JP4905213B2 - Diesel engine control device - Google Patents

Description

  The present invention relates to a control device for a diesel engine equipped with an exhaust turbocharger.

Diesel engines are widely used as automotive engines because they have the advantages of high thermal efficiency, reducing carbon dioxide emissions that contribute to global warming, and high durability and reliability. (For example, refer to Patent Document 1). However, the diesel engine has a problem that the combustion noise increases when the combustion pressure rises rapidly during the compression stroke or the combustion stroke. This combustion noise is particularly noticeable when the accelerator opening is small. Therefore, in a diesel engine, generally, at least when the accelerator opening is small, multistage injection of fuel is performed in one compression stroke or combustion stroke, so that a sudden increase in combustion pressure is prevented and combustion noise is suppressed.
JP 2006-248872 A (paragraph [0015], FIG. 1)

  By the way, in general, in a diesel engine, when the fuel is rich (high concentration), an oxygen-deficient region is locally generated in the combustion chamber, and smoke (black smoke) is likely to be generated. When injection is performed, there arises a problem that smoke is more likely to be generated. That is, when multi-stage injection is performed, fuel is further injected into the air in which the fuel is already mixed, and accordingly, a rich region is locally generated and smoke is easily generated.

  In addition, an automobile turbocharger is usually provided with an exhaust turbocharger that performs supercharging in an operating region exceeding a predetermined engine speed in order to increase output. In a diesel engine equipped with an exhaust turbocharger, when acceleration is started by depressing the accelerator with a small accelerator opening, the fuel injection amount increases almost without time delay, whereas the fuel due to supercharging The increase in combustion air is accompanied by a certain time delay (supercharging delay). Therefore, when acceleration is started with a small accelerator opening, the combustion chamber temporarily becomes deficient in oxygen due to a delay in supercharging, and smoke is particularly likely to occur.

  Therefore, in a diesel engine equipped with an exhaust turbocharger, smoke is particularly likely to occur when multistage injection of fuel is performed. In an operation state in which smoke is likely to occur, it may be possible to temporarily stop the multi-stage fuel injection, but this causes a problem that the combustion noise and thus the engine noise increase.

  The present invention has been made to solve the above-described conventional problems, and effectively prevents or prevents the generation of smoke even when performing multistage fuel injection on a diesel engine equipped with an exhaust turbocharger. It is an object to be solved to provide means for enabling suppression.

In order to solve the above problems, a control device for a diesel engine equipped with an exhaust turbocharger according to the present invention corresponds to an increase delay in air during acceleration due to a delay in supercharging of the exhaust turbocharger, Fuel injection limiting means for limiting the fuel injection amount to an upper limit value (hereinafter referred to as “injection guard value”) is provided, and the fuel injection limiting means is used when the accelerator opening is small at which the increase delay of air during acceleration increases. The injection guard value is set so that the ratio of fuel to air for fuel combustion becomes smaller than when the accelerator opening is large , and the control device supplies fuel at least in the low accelerator opening region. A fuel injection control means for performing multi-stage injection (multiple injection) in one compression stroke or combustion stroke, and the fuel injection limiting means is less when the number of injections in each multi-stage injection is large To, injection guard value, it is characterized in that set so that the ratio of the fuel is reduced to air for fuel combustion.

When the control device for a diesel engine according to the present invention, the fuel injection limiting means, when the transmission ratio of the transmission to shift the output torque of the diesel engine (gear ratio) is low-stage side is higher gear On the other hand, it is also preferable that the injection guard value is set so that the ratio of fuel to air for fuel combustion becomes small.

According to the diesel engine control apparatus of the present invention, when the injection guard value is on the low accelerator opening side, the ratio of the fuel to the air for fuel combustion is small when the accelerator opening is small in which the increase delay of air during acceleration increases. Is set to be small , the fuel injection amount is suppressed during acceleration at a low accelerator opening at which oxygen shortage occurs. For this reason, generation | occurrence | production of the smoke at the time of acceleration with a low accelerator opening degree can be prevented thru | or suppressed, suppressing a combustion noise.

Further, in the control device for a diesel engine according to the present invention, since setting the injection guard value than when less when injection number is large in each multiple injection such that the ratio of the fuel is reduced to air for fuel combustion, It is possible to effectively prevent or suppress an increase in the amount of smoke generated as the number of injections increases.

