WO2013038805A1

WO2013038805A1 - Combustion control device

Info

Publication number: WO2013038805A1
Application number: PCT/JP2012/068337
Authority: WO
Inventors: 裕史葛山; 謹河合
Original assignee: 株式会社豊田自動織機
Priority date: 2011-09-14
Filing date: 2012-07-19
Publication date: 2013-03-21
Also published as: JP5146581B1; JP2013060922A

Abstract

A combustion control device equipped with: fuel injection valves (5) that inject fuel into the combustion chamber (4) of an engine (1); an intake pressure sensor (30) that detects the intake pressure with respect to the combustion chamber (4); and an electronic control unit (27) that operates the fuel injection valves (5). The electronic control unit (27) determines the fuel injection amount and the fuel injection timing, and operates the fuel injection valves (5) so as to execute fuel injection in accordance with the fuel injection amount and the fuel injection timing, and performs a correction so as to advance the ignition timing during fuel injection when the intake pressure detected by the intake pressure sensor (30) is lower than a prescribed pressure.

Description

Combustion control device

The present invention relates to a combustion control device for an engine that performs Premixed Charge Compression Ignition (PCCI) combustion.

As a combustion control device for an engine that performs premixed compression ignition combustion, for example, a combustion control device described in Patent Document 1 is known. The combustion control device described in Patent Document 1 forms the mixture as homogeneous as possible in advance by injecting fuel several times by the injector from the middle stage to the late stage of the compression stroke of the cylinder, and then mixes the mixture by self-ignition. Burn it.

JP 2003-286879 A

However, when the premixed compression ignition combustion is performed, if the intake pressure into the combustion chamber of the engine decreases, there is a risk that an appropriate combustion waveform (heat generation rate waveform) can not be obtained. If an appropriate combustion waveform can not be obtained, it is difficult to realize appropriate premixed compression ignition combustion, which leads to an increase in combustion noise and a deterioration in emissions.

An object of the present invention is to provide a combustion control device capable of realizing appropriate premixed compression ignition combustion even when the intake pressure into the combustion chamber decreases.

The present invention is a combustion control device of an engine performing premixed compression ignition combustion, comprising: a fuel injection valve for injecting fuel into a combustion chamber of the engine; determination means for determining a fuel injection amount and a fuel injection timing; In order to carry out fuel injection according to the amount and fuel injection timing, injection control means for controlling the fuel injection valve, an intake passage for drawing air into the combustion chamber, and exhaust gas after combustion from the combustion chamber The ignition timing by fuel injection is advanced when the intake pressure detected by the intake pressure detection means for detecting the intake pressure into the combustion chamber and the intake pressure detected by the intake pressure detection means is lower than a predetermined pressure. And correction means for correcting the

When the intake pressure into the combustion chamber of the engine decreases, the amount of air taken into the combustion chamber decreases. When fuel is injected into the combustion chamber by the fuel injection valve, the oxidation reaction between the fuel and air is delayed, so an appropriate combustion waveform can not be obtained. The combustion control device of the present invention detects the intake pressure into the combustion chamber, and corrects the ignition timing by fuel injection to advance when the intake pressure is lower than a predetermined pressure. Thus, the combustion waveform when the intake pressure is lower than the predetermined pressure approaches the combustion waveform obtained when the intake pressure is the predetermined pressure. Therefore, appropriate premixed compression ignition combustion is realized. As a result, it is possible to suppress an increase in combustion noise and a deterioration in emission.

In the combustion process in premixed compression ignition combustion, the low temperature oxidation reaction (cold flame reaction) in which heat generation gradually occurs by the fuel injected into the combustion chamber and the high temperature oxidation reaction (thermal And flame reaction). The ignition timing by fuel injection is a timing at which a high temperature oxidation reaction starts to rapidly generate heat.

The determination means determines the fuel injection amount and fuel injection timing of the second fuel injection to be performed after the first fuel injection and the first fuel injection, and the injection control means determines the fuel injection amount and the fuel injection timing. Accordingly, the fuel injection valve is controlled such that the first fuel injection and the second fuel injection are sequentially performed, and the correction means detects that the intake pressure detected by the intake pressure detection means is lower than a predetermined pressure, The correction may be made to advance the ignition timing by the first fuel injection.

When the fuel is dividedly injected, the fuel combustion period in the combustion chamber becomes longer. Therefore, when the intake pressure is lower than the predetermined pressure, the combustion waveform is likely to deviate from the appropriate combustion waveform. The correction means corrects to advance the ignition timing by the first fuel injection when the detected intake pressure is lower than a predetermined pressure. Thus, the combustion waveform when the intake pressure is lower than the predetermined pressure approaches the combustion waveform obtained when the intake pressure is the predetermined pressure. The first fuel injection and the second fuel injection are divided injections of the main fuel injection for generating the required engine output, and a small amount of fuel injection performed before the main fuel injection This is different from (so-called pilot fuel injection or pre-fuel injection etc).

The correction means includes an air-fuel ratio control means for controlling an air-fuel ratio in the combustion chamber, and an injection timing advance means for advancing the fuel injection timing of the first fuel injection determined by the determination means. The advance means advances the fuel injection timing of the first fuel injection when the intake pressure detected by the intake pressure detection means is lower than a predetermined pressure, and the air fuel ratio control means detects the intake pressure by the intake pressure detection means When the intake pressure is lower than the predetermined pressure, the air-fuel ratio in the combustion chamber may be controlled to be maintained at the air-fuel ratio at the predetermined pressure.

