JPH0128209B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to an intake system for a multi-cylinder engine equipped with a supercharger. This invention relates to a device that improves scavenging action and prevents knocking.

(Prior Art) Conventionally, it has been known to provide a supercharger in the intake passage of an engine to supercharge the intake air, thereby increasing the filling efficiency of the intake air and increasing output.

In addition, as disclosed in Japanese Utility Model Publication No. 45-2321, a technique for obtaining a supercharging effect using intake pressure waves generated in the intake passage of an engine has conventionally been used in a single-cylinder engine to reduce the size of the intake pipe. Separated into two different passages, each with a separate intake port, the two intake passages are used at high engine speeds, and the lower intake passage is closed at low engine speeds, allowing for early intake. By occluding the intake air, it is possible to obtain suitable charging efficiency over a wide range of engine speeds by utilizing the supercharging effect caused by the occlusion of the intake air at the maximum pressure of the intake air, which is a function of the intake pipe dimensions and engine speed. It has been proposed that However, this method is for a single-cylinder engine, and it is not clear how to use the intake pressure waves generated in the intake passage, its structure, and operation, and it cannot be put into practical use right away. It was hot.

By the way, in a supercharged engine such as the one mentioned above, the intake air temperature increases due to the increase in intake pressure due to supercharging, so knocking is likely to occur in the low engine speed operating range, especially in the high temperature, high load, low speed operating range. There is.

Therefore, conventionally, in an engine equipped with an exhaust turbo supercharger, a wastegate valve is provided in the exhaust passage upstream of the turbine, and the operation of the wastegate valve is controlled by the intake pressure (supercharging pressure) downstream of the propeller. It is well known that the intake pressure downstream of the blower (supercharger) can be kept constant so as not to exceed a set value by letting part of the exhaust gas flow down bypassing the turbine, thereby preventing knocking. However, the prevention effect was insufficient, especially in the engine high temperature, high load, and low engine speed range.

It is also known that improving air scavenging is an effective means for preventing knocking. However, although this can be done by lengthening the overlapping period of the intake and exhaust valves to allow sufficient intake air to blow through, there is a problem in that the fuel efficiency in the normal driving range is significantly deteriorated.

(Purpose of the Invention) Therefore, in view of the above, the present invention provides an engine with a supercharger, which has an intake characteristic that when the intake port is closed, the intake air is compressed due to the inertia of the intake air, and a compression wave is generated in the intake port portion. Based on this knowledge, we have discovered that, as an engine characteristic, in the low engine speed operating range where knocking is likely to occur, the intake pressure (supercharging pressure) downstream of the supercharger is greater than the exhaust pressure applied to the exhaust port. Therefore, in a multi-cylinder engine with a supercharger, if the compression wave when the intake port of one cylinder is closed is applied immediately after the intake port of another cylinder is opened in the above operating range, the supercharging effect can be effectively achieved. The supercharging effect due to this intake inertia effect allows the intake and exhaust system to be improved even with a simple configuration by making slight design changes to the existing intake system. To effectively prevent knocking by improving scavenging action without prolonging a valve overlap period, ie, without causing deterioration of fuel efficiency.

(Structure of the Invention) The technical solution of the present invention to achieve this object is to select an arbitrary cylinder in the intake passage downstream of the supercharger in a multi-cylinder engine equipped with a supercharger, and after the intake port of the cylinder is closed. The length of the intake passage between the other cylinders that opens the intake port earliest is determined by the length of the intake passage between the other cylinders, and the intake port of one cylinder is closed in the engine operating range where the intake pressure downstream of the supercharger is greater than the exhaust pressure acting on the exhaust port. The compression wave generated in the intake port is set so that it propagates immediately after the intake port of the other cylinder opens to perform supercharging. As a result, due to the supercharging effect due to the so-called intake inertia effect, that is, when the intake and exhaust valves of the cylinder overlap, the intake pressure increases due to the propagation of the compression wave at the time of closing, and the pressure difference between intake and exhaust becomes extremely large. As a result, the blow-through of intake air is significantly promoted and scavenging is performed well.

Here, the length L of the intake passage between cylinders to obtain the above-mentioned intake inertia effect is L=(360-θ+θ ₀ )×(60/360・N)×a
...It is set to the value determined by the formula (). In the above equation (), θ is the opening timing of the intake port,
θ ₀ is the period from when the compression wave is substantially generated when the intake port is closed until the intake port is closed, and from when the intake port is opened until the time when the compression wave is propagated when the intake port is closed to effectively perform supercharging. Therefore, (360 - θ + θ ₀ ) is the period from the generation of a compression wave at the time of closing in one cylinder to the time when the intake port of another cylinder opens the earliest after the intake port of that cylinder is closed. Represents the rotation angle of the crankshaft required for propagation to the immediately following direction. Also, N is the engine rotation speed, and (60/360N) represents the time (seconds) required to rotate 1°. Further, a is the propagation velocity (sound velocity) of the pressure wave (compression wave). In addition, the above ()
The equation ignores the effect of the intake air flow on the propagation of the pressure wave, since the flow velocity is small compared to the speed of sound and causes little change in the length of the intake passage.

