cylinder, and the exhaust gas in the cylinder can be sufficiently scavenged by the fresh air. Moreover, since the intake valve lift amount is larger than the exhaust valve lift amount in this overlap period, the exhaust port opening area is relatively smaller than the intake port due to the small lift amount exhaust valve. And the fresh air supplied from the intake port into the cylinder goes to the inner part of the cylinder and
It becomes difficult to flow to the exhaust port as it is. Therefore, it is possible to effectively achieve both suppression of blow-through of fresh air and improvement of scavenging property. At that time, the switching control means controls the exhaust valve
Shift characteristics are switched according to the engine speed range,
In the low speed range of gin, the lift amount near the exhaust valve closing is small.
Become. Therefore, the overlap period per unit time
In the low speed range where the
Exhaust of fresh air by making the opening area of the intake port smaller than the intake port
It is possible to suppress blow-through to the port. At this time,
Due to the large overlap of intake / exhaust valves,
Can be scavenged. On the other hand, in the high speed range of the engine
The lift amount near the closing of the air valve increases. Because of this, high
Even if the scavenging time is relatively shorter in the high speed range than in the low speed range,
Scavenging can be secured. Also in this high speed range
Indicates that the overlap period itself is relatively short compared to the low speed range.
Therefore, the lift amount near the exhaust valve closing becomes large.
Even so, the absolute amount of fresh air will be small. Therefore,
Reduction of blow-through of fresh air and scavenging over a wide rotation range
It is possible to achieve both improvement and

According to the third aspect of the present invention, since the lift amount of the intake valve becomes larger than the lift amount of the exhaust valve during the ramp portion near the valve closing in the cam lift characteristic of the exhaust valve, the intake valve during the overlap period. It is possible to easily achieve a larger lift amount than that of the exhaust valve, and it is possible to more effectively achieve both the reduction of blow-through of fresh air and the improvement of scavenging property.

[0016]

[0017]

In the fourth aspect of the invention, when the engine is in the low load range, the start time of the ramp portion near the valve closing in the cam lift characteristic of the exhaust valve is set before the top dead center of the piston. In the state where the piston moves downward after the dead center and the cylinder internal pressure decreases, the ramp portion always corresponds, and the carry-in of burnt gas discharged from the exhaust valve to the cylinder can be effectively reduced.

According to the fifth aspect of the present invention, since the mask portion having a predetermined height is provided on the periphery of the opening of the exhaust port and on the opening side of the intake port, it is supplied from the intake port into the cylinder during the overlap period. The fresh air can be suppressed from flowing to the exhaust port as it is by the mask portion, and the blow-through of fresh air can be more effectively reduced. That is, since the lift amount of the exhaust valve during the overlap period is small, the height of the mask portion is low, or the clearance between the mask portion and the valve seat portion at the opening of the exhaust port is large due to a processing error. However, the mask portion can effectively provide resistance to the flow of fresh air that flows in a short circuit from the intake port to the exhaust port, and the blow-through can be suppressed.

[0020]

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

(Embodiment 1) FIG. 3 shows the overall construction of Embodiment 1 of the present invention. Reference numeral 1 denotes an in-line four-cylinder engine having four cylinders 2, 2, ... As shown in the enlarged detail of FIG. 2, an intake valve 37 opens and closes a lower surface of a cylinder head 1a corresponding to each cylinder 2 described above. Two intake ports 3 and 3 and two exhaust ports 32 and 32 opened and closed by the exhaust valve 38 are opened. The openings of the intake ports 3 and 3 and the openings of the exhaust ports 32 and 32 are arranged on both sides of the cylinder center O so as to face each other with the cylinder center O interposed therebetween, and the opening of one intake port 3 and the one exhaust port 32 are arranged. 2 and the center lines of the other intake port 3 and the other exhaust port 32 are set in the same direction (the left-right direction in FIG. 2).

