JP3315416B2 - Diesel engine intake system - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an intake device for a diesel engine.

[0002]

2. Description of the Related Art In recent years, in diesel engines,
Reduction of exhaust emissions, particularly reduction of NOx generation, is required. To reduce NOx generation, it is necessary to prevent the combustion temperature in the combustion chamber from excessively increasing. In general, as a technique for suppressing an unnecessary increase in the combustion temperature, improvement of fuel combustibility in a combustion chamber, introduction of exhaust gas into an intake system (EGR), and the like are known. Here, so-called swirl control, which controls the intake swirling flow in the combustion chamber, that is, the swirl strength, according to the operating state has been conventionally known as a method of improving the combustibility. For example, two intake ports are provided for each cylinder, and one of the intake ports is opened in the circumferential direction of the combustion chamber or formed in a helical shape to generate swirl. Alternatively, an on-off valve for opening and closing one intake port is provided, and the on-off valve is opened and closed according to the operating state of the engine, and the swirl strength in the combustion chamber is changed to preferably control the combustibility.
(See JP-A-62-174533).

[0003]

However, such a conventional swirl control aims at improving the engine output by mainly improving the flammability, so that it does not directly lead to the reduction of the exhaust emission. There is. In addition, EG to the intake system as a measure against NOx
The introduction of R gas has been widely performed conventionally. However, when such an EGR mechanism is provided in a supercharged engine, in the operating region where the intake pressure is higher than the exhaust pressure, it is not only impossible to normally introduce the EGR gas into the intake system,
Conversely, there is a problem that the intake air flows into the exhaust system. In particular, in the case of a mechanical supercharger, since the intake pressure is increased from a low rotation region, such a problem is remarkable.

SUMMARY OF THE INVENTION The present invention has been made to solve the above-mentioned conventional problems.
An object of the present invention is to provide an intake device for a diesel engine that can effectively reduce exhaust emissions such as NOx.

[0005]

According to a first aspect of the present invention, there is provided a fuel cell system comprising: (i) a first cylinder which is opened and closed by an intake valve and generates a swirl in each cylinder. In the intake device of a turbocharged diesel engine provided with a second intake port, (ii) the first and second intake ports generate swirl in the same rotational direction, and (iii) A first intake manifold that distributes and supplies intake air to a first intake port of a cylinder and a second intake manifold that distributes and supplies intake air to a second intake port of each cylinder are independent of each other. On the other hand, an opening / closing valve for opening and closing the intake supply path to the intake manifold is provided only on the upstream side of one of the intake manifolds, and (iv) intake air on the side provided with the opening / closing valve is provided. EG that introduces EGR gas into the collecting section
An R mechanism is connected, (v) and the on-off valve is fully closed in a low load region, partially opened in a medium load region, and fully opened in a high load region to generate a low swirl in a low load region, An on-off valve control means for generating a medium swirl in a medium load region and generating a high swirl in a high load region is provided.

According to a second aspect, in the intake device for a diesel engine according to the first aspect, the on-off valve control means includes:
When the intake pressure is higher than the exhaust pressure, a load region in which the on-off valve is partially opened is extended outside the medium load region.

[0007]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiments of the present invention will be specifically described below.
As shown in FIG. 1, each cylinder 1 of a four-cylinder diesel engine E has first and second intake ports 2, 3 and first and second intake ports 2, 3, respectively.
Second exhaust ports 4 and 5 are provided. Here, as described later, the first and second intake ports 2 and 3, respectively,
Basically, swirls in the same rotation direction can be generated. The first intake port 2 of each cylinder 1 communicates with a first independent intake passage 6, and the second intake port 3 of each cylinder 1 communicates with a second independent intake passage 7. The first and second exhaust ports 4 and 5 of each cylinder 1 communicate with an independent exhaust passage 8 respectively.

As shown in FIGS. 2 and 3, in each cylinder 1 of the engine E, a first intake valve 11 for opening and closing the first intake port 2 and a second intake valve 11 for opening and closing the second intake port 3 are provided. An intake valve 12 is provided, and the engine E includes first and second
When the intake valves 11 and 12 are opened, intake air (air) is sucked into the combustion chamber 13 from the first and second intake ports 2 and 3, and the intake air is compressed by the piston 14 to high pressure and high temperature. Thereafter, fuel is injected from the fuel injection valve 15 during the intake, the fuel is ignited and burned by the high-temperature intake, and the combustion gas is released when the exhaust valves (not shown) are opened. Exhaust port 4,5
To the independent exhaust passage 8 via the
The first and second intake valves 11 and 12 are connected to the intake cam mechanism 1.
6, the shutter is opened and closed at a predetermined timing. Here, the first intake port 2 is a tangential port that opens substantially in the circumferential direction of the combustion chamber 13,
A relatively weak swirl can be generated in the combustion chamber 13. The second intake port 3 is a helical port formed in a helical shape in the vicinity of the opening, and can generate a relatively strong swirl in the combustion chamber 13. The swirl is controlled in accordance with the operating state of the engine E, as described later, to slow down fuel combustion and reduce the amount of NOx generated.