Since the injection timing advance means advances the fuel injection timing of the first fuel injection, the ignition timing by the first fuel injection is advanced. Thus, the ignition timing by the first fuel injection reliably approaches the ignition timing obtained when the intake pressure is a predetermined pressure. Since the air-fuel ratio control means controls the air-fuel ratio in the combustion chamber to be maintained at the air-fuel ratio at the predetermined pressure, the combustion waveform approaches the combustion waveform obtained when the intake pressure is the predetermined pressure. As a result, the combustion of the premixed mixture of fuel and air is properly performed, and the increase in HC and CO of unburned components can be suppressed.

The engine further includes load detecting means for detecting the load of the engine, and the injection timing advancing means has the intake pressure detected by the intake pressure detecting means lower than a predetermined pressure and the engine load detected by the load detecting means is When it is higher than the first predetermined value, the fuel injection timing of the first fuel injection is advanced, and the air-fuel ratio control means determines that the intake pressure detected by the intake pressure detection means is lower than the predetermined pressure and When the load of the engine detected by the load detection means is higher than the first predetermined value, the air-fuel ratio in the combustion chamber may be controlled to be maintained at the air-fuel ratio at the predetermined pressure.

Generally, when the engine load is low, the amount of intake air is smaller than when the engine load is high. Therefore, when the load of the engine is lower than the first predetermined value, the ignition timing by the first fuel injection is less likely to be advanced even if the fuel injection timing of the first fuel injection is advanced. Therefore, the correction by the injection timing advancing means and the air fuel ratio control means (the fuel injection timing of the first fuel injection is advanced and controlled so that the air fuel ratio in the combustion chamber is maintained at the air fuel ratio at the predetermined pressure) As a result, the operating range in which the correction for advancing the ignition timing by the first fuel injection is performed is narrowed to the area of the engine load where it is easy to advance the ignition timing by the first fuel injection. Thereby, the ignition timing by the first fuel injection can be efficiently brought close to the ignition timing obtained when the intake pressure is a predetermined pressure.

When the intake pressure detected by the intake pressure detection means is lower than a predetermined pressure and the load of the engine detected by the load detection means is lower than a first predetermined value, the air fuel ratio control means The air-fuel ratio may be controlled to be lean with respect to the air-fuel ratio at a predetermined pressure.

When the load of the engine is lower than the first predetermined value, the air-fuel ratio control means controls the air-fuel ratio in the combustion chamber to be lean with respect to the air-fuel ratio at the predetermined pressure. As a result, the amount of air taken into the combustion chamber is sufficiently increased, so that the ignition timing by the first fuel injection is advanced even if the fuel injection timing of the first fuel injection is not particularly advanced. Therefore, the combustion waveform surely approaches the combustion waveform obtained when the intake pressure is a predetermined pressure. As a result, the combustion of the premixed mixture of fuel and air is properly performed, and the increase in unburned HC and CO can be suppressed.

The correction means is configured to set the fuel injection pressure of the first fuel injection and the second fuel injection when the engine load detected by the load detection means is higher than a second predetermined value larger than the first predetermined value. It may further include injection pressure control means for controlling to decrease.

If the intake pressure into the combustion chamber of the engine is low, ignition by the first fuel injection is delayed. Therefore, when the second fuel injection is performed, the temperature in the combustion chamber rises, and the ignition delay due to the second fuel injection is shortened. As a result, there may occur a problem that the pre-mixing time of fuel and air by the second fuel injection becomes short. In particular, when the load on the engine is high, the amount of fuel injected by the first fuel injection increases, so the temperature in the combustion chamber rises when the second fuel injection is performed. As a result, the ignitability of the fuel by the second fuel injection is improved, and the above-mentioned problems appear prominently. The injection pressure control means controls to lower the fuel injection pressure of the first fuel injection and the second fuel injection when the load of the engine is higher than a second predetermined value larger than the first predetermined value. Therefore, the second fuel injection hardly causes ignition. Therefore, the premixing time of the fuel and air by the second fuel injection becomes long, and the insufficient premixing is prevented. As a result, an increase in smoke can be suppressed.

The correction means reduces injection amount of the second fuel injection when the engine load detected by the load detection means is higher than a second predetermined value larger than the first predetermined value. May further be included.

Since the injection amount reducing means reduces the fuel injection amount of the second fuel injection when the load of the engine is higher than the second predetermined value larger than the first predetermined value, the injection pressure control means reduces the second Similar to the case of reducing the fuel injection pressure of the fuel injection, the second fuel injection hardly causes the ignition. Therefore, the premixing time of fuel and air is prolonged, and the lack of premixing is prevented. As a result, an increase in smoke can be suppressed.

The exhaust gas recirculation passage is disposed to connect the exhaust gas passage and the intake gas passage, and is disposed in an exhaust gas recirculation passage for recirculating a portion of the exhaust gas as exhaust gas recirculation gas into the combustion chamber. The air-fuel ratio control means may control the air-fuel ratio in the combustion chamber by controlling the valve means such that the amount of recirculation of the exhaust gas recycle is reduced. .

Since the valve means for adjusting the amount of recirculation of the exhaust gas recirculation is used, the air-fuel ratio in the combustion chamber can be maintained at the air-fuel ratio at the predetermined pressure with a simple configuration and with certainty.

According to the present invention, it is possible to provide a combustion control device capable of realizing appropriate premixed compression ignition combustion even when the intake pressure into the combustion chamber decreases.