Each of the intake ports 3 constitutes a downstream end portion of the intake passage 4, and the intake passage 4 has four independent intake passages 5, 5, ...
And the four independent intake passages 5, 5, at the collecting portion 4a at the downstream end.
One collective intake passage 6 in which the upstream ends of ...
And an upstream end of the collective intake passage 6 is connected to an air cleaner 7 for cleaning intake air (intake air). An air flow meter 8 for detecting the intake air amount, a throttle valve 9 for narrowing the collective intake passage 6 (intake passage 4), are arranged in the collective intake passage 6 from the air cleaner 7 toward the downstream side.
A supercharger 10 that compresses intake air (intake air) to supercharge it, and an intercooler 2 that cools the air compressed by the supercharger 10.
1 and 1 are provided. Further, in the vicinity of the intake port 3 of each independent intake passage 5, an injector 2 for injecting and supplying fuel is provided.
2 are provided.

The supercharger 10 is an internal compression type mechanical supercharger, which includes male and female rotors 14 and 15 supported by rotating shafts 12 and 13 in a housing 11.
4 and 15 are gears 1 attached to the respective rotary shafts 12 and 13.
It rotates in the opposite direction due to the meshing of 6 and 17. A pulley 18 is attached to the rotary shaft 12 of the one rotor 14, and the pulley 18 is drivingly connected to a pulley 19 attached to the crankshaft 1b of the engine 1 via a transmission belt 20. The intake air is sucked into the housing 11 by rotating 14 and 15, and the air is compressed and discharged from the housing 11.

The relief passage 2 is provided in the collecting portion 4a of the intake passage 4 (the connecting portion between the independent intake passage 5 and the collective intake passage 6).
3 is connected to one end (upstream end), and the other end (downstream end) of the relief passage 23 is connected to the collective intake passage 6 on the upstream side of the supercharger 10 on the downstream side of the throttle valve 9 and the supercharger. A part of the air (intake air) discharged from the machine 10 is relieved to the intake passage 4 on the upstream side of the supercharger 10 by the relief passage 23. Further, the relief passage 23 is provided with a supercharging pressure control valve 24 which controls the supercharging pressure to the engine 1 by opening and closing the relief passage 23 and adjusting the relief amount. The control valve 24 is drivingly connected to an actuator 25.
The actuator 25 includes a diaphragm 26 connected to the valve 24, a pressure chamber 28 defined in the casing 27 by the diaphragm 26, and the pressure chamber 28.
And a spring 29 for urging the valve 24 in the closing direction, and the pressure chamber 28 communicates with the collecting portion 4a of the intake passage 4 via a boost pressure introducing passage 30. A duty solenoid valve 31 is arranged in the supercharging pressure introducing passage 30. The duty solenoid valve 31 is controlled to adjust the introduction pressure into the pressure chamber 28 to control the supercharging pressure. When the opening degree of the valve 31 is increased, the pressure introduced into the pressure chamber 28 is increased to decrease the opening degree of the boost pressure control valve 24 and the relief amount is decreased to increase the boost pressure, while the duty solenoid is increased. When the opening degree of the valve 31 is reduced, the pressure introduced into the pressure chamber 28 is lowered to increase the opening degree of the supercharging pressure control valve 24, and the relief amount is increased to lower the supercharging pressure. .

On the other hand, the exhaust port 32 of each cylinder 2 constitutes an upstream end portion of the exhaust passage 33, and the exhaust passage 33 has four independent exhaust passages 34, 34 whose upstream end is the exhaust port 32. , And one collective exhaust passage 35 in which the downstream ends of the four independent exhaust passages 34, 34, ... Are collectively connected to the upstream end collecting portion 33a. An exhaust gas purification device 36 that purifies the exhaust gas is provided.

The engine 1 is equipped with a suction / removal mechanism for each cylinder 2.
A valve mechanism 39 for opening and closing the exhaust valves 37, 38 is provided. The valve mechanism 39 is used for the crankshaft 1 of the engine 1.
b has intake and exhaust camshafts 41 and 42 which are rotationally driven in synchronization via the timing pulleys 40 and 40 and a timing belt (not shown). The intake camshaft 41 includes two cylinders of each cylinder 2. Intake valves 37, 37
Cams 43 and 43 are formed corresponding to
Each cam 43 pushes the rocker arm 44 to swing it around the shaft 45 to open and close the intake valve 37.

