JPH02245460A - Intake device for direction injection type diesel engine - Google Patents

Abstract

PURPOSE:To maintain proper intake swirl and exhaust gas recirculation(EGR) at all times by carrying out hot EGR control at a low load and cold EGR control at a high load respectively in the EGR range of an engine. CONSTITUTION:A main intake port A introduces intake air in such a way as to form intake swirl C in an engine combustion chamber B. On the other hand, an exhaust gas recirculation passage D introduces exhaust gas into the engine combustion chamber B so as to weaken the intake swirl C. In the aforesaid construction, an air supply passage E and an exhaust gas recirculation(EGR) passage D are respectively controlled with an EGR control means F. Furthermore, the EGR control means F makes hot EGR control at a low load depending upon engine operation mode, while making cold EGR control at a high load. As a result, it is possible to maintain pertinent intake swirl and EGR suitable for the engine operation mode, and improve engine operation performance and fuel consumption.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to an intake system for a direct injection diesel engine.

(Prior Art) Conventionally, as described in, for example, Japanese Patent Application Laid-Open No. 63-140820, there has been a so-called variable swirl type direct injection system in which the strength of the intake swirl flow is made variable to improve combustion performance. Intake systems for diesel engines are well known.

The formation of intake swirl is originally done from the perspective of increasing the flame propagation speed and improving combustion performance, but if the swirl (swirl ratio) is too strong during ignition, the flame will blow out and be extinguished. There is a problem that the ignitability deteriorates if the Generally, when the combustibility deteriorates, the amount of HC (smoke) generated increases due to incomplete combustion. However, as the combustibility improves and the temperature of the combustion gas increases, the amount of 1-I C generated decreases, but this time N0x (
The amount of nitrogen oxides) generated increases. Therefore, recently, in addition to the above-mentioned main intake port that forms an intake swirl in the combustion chamber of the engine, a sub-intake port that communicates with the EGrt passage for exhaust gas recirculation has been provided, and the sub-intake port is connected to the main intake port. The intake air is introduced in a direction that weakens the swirl flow formed by A configuration is adopted in which the temperature of the intake air is raised in such a way as to contribute to improving the ignitability.

(Problem to be Solved by the Invention) However, unlike the latter prior art configuration described above, the strength of the intake swirl cannot be made variable by simply increasing the amount of exhaust gas recirculation only at low engine speeds. , there is a problem that the same merits of swirl control cannot be obtained in other operating ranges. In addition, in the case of the configuration of the same prior art, NOx can be reduced by increasing the recirculation amount (EGRI) of exhaust gas, which is an inert gas, from the sub-intake port, but doing so will reduce the pond surface and fuel consumption. This is accompanied by problems such as deterioration and increased amount of HC generated. Therefore, with the above-mentioned conventional simple EGR control, it is only possible to improve exhaust emissions with low efficiency and a low degree of freedom within an extremely restricted range determined by the balance between NOx reduction, fuel efficiency improvement, HC reduction, etc. I couldn't do it.

(Means for Solving Problem R) The present invention was made with the aim of solving the above problems, and includes a main intake port that introduces intake air to form an intake swirl in an engine combustion chamber. , an exhaust gas recirculation passage for introducing exhaust gas into the engine combustion chamber so as to weaken the intake swirl formed by the main intake port; EGR performs hot EGR control under load operation, while performing cold EGR control under high load operation.
This device is characterized by being provided with a control means.

(Function) In the configuration of the intake system of the direct injection diesel engine of the present invention, the main intake port that forms an intake swirl in the engine combustion chamber and the υ force in the direction of weakening the intake swirl flow formed by the main intake port. In a direct injection diesel engine, which is equipped with an exhaust gas recirculation passage that introduces gas, hot EGR control is performed in the exhaust gas recirculation region of the engine during low load operating conditions, and cold EGR control is performed during high load operating conditions. It is supposed to be done.

Therefore, first, in the exhaust gas recirculation region (EGR region), whether in the hot EGR region or the cold EGR region, the swirl flow is reduced by the swirl flow weakening effect of the exhaust gas recirculation passage, and as a result, the swirl flow is reduced. Generally, the amount of NOx generated will decrease.

When the engine is in a low-load operating range and the in-cylinder temperature is low, both ignition and combustibility are poor, resulting in incomplete combustion and HC.
In areas where a large amount of gas is generated, firstly, the swirl flow for improving ignition performance is reduced by recirculating exhaust gas to improve ignitability, and at the same time, so-called hot EGR control is performed by recirculating the exhaust gas. Increasing the temperature inside the cylinder further improves combustibility. As a result, HC is less likely to occur.

