JP5071271B2 - Compression self-ignition internal combustion engine - Google Patents

Description

  The present invention relates to a compression self-ignition internal combustion engine that estimates ignitability of fuel and performs engine control based on the estimated ignitability.

  The fuel used for the operation of the internal combustion engine has different ignitability depending on the cetane number. If the ignitability of the fuel is different, a deviation occurs in the ignition timing, so it is necessary to control the internal combustion engine in accordance with the ignitability.

  Japanese Patent Application Laid-Open No. 2007-187148 describes a control device for an internal combustion engine that estimates the cetane number of fuel in an engine operating state. More specifically, this apparatus is provided with an in-cylinder pressure sensor in the cylinder, detects the ignition timing from the pressure change per unit time in the cylinder, and estimates the cetane number based on the ignition timing. According to this apparatus, the above problem can be solved by accurately detecting the cetane number.

JP 2007-187148 A JP 2005-344557 A

  However, providing an in-cylinder pressure sensor in a cylinder may cause design difficulties because space is limited.

  The present invention has been made in view of this point, and accurately estimates the ignitability of the fuel being used without reflecting the in-cylinder pressure sensor in the cylinder, and reflects it in the engine control.

The invention of claim 1 is a fuel injection means for directly injecting fuel into a cylinder, a temperature detection means for detecting the temperature of exhaust gas discharged from the cylinder, and the temperature and use of the exhaust gas detected in a predetermined operating state. The storage means storing the relationship between the cetane number of the fuel being determined as the cetane number of the fuel being lower as the temperature of the exhaust gas is higher, and the temperature of the exhaust gas detected in the predetermined operating state and the relationship An ignitability estimation means for estimating the cetane number of the fuel and an engine control means for controlling the engine in accordance with the estimated cetane number are a compression self-ignition internal combustion engine.

  The invention according to claim 2 is the compression ignition type internal combustion engine according to claim 1, wherein the predetermined operation state is an idle operation state.

  The invention of claim 3 further includes an injection timing control means for controlling the fuel injection timing, and the predetermined operating state is an operating state in which the fuel injection timing is controlled to a predetermined timing that is retarded from the compression top dead center. 3. The compression self-ignition internal combustion engine according to claim 1, wherein the internal combustion engine is a compression self-ignition type engine.

  The invention of claim 4 further includes a reflux means for refluxing a part of the exhaust gas into the cylinder, and a reflux amount control means for controlling a reflux amount to be refluxed into the cylinder by the reflux means, First rule control means for controlling the reflux amount in accordance with a predetermined first rule, and second rule control means for controlling the reflux amount in accordance with a second rule in which the reflux amount is set to be larger than the first rule. 4. The compression ignition type internal combustion engine according to claim 1, wherein the predetermined operating state is an operating state in which the recirculation amount is controlled to a predetermined recirculation amount according to the second rule. .

  A fifth aspect of the present invention is the compression self-ignition internal combustion engine according to any one of the first to fourth aspects, wherein the temperature detecting means is provided in the exhaust passage in the vicinity of the internal combustion engine.

According to the first aspect of the present invention, the cetane number of the fuel can be estimated without providing an in-cylinder pressure sensor in the cylinder.

  According to the invention of claim 2, since the difference in the exhaust gas temperature due to the difference in the ignitability of the fuel tends to occur during the idling operation, the ignitability can be estimated with higher accuracy.

  According to the invention of claim 3, since the fuel injection timing is set to a predetermined timing that is retarded from the compression top dead center, a difference in exhaust gas temperature due to a difference in fuel ignitability is likely to occur. Can be used to estimate ignitability.

  According to the invention of claim 4, as the recirculation amount increases, the difference in the exhaust gas temperature due to the difference in the ignitability of the fuel is likely to occur, so that the ignitability can be estimated with higher accuracy.

  According to the invention of claim 5, since the temperature detecting means is disposed near the internal combustion engine, the temperature of the exhaust gas discharged from the cylinder can be detected more accurately.

  Embodiments of the present invention will be described below.

[Configuration of internal combustion engine]
FIG. 1 shows an overall view of a compression self-ignition internal combustion engine.
An intake passage 12 and an exhaust passage 13 are connected to the engine body 11. The intake passage 12 and the exhaust passage 13 are provided with a supercharger 14 in the middle of the passage.

