Internal combustion engine control system

Abstract

To provide a control system for an internal combustion engine capable of attaining optimal introduction amount of exhaust circulation gas according to a mixing ratio of biofuel.SOLUTION: A control system is for an internal combustion engine that can use fuel with which biofuel is mixed. The control system for the internal combustion engine includes: an exhaust gas circulation device for introducing exhaust circulation gas to the internal combustion engine; the internal combustion engine; and a control device for controlling the exhaust gas circulation device. The control device changes the introduction amount of the exhaust circulation gas in the same operating condition in accordance with a mixing ratio of the biofuel.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present disclosure relates to control systems for internal combustion engines. [Background technology]

[0002] Conventionally, there is known an exhaust gas recirculation device that recirculates exhaust gas from an internal combustion engine and introduces it into the internal combustion engine (see, for example, Patent Document 1). Patent Document 1 discloses a control system for an internal combustion engine that changes the amount of exhaust gas recirculation introduced depending on the octane number of the fuel in a compression ignition type gasoline engine. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Patent No. 6763437 Summary of the Invention [Problem to be solved by the invention]

[0004] In recent years, in order to reduce carbon dioxide emissions, fuel mixtures in which biofuels are mixed with petroleum-derived fuels have been sold. Biofuels have a lower calorific value than conventional fuels. For this reason, it is preferable to change the amount of exhaust gas recirculation introduced depending on the mixing ratio of biofuel.

[0005] An object of the present disclosure is to provide a control system for an internal combustion engine that can realize an optimal amount of exhaust recirculation gas introduced according to the mixing ratio of biofuel. [Means for solving the problem]

[0006] The present disclosure relates to a control system for an internal combustion engine capable of using fuel mixed with biofuel, and includes an exhaust gas recirculation device that introduces exhaust gas recirculation gas into the internal combustion engine, the internal combustion engine, and a control device that controls the exhaust gas recirculation device. The control device changes the amount of exhaust gas recirculation gas introduced under the same operating conditions in accordance with the mixing ratio of the biofuel.

[0007] According to this internal combustion engine control system, even under the same operating conditions, the amount of exhaust recirculation gas introduced is changed according to the mixture ratio of biofuel, thereby realizing the optimal amount of exhaust recirculation gas introduced according to the mixture ratio of biofuel. Effect of the Invention

[0008] According to the present disclosure, it is possible to provide a control system for an internal combustion engine that can realize an optimal amount of exhaust recirculation gas introduced according to the mixing ratio of biofuel. [Brief description of the drawings]

[0009] [Figure 1] 1 is a system diagram of an internal combustion engine control system according to an embodiment of the present disclosure. [Diagram 2] FIG. 4 is a diagram showing a mixture ratio determined by a control device according to an embodiment of the present disclosure. [Diagram 3] 4 is a flowchart showing a control procedure of a control device according to an embodiment of the present disclosure. [Figure 4] 1 is a graph showing the relationship between the amount of particulate matter (PM amount) and the amount of nitrogen oxides (NOx amount) generated versus the amount of exhaust recirculation gas introduced for B0 (100% diesel) fuel and B100 (100% biofuel) fuel according to an embodiment of the present disclosure. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0010] Hereinafter, an embodiment of the present disclosure will be described with reference to the drawings. In the following description, the upstream side with respect to the flow direction of intake air or exhaust air will be referred to as "upstream" and the downstream side will be referred to as "downstream".

[0011] As shown in FIG. 1, a control system 1 of an internal combustion engine 2 includes a fuel injection valve (an example of an injection valve) 2c, a filter 4, a PM sensor (an example of a detection unit) 6, an exhaust gas recirculation device 8, a fuel tank 10, a fuel filler lid 12, a turbocharger 14, an intercooler 16, a throttle valve 18, and a control device 20. The internal combustion engine 2 of this embodiment is a diesel engine that can use biofuel (an example of a first fuel) and diesel (an example of a second fuel) in the fuel tank 10. The internal combustion engine 2 sends intake air from an intake passage 2a to a cylinder 2b, where the intake air is mixed with fuel injected from a fuel injection valve 2c. The internal combustion engine 2 compresses the mixture with a piston 2d and self-ignites it. The internal combustion engine 2 of this embodiment is mounted on a vehicle (for example, an automobile).

