JP4248178B2 - Internal combustion engine - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an internal combustion engine.
[0002]
[Prior art]
As a method for reducing the amount of nitrogen oxide (NOx) discharged from an internal combustion engine, exhaust gas recirculation (EGR: Exhaust Gas) that recirculates part of the exhaust gas flowing through the exhaust passage of the internal combustion engine to the intake passage of the internal combustion engine A method using a recirculation apparatus has been proposed.
[0003]
The EGR device uses water vapor (H₂O), carbon monoxide (CO), carbon dioxide (CO₂), Etc., to reduce the combustion speed and temperature of the air-fuel mixture in the combustion chamber of the internal combustion engine, thereby reducing the nitrogen oxide (NOx) generated during combustion. The amount is reduced.
[0004]
By the way, since EGR gas has a relatively high specific heat ratio and requires a large amount of heat to raise the temperature, the higher the EGR gas ratio in the intake air, the lower the combustion temperature in the cylinder. As the combustion temperature decreases, the amount of NOx generated also decreases. Therefore, the higher the EGR gas ratio, the lower the NOx emission.
[0005]
However, as the EGR gas ratio is increased, the generation amount of soot begins to increase abruptly at a certain ratio or more. The normal EGR control is performed at a lower EGR gas ratio than the soot starting to increase rapidly.
[0006]
However, as the EGR gas ratio is further increased, soot rapidly increases as described above, but there is a peak in the generation amount of this soot, and when the EGR gas ratio is further increased beyond this peak, This time, wrinkles start to decrease rapidly, and finally it hardly occurs.
[0007]
This is because when the temperature of the fuel during combustion in the combustion chamber and the surrounding gas is below a certain temperature, the growth of hydrocarbons (HC) stops at an intermediate stage before reaching soot, and the temperature of the fuel and the surrounding gas is reduced. This is because the hydrocarbon (HC) grows to soot all at once when the temperature rises above a certain temperature.
[0008]
Therefore, if the temperature of the fuel during combustion in the combustion chamber and the temperature of the gas around the fuel are suppressed below the temperature at which the growth of hydrocarbon (HC) stops halfway, soot will not be generated. In this case, the endothermic effect of the gas around the fuel when the fuel burns greatly affects the temperature of the fuel and the surrounding gas, and the endothermic amount of the gas around the fuel, that is, EGR, according to the amount of heat generated during fuel combustion. It is possible to suppress the generation of soot by adjusting the gas ratio.
[0009]
Combustion as described above (hereinafter referred to as low temperature combustion) can reduce NOx and soot emissions. However, since combustion is performed with a small amount of fresh air, a stable combustion state can be obtained. The fuel injection timing that can be performed is limited to a narrow range. That is, if the fuel injection timing is advanced, the injected fuel is exposed to the high-temperature gas for a long time, so that the temperature of the fuel during combustion and the surrounding gas becomes high, resulting in smoke and combustion noise. On the other hand, if the fuel injection timing is delayed, the temperature of the fuel does not rise, so that the amount of fuel that does not cause combustion increases, leading to misfire.
[0010]
In order to solve such a problem, for example, in Japanese Patent Application Laid-Open No. 2000-120487, the combustion pressure in the combustion chamber is detected and it is determined whether or not good combustion is performed from the change in the combustion pressure. When the combustion state is a region where smoke is generated, a region where combustion noise is generated, or a region where misfiring occurs, the fuel injection timing is changed to improve the combustion state.
[0011]
[Problems to be solved by the invention]
However, in order to extract the control parameter based on the waveform of the combustion pressure, the processing capacity of the CPU must be high, and the cost increases when the mounting of the vehicle is taken into account, and the apparatus becomes complicated. Further, there are cases where it is difficult to improve the combustion state simply by advancing or retarding the fuel injection timing, and a control method in such a case has not been mentioned.
[0012]
The present invention has been made in view of the above-described problems, and an object of the present invention is to provide a technique for stabilizing the combustion state during low-temperature combustion in an internal combustion engine by correcting the fuel injection timing.
[0013]
[Means for Solving the Problems]
  In order to achieve the above object, the internal combustion engine of the present invention employs the following means. That is,
  Fuel supply means for supplying fuel into the cylinders of the internal combustion engine;
  An EGR device that recirculates part of the exhaust gas to the intake system of the internal combustion engine;
  Increase the amount of recirculated EGR gas to increase the maximum amount of soot and then increase the amount of EGR gas. Combustion state switching means for selecting and switching either normal combustion to be recirculated,
  Pressure detecting means for detecting the pressure at the compression top dead center in the cylinder and the maximum pressure during the expansion stroke;
  An operating state detecting means for detecting an operating state of the internal combustion engine;
The deviation between the maximum pressure during the expansion stroke in the cylinder and the pressure at the compression top dead center just before it,The value when the combustion state of the internal combustion engine becomes unstable isFrom the engine operating state detected by the operating state detecting meansMisfire level calculating means for calculating;
The deviation between the maximum pressure during the expansion stroke in the cylinder and the pressure at the compression top dead center just before it,The value when the combustion state of the internal combustion engine is optimalFrom the engine operating state detected by the operating state detecting meansTarget level calculation means for calculating,
Pressure deviation calculating means for calculating a deviation between the maximum pressure during the expansion stroke in the cylinder detected by the pressure detecting means during the low temperature combustion and the pressure at the compression top dead center immediately before the expansion stroke;
  The pressure deviation calculated by the pressure deviation calculating means isA value greater than the value calculated by the misfire level calculating means,The pressure deviation calculated by the pressure deviation calculating means isIf it is larger than the value calculated by the target level calculation meansThe pressure deviation calculated by the pressure deviation calculating means is set to the value calculated by the target level calculating means.Retard the fuel injection timing,The pressure deviation calculated by the pressure deviation calculating means isIf it is smaller than the value calculated by the target level calculation meansThe pressure deviation calculated by the pressure deviation calculating means is set to the value calculated by the target level calculating means.Fuel injection timing correction means for advancing the fuel injection timing;
  It is characterized by having
[0014]
  The greatest feature of the present invention is that the maximum pressure during low-temperature combustion in an internal combustion engineDeviation between pressure and compression top dead centerPaying attention to the fact that fluctuates depending on the combustion state, the value is more than the value when it is estimated that misfire has occurred.deviationWhen is large, the fuel injection timing is corrected so as to obtain a value obtained in an optimum combustion state.