FIG. 1 is a schematic configuration view showing a diesel engine provided with a combustion control device according to an embodiment of the present invention. FIG. 2 is a flowchart showing a processing procedure executed by the ECU shown in FIG. FIG. 3 is a graph showing the heat release rate waveform under the condition where the engine load is in the low load region. FIG. 4 is a graph showing the level of combustion noise and the emission concentration of HC and CO under the condition where the engine load is in the low load region. FIG. 5 is a graph showing the heat release rate waveform under the condition where the engine load is in the medium load region. FIG. 6 is a graph showing the amount of generated NOx and the level of combustion noise under the condition where the engine load is in the medium load region. FIG. 7 is a graph showing the heat release rate waveform under the condition where the engine load is in the high load region. FIG. 8 is a graph showing the smoke generation rate and the pre-mixing time by the second fuel injection under the condition where the engine load is in the high load range. FIG. 9 shows the characteristics of the combustion waveform when only the fuel injection timing of the first fuel injection is advanced, and the case where the fuel injection timing of the first fuel injection and the second fuel injection are advanced. Of the characteristics of the combustion waveform of

Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the drawings.

FIG. 1 is a schematic configuration view showing a diesel engine provided with a combustion control device according to an embodiment of the present invention. As shown in FIG. 1, the diesel engine 1 is a four-cylinder in-line diesel engine that performs homogeneous charge compression ignition (PCCI), and includes a common rail fuel injection device. The diesel engine 1 comprises an engine body 2 in which four cylinders 3 are arranged.

Each cylinder 3 is provided with an injector (fuel injection valve) 5 for injecting fuel into the combustion chamber 4. The injectors 5 inject fuel radially from the injection nozzle 5a. Each injector 5 is connected to the common rail 6. The common rail 6 is connected to the high pressure pump 8 through the fuel supply pipe 7. The common rail 6 stores high pressure fuel supplied from the high pressure pump 8 and uniformly supplies the fuel to each injector 5. A rail pressure adjusting valve 9 is disposed in the fuel supply pipe 7 to adjust the pressure of the fuel in the common rail 6 (common rail pressure).

An intake passage 10 for drawing air into the combustion chamber 4 is connected to the engine body 2 via an intake manifold 11. An exhaust passage 12 for discharging exhaust gas after combustion is connected to the engine body 2 via an exhaust manifold 13.

In the intake passage 10, an air cleaner 14, a compressor 16 of a turbocharger 15, an intercooler 17, and a throttle valve 18 are disposed from the upstream side toward the downstream side. The throttle valve 18 reduces the passage area of the intake passage 10. When the passage area of the intake passage 10 is narrowed by the throttle valve 18, a negative pressure is generated downstream of the throttle valve 18. This enables exhaust gas recirculation (EGR) described later. In the exhaust passage 12, the turbine 19 of the turbocharger 15 and the DPF 20 with a catalyst are disposed.

The diesel engine 1 includes an exhaust gas recirculation (EGR) device 21 that recirculates a part of the exhaust gas after combustion into the combustion chamber 4 as an exhaust gas recirculation gas (EGR gas). The EGR device 21 is arranged to connect the intake passage 10 and the exhaust manifold 13. The EGR device 21 has an EGR passage 22, an EGR valve (valve means) 23, an EGR cooler 24, a bypass passage 25, and a switching valve 26. The EGR passage 22 connects the intake passage 10 and the exhaust manifold 13 to recirculate the EGR gas. The EGR valve 23 adjusts the amount of recirculation of EGR gas from the exhaust manifold 13 to the intake passage 10. The EGR cooler 24 cools the EGR gas passing through the EGR passage 22. The bypass passage 25 is connected to the EGR passage 22 so as to bypass the EGR cooler 24. The switching valve 26 switches the flow path of the EGR gas to the EGR cooler 24 side or the bypass passage 25 side.

Each of the injectors 5, the rail pressure adjustment valve 9, the throttle valve 18, the EGR valve 23, and the switching valve 26 described above are controlled by an electronic control unit (ECU) (controller) 27. A crank angle sensor 28, an accelerator opening sensor 29, and an intake pressure sensor 30 are connected to the ECU 27.

The crank angle sensor 28 detects a rotation angle (crank angle) of a crankshaft to which a piston (not shown) is connected. Based on the output from the crank angle sensor 25, the number of rotations of the engine body 2 (engine rotation number) can be calculated. The accelerator opening degree sensor 29 detects the depression angle (accelerator opening degree) of the accelerator pedal as an alternative value of the load (engine load) of the engine body 2. The accelerator opening degree sensor 29 functions as a load sensor (load detection means). In a diesel engine equipped with a common rail fuel injection system, the fuel injection amount is electronically controlled, and it is also possible to use the fuel injection amount as a substitute value for the engine load. The intake pressure sensor 30 detects the pressure of air taken into the combustion chamber 4 (intake pressure into the combustion chamber 4). The intake pressure sensor 30 functions as an intake pressure detection unit. The intake pressure sensor 30 is disposed, for example, at the downstream end of the intake passage 10.

Detection signals of the crank angle sensor 28, the accelerator opening degree sensor 29, and the intake pressure sensor 30 are input to the ECU 27. The ECU 27 performs predetermined processing, and controls the injector 5, the rail pressure adjustment valve 9, the throttle valve 18, the EGR valve 23, and the switching valve 26.

The injector 5, the common rail 6, the fuel supply pipe 7, the high pressure pump 8, the rail pressure adjusting valve 9, the intake passage 10, the exhaust passage 12, the throttle valve 18, the exhaust gas recirculation device 21, the ECU 27, and the sensors 28 to 30 The combustion control apparatus 31 of the form is comprised. The combustion control device 31 sucks air into the combustion chamber 4 and injects the fuel from the injectors 5 into the combustion chamber 4 in multiple cycles in one cycle of the intake stroke, compression stroke, expansion stroke, and exhaust stroke. (Divided injection) is controlled to perform premixed compression ignition combustion.

FIG. 2 is a flowchart showing the processing procedure executed by the ECU 27. In this process, the injector 5, the rail pressure adjusting valve 9, and the EGR valve 23 are controlled based on the detection signals of the sensors 28-30.

