JP4134861B2 - Control device for premixed compression ignition type internal combustion engine - Google Patents

Description

  The present invention relates to a control device for a premixed compression ignition type internal combustion engine.

  Technology for switching between fuel used when starting an internal combustion engine or when the catalyst is inactive and other fuel used when the catalyst is inactive (see, for example, Patent Document 1). When the catalyst is inactive, auxiliary fuel is mixed and the catalyst HC is mixed. A technique for increasing the catalyst temperature by improving the conversion rate (for example, see Patent Document 2), and a technique for increasing the use ratio of a fuel having a lower octane number as the load is lower in an internal combustion engine using fuels having different octane numbers (for example, patents). Reference 3) is known.

JP 2001-193511 A JP-A-56-154146 JP 2000-179368 A

  By the way, since the exhaust purification catalyst does not reach the activation temperature at the time of cold start, there is a possibility that the purification rate of harmful substances such as unburned fuel in the exhaust purification catalyst is lowered. Therefore, it is necessary to quickly raise the exhaust purification catalyst to the activation temperature. Further, at the time of cold start, since the temperature of the internal combustion engine is low, the evaporation of fuel becomes slow and the startability of the internal combustion engine is inferior.

  The present invention has been made in view of the above-described problems, and in a control device for a premixed compression ignition type internal combustion engine using a plurality of types of fuel, the startability deterioration, catalyst, which can be a problem during cold start It aims at providing the technique which suppresses the delay of activation.

In order to achieve the above object, a control device for a premixed compression ignition type internal combustion engine according to the present invention employs the following means. That is,
Premixed compression ignition type internal combustion engine equipped with an exhaust purification catalyst for purifying harmful substances in exhaust gas, supplying a plurality of different types of volatile fuel, and controlling the ratio of the fuel supplied into the cylinder according to the engine state In the engine control device,
Cold start determination means for determining whether or not the internal combustion engine is a cold start at the time of starting,
When it is determined that the cold start is determined by the cold start determination means, the ratio of fuel having higher volatility in the fuel supplied into the cylinder than when it is determined that the cold start is not performed It is characterized by making it high.

  The most important feature of the present invention is that a pre-mixed gas is formed mainly by using a highly volatile fuel at the time of cold start of the internal combustion engine, and further the fuel is burned well so that the early activation of the exhaust purification catalyst. It is to plan.

In the control device of the premixed compression ignition type internal combustion engine configured as described above, the supply ratio of highly volatile fuel is increased when the internal combustion engine is cold started. Here, the higher the fuel volatility, the greater the amount of fuel evaporation, and the better the flame propagation after ignition. Therefore, by increasing the supply ratio of the highly volatile fuel at the cold start, the fuel can be burned well and the temperature of the exhaust can be raised. As a result, the temperature of the exhaust purification catalyst can be quickly raised and activated. Further, by increasing the supply ratio of highly volatile fuel, the fuel can be burned well, and the startability of the internal combustion engine can be improved. Here, the “cold start” is not limited to the start when the temperature of the internal combustion engine is close to the ambient temperature, but can also include a start at a temperature before the completion of warm-up. “Volatile” means the property of having a low boiling point or sublimation temperature at normal pressure and a high vapor pressure at normal temperature.

In the present invention, further comprising catalyst activity determination means for determining whether or not the exhaust purification catalyst is activated,
When it is determined by the catalyst activity determining means that the exhaust purification catalyst is not activated, the intake air amount of the internal combustion engine is decreased and it is determined that the catalyst is activated by the catalyst activity determining means. The fuel can be burned by increasing the ratio of the more volatile fuel out of the fuel supplied into the cylinder.

  In the control device of the premixed compression ignition type internal combustion engine configured as described above, when the exhaust purification catalyst is not activated, the supply ratio of the fuel with higher volatility, that is, the fuel with higher exhaust temperature is increased. And raise the exhaust temperature. Here, when a fuel having higher volatility is used, combustion can be performed with a lower air-fuel ratio. By reducing the intake air amount, it is possible to increase the amount of heat generated by the fuel with respect to the exhaust amount without causing an increase in torque, and as a result, the exhaust temperature can be increased. Further, that the exhaust purification catalyst is activated means that it is in a state where it is possible to purify harmful substances in the exhaust to a permissible range, and this permissible range is determined by a regulation value or the like.