[0015]
  In the internal combustion engine configured as described above, either normal combustion or low temperature combustion is selected based on the operating state. When low temperature combustion is selected, it is necessary to control the fuel injection timing within a narrow range, so that the fuel injection timing is corrected by the fuel injection timing correction means, and the fuel injection timing is optimized. Here, during low temperature combustion, the peak of combustion pressure appears after compression top dead center, and this maximum pressureAnd the pressure at the compression top dead center isIt varies depending on the combustion state. In the present invention, the misfire level calculation means is the highest pressure estimated to be detected when a misfire occurs in the operating state at that time.Deviation between pressure and compression top dead centerAsk for. Obtained in this wayPressure deviation and pressure deviation obtained by pressure detection meansIt is possible to determine whether or not misfire has occurred. If it is determined that no misfire has occurred, the fuel injection timing correction means determines the target maximum pressure calculated by the target level calculation means.Deviation between pressure and compression top dead centerBased on this, it is possible to correct the fuel injection timing and obtain the optimum fuel injection timing.
[0022]
  In the present invention, the internal combustion engine includes a plurality of cylinders,The pressure deviation calculated by the pressure deviation calculating means isIf the specified number of cycles has been continuously outside the specified range,Pressure deviations respectively calculated by the pressure deviation calculating meansWhen there is little variation among cylinders,Pressure deviationThe fuel injection timing correction means corrects the fuel injection timing of the cylinders outside the predetermined range by using the average value of the cylinders. On the other hand, when the variation between the cylinders is large, the fuel injection timing correction means The correction of the fuel injection timing of the outside cylinder may not be performed.
[0023]
In the internal combustion engine configured as described above, when the pressure detection unit cannot detect the pressure normally due to some cause, the average value of the values detected by the pressure detection unit in other cylinders is obtained. Based on this, it becomes possible to correct the fuel injection timing. In this case, when the variation between the cylinders is large, overcorrection can be suppressed by prohibiting correction of the fuel injection timing.
[0030]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, specific embodiments of the internal combustion engine according to the present invention will be described with reference to the drawings. Here, the case where the internal combustion engine according to the present invention is applied to a diesel engine for driving a vehicle will be described as an example.
[0031]
FIG. 1 is a diagram showing a schematic configuration of an engine 1 and its intake / exhaust system according to the present embodiment.
[0032]
An engine 1 shown in FIG. 1 is a water-cooled four-cycle diesel engine having four cylinders 2.
[0033]
The engine 1 includes a fuel injection valve 3 that injects fuel directly into the combustion chamber of each cylinder 2. Each fuel injection valve 3 is connected to a pressure accumulation chamber (common rail) 4 that accumulates fuel to a predetermined pressure. A common rail pressure sensor 4 a that outputs an electrical signal corresponding to the fuel pressure in the common rail 4 is attached to the common rail 4.
[0034]
The common rail 4 communicates with a fuel pump 6 through a fuel supply pipe 5. This fuel pump 6 is a pump that operates using the rotational torque of the output shaft (crankshaft) of the engine 1 as a drive source, and a pump pulley 6 a attached to the input shaft of the fuel pump 6 is connected to the output shaft (crankshaft) of the engine 1. ) And the belt pulley 7 are connected to each other.
[0035]
In the fuel injection system configured as described above, when the rotational torque of the crankshaft is transmitted to the input shaft of the fuel pump 6, the fuel pump 6 transmits the rotational torque transmitted from the crankshaft to the input shaft of the fuel pump 6. The fuel is discharged at a pressure according to the pressure.
[0036]
The fuel discharged from the fuel pump 6 is supplied to the common rail 4 via the fuel supply pipe 5, accumulated in the common rail 4 up to a predetermined pressure, and distributed to the fuel injection valves 3 of each cylinder 2. When a drive current is applied to the fuel injection valve 3, the fuel injection valve 3 opens, and as a result, fuel is injected from the fuel injection valve 3 into the cylinder 2.
[0037]
Next, an intake branch pipe 8 is connected to the engine 1, and each branch pipe of the intake branch pipe 8 communicates with a combustion chamber of each cylinder 2 via an intake port (not shown).
[0038]
An in-cylinder pressure sensor 37 that outputs an electrical signal corresponding to the pressure in the cylinder 2 is attached to the combustion chamber of each cylinder 2.
[0039]
The intake branch pipe 8 is connected to an intake pipe 9. An air flow meter 11 that outputs an electrical signal corresponding to the mass of the intake air flowing through the intake pipe 9 is attached to the intake pipe 9.
[0040]
An intake throttle valve 13 for adjusting the flow rate of the intake air flowing through the intake pipe 9 is provided at a portion of the intake pipe 9 located immediately upstream of the intake branch pipe 8. The intake throttle valve 13 is provided with an intake throttle actuator 14 that is configured by a step motor or the like and that drives the intake throttle valve 13 to open and close.
[0041]
The intake pipe 9 located between the air flow meter 11 and the intake throttle valve 13 is provided with a compressor housing 15a of a centrifugal supercharger (turbocharger) 15 that operates using exhaust energy as a drive source. The intake pipe 9 downstream of 15a is provided with an intercooler 16 for cooling the intake air that has been compressed in the compressor housing 15a and has reached a high temperature.
[0042]
In the intake system configured as described above, the intake air flows into the compressor housing 15 a via the intake pipe 9.
[0043]
The intake air flowing into the compressor housing 15a is compressed by the rotation of the compressor wheel built in the compressor housing 15a. The intake air that has been compressed in the compressor housing 15a and has reached a high temperature is cooled by the intercooler 16, and then the flow rate is adjusted by the intake throttle valve 13 as necessary to flow into the intake branch pipe 8. The intake air that has flowed into the intake branch pipe 8 is distributed to the combustion chambers of the respective cylinders 2 through the respective branch pipes, and is burned using the fuel injected from the fuel injection valves 3 of the respective cylinders 2 as an ignition source.