(Effects of the Invention) Therefore, according to the present invention, in a multi-cylinder engine with a supercharger, the supercharging effect due to the intake inertia effect is reduced between the cylinders in the engine low-speed operating range where the supercharging pressure is greater than the exhaust pressure. As a result, even with a simple configuration by making slight design changes to the existing intake system, it is possible to shorten the overlap period of intake and exhaust air and improve the scavenging effect while ensuring good fuel efficiency. It is possible to effectively prevent the occurrence of knocking, and also to facilitate its implementation and reduce costs.

(Example) Hereinafter, an example as a specific example of the technical means of the present invention will be described based on the drawings.

1 and 2 show a first embodiment as a basic structural example in which the present invention is applied to a two-cylinder four-stroke engine. In the figure, 1A and 1B are the first cylinder and the second cylinder, and 2 is each cylinder 1A,
1B is a combustion chamber formed by a cylinder 3 and a piston 4.

Reference numeral 5 denotes a main intake passage whose one end opens to the atmosphere via an air cleaner 6 to supply intake air to each cylinder 1A, 1B, and an air flow meter 7 for detecting the intake air flow rate is provided in the main intake passage 5. A throttle valve 8 is provided downstream of the air flow meter 7 to control the amount of intake air. The main intake passage 5 includes first and second intake passages 5a and 5b having the same shape and dimensions downstream of the throttle valve 8.
After being branched into, the combustion chambers 2, 2 of the respective cylinders 1A, 1B are communicated via intake ports 9, 9, respectively.

Electromagnetic valve type fuel injection nozzles 10, 10 are provided in each of the intake passages 5a, 5b, respectively, and the combustion injection amount is controlled according to the intake air flow rate based on the output of the air flow meter 7.

Further, a branch portion of the main intake passage 5 is located downstream of the throttle valve 8, and constitutes a communication passage 11 that communicates the first and second intake passages 5a, 5b with each other. The passage area Ac of the communication passage 11 is set to be equal to or larger than the minimum passage area A of each intake passage 5a, 5b (Ac≧A), so that pressure waves can be propagated effectively with less attenuation. I have to. Although not shown in the figure, there is a connection between the throttle valve 8 of the main intake passage 5 and the branch part (communication passage 11) to prevent surging of intake air during transient operation such as during acceleration or deceleration of the engine. It is preferable to provide a surge tank with a predetermined volume to prevent surges and ensure good response of the fuel.

Further, 12a and 12b are first and second exhaust passages, each of which has one end connected to the combustion chambers 2, 2 of each cylinder 1A, 1B via exhaust ports 13, 13, and discharges exhaust gas from the combustion chamber 2. The downstream ends of each of the exhaust passages 12a and 12b are respectively combined into the main exhaust passage 12 and then opened to the atmosphere, and a catalyst device 14 for purifying exhaust gas is provided in the middle of the main exhaust passage 12. is interposed. still,
15 is an intake valve that opens and closes the intake port 9, and 16 is an exhaust valve that opens and closes the exhaust port 13.

On the other hand, 17 is an exhaust turbo supercharger, and the supercharger 17 includes a turbine 17a disposed upstream of the catalyst device 14 in the main exhaust passage 12 and rotationally driven by the exhaust gas flow, and a main intake passage. The blower 17b is disposed between the air flow meter 7 of No. 5 and the throttle valve 8 and is driven by the turbine 17a.
This supercharges A and 1B.

Further, reference numeral 18 denotes a bypass passage which has one end opened upstream of the turbine 17a of the main exhaust passage 12 and the other end opened downstream of the turbine 17a to bypass the turbine 17a. A waste gate valve 19 is provided which is operated and controlled according to the intake pressure (supercharging pressure) in the main intake passage 5 of the engine. is opened to cause the exhaust gas flow to flow down through the bypass passage 18, bypassing the turbine 17a, thereby maintaining the supercharging pressure at a constant level so as not to exceed a set value. That is, as shown in FIG. 5, the supercharging pressure, that is, the intake pressure Pin downstream of the supercharger 17 (blower 17b), temporarily increases as the engine speed increases, even at a relatively steep slope, and then increases. ,
The characteristics are set such that when the rotation speed exceeds a predetermined value, the waste gate valve 19 is operated to maintain the set value. On the other hand, turbine 1
The exhaust pressure upstream of 7a, that is, the exhaust pressure Pex acting on the exhaust port 13, gradually increases as the engine speed increases, and when it exceeds a predetermined speed, the pressure becomes higher than the set upper limit supercharging pressure. show. Therefore, as shown in Figure 5, the above intake pressure Pin
In the engine operating range where Pex is greater than the exhaust pressure Pex, for example, in the low engine speed region of 2000 to 4000 rpm, the exhaust pressure Pex is greater than the intake pressure.
When the engine is operated at a speed higher than Pin, for example, a high engine speed region of 5000 rpm or more will occur.

