JP2016061165A - Control device of diesel engine - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a control device of a diesel engine capable of suppressing degradation of exhaust emission by performing combustion control corresponding to properties of fuel.SOLUTION: A control device performing combustion control of a fuel in a diesel engine (10), includes: kinetic viscosity detecting means (33) detecting kinetic viscosity of the fuel; and switching means (17, 26, 40) for switching combustion control from prescribed control set while assuming the fuel of prescribed properties, to soot suppression control for suppressing an amount of soot discharged accompanied with combustion of the fuel, in a case when the kinetic viscosity detected by the kinetic viscosity detecting means is lower than a first determination value, and higher than a second determination value set to be higher than the first determination value.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a control device that executes fuel combustion control in a diesel engine.

  The fuel for diesel engines on the market varies greatly in properties. For this reason, the combustion state changes greatly depending on the properties of the fuel, which may cause deterioration of exhaust emission, misfire, and the like.

  Therefore, there is one that detects the cetane number of fuel based on the combustion state of fuel injected by pilot injection (see Patent Document 1).

JP 2006-226188 A

  However, even if the cetane number of the fuel is detected, there is a case where deterioration of exhaust emission cannot be suppressed only by executing the combustion control according to the cetane number. For example, when the aromatic component and the side chain component contained in the fuel are relatively large, the inventor of the present application paid attention to the fact that the fuel becomes difficult to burn and the amount of soot discharged increases. .

  The present invention has been made to solve these problems, and a main object of the present invention is to control a diesel engine that can suppress deterioration of exhaust emission by executing combustion control according to the properties of the fuel. To provide an apparatus.

  The present invention employs the following means in order to solve the above problems.

  The present invention is a control device that performs combustion control of fuel in a diesel engine, wherein kinematic viscosity detecting means for detecting the kinematic viscosity of the fuel, and the kinematic viscosity detected by the kinematic viscosity detecting means is When the fuel control is lower than the first determination value and higher than the second determination value set higher than the first determination value, the combustion control is changed from the predetermined control set assuming a fuel having a predetermined property to the fuel. Switching means for switching to soot suppression control that suppresses the amount of soot discharged with the combustion of.

  When the straight chain of the molecule contained in the fuel is shortened and the number of carbon atoms is reduced, the side chain component is relatively increased and the number of hydrogen is relatively decreased, so that the fuel is difficult to burn. The smaller the number of molecular carbons contained in the fuel, the lower the kinematic viscosity of the fuel. Further, when the polycyclic aromatic component contained in the fuel increases, the fuel becomes difficult to burn. As the polycyclic aromatic component contained in the fuel increases, the kinematic viscosity of the fuel tends to increase.

  In this regard, according to the above configuration, the kinematic viscosity of the fuel is detected by the kinematic viscosity detecting means. When the detected kinematic viscosity is lower than the first determination value and higher than the second determination value set higher than the first determination value, the fuel combustion control assumes a fuel having a predetermined property. The predetermined control thus set is switched to the soot suppression control that suppresses the amount of soot discharged with the combustion of fuel. For this reason, when it becomes difficult to combust the fuel, the combustion control of the fuel can be switched from the predetermined control to the suppression control sooting, and the deterioration of the exhaust emission can be suppressed.

The schematic diagram which shows a diesel engine and its periphery structure. The distribution map which shows fuel distribution with respect to a fuel density, a cetane number, and kinematic viscosity. The flowchart which shows the process sequence of the combustion control of 1st Embodiment. The flowchart which shows the process sequence of the combustion control of 2nd Embodiment.

(First embodiment)
Hereinafter, a first embodiment will be described with reference to the drawings. This embodiment is applied to a diesel engine for a vehicle, and is embodied as a control device that controls combustion of fuel injected by a fuel injection valve.

  First, the outline of the diesel engine 10 will be described with reference to FIG. The diesel engine 10 is, for example, an in-line four-cylinder diesel engine, and only one cylinder (cylinder) is shown in FIG. As shown in the figure, the diesel engine 10 includes a cylinder block 11, a piston 12, a cylinder head 13, an intake passage 14, an exhaust passage 15, an intake valve 16, an injector 17, an exhaust valve 18, a VVT 21, an EGR device 26, and the like. ing.