[0044]
On the other hand, an exhaust branch pipe 18 is connected to the engine 1, and each branch pipe of the exhaust branch pipe 18 communicates with a combustion chamber of each cylinder 2 via an exhaust port (not shown).
[0045]
The exhaust branch pipe 18 is connected to the turbine housing 15 b of the centrifugal supercharger 15. The turbine housing 15b is connected to an exhaust pipe 19, and the exhaust pipe 19 is connected to a muffler (not shown) downstream.
[0046]
In the middle of the exhaust pipe 19, a particulate filter (hereinafter simply referred to as a filter) 20 carrying an NOx storage reduction catalyst is provided. An exhaust gas temperature sensor 24 that outputs an electrical signal corresponding to the temperature of the exhaust gas flowing through the exhaust pipe 19 is attached to the exhaust pipe 19 upstream of the filter 20.
[0047]
The exhaust pipe 19 downstream of the filter 20 is provided with an exhaust throttle valve 21 for adjusting the flow rate of the exhaust gas flowing through the exhaust pipe 19. The exhaust throttle valve 21 is provided with an exhaust throttle actuator 22 that is configured by a step motor or the like and that drives the exhaust throttle valve 21 to open and close.
[0048]
In the exhaust system configured as described above, the air-fuel mixture (burned gas) combusted in each cylinder 2 of the engine 1 is discharged to the exhaust branch pipe 18 through the exhaust port, and then centrifugally supercharged from the exhaust branch pipe 18. Flows into the turbine housing 15b of the machine 15. The exhaust gas flowing into the turbine housing 15b rotates the turbine wheel rotatably supported in the turbine housing 15b using the energy of the exhaust gas. At that time, the rotational torque of the turbine wheel is transmitted to the compressor wheel of the compressor housing 15a described above.
[0049]
The exhaust discharged from the turbine housing 15b flows into the filter 20 through the exhaust pipe 19, and particulate matter (hereinafter simply referred to as PM) in the exhaust is collected. The NOx storage reduction catalyst (hereinafter simply referred to as NOx catalyst) stores (absorbs or adsorbs) nitrogen oxides (NOx) in the exhaust when the oxygen concentration in the exhaust flowing into the NOx catalyst is high. . On the other hand, the NOx catalyst releases the stored nitrogen oxide (NOx) when the oxygen concentration of the exhaust gas flowing into the NOx catalyst decreases. At that time, if a reducing component such as hydrocarbon (HC) or carbon monoxide (CO) is present in the exhaust, the NOx catalyst converts nitrogen oxide (NOx) released from the NOx catalyst to nitrogen (N₂). The exhaust gas from which PM is collected by the filter 20 is released into the atmosphere through the muffler.
[0050]
Further, the exhaust branch pipe 18 and the intake branch pipe 8 have an exhaust recirculation passage (hereinafter referred to as an EGR passage) 25 for recirculating a part of the exhaust gas flowing through the exhaust branch pipe 18 to the intake branch pipe 8. It is communicated through. In the middle of the EGR passage 25, a flow rate adjusting valve is configured with an electromagnetic valve or the like, and changes the flow rate of exhaust gas (hereinafter referred to as EGR gas) flowing through the EGR passage 25 in accordance with the magnitude of applied power. (Hereinafter referred to as an EGR valve) 26 is provided.
[0051]
An EGR cooler 27 that cools the EGR gas flowing in the EGR passage 25 is provided in the middle of the EGR passage 25 and upstream of the EGR valve 26. The EGR cooler 27 is provided with a cooling water passage (not shown), and a part of the cooling water for cooling the engine 1 circulates.
[0052]
In the exhaust gas recirculation mechanism configured as described above, when the EGR valve 26 is opened, the EGR passage 25 becomes conductive, and a part of the exhaust gas flowing through the exhaust branch pipe 18 flows into the EGR passage 25. Then, it is guided to the intake branch pipe 8 through the EGR cooler 27.
[0053]
At that time, in the EGR cooler 27, heat exchange is performed between the EGR gas flowing in the EGR passage 25 and the cooling water of the engine 1 to cool the EGR gas.
[0054]
The EGR gas recirculated from the exhaust branch pipe 18 to the intake branch pipe 8 via the EGR passage 25 is guided to the combustion chamber of each cylinder 2 while being mixed with fresh air flowing from the upstream side of the intake branch pipe 8.
[0055]
Here, the EGR gas contains water (H₂O) and carbon dioxide (CO₂) And the like, and since an inert gas component having a high heat capacity is not included, if the EGR gas is contained in the mixture, the combustion temperature of the mixture is lowered. Therefore, the amount of nitrogen oxide (NOx) generated is suppressed.
[0056]
Further, when the EGR gas is cooled in the EGR cooler 27, the temperature of the EGR gas itself is reduced and the volume of the EGR gas is reduced. Therefore, when the EGR gas is supplied into the combustion chamber, the atmospheric temperature in the combustion chamber is reduced. Is not increased unnecessarily, and the amount of fresh air (volume of fresh air) supplied into the combustion chamber is not unnecessarily reduced.
[0057]
The engine 1 is provided with an electronic control unit (ECU) 35 for controlling the engine 1. The ECU 35 is a unit that controls the operating state of the engine 1 according to the operating conditions of the engine 1 and the driver's request.
[0058]
Various sensors such as a common rail pressure sensor 4a, an air flow meter 11, an exhaust temperature sensor 24, a crank position sensor 33, an accelerator opening sensor 36, an in-cylinder pressure sensor 37, and the like are connected to the ECU 35 through electric wiring. The output signal is input to the ECU 35.
[0059]
On the other hand, the fuel injection valve 3, the intake throttle actuator 14, the exhaust throttle actuator 22, the EGR valve 26, and the like are connected to the ECU 35 via electrical wiring, and the ECU 35 can control the above-described parts. Yes.
[0060]
Here, the ECU 35 includes a CPU 351, a ROM 352, a RAM 353, and an A / D converter (A / D) 354.
[0061]
The ROM 352 stores various application programs and a control map.