  Each cylinder 15 of the engine body 11 is provided with an electromagnetic fuel injection valve 16 that injects fuel directly into the cylinder. By performing opening / closing control of the electromagnetic fuel injection valve 16, the fuel injection timing and the fuel injection amount can be controlled. The fuel injected by the electromagnetic fuel injection valve 16 is supplied from the fuel tank 17. A fuel supply port 18 of the fuel tank 17 is provided with a fuel supply sensor 18 that detects opening and closing of the fuel supply port.

  The internal combustion engine is also provided with a recirculation passage 19 that connects the intake passage 12 and the exhaust passage 13. A part of the exhaust gas discharged from the cylinder can be recirculated to the intake passage 12 via the recirculation passage 19. A reflux valve 20 is provided in the reflux passage 19, and the amount of reflux can be controlled by controlling the opening degree of the reflux valve 20.

  A temperature sensor 21 is provided in the exhaust manifold of the exhaust passage 13. The temperature of the exhaust gas discharged from the cylinder can be detected by the temperature sensor 21.

  The internal combustion engine is controlled by an ECU (Electron Control Unit) 22. The ECU 22 receives signals output from the temperature sensor 21, accelerator opening sensor 23, crank angle sensor 24, engine water temperature sensor 25, intake air amount sensor 26, and oil supply sensor 18. Based on the input signal, the ECU 22 performs arithmetic processing according to a predetermined program. Then, a signal obtained based on the arithmetic processing is output to the intake valve 28, the recirculation valve 20, and the electromagnetic fuel injection valve 16 provided in the intake passage 12. The internal combustion engine is controlled based on this output signal.

[Fuel ignitability]
The fuel used for the internal combustion engine has different ignitability depending on the cetane number. When a fuel having a high cetane number, that is, a fuel having high ignitability is used, the time from when the fuel is injected into the cylinder until ignition is shortened. Therefore, the fuel injected into the cylinder may be ignited before it is sufficiently mixed with air. As a result, engine output may be reduced and smoke may be generated.

  On the other hand, when a fuel with a low cetane number, that is, a fuel with low ignitability is used, the time from when the fuel is injected into the cylinder until ignition is increased. Therefore, the exhaust gas may be discharged from the cylinder before the fuel is completely burned. As a result, engine output is reduced, misfires, and unburned fuel are easily discharged.

  For these reasons, it is necessary to perform engine control according to the ignitability of the fuel.

[Ignition method]
A method for estimating the ignitability of the fuel based on the temperature of the exhaust gas discharged from the cylinder will be described with reference to FIGS.

  FIG. 2 shows the pressure change in the cylinder during engine operation. A solid line in FIG. 2 shows a change in the in-cylinder pressure when the engine is operated using a fuel having a high cetane number, and a broken line shows an operation of the engine using a fuel having a low cetane number. This is a change in in-cylinder pressure. In the solid line and the broken line, the operating conditions other than the cetane number of fuel (for example, fuel injection amount, fuel injection timing, engine speed, etc.) are the same. A thick arrow indicates the time when fuel is injected into the cylinder.

  In both the solid line and the broken line, the cylinder pressure rapidly increases after fuel injection. This sudden increase in in-cylinder pressure is due to the combustion of the injected fuel. The injected fuel is ignited at the point where the pressure suddenly increases.

Comparing the ignition timing of the fuel, it can be seen that the fuel having a high cetane number ignites earlier than the fuel having a low cetane number. In the case of a fuel having a high cetane number, combustion is also completed early because the fuel is ignited early. In general, it is known that the exhaust gas temperature is lowered when the combustion of fuel is completed at an early stage.
Therefore, when the cetane number of the fuel is high, the exhaust gas temperature discharged from the cylinder becomes low.

  On the other hand, when the cetane number of the fuel is low, the ignition of the injected fuel is slower than the fuel having a high cetane number. Accordingly, the end of the combustion of the fuel is accordingly delayed, and the temperature of the exhaust gas discharged from the cylinder becomes higher than that of the fuel having a high cetane number.