  The cylinder block 11 is formed with four cylinders 11a. Each cylinder 11a accommodates a piston 12 in a reciprocable manner. A cylinder head 13 is assembled to the cylinder block 11. A combustion chamber is formed by the cylinder 11 a, the piston 12, and the cylinder head 13.

  An intake passage 14 is connected to the cylinder block 11. The intake passage 14 is connected to each cylinder 11 a via an intake manifold and an in-head passage 14 a in the cylinder head 13. The camshafts 19A and 19B are rotated by the rotation of the crankshaft (not shown) of the diesel engine 10. Each intake valve 16 is driven based on the rotation of the camshaft 19A, and each in-head passage 14a is opened and closed by each intake valve 16. The VVT 21 (variable valve timing device) makes the opening / closing timing of the intake valve 16 variable by adjusting the rotational phase of the crankshaft and the camshaft 19A.

  An exhaust passage 15 is connected to the cylinder block 11. The exhaust passage 15 is connected to each cylinder 11 a via an exhaust manifold and an in-head passage 15 a in the cylinder head 13. Each exhaust valve 18 is driven based on the rotation of the camshaft 19B, and each head passage 15a is opened and closed by each exhaust valve 18.

  Fuel is pumped to the common rail 20 by a fuel pump (not shown). The common rail 20 (accumulation container) holds fuel in an accumulator state. The injector 17 (fuel injection valve) injects the fuel held in the common rail 20 in a pressure accumulation state into the cylinder 11a.

  The EGR device 26 (exhaust gas recirculation device) includes an EGR passage 27 and an EGR valve 28. The EGR passage 27 connects the exhaust passage 15 and the intake passage 14. The EGR passage 27 is provided with an EGR valve 28 that opens and closes the EGR passage 27. The EGR device 26 introduces part of the exhaust gas in the exhaust passage 15 into the intake air in the intake passage 14 according to the opening degree of the EGR valve 28.

  In the intake stroke of the diesel engine 10, air is sucked into the cylinder 11a through the intake passage 14, and the air is compressed by the piston 12 in the compression stroke. In the vicinity of the compression top dead center, fuel is injected into the cylinder 11a by the injector 17, and the fuel injected in the combustion stroke is self-ignited and burned. In the exhaust stroke, the exhaust in the cylinder 11 a is exhausted through the exhaust passage 15. Part of the exhaust gas in the exhaust passage 15 is introduced into the intake air in the intake passage 14 by the EGR device 26.

  The diesel engine 10 is provided with an in-cylinder pressure sensor 31 and a fuel density sensor 32. The in-cylinder pressure sensor 31 detects the pressure in the cylinder 11a. The fuel density sensor 32 detects the density of the fuel supplied to the injector 17. The fuel density sensor 32 detects the density of the fuel based on, for example, a natural vibration period measurement method. A fuel tank (not shown) of the diesel engine 10 is provided with a kinematic viscosity sensor 33 and a fuel amount sensor 34. The kinematic viscosity sensor 33 (kinematic viscosity detecting means) is, for example, a capillary viscometer or a kinematic viscometer based on a thin wire heating method, and detects the kinematic viscosity of the fuel in the fuel tank. The fuel amount sensor 34 detects the amount of fuel in the fuel tank. The fuel density sensor 32 and the kinematic viscosity sensor 33 include a heater, and detect the density and kinematic viscosity of the fuel, respectively, in a state where the fuel is heated to a predetermined temperature by the heater.

  The ECU (Electric Control Unit) 40 is a known microcomputer including a CPU, a ROM, a RAM, a storage device, an input / output interface, and the like. The ECU 40 is based on detection values of various sensors such as a crank angle sensor, a coolant temperature sensor, an accelerator opening sensor, an in-cylinder pressure sensor 31, a fuel density sensor 32, a kinematic viscosity sensor 33, and a fuel amount sensor 34, and the injector 17, VVT 21. The EGR device 26 and the like are controlled. Specifically, the control states of the injector 17, the VVT 21, and the EGR device 26 are adapted in accordance with the operation state of the diesel engine 10 so that the fuel combustion state is optimized assuming a standard property fuel in advance. Yes. The ECU 40 controls each device so as to achieve an adapted control state (predetermined control) based on detection values of various sensors. The ECU 40 causes the injector 17 to execute pilot injection and main injection. The injector 17, the EGR device 26, and the ECU 40 constitute a control device that performs fuel combustion control in the diesel engine 10.