[0062]
The RAM 353 stores output signals from the sensors, calculation results of the CPU 351, and the like. The calculation result is, for example, the engine speed calculated based on the time interval at which the crank position sensor 33 outputs a pulse signal. These data are rewritten to the latest data every time the crank position sensor 33 outputs a pulse signal.
[0063]
The CPU 351 operates in accordance with an application program stored in the ROM 352.
[0064]
By the way, when the engine 1 is operated with lean combustion, the air-fuel ratio of the exhaust discharged from the engine 1 becomes a lean atmosphere, and the oxygen concentration of the exhaust becomes high, so that nitrogen oxide (NOx) contained in the exhaust is NOx. When the lean combustion operation of the engine 1 is continued for a long period of time, the NOx storage capacity of the NOx catalyst is saturated, and nitrogen oxides (NOx) in the exhaust gas are removed by the NOx catalyst. Without being released into the atmosphere.
[0065]
In particular, in a diesel engine such as the engine 1, the lean air-fuel ratio mixture is combusted in the most operating region, and the exhaust air-fuel ratio becomes the lean air-fuel ratio in the most operating region accordingly. The NOx occlusion capacity is easily saturated. Here, the lean air-fuel ratio means, for example, 20 to 50 in a diesel engine, and a region in which NOx cannot be purified by a three-way catalyst.
[0066]
Therefore, when the engine 1 is operated in lean combustion, before the NOx occlusion capacity of the NOx catalyst is saturated, the oxygen concentration in the exhaust gas flowing into the NOx catalyst is lowered and the concentration of the reducing agent is increased, and the NOx catalyst occludes. It is necessary to reduce the formed nitrogen oxides (NOx).
[0067]
As a method of reducing the oxygen concentration in the exhaust gas in this way, after adding the fuel in the exhaust gas or increasing the amount of recirculated EGR gas to increase the amount of soot to the maximum, further increase the EGR gas amount. There is a low temperature combustion (Japanese Patent No. 3116876).
[0068]
Here, the low temperature combustion will be described.
[0069]
As described above, conventionally, EGR has been used to suppress the generation of NOx. Since the EGR gas has a relatively high specific heat ratio and requires a large amount of heat to raise the temperature, the combustion temperature in the cylinder 2 decreases as the EGR gas ratio in the intake air increases. As the combustion temperature decreases, the amount of NOx generated also decreases. Therefore, the higher the EGR gas ratio, the lower the NOx emission.
[0070]
However, as the EGR gas ratio is increased, the generation amount of soot begins to increase abruptly at a certain ratio or more. Normal EGR control is performed at a lower EGR gas ratio than when soot begins to increase rapidly.
[0071]
However, as the EGR gas ratio is further increased, soot rapidly increases as described above, but there is a peak in the generation amount of this soot, and when the EGR gas ratio is further increased beyond this peak, This time, wrinkles start to decrease rapidly, and finally it hardly occurs.
[0072]
This is because when the temperature of the fuel during combustion in the combustion chamber and the surrounding gas is below a certain temperature, the growth of hydrocarbons (HC) stops at an intermediate stage before reaching soot, and the temperature of the fuel and the surrounding gas is reduced. This is because the hydrocarbon (HC) grows to soot all at once when the temperature rises above a certain temperature.
[0073]
Therefore, no soot will be generated if the combustion during combustion in the combustion chamber and the gas temperature around it are controlled below the temperature at which hydrocarbon (HC) growth stops midway. In this case, the endothermic effect of the gas around the fuel when the fuel burns greatly affects the temperature of the fuel and the surrounding gas, and the endothermic amount of the gas around the fuel, that is, EGR, according to the amount of heat generated during fuel combustion. It is possible to suppress the generation of soot by adjusting the gas ratio.
[0074]
On the other hand, hydrocarbons (HC) that have stopped growing before reaching soot can be oxidized by the NOx storage reduction catalyst supported on the filter 20. Therefore, hydrocarbon (HC) generated by low temperature combustion works as a reducing agent.
[0075]
Thus, low temperature combustion is based on purifying hydrocarbons (HC) whose growth has stopped before reaching soot with a NOx storage reduction catalyst or the like. Therefore, when the NOx storage reduction catalyst or the like is not activated, it is difficult to use low temperature combustion because hydrocarbons (HC) are not purified but are released into the atmosphere.
[0076]
Further, the temperature of the fuel during combustion in the cylinder 2 and the gas temperature around it can be controlled to a temperature below the temperature at which the growth of hydrocarbons (HC) stops halfway. It is.
[0077]
Therefore, in the present embodiment, low-temperature combustion control is performed when the engine 1 is operating at a low rotation and low load and when the NOx storage reduction catalyst carried on the filter 20 reaches the active region.
[0078]
Whether it is in the active region or not can be determined based on an output signal of the exhaust temperature sensor 24 or the like.
[0079]
In this way, in low-temperature combustion, hydrocarbon (HC) as a reducing agent can be supplied to the NOx storage reduction catalyst while suppressing the emission of PM typified by soot, and NOx can be reduced and purified.
[0080]
In addition, when low-temperature combustion is performed, active oxygen is released by the hydrocarbon (HC) that has flowed into the filter 20, so that PM is easily oxidized and the amount that can be removed by oxidation per unit time is improved. Further, the hydrocarbon (HC) removes oxygen poisoning of the catalyst and increases the activity of the catalyst, so that active oxygen is easily released. Furthermore, the temperature of the filter 20 rises due to the oxidation reaction of hydrocarbon (HC). Then, PM is oxidized and burned by active oxygen and removed.
[0081]
Furthermore, heat is generated when the hydrocarbon (HC) is oxidized, and the temperature of the filter 20 can be increased or maintained.
[0082]
When supplying the reducing agent to the filter 20 by such low temperature combustion, the CPU 351 first obtains the target air-fuel ratio. The target air-fuel ratio can be obtained by determining a map based on the operating state of the engine 1 in advance. Next, the CPU 351 calculates a target opening degree of the intake throttle valve 13 according to the target air-fuel ratio, and controls the intake throttle valve 13 to become the target opening degree. Next, the CPU 351 calculates a target opening degree of the EGR valve 26 corresponding to the target air-fuel ratio, and controls the EGR valve 26 so as to become the target opening degree. Further, the CPU 351 calculates the fuel injection amount and the fuel injection start timing. The target opening, the fuel injection amount, and the fuel injection start timing of the intake throttle valve 13 and the EGR valve 26 are calculated based on a map obtained in advance.
