Engine control device

Abstract

To promote an improvement of combustion stability and an improvement of fuel economy when using fuels which are different in fuel properties.SOLUTION: An ECU 60 comprises: an index calculation part for calculating a first index indicating a marginal degree of anti-knocking, and a second index indicating necessary ignition energy necessary for normal ignition as indices related fuel properties; a first control part for setting a target in-cylinder temperature on the basis of the first index, and controlling the in-cylinder temperature on the basis of the target in-cylinder temperature as in-cylinder temperature control for controlling the in-cylinder temperature immediately before combustion; and a second control part for setting a target EGR rate on the basis of the second index, and controlling the EGR rate on the basis of the target EGR rate as EGR control for controlling the EGR rate by an EGR device.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The disclosure of this specification relates to an engine control device.

Background Art

[0002] According to EGR (Exhaust Gas Recirculation) that returns the exhaust gas discharged from the engine back to the intake side for reuse, it is possible to reduce the combustion temperature in the cylinder to reduce the NOx emission amount, and at the same time reduce the pumping loss to improve the fuel efficiency. Further, in the technology described in Patent Document 1, the target coolant temperature is set higher as the target EGR rate increases, and when the target EGR rate and the target coolant temperature fluctuate, the actual EGR rate is not immediately changed, but gradually changed according to the transition of the change in the actual coolant temperature that follows the target coolant temperature. Thereby, while increasing the EGR rate as much as possible, it is intended to prevent the destabilization of the combustion of the air-fuel mixture.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] By the way, in recent years, as alternative fuels to gasoline, alcohol mixed fuels obtained by mixing alcohols such as ethanol with gasoline and alcohol fuels of 100% alcohol have been proposed. Further, alternative fuels have different properties from gasoline. In this case, as described above, it is possible to improve the fuel efficiency with the implementation of EGR. However, if the fuel properties are different, there is a concern that a sufficient fuel efficiency improvement effect cannot be obtained. Further, if the fuel properties are different, there is a concern that misfire may occur due to an excessive decrease in the cylinder temperature accompanying fuel vaporization in the cylinder, and the combustion variation may increase.

[0005] The present invention has been made in view of the above problems, and an object thereof is to provide an engine control device capable of improving combustion stability and fuel efficiency when using fuels having different properties.

Means for Solving the Problems

[0006] The invention for solving the above problems is applied to a spark ignition engine including an ignition device that ignites in the cylinder and an EGR device that recirculates exhaust gas to the intake passage side, an index calculation unit that calculates a first index indicating a margin of knocking resistance and a second index indicating a required ignition energy required for normal ignition as indices related to fuel properties, as in-cylinder temperature control for controlling the in-cylinder temperature immediately before combustion, a first control unit that sets a target in-cylinder temperature based on the first index and controls the in-cylinder temperature based on the target in-cylinder temperature, as EGR control for controlling the EGR rate by the EGR device, a second control unit that sets a target EGR rate based on the second index and controls the EGR rate based on the target EGR rate, and includes.

[0007] For fuels with different properties, it is conceivable that the margin of knocking resistance, which is an index for performing appropriate ignition while suppressing the occurrence of knocking, and the required ignition energy, which is an index for performing EGR while maintaining combustion stability, are different. Also, in an engine, by controlling the engine state according to the margin of knocking resistance and required ignition energy of the fuel, it is possible to improve combustion stability and fuel efficiency.

[0008] That is, if the margin of knocking resistance varies, the upper limit temperature allowed as the in-cylinder temperature also varies. The greater the margin of knocking resistance, the higher the in-cylinder temperature can be increased while suppressing the occurrence of knocking. By increasing the in-cylinder temperature, the combustion stability in the engine can be enhanced. Also, if the necessary ignition energy required for normal ignition varies, the EGR limit on the upper limit side of the EGR rate varies. The smaller the necessary ignition energy, the larger the EGR limit becomes, and it becomes possible to increase the EGR rate. By increasing the EGR rate, the effect of improving fuel efficiency can be enhanced.