[0012] In this embodiment, in the internal combustion engine 2, exhaust gas discharged from the cylinder 2b rotates a turbine 14a of a turbocharger 14. The turbine 14a rotates a compressor 14b arranged coaxially therewith, and supercharges the intake air. The supercharged intake air is cooled by an intercooler 16. However, the turbocharger 14 is not necessarily required.

[0013] The filter 4 is disposed in an exhaust purification device 3 that purifies exhaust gas. The filter 4 collects particulate matter contained in the exhaust gas. In this embodiment, the filter 4 is a diesel particulate filter that collects particulate matter (PM) from a diesel engine. An oxidation catalyst 4a is disposed upstream of the filter 4. The exhaust purification device 3 may also have a NOx trap, a urea selective reduction catalyst, or the like (not shown) disposed downstream of the filter 4.

[0014] The PM sensor 6 is disposed upstream of the filter 4 and detects the accumulation state of particulate matter. The PM sensor 6 is a sensor whose current value changes when particulate matter accumulates. Specifically, when particulate matter accumulates, the current flows more easily and the current value increases. The PM sensor 6 has a heater 6a. The heater 6a burns and removes particulate matter accumulated on the PM sensor 6. Other configurations of the PM sensor 6 may be similar to those of existing PM sensors, and detailed description will be omitted. In this embodiment, the PM sensor 6 is disposed between the oxidation catalyst 4a and the filter 4. This can prevent the adhesion of fuel residues and the like to the PM sensor 6. However, the PM sensor 6 may be disposed upstream of the oxidation catalyst 4a. The PM sensor 6 is electrically connected to the control device 20 and transmits a current value to the control device 20. In addition, the operation of the heater 6a is controlled by the control device 20.

[0015] The exhaust recirculation device 8 is a device that introduces exhaust recirculation gas into the internal combustion engine 2. More specifically, the exhaust recirculation device 8 is a device that recirculates the exhaust discharged from the cylinder 2b to the intake passage 2a. The exhaust recirculation device 8 has an exhaust recirculation passage 8a and an exhaust recirculation valve 8b. The exhaust recirculation passage 8a connects the exhaust passage 4b ​​and the intake passage 2a. The exhaust recirculation valve 8b is provided on the exhaust recirculation passage 8a, and introduces the exhaust recirculation gas recirculated from the exhaust into the intake passage 2a by opening and closing the exhaust recirculation passage 8a. The exhaust recirculation valve 8b is electrically connected to the control device 20 and is controlled by the control device 20. The control device 20 controls the exhaust recirculation valve 8b to control the amount of exhaust recirculation gas introduced into the intake air. In this embodiment, the control device 20 controls the throttle valve 18 to generate a negative pressure in the intake passage 2a by closing the throttle valve 18. The control device 20 can also control the amount of exhaust recirculation gas introduced by this.

[0016] The fuel tank 10 is a device for storing biofuel and diesel and supplying them to the fuel injection valve 2c. In this embodiment, the fuel tank 10 has a fuel filler lid 12 that opens and closes a fuel filler port 10a, and a fuel level sensor 10b. The fuel filler lid 12 is electrically connected to the control device 20 and transmits the open / closed state of the fuel filler lid 12 to the control device 20. The fuel level sensor 10b is electrically connected to the control device 20 and transmits the remaining amount of fuel in the fuel tank 10 (fuel level) to the control device 20.

[0017] The control device 20 executes a determination control to determine the blending ratio (mixing rate) of the biofuel and the diesel fuel based on a first deposition amount, which is a preset amount of particulate matter deposited by the biofuel, a second deposition amount, which is a preset amount of particulate matter deposited by the diesel fuel, and a third deposition amount of particulate matter detected by the PM sensor 6.

[0018] More specifically, as shown in Fig. 2, the control device 20 stores the change in a first deposition amount (see the dashed line in Fig. 2), which is the deposition amount of particulate matter during a predetermined time, when only biofuel is used in the internal combustion engine 2. The control device 20 also stores the change in a second deposition amount (see the dashed line in Fig. 2), which is the deposition amount of particulate matter during a predetermined time, when only diesel is used in the internal combustion engine 2. The predetermined time may be the time during which the change in the first deposition amount and the change in the second deposition amount are measured by experiment. The control device 20 compares the first deposition amount, the second deposition amount, and the third deposition amount obtained from the PM sensor 6 (see the solid line in Fig. 2), to determine the mixing ratio of biofuel and diesel.