In addition, the above connection between the first cylinder 1A and the second cylinder 1B, which is the other cylinder whose intake port 9 is opened earliest after the intake port 9 of the first cylinder 1A is closed (the intake valve 16 is closed). Intake passage length L via passage 11 (that is, intake port 9 of both cylinders 1A, 1B,
9) is the passage length lc of the communication passage 11 and the first and second intake passages 5a, 5 downstream of the communication passage 11.
The sum of the path lengths l and l of b (L=lc
+2l), and in the engine operating range where the intake pressure Pin is greater than the exhaust pressure Pex, both cylinders 1A and 1B
The value is set to the value determined by the above equation () so as to obtain the intake inertia effect between the two. in particular,
Intake port opening period θ (intake valve opening period) = 230
~270°, invalid period θ ₀ = 30°, engine speed N =
When 2000 to 4000 rpm and sound velocity a = 376 m/s (at 80°C), L = 1.88 to 5.01 m from equation ().

Next, the operation of the first embodiment will be explained with reference to FIG. 6. As shown in FIG.
(Blower 17b) The engine operating range where the downstream intake pressure Pin (supercharging pressure) is larger than the exhaust pressure Pex acting on the exhaust port 13, that is, the engine low-speed operating range where knocking is likely to occur (for example, 2000
~4000rpm), from the above relationship of Pin>Pex,
When one cylinder, for example, the intake port 9 of the first cylinder 1A, is closed, the compression wave generated near the intake port 9 is determined by setting the passage length L between both cylinders 1A and 1B to the value determined by the above equation (). As a result, the air is effectively propagated through the first intake passage 5a → the communication passage 11 → the second intake passage 5b immediately after the intake port 9 of the second cylinder 1B, which is another cylinder, is opened. As a result, this compression wave at closing forces the intake air into the combustion chamber 2 from the intake port 9 of the second cylinder 1B at the beginning of the intake stroke, thereby performing supercharging (intake inertia effect). Similarly, in the first cylinder 1A, the closing compression wave propagates from the second cylinder 1B to the intake port 9 at the beginning of the intake stroke, thereby performing supercharging.

Therefore, due to the supercharging effect due to the intake inertia effect between the cylinders 1A and 1B, the intake pressure immediately after the opening of the intake port 9 of each cylinder 1A and 1B, that is, when the intake and exhaust valves overlap, is equal to the above Pin. In addition to this, the pressure of the propagated compression wave at the time of closing is added, and the differential pressure with the exhaust pressure Pex increases significantly, thereby significantly promoting the blow-through of intake air. As a result, it is possible to improve the scavenging action while keeping the overlap period of the intake and exhaust valves short, thereby effectively preventing the occurrence of knocking while ensuring good fuel efficiency.

In that case, the first and second intake passages 5a and 5, which are pressure wave propagation paths for obtaining the intake inertia effect,
b and the communication passage 11 (branching part of the main intake passage 5) are located downstream of the throttle valve 8, so the pressure waves (compression waves) are not attenuated by the throttle valve 8, and the communication passage 11 is located downstream of the throttle valve 8. Communication area Ac
is greater than or equal to the minimum passage area A of each intake passage 5a, 5b, so that the resistance to the propagation of pressure waves is small;
Therefore, the above-mentioned intake inertia effect can be effectively exerted.

Furthermore, the fuel injection nozzle 10 as a fuel supply device includes each intake passage 5a, 5b downstream of the communication passage 11.
Therefore, it is possible to prevent deterioration of fuel responsiveness due to an increase in the length of the intake passage and ensure good fuel responsiveness.

In addition, the supercharging effect due to the intake inertia effect can be obtained by setting the passage length L between the two cylinders 1A and 1B as described above, so a slight design change to the existing intake system is required, and the structure is extremely simple and therefore can be implemented easily and at low cost.

It should be noted that the present invention is not limited to the above-mentioned embodiments, but also includes various other modifications. For example, although the first embodiment described above shows an example in which the present invention is applied to a two-cylinder four-stroke engine, the present invention can also be applied to various other multi-cylinder engines. For example, as an example, FIG. 3 shows a second embodiment applied to a four-cylinder, four-stroke engine (the same parts as in the first embodiment are given the same reference numerals and their explanations are omitted).