As shown in FIG. 2, the ECU 27 first determines the fuel injection amount and fuel injection timing of the second fuel injection performed after the first fuel injection and the first fuel injection (S101). Here, the ECU 27 determines the fuel injection amount and the fuel injection timing based on the engine speed detected by the crank angle sensor 28 and the accelerator opening (engine load) detected by the accelerator opening sensor 29. Do.

Subsequently, the ECU 27 determines whether the intake pressure detected by the intake pressure sensor 30 is lower than a reference pressure (for example, the atmospheric pressure) (S102). If the ECU 27 determines that the intake pressure is lower than the reference pressure, the ECU 27 determines whether the engine load detected by the accelerator opening sensor 29 is lower than the low load threshold (S103). The low load side threshold is set to, for example, an opening of 30% with respect to the accelerator fully open. The ECU 27 may determine whether the engine load detected by the accelerator opening sensor 29 is less than or equal to the low load threshold value in the process of S103.

When the ECU 27 determines that the engine load is lower than the low load threshold, the air-fuel ratio (A / F) in the combustion chamber 4 at that time is made lean with respect to the air-fuel ratio set at the reference pressure. In other words, control is performed to become larger than the air-fuel ratio set at the reference pressure (S104). Here, the ECU 27 controls the air-fuel ratio by controlling the EGR valve 23. Specifically, the ECU 27 increases the amount of intake air into the combustion chamber 4 by controlling the EGR valve 23 so as to reduce the amount of recirculation of EGR gas to the intake passage 10. The air-fuel ratio is made lean by increasing the amount of intake air into the combustion chamber 4 without changing the fuel injection amount into the combustion chamber 4. The amount to make the air-fuel ratio lean may be increased, for example, as the intake pressure and the engine load are lower.

By making the air-fuel ratio lean as described above, the amount of intake air into the combustion chamber 4 increases. For this reason, when fuel is injected from the injector 5 into the combustion chamber 4, the ignition timing of the premixed mixture of air and fuel advances.

When the ECU 27 determines that the engine load is not lower than the low load threshold, the ECU 27 controls the air-fuel ratio in the combustion chamber 4 at that time to be maintained at the air-fuel ratio set at the reference pressure (S105) . Here too, the ECU 27 controls the air-fuel ratio by controlling the EGR valve 23. When the intake pressure into the combustion chamber 4 decreases, the amount of intake air into the combustion chamber 4 decreases. Therefore, in order to maintain the air-fuel ratio at the air-fuel ratio set at the reference pressure, it is necessary to increase the amount of intake air into the combustion chamber 4 by the amount by which the amount of intake air decreases. The ECU 27 controls the EGR valve 23 to reduce the amount of EGR gas recirculated to the intake passage 10 in accordance with the decrease in the amount of intake air. As a result, the amount of intake air into the combustion chamber 4 increases, and the air-fuel ratio is maintained at the air-fuel ratio set at the reference pressure.

Subsequently, the ECU 27 advances the fuel injection timing of the first fuel injection and the second fuel injection determined by the processing in S101 (S106). The amount of advance of the fuel injection timing may be, for example, an amount according to the intake pressure and the engine load, or may be a predetermined constant amount.

By advancing the fuel injection timing of the fuel injection as described above, when fuel is injected from the injector 5 into the combustion chamber 4, the ignition timing of the premixed mixture of air and fuel is advanced.

Subsequently, the ECU 27 determines whether the engine load detected by the accelerator opening sensor 29 is higher than the high load threshold (S107). The high load side threshold value is a value larger than the low load side threshold value, and is set to, for example, an opening degree of 60% with respect to full accelerator opening.

When the ECU 27 determines that the engine load is higher than the high load threshold value, the ECU 27 controls the rail pressure adjusting valve 9 so as to reduce the common rail pressure from a preset value (S108). As a result, the fuel injection pressure from the injector 5 is reduced. The amount of reduction of the common rail pressure may be, for example, an amount corresponding to the intake pressure and the engine load, or may be a preset fixed amount.

Subsequently, the ECU 27 decreases the fuel injection amount of the second fuel injection determined by the processing in S101, and the fuel injection amount of the first fuel injection determined in S101 by the reduction amount of the fuel injection amount. The amount is increased (S109). The amount of decrease of the fuel injection amount may be, for example, an amount according to the intake pressure and the engine load, or may be a preset constant amount.

When the ECU 27 determines that the intake pressure is not lower than the reference pressure based on the processing in S102, when the processing in S104 is executed, the engine load is higher than the high load threshold based on the processing in S107. When it is determined that there is no, or when the process of S109 is performed, each injector 5 is controlled so that the first fuel injection and the second fuel injection are sequentially performed (S110).

When the ECU 27 determines that the intake pressure is not lower than the reference pressure based on the process of S102, or when the process of S104 is performed, the fuel injection amount and the fuel injection determined by the process of S101 The first fuel injection and the second fuel injection are sequentially performed according to the timing. When the ECU 27 determines that the engine load is not higher than the high load threshold based on the processing at S107, the fuel injection amount determined by the processing at S101 and the fuel injection timing corrected by the processing at S106 The first fuel injection and the second fuel injection are sequentially performed according to When the process of S109 is executed, the ECU 27 performs the first fuel injection and the second fuel injection according to the fuel injection amount corrected by the process of S109 and the fuel injection timing determined by the process of S101. Implement sequentially.

The ECU 27 (in particular, the process in S101) constitutes a determination means for determining the fuel injection amount and the fuel injection timing. The ECU 27 (in particular, the process at S110) constitutes an injection control means for controlling the fuel injection valve (injector 5) so as to carry out the fuel injection according to the fuel injection amount and the fuel injection timing. The ECU 27 (particularly, the processing in S102 to S109) corrects the ignition timing by fuel injection to advance when the intake pressure detected by the intake pressure detection means (intake pressure sensor 30) is lower than a predetermined pressure. Constitute correction means.