  In the present invention, the fuel cell further includes temperature detection means for detecting the temperature of the exhaust purification catalyst, and the higher the temperature detected by the temperature detection means, the higher the volatility of the fuel supplied into the cylinder. The ratio of can be lowered.

  In the control device for the premixed compression ignition type internal combustion engine configured as described above, the temperature of the exhaust gas decreases as the temperature of the exhaust gas purification catalyst increases, and the exhaust gas having a temperature corresponding to the temperature of the exhaust gas purification catalyst is discharged to the exhaust gas purification catalyst. Can be allowed to flow into.

  In the control device for a premixed compression ignition type internal combustion engine according to the present invention, the startability is improved by increasing the fuel supply ratio at which the exhaust temperature becomes high at the cold start, and the temperature of the exhaust purification catalyst is quickly increased. Can be raised.

  Hereinafter, specific embodiments of a premixed compression ignition type internal combustion engine according to the present invention will be described with reference to the drawings. Here, a case where the premixed compression ignition internal combustion engine according to the present invention is applied to a diesel engine for driving a vehicle will be described as an example.

  FIG. 1 is a diagram showing a schematic configuration of an engine 1 and an intake / exhaust system thereof according to this embodiment.

  An engine 1 shown in FIG. 1 is an internal combustion engine that has a cylinder 2 and can be operated by premixed combustion and diffusion combustion.

  The engine 1 is provided with an in-cylinder fuel injection valve 3 that injects light oil into the cylinder 2.

  An intake passage 4 is connected to the engine 1. The intake passage 4 is provided with an in-intake fuel injection valve 5 for injecting gasoline during intake air flowing through the intake passage 4.

In addition, gasoline has higher volatility than light oil. Therefore, in this embodiment, gasoline is used as a highly volatile fuel, and light oil is used as a low volatile fuel.

  The intake passage 4 is provided with an intake throttle valve 41 for adjusting the flow rate of intake air flowing through the intake passage 4. The intake throttle valve 41 is provided with an intake throttle actuator 42 that is configured by a step motor or the like and that drives the intake throttle valve 41 to open and close.

On the other hand, an exhaust passage 6 is connected to the engine 1. An exhaust purification catalyst 7 for purifying harmful substances in the exhaust is provided in the middle of the exhaust passage 6. The exhaust purification catalyst 7 includes a selective reduction type NOx catalyst 7a on the upstream side and an oxidation catalyst 7b on the downstream side. This selective reduction type NOx catalyst 7a has an atmosphere in which the exhaust gas flowing in has an excess of oxygen, and a reducing agent (HC or the like).
Is a catalyst that reduces or decomposes NOx contained in the exhaust gas. In the present embodiment, when the exhaust purification catalyst 7 is simply used, both the selective reduction type NOx catalyst 7a and the oxidation catalyst 7b are shown.

  The exhaust passage 6 downstream of the exhaust purification catalyst 7 is provided with an exhaust temperature sensor 8 that outputs a signal corresponding to the temperature of the exhaust flowing through the exhaust passage 6. The exhaust temperature sensor 8 can detect the temperature of the exhaust gas flowing out from the exhaust purification catalyst 7 and measure the floor temperature of the exhaust purification catalyst 7.

  Here, when a drive current is applied to the in-cylinder fuel injection valve 3, the in-cylinder fuel injection valve 3 is opened, and as a result, light oil is injected from the in-cylinder fuel injection valve 3 into the cylinder 2. On the other hand, when a drive current is applied to the intake fuel injection valve 5, the intake fuel injection valve 5 is opened, and as a result, gasoline is injected from the intake fuel injection valve 5 into the intake passage 4. The gasoline injected into the intake passage 4 forms an air-fuel mixture with air and is sucked into the cylinder 2. Thereby, premixed combustion becomes possible. On the other hand, premixed combustion can also be performed by injecting light oil from the in-cylinder fuel injection valve 3 during the intake stroke. Further, the amount and supply ratio of the fuel injected from the in-cylinder fuel injection valve 3 and the in-intake fuel injection valve 5 are calculated from a map of the engine speed and load. Further, the fuel injection timing is also calculated from a map from the engine speed and the engine load. These maps are obtained in advance by experiments or the like.