[0019] In this embodiment, the control device 20 calculates an estimated deposition amount (see the two-dot chain line in FIG. 2) according to the mixture ratio of biofuel and diesel based on the first deposition amount and the second deposition amount. The control device 20 acquires a third deposition amount corresponding to the deposition amount of particulate matter actually flowing in the exhaust gas from the current value of the PM sensor 6. The control device 20 judges whether the actual mixture ratio is higher or lower than the estimated mixture ratio by comparing the acquired third deposition amount with the estimated deposition amount. When the third deposition amount is higher than the estimated mixture ratio, the control device 20 corrects the ratio of diesel to be higher than the estimated ratio. On the other hand, when the third deposition amount is lower than the estimated mixture ratio, the control device 20 corrects the ratio of biofuel to be higher than the estimated ratio. This allows the control device 20 to judge the mixture ratio. The PM sensor 6 has a dead zone for a certain period until the particulate matter is deposited on the sensor element of the PM sensor 6. The control device 20 calculates the estimated deposition amount during this period as well.

[0020] The control device 20 determines the introduction ratio of the exhaust recirculation gas, and controls the opening degree of the exhaust recirculation valve 8b so that the introduction amount of the exhaust recirculation gas becomes the introduction ratio determined with respect to the intake air amount detected by the air flow sensor 22 attached to the air cleaner 32. The control device 20 may determine the introduction ratio of the exhaust recirculation gas based on a map that defines the introduction ratio of the exhaust recirculation gas for each operating range of the internal combustion engine 2.

[0021] Furthermore, when a regeneration condition (an example of a first condition) for the filter 4 is satisfied, the control device 20 executes regeneration control to regenerate the filter 4. In this embodiment, the control device 20 determines whether the regeneration condition for the filter 4 is satisfied based on whether the amount of particulate matter deposited on the filter 4 is equal to or greater than a predetermined amount. Whether a predetermined amount of particulate matter has deposited can be detected, for example, by the pressure difference between before and after the filter. Alternatively, whether a predetermined amount of particulate matter has deposited may be detected by the PM sensor 6.

[0022] Furthermore, in this embodiment, a temperature rise control is executed to raise the exhaust temperature upstream of the filter 4 before regenerating the filter 4. In the temperature rise control, the control device 20 injects fuel from the fuel injection valve 2c in the latter half of the expansion stroke of the internal combustion engine 2. As a result, the fuel is supplied to the oxidation catalyst 4a arranged upstream of the filter 4. The fuel supplied to the oxidation catalyst 4a diffuses into and is adsorbed in the oxidation catalyst 4a, and undergoes a combustion reaction. As a result, the temperature of the exhaust gas that has passed through the oxidation catalyst 4a increases. As a result, the exhaust gas flowing into the filter 4 becomes hot. The hot exhaust gas burns the particulate matter captured in the filter 4, and regenerates the filter 4.

[0023] Furthermore, even if the regeneration condition for the filter 4 is satisfied, the control device 20 prohibits the regeneration control for the filter 4 when a condition for prohibiting the regeneration of the filter 4 (an example of a second condition) is satisfied.

[0024] For example, the control device 20 prohibits the regeneration control of the filter 4 when the internal combustion engine 2 is operated under a predetermined load. The predetermined load is, for example, when the accelerator pedal 30 is fully depressed. In such a case, the output required of the internal combustion engine 2 is high. In such a state of the internal combustion engine 2, the fuel injection amount also increases. For this reason, the control device 20 needs to use the fuel for the output of the internal combustion engine 2, rather than for the temperature increase control.

[0025] Also, for example, when the internal combustion engine 2 is operated at low revolutions and the vehicle speed is low, if the revolution speed of the internal combustion engine 2 increases due to regeneration of the filter 4, the user of the vehicle may feel uncomfortable. In such a state, the control device 20 may determine that the regeneration conditions are not satisfied.