[0009] In this regard, in the present invention, as indices related to fuel properties, a first index indicating the margin of knocking resistance and a second index indicating the necessary ignition energy are calculated. Then, in the in-cylinder temperature control for controlling the in-cylinder temperature immediately before combustion, the target in-cylinder temperature is set based on the first index, and the in-cylinder temperature is controlled based on the target in-cylinder temperature. Also, in the EGR control for controlling the EGR rate by the EGR device, the target EGR rate is set based on the second index, and the EGR rate is controlled based on the target EGR rate. In this case, according to the above in-cylinder temperature control, the occurrence of knocking and misfire can be suppressed, and the combustion stability can be improved. Also, according to the above EGR control, the EGR rate can be suitably increased to improve fuel efficiency. As a result, when using fuels with different properties, it is possible to improve both combustion stability and fuel efficiency.

Brief Description of the Drawings

[0010]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Figure 6

Figure 7

Mode for Carrying Out the Invention

[0011] The engine control device of this embodiment is applied to a spark-ignition multi-cylinder engine mounted on a vehicle. As shown in FIG. 1, the engine 10 has a cylinder block 12 and a cylinder head 14. A piston 13 is reciprocally accommodated in each cylinder of the cylinder block 12. Further, a combustion chamber 15 is defined by the inner wall of the cylinder, the cylinder head 14, and the piston 13. The combustion chamber 15 communicates with the intake passage 16 via the intake valve 18 and with the exhaust passage 17 via the exhaust valve 19. An injector 22 for directly injecting fuel into the combustion chamber 15 and a spark plug 23 for igniting the fuel-air mixture in the combustion chamber 15 are provided in the cylinder head 14. Although not shown, the fuel supply system has a fuel tank and a fuel pump, and the fuel in the fuel tank is pressurized by the fuel pump, and the high-pressure fuel is injected from the injector 22.

[0012] A surge tank 21 is arranged in the intake passage 16. An intake pressure sensor 24 for detecting the intake pressure, which is the pressure in the intake pipe, is provided in the surge tank 21. A throttle valve 25 is provided upstream of the surge tank 21 in the intake passage 16. A catalyst such as a three-way catalyst for purifying CO, HC, NOx, etc. in the exhaust gas is provided in the exhaust passage 17.

[0013] The cylinder block 12 and the cylinder head 14 are provided with a water jacket 41. In the water jacket 41, the engine is cooled by circulating engine cooling water as a coolant. Further, a water temperature sensor 26 for detecting the water temperature of the engine cooling water is provided in the water jacket 41. A circulation path 51 of the engine cooling water is connected to the water jacket 41. The circulation path 51 is provided with a water pump 42, a radiator 43, and a flow path switching valve 44. The engine cooling water circulates through the circulation path 51 by the water pump 42. The radiator 43 cools the engine cooling water using the running wind or the like when the vehicle is running. A bypass path 52 is connected to the circulation path 51, and the flow path switching valve 44 switches between a flow path through which the engine cooling water circulates through the radiator 43 and a flow path through which the engine cooling water circulates through the bypass path 52, that is, a flow path through which the engine cooling water circulates bypassing the radiator 43.

[0014] The engine 10 is provided with an EGR device 30 that recirculates a part of the exhaust gas to the intake side. The EGR device 30 has an EGR passage 31 connecting the exhaust passage 17 and the surge tank 21 of the intake passage 16, and an EGR valve 32 and an EGR cooler 33 are provided in the EGR passage 31. The EGR rate, which is the mixing ratio of the exhaust gas in the inflow gas flowing into the combustion chamber 15, is adjusted by the opening degree of the EGR valve 32.

[0015] The EGR cooler 33 is a water-cooled cooling device that cools the EGR gas using the engine cooling water. The EGR gas is cooled by flowing the engine cooling water through a branch path 53 branched from the circulation path 51. A regulating valve 45 for regulating the flow rate of the engine cooling water passing through the EGR cooler 33 is provided in the branch path 53, and the degree of cooling of the EGR gas is adjusted by the opening degree of the regulating valve 45.