On the other hand, when the engine is in a high-load operating range, a cold EGR effect is realized by the recirculation of low-temperature exhaust gas, and NOx can be reduced particularly effectively.

(Effects of the Invention) Therefore, according to the intake system for a direct injection diesel engine of the present invention, it becomes possible to realize appropriate swirl level control and EGR action according to the operating condition of the engine, thereby improving operating performance. Improvements in fuel efficiency as well as improvements in fuel efficiency 1. Furthermore, it can greatly contribute to improving exhaust emissions.

(Embodiment) FIGS. 2 to 7 show the configuration of an intake system for a direct diesel engine according to a first embodiment of the present invention.

First, in FIG. 2, reference numeral 1 denotes an engine main body, and the engine main body 1 is constituted by an in-line four-cylinder engine having four engines 2a to 2d, numbered first to fourth. Each of these cylinders 2a to 2d is provided with an exhaust bow 3a to 3d and a basic main intake port 48 to 4d having a swirl generating function, respectively. The plurality of main intake bows) 4a to 4d include an intake manifold 5.
The branch passages 5a to 5d are connected to the upstream intake passage 20 via the intake manifold 5. Further, branch passages 6a to 6d of the exhaust manifold 6 are connected to the exhaust ports 3a to 3d, respectively.

The engine main body 1 includes a cylinder block 7, a cylinder head 8, and a piston 9 fitted into the cylinder block 7, as shown in FIG. 3, for example.
A cavity 10 is formed in the top surface of the piston 9. For example, a hole nozzle type fuel injection valve 11 is oriented in this cavity lO, and the direct injection fuel from this fuel injection valve 11 is directly injected into the cavity 10.
It is configured as a so-called Mann type (evaporative combustion type) in which the fuel is spread in a thin film on the surrounding wall surface and burned.

Each of the above main intake ports 4a to 4d and exhaust bow) 3
a to 3d are respectively formed and provided in the cylinder head 8, and main intake ports 4a to 4d are connected to the intake valve 1.
2a=12d, and exhaust ports 3a to 3d are opened at known timings by exhaust valves (paths shown) in synchronization with the rotation of a crankshaft (not shown). In this embodiment, the main intake ports 4a to 4d are, for example, helical ports as shown in FIG.
The intake air passing through the main intake ports 4a to 4d is supplied into the combustion chambers of the respective cylinders while being swirled in the direction of the arrow, thereby forming an intake swirl flow.

On the other hand, reference numerals 13a to 13d indicate each of the main intake ports 4 mentioned above.
These are sub-intake ports that introduce intake air in a direction that weakens the intake swirl flow formed by sub-intake ports 13a-4d, and the upstream sides of these sub-intake ports 13a-13d are connected to sub-intake passages 17, respectively.
The exhaust manifold 6 and the fresh air supply passage 30 are connected to each other via the exhaust manifold 6 and the fresh air supply passage 30, respectively. A three-way solenoid valve 18 having an 0N10FF function is interposed at the convergence part of the sub-intake passage 17 with the exhaust manifold 6 side and the fresh air supply passage 30, and a three-way solenoid valve 18 with an 0N10FF function is installed downstream of the auxiliary intake passage 17. A water supply passage 22 through which cooling water is supplied from an attached radiator is communicated via a water injection valve 21 in the middle thereof. Fresh air or exhaust gas cooled by the water injected in a mist form by the water injection valve 21 passes through the sub-intake passage 17 to the sub-intake port 13a-1 of each cylinder.
3d.

On the other hand, the code 100 is the three-way solenoid valve 18 and the water injection valve 21.
etc., depending on the engine operating range as shown in Fig. 6,
This is an engine control unit that performs swirl control with control contents as shown in FIG. The engine control unit 100 also has engine rotation speed detection data Nε from the engine rotation speed sensor, accelerator opening detection data θ^CC from the accelerator opening sensor,
Coolant temperature detection data T and the like from the engine coolant temperature sensor are each input at predetermined intervals.

Next, swirl level control by the engine control unit 100 will be explained in detail with reference to the characteristic diagram in FIG. 6 and the flowchart in FIG. 5.

First, after initializing each part of the control factors, the engine rotation speed Nε is detected in step S, and the accelerator opening degree θ^CC is detected in step S. Based on these, one of the After specifying the operating range, it is determined whether the current engine operating range is a control range in which the above-mentioned auxiliary intake passage 17 should be utilized.

As a result, if the determination is YES, the process further proceeds to step S to determine whether or not it is a hot EGG' (area).