  FIG. 2 is a distribution diagram showing the distribution of fuel with respect to fuel density, cetane number, and kinematic viscosity. When the straight chain of the molecule contained in the fuel is shortened and the number of carbon atoms is reduced, the side chain component is relatively increased and the number of hydrogen is relatively decreased, so that the fuel is difficult to burn. The smaller the number of molecular carbons contained in the fuel, the lower the kinematic viscosity of the fuel. Further, when the polycyclic aromatic component contained in the fuel increases, the fuel becomes difficult to burn. As the polycyclic aromatic component contained in the fuel increases, the kinematic viscosity of the fuel tends to increase. Therefore, in the region where the kinematic viscosity of the fuel is lower than the first determination value (low kinematic viscosity region) and the region where the fuel kinematic viscosity is higher than the second determination value (high kinematic viscosity region), The inventor of the present application has focused on increasing the amount of soot discharged.

  Here, as shown in the figure, with respect to the density of the fuel, the kinematic viscosity tends to decrease as the density decreases, and the kinematic viscosity tends to increase as the density increases. Further, with respect to the cetane number of the fuel, the lower the cetane number, the lower the kinematic viscosity, and the higher the cetane number, the higher the kinematic viscosity. For this reason, in the map centering on the density and cetane number of the fuel, as indicated by an arrow, the kinematic viscosity decreases toward the lower left in the figure and increases toward the upper right in the figure. The map of FIG. 2 is obtained by previously obtaining the relationship between the fuel density, the cetane number, and the kinematic viscosity for the fuel handled in the market.

  In the present embodiment, the combustion control is normally performed when the kinematic viscosity detected by the kinematic viscosity sensor 33 is lower than the first determination value and higher than the second determination value set higher than the first determination value. It switches from the combustion control (predetermined control) by adaptation to the soot suppression control which suppresses the amount of soot discharged | emitted with fuel combustion. FIG. 3 is a flowchart showing a processing procedure for combustion control. This series of processing is repeatedly executed by the ECU 40 at a predetermined cycle (for example, every injection by the injector 17).

  First, it is determined whether a condition for detecting the property of the fuel is satisfied (S11). Specifically, it is determined whether or not refueling has been performed based on the fuel amount detected by the fuel amount sensor 34, and when it is determined that refueling has been performed, a condition for detecting the properties of the fuel is satisfied. judge. In S11, when the fuel amount detected by the fuel amount sensor 34 has increased, it is determined only once that fueling has been performed.

  If it is determined in S11 that the condition for detecting the property of the fuel is not satisfied (S11: NO), this series of processes is temporarily ended (END). On the other hand, if it is determined in S11 that the condition for detecting the properties of the fuel is satisfied (S11: YES), the kinematic viscosity of the fuel in the fuel tank is detected by the kinematic viscosity sensor 33 (S12).

  Subsequently, it is determined whether or not the detected kinematic viscosity is smaller than the first determination value (S13). The first determination value is a kinematic viscosity lower than the kinematic viscosity of a standard property fuel (a fuel of a predetermined property), and the kinematic viscosity at which the amount of soot discharged with the combustion of the fuel is larger than the predetermined amount. Is set to

  In the determination of S13, when it is determined that the detected kinematic viscosity is smaller than the first determination value (S13: YES), the soot suppression that suppresses the amount of soot discharged with the combustion of fuel from the combustion control by the normal adaptation Switch to control (S14). As the soot suppression control, control for increasing oxygen used when the fuel is burned is employed. Specifically, the fuel pressure in the common rail 20 (the fuel injection pressure by the injector 17) is increased by the fuel pump, in which the opening degree of the EGR valve 28 is decreased by the EGR device 26 as compared with the combustion control by the normal adaptation. , At least one of increasing the intake pressure by the VVT 21 is executed. Further, as the soot suppression control, after-injection in which fuel is injected after the main injection of fuel by the injector 17 may be performed.