[0016] The ECU 60 is an electronic control unit mainly composed of a microcomputer including a CPU, a ROM, a RAM, etc. By executing various control programs stored in the ROM, it performs various controls on the engine 10 according to the engine operating state each time. Specifically, the ECU 60 inputs various detection signals from an intake pressure sensor 24, a rotational speed sensor (not shown), etc., and controls the operations of the injector 22 and the spark plug 23 based on the detection signals.

[0017] The ECU 60 performs in-cylinder temperature control for controlling the in-cylinder temperature, which is the temperature inside the cylinder (inside the combustion chamber 15) immediately before combustion, and EGR control for controlling the EGR rate by the EGR device 30 in order to improve the combustion stability of the engine 10. In this embodiment, as the in-cylinder temperature control, the temperature of the engine cooling water (i.e., the engine water temperature) is controlled, and the in-cylinder temperature is increased by increasing the engine water temperature. Specifically, the ECU 60 sets a target water temperature and controls the flow path switching valve 44 and the water pump 42 to make the actual water temperature match the target water temperature. For example, the target water temperature is set based on the required torque of the engine 10, and the higher the torque, the lower the set temperature. In this case, when increasing the engine water temperature, for example, the ECU 60 causes the engine cooling water to flow around the radiator 43 or reduces the flow rate of the engine cooling water flowing into the radiator 43 by controlling the flow path switching valve 44. Or it is also possible to increase the engine water temperature by reducing the pumping amount of the engine cooling water by the water pump 42.

[0018] As for in-cylinder temperature control, it is also possible to control the temperature of the intake air flowing into the combustion chamber 15. Specifically, the ECU 60 sets a target intake air temperature and controls the temperature of the EGR gas by adjusting the degree of cooling by the EGR cooler 33 so that the intake air temperature matches the target intake air temperature. For example, the target intake air temperature is set based on the required torque of the engine 10, and the higher the torque, the lower the set temperature. In this case, when the ECU 60 increases the intake air temperature, for example, it reduces the engine coolant flowing through the branch passage 53 by controlling the control valve 45 to reduce the degree of cooling of the EGR gas by the EGR cooler 33.

[0019] Also, as EGR control, the ECU 60 controls the opening degree of the EGR valve 32 based on the required torque of the engine 10 to control the EGR rate. Specifically, when in the medium load operation state and the required torque is medium, the target ECU rate is increased to perform EGR control, and when in the low load operation state or the high load operation state and the required torque is low or high, the target ECU rate is decreased to perform EGR control.

[0020] In this embodiment, in the engine 10, in addition to gasoline, it is possible to use an alcohol mixed fuel in which alcohol such as ethanol is mixed with gasoline, and the in-cylinder temperature control and EGR control are implemented according to the properties of the fuel used each time. Specifically, when the fuel properties are different, the margin of knocking resistance and the necessary ignition energy required for normal ignition are different. Therefore, it is conceivable to implement in-cylinder temperature control and EGR control using an index (first index) indicating the margin of knocking resistance and an index (second index) indicating the necessary ignition energy required for normal ignition.

[0021] However, in the present embodiment, paying attention to the fact that the required ignition energy as an index related to the fuel properties has a correlation with the EGR limit which is the limit value on the upper limit side of the EGR rate, the EGR limit is calculated as an index indicating the required ignition energy. In this case, the required ignition energy and the EGR limit have a relationship such that the smaller the required ignition energy, the larger the EGR limit, and conversely, the larger the required ignition energy, the smaller the EGR limit. The ECU 60 calculates the knocking margin A and the EGR limit B as indices related to the fuel properties, and based on these respective indices A and B, in-cylinder temperature control and EGR control are carried out.

[0022] The calculation procedures of the respective indices related to the fuel properties are described below using the flowchart of FIG. 2. The processing in FIG. 2 is repeatedly executed by the ECU 60 at a predetermined cycle.

[0023] In FIG. 2, in step S11, it is determined whether it is immediately after fuel replenishment to the fuel tank. This determination may be made based on, for example, received information from the fuel replenishment facility, detection information of the fuel quantity sensor in the fuel tank, opening / closing information of the fuel replenishment port, and the like. If it is immediately after fuel replenishment, the process proceeds to step S12, and if it is not immediately after fuel replenishment, this process ends.