As shown in FIG. 1 again, an intake device A is provided for supplying intake air to the engine E, and a common intake passage 20 of the intake device A is provided in order from the upstream side in the intake air flow direction. Air cleaner 21 for removing dust in intake air
And a blower 22a of the exhaust turbocharger 22. The supercharger 22 is provided to increase the output of the engine E. And this common intake passage 2
0 branches downstream toward a first branch intake passage 23 and a second branch intake passage 24 in which an on-off valve 25 is provided. As will be described later, the opening of the on-off valve 25 is controlled by the control unit 36. Here, the downstream end of the first branch intake passage 23 is connected to the first intake collecting portion 26 (surge tank),
The downstream end of the branch intake passage 24 is connected to a second intake collecting portion 28 (surge tank). The upstream end of each first independent intake passage 6 described above is connected to the first intake collecting section 26, and the upstream end of each second independent intake passage 7 is connected to the second intake collecting section 28. In addition, each independent exhaust passage 8 is gathered into one common exhaust passage 32 at an exhaust collecting portion 31, and the common exhaust passage 32 includes a turbine of the turbocharger turbocharger 22 in order from the upstream side in the exhaust flow direction. 22b,
An exhaust gas purification device 33 using a predetermined catalyst is interposed.

In order to introduce EGR gas into the intake system, an EGR passage 34 having one end connected to the exhaust collecting section 31 and the other end connected to the second intake collecting section 28 is provided. The EGR passage 34 has an EGR opening and closing
A control valve 35 is provided. Here, the EGR control valve 3
The control unit 36 controls the engine E
It is opened and closed according to the operating state of the vehicle. Such EGR gas is introduced to lower the combustion temperature and reduce the amount of generated NOx. The control unit 36 corresponds to the on-off valve control means described in claims 1 and 2.

In this embodiment, the swirl intensity generated by the first and second intake ports 2 and 3 and the EGR are set to a predetermined value in order to reduce the amount of NOx generated while increasing the engine output. These control methods are described below with reference to FIGS. 1 to 3 as appropriate.

The swirl is controlled by changing the opening of the on-off valve 25 by the control unit 36. As described above, Japanese Patent Application Laid-Open No. Sho 62-174
In the conventional swirl control means disclosed in Japanese Patent No. 533, a large number of open / close valves are required because the open / close valves are provided for each cylinder. However, in the present invention, only one open / close valve 25 is required. The intake device A is simplified.

As shown in FIG. 4, in a low load region where the engine load is equal to or less than the predetermined value θ ₁ (at a low load), the on-off valve 25 is fully closed. In this case, no intake air is supplied to the second intake collecting section 28, so that intake air is supplied to the combustion chamber 13 only from the first intake port 2. As described above, since the first intake port 2 is a tangential port,
A relatively weak swirl is generated in the combustion chamber 13 (hereinafter, referred to as low swirl).

In a medium load region where the engine load exceeds θ ₁ and is equal to or less than the predetermined value θ ₂ (at a medium load), the on-off valve 25
Is partially opened at a predetermined opening degree (hereinafter, this state is referred to as a half-open state). In this case, since the second branch intake passage 24 is throttled by the on-off valve 25, the amount of intake air supplied to the second intake collecting section 28 is reduced. Further, the intake pressure in the second intake collecting section 28 becomes considerably low. Therefore, the intake air is supplied from the first intake port 2 to the combustion chamber 13 in the same manner as when the load is low, and the intake air generates the same swirl as that when the load is low. On the other hand, the amount of intake air flowing into the combustion chamber 13 from the second intake port 3 is small. Here, the second intake port 3 is a helical port as described above, and originally generates a relatively strong swirl. In this case, the amount of intake is small, so the second intake port 3 is connected to the combustion chamber. The intake air flowing into 13 produces only a weak swirl. Therefore, a medium swirl is generated by the intake air flowing into the combustion chamber 13 from both the intake ports 2 and 3 (hereinafter, this is referred to as a medium swirl).