  Here, FIG. 2 is a diagram showing an example of the relationship among the engine speed, the engine generated torque, and the engine combustion state.

  In the operation region (1) where the engine speed is low and the engine generated torque is small, the light oil supply ratio is increased, and the light oil injection timing is, for example, between 60 degrees and 90 degrees before top dead center at the crank angle. To do. Gasoline is injected during the intake stroke. In this operation region (1), the engine 1 is operated mainly by the combustion of light oil, but a small amount of gasoline is also supplied to improve the ignitability of the light oil. That is, in the operation region (1), a combustion mode in which premixed combustion with light oil and gasoline is performed is selected. The fuel supply ratio is, for example, 10% of gasoline to 90% of light oil. Here, the supply timing of the light oil into the cylinder 2 is made earlier than usual, and a premixed gas is formed with gasoline and light oil. In this operation region (1), only light oil may be supplied.

  Further, in the operation region (2) where the engine speed and the engine generated torque are medium, the gasoline supply amount is increased as compared with the operation region (1), and the injection timing of the light oil is dead at a crank angle, for example. It is between 60 degrees and 90 degrees before the point. Gasoline is injected during the intake stroke. Also in this operation region (2), the supply timing of light oil into the cylinder 2 is made earlier than usual, and a premixed gas is formed with light oil and gasoline. That is, in the operation region (2), a combustion mode in which premixed combustion with light oil and gasoline is performed is selected. Further, the gasoline supply ratio is increased as the engine speed or engine generated torque increases.

  Further, in the operation region (3) where the engine speed is high and the engine generated torque is large, the gasoline supply amount is compared with the high rotation high load side immediately before the operation region (2) is switched to the operation region (3). And the light oil injection timing is, for example, between 30 degrees before top dead center and 10 degrees after top dead center at a crank angle. Gasoline is injected during the intake stroke. In this operation region (3), the engine 1 is operated mainly by light oil, but gasoline is also supplied to improve the ignitability of light oil. That is, in the operation region (3), a combustion mode that mainly performs diffusion combustion with light oil is selected.

The engine 1 configured as described above is provided with an electronic control unit (ECU: Electronic Control Unit) 9 for controlling the engine 1. This ECU 9
It is a unit that controls the operating state of the engine 1 in accordance with the operating conditions of the engine 1 and the driver's request.

  Various sensors are connected to the ECU 9 via electric wiring, and in addition to the various sensors described above, an output signal of a water temperature sensor 10 that is attached to the engine 1 and measures the cooling water temperature of the engine 1 is input to the ECU 9. It has become. On the other hand, the in-cylinder fuel injection valve 3, the intake fuel injection valve 5 and the like are connected to the ECU 9 via electric wiring, and can be controlled. The ECU 9 stores various application programs and various control maps.

  By the way, when the engine 1 is cold-started, the fuel is difficult to evaporate, so that the fuel adheres to the cylinder wall surface and the fuel is difficult to ignite. Thus, when it becomes difficult to ignite fuel, the startability of the engine 1 will deteriorate.

  Here, light oil is less likely to evaporate at a lower temperature than gasoline. This is because light oil is less volatile than gasoline. Therefore, if a large amount of light oil is used when the engine 1 is cold started, the light oil is difficult to evaporate and therefore the engine 1 is difficult to start. However, since the engine speed is low and the engine generated torque is small when the engine 1 is started, according to the map of FIG. 2, it corresponds to the operation region (1), and light oil is mainly used as fuel. Thereby, the startability at the time of the cold start of the engine 1 will deteriorate.

  In this regard, in this embodiment, the gasoline supply ratio is increased when the engine 1 is cold started. For example, when the engine 1 is started and the coolant temperature obtained from the water temperature sensor 10 is lower than a specified temperature, the supply ratio of gasoline to light oil is set to, for example, 9 pairs as a cold start. Set to 1. On the other hand, when the cooling water temperature or the intake air temperature is equal to or higher than a specified temperature, the supply ratio of gasoline to light oil is set to 1: 9, for example, not during cold start. Since light oil is needed to ignite gasoline, it supplies at least the amount necessary for ignition. That is, light oil has better ignitability than gasoline and can be a fire type, but even if light oil particles are ignited, flame propagation is difficult unless a premixed gas is formed around them. Therefore, it is necessary to form a premixed gas. On the other hand, since it is difficult to ignite even if only gasoline is supplied, it is necessary to supply light oil with good ignitability into the cylinder.