[0024] In step S12, as each property value of the fuel to be used, the octane number RON1 indicating the difficulty of knocking, the latent heat of vaporization HoV1 which is the amount of heat absorbed when the fuel changes from a liquid to a gas, and the laminar burning speed SL1 indicating the flame propagation speed with respect to the unburned air-fuel mixture are calculated. At this time, it is conceivable that the types of the fuel remaining in the fuel tank and the newly replenished fuel are different, and based on the property values of the remaining fuel and the replenished fuel, the property values of the fuel after fuel replenishment may be calculated.

[0025] Here, it is assumed that, in addition to gasoline, an alcohol-blended fuel in which alcohol such as ethanol is mixed with gasoline is used as the fuel in the fuel tank. Based on the alcohol concentration Xold of the fuel remaining in the fuel tank before refueling and the alcohol concentration Xadd of the newly refueled fuel, the alcohol concentration Xnew of the fuel in the fuel tank after refueling is calculated. The alcohol concentration Xnew may be calculated using the following Equation 1. Xnew=(Xold×Vold+Xadd×Vadd)÷(Vold+Vadd) (Equation 1) In Equation 1, Vold is the amount of remaining fuel in the fuel tank before refueling, and Vadd is the amount of additional fuel added by refueling. Note that the alcohol concentration Xadd and the additional fuel amount Vadd of the additional fuel may be obtained, for example, by communication from a fuel refueling facility.

[0026] Then, for the fuel after refueling, while taking into account the alcohol concentration Xnew, as fuel property values, the octane number RON1, the latent heat of vaporization HoV1, and the laminar burning velocity SL1 are calculated. Specifically, the octane number RON1 is calculated using the relationship in Fig. 3(a), the latent heat of vaporization HoV1 is calculated using the relationship in Fig. 3(b), and the laminar burning velocity SL1 is calculated using the relationship in Fig. 3(c). According to Figs. 3(a) to 3(c), the higher the alcohol concentration Xnew, the higher the calculated values of the octane number RON1, the latent heat of vaporization HoV1, and the laminar burning velocity SL1, respectively.

[0027] Thereafter, in step S13, based on the octane number RON1, the latent heat of vaporization HoV1, and the laminar burning velocity SL1, the knocking margin A based on gasoline and the EGR limit B are calculated.

[0028] Regarding the calculation of the knocking margin A, specifically, based on the octane number RON0 of gasoline, the difference ΔRON between the octane number RON0 and the octane number RON1 of the fuel to be used is calculated. Then, using the relationship shown in Fig. 4(a), the knocking margin A is calculated based on the octane number difference ΔRON and the latent heat of vaporization HoV1 of the fuel to be used. At this time, the larger the octane number difference ΔRON, the larger the knocking margin A. Also, the larger the latent heat of vaporization HoV1, the greater the temperature drop in the cylinder, so the knocking margin A becomes larger. That is, the higher the alcohol concentration Xnew of the fuel to be used, the higher the octane number difference ΔRON and the latent heat of vaporization HoV1, so the knocking margin A becomes larger.

[0029] Regarding the calculation of the EGR limit B, specifically, based on the laminar burning speed SL0 of gasoline, the difference ΔSL between the laminar burning speed SL0 of gasoline and the laminar burning speed SL1 of the fuel to be used is calculated. Then, using the relationship shown in Fig. 4(b), the EGR limit B is calculated based on the difference ΔSL in the laminar burning speed SL and the latent heat of vaporization HoV1 of the fuel to be used. At this time, the larger the difference ΔSL in the laminar burning speed SL, the better the combustibility, so the EGR limit B becomes larger. Also, the smaller the latent heat of vaporization HoV1, the smaller the temperature drop in the cylinder, and the deterioration of combustibility is suppressed, so the EGR limit B becomes larger.

[0030] In step S14, it is determined whether the knocking margin A is greater than 0. The knocking margin A being greater than 0 means that the currently used fuel has a larger knocking margin A than gasoline. If the knocking margin A is greater than 0, proceed to step S14. If the knocking margin A is not greater than 0, end this process.