[0026] Additionally, the control device 20 may prohibit regeneration control when the exhaust temperature is too low or too high for regenerating the filter 4. In any case, the control device 20 may monitor parameters such as the exhaust temperature, the fuel injection amount, the rotation speed of the internal combustion engine 2, and the vehicle speed according to the operating state of the internal combustion engine 2 and the traveling state of the vehicle, and may prohibit regeneration control of the filter 4 based on these parameters.

[0027] In addition, the control device 20 may control each device, such as the fuel injection valve 2c, the exhaust gas recirculation valve 8b, and the supercharging pressure of the supercharger 14, based on values ​​acquired from sensors such as the airflow sensor 22 and the accelerator position sensor 30a, so that the internal combustion engine 2 is in a desired operating state. The control device 20 is actually an ECU (Electronic Control Unit) configured by a microcomputer including a calculation device, a memory, an input / output buffer, and the like. The control device 20 controls each device based on a map and a program stored in the memory so that the internal combustion engine 2 is in a desired operating state. Note that the various controls are not limited to processing by software, and can also be processed by dedicated hardware (electronic circuits).

[0028] Next, a control procedure executed by the control device 20 will be described with reference to the flowchart of Fig. 3. The control device 20 starts a control operation when an ignition switch (not shown) is turned on.

[0029] In step S1, the control device 20 acquires the mixing ratio (mixing rate) of biofuel and diesel. After acquiring the mixing ratio, the control device 20 proceeds to step S2. The control device 20 may acquire the mixing ratio when it is determined that refueling has occurred. The control device 20 may detect the open / closed state of the fuel filler lid 12, and determine that refueling has started when the fuel filler lid 12 is open. Alternatively, the control device 20 may determine that refueling has occurred when it is determined that the fuel level has risen.

[0030] In step S2, the control device 20 judges whether the mixture ratio has increased. The control device 20 may execute judgment control after refueling, and judge whether the mixture ratio has increased compared to before refueling when the judgment control is executed. The control device 20 may also execute judgment control at predetermined time intervals, and judge that the mixture ratio has increased if the mixture ratio when the current judgment control is executed has increased compared to when the previous judgment control was executed. If the control device 20 judges that the mixture ratio has increased (step S2 YES), it proceeds to step S3. If the control device 20 judges that the mixture ratio has not increased (step S2 NO), it returns the process to step S1.

[0031] In step S3, the control device 20 increases the amount of exhaust recirculation gas introduced under the same operating conditions. For example, assume that the amount of exhaust recirculation gas introduced under a given operating condition is 10 percent of the intake air volume when only diesel (zero percent biofuel) is used. Then, assume that fuel is added and the mixture ratio of biofuel increases to 30 percent. In this case, the control device 20 may increase the amount of exhaust recirculation gas introduced to 30 percent of the intake air volume.

[0032] Biofuel has a lower calorific value than diesel. Therefore, even if the amount of exhaust recirculation gas introduced is increased, particulate matter (soot) is less likely to be produced. Therefore, the control device 20 may increase the amount of exhaust recirculation gas to a greater extent the higher the mixing ratio of biofuel. This makes it possible to suppress pumping losses and improve fuel efficiency. After increasing the amount of exhaust recirculation gas introduced, the control device 20 proceeds to step S4.

[0033] In step S4, the control device 20 determines whether or not the regeneration condition for the filter 4 is satisfied. If the control device 20 determines that the regeneration condition for the filter 4 is satisfied (YES in step S4), the control device 20 proceeds to step S5 and counts the number of times that the regeneration condition for the filter 4 is satisfied. After counting the number of times that the regeneration condition for the filter 4 is satisfied, the control device 20 proceeds to step S6.

[0034] In step S6, the control device 20 judges whether or not the prohibition condition for regeneration control is satisfied. If the control device 20 judges that the prohibition condition for regeneration control is satisfied (YES in step S6), the control device 20 advances the process to step S7.

[0035] In step S7, the control device 20 determines whether the count number of times the regeneration condition is satisfied is equal to or greater than a predetermined number (predetermined number of times satisfied). If the control device 20 determines that the count number of times the regeneration condition is satisfied is equal to or greater than the predetermined number of times, the control device 20 advances the process to step S8.