[0083]
By performing low-temperature combustion in this way, the oxygen concentration in the exhaust gas flowing into the filter 20 is reduced, the concentration of the reducing agent is increased, the nitrogen oxide (NOx) occluded in the filter 20 is reduced, and the filter It is possible to raise the temperature of 20.
[0084]
By the way, since the low-temperature combustion is performed with little fresh air, the combustion state may become unstable unless the fuel injection timing and the air-fuel ratio are set within a narrow range.
[0085]
Here, in the conventional internal combustion engine, the pressure in the cylinder at the time of low-temperature combustion is measured, and it is determined whether or not the combustion state is good based on the measured combustion pressure waveform.
[0086]
However, since a certain amount of time is required to correct the fuel injection timing by analyzing the measured combustion pressure waveform, if the processing speed of the CPU is slow, the analysis is not in time and it is difficult to correct the fuel injection timing. In addition, the combustion state may not be improved by simply advancing or retarding the fuel injection timing.
[0087]
Therefore, in this embodiment, by using only the pressure at the compression top dead center and the maximum pressure thereafter as parameters, it is possible to easily analyze the combustion state and correct the fuel injection timing.
[0088]
FIG. 2 is a diagram showing a schematic configuration of the in-cylinder pressure detecting device according to the present embodiment.
[0089]
In addition to the CPU 351 and the A / D 354, the ECU 35 includes a multiplexer 355 and a peak hold amplifier 356. Further, an in-cylinder pressure sensor 37 is connected to the ECU 35.
[0090]
The in-cylinder pressure sensor 37 outputs a signal corresponding to the pressure in the cylinder. The multiplexer 355 selects and switches the in-cylinder pressure sensor 37 of the cylinder 2 to be sampled based on a signal from the CPU 351. The peak hold amplifier 356 stores only the highest sampled pressure value. The start time and end time for storing the pressure and the deletion of the stored value are controlled by a signal from the CPU 351. The A / D 354 converts the analog signal detected by the in-cylinder pressure sensor 37 into a digital signal. The CPU 351 corrects the fuel injection timing based on the cylinder pressure detected by the cylinder pressure sensor 37.
[0091]
FIG. 3 is a timing chart showing the timing of the output signal of the in-cylinder pressure sensor and the timing of taking in the pressure data.
[0092]
The sensor output is a value obtained from the output signal of the in-cylinder pressure sensor 37. The multiplexer control signal is a signal that is issued to determine the cylinder that is the target for reading the pressure data, and determines the target cylinder based on the magnitude of four stages. The peak hold amplifier sampling permission signal designates the pressure reading range. Only when the peak hold amplifier sampling permission signal has been issued, the peak hold amplifier 356 reads the output signal of the in-cylinder pressure sensor 37. A data reset signal is issued to erase the stored pressure data. In the A / D 354, the pressure Ptdc at the compression top dead center and the highest pressure among the sampled pressures are converted into digital data and read into the CPU 351. The crank position at the compression top dead center and maximum pressure is obtained by Ne pulse interruption.
[0093]
Here, FIG. 4 is a diagram illustrating the concept of the control method according to the present embodiment.
[0094]
  In this embodimentThe bulgeThe fuel injection timing is corrected based on the deviation between the maximum pressure Pmax during the tension stroke and the pressure Ptdc at the compression top dead center.Done. That is,The fuel injection timing is corrected so that the deviation ΔP between the maximum pressure Pmax during the expansion stroke and the pressure Ptdc at the compression top dead center becomes a target. Here, when the fuel injection timing is advanced, the deviation ΔP increases, and when the fuel injection timing is retarded, the deviation ΔP decreases. Accordingly, in the present embodiment, when the measured pressure deviation is larger than the target deviation, the fuel injection timing is retarded, while the measured pressure deviation is smaller than the target deviation. If the fuel injection timing is advancedThe
[0095]
Next, a specific correction method for the fuel injection timing according to the present embodiment will be described.
[0096]
FIG. 5 is a flowchart showing a flow for correcting the fuel injection timing according to the present embodiment.
[0097]
In step S101, it is determined whether low temperature combustion is being performed. If an affirmative determination is made in step S101, the process proceeds to step S102. On the other hand, if a negative determination is made, this routine is terminated and normal combustion is continued.
[0098]
In step S102, the target cylinder in this routine is determined. For example, the cylinder in which fuel is injected next time. In response to a signal from the CPU 351, the multiplexer 355 selects the cylinder pressure sensor 37 of the cylinder 2 to be sampled. The maximum value Pmax of the sampled pressure is stored in the peak hold amplifier 356, and the pressure Ptdc at the compression top dead center is stored in the RAM 353.
[0099]
In step S103, it is determined whether or not the data has been updated normally. That is, the CPU 351 determines whether or not the pressure Ptdc at the compression top dead center and the maximum pressure Pmax at the expansion stroke have been updated. If the data update is not performed normally, a failure of the in-cylinder pressure sensor 37 may be considered, and the subsequent processing is performed by the data update abnormality logic. If an affirmative determination is made in step S103, the process proceeds to step S104. On the other hand, if a negative determination is made, the process proceeds to step S105.
[0100]
In step S104, the value stored in the peak hold amplifier 356 is stored in the RAM 353, the update flag is turned ON, and the detection failure counter is cleared. Here, the update flag and the detection failure counter are variables given to each cylinder 2. The update flag is turned on when the sampling data is updated normally, and is turned off when the sampling data is not updated. The The detection failure counter is a value indicating the number of times data has not been updated normally.
[0101]
In step S105, a data update abnormality logic that is performed to correct the fuel injection timing is executed even if the data update is not normally performed. Specific contents will be described in step S301 and subsequent steps.