In a high load region where the engine load exceeds θ ₂ (at high load), the on-off valve 25 is fully opened. In this case, the normal intake air flows into the combustion chamber 13 from the second intake port 3, and a relatively strong swirl is generated in the combustion chamber 13 by the intake air. It should be noted that the swirl of the same level as the low load is generated by the intake from the first intake port 2. Therefore, a strong swirl is generated in the combustion chamber 13 by the intake ports 2 and 3 (hereinafter, this is referred to as a high swirl).

That is, low swirl is generated at low load, medium swirl is generated at medium load, and high swirl is generated at high load. In general, the stronger the swirl, the more stratified the intake air in the combustion chamber 13 is, and the slower the fuel burns, the more the combustion temperature rises.
The amount of generation is reduced. However, in a diesel engine, when the load is low, that is, when the amount of combustion injection is small, if the swirl is too strong, the intake air becomes lean and ignition becomes difficult. Then, when the fuel is ignited thereafter, the fuel rapidly burns, so that the combustion temperature rises, and NO
x The amount of generation increases. Therefore, when the engine load is low, the swirl is reduced. Thus, the swirl intensity is controlled according to the engine load, and the NOx generation amount is reduced.

The EGR control is performed by the control unit 36
This is performed by opening and closing the EGR control valve 35. In this embodiment, basically, the engine load is θ
Open the EGR control valve 35 in the load region within a ₁ through? _2, so that to introduce the EGR gas into the intake system. It should be noted that the EGR control valve 25 may be opened even in the low load region to introduce the EGR gas into the combustion chamber 13. However, in this case, since the on-off valve 25 is closed, only the EGR gas flows from the second intake port 3 into the combustion chamber 13. Generally, as the amount of EGR gas increases, the combustion temperature is suppressed, and the amount of generated NOx is reduced. However, when the load is high, the fuel injection amount is large, so if EGR gas is introduced, the amount of air (oxygen) required for fuel combustion becomes insufficient by that amount,
The engine output is reduced, and smoke is generated due to incomplete combustion. Therefore, in the high load region where the load exceeds theta ₂ are not performed introduction of EGR gas. Further, in the present embodiment, when the EGR gas is introduced into the second intake collecting portion 28 in a low load region where the load is θ ₁ or less,
Only the EGR gas is supplied from the second intake port 3 into the combustion chamber 13. Therefore, the introduction of the EGR gas is not performed in the low load region. As described above, basically, the EGR gas is supplied to the intake system according to the engine load, the unnecessary rise of the combustion temperature in the combustion chamber 13 is prevented, and the NOx generation amount is reduced.

In the present embodiment, in order to increase the output of the engine E, the exhaust turbo type turbocharger 2 is installed in the intake device A.
2 are provided. Therefore, as shown in FIG. 5, in the high speed region where the engine speed is greater than N _1, the intake pressure is higher than exhaust pressure. Therefore, as described above, in a normal supercharged engine, when the EGR valve is opened in such a high rotation region, the intake air flows back to the exhaust system. However, in the present embodiment, as described above, when the on-off valve 25 is in the half-open state, the second intake manifold 2
The intake pressure in 8 decreases, and this intake pressure becomes lower than the exhaust pressure. That is, by setting the on-off valve 25 to the half-open state, the EGR gas can be introduced into the intake system even in a region where the intake pressure is higher than the exhaust pressure. As shown in FIG. 6, in the present embodiment, the engine load is θ ₁ regardless of the rotational speed.
The EGR gas is introduced in a medium load region of? ₂ , and the hatched portion in this region is a region where introduction of the EGR gas is impossible in the conventional turbocharged engine. When a mechanical supercharger is used as the supercharger, the intake pressure may be higher than the exhaust pressure from the low rotation range, but according to the present invention, such a mechanical supercharger is provided. Even if it is set, the EGR gas can be introduced into the intake system at any time by setting the on-off valve 25 to the half-open state.

As described above, basically, when the load is θ ₂
When the EGR gas is introduced into the intake system in a high load region exceeding the range, the output decreases or smoke occurs. Therefore, although in such a high load region is not to introduce the EGR gas into the intake system, in the high speed region where the engine speed is greater than N _1, the amount of intake air pressure in the intake is high, is supplied to the combustion chamber 13 Increase. Therefore, in the high speed region exceeding N _1, at the time of high load because the air is sufficient, EGR
Even if gas is introduced, the output is not reduced or smoke is unlikely to occur.

