Device for controlling internal combustion engine, and internal combustion engine

Abstract

On the basis of a relationship between the rate of non-burning of fuel and an equivalence ratio, the present invention: determines a limit equivalence ratio that serves as a target of the equivalence ratio and is derived from an upper limit value of the rate of non-burning in accordance with the oxygen content actually detected from fuel used in an internal combustion engine; establishes a target value for the oxygen concentration of an intake manifold so as to achieve the limit equivalence ratio; and controls an EGR rate so as to achieve the target value.

Description

Control device for internal combustion engines and internal combustion engines

[0001] The present invention relates to a control device for an internal combustion engine and to an internal combustion engine.

[0002] A technology has been disclosed for a fuel injection control device for an internal combustion engine that appropriately responds to changes in calorific value and combustibility due to changes in oxygen content by correcting the fuel injection amount according to the oxygen content of the fuel (Patent Document 1). Specifically, a configuration has been disclosed in which a target injection amount is calculated based on the operating state of the internal combustion engine, and this target injection amount is corrected by a correction means according to the oxygen content of the fuel, thereby ensuring stable engine performance even when using fuels with different oxygen content.

[0003] Japanese Patent Publication No. 2004-108231

[0004] Incidentally, the unburned rate (unburned carbon rate) tends to increase in response to the increase in the equivalent ratio due to an increase in the EGR rate. In control systems that reduce NOx by increasing the EGR rate up to the allowable limit (upper limit) of the unburned rate, if an EGR rate that has been pre-calculated assuming an oxygen content of Ro = 0 is used, the unburned rate decreases when the actual oxygen content of Ro is greater than 0. In other words, there is still room to further reduce NOx.

[0005] One of the objectives of the present invention is to provide a control device for an internal combustion engine and an internal combustion engine that can further reduce NOx emissions even when the oxygen content of the fuel differs.

[0006] One aspect of the present invention is a control device for an internal combustion engine, which determines a target limit equivalent ratio based on the relationship between the unburned fuel rate and the equivalent ratio, according to the oxygen content actually detected from the fuel used in the internal combustion engine, sets a target value for the oxygen concentration in the intake manifold so that it reaches the limit equivalent ratio, and controls the EGR rate so that it reaches the target value.

[0007] Here, based on a predetermined relationship between the oxygen concentration and NOx concentration of the intake manifold, it is preferable to determine the NOx flow rate into the catalyst from the NOx concentration corresponding to the oxygen concentration of the intake manifold calculated from the EGR rate according to the oxygen content, and the amount of catalyst gas passing through the catalyst determined from the EGR rate, and then control the amount of reducing additive supplied to the catalyst according to the NOx flow rate.

[0008] Furthermore, it is preferable to determine a modified oxygen concentration based on the slope of the logarithmic value log(NOx concentration) of the NOx concentration with respect to the oxygen concentration of the intake manifold, calculate a modified NOx concentration by correcting the NOx concentration using the modified oxygen concentration, determine the NOx flow rate into the catalyst from the modified NOx concentration and the amount of catalyst gas passing through the catalyst determined from the EGR rate, and control the amount of reducing additive supplied to the catalyst according to the NOx flow rate.

[0009] Furthermore, it is preferable to use a modified equivalent ratio that has been adjusted to account for the increased effect of fuel spray penetration in the combustion chamber of an internal combustion engine, determine the limit equivalent ratio which is a target value of the modified equivalent ratio determined from the upper limit of the unburned fuel rate, set a target value for the oxygen concentration in the intake manifold so that it reaches the limit equivalent ratio, and control the EGR rate so that it reaches that target value.

[0010] Furthermore, the corrected equivalent ratio is preferably obtained from a function obtained by multiplying the equivalent ratio by (bore radius of the cylinder of the internal combustion engine / spray penetration into the combustion chamber of the internal combustion engine at the end of fuel injection).

[0011] Another aspect of the present invention is an internal combustion engine characterized by being controlled by the control device for the internal combustion engine described above.

[0012] According to the present invention, NOx emissions can be further reduced even when the oxygen content of the fuel differs.