The ECU 27 (particularly, the processing in S102 to S105) constitutes an air-fuel ratio control unit that controls the air-fuel ratio in the combustion chamber 4. The ECU 27 (in particular, the process at S106) constitutes an injection timing advancing means for advancing the fuel injection timing of the first fuel injection determined by the determining means. The ECU 27 (in particular, the processing in S107 and S108) is executed when the engine load detected by the load detection means (the accelerator opening sensor 29) is higher than a second predetermined value larger than the first predetermined value. An injection pressure control means is configured to perform control to lower the fuel injection pressure of the first fuel injection and the second fuel injection. The ECU 27 (in particular, the processing in S107 and S109) is performed when the engine load detected by the load detection means (the accelerator opening sensor 29) is higher than a second predetermined value larger than the first predetermined value. The fuel injection amount reducing means is configured to reduce the fuel injection amount of the second fuel injection.

When the intake pressure into the combustion chamber 4 becomes lower due to the influence of the change of the atmospheric pressure, the amount of air taken into the combustion chamber 4 decreases. Therefore, when the fuel is injected into the combustion chamber 4 by the injector 5, the oxidation reaction between the fuel and the air is delayed. Therefore, the heat generation rate waveform (combustion waveform) deviates from the heat generation rate waveform obtained when the intake pressure is the reference pressure, and the same premixed compression ignition combustion is realized as when the intake pressure is the reference pressure. Is difficult. In this case, combustion noise may increase, and unburned HC and CO are likely to be generated due to combustion deterioration.

In the present embodiment, when the intake pressure into the combustion chamber 4 is lower than the reference pressure, the engine load is in the middle load range from the low load threshold to the high load threshold. The air-fuel ratio set at the reference pressure is maintained so as to secure the intake air amount of 1 and the fuel injection timing of the first fuel injection and the second fuel injection is advanced. As a result, the ignition timing of the premixed mixture of fuel and air substantially matches the ignition timing when the intake pressure is the reference pressure, so a heat release rate waveform is obtained when the intake pressure is the reference pressure It approaches the heat release rate waveform. Since the combustion of the premixed mixture is properly performed, it is possible to suppress an increase in combustion noise and an increase in HC and CO of unburned components. NOx can be reduced as compared with the case where the air-fuel ratio in the combustion chamber 4 is made lean.

When the intake pressure into the combustion chamber 4 is lower than the reference pressure, the amount of intake air into the combustion chamber 4 can be secured under the condition that the engine load is in the high load region higher than the high load threshold. The air-fuel ratio set at the time of the reference pressure is maintained, and the fuel injection timing of the first fuel injection and the second fuel injection is advanced. Furthermore, as the common rail pressure is reduced, the fuel injection pressure from the injector 5 is reduced, and the fuel injection amount of the second fuel injection is reduced. Thus, as described above, the heat release rate waveform approaches the heat release rate waveform obtained when the intake pressure is the reference pressure.

When the intake pressure into the combustion chamber 4 is low, the ignition by the first fuel injection is delayed, so the temperature (in-cylinder temperature) in the combustion chamber 4 rises when the second fuel injection is performed. In particular, when the engine load is in the high load range, the amount of fuel injected by the first fuel injection increases, so the temperature in the combustion chamber 4 further increases when the second fuel injection is performed. easy. Therefore, the ignitability of the fuel by the second fuel injection is improved, and the ignition delay by the second fuel injection is easily shortened. However, as described above, since the fuel injection pressure from the injector 5 is reduced and the fuel injection amount of the second fuel injection is reduced, shortening of the ignition delay due to the second fuel injection can be suppressed. Therefore, the pre-mixing time by the second fuel injection becomes longer, and the insufficient pre-mixing of fuel and air is prevented. As a result, an increase in smoke can be suppressed.

Under conditions where the engine load is in the low load range, the ignitability of the premixed mixture of fuel and air is poor. If the intake pressure into the combustion chamber 4 is low, the first fuel injection is carried out at an early stage where the pressure in the combustion chamber 4 (in-cylinder pressure) is low. Under the circumstances, the air-fuel ratio set at the reference pressure is maintained so that the amount of intake air into the combustion chamber 4 is maintained, and the fuel injection timing of the first fuel injection and the second fuel injection is When the advance angle is advanced, the first fuel injection is performed at a stage where the in-cylinder pressure is lower. In this case, the spray travel distance of the fuel is extended, and the amount of spray adhering to the wall surface of the combustion chamber 4 is large. For this reason, the inhibitory effect of HC and CO increase may fall.

When the intake pressure into the combustion chamber 4 is lower than the reference pressure, the air-fuel ratio in the combustion chamber 4 is set at the reference pressure under a condition where the engine load is in the low load region lower than the low load threshold. It is made lean with respect to the air fuel ratio. As a result, the amount of air taken into the combustion chamber 4 is sufficiently large, and the ignition timing of the premixed mixture of fuel and air is earlier even if the fuel injection timing of the first fuel injection is not advanced. Therefore, the ignition timing of the premixed gas substantially coincides with the ignition timing when the intake pressure is the reference pressure, and the heat release rate waveform approaches the heat release rate waveform obtained when the intake pressure is the reference pressure. . Therefore, the combustion of the premixed gas is properly performed, and it is possible to suppress an increase in combustion noise and an increase in HC and CO of unburned components.