If the result is YES (hot EGR region: low load region), the process proceeds to step S, where the three-way solenoid valve 18 at the downstream end of the auxiliary intake passage 17 is turned on (opened) to enable exhaust EGR. After the state is established, the process further proceeds to step S, where the water injection valve 21 is turned OFF'F'' to prohibit water injection.

As a result, a large amount of hot exhaust gas is introduced even in low load regions where the combustion temperature is low and there is a large amount of surplus air that does not participate in combustion, which increases the cylinder temperature and impairs combustion performance. will improve. As a result, not only fuel efficiency improves, but also NOx is reduced by the so-called EGR effect (inert gas effect). Moreover, the hot exhaust gas is introduced in a direction that weakens the intake swirl formed in the main intake ports 4a to 4d, thereby improving the ignitability itself. Therefore, it goes without saying that the amount of HC generated and the fuel consumption rate will also decrease.
The effect of reducing NOx due to the EGR action can also be obtained (see Fig. 7).

On the other hand, if a No determination is made in the above step S as it is not in the sub-intake passage control region, then the other side step S
7, the three-way solenoid valve 18 is set to 0FF (closed) to close the auxiliary intake passage 17.

As a result, in this case, normal swirl operation is performed instead of hot EGR and cold air region.

Furthermore, if the sub-intake passage control area is not the hot EGR area determined as No in the step S4, the process further proceeds to step SIl, and this time the cold EGR area (medium/high load area) is selected. Determine whether or not.

If the result is YES, the process proceeds to step S, where the 3-way solenoid valve 8 is first turned ON (opened) to open the auxiliary intake passage 17, and at the next step S to, the water injection valve described above is turned ON (opened). is turned on to lower the temperature of the recirculated exhaust gas to perform so-called cold EGR.

As a result, in this case, the exhaust gas whose temperature has decreased is introduced so as to obtain the maximum EGR effect in a state where the specific volume is small, and compared to the low load range such as during medium and high load operating conditions. It is suitable for effectively functioning the EGR function in an operating range where the combustion temperature is high and the amount of surplus air is small. Moreover, as a result, the NOx reduction effect is also high (see FIG. 8).

On the other hand, if the determination in step S is NO because it is not a cold EGR region, the process further proceeds to step S, where it is determined whether or not the cold air region is present.

If the result is YES (cold air region), the process proceeds to step Sat, where the three-way solenoid valve 18 is opened to the fresh air supply passage 30 side, and the water injection valve 21 is turned on in the following step S11. Water is injected into the supplied fresh air to lower the intake temperature, and the fresh air, which is made into cold air by lowering the intake temperature, is supplied into the engine combustion chamber from the sub-intake ports 13a=13d.

On the other hand, if a No determination is made in step Sll as it is not the cold air region, the process proceeds to step S14, where the three-way solenoid valve 18 is opened to the fresh air supply passage 30 side, allowing fresh air to be supplied. On the other hand, step S16
By turning the water injection valve 21 OFF'F', a normal fresh air supply state is realized.

[Brief explanation of drawings]

FIG. 1 is a diagram corresponding to the claims of the present invention, FIG. 2 is a schematic diagram showing the system configuration of an intake device for a direct injection diesel engine according to an embodiment of the present invention, and FIGS.
Each figure is an enlarged sectional view of the main parts of the same intake device, and FIG.
A flowchart showing the control operation of the device, FIG. 6 is a graph showing the control region in the same embodiment, FIG. 7 is a graph showing the hot EGR effect in the low load region in the same embodiment, and FIG. 8 is the cold E in the middle and high load area.
It is a graph showing the GR effect. l...Engine body 2a to 2d...First to fourth cylinders 3a to 3d...Exhaust ports 48 to 4d...Main intake port 5...Intake manifold 7... ... Cylinder block 8 ... Cylinder head 9 ... Piston l [ ... Fuel injection valve 13a - 13d ... Sub intake port 17 ... EGR passage 18 ... 3 sides Solenoid valve 21...Water injection valve, fresh air supply passage, engine control unit Figure 2 Figure 4 Figure 7 (Hot EGR) Figure 8 (Cold EGR)

Claims (1)

[Claims] 1. A main intake port that introduces intake air so as to form an intake swirl in the engine combustion chamber, and an exhaust gas recirculation passage that introduces exhaust gas into the engine combustion chamber so as to weaken the intake swirl formed by the main intake port. In a direct injection diesel engine comprising: an EGR control means that performs hot EGR control in a low load operating state and cold EGR control in a high load operating state in the exhaust gas recirculation region of the engine; Features of direct injection diesel engine intake system.