  Subsequently, misfire suppression control for suppressing fuel misfire is executed (S15). As the misfire suppression control, at least one of increasing the injection amount in the pilot injection of the fuel by the injector 17 and retarding the timing of the pilot injection in the compression stroke of the diesel engine 10 as compared with the combustion control by the normal adaptation. Run one. Thereafter, this series of processing is temporarily terminated (END). In addition, the soot suppression control of S14 and the misfire suppression control of S15 are continued until the combustion control is next switched.

  On the other hand, when it is determined in S13 that the detected kinematic viscosity is not smaller than the first determination value (S13: NO), it is determined whether or not the detected kinematic viscosity is larger than the second determination value ( S16). The second determination value is set to a kinematic viscosity that is higher than the kinematic viscosity of the fuel having a standard property, and the amount of soot discharged with the combustion of the fuel is larger than a predetermined amount.

  In the determination of S16, when it is determined that the detected kinematic viscosity is greater than the second determination value (S16: YES), the soot suppression that suppresses the amount of soot discharged from the combustion control by the normal adaptation in accordance with the combustion of the fuel Switch to control (S17). The process of S17 is the same as the process of S14. Thereafter, this series of processing is temporarily terminated (END). Note that the soot suppression control in S17 continues until the combustion control is next switched.

  On the other hand, when it is determined in S16 that the detected kinematic viscosity is not larger than the second determination value (S16: NO), the combustion control normally adapted is executed (S18). Specifically, based on the detection values of various sensors, the fuel injection amount by the injector 17, the opening / closing timing of the intake valve 16 by the VVT 21, and the EGR valve of the EGR device 26 so as to achieve a pre-adapted control state. The opening degree (EGR amount) is controlled. Thereafter, this series of processing is temporarily terminated (END). In the above, the processing of S12 to S17 corresponds to processing as switching means.

  The embodiment described in detail above has the following advantages.

  The kinematic viscosity of the fuel is detected by the kinematic viscosity sensor 33. When the detected kinematic viscosity is lower than the first determination value and higher than the second determination value set higher than the first determination value, the fuel combustion control is performed with a fuel having a standard property. It is switched from the combustion control (predetermined control) by the normal adaptation set assuming (the fuel of the predetermined property) to the soot suppression control that suppresses the amount of soot discharged with the combustion of the fuel. For this reason, when it becomes difficult to combust the fuel, the combustion control of the fuel can be switched from the predetermined control to the suppression control sooting, and the deterioration of the exhaust emission can be suppressed.

  ・ The kinematic viscosity is lower than the kinematic viscosity of the fuel with the standard properties, and is detected from the kinematic viscosity (first judgment value) in which the amount of soot discharged with the combustion of the fuel exceeds the predetermined amount. When the kinematic viscosity is low, the control is switched to the soot suppression control. For this reason, the soot discharge amount can be suppressed in the fuel having a low kinematic viscosity in which the soot discharge amount tends to increase.

  -The kinematic viscosity is higher than the kinematic viscosity of the fuel with the standard properties, and the amount of soot discharged with the combustion of the fuel is detected to be higher than the predetermined amount (second judgment value). When the kinematic viscosity is high, the control is switched to the soot suppression control. For this reason, the soot discharge amount can be suppressed in the fuel having a high kinematic viscosity in which the soot discharge amount is likely to increase.

  The normal combustion control (predetermined control) of the diesel engine 10 is set so as to optimize the combustion state assuming a fuel with standard properties. And when the property of the fuel is the property of easily discharging soot, the combustion control of the fuel is switched from the predetermined control to the soot suppression control, so that the exhaust emission can be prevented from deteriorating.

  For example, when the density is constant, the lower the kinematic viscosity of the fuel, the lower the cetane number of the fuel. When the cetane number of the fuel is low, the ignitability of the fuel is deteriorated, so that fuel misfire is likely to occur. In this regard, when the kinematic viscosity detected by the kinematic viscosity sensor 33 is lower than the first determination value, the misfire suppression control for suppressing the misfire of the fuel is executed together with the soot suppression control. Therefore, it is possible to suppress the soot discharge amount and to suppress the occurrence of misfire.