On the other hand, the exhaust camshaft 42 is formed with two first cams 46, 46 and one second cam 47 corresponding to each cylinder 2, and these two types of cams 46, 47 are provided. Rocker arm 4 by either one of
8 and 49 are pushed and rocked around the shaft 58 to open / close the exhaust valve 38. That is, the valve operating mechanism 39 is provided with an exhaust valve lift switching mechanism 50 for switching the use of the cams 46 and 47 for each cylinder 2 to change the lift characteristic of the exhaust valve 38 in two ways. As shown in FIGS. 4 and 5, the two second cams 47, 47 are the same as the first cam 4.
It is arranged on both sides of 6. The rocker arm is also composed of a first rocker arm 48 which is pushed by the first cam 46 and two second rocker arms 49 and 49 which are arranged side by side and are pushed by the second cams 47 and 47, respectively. The upper ends of the valve stems of the exhaust valves 38 are in contact with the tips of the respective second rocker arms 48, 49.

Further, as shown in FIG. 5, a through hole 51 extending in parallel with the cam shaft 42 is formed in an intermediate portion of the central first rocker arm 48, and each through hole 51 has a side surface of the first rocker arm 48. A pair of engaging pins 52, 52 that can be retracted from the housing are slidably accommodated. Also, the first rocker arm 4 of the second rocker arm 49, 49 on both sides
8, the engaging hole 5 is provided on the side surface facing the through hole 5 corresponding to the through hole 51.
3 is formed in the engaging hole 53, and the spring receiver 5 that comes into contact with the tip of the engaging pin 52 of the first rocker arm 48 is formed in the engaging hole 53.
4 is slidably fitted. This spring receiver 5
4 is urged in a direction in which the engaging pin 52 is retracted by a spring 55 that is compressed between the engaging hole 53 and the bottom of the engaging hole 53, and the stroke end thereof is positioned so as not to project from the side surface of the second rocker arm 49.

Further, a hydraulic pressure supply path 56 for supplying hydraulic pressure is provided in the through hole 51 on the rear surface side of the engagement pin 52 in the first rocker arm 48, and as shown in FIG. 57 is provided. Then, when the electromagnetic valve 57 is closed, hydraulic pressure is not applied to the back side of each engagement pin 52, and the engagement pin 52 is pushed back by the urging force of the spring 55 so as to be retracted into the through hole 51. 48 and second rocker arm 49,4
By disconnecting the connection with 9, the exhaust valve 38 is opened and closed by the second cam 47. On the other hand, when the solenoid valve 57 is opened, hydraulic pressure is applied to the back side of each engagement pin 52, the engagement pin 52 is projected from the through hole 51 against the biasing force of the spring 55, and the tip end thereof is provided. The half portion is engaged with the engagement hole 53 of the second rocker arm 49, and by this engagement pin 52, the first rocker arm 48 and the second rocker arms 49, 49.
The exhaust valve 38 is connected to the first
The cam 46 is adapted to open and close.

As a feature of the present invention, as shown in FIG.
The valve operating mechanism 39 sets the opening / closing timings of the intake / exhaust valves 37, 38 so that the valve opening periods overlap in the entire operating range including the high load range of the engine 1.
Further, the profile of the cam crests of the first and second cams 46, 47 of the exhaust camshaft 42 is such that, when the exhaust valve 38 is lifted, the lift amount at least near the valve closing differs between large and small. As shown in FIG. 1, the lift amount of the second cam 47 near the valve closing of the lift characteristic of the exhaust valve 38 is set to be smaller than the lift amount of the first cam 46 near the valve closing of the same lifting characteristic. There is. The lift characteristic of the exhaust valve 38 by the first cam 46 is determined by the intake valve 37.
It has the same lift characteristics. Due to the lift characteristic of the exhaust valve 38 by the second cam 47, the lift amount h of the intake valve 37 at the closing timing of the exhaust valve 38 is larger than the lift amount H of the exhaust valve 38 at the opening timing of the intake valve 37. To (h
> H), in other words, the lift amount of the intake valve 37 depends on the exhaust valve 38.
Of the intake / exhaust valves 37, 3 for a period greater than the lift amount of
It is set so as to be half or more of the entire valve opening overlap period TOL of 8. More specifically, in the cam lift characteristic of the exhaust valve 38, the lift amount of the intake valve 37 is changed to be larger than the lift amount of the exhaust valve 38 during the ramp portion R near the valve closing, In addition, the start timing r of the ramp portion R is the top dead center T of the piston (not shown).
It is said to be before DC.