[0013] This figure shows an example of the configuration of an internal combustion engine in an embodiment of the present invention. This figure shows a control method for an internal combustion engine in an embodiment of the present invention. This figure shows the relationship between the equivalent ratio of the fuel to its oxygen content and the unburned carbon content. This figure shows the properties of the supplied fuel in an embodiment of the present invention. This figure shows the specifications of the internal combustion engine in an embodiment of the present invention. This figure shows the operating conditions in an embodiment of the present invention. This figure shows the relationship between the fuel's oxygen content and its critical equivalent ratio. This figure shows the definition of variables in an embodiment of the present invention. This figure shows the relationship between the oxygen concentration and NOx concentration in the intake manifold. This figure shows the spray spread within the cylinder of the internal combustion engine. This figure shows the relationship between the modified equivalent ratio of the fuel to its oxygen content and the unburned carbon content. This figure shows a modified example of the control method for an internal combustion engine in an embodiment of the present invention.

[0014] Figure 1 shows a specific example of the configuration of an internal combustion engine 100 in an embodiment of the present invention. The internal combustion engine 100 is composed of an engine body 10, an intake pipe 12, a throttle valve 14, a turbo turbine 16, an intercooler 18, an intake manifold 20, an exhaust manifold 22, an exhaust pipe 24, an SCR catalyst 26, a catalyst additive valve 28, an EGR piping 30, an EGR valve 32, an oxygen content sensor 34, and a control unit 36.

[0015] The engine body 10 is the heart of the internal combustion engine and generates power by burning fuel. The intake manifold 12 takes in air from the outside and supplies it to the engine body 10. The throttle valve 14 controls the amount of air taken in through the intake manifold 12. The turbo turbine 16 uses the energy of the exhaust gas to supercharge the intake air and supply it to the engine body 10. This improves the efficiency of the internal combustion engine 100. The intercooler 18 cools the air compressed by the turbo turbine 16, increasing its density and improving combustion efficiency.

[0016] The intake manifold 20 is a pipe for evenly distributing the air-fuel mixture cooled in the intercooler 18 to each cylinder of the engine body 10. In the engine body 10, fuel combustion occurs to generate power. The exhaust manifold 22 is provided for collecting the exhaust gas after combustion and guiding it to the exhaust pipe 24. The exhaust gas is discharged to the outside through the exhaust pipe 24, and in the process, it passes through the SCR catalyst 26. The SCR catalyst 26 is a device that decomposes and removes harmful substances in the exhaust gas through a chemical reaction. The catalyst addition valve 28 is a valve for supplying an additive for promoting the catalytic reaction in the SCR catalyst 26. For example, urea is used as the additive.

[0017] Further, the EGR pipe 30 is a pipe for recirculating a part of the exhaust gas from the exhaust manifold 22 and returning it to the combustion chamber of the engine body 10. The EGR valve 32 is a valve for controlling the flow rate of this recirculation. By applying EGR, the amount of NOx discharged as exhaust gas can be suppressed.

[0018] The oxygen content rate sensor 34 measures the oxygen concentration in the fuel and is used for optimizing combustion efficiency and exhaust gas treatment.

[0019] The control unit 36 controls the internal combustion engine 100. The control unit 36 controls so that appropriate torque is output from the internal combustion engine 100 according to the accelerator operation of the driver. For example, it adjusts the timing and amount of fuel injection, the opening degree of the throttle valve 14, etc., and performs appropriate fuel supply according to the load and operating conditions of the internal combustion engine 100. Also, it detects the components of the exhaust gas and adjusts the fuel mixture ratio as necessary. Further, it adjusts the amount and supply timing of the additive supplied from the catalyst addition valve 28 to the SCR catalyst 26.

[0020] In the present embodiment, the control unit 36 detects and measures the oxygen content rate Ro in the fuel by the oxygen content rate sensor 34, and controls the opening degree of the EGR valve 32 based on the oxygen content rate Ro to adjust the EGR rate.

[0021] Hereinafter, referring to the flowchart of FIG. 2, the control of the EGR rate in the internal combustion engine 100 will be described.