FIG. 3 is a map showing the relationship between the cetane number FCNTex of fuel in a predetermined operation state and the temperature Tex of exhaust gas discharged from the cylinder, and is created as follows.
First, the operating conditions (fuel injection timing, recirculation amount, engine speed, etc.) in map creation are determined. Then, the internal combustion engine is operated under the above operating conditions using a fuel having a known cetane number, and the temperature of the exhaust gas at that time is detected.
Next, the fuel is replaced with a fuel having a cetane number different from that described above, the fuel is operated under the same operating conditions as the above operating conditions, and the temperature of the exhaust gas is detected.
This is repeated, and the relationship between the cetane number of the fuel and the temperature of the exhaust gas is summarized as shown in the map of FIG. By fixing only the cetane number while fixing the above operating conditions, the temperature of the exhaust gas according to the difference in cetane number can be obtained.

Note that the estimation of the cetane number of the fuel is performed by using the map of FIG. 3 stored in the ECU 22.
First, the internal combustion engine is controlled under the same conditions as those when the map is created, and the temperature of the exhaust gas at that time is detected. If the operating conditions are the same as those at the time of creation, the relationship of the map in FIG. 3 is established. Therefore, it can be estimated from the map that the cetane number of the fuel corresponding to the detected temperature of the exhaust gas is the fuel used in the engine.

[Specific processing 1]
Hereinafter, specific processing for estimating the ignitability of fuel will be described with reference to the flowchart of FIG.
First, in S101, the ECU 22 reads the engine operating state such as the engine speed, the fuel injection amount, and the engine water temperature.

In step S102, it is determined whether fuel has been supplied. After refueling, the cetane number fluctuates as new fuel is refueled. Therefore, in order to perform engine control according to the cetane number of the fuel that has been refueled, in this embodiment, the cetane number is estimated when it is determined that fuel refueling has been performed.
Note that the fuel injected into the cylinder in the operation immediately after refueling may be the fuel before refueling remaining in the pipe. Therefore, the fuel ignitability is estimated after a predetermined time of operation after it is determined that fuel has been refueled. It is more preferable to carry out.
Fuel supply is determined based on a signal from a fuel supply sensor 18 provided at a fuel supply port of the fuel tank 17. If it is determined from the signal from the fuel supply sensor 18 that the fuel filler port has been opened from the time of the previous ignitability estimation to the time of the current ignitability estimation, it is assumed that new fuel has been supplied and the routine proceeds to S103. If it is determined that the refueling port remains closed, it is considered that no fuel has been refueled, and the flowchart ends.

  In S103, it is determined based on the data detected in S101 whether or not the engine is idling. The operation condition at the time of creating the map in FIG. 3 is idle operation. In this embodiment, in this step, when it is determined that the operating state of the internal combustion engine is the same idle operation as that at the time of creating the map, the fuel is estimated. This is because since the operating conditions are the same, the relationship between the cetane number of the fuel and the temperature of the exhaust gas shown in the map is established, and the cetane number of the fuel can be estimated.

The reason why the idling operation is cited as a condition for estimating the cetane number of the fuel is as follows.
When the engine is heavily loaded, the temperature inside the cylinder is higher than when the engine is lightly loaded. Therefore, even if fuel with a low cetane number is injected, it may ignite immediately after fuel injection, and there may be no difference in ignition timing from when a fuel with a high cetane number is used. In this case, there is no difference in exhaust gas temperature due to the difference in ignitability, and accurate ignitability cannot be estimated.
In the present embodiment, it is possible to perform highly accurate estimation by estimating the cetane number during idle operation where the engine is stable and the temperature in the cylinder is low.
If it is determined in S103 that the engine is in the idle operation state, the process proceeds to S104. If it is determined that the engine is not in the idle operation state, the flowchart ends.