The supercharging pressure control valve 24, each injector 22 and the solenoid valve 57 are controlled by a control unit 61. The control unit 61 includes a crankshaft 1b of the engine 1.
At least the output signal of the engine rotation speed sensor 63 for detecting the engine rotation speed by the rotation and the output signal of the air flow meter 8 are input.

Then, by the signal processing of the CPU in the control unit 61, the fuel injection amount is set based on the signal from the air flow meter 8 and the output signal of the engine speed sensor 63, and the set injection is performed in the intake stroke of each cylinder 2. A quantity signal is output to the injector 22 so that fuel is injected and supplied from the injector 22 in the intake stroke.

Further, the control unit 61 is provided with a switching control section 64 constituted by the signal processing function of the CPU, and the switching control section 64 controls the exhaust valve lift switching mechanism 50 as follows. Is configured. That is, the electromagnetic valve 57 in the exhaust valve lift switching mechanism 50 is opened / closed according to the rotation range of the engine 1,
In the low speed range of the engine 1, the electromagnetic valve 57 is closed to disconnect the connection between the first rocker arm 48 and the second rocker arms 49, 49, so that the exhaust valve 38 is opened and closed by the second cam 47 to lift the exhaust valve 38. By switching the characteristics so that the lift amount near the valve closing becomes small, in the high speed region of the engine 1, the solenoid valve 57 is opened to integrally connect the first and second rocker arms 48, 49. The exhaust valve 38 is driven to open and close by the first cam 46, and its lift characteristic is switched so that the lift amount near the valve is increased.

Next, the operation of the above embodiment will be described. During operation of the engine 1, when the piston is near the top dead center TDC at the end of the exhaust stroke (early of the intake stroke), suction /
The opening of the exhaust valves 37 and 38 overlap, and during this overlap period TOL, the fresh air supercharged by the supercharger 10 is supplied into each cylinder 2, and the inside of the cylinder 2 is sufficiently filled by this fresh air. Be scavenged.

At the same time, the control unit 61 switches the solenoid valve 57 to open and close to control the exhaust valve lift switching mechanism 50, and the lift characteristic of the exhaust valve 38 in the overlap period TOL with the intake valve 37 changes. . That is, in the low speed range of the engine 1, the electromagnetic valve 57 is closed to disconnect the connection between the first rocker arm 48 and the second rocker arms 49, 49, which causes the two exhaust valves 38, 38 of each cylinder 2 to move to the second exhaust valve 38, 38. It is opened and closed by a cam 47. In the lift characteristic of the exhaust valve 38 by the second cam 47, as shown in FIG. 1, the ramp portion R near the valve is closed.
Since the lift amount of the intake valve 37 is changed to become larger than the lift amount of the exhaust valve 38 during the period of, and the lift amount of the exhaust valve 38 is set to be small, the intake / exhaust valve 37, 38 overlap period TOL per unit time
Even in the low speed range where is relatively longer than the high speed range, the lift amount of the intake valve 37 is longer than the exhaust valve 38 in the overlap period TOL, and the lift amount of the exhaust valve 38 is increased during that period. It becomes smaller than the intake valve 37 and the opening area of the exhaust port 32 becomes relatively smaller than that of the intake port 3, and the fresh air supplied from the intake port 3 into the cylinder 2 flows to the exhaust port 32 in a short-circuited manner. It becomes difficult, and the blow-through of fresh air can be reduced.

At this time, since the start timing r of the ramp portion R in the cam lift characteristic of each exhaust valve 38 is set before the top dead center TDC of the piston, the top dead center TDC thereof is set.
In the state where the piston is lowered and the pressure in the cylinder 2 is lowered after the above, the ramp portion R always corresponds. As a result, even if scavenging is not possible when the engine 1 has a low load, the backflow of burnt gas from the exhaust valve 38 can be suppressed instead.