[0022] First, the oxygen content Ro of the fuel is detected by the oxygen content sensor 34 installed on the common rail 21. Since the value of the oxygen content Ro does not change in a short period of time, it is sufficient to detect it once, for example, between the start and stop of the internal combustion engine 100, or at an appropriate detection frequency depending on the distance traveled.

[0023] Here, the ratio of the total mass of carbon contained in soot, carbon monoxide (CO), and total hydrocarbons (THC) in the exhaust gas to the total mass of carbon contained in the fuel is defined as the unburned carbon ratio (or simply the unburned ratio).

[0024] Figure 3 shows the results of an actual measurement of the relationship between the equivalent ratio φ of the fuel to its oxygen content Ro and the unburned carbon ratio. Figures 4 to 6 show the properties of the test fuel used in the measurement, the specifications of the internal combustion engine 100, and the operating conditions, respectively.

[0025] In the actual measurements, the amount of heat input was kept the same for each fuel, and the equivalence ratio φ was changed according to the EGR rate. The tendency of the unburned carbon content to increase with increasing equivalence ratio φ differs depending on the oxygen content Ro of the fuel; the higher the oxygen content Ro, the more the increase in the unburned carbon content can be suppressed up to a higher equivalence ratio φ, i.e., the higher the EGR rate can be. The higher the EGR rate, the lower the NOx in the exhaust gas. The equivalence ratio φ at which the upper limit of the acceptable unburned carbon content is reached is denoted as the critical equivalence ratio φcr, and the EGR rate at that point is defined as the critical EGR rate. In this case, the larger the critical equivalence ratio φcr, the larger the critical EGR rate, and as a result, NOx can be suppressed.

[0026] Figure 7 shows an example of the relationship between the critical equivalent ratio φcr and each oxygen content rate Ro when the allowable value for the unburned carbon content is set to 1%. As shown in Figure 7, the critical equivalent ratio φcr shows a monotonically increasing trend with respect to the oxygen content rate Ro. That is, if the relationship between the oxygen content rate Ro and the critical equivalent ratio φcr is determined in advance, the critical equivalent ratio φcr with respect to the oxygen content rate Ro can be determined after detecting the oxygen content rate Ro, relative to the target value of the unburned carbon content.

[0027] Next, the control performed by the control unit 36 of the internal combustion engine 100 in the present embodiment will be described. FIG. 8 shows the definitions of various variables used in the following description.

[0028] In the internal combustion engine 100, the intake pipe 12 and the EGR pipe 30 merge in the intake manifold 20, and the fresh gas from the intake pipe 12 and the EGR gas from the EGR pipe 30 merge. Let the composition of the oxygen-containing fuel be C ｎ H ｍ O ｌ Then, the oxidation reaction of the fuel is represented by Equation (1), and the equivalence ratio φ is given by Equation (2).

[0029] Here, the ratio l / n of the number of oxygen atoms l to the number of carbon atoms n in the composition C ｎ H ｍ O ｌ is shown by Equation (3) using the oxygen content rate Ro.

[0030] Solving Equation (2) for y ｉｎ，Ｏ２ yields Equation (4). The target oxygen mass concentration y ｉｎ，Ｏ２，ｔｒｇ in the intake manifold 20 with respect to the limit equivalence ratio φcr is given by Equation (5).

[0031] Assuming steady or slow transient operating conditions and assuming quasi-steady state, the oxygen concentration in the exhaust manifold 22 is equal to the oxygen concentration y ｅｘ，Ｏ２ in the exhaust gas. Assuming that the fuel burns completely as in Equation (1), Equation (6) is obtained from the law of conservation of mass.

[0032] ｅｘ，Ｏ２ in Equation (6) yields Equation (7).

[0033] Substituting m ａｉｒ / m ｆ = A / F into Equation (7) gives Equation (8).

[0034] Assuming quasi-steady state, the oxygen concentration y ｅｇｒ，Ｏ２The oxygen concentration y of the exhaust manifold 22 ｅｘ，Ｏ２ Assuming that it is equal to , we get equation (9). Furthermore, the oxygen concentration y of the intake manifold 20 ｉｎ，Ｏ２ Using the EGR rate, equation (10) can be obtained from the conservation of mass.