[0031] In step S15, an EGR limit extension amount C associated with an increase in the knocking margin A is calculated. The EGR limit extension amount C is an increase width that extends the upper limit value of the EGR rate toward the increase side in accordance with the increase in the in-cylinder temperature when the in-cylinder temperature can be increased as the knocking margin A increases. In this step S15, for example, using the relationship shown in FIG. 4(c), the increase amount ΔT of the in-cylinder temperature is calculated based on the knocking margin A, and for example, using the relationship shown in FIG. 4(d), the EGR limit extension amount C is calculated based on the increase amount ΔT of the in-cylinder temperature. In this case, the larger the knocking margin A, the larger the calculated value of the increase amount ΔT of the in-cylinder temperature. Also, the larger the increase amount ΔT of the in-cylinder temperature, the larger the calculated value of the EGR limit extension amount C.

[0032] Note that it is also possible to combine the relationships of FIGS. 4(c) and 4(d) and calculate the EGR limit extension amount C based on the knocking margin A.

[0033] Next, the in-cylinder temperature control and the EGR control using each index related to the fuel properties will be described in detail.

[0034] In the present embodiment, gasoline is used as the reference fuel, and it is determined whether the knocking margin A deviates from gasoline by a predetermined amount or more, and it is determined whether the EGR limit B deviates from gasoline by a predetermined amount or more. Based on these determination results, in-cylinder temperature control with a target in-cylinder temperature different from that when using gasoline and EGR control with a target EGR rate different from that when using gasoline are selectively implemented. More specifically, the ECU 60 selectively implements in-cylinder temperature control that raises the target in-cylinder temperature compared to when using gasoline and EGR control that raises the target EGR rate compared to when using gasoline based on the determination result of whether the knocking margin A is larger than gasoline and the determination result of whether the EGR limit B is larger than gasoline.

[0035] Further, when the ECU 60 determines that the knocking margin A is larger than that of gasoline and the EGR limit B is not larger than that of gasoline, it determines whether to perform EGR control to increase the target EGR rate higher than when using gasoline based on the EGR limit B and the EGR limit extension amount C.

[0036] Figure 5 is a flowchart showing the processing procedures of in-cylinder temperature control and EGR control using each index related to fuel properties. This process is repeatedly executed by the ECU 60 at a predetermined cycle.

[0037] In step S21, the knocking margin A of the currently used fuel, the EGR limit B, and the EGR limit extension amount C are read out.

[0038] Thereafter, in step S22, it is determined whether the knocking margin A is larger than the first reference TH1, and in step S23, it is determined whether the EGR limit B is larger than the second reference TH2. If both steps S22 and S23 are affirmed, the process proceeds to step S24. The affirmation of both steps S22 and S23 means that the knocking margin A is larger than that of gasoline and the EGR limit B is larger than that of gasoline.

[0039] In step S24, both in-cylinder temperature control to increase the target in-cylinder temperature higher than when using gasoline according to the knocking margin A and EGR control to increase the target EGR rate higher than when using gasoline according to the EGR limit B and the EGR limit extension amount C are performed. Here, when engine coolant temperature control is performed as the in-cylinder temperature control, the target coolant temperature is set using the relationship shown in FIG. 6. In FIG. 6, the target coolant temperature of the coolant temperature control when using gasoline is shown by a solid line, and the target coolant temperature when the knocking margin A is larger than that of gasoline is shown by a broken line. In this case, the larger the knocking margin A with respect to gasoline, the higher the target coolant temperature is set.

[0040] Also, in EGR control, the target EGR rate is set using the relationship shown in FIG. 7. In FIG. 7, the target EGR rate for EGR control when using gasoline is shown by the solid line, and the target EGR rate when the EGR limit B is larger than that of gasoline is shown by the dashed line. The target EGR rate shown by the dashed line is determined based on the sum of the EGR limit B and the EGR limit extension amount C. In this case, the larger the EGR limit B is with respect to gasoline, the higher the target EGR rate is set. Incidentally, as described above, the EGR limit B is correlated with the required ignition energy. In terms of the relationship between the required ignition energy and the target EGR rate, the smaller the required ignition energy is with respect to gasoline, the higher the target EGR rate is set.