Incidentally, FIG. 6 shows the configuration of the first embodiment,
Specifically, the flow of fresh air is displayed by its velocity vector, and the crank angle increases in accordance with FIG. 6 (a) → (d). Further, FIG. 13 shows the same characteristic in the conventional example in which the lift amount of the exhaust valve 38 is set large, and FIG. 14 shows another conventional example in which a mask portion 59 'is projected between the intake / exhaust port openings in this conventional example. The same characteristics in each example are shown.
Comparing FIG. 6 with FIG. 13 and FIG. 14, the flow of the fresh air supplied from the intake port 3 into the cylinder 2 toward the exhaust port 32 is suppressed as it is, and in particular, the gas is exhausted below the exhaust valve 38. It can be seen that the air flows in the direction opposite to the direction toward the opening of 32, and the blow-through of fresh air is reduced.

On the other hand, in the high speed range of the engine 1, the solenoid valve 57 is opened to connect the first rocker arm 48 and the second rocker arm 49, 49, whereby the exhaust valves 38, 38 is opened and closed by the first cam 46. The lift characteristic of the exhaust valve 38 by the first cam 46 is the same as that of the intake valve 37 as shown in FIG. 1, and the lift amount near the closed position of the exhaust valve 38 becomes large. Therefore, even if the scavenging time becomes shorter in the high speed region than in the low speed region, the scavenging property can be secured. still,
In this high speed range, the overlap period TOL itself becomes relatively shorter than in the low speed range, so the exhaust valve 38
The absolute amount of fresh air blow-through is small even if the lift amount in the vicinity of the valve is increased.

Therefore, in this embodiment, it is possible to effectively achieve both reduction of blow-through of fresh air and improvement of scavenging property over a wide rotation range of the engine 1 from a low speed region to a high speed region.

(Embodiment 2) FIG. 7 shows Embodiment 2 of the present invention (note that the same parts as those in FIG. 2 are designated by the same reference numerals and their detailed description will be omitted).

In this embodiment, on the lower surface of the cylinder head 1a of the engine 1, a mask having a predetermined height is formed on the periphery of the opening of the two exhaust ports 32, 32 corresponding to each cylinder 2 and on the opening side of the intake ports 3, 3. The part 59 is integrally provided.

Therefore, in the case of this embodiment, the mask portion 59 having a predetermined height is provided on the opening peripheral edge of each exhaust port 32 and on the opening side of the intake port 3, and the exhaust valve 38 is closed during the overlap period TOL. Since the lift amount in the vicinity of the valve is small, the height of the mask portion 59 is low, or the clearance between the mask portion 59 and the valve seat portion at the opening of each exhaust port 32 is large due to the processing error. Even if there is, resistance is given by the mask portion 59 to the flow of fresh air flowing from the intake port 3 to the exhaust port 32 in a short circuit during the overlap period TOL, and the fresh air is prevented from flowing to the exhaust port 32 as it is. As a result, the blow-through of fresh air can be reduced more effectively.

FIG. 8 shows the flow of fresh air in the second embodiment.
It can be seen that the mask portion 59 effectively suppresses the flow of fresh air supplied from the intake port 3 into the cylinder 2 toward the exhaust port 32 as it is.

(Specific Example) According to the present inventor, the conventional example in which the lift characteristic of the exhaust valve 38 during the overlap period TOL of the intake / exhaust valves 37, 38 is made equal to that of the intake valve 37, and the exhaust valve 38 is closed. For the example of the present invention in which the lift amount in the vicinity of the valve was made small, the amount of blow-through fresh air and the scavenging amount (the residual gas amount discharged from the cylinder 2) during the overlap period TOL were specifically measured. The results shown in FIG. 12 were obtained.

There are two kinds of overlap periods TOL of the intake / exhaust valves 37 and 38. One is the intake valve 37 opened at a crank angle of 34 ° before top dead center and the crank of 13 ° after top dead center. During the large overlap period (47 ° in crank angle) where the exhaust valve 38 closes at a corner, the intake valve 37 opens at a crank angle of 17 ° before top dead center and the crank angle of 6.5 ° after top dead center in other cases. Thus, the exhaust valve 38 is closed during a small overlap period (crank angle is 23.5 °). The lift characteristics of the intake / exhaust valves 37 and 38 during the large overlap period are shown in FIG. 9, and the same characteristics during the small overlap period are shown in FIG. 11 (only the example of the present invention is shown). Further, the engine speed at the time of measurement is 1500 rpm, and the supercharging ability of the supercharger 10 is constant.