In this example, the first to fourth intake passages 5a to 5 communicate with the cylinders 1A to 1D via intake ports 9, respectively.
5d is connected to a branch 11' downstream of the throttle valve 8 of the main intake passage 5, and is connected to the branch 11' of the main intake passage 5.
Intake passage 5 from 1 to intake port 9 of each cylinder
The lengths of a, 5b, 5c, and 5d are set to be equal. Furthermore, the first cylinder 1A, the fourth cylinder 1D, and the fourth cylinder 1D, which are in the relationship between any cylinder in the 1-3-4-2 ignition order and the other cylinder whose intake port opens earliest after the intake port of that cylinder is closed, 2 cylinder 1
Inter-cylinder passage length between B and third cylinder 1C
L _1-4 and L _2-3 are each set to the values determined by the above formula (), and the above L _{1- 4} and L _2-3 are preferably set to be substantially the same as shown in the figure. Therefore, as shown in FIG. 7, the mode of action of the intake inertia effect is as follows: 1st cylinder → 4th cylinder, 3rd cylinder → 2nd cylinder, 4th cylinder →
Supercharging is performed by acting sequentially on the first cylinder, second cylinder, and third cylinder, thereby improving scavenging.

Further, FIG. 4 shows a third embodiment applied to an in-line six-cylinder four-stroke engine. In this example, the intake passages 5a to 5f of each cylinder 1A to 1F are branched downstream of the throttle valve 8 of the main intake passage 5, and the communication passage 1
1", and are set to have the same length. Also, in the ignition order of 1-5-3-6-2-4, any cylinder and the intake port of that cylinder are connected to each other at the earliest after the intake port is closed. 1st cylinder 1A, 6th cylinder 1F, and 2nd cylinder 1 in relation to other cylinders that open
B and 5th cylinder 1E, 3rd cylinder 1C and 4th cylinder 1D
The length of the passage between each cylinder is set equal to the value determined by the above equation (). Therefore, as shown in Fig. 8, the intake inertia effect changes from the 1st cylinder to the 6th cylinder.
Cylinder, 5th cylinder → 2nd cylinder, 3rd cylinder → 4th cylinder, 6th cylinder → 1st cylinder, 2nd cylinder → 5th cylinder,
It acts sequentially from the 4th cylinder to the 3rd cylinder, and scavenging is improved in each cylinder.

Furthermore, in each of the above embodiments, a single intake passage communicates with each cylinder via the intake port.
It can also be applied to systems where two intake passages, one for low load and one for high load, are communicated independently.
In this case, the length of the passage between the cylinders may be set so as to obtain the intake inertia effect in either the low-load intake system or the high-load intake system, and preferably the high-load intake passage is used for the low-load intake system. Since the area of the passage is larger than that of the passage and the attenuation of pressure waves can be kept small, it is advantageous to set it between cylinders in a high-load intake system.

Furthermore, in each of the above embodiments, the exhaust turbo supercharger 17 is used as the supercharger, but other various known superchargers such as a supercharging pump can be used.

[Brief explanation of drawings]

The drawings show embodiments of the present invention, and FIGS. 1 and 2 are an explanatory diagram of the overall configuration and a schematic diagram of the main parts of the first embodiment, and FIG. 3 is a diagram equivalent to FIG. 1 showing the second embodiment. , FIG. 4 is a diagram corresponding to FIG. 1 showing the third embodiment,
FIG. 5 is a diagram showing the characteristics of intake pressure and exhaust pressure with respect to engine speed, and FIGS. 6, 7, and 8 are intake inertia effects in the first, second, and third embodiments, respectively. FIG. 1A to 1F...Cylinder, 5...Main intake passage, 5a
~5f...Intake passage, 8...Throttle valve, 9...
...Intake port, 10...Fuel injection nozzle, 12...
...Main exhaust passage, 12a to 12f...Exhaust passage, 1
3...Exhaust port, 17...Exhaust turbo supercharger,
19...Wastegate valve.

Claims (1)

[Claims] 1. In a multi-cylinder engine equipped with an intake passage communicating with each cylinder via an intake port, an exhaust passage communicating with each cylinder via an exhaust port, and a supercharger provided in the intake passage, In the intake passage downstream of the charger, the length of the intake passage between a given cylinder and the other cylinder whose intake port opens earliest after the intake port of that cylinder is closed is determined by the intake pressure downstream of the supercharger acting on the exhaust port. In the engine operating range where the pressure is higher than the exhaust pressure, the compression wave generated at the intake port of one cylinder when the intake port of that cylinder is closed is set so that it propagates immediately after the intake port of the other cylinder opens to perform supercharging. This is an intake system for a multi-cylinder engine.