FIG. 3 is a graph showing an example of a heat release rate waveform under a situation where the engine load is in a low load region. In FIG. 3, a plurality of heat release rate waveforms obtained under various conditions are shown. The broken line P represents the heat release rate waveform when the intake pressure is the reference pressure. The thin solid line Q represents the heat release rate waveform when the intake pressure is lower than the reference pressure by 20 kPa. A thick solid line R represents a heat generation rate waveform when the air fuel ratio is made lean with respect to the air fuel ratio when the intake pressure is lower than the reference pressure by 20 kPa and the intake pressure is the reference pressure.

As can be seen from FIG. 3, when the intake pressure is lower than the reference pressure by 20 kPa, the ignition delay causes the heat release rate waveform to deviate significantly from the heat release rate waveform when the intake pressure is the reference pressure (broken line P and fine See solid line Q). Even when the intake pressure is lower than the reference pressure by 20 kPa, the air release ratio is made lean with respect to the air-fuel ratio when the intake pressure is the reference pressure, whereby the heat release rate waveform is the intake pressure being the reference pressure It approaches the heat release rate waveform of time (see the broken line P and the thick solid line R).

FIG. 4 is a graph showing an example of the level of combustion noise and the emission concentration of HC and CO under a situation where the engine load is in a low load region. FIG. 4 shows an example of the level of combustion noise and the emission concentration of HC and CO under the same conditions as the conditions under which the plurality of heat release rate waveforms shown in FIG. 3 were obtained. As can be seen from FIG. 4, even when the intake pressure is lower than the reference pressure (P _ref ) by 20 kPa, the air-fuel ratio is made lean relative to the air-fuel ratio when the intake pressure is the reference pressure (P _ref ) Thus, the level of combustion noise and the generation rates of HC and CO hardly change compared to when the intake pressure is the reference pressure (P _ref ). In particular, the exhaust concentration of HC and CO is sufficiently lower than the case where the intake pressure is 20 kPa lower than the reference pressure (P _ref ) and the air fuel ratio is not leaned.

FIG. 5 is a graph showing an example of the heat release rate waveform under the condition that the engine load is in the medium load region. Also in FIG. 5, a plurality of heat release rate waveforms obtained under various conditions are shown. The broken line P represents the heat release rate waveform when the intake pressure is the reference pressure. An alternate long and short dash line Q represents a heat release rate waveform when the intake pressure is lower than the reference pressure by 20 kPa. The thin solid line R represents the heat release rate waveform when the air fuel ratio is made lean with respect to the air fuel ratio when the intake pressure is lower than the reference pressure by 20 kPa and the intake pressure is the reference pressure. A thick solid line S represents a heat release rate waveform when the intake pressure is lower than the reference pressure by 20 kPa and the fuel injection timing of the first fuel injection and the second fuel injection is advanced.

As can be seen from FIG. 5, when the intake pressure is lower than the reference pressure by 20 kPa, the heat release rate waveform is largely deviated from the heat release rate waveform when the intake pressure is the reference pressure (broken line P). And one-dotted chain line Q). Even when the intake pressure is lower than the reference pressure by 20 kPa, the air-fuel ratio is made lean with respect to the air-fuel ratio when the intake pressure is the reference pressure, or the fuel injection timing is advanced. The heat release rate waveform due to fuel injection approaches the heat release rate waveform when the intake pressure is the reference pressure (see dashed line P, thin solid line R, and thick solid line S).

FIG. 6 is a graph showing an example of the amount of generated NOx and the level of combustion noise in a situation where the engine load is in the medium load region. FIG. 6 shows the generation amount of NOx and the level of combustion noise under the same conditions as the conditions under which the plurality of heat release rate waveforms shown in FIG. 5 were obtained. As can be seen from FIG. 6, even if the intake pressure is lower than the reference pressure (P _ref ) by 20 kPa, the fuel injection timing is advanced, so that the combustion noise level is equal to the reference pressure (P _ref ). It hardly changes compared to when. When the fuel injection timing is advanced when the intake pressure is lower than the reference pressure (P _ref ) by 20 kPa, the air-fuel ratio with respect to the air-fuel ratio when the intake pressure is the reference pressure (P _ref ) The amount of NOx generated is sufficiently smaller than when the engine is leaned.

FIG. 7 is a graph showing an example of the heat release rate waveform under the condition where the engine load is in the high load region. Also shown in FIG. 7 are multiple heat release rate waveforms under various conditions. The broken line P represents the heat release rate waveform when the intake pressure is the reference pressure. An alternate long and short dash line Q represents a heat release rate waveform when the intake pressure is lower than the reference pressure by 30 kPa. A thin solid line R represents a heat release rate waveform when the fuel injection timing of the first fuel injection and the second fuel injection is advanced when the intake pressure is lower than the reference pressure by 30 kPa. In the thick solid line S, when the intake pressure is lower than the reference pressure by 30 kPa, in addition to the advance angle of the fuel injection timing of the first fuel injection and the second fuel injection, the common rail pressure is reduced and the second It represents the heat release rate waveform when the fuel injection amount of the fuel injection is reduced.

As can be seen from FIG. 7, when the intake pressure is lower than the reference pressure by 30 kPa, the heat release rate waveform is largely deviated from the heat release rate waveform when the intake pressure is the reference pressure (broken line P). And one-dotted chain line Q). Even if the intake pressure is lower than the reference pressure by 30 kPa, the fuel injection timing is advanced, so that the heat release rate waveform due to the first fuel injection is a heat release rate waveform when the intake pressure is the reference pressure. It approaches (refer broken line P, thin solid line R, and thick solid line S).