[0036] In step S8, the control device 20 determines whether the forced regeneration conditions for the filter 4 are satisfied. In this embodiment, the control device 20 relaxes the conditions for prohibiting regeneration control as the number of times that the regeneration conditions for the filter 4 are satisfied increases. For example, in a state in which the internal combustion engine 2 is operated at low revolutions and the vehicle speed is low, which has been prohibited to cause discomfort to the vehicle user, the forced regeneration conditions are satisfied if the number of times that the regeneration conditions for the filter 4 are satisfied is equal to or greater than a predetermined number of times. If the control device 20 determines that the forced regeneration conditions for the filter 4 are not satisfied (NO in step S8), the process proceeds to step S9.

[0037] In step S9, the control device 20 executes correction control to reduce the amount of exhaust recirculation gas introduced, which is the amount by which the introduction amount is reduced, from the amount of exhaust recirculation gas introduced, which was increased in step S3. For example, if the control device 20 increases the amount of exhaust recirculation gas introduced with respect to the intake air volume from 10 percent to 30 percent in step S3, the control device 20 may execute correction control to reduce the amount of exhaust recirculation gas introduced with respect to the intake air volume from 30 percent to 20 percent (a reduction amount of 10 percent).

[0038] In this way, when the regeneration conditions are met but the regeneration control of the filter 4 is not executed due to the prohibition conditions, the control device 20 reduces the increased amount of exhaust recirculation gas introduced to prevent an increase in the amount of particulate matter deposited on the filter 4. On the other hand, the control device 20 reduces the reduction amount the more times the regeneration conditions of the filter 4 are met (number of times met). The more times the regeneration conditions of the filter 4 are met, the closer it is to executing forced regeneration control. Therefore, even if the amount of particulate matter deposited increases due to the introduction of exhaust recirculation gas, it is removed by executing forced regeneration control. After executing the correction control, the control device 20 returns the process to step S1.

[0039] In step S2, if the controller 20 determines that the mixture ratio has not increased (step S2 NO), the controller 20 returns the process to step S1. In step S4, if the controller 20 determines that the regeneration condition of the filter 4 is not satisfied (step S4 NO), the controller 20 returns the process to step S1.

[0040] In step S6, when the control device 20 determines that the prohibition condition is not satisfied (NO in step S6), the control device 20 advances the process to step S10 and executes regeneration control.

[0041] In step S7, when the control device 20 determines that the count number of times the regeneration condition of the filter 4 is satisfied is less than the predetermined number (step S7 NO), the control device 20 returns the process to step S1. In other words, when the count number of times the regeneration condition of the filter 4 is satisfied is less than the predetermined number, the control device 20 does not execute the correction control. The regeneration condition of the filter 4 is more likely to be satisfied as the amount of accumulated particulate matter increases. When the count number of the filter 4 is small and the amount of accumulated particulate matter is small, the control device 20 does not need to execute the correction control. In step S7, the control device 20 determines whether the count number of times the regeneration condition of the filter 4 is satisfied exceeds the predetermined number. When the control device 20 determines that the count number exceeds the predetermined number (step S7 YES), the control device 20 proceeds to the process to step S8. In step S7, when the control device 20 determines that the count number does not reach the predetermined number (step S7 NO), the control device 20 returns the process to step S1.

[0042] In step S8, the control device 20 judges whether the forced regeneration condition is satisfied. If the control device 20 judges that the forced regeneration condition of the filter 4 is not satisfied (step S8 NO), the control device 20 advances the process to step S9, performs correction control, and returns the process to step S1. If the control device 20 judges that the forced regeneration condition of the filter 4 is satisfied (step S8 YES), the control device 20 advances the process to step S10. In step S10, the control device 20 executes regeneration control, and returns the process to step S1. If the control device 20 judges that the forced regeneration condition is not satisfied in step S8 (step S8 NO), the control device 20 advances the process to step S9. In step S9, the control device 20 performs correction control, and returns the process to step S1. The control device 20 repeatedly executes the processes from step S1 to step S10 at predetermined time intervals.