  The misfire suppression control includes control for increasing the amount of fuel injected by pilot injection, so that combustion of fuel injected by pilot injection can be stabilized, and fuel misfire can be suppressed.

  The misfire suppression control includes control for retarding the timing of pilot injection in the compression stroke of the diesel engine 10, so that pilot injection can be performed when the pressure and temperature in the combustion chamber further increase. For this reason, combustion of fuel injected by pilot injection can be stabilized, and fuel misfire can be suppressed.

  The soot suppression control includes control for increasing oxygen used when the fuel is combusted, so that combustion of the fuel can be promoted and soot emission can be suppressed.

  Since the soot suppression control includes after-injection in which fuel is injected after the main injection of fuel, soot generated by the main injection can be combusted by after-injection, and soot emission can be suppressed.

(Second Embodiment)
There may be a difference between the kinematic viscosity detected by the kinematic viscosity sensor 33 and the kinematic viscosity estimated by another method. When the kinematic viscosity detected in the vicinity of the high kinematic viscosity region in FIG. 2 is higher than the estimated kinematic viscosity, the actual soot discharge amount may be larger than the estimated soot discharge amount. Therefore, in the second embodiment, the kinematic viscosity of the fuel is estimated separately from the kinematic viscosity sensor 33, and the second determination value is set higher than the estimated kinematic viscosity by a predetermined value. Hereinafter, the second embodiment will be described focusing on differences from the first embodiment.

  FIG. 4 is a flowchart showing a processing procedure for combustion control. This series of processing is repeatedly executed by the ECU 40 at a predetermined cycle (for example, every injection by the injector 17).

  The processes of S21 to S25 are the same as the processes of S11 to S15 in FIG. When it is determined in S23 that the detected kinematic viscosity is not smaller than the first determination value (S23: NO), the fuel density sensor 32 detects the density of the fuel in the fuel tank (S26). .

  Subsequently, the cetane number of the fuel is detected (S27). As a method for detecting the cetane number, a known method such as a method for detecting the cetane number based on the combustion state of the fuel injected by the pilot injection described in Patent Document 1 described above may be used.

  Subsequently, the kinematic viscosity of the fuel is estimated based on the detected fuel density and cetane number (S28). Specifically, the kinematic viscosity of the fuel corresponding to the detected fuel density and cetane number is estimated using the map showing the relationship between the fuel density, cetane number, and kinematic viscosity in FIG.

  Subsequently, a second determination value is set based on the estimated kinematic viscosity of the fuel (S29). Specifically, the second determination value is set higher than the estimated kinematic viscosity by a predetermined value by adding a predetermined value to the estimated kinematic viscosity. Note that the second determination value may be set higher than the estimated kinematic viscosity by a predetermined value by multiplying the estimated kinematic viscosity by a coefficient.

  The subsequent processes of S30 to S32 are the same as the processes of S16 to S18 of FIG. Then, this series of processing is temporarily ended (END). In the above, the process of S26 corresponds to the process as the density detection means, the process of S27 corresponds to the process as the cetane number detection means, and the processes of S26 to S28 correspond to the process as the kinematic viscosity estimation means. , S22 to S31 correspond to processing as switching means.

  The embodiment described in detail above has the following advantages. Here, only advantages different from the first embodiment will be described.

  The second determination value is set higher than the kinematic viscosity estimated by the kinematic viscosity sensor 33 by a predetermined value. For this reason, when there is a possibility that the actual amount of soot discharged may be larger than the estimated amount of soot discharged, the amount of discharged soot can be suppressed. Furthermore, since the second determination value can be set flexibly, the amount of soot discharged is suppressed not only when the amount of soot discharged is particularly large but also when the amount of soot discharged is slightly higher than expected. can do.

  Note that the second embodiment may be modified as follows.