FIG. 8 is a graph showing an example of the smoke generation rate and the premixing time by the second fuel injection under a situation where the engine load is in the high load range. FIG. 8 shows the smoke generation rate and the premixing time by the second fuel injection under the same conditions as the conditions under which the plurality of heat release rate waveforms shown in FIG. 7 were obtained. As can be seen from FIG. 8, even when the intake pressure is lower than the reference pressure (P _ref ) by 30 kPa, the common rail pressure is reduced in addition to the advance of the fuel injection timing, and the fuel injection amount for the second fuel injection As a result, the smoke generation rate hardly changes compared to when the intake pressure is the reference pressure (P _ref ). When the common rail pressure is reduced and the fuel injection amount for the second fuel injection is reduced, the premixing time by the second fuel injection is longer than when the processing is not performed, The incidence of smoke is low.

As described above, according to the present embodiment, even when the intake pressure into the combustion chamber 4 is lower than the reference pressure, the combustion waveform by the first fuel injection and the intake pressure become the reference pressure regardless of the engine load. It approaches the combustion waveform when it is. Thereby, substantially the same premixed compression ignition combustion is realized as when the intake pressure is the reference pressure. As a result, it is possible to suppress an increase in combustion noise and a deterioration in emission.

In another aspect, the present embodiment is a combustion control device for an engine that performs premixed compression ignition combustion, including a fuel injection valve that injects fuel into a combustion chamber of the engine, and intake air for drawing air into the combustion chamber. The fuel cell system includes a passage, an exhaust passage for discharging exhaust gas after combustion from the combustion chamber, an intake pressure sensor for detecting an intake pressure into the combustion chamber, and a controller for operating a fuel injection valve. The fuel injection valve is operated to determine the injection amount and the fuel injection timing, and the fuel injection is performed according to the determined fuel injection amount and the fuel injection timing, and the intake pressure detected by the intake pressure sensor is higher than a predetermined pressure When it is low, correction is made to advance the ignition timing by fuel injection. The controller determines a fuel injection amount and a fuel injection timing of the second fuel injection to be performed after the first fuel injection and the first fuel injection, and the first according to the determined fuel injection amount and the fuel injection timing. The fuel injection valve is operated so that the second fuel injection and the second fuel injection are sequentially performed, and when the intake pressure detected by the intake pressure sensor is lower than the predetermined pressure, the ignition timing by the first fuel injection It may be corrected to advance the The controller advances the fuel injection timing of the first fuel injection when the intake pressure detected by the intake pressure sensor is lower than the predetermined pressure, and sets the air-fuel ratio in the combustion chamber to the air-fuel ratio at the predetermined pressure. It may be controlled to maintain. The combustion control device further includes a load sensor for detecting a load of the engine, and the controller is configured to set an engine load detected by the load sensor at a lower intake pressure detected by the intake pressure sensor than the predetermined pressure. When it is higher than the predetermined value of 1, the fuel injection timing of the first fuel injection may be advanced to maintain the air-fuel ratio in the combustion chamber at the air-fuel ratio at the predetermined pressure. When the intake pressure detected by the intake pressure sensor is lower than the predetermined pressure and the load of the engine detected by the load sensor is lower than the first predetermined value, the controller determines the air fuel ratio in the combustion chamber Control may be performed to make the air-fuel ratio lean at a predetermined pressure. The combustion control device is disposed to connect the exhaust passage and the intake passage, and is disposed in an exhaust gas recirculation passage for recirculating a portion of the exhaust gas as exhaust gas recirculation gas into the combustion chamber, and disposed in the exhaust gas recirculation passage. The air-fuel ratio in the combustion chamber may be controlled by further comprising a valve for adjusting the amount of recirculation of the circulating gas, and the controller controls the valve so as to reduce the amount of recirculation of the exhaust gas recirculation. The controller reduces the fuel injection pressure of the first fuel injection and the second fuel injection when the engine load detected by the load sensor is higher than a second predetermined value larger than the first predetermined value. It may be controlled to The controller may decrease the fuel injection amount of the second fuel injection when it is higher than the second predetermined value detected by the load sensor.

In yet another aspect, the present embodiment is a combustion control device for an engine that performs premixed compression ignition combustion, including a fuel injection valve that injects fuel into a combustion chamber of the engine, and a device for drawing air into the combustion chamber. An intake passage, an exhaust passage for discharging exhaust gas after combustion from the combustion chamber, an intake pressure sensor for detecting an intake pressure into the combustion chamber, a fuel injection amount and a fuel injection timing are determined, and the fuel injection determined The fuel injection valve is operated to carry out the fuel injection according to the amount and the fuel injection timing, and when the intake pressure detected by the intake pressure sensor is lower than the predetermined pressure, the ignition timing by the fuel injection is advanced. And a controller configured to correct.

The present invention is not limited to the above embodiment. For example, in the above embodiment, when the engine load is higher than the low load threshold, the fuel injection timing of the first fuel injection and the second fuel injection is advanced, but the fuel injection of the second fuel injection is performed Only the fuel injection timing of the first fuel injection may be advanced without advancing the timing. The combustion waveform in this case is a waveform shown by a solid line X in FIG. The broken line Y shown in FIG. 9 shows the combustion waveform when the fuel injection timing of the second fuel injection is advanced. As a result, the heat release rate waveform by the first fuel injection and the second fuel injection further approaches the heat release rate waveform when the intake pressure is the reference pressure, and there is little change in timbre even when the intake pressure changes.

In the above embodiment, when the engine load is higher than the high load threshold, the common rail pressure is reduced and the fuel injection amount for the second fuel injection is reduced, but the control mode is not limited to this. Only one of the decrease in common rail pressure and the decrease in fuel injection amount of the second fuel injection may be performed.