[0041] Note that in FIG. 6, when the knocking margin A is larger than that of gasoline, the target water temperature is increased by a certain width regardless of the engine's required torque. However, the increase width of the target water temperature may be made variable according to the required torque. Also, in FIG. 7, when the EGR limit B is larger than that of gasoline, the target EGR rate is increased by a certain width regardless of the engine's required torque. However, the increase width of the target EGR rate may be made variable according to the required torque.

[0042] Also, when step S22 is affirmed and step S23 is negated, the process proceeds to step S25. In step S25, it is determined whether the sum of the EGR limit B and the EGR limit extension amount C is larger than the third reference TH3. That is, when the knocking margin A is larger than that of gasoline and the EGR limit B is not larger than that of gasoline, the determination in step S25 is made.

[0043] When step S25 is affirmed, the process proceeds to step S24. In step S24, as described above, both in-cylinder temperature control to increase the target in-cylinder temperature more than when using gasoline according to the knocking margin A and EGR control to increase the target EGR rate more than when using gasoline according to the EGR limit B and the EGR limit extension amount C are carried out.

[0044] If step S25 is negated, the process proceeds to step S26. In step S26, only in-cylinder temperature control for increasing the target in-cylinder temperature compared to when using gasoline and EGR control for increasing the target EGR rate compared to when using gasoline are performed. In this case, using the relationship shown in FIG. 6, the target coolant temperature is set based on the knocking margin A, and the engine coolant temperature is controlled based on the target coolant temperature.

[0045] That is, in step S25, when it is determined that the knocking margin A is larger than that of gasoline and the EGR limit B is not larger than that of gasoline (when step S22 is YES and step S23 is NO), based on the EGR limit B and the EGR limit extension amount C, it is determined whether to perform EGR control for increasing the target EGR rate compared to when using gasoline. Then, only when the implementation of EGR control for increasing the target EGR rate compared to when using gasoline is permitted, that EGR control is performed (step S24).

[0046] Here, in step S26, since the EGR limit B is equal to or less than TH2 and B + C is equal to or less than TH3, the target EGR rate is not increased compared to when using gasoline. In this case, the required ignition energy is larger than that of gasoline, and the EGR limit extension amount C is not very large, so there is concern about the occurrence of misfire due to an increase in the EGR rate. Considering this, the target EGR rate is not increased compared to when using gasoline, so the occurrence of combustion fluctuations due to the occurrence of misfire is suppressed.

[0047] If step S22 is negated, in step S27, it is determined whether the EGR limit B is larger than the second reference TH2. If step S27 is affirmed, the process proceeds to step S28. In step S28, only EGR control for increasing the target EGR rate compared to when using gasoline and in-cylinder temperature control for increasing the target in-cylinder temperature compared to when using gasoline are performed. In this case, using the relationship shown in FIG. 7, the target EGR rate is set based on the EGR limit B, and the EGR control is performed based on the target EGR rate.

[0048] When step S22 is negated and step S27 is affirmed, it means that the knocking margin A is not larger than that of gasoline and the EGR limit B is larger than that of gasoline. In this case, there is concern about the occurrence of knocking due to increasing the target water temperature. Considering this, in step S28, the target EGR rate is increased compared to when using gasoline, but the target water temperature is not increased compared to when using gasoline, so the occurrence of knocking is suppressed while increasing the EGR rate as much as possible.

[0049] When both steps S22 and S27 are negated, this process is terminated as it is. In this case, since the fuel used is considered to be gasoline, in-cylinder temperature control and EGR control when using gasoline are implemented.

[0050] According to the present embodiment described in detail above, the following excellent effects can be obtained.

[0051] As indices related to fuel properties, the knocking margin A and the EGR limit B (an index indicating the required ignition energy) are calculated. Then, in the in-cylinder temperature control for controlling the in-cylinder temperature immediately before combustion, the target in-cylinder temperature is set based on the knocking margin A, and the in-cylinder temperature is controlled based on the target in-cylinder temperature. Also, in the EGR control for controlling the EGR rate by the EGR device 30, the target EGR rate is set based on the EGR limit B, and the EGR rate is controlled based on the target EGR rate. In this case, according to the above in-cylinder temperature control, the occurrence of knocking and misfire can be suppressed, and the combustion stability can be improved. Also, according to the above EGR control, the EGR rate can be suitably increased to improve the fuel efficiency. As a result, it is possible to improve the combustion stability and the fuel efficiency when using fuels with different properties.