[0035] The target value of the oxygen concentration in the intake manifold 20 is given by equation (5), so the EGR rate R is set so that equation (10) becomes the target value. ｅｇｒ，ｍｏｄ The error is calculated repeatedly until it converges.

[0036] When the oxygen content ratio Ro > 0, the oxygen concentration in the intake manifold 20 is updated from what was assumed for an oxygen content ratio of Ro = 0, so the amount of NOx emitted changes. Therefore, it is necessary to correct the amount of urea added to the SCR according to the change in NOx. Here, the relationship between the oxygen concentration and NOx concentration in the intake manifold 20 is determined in advance, and the change in NOx concentration is predicted.

[0037] Figure 9 shows the relationship between the oxygen concentration and NOx concentration in the intake manifold 20 of the internal combustion engine 100 in an experiment. Regardless of the oxygen content Ro, the oxygen concentration y in the intake manifold 20 ｉｎ，Ｏ２ and log １０ (NOx) has a linear relationship and can be represented by a single line. Using the slope a(Ne,Q) of this relationship, the oxygen concentration yin, O2, base(Ne,Q) and NOx concentration x of the intake manifold 20 with an oxygen content of Ro=0 are given. ＮＯｘ，ｂａｓｅ (Ne, Q) and the oxygen concentration y of the updated intake manifold 20 ｉｎ，Ｏ２，ｍｏｄ Using this, the NOx concentration can be calculated from formula (11). Note that Ne is the engine speed and Q is the fuel injection amount.

[0038] Flow rate G passing through the exhaust manifold 22 ｃｙｌ This is expressed by formula (12). Therefore, considering EGR, the NOx flow rate G into the SCR catalyst 26 is ＮＯｘ，ｔｏＣａｔThis is given by equation (13). Therefore, based on the NOx flow rate in equation (13), the amount of reducing additive to be supplied from the catalyst addition valve 28 to the SCR catalyst 26 can be determined. The amount of additive necessary to appropriately reduce the desired NOx flow rate in the SCR catalyst 26 can be determined in advance and stored in the control unit 36.

[0039] Returning to the flowchart in Figure 2, the above process will be explained step by step. First, the oxygen content Ro of the fuel introduced into the common rail 21 is measured by the oxygen content sensor 34 (step S10). Also, the fuel injection amount Q is set based on the operating conditions of the internal combustion engine 100, such as the engine speed Ne (step S12). Based on these conditions, the limiting equivalent ratio φcr of the equivalent ratio φ is set based on the relationship shown in Figure 7 (step S14).

[0040] Based on equation (5), the target oxygen mass concentration y in the intake manifold 20 relative to the critical equivalent ratio φcr is given by ｉｎ，Ｏ２，ｔｒｇ The EGR rate R is calculated (step S16). ｅｇｒ，ｍｏｄ R as the initial value ｅｇｒ，ｂａｓｅ Set (step S18), and based on formula (8), the oxygen concentration y in the exhaust gas ｅｘ，Ｏ２ (Step S20) is calculated. Also, assuming that the oxygen concentration in the EGR piping 30 is equal to the oxygen concentration in the exhaust manifold 22, the oxygen concentration y in the EGR gas is calculated based on formula (9). ｅｇｒ，Ｏ２ (Step S22) is calculated. Furthermore, the oxygen concentration y of the intake manifold 20 is obtained from formula (10). ｉｎ，Ｏ２ (Step S24)

[0041] The oxygen concentration y of the intake manifold 20, determined in step S24. ｉｎ，Ｏ２ And the target oxygen concentration y of the intake manifold 20 determined in step S16 ｉｎ，Ｏ２，ｔｒｇ and the difference ε (= oxygen concentration y) ｉｎ，Ｏ２ - Oxygen concentration y ｉｎ，Ｏ２，ｔｒｇ It is determined whether the EGR rate R has converged to 0 (or to a value below the set threshold). If the convergence condition is not met, the process moves to step S28, and the EGR rate R ｅｇｒ，ｍｏｄThe process is returned to step S20 by changing the difference ε × correction value c, and the oxygen concentration y of the intake manifold 20 is changed. ｉｎ，Ｏ２ The process of finding the value is repeated. If the convergence condition is not met, the process moves to step S30.