  When the kinematic viscosity detected in the vicinity of the low kinematic viscosity region in FIG. 2 is lower than the estimated kinematic viscosity, the actual soot discharge amount may be larger than the estimated soot discharge amount. Therefore, the first determination value may be set lower than the estimated kinematic viscosity by a predetermined value, and the processes of S13 to S15 in FIG. 3 may be performed. According to such a configuration, the soot discharge amount can be suppressed when there is a possibility that the actual soot discharge amount may be larger than the estimated soot discharge amount. Furthermore, since the first determination value can be set flexibly, the amount of soot discharged is suppressed not only when the amount of soot discharged is particularly large but also when the amount of soot discharged is slightly larger than expected. can do.

  Further, the above embodiments may be modified as follows.

  In the combustion control of FIGS. 3 and 4, the misfire suppression control of S15 and S25 can be omitted. Even in such a case, when the fuel becomes difficult to burn, the fuel combustion control can be switched from the predetermined control to the soot suppression control, and the deterioration of the exhaust emission can be suppressed.

  -When the diesel engine 10 is operated for a predetermined period or when the vehicle travels a predetermined distance, it may be determined that the condition for detecting the property of the fuel is satisfied.

  DESCRIPTION OF SYMBOLS 10 ... Diesel engine, 17 ... Injector, 26 ... EGR apparatus, 33 ... Kinematic viscosity sensor, 40 ... ECU.

Claims (11)

A control device for performing combustion control of fuel in a diesel engine (10),
Kinematic viscosity detecting means (33) for detecting the kinematic viscosity of the fuel;
When the kinematic viscosity detected by the kinematic viscosity detecting means is lower than a first determination value and higher than a second determination value set higher than the first determination value, the combustion control is performed with a predetermined property. Switching means (17, 26, 40) for switching from a predetermined control set on the assumption of the fuel to a soot suppression control that suppresses the amount of soot discharged with combustion of the fuel;
A control device for a diesel engine, comprising:   The first determination value is a kinematic viscosity that is lower than the kinematic viscosity of the fuel having the predetermined property, and the kinematic viscosity at which the amount of soot discharged with combustion of the fuel is larger than a predetermined amount. The control device of the diesel engine described in 1.   2. The second determination value is a kinematic viscosity higher than a kinematic viscosity of the fuel having the predetermined property, and a kinematic viscosity at which an amount of soot discharged with combustion of the fuel is larger than a predetermined amount. Or the control apparatus of the diesel engine of 2. Cetane number detection means (17, 31, 40) for detecting the cetane number of the fuel;
Density detecting means (32) for detecting the density of the fuel;
Kinematic viscosity estimating means (40) for estimating the kinematic viscosity of the fuel based on the cetane number detected by the cetane number detecting means and the density detected by the density detecting means,
3. The diesel engine control device according to claim 1, wherein the switching unit sets the second determination value higher than the kinematic viscosity estimated by the kinematic viscosity estimating unit by a predetermined value. Cetane number detection means for detecting the cetane number of the fuel;
Density detecting means for detecting the density of the fuel;
Kinematic viscosity estimating means for estimating the kinematic viscosity of the fuel based on the cetane number detected by the cetane number detecting means and the density detected by the density detecting means,
2. The control device for a diesel engine according to claim 1, wherein the switching unit sets the first determination value lower than the kinematic viscosity estimated by the kinematic viscosity estimating unit by a predetermined value.   The control device for a diesel engine according to any one of claims 1 to 5, wherein the predetermined control is combustion control that is set so as to optimize a combustion state assuming a fuel having a standard property.   When the kinematic viscosity detected by the kinematic viscosity detecting means is lower than the first determination value, the switching means (17, 40) is configured to suppress misfire of the fuel together with the soot suppression control. The control apparatus of the diesel engine of any one of Claims 1-6 which performs.   The control device for a diesel engine according to claim 7, wherein the misfire suppression control includes control for increasing an injection amount of the fuel by pilot injection.   The control device for a diesel engine according to claim 7 or 8, wherein the misfire suppression control includes control for retarding a pilot injection timing in a compression stroke of the engine.   The control device for a diesel engine according to any one of claims 1 to 9, wherein the soot suppression control includes control for increasing oxygen used when the fuel is combusted.   The control device for a diesel engine according to any one of claims 1 to 10, wherein the soot suppression control includes after-injection in which fuel is injected after main injection of the fuel.