According to FIGS. 10 and 12, although the scavenging amount is slightly reduced in the example of the present invention as compared with the conventional example, the blow-through amount of fresh air can be reduced, and particularly in the case of a large overlap period, a remarkable effect is obtained. . Further, it can be seen that in the case where the mask portion 59 is provided (Embodiment 2 of the present invention), it is possible to secure an increase in the scavenging amount and reduce the fresh air blow-through amount.

In each of the above embodiments, the opening / closing of the intake / exhaust valves 37, 38 is made to overlap over the entire operating region of the engine 1, but at least in the high load region. You may Also,
The start timing r of the ramp portion R in the cam lift characteristic of the exhaust valve 38 before the top dead center TDC of the piston may be limited to the low load region of the engine 1.

In the above embodiment, the number of intake / exhaust ports 3 and 32 is two, but the present invention has one intake / exhaust port 3 and one intake port. It can also be applied to an engine with a mechanical supercharger having three exhaust ports and two exhaust ports.

[0049]

As described above, according to the first aspect of the invention, the openings of the intake port opened and closed by the intake valve and the exhaust port opened and closed by the exhaust valve to the cylinder face each other with the center of the cylinder interposed therebetween. And the center lines of the openings of the intake / exhaust ports are set in the same direction as each other, the valve opening periods overlap when the engine is at least in the high load region. The intake / exhaust valve opening / closing timing is set so that
The lift characteristics due to the cam of the exhaust valve are set so that the lift amount of the intake valve at the closing timing of the exhaust valve is larger than the lift amount of the exhaust valve at the opening timing of the intake valve. Further, in the invention of claim 2, the period in which the lift amount of the intake valve is larger than the lift amount of the exhaust valve is set to half or more of the entire valve opening overlap period of the intake / exhaust valves. And the exhaust valve riff
Multiple characteristics are set so that the lift amount near the valve is different.
Then, in the low speed range of the engine, reduce the above lift amount,
Configuration to switch to increase the lift amount in the high speed range
And Therefore, according to these inventions, the period during which the lift amount of the intake valve is larger than that of the exhaust valve in the overlap period is lengthened, and the opening area of the exhaust port can be made relatively smaller than that of the intake port during that period. It is possible to suppress the fresh air supplied to the cylinder from flowing to the exhaust port as it is. Therefore, with a simple structure that changes the lift characteristics of the intake / exhaust valve, it is possible to improve the scavenging property while satisfactorily reducing the blow-by of fresh air With that ability ,
A wide engine with both reduced blow-through and improved scavenging performance
It can be achieved over the rotation range.

According to the third aspect of the present invention, the lift amount of the intake valve is changed to be larger than the lift amount of the exhaust valve during the ramp portion near the valve closing in the cam lift characteristic of the exhaust valve. Thus, it is possible to easily achieve a lift amount of the intake valve larger than that of the exhaust valve in the overlap period, and it is possible to more effectively achieve both reduction of blow-through of fresh air and improvement of scavenging property.

[0051]

According to the fourth aspect of the invention, when the engine is in the low load region, the start time of the ramp portion near the valve closing in the cam lift characteristic of the exhaust valve is before the top dead center of the piston, so that the top dead center. When the piston lowers and the cylinder internal pressure decreases after, the ramp portion can always be made to correspond, and carry-in of discharged burned gas to the cylinder can be suppressed.

According to the fifth aspect of the invention, the mask portion having a predetermined height is provided on the opening peripheral side of the exhaust port on the opening side of the intake port, so that the air is supplied from the intake port into the cylinder during the overlap period. It is possible to suppress the fresh air from directly flowing to the exhaust port by the mask, and to more effectively reduce the blow-through of the fresh air.

[Brief description of drawings]

FIG. 1 is a characteristic diagram showing lift characteristics of an intake / exhaust valve according to a first embodiment of the present invention.