In S104, the fuel injection timing InjTm is set to a predetermined injection timing InjT1 that is retarded from the compression top dead center. The predetermined injection timing InjT1 is assumed to be the same as the injection timing stored in the ECU 22 when the map indicating the relationship between the cetane number of the fuel and the temperature of the exhaust gas is created. The reason is that if the operating state is different from that at the time of creating the map, the correspondence relationship between the cetane number of the fuel and the temperature of the exhaust gas does not hold and estimation cannot be performed.
The reason why the injection timing is retarded from the compression top dead center is as follows.
When the piston is near compression top dead center, the cylinder is in a high temperature and high pressure state, so even if the cetane number of the fuel is low, it ignites immediately after fuel injection, and fuel with a high cetane number was used. There may be no difference in ignition timing with time. In this case, there is no difference in exhaust gas temperature due to the difference in ignitability, and accurate ignitability cannot be estimated.
In addition, when fuel is injected on the advance side from the compression top dead center, it takes time from the end of combustion of the injected fuel until the exhaust gas is discharged from the cylinder, so that a temperature difference between the exhaust gases hardly occurs.
Therefore, in view of the above problem, the fuel injection timing is set to the above timing in order to perform highly accurate estimation.
If the fuel injection timing is set to be retarded by a predetermined time or more from the compression top dead center, it is assumed that the fuel does not ignite due to a decrease in temperature and pressure in the cylinder. Therefore, the fuel injection must be set to the advance side at least from the predetermined time at which the fuel ignition occurs.
When the fuel injection timing InjTm is set to the predetermined injection timing InjT1 that is retarded from the compression top dead center in S104, the process proceeds to S105.

In S105, the recirculation amount EGRR is set to a predetermined recirculation amount EGR1 that is larger than the normal operation state (operation state in which fuel ignitability is not estimated). That is, in the present embodiment, in the operating state in which the estimation of fuel ignitability is not performed, the recirculation amount control is performed according to a predetermined first rule. On the other hand, when estimating the ignitability of the fuel, the recirculation amount is controlled according to the second rule in which the recirculation amount is set larger than that of the first rule.
This predetermined recirculation amount EGR1 is assumed to be the same value as the recirculation amount stored in the ECU 22 when the map showing the relationship between the cetane number of the fuel and the temperature of the exhaust gas is created. The reason is that, similarly to the reason described in S104, if the operating state is different from that at the time of creating the map, the correspondence relationship between the cetane number of the fuel and the temperature of the exhaust gas is not established, and estimation cannot be performed.

The reason why the reflux amount is made larger than that in the normal operating state is as follows.
When recirculation is performed during operation of the internal combustion engine, the amount of air newly flowing into the cylinder decreases as the recirculation amount increases, so that the oxygen concentration in the cylinder decreases. When the oxygen concentration in the cylinder is low, the injected fuel is difficult to ignite, and a difference in ignition timing due to a difference in ignitability tends to occur.
Therefore, the temperature difference of the exhaust gas due to the difference in the ignitability of the fuel becomes clearer, and the ignitability can be estimated with high accuracy. Therefore, the recirculation amount is set larger than that in the normal state.
If the recirculation amount EGRR is set to the predetermined recirculation amount EGR1 in S105, the process proceeds to S106.

  In S106, the temperature sensor 21 detects the temperature of the exhaust gas discharged from the cylinder. If the temperature of exhaust gas is detected, it will progress to S107.

  In S107, the cetane number of the fuel is estimated based on the temperature of the exhaust gas detected by the temperature sensor 21. Estimating the cetane number by applying the detected exhaust gas temperature to a map that shows the relationship between the cetane number FCNTex of the fuel and the temperature Tex of the exhaust gas discharged from the cylinder stored in the ECU 22 in advance. To do.

  In S108, the ECU 22 reads the cetane number FCNTex of the fuel estimated in S107.

In S109, the cetane number FCNTex read in S108 is reflected in the engine control. The engine is controlled by correcting the fuel injection timing, the fuel injection amount, etc. according to the cetane number of the fuel.
For example, if the cetane number of the fuel is low, the ignition timing of the fuel will be retarded. Therefore, it is possible to prevent the deviation of the ignition timing by advancing the fuel injection timing so that the desired ignition timing is reached. it can. In addition, when the cetane number of the fuel is high, the ignition timing of the fuel is ignited early and the desired engine output cannot be obtained. Therefore, it is possible to prevent the engine output from decreasing by increasing the fuel injection amount accordingly. it can.