[0052] The higher the RON1 octane number of the fuel, the less likely knocking is to occur, and the higher the latent heat of vaporization HoV1 of the fuel, the less likely knocking is to occur. Therefore, the margin of knock resistance A can be determined based on these RON1 octane number and latent heat of vaporization HoV1. Also, the higher the laminar burning speed SL1 of the fuel used, the larger the EGR limit B (the smaller the required ignition energy), and the lower the latent heat of vaporization HoV1 of the fuel, the larger the EGR limit B. Therefore, the required ignition energy (EGR limit B) can be determined based on these laminar burning speed SL1 and latent heat of vaporization HoV1.

[0053] The higher the margin of knock resistance A, the higher the target in-cylinder temperature is set, and the smaller the required ignition energy, the higher the target EGR rate is set. As a result, the target in-cylinder temperature can be appropriately set according to the margin of knock resistance A, and the target EGR rate can be appropriately set according to the required ignition energy.

[0054] Using gasoline as the reference fuel, it is determined whether the margin of knock resistance A deviates from that of gasoline by a predetermined amount or more, and it is determined whether the EGR limit B correlated with the required ignition energy deviates from that of gasoline by a predetermined amount or more. Based on these determination results, in-cylinder temperature control with a target in-cylinder temperature different from that when using gasoline and EGR control with a target EGR rate different from that when using gasoline are selectively implemented. As a result, in-cylinder temperature control and EGR control can be appropriately implemented according to the properties of the fuel used each time.

[0055] In an engine using gasoline as a reference fuel, it is conceivable that a mixed fuel in which gasoline is mixed with a different fuel such as alcohol is used. Then, in the fuel used in the engine 10, it is determined that the knocking margin A is larger than that of gasoline, and the EGR limit B is larger than that of gasoline (in other words, the required ignition energy is smaller than that of gasoline). Based on these determination results, in-cylinder temperature control that raises the target in-cylinder temperature compared to when using gasoline and EGR control that raises the target EGR rate compared to when using gasoline are selectively implemented. Thereby, even when a different fuel is mixed with gasoline, in-cylinder temperature control and EGR control can be appropriately implemented.

[0056] When it is determined that the knocking margin A is larger than that of gasoline and it is determined that the EGR limit B is not larger than that of gasoline (in other words, the required ignition energy is not smaller than that of gasoline), based on the EGR limit B and the EGR limit extension amount C determined according to the knocking margin A, it is determined whether to implement EGR control that raises the target EGR rate compared to when using gasoline. In this case, when the knocking margin A is larger than that of gasoline, it is possible to increase the upper limit value of the EGR rate according to the margin A (that is, extend the EGR limit). Therefore, even if the EGR limit B is not larger than that of gasoline, it is possible to raise the target EGR rate compared to when using gasoline, expecting that the upper limit value of the EGR rate will increase according to the knocking margin A. Thereby, a fuel consumption improvement effect can be obtained.

[0057] (Other embodiments) The above embodiment may be modified as follows, for example.

[0058] ·In the above-described embodiment, when it is determined that the knocking margin A is larger than that of gasoline and the EGR limit B is not larger than that of gasoline (that is, when step S22 in FIG. 5 is YES and step S23 is NO), based on the EGR limit B and the EGR limit extension amount C, a determination (step S25) is made as to whether to implement EGR control to increase the target EGR rate compared to when using gasoline. However, this determination may be omitted. In this case, when it is determined that the knocking margin A is larger than that of gasoline and the EGR limit B is not larger than that of gasoline, only in-cylinder temperature control to increase the target in-cylinder temperature compared to when using gasoline is implemented, out of in-cylinder temperature control to increase the target in-cylinder temperature compared to when using gasoline and EGR control to increase the target EGR rate compared to when using gasoline.