  Here, the “specified temperature” may be obtained in advance through experiments or the like as the cooling water temperature at which the fuel is difficult to ignite when the supply ratio of gasoline to light oil is, for example, 1: 9. Moreover, it is good also as the temperature after completion of warming-up, for example, it is good also when the cooling water temperature is 70 degreeC.

  In the present embodiment, the gasoline supply ratio may be increased as the coolant temperature decreases. Here, the relationship between the temperature of the cooling water and the supply ratio of gasoline can be obtained in advance through experiments or the like and mapped, and the supply ratio of gasoline can be obtained by substituting the cooling water temperature into the map.

  Thus, by increasing the supply ratio of gasoline, which is a highly volatile fuel, when the engine 1 is cold started, it is possible to improve the ignitability of the fuel and further the startability of the engine 1.

  In the present embodiment, the supply ratio of highly volatile fuel, that is, gasoline, is increased when the exhaust purification catalyst 7 is heated.

  In the present embodiment, the basic configuration of the engine 1 and other hardware to be applied is the same as that of the first embodiment, and thus the description thereof is omitted.

By the way, when the exhaust purification catalyst 7 does not rise to the activation temperature, the purification rate of harmful components in the exhaust in the exhaust purification catalyst 7 decreases. However, combustion by premixed compression ignition can suppress NOx emission, but HC and CO may be emitted. In this case, it is assumed that the exhaust purification catalyst 7 on the downstream side is used for purification. However, if the exhaust purification catalyst 7 is not activated, the purification rate of HC and CO decreases, so that the exhaust purification catalyst 7 It is important to increase the temperature quickly to the activation temperature for activation.

  Here, gasoline has higher volatility than light oil and can be burned near the stoichiometric air-fuel ratio. When gasoline is burned near the stoichiometric air-fuel ratio, the exhaust air temperature becomes higher because the intake air amount of the engine 1 is smaller than when light oil is burned at a lean air-fuel ratio. That is, if the intake air amount is decreased by reducing the intake throttle valve 41 and the air-fuel ratio is lowered, the flow rate of the exhaust gas can be decreased and the temperature of the exhaust gas can be increased. Here, since the intake air amount is reduced and the intake air is compressed from a low pressure state, the temperature at the end of the compression stroke is lowered, so that the low-volatile fuel does not evaporate and adheres to the cylinder wall surface and is difficult to ignite. Therefore, unburned fuel may be discharged. Therefore, in this embodiment, the intake throttle valve 41 is throttled to raise the exhaust gas temperature while increasing the gasoline supply ratio.

  In this way, when gasoline is burned, the temperature of the exhaust can be made higher than when light oil is burned, and therefore the exhaust purification catalyst 7 can be raised in temperature quickly.

In this embodiment, the feed ratio between gasoline and light oil is feedback-controlled based on the exhaust temperature obtained from the output signal of the exhaust temperature sensor 8, that is, the temperature of the exhaust purification catalyst 7. For example, when the exhaust temperature obtained by the exhaust temperature sensor 8 is equal to or lower than the activation temperature of the exhaust purification catalyst 7, the gasoline supply ratio is 90%, and the remaining 10% is light oil. On the other hand, when the temperature of the exhaust gas becomes higher than the activation temperature, the gasoline supply ratio is 10%, and the remaining 90% is light oil. Here, the activation temperature can be set to, for example, 210 ° C., which is a temperature capable of oxidizing HC in light oil. Further, the fuel supply ratio may be changed until either the selective reduction type NOx catalyst 7a or the oxidation catalyst 7b reaches the activation temperature, and the fuel supply ratio is changed until both the catalysts 7a, 7b reach the activation temperature. You may make it do.

  Thus, when the temperature of the exhaust purification catalyst 7 is lower than the activation temperature, the exhaust gas temperature can be increased by increasing the supply ratio of gasoline, which is a fuel having higher volatility than light oil, The exhaust purification catalyst 7 can be quickly heated up to the activation temperature.