In general, when the gear ratio of the transmission is on the low speed stage side, the increase in engine speed during acceleration is faster than when the transmission is on the high speed stage side, so the fuel injection amount increases rapidly. For this reason, smoke is likely to occur due to a delay in boosting of the supercharging pressure (supercharging delay). Therefore, in the control apparatus for a diesel engine according to the present invention, when the transmission gear ratio is on the low speed stage side, the injection guard value is smaller than on the high speed stage side, and the ratio of fuel to air for fuel combustion is small. In the case of setting so as to be, it is possible to effectively prevent or suppress the generation of smoke during acceleration at the low speed stage side.

Hereinafter, embodiments of the present invention (best mode for carrying out the present invention) will be described in detail with reference to the accompanying drawings.
As shown in FIG. 1, a direct injection diesel engine 1 with an exhaust turbocharger according to the present invention (hereinafter referred to as “engine 1” for short) includes a cylinder head 2 and a cylinder block 3 that form an outer shell. It has. Although FIG. 1 shows only one cylinder (cylinder), the engine 1 is a multi-cylinder engine (for example, an in-line four-cylinder engine) having a plurality of cylinders.

  Although not shown in detail, the engine 1 is an automobile engine, and the output torque of the engine 1 is an automatic equipped with a torque converter and a transmission having forward 1st to 6th speeds and reverse gears. After being changed by the transmission mechanism in accordance with the transmission gear ratio of the selected gear stage, it is transmitted to the drive wheels via a power transmission mechanism such as a reduction gear mechanism and a differential device. In the present invention, the forward speed of the transmission is not limited to 1st to 6th speed (for example, 1st to 4th speed, 1st to 5th speed may be used). Further, a manual multi-stage transmission may be used instead of the automatic transmission mechanism.

  In each cylinder of the engine 1, air is taken into the combustion chamber 6 from the intake port 5 in the intake stroke in which the intake valve 4 is opened. The air in the combustion chamber 6 is compressed by a piston 8 fitted in a cylinder 7 (cylinder) to be in a high temperature / high pressure state. In the compression stroke or combustion stroke, fuel (for example, light oil) is injected from the fuel injection valve 9 into the high-temperature and high-pressure air in the combustion chamber 6 in one or more stages, and this fuel self-ignites and burns. To do. The combustion gas, that is, the exhaust gas generated by the combustion of the fuel is discharged to the exhaust port 11 in the exhaust stroke in which the exhaust valve 10 is opened. These strokes are repeated, and the piston 8 reciprocates in the cylinder 7. The reciprocating motion of the piston 8 is converted into a rotational motion of a crankshaft (not shown) by the connecting rod 12 or the like.

  In order to supply fuel combustion air (hereinafter referred to as “intake air”) to the combustion chamber 6 of the engine 1, a common intake passage 15 whose front end (upstream end) is open to the atmosphere is provided. The common intake passage 15 includes an air cleaner 16 that removes foreign matters such as dust in the intake air in order from the upstream side in the flow direction of the intake air (indicated by white arrows in FIG. 1), and the engine 1. , A compressor 17a of an exhaust turbocharger 17 for supercharging, an intercooler 18 for cooling intake air whose temperature has increased due to supercharging, and an intake throttle valve 19 for controlling the flow rate of the intake air are provided. Yes.

  The downstream end of the common intake passage 15 is connected to a surge tank 20 that stabilizes the flow of intake air. The surge tank 20 is connected to an upstream end of an independent intake passage 21 provided for each cylinder and independent of each other. The downstream ends of these independent intake passages 21 are respectively connected to the intake ports 5 of the corresponding cylinders.

In order to discharge the combustion gas of the engine 1, that is, the exhaust gas, an exhaust passage 23 whose upstream end communicates with the exhaust port 11 is provided in the exhaust gas flow direction (indicated by a black arrow in FIG. 1). ing. In the exhaust passage 23, the turbine 17b of the exhaust turbocharger 17, the catalytic converter 24 for purifying the exhaust gas, carbon contained in the exhaust gas, soot, A filter 25 (diesel particulate filter) for collecting fine particles (particulates) such as hydrocarbons is provided. The catalytic converter 24 includes an oxidation catalyst that supports platinum or platinum added with palladium, and oxidizes CO and HC in the exhaust gas to generate CO ₂ and H ₂ O. It promotes the oxidation reaction.

  Further, an EGR passage 27 is provided for returning a part of the exhaust gas in the exhaust passage 23 upstream of the turbine 17b to the common intake passage 15 between the intercooler 18 and the surge tank 20 as EGR gas. The EGR passage 27 is provided with a water-cooled EGR cooler 28 for cooling the EGR gas and an EGR control valve 29 for controlling the flow rate of the EGR gas in order from the upstream side in the flow direction of the EGR gas (exhaust gas). It has been. Thereby, a part of the exhaust gas in the exhaust passage 23 can be recirculated to the common intake passage 15 while the flow rate is controlled by the EGR control valve 29.