In the above embodiment, when the engine load is higher than the high load threshold, the advance amount of the fuel injection timing of the first fuel injection is not changed when the common rail pressure is reduced, but the control mode is the same. It is not limited to. When the common rail pressure is reduced, the fuel injection timing of the first fuel injection may be further advanced. In this case, the heat release rate waveform is closer to the heat release rate waveform obtained when the intake pressure is the reference pressure. When the amount of decrease of the common rail pressure is made variable, the amount of advance of the fuel injection timing of the first fuel injection may be changed to an amount according to the amount of decrease of the common rail pressure.

In the above embodiment, the air-fuel ratio in the combustion chamber 4 is controlled by adjusting the flow rate of the EGR gas by the EGR valve 23, but the control aspect of the air-fuel ratio is not limited to this. For example, the air-fuel ratio in the combustion chamber 4 may be controlled by changing the supercharging pressure of the turbocharger.

In the above embodiment, the main fuel injection is divided into the first fuel injection and the second fuel injection twice, but the aspect of the fuel injection is not limited to this. The main fuel injection may be performed only once. In this case, if the engine load is lower than the low load threshold, the air-fuel ratio is made leaner than the air-fuel ratio when the intake pressure is the reference pressure, and if the engine load is higher than the low load threshold, the intake pressure The main fuel injection timing is advanced while maintaining the air-fuel ratio when the reference pressure is the reference pressure.

The present invention is applicable to a fuel injection device of an engine that performs premixed compression ignition combustion.

DESCRIPTION OF SYMBOLS 1 ... diesel engine, 4 ... combustion chamber, 5 ... injector (fuel injection valve), 10 ... intake passage, 12 ... exhaust passage, 22 ... EGR passage (exhaust recirculation passage), 23 ... EGR valve (valve means), 27 ... ECU (determination means, injection control means, correction means, air-fuel ratio control means, injection timing advance means, injection pressure control means, injection amount reduction means), 29 ... accelerator opening sensor (load detection means), 30 ... suction Pressure sensor (intake pressure detection means), 31 ... combustion control device.

Claims

An engine combustion control device for performing premixed compression ignition combustion, comprising:
A fuel injection valve for injecting fuel into a combustion chamber of the engine;
Determining means for determining a fuel injection amount and a fuel injection timing;
Injection control means for controlling the fuel injection valve so as to carry out fuel injection according to the fuel injection amount and the fuel injection timing;
An intake passage for drawing air into the combustion chamber;
An exhaust passage for discharging exhaust gas after combustion from the combustion chamber;
Intake pressure detection means for detecting an intake pressure into the combustion chamber;
And a correction unit that corrects the ignition timing by the fuel injection to advance when the intake pressure detected by the intake pressure detection unit is lower than a predetermined pressure.
The combustion control device according to claim 1, wherein
The determination means determines a fuel injection amount and a fuel injection timing of a first fuel injection and a second fuel injection to be performed after the first fuel injection,
The injection control means controls the fuel injection valve so that the first fuel injection and the second fuel injection are sequentially performed according to the fuel injection amount and the fuel injection timing,
The correction means corrects the ignition timing by the first fuel injection to advance when the intake pressure detected by the intake pressure detection means is lower than the predetermined pressure.
The combustion control device according to claim 2,
The correction means has an air fuel ratio control means for controlling an air fuel ratio in the combustion chamber, and an injection timing advance means for advancing the fuel injection timing of the first fuel injection determined by the determination means. And
The injection timing advance means advances the fuel injection timing of the first fuel injection when the intake pressure detected by the intake pressure detection means is lower than the predetermined pressure,
The air-fuel ratio control means controls the air-fuel ratio in the combustion chamber to be maintained at the air-fuel ratio at the predetermined pressure when the intake pressure detected by the intake pressure detection means is lower than the predetermined pressure. Do.
The combustion control device according to claim 3,
The apparatus further comprises load detection means for detecting the load of the engine,
The injection timing advance means is configured such that the intake pressure detected by the intake pressure detection means is lower than the predetermined pressure, and the load of the engine detected by the load detection means is greater than a first predetermined value. When it is high, advance the fuel injection timing of the first fuel injection,
The air-fuel ratio control means is configured such that the intake pressure detected by the intake pressure detection means is lower than the predetermined pressure, and the load of the engine detected by the load detection means is greater than the first predetermined value. When it is high, the air-fuel ratio in the combustion chamber is controlled to be maintained at the air-fuel ratio at the predetermined pressure.
The combustion control device according to claim 4,
The air-fuel ratio control means is configured such that the intake pressure detected by the intake pressure detection means is lower than the predetermined pressure, and the load of the engine detected by the load detection means is greater than the first predetermined value. When the pressure is low, the air-fuel ratio in the combustion chamber is controlled to be lean with respect to the air-fuel ratio at the predetermined pressure.
The combustion control device according to claim 4 or 5, wherein
The correction means is configured to perform the first fuel injection and the second fuel when the load of the engine detected by the load detection means is higher than a second predetermined value larger than the first predetermined value. The fuel injection system further includes injection pressure control means for controlling to decrease the fuel injection pressure of the injection.
The combustion control device according to any one of claims 4 to 6, wherein
The correction means decreases the fuel injection amount of the second fuel injection when the load of the engine detected by the load detection means is higher than a second predetermined value larger than the first predetermined value. Means for reducing the amount of injection.
The combustion control device according to any one of claims 3 to 7, wherein
An exhaust gas recirculation passage disposed so as to connect the exhaust gas passage and the intake gas passage, for recirculating a portion of the exhaust gas into the combustion chamber as an exhaust gas recirculation gas;
And valve means disposed in the exhaust gas recirculation passage for adjusting the amount of recirculation of the exhaust gas recirculation.
The air-fuel ratio control means controls the air-fuel ratio in the combustion chamber by controlling the valve means so as to reduce the amount of recirculation of the exhaust gas recirculation.