[0102]
In step S106, a pressure difference ΔP between the maximum pressure Pmax during the expansion stroke and the pressure Ptdc at the compression top dead center is calculated. The CPU 351 reads the maximum pressure Pmax during the expansion stroke and the pressure Ptdc at the compression top dead center stored in the RAM 353 and calculates the deviation. The calculated pressure difference ΔP is stored in the RAM 353.
[0103]
In step S107, it is determined whether or not the pressure difference ΔP calculated in step S106 is greater than the misfire determination level. Here, the misfire determination level is a pressure difference detected when a misfire occurs, and is obtained in advance by an experiment or the like. If an affirmative determination is made in step S107, the process proceeds to step S108. On the other hand, if a negative determination is made, the process proceeds to step S109.
[0104]
In step S108, a feedback correction value is calculated, and the forced advance angle counter is cleared. Specific contents will be described in step S201 and subsequent steps.
[0105]
In step S109, a misfire recovery logic is executed. Specific contents will be described in step S401 and subsequent steps.
[0106]
In step S110, misfire determination level calculation logic is executed. Specific contents will be described in step S501 and subsequent steps.
[0107]
In step S111, the forced advance angle counter is cleared. The forced advance angle counter indicates the number of times of forced advance angle performed in step S401 and subsequent steps.
[0108]
In step S112, the fuel injection timing is corrected.
[0109]
As described above, the correction value of the fuel injection timing is calculated, and the fuel injection timing is corrected in order to obtain an optimal combustion state.
[0110]
Next, the flow for calculating the correction value of the fuel injection timing will be described.
[0111]
FIG. 6 is a flowchart showing a flow for calculating the correction value of the fuel injection timing.
[0112]
In step S201, the target pressure difference ΔPt (hereinafter referred to as target pressure difference ΔPt), which is the pressure difference between the maximum pressure Pmax in the expansion stroke and the pressure Ptdc at the compression top dead center, is calculated in step S106. The deviation from the calculated pressure difference ΔP is calculated. The target pressure difference ΔPt is calculated based on the relationship between the engine speed and the load obtained in advance through experiments or the like, mapped and stored in the ROM 352. The engine speed is obtained from the output signal of the crank position sensor 33, and the load is obtained from the output signal of the accelerator opening sensor 36 or the fuel injection amount (the valve opening time of the fuel injection valve 3).
[0113]
  In step S202, insensitivebandProcessing is performed. InsensitivebandIndicates a range in which the deviation between the target pressure difference ΔPt and the pressure difference ΔP calculated in step S201 is small, and is provided to avoid unnecessary correction. In other words, the variation between combustion cycles becomes large during low-temperature combustion, so correction is prohibited within the range of variation.The
[0114]
  Here, FIG. 7 shows engine speed and load and insensitivity.bandIt shows an example of the relationship with the width of. The higher the engine speed, the less sensitivebandThe width of becomes narrower. However, depending on the type of engine, there may be large variations in a specific area.bandThe width of is widened. In addition, in the operation region where switching between low-temperature combustion and normal combustion frequently occurs, the variation becomes large, so it is insensitive.bandThe width of is widened.
[0115]
  On the other hand, when the load increases, it becomes difficult to perform low-temperature combustion, and the combustion is switched to normal combustion. Therefore, the greater the load, the less sensitivebandThe width of becomes wide.
[0116]
  Also, it is insensitive when transitioning from steady operation to transient operation or when transitioning from transient operation to steady operation.bandIn such cases, it is insensitive.bandSet the width of to 0. Furthermore, when transitioning from transient operation to steady operation, it is insensitive depending on the number of cycles or time.bandThe insensitivity obtained from Fig. 7 gradually from 0bandIncrease to the width of.
[0117]
  Here, FIG. 8 shows the number of cycles or time and insensitivity.bandIt is the figure which showed the relationship with the correction | amendment term of width | variety. InsensitivebandUntil the number of cycles or time for which the width correction term becomes 1 has elapsed, the correction term obtained from the number of cycles or time can be found in FIG.bandNewly insensitive to the value multiplied by the width ofbandUsed as the width of
[0118]
  Deviation between target pressure difference ΔPt and pressure difference ΔP is insensitivebandWhen it is within the range of the width, the pressure difference ΔP is handled as being equal to the target pressure difference ΔPt.
[0119]
Step S203 calculates a PID term. The PID term is calculated based on the deviation between the target pressure difference ΔPt and the pressure difference ΔP.
[0120]
In step S204, a feedback correction term for the injection timing is calculated. The PID term calculated in step S203 is added as a correction term to the normal fuel injection timing. Here, for example, when feedback control becomes difficult due to a failure of the in-cylinder pressure sensor 37, the correction term is not added.
[0121]
In step S205, upper and lower limit guards are applied. Here, applying the upper / lower limit guard means that when the corrected fuel injection timing calculated in step S204 is outside the allowable range, it is determined as abnormal, and the correction is prohibited. For example, such a state is caused by deterioration of the fuel injection valve 3 and various sensors. The upper limit value and the lower limit value of the fuel injection timing are obtained in advance through experiments or the like and stored in the ROM 352. Only when the fuel injection timing is within the range from the lower limit value to the upper limit value, the fuel injection is performed using the corrected fuel injection timing obtained by this routine.
[0122]
In this way, it is possible to calculate the corrected fuel injection timing.
[0123]
Next, the data update abnormality logic executed in step S105 will be described.
[0124]
FIG. 9 is a flowchart showing the flow of the data update abnormality logic.
[0125]
In step S301, the update flag is turned off and 1 is added to the detection failure counter.
[0126]
In step S302, it is determined whether the detection failure counter is larger than a fail determination value. Here, the output signal of the in-cylinder pressure sensor 37 may not be read properly due to the influence of noise or the like. Therefore, in such a case, it is not determined that the cylinder pressure sensor 37 is defective. On the other hand, when the output signal of the in-cylinder pressure sensor 37 cannot be obtained continuously, a sensor failure or the like is considered. Here, the fail determination value is obtained in advance by experiments or the like and stored in the ROM 352. When the detection failure counter value is larger than the fail determination value, it is determined that a sensor failure or the like has occurred, and the output signal of the cylinder pressure sensor 37 of the target cylinder 2 is not used. If an affirmative determination is made in step S302, the process proceeds to step S303, whereas if a negative determination is made, the process proceeds to step S304.