  Further, after the temperature of the exhaust purification catalyst 7 rises to a temperature at which light oil can be oxidized, the HC in the light oil can be supplied to the exhaust purification catalyst 7 by increasing the supply ratio of the light oil. The temperature of the exhaust purification catalyst 7 can be maintained by the oxidation reaction heat.

  In this embodiment, the supply ratio of gasoline to light oil may be changed stepwise based on the bed temperature of the exhaust purification catalyst 7. Here, the temperature of the exhaust purification catalyst 7 is divided into a plurality of stages, the fuel supply ratio is changed at each stage, and the gasoline supply ratio becomes lower as the temperature of the exhaust purification catalyst 7 becomes higher. May be. That is, the supply ratio of gasoline, which is a fuel having a higher exhaust temperature, may be lowered stepwise. Here, the relationship between the temperature of the exhaust purification catalyst 7 and the fuel supply ratio can be obtained in advance through experiments or the like and mapped, and the temperature of the exhaust purification catalyst 7 can be substituted into the map to obtain the fuel supply ratio. . At this time, the fuel supply ratio may be determined so that HC in the light oil does not flow downstream of the exhaust purification catalyst 7.

  In this embodiment, the supply ratio of gasoline to light oil may be gradually changed based on the bed temperature of the exhaust purification catalyst 7. That is, the supply ratio of gasoline, which is a fuel having a higher exhaust temperature, may be gradually lowered. Here, the relationship between the temperature of the exhaust purification catalyst 7 and the fuel supply ratio can be obtained by an experiment or the like in advance and mapped, and the temperature of the exhaust purification catalyst 7 can be substituted into the map to obtain the fuel supply ratio. . At this time, the fuel supply ratio may be determined so that HC in the light oil does not flow downstream of the exhaust purification catalyst 7.

  As described above, according to the present embodiment, the temperature of the exhaust gas is increased by increasing the supply ratio of highly volatile fuel, that is, gasoline, when the temperature of the exhaust gas purification catalyst 7 is raised. The temperature can be quickly raised to the activation temperature.

  In Example 1 and Example 2, gasoline is used as the highly volatile fuel and light oil is used as the less volatile fuel. However, instead of this, light gas oil is used as the highly volatile fuel. Alternatively, heavy gas oil may be employed as a low-volatile fuel.

It is a figure which shows schematic structure of the engine by the Example of this invention, and its intake / exhaust system. It is the figure which showed an example of the relationship between an engine speed, an engine generation torque, and an engine combustion state.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Engine 2 Cylinder 3 In-cylinder fuel injection valve 4 Intake passage 5 In-intake fuel injection valve 6 Exhaust passage 7 Exhaust purification catalyst 7a Selective reduction type NOx catalyst 7b Oxidation catalyst 8 Exhaust temperature sensor 9 ECU
10 Water temperature sensor 41 Intake throttle valve 42 Intake throttle actuator

Claims (3)

In a control device for a premixed compression ignition internal combustion engine that includes an exhaust purification catalyst that purifies harmful substances in exhaust gas, and that controls the ratio of a plurality of types of volatile fuel that are supplied into the cylinder according to the engine state ,
Cold start determination means for determining whether or not the internal combustion engine is a cold start at the time of starting,
When it is determined that the cold start is determined by the cold start determination means, the ratio of fuel having higher volatility in the fuel supplied into the cylinder than when it is determined that the cold start is not performed A control device for a premixed compression ignition type internal combustion engine, characterized in that Further comprising catalyst activity determination means for determining whether or not the exhaust purification catalyst is activated;
When it is determined by the catalyst activity determining means that the exhaust purification catalyst is not activated, the intake air amount of the internal combustion engine is decreased and it is determined that the catalyst is activated by the catalyst activity determining means. 2. The control apparatus for a premixed compression ignition type internal combustion engine according to claim 1, wherein the fuel is burned by increasing a ratio of fuel having higher volatility in the fuel supplied into the cylinder than in the case. The apparatus further comprises temperature detection means for detecting the temperature of the exhaust purification catalyst, and the higher the temperature detected by the temperature detection means, the lower the proportion of fuel that is more volatile among the fuel supplied into the cylinder. The control device for a premixed compression ignition type internal combustion engine according to claim 1 or 2.

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