[0059] ·In the above-described embodiment, while taking into account the alcohol concentration Xnew after fuel replenishment, as fuel property values, the octane number RON1, the latent heat of vaporization HoV1, and the laminar burning speed SL1 are calculated, and based on these fuel property values, the knocking margin A and the EGR limit B based on gasoline are calculated. However, this may be changed. Specifically, the relationships between the alcohol concentration Xnew and the knocking margin A and between the alcohol concentration Xnew and the EGR limit B may be stored in advance in a map or the like, and the knocking margin A and the EGR limit B may be directly calculated from the alcohol concentration Xnew.

[0060] ·The present invention can be applied not only to engines for vehicles but also to engines other than those for vehicles.

[0061] ·The control unit and its method described in the present disclosure may be implemented by a dedicated computer provided by configuring a processor and a memory programmed to execute one or more functions embodied by a computer program. Alternatively, the control unit and its method described in the present disclosure may be implemented by a dedicated computer provided by configuring a processor with one or more dedicated hardware logic circuits. Or, the control unit and its method described in the present disclosure may be implemented by one or more dedicated computers configured by a combination of a processor and a memory programmed to execute one or more functions and a processor configured by one or more hardware logic circuits. Further, the computer program may be stored in a computer-readable non-transitory tangible recording medium as instructions executable by a computer.

Explanation of Signs

[0062] ·10…Engine, 23…Spark plug, 30…EGR device, 60…ECU

Claims

【Claim 1】 An ignition device (23) that ignites inside the cylinder, and an EGR device (30) that recirculates exhaust to the intake passage side, and is applied to a spark ignition engine (10) that enables the use of a mixed fuel in which a different fuel is mixed with gasoline. An engine control device (60) that controls the in-cylinder temperature immediately before combustion and controls the EGR rate by the EGR device on the premise of using gasoline. An acquisition unit that acquires the octane number, latent heat of vaporization, and laminar burning velocity of a mixed fuel in which gasoline and a different fuel are mixed in the fuel tank. As an index related to the fuel properties of the mixed fuel in the fuel tank, a first index indicating the margin of knocking resistance is calculated based on the octane number and latent heat of vaporization acquired by the acquisition unit, using a relationship in which the first index increases as the octane number is larger than the octane number of gasoline and the first index increases as the latent heat of vaporization is larger. Also, a second index indicating the EGR limit, which is the upper limit value of the EGR rate and increases as the necessary ignition energy required for normal ignition is smaller, is calculated based on the laminar burning velocity and latent heat of vaporization acquired by the acquisition unit, using a relationship in which the second index increases as the laminar burning velocity is larger than the laminar burning velocity of gasoline and the second index increases as the latent heat of vaporization is smaller. An index calculation unit. A first determination unit that determines that the margin of knocking resistance as the first index is larger than that of gasoline. A second determination unit that determines that the EGR limit as the second index is larger than that of gasoline. As in-cylinder temperature control for controlling the in-cylinder temperature immediately before combustion, a target in-cylinder temperature that is higher than when using gasoline and becomes higher as the margin of knocking resistance as the first index is larger is set, and the in-cylinder temperature is controlled based on the target in-cylinder temperature. A first control unit. As EGR control for controlling the EGR rate by the EGR device, a target EGR rate that is higher than when using gasoline and becomes higher as the EGR limit as the second index is larger is set, and the EGR rate is controlled based on the target EGR rate. A second control unit. Comprising. When it is determined by the first determination unit that the knocking margin is larger than that of gasoline and it is determined by the second determination unit that the EGR limit is larger than that of gasoline, the in-cylinder temperature control by the first control unit and the EGR control by the second control unit are performed. When it is determined by the first determination unit that the knocking margin is larger than that of gasoline and it is determined by the second determination unit that the EGR limit is not larger than that of gasoline, it is determined whether or not an added EGR limit obtained by adding an EGR limit extension amount, which is set to a larger value as the knocking margin is larger, to the EGR limit is larger than a predetermined reference value. If the added EGR limit is larger than the reference value, the in-cylinder temperature control by the first control unit and the EGR control by the second control unit are performed. If the added EGR limit is not larger than the reference value, only the in-cylinder temperature control is performed out of the in-cylinder temperature control by the first control unit and the EGR control by the second control unit. An engine control device.

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