  Fuel is supplied to the fuel injection valve 9 of each cylinder from a fuel tank (not shown) through a fuel passage 31. A high pressure fuel pump 32 that discharges fuel at a high pressure (for example, 1000 to 2000 atmospheres) and a common rail 33 (fuel distributor) that stores high pressure fuel are interposed in the fuel passage 31. The high pressure fuel pump 32 operates so that the fuel pressure in the common rail 33 is maintained at a predetermined value or higher. As a result, the fuel injection valve 9 can perform a desired number of fuel injections (multi-stage injection) in a range of 1 to 4 times in one compression stroke or combustion stroke of each cylinder of the engine 1. ing. The combustion injection valve 9 can arbitrarily set the fuel injection amount and the injection timing of each injection in the multistage injection (see FIG. 5). In addition, the frequency | count of multistage injection is not necessarily limited to 1-4 times, and may be more or less than this (for example, 1-3 times, 1-5 times).

  The engine 1 is provided with various sensors in order to collect various information related to the operating state. That is, the common intake passage 15 is provided with an air flow sensor 35 for detecting the intake air amount at a portion slightly downstream of the air cleaner 16. Further, in the common intake passage 15, an intake air temperature sensor 36 that detects the temperature of intake air (intake air temperature) at a portion slightly downstream of the intake throttle valve 19 (upstream from the connection portion with the EGR passage 27), An intake pressure sensor 37 that detects the pressure of the intake air (intake pressure) is provided.

Further, the engine 1 includes a rotation speed sensor 38 that detects the engine rotation speed, a crank angle sensor 39 that detects the crank angle, a water temperature sensor 40 that detects the temperature of the coolant of the engine 1 (engine water temperature), and an accelerator. An accelerator opening sensor 41 (see FIG. 2) for detecting the opening is provided. The exhaust passage 23 of the engine 1 is provided with a first O ₂ sensor 42 (linear O ₂ sensor) that detects the oxygen concentration in the exhaust gas at a position slightly upstream of the turbine 17b. Further, the exhaust passage 23 is provided with a first exhaust pressure sensor 43 that detects the pressure of the exhaust gas at a portion between the catalytic converter 24 and the filter 25, and the exhaust gas at a portion slightly downstream of the filter 25. A second exhaust pressure sensor 44 for detecting the pressure of the exhaust gas, an exhaust temperature sensor 45 for detecting the temperature of the exhaust gas, and a _second O ₂ sensor 46 (linear O ₂ sensor) for detecting the oxygen concentration in the exhaust gas. ing.

  As shown in FIG. 2, the engine 1 is provided with a control unit 50 including a computer in order to perform various controls of the engine 1. The control unit 50 is a comprehensive control means of the engine 1 including “fuel injection control means” and “fuel injection restriction means” described in the section for solving the problem. Although not shown in detail, the control unit 50 includes an input / output unit that inputs and outputs control signals, a storage unit (ROM, RAM, etc.) that stores data, a central processing unit (CPU), a timer counter, and the like. I have.

  The control unit 50 controls the fuel injection control by controlling the fuel injection valve 9, the supercharger 17, the intake throttle valve 19, the EGR control valve 29, and the like based on various data detected by the sensors 35 to 46. (Including fuel injection restriction control), EGR control, supercharging control, and the like are performed. Note that the EGR control and the supercharging control are well known to those skilled in the art, and such control is not the gist of the present invention, so the description thereof is omitted.

Hereinafter, the control method of fuel injection control (including fuel injection restriction control) according to the present invention, which is executed by the control unit 50, will be described in detail with reference to the flowchart shown in FIG.
As shown in FIG. 3, in this fuel injection control, when the control is started (start), first, in step S1, various signals detected by the sensors 35 to 46 are read.

  Subsequently, in step S2, the fuel injection amount of the fuel injection valve 9 is basically calculated based on the accelerator opening (engine load) and the engine speed. Specifically, the required fuel injection amount is calculated based on the accelerator opening and the engine speed, for example, using a fuel injection amount map having characteristics as shown in FIG. The fuel injection amount map is stored in the memory of the control unit 50 in the form of digital data.

  Next, in step S3, basically, the number of fuel injections of the fuel injection valve 9 in one compression stroke or combustion stroke is calculated based on the engine load (accelerator opening) and the engine speed. Specifically, the number of fuel injections is calculated based on the engine load and the engine speed using, for example, an injection number map having the characteristics shown in FIG. The injection number map is stored in the memory of the control unit 50 in the form of digital data.