[0127]
In step 303, it is determined whether or not the correction value of the fuel injection timing of the other cylinders is equal to or less than a predetermined value. Here, it is determined whether or not the output value of the in-cylinder pressure sensor 37 obtained in the other cylinder can be used. Here, the predetermined value as the determination condition indicates an allowable upper limit value of the variation between the cylinders, and is obtained in advance by an experiment or the like. When the variation between the cylinders is small, it is estimated that the correction value of the target cylinder 2 is also within a predetermined range. On the other hand, when the variation between the cylinders is large, there is a possibility that the correction value of the target cylinder 2 also varies as compared with other cylinders. Therefore, when the variation in correction values among other cylinders is small, those average values are used, and when the variation in correction values between other cylinders is large, the correction is prohibited. If an affirmative determination is made in step S303, the process proceeds to step S305. On the other hand, if a negative determination is made, the process proceeds to step S306.
[0128]
In step S304, the correction value obtained last time for the target cylinder is used. For example, when the output signal of the in-cylinder pressure sensor 37 is not read due to the influence of noise or the like, the correction value calculated in the previous routine is used.
[0129]
In step S305, the average value of the correction values of the other cylinders is used as the correction value of the target cylinder.
[0130]
In step S306, since the variation among the cylinders is large, even if the average value is used as in step S305, it is not always an appropriate value, and thus correction of the fuel injection timing of the target cylinder is prohibited. Further, a sensor fail flag indicating an abnormality of the in-cylinder pressure sensor 37 is turned ON.
[0131]
In this way, even when the output signal of the in-cylinder pressure sensor 37 cannot be obtained, it may be possible to correct the fuel injection timing, and the opportunity for fuel injection timing correction can be expanded.
[0132]
Next, the misfire recovery logic flow executed in step S109 will be described.
[0133]
FIG. 10 is a flowchart showing the flow of the misfire recovery logic.
[0134]
In step S401, 1 is added to a forced advance counter that indicates the number of times of forced advance.
[0135]
In step S402, it is determined whether the forced advance angle counter value is 1. In order to make the correction method different between the first misfire and the second and subsequent misfires, the number of times of forced advance is determined. If an affirmative determination is made in step S402, the process proceeds to step S403. On the other hand, if a negative determination is made, the process proceeds to step S404.
[0136]
In step S403, the forced advance value is added to the correction value calculated in the previous routine. Here, when the fuel injection timing is advanced, the temperature of the fuel is raised by the compressed intake air, and ignition is easy. Therefore, misfire can be suppressed. A predetermined value is added to the correction value calculated in the previous routine so long as the corrected fuel injection timing does not exceed the basic fuel injection timing obtained from the engine speed and load.
[0137]
In step S404, the correction value obtained in the previous routine is cleared.
[0138]
In step S405, a forced advance value is obtained.
[0139]
Here, FIG. 11 is a diagram showing the relationship between the forced advance angle counter value and the forced advance angle value. The value of the forced advance angle counter is substituted into this map to obtain the forced advance value, and this value becomes the correction value.
[0140]
In step S406, it is determined whether or not the fuel injection timing correction value is smaller than the allowable advance angle upper limit value. If the advance value of the fuel injection timing is equal to or higher than the advance angle upper limit value, it is considered that there are other factors that cannot suppress the occurrence of misfire by the advance angle of the fuel injection. Therefore, a separate low-temperature combustion abnormality determination logic is performed. If an affirmative determination is made in step S406, the process proceeds to step S407. On the other hand, if a negative determination is made, the process proceeds to step S408.
[0141]
In step S407, it is determined whether or not the value of the forced advance angle counter is less than the upper limit value. When the forced advance angle is performed a predetermined number of times or more, it is considered that there are other factors that cannot suppress the occurrence of misfire by the forced advance angle. Therefore, a separate low-temperature combustion abnormality determination logic is performed. If an affirmative determination is made in step S407, this routine is terminated. On the other hand, if a negative determination is made, the process proceeds to step S408.
[0142]
In step S408, the low temperature combustion temporary abnormality flag is turned ON. Further, the forced advance angle value is set to 0, and the process proceeds to the low temperature combustion abnormality determination logic. In the present embodiment, the description of the low-temperature combustion abnormality determination logic is omitted.
[0143]
In this way, it is possible to advance the fuel injection timing after the misfire has occurred and suppress the subsequent misfire occurrence.
[0144]
Next, the flow of the misfire determination level calculation logic executed in step S110 will be described.
[0145]
FIG. 12 is a flowchart showing a flow of misfire determination level calculation logic. This routine increases the margin for misfire judgment by reducing the magnitude of the misfire judgment level when the pressure difference ΔP does not become larger than the misfire judgment level even when forced advance is performed. The purpose is to suppress misjudgment of misfire caused.
[0146]
In step S501, it is determined whether forced advance is performed based on step S401 and subsequent steps.
[0147]
If an affirmative determination is made in step S501, the process proceeds to step S502. On the other hand, if a negative determination is made, this routine ends.
[0148]
In step S502, it is determined whether or not the pressure difference ΔP is equal to or less than the misfire determination level. That is, in this step, it is determined whether or not misfire has occurred. If an affirmative determination is made in step S502, the process proceeds to step S503. On the other hand, if a negative determination is made, this routine ends.
[0149]
In step S503, a predetermined value is added to the correction value for correcting the misfire determination level. The misfire determination is performed based on a value obtained by subtracting the misfire determination correction value from the misfire determination level. Here, the basic misfire determination level is calculated from a map of the engine speed, the load, and the misfire determination level. However, if the pressure difference ΔP does not become larger than the misfire determination level even if the fuel injection timing is forcibly advanced, the misfire determination level is corrected and reduced. This is performed in order to correct the misfire determination level to an appropriate value with respect to variations between apparatuses.
[0150]
In step S504, it is determined whether or not the correction value obtained in step S503 is equal to or greater than a predetermined value indicating an allowable limit. When the correction value is equal to or greater than the predetermined value indicating the allowable limit, it is considered that misfire has occurred due to other factors, and therefore, the control proceeds to a separate low-temperature combustion abnormality determination logic without further correction.