[Specific processing 2]
In the flowchart of FIG. 4, a map showing the relationship between the cetane number of fuel and the ignitability in a predetermined operating state is stored in the ECU 22, and the same operating state as that at the time of creating the map is reproduced. Estimating.
On the other hand, in the flowchart of FIG. 5, the ECU 22 stores in advance a map showing the relationship between the cetane number and the ignitability of the fuel for each of various operating states, so that the ignition of the fuel can be performed without reproducing the operating state. This is to estimate sex.

  The flowchart of FIG. 5 is obtained by deleting steps S104 and S105 of the flowchart of FIG. 4 and replacing the cetane number estimation method performed in S107 with the method of S207. As described above, unlike the case of FIG. 4, the ECU 22 is assumed to store maps for various operating states.

  In S207 of FIG. 5, a map created in the same operating state as the engine operating state read in S101 is selected from a plurality of maps stored in the ECU 22. Then, the cetane number FCNTex of the fuel is estimated based on the selected map and the detected temperature of the exhaust gas. This makes it possible to estimate the cetane number more simply without reproducing the operating state.

  The flowchart shown in FIG. 5 is the same as the flowchart shown in FIG. 4 except for the above points, and the other description is omitted.

The above is the embodiment of the present invention.
In the above-described embodiment, the temperature sensor 21 is provided in the exhaust manifold of the exhaust passage 13, but it is not limited to this as long as it is provided in the exhaust passage.
If a temperature sensor is provided, it is more preferable to provide the exhaust passage upstream of the supercharger 14. This is because the thermal energy of the exhaust gas is consumed as kinetic energy in the supercharger 14, and this amount becomes an error when detecting the exhaust gas temperature.

  Further, in order to determine whether or not fuel has been supplied, a fuel supply sensor 18 is provided at the fuel supply port, and the determination is based on the signal, but a liquid level sensor that detects the level of the fuel in the fuel tank is used. It may be. It is considered that the fuel has been refueled when a rise in the liquid level above a predetermined level is detected between the previous estimation of the ignitability of the fuel and the current estimation. to decide.

1 is an overall view of a compression self-ignition internal combustion engine. It is a figure which shows the pressure change in the cylinder during engine operation. It is a figure which shows the relationship between the cetane number of the fuel in a predetermined driving | running state, and the temperature of the waste gas discharged | emitted from a cylinder. It is a flowchart performed in implementing this invention. It is a flowchart performed in implementing this invention.

Explanation of symbols

11 Engine body 15 Cylinder 16 Electromagnetic fuel injection valve 17 Fuel tank 18 Refueling sensor 19 Recirculation passage 20 Recirculation valve 21 Temperature sensor

Claims (5)

Fuel injection means for directly injecting fuel into the cylinder;
Temperature detecting means for detecting the temperature of the exhaust gas discharged from the cylinder;
Storage means for storing the relationship between the temperature of the exhaust gas detected in a predetermined operation state and the cetane number of the fuel being used, as the higher the temperature of the exhaust gas, the lower the cetane number of the fuel ;
Ignitability estimating means for estimating the cetane number of the fuel based on the temperature of the exhaust gas detected in the predetermined operating state and the relationship;
Engine control means for controlling the engine according to the estimated cetane number ;
A compression self-ignition internal combustion engine comprising:   The compression self-ignition internal combustion engine according to claim 1, wherein the predetermined operation state is an idle operation state. An injection timing control means for controlling the fuel injection timing;
3. The compression ignition type internal combustion engine according to claim 1, wherein the predetermined operation state is an operation state in which the fuel injection timing is controlled to a predetermined timing that is retarded from the compression top dead center. organ. Recirculation means for recirculating part of the exhaust gas into the cylinder;
A recirculation amount control means for controlling a recirculation amount recirculated into the cylinder by the recirculation means;
The reflux amount control means includes first rule control means for controlling the reflux amount according to a predetermined first rule;
A second rule control means for controlling the reflux amount according to a second rule in which the reflux amount is set to be larger than the first rule;
4. The compression self-ignition internal combustion engine according to claim 1, wherein the predetermined operating state is an operating state in which the recirculation amount is controlled to a predetermined recirculation amount according to the second rule.   The compression self-ignition internal combustion engine according to any one of claims 1 to 4, wherein the temperature detection means is provided in the exhaust passage in the vicinity of the internal combustion engine.

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