  As shown in FIG. 5, in this engine 1, the number of fuel injections is increased stepwise as the engine speed generally decreases. Particularly, in the low load region, that is, the low accelerator opening region, the number of fuel injections is increased stepwise from the first stage injection to the fourth stage injection as the engine speed decreases. The reason for changing the number of fuel injections in this way is mainly to reduce combustion noise. In addition, the broken line respectively described in the 1st stage injection-4 stage | paragraph injection (injection frequency is 1-4 times) area | region in FIG. 5 has shown typically the quantity and timing of fuel injection in each area | region.

  After the fuel injection amount and the number of injections of the fuel injection valve 9 are thus calculated in steps S2 to S3, the injection guard value is calculated in step S4. Here, the injection guard value is an upper limit value of a fuel injection amount (or a ratio of fuel to intake air) provided to prevent or suppress the occurrence of smoke. That is, when the fuel injection amount calculated based on the accelerator opening and the engine speed in step S2 exceeds the injection guard value, the fuel injection amount is set to this injection guard value.

  As is clear from FIG. 5, the fuel injection valve 9 of the engine 1 performs multi-stage injection in the low accelerator opening region (particularly in the low rotation region), so smoke is likely to occur. Further, when acceleration is started in a low accelerator opening state, smoke is more likely to occur due to a supercharging delay. Therefore, an injection guard value is provided in order to prevent or suppress the occurrence of such smoke. The injection guard value is preferably set according to the accelerator opening, the number of fuel injections, and the transmission gear ratio (speed stage) in order to more reliably prevent or suppress the occurrence of smoke. .

  In addition, the broken line L in FIG. 4 has shown an example of the injection guard value at the time of non-supercharging. That is, when the exhaust turbocharger 17 is not operating and the fuel injection amount calculated based on the accelerator opening and the engine speed exceeds the injection guard value, the fuel injection amount is Reduced to injection guard value.

As shown in FIG. 6, the injection guard value is set to a leaner side (the fuel injection amount is smaller) as the accelerator opening (engine load) is smaller. In FIG. 6, the injection guard value represents the oxygen concentration of the exhaust gas detected by the first O ₂ sensor 42. This is because there is a unique relationship between the fuel injection amount (ratio of fuel to intake air) and the oxygen concentration in the exhaust gas, so the fuel injection amount (intake) depends on the oxygen concentration in the exhaust gas. This is because the ratio of fuel to air) can be expressed, and the oxygen concentration in the exhaust gas can be easily detected. In this embodiment, therefore, the injection guard value is represented by the oxygen concentration in the exhaust gas, and the actual fuel injection amount (ratio of fuel to intake air) is determined by the first O ₂ sensor 42. It is expressed by oxygen concentration.

  Further, as shown in FIG. 7, in this engine 1, the injection guard value is corrected (set) to the lean side as the number of fuel injections in one compression stroke or combustion stroke increases. This is because smoke is more likely to occur due to overlapping fuel as the number of fuel injections increases.

  Also, as shown in FIG. 8, when the transmission gear ratio is on the low speed side, the injection guard value is set to be leaner than on the high speed side. In FIG. 8, the injection guard value is represented by the oxygen concentration of the exhaust gas. This is because smoke is more likely to occur due to a supercharging delay when the transmission gear ratio is on the low speed side than on the high speed side.

  Thus, in the engine 1, the injection guard value is set or corrected in accordance with the accelerator opening, the number of fuel injections, and the transmission gear stage or gear ratio. However, in order to simplify the calculation and reduce the load on the control unit 50, the injection guard value may be set based only on the accelerator opening. Alternatively, the injection guard value may be set on the basis of the accelerator opening and the number of fuel injections, or on the basis of the accelerator opening and the gear ratio or the gear position.

  It should be noted that when the EGR control valve 29 is closed and the introduction of EGR gas to the intake system is stopped (EGR cut), if EGR gas remains in the intake system, for example, the EGR control valve 29 is Smoke is likely to occur within a certain time after closing, and therefore the injection guard value may be made slightly lower.