[0151]
In step S505, the low temperature combustion temporary abnormality flag is turned ON. Further, the forced advance angle value is set to 0, and the process proceeds to the low temperature combustion abnormality determination logic. In the present embodiment, the description of the low-temperature combustion abnormality determination logic is omitted.
[0152]
In this way, it is possible to correct the fuel injection timing in consideration of variations between apparatuses.
[0153]
Here, in the conventional internal combustion engine, the fuel injection timing is corrected by analyzing the pressure waveform in the cylinder. However, high-speed processing is required to analyze the pressure waveform, and application to vehicles has been difficult. Further, simply correcting the fuel injection timing is not sufficient for returning to the normal combustion state early after the occurrence of misfire.
[0154]
In this respect, in the present embodiment, it is possible to correct the fuel injection timing based on the pressure at the compression top dead center and the maximum pressure thereafter, so there is no need to use a high-speed CPU, and the vehicle Can be easily installed. Moreover, even if misfire occurs, it is possible to return to the normal combustion state at an early stage, and to further suppress overcorrection due to variations among devices.
[0155]
【The invention's effect】
  In the internal combustion engine according to the present invention, it is possible to detect the occurrence of misfire based on the pressure at the compression top dead center and the maximum pressure thereafter. Also, maximum pressure and pressure at compression top dead centerDeviation fromBased on this, the fuel injection timing can be corrected. Therefore, the combustion state at the time of low temperature combustion can be stabilized.
[Brief description of the drawings]
FIG. 1 is a schematic configuration diagram illustrating an engine to which an internal combustion engine according to an embodiment of the present invention is applied and an intake / exhaust system thereof.
FIG. 2 is a diagram showing a schematic configuration of an in-cylinder pressure detection device.
FIG. 3 is a timing chart showing the timing of the output signal of the in-cylinder pressure sensor and the timing for taking in pressure data.
FIG. 4 is a diagram showing a concept of a control method according to the present embodiment.
FIG. 5 is a flowchart showing a flow for correcting a fuel injection timing.
FIG. 6 is a flowchart showing a flow for calculating a correction value for fuel injection timing.
[Fig. 7] Engine speed, load and insensitivitybandIt shows an example of the relationship with the width of.
[Figure 8] Cycle count or time and insensitivitybandIt is the figure which showed the relationship with the correction | amendment term of width | variety.
FIG. 9 is a flowchart showing a flow of data update abnormality logic.
FIG. 10 is a flowchart showing a flow of misfire recovery logic.
FIG. 11 is a diagram showing a relationship between a forced advance angle counter value and a forced advance angle value.
FIG. 12 is a flowchart showing a flow of misfire determination level calculation logic.
[Explanation of symbols]
1 ... Engine
1a ... Crank pulley
2. Cylinder
3. Fuel injection valve
4 ... Common rail
4a ... Common rail pressure sensor
5. Fuel supply pipe
6. Fuel pump
6a ... Pump pulley
8 ... Intake branch pipe
9. Intake pipe
18 ... Exhaust branch pipe
19 ... Exhaust pipe
20 ... Particulate filter
21 ... Exhaust throttle valve
24 ... Exhaust temperature sensor
25 ... EGR passage
26 ... EGR valve
27 ... EGR cooler
33 ... Crank position sensor
35 ... ECU
36 Accelerator opening sensor
37 ... In-cylinder pressure sensor

Claims (2)

Fuel supply means for supplying fuel into the cylinders of the internal combustion engine;
An EGR device that recirculates part of the exhaust gas to the intake system of the internal combustion engine;
Increase the amount of soot generated by increasing the amount of recirculated EGR gas, and then increase the amount of EGR gas, and then increase the amount of EGR gas. Combustion state switching means for selecting and switching either normal combustion to be recirculated,
Pressure detecting means for detecting the pressure at the compression top dead center in the cylinder and the maximum pressure during the expansion stroke;
An operating state detecting means for detecting an operating state of the internal combustion engine;
A deviation between the pressure at the maximum pressure and the compression top dead center immediately before in the expansion stroke in the cylinder, the value of the case where the combustion state of the internal combustion engine becomes unstable, by the operating condition detecting means Misfire level calculating means for calculating from the detected engine operating state ;
A deviation between the maximum pressure during the expansion stroke in the cylinder and the pressure at the compression top dead center just before that is detected by the operating state detecting means when the combustion state of the internal combustion engine is optimum. Target level calculation means for calculating from the engine operating state ,
Pressure deviation calculating means for calculating a deviation between the maximum pressure during the expansion stroke in the cylinder detected by the pressure detecting means during the low temperature combustion and the pressure at the compression top dead center immediately before the expansion stroke;
When the pressure deviation calculated by the pressure deviation calculating means is larger than the value calculated by the misfire level calculating means, the pressure deviation calculated by the pressure deviation calculating means is calculated by the target level calculating means. If the value is larger than the calculated value, the fuel injection timing is retarded so that the pressure deviation calculated by the pressure deviation calculating means becomes the value calculated by the target level calculating means , and the pressure deviation calculating means calculates When the pressure deviation is smaller than the value calculated by the target level calculation means, the fuel injection timing is set so that the pressure deviation calculated by the pressure deviation calculation means becomes the value calculated by the target level calculation means. Fuel injection timing correction means for advancing,
An internal combustion engine comprising: The internal combustion engine is provided with a plurality of cylinders, one of when the pressure deviation of the pressure difference calculation means has calculated the cylinder becomes a predetermined range continuously a predetermined number of cycles, the in the other cylinders When the cylinder-to-cylinder variation in pressure deviation calculated by the pressure deviation calculating means is small, the fuel injection timing correcting means uses the average value of the pressure deviation in the other cylinders, and the fuel injection timing correcting means uses the fuel in the cylinders outside the predetermined range. 2. The fuel injection timing correction unit according to claim 1, wherein the fuel injection timing correction unit does not correct the fuel injection timing of the cylinder that is out of the predetermined range when the injection timing is corrected while the variation between cylinders is large. Internal combustion engine.

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