[0042] The required oxygen concentration y of the intake manifold 20 ｉｎ，Ｏ２ The oxygen concentration y of the intake manifold 20 ｉｎ，Ｏ２，ｍｏｄ Set to (step S30), and based on the relationship between the oxygen concentration and NOx concentration in the intake manifold 20, the slope a(Ne,Q) and the NOx concentration x are determined by formula (11). ＮＯｘ，ｍｏｄ The flow rate G passing through the exhaust manifold 22 is determined (step S32). Then, based on formulas (12) and (13), the flow rate G is determined. ｃｙｌ and the NOx flow rate G into the SCR catalyst 26 ＮＯｘ，ｔｏＣａｔ The NOx flow rate G into the SCR catalyst 26 is calculated (step S34). ＮＯｘ，ｔｏＣａｔ The appropriate amount of reducing additive is determined (step S36).

[0043] The system determines whether to repeat the process (step S38). If the process is to be repeated, it returns to step S12; otherwise, the process terminates.

[0044] As described above, the control unit 36 ​​of the internal combustion engine 100 and its control method allow for the application of control that appropriately reduces emitted NOx even when the oxygen content of the fuel differs.

[0045] [Modification] As shown in Figure 3, the critical equivalent ratio φcr with respect to the upper limit of the unburned fuel ratio changes depending on the oxygen content Ro of the fuel. Therefore, the critical equivalent ratio φcr depends not only on the engine speed Ne and injection amount Q, but also on the oxygen content Ro of the fuel. Consequently, in order to determine the critical equivalent ratio φcr, it is necessary to prepare a map with engine speed Ne, injection amount Q, and oxygen content Ro as parameters, which increases the number of parameters and makes control complicated. Therefore, a method is provided to reduce the dependence of the oxygen content Ro on the unburned fuel ratio by modifying the equivalent ratio φ.

[0046] The relationship between the equivalence ratio φ and the unburned rate changes with the oxygen content Ro due to the following two factors: (1) As the oxygen content Ro increases, the local equivalence ratio φ within the spray decreases, so the rich region in the local area shrinks and the unburned rate decreases. (2) In order to maintain the same indicated mean effective pressure (IMEP), the fuel injection amount increases, which increases the spray momentum, expands the spray region within the cylinder, and increases the air utilization rate.

[0047] Figure 10 shows the results of 3D-CFD calculations of the change in the spray region within the combustion chamber of the engine body 10 with respect to the air utilization rate. The calculation conditions are as shown in Figures 4 to 6. When the oxygen content Ro is high, the spray region within the cylinder of the engine body 10 increases, that is, the entrainment of ambient air into the spray increases, and the equivalent ratio φ within the spray decreases. Consequently, the unburned rate decreases.

[0048] Therefore, a correction is made to the equivalence ratio φ as shown in formula (14) (hereinafter referred to as the corrected equivalence ratio φ). ｍｏｄｉｆｉｅｄ (This is how it is written.) The correction for (1) above is (1 - C × Ro), and the correction for (2) above is 1 / (x ｉｎｊｅｎｄ / R ｃｙｌ ) corresponds to each of these. ｊｎｊｅｎｄ : Spray penetration at the end of spraying, R ｃｙｌ : Bore radius, C: Constant.

[0049] Spray penetration S at the end of spraying ｊｎｊｅｎｄ This can be expressed as equation (15) using the Waguri momentum equation (see Waguri Yutaro et al., "Study on the Reach of Diesel Engine Fuel Spray," Transactions of the Japan Society of Mechanical Engineers, 621. 436.038. pp.820-826).

[0050] Note: Spray penetration S at the end of spraying ｊｎｊｅｎｄ An empirical formula may also be used (see Hiroyuki Hiroyasu et al., "Reach distance and spray angle of diesel spray," Transactions of the Japan Society of Mechanical Engineers, 621.436.038, No.21, 1980). Here, ΔP ｃｒ : Differential pressure between injection pressure and ambient pressure, ρ ｇ : Atmospheric density, d ｎ: Spray nozzle diameter, θ: Spray angle (full width), t ｉｎｊｅｎｄ : This is the injection period. The spray angle θ may be a function as shown in equation (16) (see Hiroyuki Hiroyasu et al., "Reach distance and spray angle of diesel spray," Transactions of the Japan Society of Mechanical Engineers, 621.436.038, No.21, 1980), or a constant may be used. Here, μ ｇ This is the viscosity coefficient of air.