Next, in step S5, the oxygen concentration of the exhaust gas detected by the first O ₂ sensor 42 (hereinafter referred to as “oxygen concentration detection value”) is changed to the injection guard value (the oxygen concentration of the exhaust gas) calculated in step S4. It is determined whether or not the converted value is exceeded. Here, when it is determined that the oxygen concentration detection value exceeds the injection guard value (YES), in step S6, the fuel injection amount of the fuel injection valve 9 (the ratio of fuel to intake air) reaches the injection guard value. Reduced weight. That is, the fuel injection amount is set to the injection guard value. Thereafter, the process returns to step S1. On the other hand, if it is determined in step S5 that the oxygen concentration detection value is equal to or less than the injection guard value (NO), there is no need to limit the fuel injection amount, so step S6 is skipped and the process returns to step S1. .

Meanwhile, the oxygen concentration detected by the first 1O ₂ sensor 42, the capacity of the exhaust passage 23 or the second 1O ₂ sensor 42 response delay of itself, accompanied by a slight time delay. Therefore, without using the oxygen concentration detected by the first O ₂ sensor 42, the intake air amount, fuel injection amount, intake air temperature, exhaust gas temperature, engine shape (volume, etc.), intake system and exhaust system shape (Volume, length, cross-sectional area, etc.) etc. are used to estimate the oxygen concentration of the exhaust gas using the generally known mass balance theory and thermodynamic theory, and use this estimated oxygen concentration. Step S5 may be executed.

The first O ₂ sensor 42 may not be provided, and step S5 may be executed using the oxygen concentration detected by the _second O ₂ sensor 46. However, in this case, the time delay of the oxygen concentration detection value is greater than when the first O ₂ sensor 42 is used.

  As described above, according to the fuel injection control of the engine 1, it is possible to prevent or suppress the generation of smoke during acceleration at a low accelerator opening while suppressing combustion noise.

It is a mimetic diagram showing the system configuration of the diesel engine provided with the exhaust turbocharger concerning the embodiment of the invention. It is a block diagram which shows the structure of the control system of the diesel engine shown in FIG. 2 is a flowchart showing a control method of fuel injection control (including fuel injection restriction control) of the diesel engine shown in FIG. 1. It is a figure (fuel injection amount map) which shows the fuel-injection characteristic of the fuel injection valve with respect to an accelerator opening and an engine speed. It is a figure (fuel injection frequency map) which shows the setting method of the fuel injection frequency of a fuel injection valve with respect to an engine load and an engine speed. It is a figure which shows the change characteristic of the injection guard value with respect to an accelerator opening. It is a figure which shows the change characteristic of the injection guard value with respect to the frequency | count of fuel injection. It is a figure which shows the change characteristic of the injection guard value with respect to a gear ratio (speed stage).

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Diesel engine (engine), 2 cylinder head, 3 cylinder block, 4 intake valve, 5 intake port, 6 combustion chamber, 7 cylinder, 8 piston, 9 fuel injection valve, 10 exhaust valve, 11 exhaust port, 12 connecting rod, 15 common intake passage, 16 air cleaner, 17 exhaust turbocharger, 17a compressor, 17b turbine, 18 intercooler, 19 intake throttle valve, 20 surge tank, 21 independent intake passage, 23 exhaust passage, 24 catalytic converter, 25 filter, 27 EGR passage, 28 EGR cooler, 29 EGR control valve, 31 fuel passage, 32 high pressure fuel pump, 33 common rail, 35 air flow sensor, 36 intake air temperature sensor, 37 intake air pressure sensor, 38 rpm sensor, 39 crank angle sensor, 40 water temperature Sensor, 41 accelerator opening Sensor, 42 1st O ₂ sensor, 43 1st exhaust pressure sensor, 44 2nd exhaust pressure sensor, 45 Exhaust temperature sensor, 46 _2nd O ₂ sensor, 50 Control unit.

Claims (2)

A control device for a diesel engine equipped with an exhaust turbocharger,
Corresponding to the increase delay of the air at the time of acceleration due to the supercharging delay of the exhaust turbo supercharger, the fuel injection limiting means for limiting the fuel injection amount to the upper limit value,
The fuel injection limiting means is configured to reduce the ratio of fuel to air for fuel combustion with respect to when the accelerator opening is large, when the accelerator opening is small when the increase delay of air during acceleration is large. Set an upper limit ,
And the control device is provided with a fuel injection control means for multi-stage injection of fuel at least in the low accelerator opening range, the fuel injection limiting means, when the number of injections in each multi-stage injection is large, The diesel engine control apparatus , wherein the upper limit value is set so that a ratio of fuel to air for fuel combustion becomes small . The fuel injection limiting means sets the upper limit value to the fuel for air for fuel combustion when the gear ratio of the transmission for shifting the output torque of the diesel engine is on the low speed side. The diesel engine control device according to claim 1, wherein the ratio is set to be small.

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