[0043] As described above, according to the control system 1 for the internal combustion engine 2 of the present disclosure, even if the internal combustion engine 2 is in the same operating condition, the amount of exhaust recirculation gas introduced is changed according to the mixture ratio of biofuel. As shown in FIG. 4, generally, the amount of nitrogen oxides generated (NOx amount) decreases as the amount of exhaust recirculation gas introduced increases, while the amount of particulate matter generated (PM amount) increases. When the amount of exhaust recirculation gas introduced is increased from the circled region A in FIG. 4 to the circled region B in FIG. 4, the amount of PM increases extremely with B0 (diesel) fuel, while the amount of NOx is difficult to decrease. On the other hand, when the amount of exhaust recirculation gas is increased with B100 (bio) fuel, the amount of PM does not increase compared to B0 fuel, while the amount of NOx is reduced. Therefore, the control device 20 can reduce the amount of NOx while suppressing the increase in the amount of PM by increasing the amount of exhaust recirculation gas as the mixture ratio of biofuel increases. If the amount of NOx (NOx emission) decreases, for example, the frequency of NOx purge control of the NOx trap or the frequency of injection of urea water of the urea selective reduction catalyst can be suppressed. This makes it possible to reduce fuel consumption and urea water consumption.

[0044] <Other embodiments> Although the embodiment of the present disclosure has been described above, the present disclosure is not limited to the above embodiment, and various modifications are possible without departing from the gist of the invention. In particular, the multiple modifications described in this specification can be arbitrarily combined as necessary.

[0045] (a) In the above embodiment, a diesel engine using the filter 4 has been described as an example, but the present disclosure is not limited thereto. The internal combustion engine 2 may be a gasoline engine. In this case, the internal combustion engine 2 may be an internal combustion engine 2 capable of using bioethanol fuel (an example of a first fuel) and gasoline (an example of a second fuel). In addition, in this case, the filter 4 may be a gasoline particulate filter.

[0046] (b) In the above embodiment, the control system 1 for the internal combustion engine 2 is applied to a vehicle equipped with a diesel engine, but the present disclosure is not limited to this. For example, the control system 1 for the internal combustion engine 2 may be applied to a plug-in hybrid electric vehicle (PHEV) that can be externally charged or externally powered.

[0047] (c) In the above embodiment, the control device 20 executes the determination control to determine the mixture ratio of biofuel and diesel, and obtains the mixture ratio, but the present disclosure is not limited to this. For example, the control device 20 may obtain the mixture ratio using the output value of a biofuel mixture ratio sensor that is installed in a fuel system such as the fuel tank 10 or a fuel pipe connected to the fuel tank 10 and is capable of detecting the mixture ratio of biofuel and diesel. [Explanation of symbols]

[0048] 1: Control system 2: Internal combustion engine 4: Filter 8: Exhaust recirculation system 20: Control device

Claims

1. A control system for an internal combustion engine capable of using fuel blended with biofuel, comprising: an exhaust gas recirculation device that introduces exhaust gas recirculation gas into the internal combustion engine; A control device for controlling the internal combustion engine and the exhaust gas recirculation device; A filter that collects particulate matter in the exhaust gas of the internal combustion engine; Equipped with the control device changes the amount of the exhaust recirculation gas introduced under the same operating conditions of the internal combustion engine in accordance with the mixing ratio of the biofuel; The higher the mixing ratio of the biofuel, the more the amount of the exhaust gas recirculation gas introduced is increased; executing a regeneration control for regenerating the filter when a first condition for permitting regeneration of the filter based on a state of the filter is satisfied and a second condition for prohibiting regeneration of the filter based on an operating state of the internal combustion engine is not satisfied; When the second condition is satisfied, a reduction amount of the exhaust recirculation gas is obtained by reducing the increased amount of the exhaust recirculation gas introduced as the mixing ratio of the biofuel increases, and a correction control is executed to introduce into the internal combustion engine an amount of the exhaust recirculation gas obtained by subtracting the reduction amount from the increased amount of the exhaust recirculation gas introduced as the mixing ratio of the biofuel increases. Control system for internal combustion engines.

2. The control device, in the correction control, decreases the reduction amount as the number of times a first condition is satisfied increases.

2. The control system for an internal combustion engine according to claim 1.

3. The control device acquires an accumulation amount of the particulate matter trapped in the filter, and executes the correction control when the accumulation amount is equal to or greater than a predetermined amount.

3. A control system for an internal combustion engine according to claim 1 or 2.

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