[0051] By adjusting the constant C, the corrected equivalent ratio φ ｍｏｄｉｆｉｅｄ The relationship between this and the unburned rate is shown in Figure 11. Compared with Figure 3, the corrected equivalent ratio φ ｍｏｄｉｆｉｅｄ By using this method, the influence of the oxygen content (Ro) on the unburned rate can be reduced. In other words, the target corrected equivalent ratio φmodified,cr remains the same regardless of the oxygen content (Ro).

[0052] In this case, part A of step S14 in the flowchart shown in Figure 2 can be replaced as shown in Figure 12. Specifically, the corrected equivalent ratio φ ｍｏｄｉｆｉｅｄ Using this, the spray penetration S at the end of the injection ｊｎｊｅｎｄ After calculating the critical equivalent ratio φcr, calculate the critical equivalent ratio φcr.

[0053] By applying this type of processing, the number of parameters required to determine the critical equivalent ratio φcr can be reduced, thereby lowering the processing load on the control unit 36.

[0054] 10 Engine body, 12 Intake pipe, 14 Throttle valve, 16 Turbo turbine, 18 Intercooler, 20 Intake manifold, 21 Common rail, 22 Exhaust manifold, 24 Exhaust pipe, 26 SCR catalyst, 28 Catalytic converter valve, 30 EGR piping, 32 EGR valve, 34 Oxygen content sensor, 36 Control unit, 100 Internal combustion engine.

Claims

1. A control device for an internal combustion engine, which determines a target limit equivalent ratio based on the relationship between the unburned fuel rate and the equivalent ratio, according to the oxygen content actually detected from the fuel used in the internal combustion engine, sets a target value for the oxygen concentration in the intake manifold so that it reaches the limit equivalent ratio, and controls the EGR rate so that it reaches the target value.

2. A control device for an internal combustion engine according to claim 1, wherein, based on a preset relationship between the oxygen concentration and NOx concentration of the intake manifold, the NOx flow rate into the catalyst is determined from the NOx concentration corresponding to the oxygen concentration of the intake manifold calculated from the EGR rate according to the oxygen content, and the amount of catalytic gas passing through the catalyst determined from the EGR rate, and the amount of reducing additive supplied to the catalyst is controlled according to the NOx flow rate.

3. A control device for an internal combustion engine according to claim 2, wherein, based on the relationship between the logarithmic conversion value log(NOx concentration) of the NOx concentration and the oxygen concentration of the intake manifold, a modified oxygen concentration is determined according to the slope of the logarithmic conversion value and the oxygen concentration of the intake manifold; a modified NOx concentration is calculated by correcting the NOx concentration using the modified oxygen concentration; the NOx flow rate into the catalyst is determined from the modified NOx concentration and the amount of catalyst gas passing through the catalyst determined from the EGR rate; and the amount of reducing additive supplied to the catalyst is controlled according to the NOx flow rate.

4. A control device for an internal combustion engine according to any one of claims 1 to 3, wherein a modified equivalent ratio, which is a target value of the modified equivalent ratio determined from the upper limit of the unburned fuel rate, is used to determine the limit equivalent ratio, which is a target value of the modified equivalent ratio determined from the upper limit of the unburned fuel rate, a target value of the oxygen concentration in the intake manifold is set to reach the limit equivalent ratio, and the EGR rate is controlled to reach the target value.

5. A control device for an internal combustion engine according to claim 4, wherein the corrected equivalent ratio is obtained from a function obtained by multiplying the equivalent ratio by (bore radius of the cylinder of the internal combustion engine / spray penetration into the combustion chamber of the internal combustion engine at the end of fuel injection).

6. An internal combustion engine controlled by an internal combustion engine control device according to any one of claims 1 to 5.

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