FIG. 2 is a plan view showing the positions of intake / exhaust ports that open to the cylinder in the first embodiment.

FIG. 3 is an overall configuration diagram of an intake / exhaust system of the engine.

FIG. 4 is a schematic front view schematically showing an exhaust valve lift switching mechanism.

FIG. 5 is a schematic plan view schematically showing an exhaust valve lift switching mechanism.

FIG. 6 is an explanatory diagram specifically showing movements of fresh air and combustion gas during an overlap period.

FIG. 7 is a view corresponding to FIG. 2 showing a second embodiment of the present invention.

8 is a view corresponding to FIG. 6 showing the second embodiment.

FIG. 9 is a characteristic diagram specifically showing lift characteristics of intake / exhaust valves during a large overlap period.

FIG. 10 is a characteristic diagram specifically showing a fresh air blow-through amount and a scavenging amount in a large overlap period.

FIG. 11 is a characteristic diagram specifically showing lift characteristics of intake / exhaust valves during a small overlap period.

FIG. 12 is a characteristic diagram specifically showing a fresh air blow-through amount and a scavenging amount in a small overlap period.

13 is a view corresponding to FIG. 6 showing a conventional example.

FIG. 14 is a view corresponding to FIG. 6 showing another conventional example.

[Explanation of symbols]

1 engine 2 cylinders 3 intake ports 10 supercharger 32 exhaust port 37 Intake valve 38 Exhaust valve 43 Intake cam 46,47 Exhaust cam 50 Exhaust valve lift switching mechanism 59 Mask part 61 Control unit 64 switching control unit (switching control means) R lamp section Tol overlap period H Exhaust valve lift when intake valve opens h Intake valve lift when exhaust valve is closed r Lamp start time

─────────────────────────────────────────────────── ─── Continuation of the front page (56) References JP-A-2-119641 (JP, A) JP-A-63-289207 (JP, A) Actual development Shou 63-170533 (JP, U) (58) Field (Int.Cl. ⁷ , DB name) F02B 29/08

Claims (5)

(57) [Claims] 1. An intake port opened / closed by an intake valve and an exhaust port opened / closed by an exhaust valve are arranged so that their openings to the cylinder are opposed to each other with the center of the cylinder interposed therebetween, and In the engine with a mechanical supercharger in which the center lines of the openings are set in the same direction, the opening / closing timings of the intake / exhaust valves are set so that the valve opening periods overlap at least when the engine is in the high load range. and sets, the lift characteristics of the cams of the intake / exhaust valve, set to the lift amount of the timing of the intake valve closing of the exhaust valve to lift amount of the exhaust valve opening timing of the intake valve is increased, the exhaust valve The lift characteristics of the
Set to multiple, and the lift amount of the above exhaust valve is reduced in the low speed range of the engine.
However, in the high speed range, the exhaust valve lift
A scavenging device for an engine with a mechanical supercharger, which is provided with a switching control means for changing over. 2. The scavenging device for an engine with a mechanical supercharger according to claim 1, wherein a period during which the lift amount of the intake valve is greater than the lift amount of the exhaust valve is the entire intake / exhaust valve opening overlap period. The scavenging device for an engine with a mechanical supercharger, which is characterized in that it is more than half of the above. 3. The scavenging device for an engine with a mechanical supercharger according to claim 1, wherein the lift amount of the intake valve is greater than the lift amount of the exhaust valve during the period of the ramp portion near the valve closing in the cam lift characteristic of the exhaust valve. A scavenging device for an engine with a mechanical supercharger, characterized in that it is configured so that it also increases. 4. The scavenging device for an engine with a mechanical supercharger according to claim 1, wherein in a low load region of the engine, the start time of the ramp portion near the valve closing in the cam lift characteristic of the exhaust valve is set to the top dead center of the piston. A scavenging device for an engine with a mechanical supercharger, which is characterized by what was done before. 5. A scavenging device for an engine with a mechanical supercharger according to claim 1, wherein a mask portion having a predetermined height is provided at the periphery of the opening of the exhaust port and at the opening side of the intake port. Scavenging device for a supercharged engine.