[0020] Therefore, as shown in FIG. 7, the rotational speed is N ₁
In the high rotation region exceeding, the engine load for switching the on-off valve 25 from half open to full open may be changed to a predetermined value β higher than θ ₂ . In this way, N
Ox generation can be reduced. Further, in such a high rotation region, the intake pressure in the combustion chamber is high, so that the oxygen concentration becomes high, and the fuel is easily burned. Therefore,
Even if the swirl becomes somewhat strong, the ignitability does not deteriorate. Therefore, in the high speed region exceeding N _1, the on-off valve 2 may be changed to a predetermined value of the engine load lower than the theta ₁ switching to half-open α from the fully closed. In this way, the NOx generation amount can be reduced to a lower load region.

[0021]

According to the first aspect of the present invention, since only the on-off valve is provided on one of the upstream sides of the two intake collecting portions, only one on-off valve for switching the swirl strength is required. Compared to a conventional intake device in which an on-off valve is provided for each cylinder, the intake device can be simplified and cost can be reduced. In addition, when the load is high, the first and second intake ports generate swirl in the same rotational direction to generate high swirl in the combustion chamber, so that the combustion of the fuel is slowed down, and an unnecessary rise in the combustion temperature is prevented. Therefore, the amount of generated NOx is reduced. Also,
In general, excessive swirl reduces ignitability, but at medium load the swirl is weakened and at low load it is further weakened, so that the ignitability of fuel does not decrease, and rapid combustion of fuel due to ignition delay is prevented, The amount of generated NOx is reduced. Further, since the EGR gas can be easily introduced into the intake system between the medium load region and the low load region, the combustion temperature is reduced and the NOx generation amount is reduced. In addition, since the supercharger is provided in the engine, the intake pressure may be higher than the exhaust pressure in the medium load range. Even in such a case, the EGR gas can be introduced into the intake system, and NOx
The amount of generation is reduced.

According to the second aspect, the same operation and effect as those of the first aspect can be obtained. Further, in the rotation region where the intake pressure is higher than the exhaust pressure, the load region for introducing the EGR gas is expanded, so that the effect of reducing the NOx generation amount is further enhanced.

[Brief description of the drawings]

FIG. 1 is a system configuration diagram of a diesel engine and an intake device thereof according to an embodiment of the present invention.

FIG. 2 is an explanatory elevational sectional view around an intake port of the engine shown in FIG. 1;

FIG. 3 is an explanatory plan sectional view around an intake port of the engine shown in FIG. 1;

FIG. 4 is a diagram showing the opening / closing characteristics of an on-off valve with respect to an engine load and an engine speed;

FIG. 5 is a diagram showing characteristics of an intake pressure and an exhaust pressure with respect to an engine speed.

FIG. 6 is a diagram showing an EGR gas introduction region with respect to an engine load and an engine speed;

FIG. 7 shows a rotation range where the intake pressure is higher than the exhaust pressure,
FIG. 7 is a view similar to FIG. 6 in which an R gas introduction region is expanded.

[Explanation of symbols]

 A: Intake device E: Diesel engine 2,3 ... First and second intake ports 11,12 ... First and second intake valves 22 ... Exhaust turbocharger 25 ... On-off valve 26 ... First intake manifold 28 ... Second intake collecting section 34 EGR passage 35 EGR control valve 36 Control unit

Continuation of the front page (58) Field surveyed (Int. Cl. ⁷ , DB name) F02B 31/02 F02D 43/00 301 F02M 25/07 580

Claims (2)

(57) [Claims] An intake system for a turbocharged diesel engine provided with first and second intake ports, each of which is opened and closed by an intake valve and generates a swirl, in each cylinder. , A second intake port for generating a swirl in the same rotational direction, a first intake manifold for distributing and supplying intake air to the first intake port of each cylinder, and a second intake port for each cylinder. And a second intake manifold for distributing and supplying intake air to the intake port of each of the intake ports is provided independently of each other, while an intake supply path to the intake manifold is provided only upstream of one of the intake manifolds An EGR mechanism for introducing EGR gas is connected to the intake manifold on the side where the on-off valve is provided, and the on-off valve is fully closed in a low load region, and in an intermediate load region Partially open and in high load areas By fully open,
An intake device for a diesel engine, comprising: an on-off valve control unit that generates a low swirl in a low load region, generates a medium swirl in a medium load region, and generates a high swirl in a high load region. 2. The intake device for a diesel engine according to claim 1, wherein the on-off valve control means extends a load region in which the on-off valve partially opens when the intake pressure is higher than the exhaust pressure to outside the middle load region. An intake device for a diesel engine, characterized in that: