Control system for internal combustion engines

Abstract

The present invention provides an internal combustion engine control system that can perform appropriate control to suppress the emission of unburned hydrocarbons according to the operating conditions of the internal combustion engine. [Solution] The control system for an internal combustion engine is a control system for an internal combustion engine that performs post-injection capable of raising the temperature of exhaust gas, and comprises an opening / closing device for opening and closing the exhaust pipe of the internal combustion engine, and a control device for controlling the opening / closing device, wherein when the intake air of the internal combustion engine is in a low temperature and low pressure state and the load on the internal combustion engine is low load, the control device performs either a first control that closes the opening / closing device or a second control that opens the opening / closing device and performs post-injection, depending on the operating state of the internal combustion engine.

Description

Technical Field

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[0001] The present disclosure relates to a control system for an internal combustion engine.

Background Art

[0002] Conventionally, a control system for an internal combustion engine having an exhaust shutter has been known (see, for example, Patent Document 1). The control system of Patent Document 1 increases the in-cylinder pressure and improves the ignition property by closing the exhaust shutter. When the ignition property is improved, the emission of unburned hydrocarbons is suppressed.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] When an exhaust shutter is used, while the ignition property improves, the exhaust resistance increases. As a result, depending on the operating conditions of the internal combustion engine, there are situations where it cannot be used. Patent Document 1 does not disclose what control to execute in such a case.

[0005] An object of the present disclosure is to provide a control system for an internal combustion engine that can execute appropriate control capable of suppressing the emission of unburned hydrocarbons according to the operating conditions of the internal combustion engine.

Means for Solving the Problems

[0006] The control system for an internal combustion engine according to this disclosure is a control system for an internal combustion engine that performs post-injection capable of raising the temperature of exhaust gas, and comprises a switch for opening and closing the exhaust pipe of the internal combustion engine, and a control device for controlling the switch, wherein when the intake air of the internal combustion engine is in a low temperature and low pressure state and the load on the internal combustion engine is low load, the control device performs either a first control that closes the switch, or a second control that opens the switch and performs post-injection, depending on the operating state of the internal combustion engine. [Effects of the Invention]

[0007] According to this internal combustion engine control system, depending on the operating conditions of the internal combustion engine, either the first control or the second control can be executed to suppress the emission of unburned hydrocarbons. [Brief explanation of the drawing]

[0008] [Figure 1] A system diagram of a control system for an internal combustion engine according to one embodiment of the present disclosure. [Figure 2] A diagram showing a spray configuration according to one embodiment of the present disclosure. [Figure 3] A diagram showing the injection pattern in response to a load according to one embodiment of the present disclosure. [Figure 4] A flowchart illustrating a control procedure performed by a control device according to one embodiment of the present disclosure. [Modes for carrying out the invention]

[0009] Hereinafter, one embodiment of this disclosure will be described with reference to the drawings.

[0010] As shown in Figure 1, the control system 1 for the internal combustion engine E includes a fuel injector 2, an exhaust gas purification device 4, an opening / closing device 6, an intake air temperature detection device 8, an intake air pressure detection device 10, a control device 12, and an accelerator pedal 14. The control system 1 for the internal combustion engine E in this embodiment is mounted on a vehicle C. In this embodiment, the internal combustion engine E is a four-stroke diesel engine that injects fuel directly into the cylinder N and causes autoignition.

[0011] The fuel injector 2 performs fuel injection to supply fuel to cylinder N. In this embodiment, the fuel injector 2 is connected to a fuel injection pump 22 and a pressure accumulator such as a common rail (not shown). The fuel injector 2 is electrically connected to a control device 12, and the injection amount and injection stage are controlled by the control device 12.

[0012] As shown in Figure 2, in this embodiment, the fuel injector 2 injects a pilot injection PiI, a pre-injection PrI, a main injection MI, an after-injection AI, and a post-injection PI per cycle, with intake, compression, expansion, and exhaust being considered as one cycle.

[0013] The main injection (MI) is injected from the compression stroke to the expansion stroke. The main injection (MI) injects the majority of the fuel to be injected per cycle. The pilot injection (PiI) is injected before the main injection (MI). The pilot injection (PiI) is injected in small amounts and can increase the combustion temperature inside the cylinder N, thereby reducing the ignition delay of the main injection (MI). Furthermore, the pilot injection (PiI) can suppress the rapid pressure increase of the main injection (MI) and reduce combustion noise. The pre-injection (PrI) is injected immediately before the main injection (MI). The pre-injection (PrI) is injected in small amounts and can reduce combustion noise and nitrogen oxides. The after-injection (AI) is injected after the main injection (MI). The after-injection (AI) is mainly used to burn any fuel that was not burned by the main injection (MI). The post-injection (PI) is injected after the after-injection (AI). The post-injection (PI) is performed, for example, to increase the temperature of the exhaust gas purification device (4).

[0014] As shown in Figure 1, the exhaust gas purification device 4 is a device that purifies the exhaust gas emitted from the internal combustion engine E. The exhaust gas purification device 4 may include, for example, a diesel particulate filter that captures particulate matter in the exhaust gas, a NOx trap that captures NOx, or a urea selective reduction catalytic system that reduces NOx using urea.

[0015] The switching device 6 is a device that opens and closes the exhaust pipe 16 of the internal combustion engine E. In this embodiment, the switching device 6 is a butterfly-type switching valve that opens and closes the passage of the exhaust pipe 16. The switching device 6 is installed downstream of the exhaust purification device 4. The switching device 6 is electrically connected to the control device 12 and the degree of valve opening is controlled.

[0016] The intake air temperature detection device 8 is located in the intake manifold (or similar) connected to the intake port 18 and detects the intake air temperature T, which is the temperature of the air flowing into the cylinder N. The intake air temperature detection device 8 is electrically connected to the control device 12.

[0017] The intake pressure detection device 10 is located in the intake pipe connected to the intake port 18 and is a device that detects the intake pressure P, which is the pressure of the air flowing into the cylinder N. The intake pressure detection device 10 is electrically connected to the control device 12.

[0018] The control device 12 is electrically connected to the accelerator pedal 14 and obtains the opening degree of the accelerator pedal 14 pressed by the user of vehicle C. From the opening degree of the accelerator pedal 14, the control device 12 determines the required output (or required torque) Q to be requested from the internal combustion engine E. Based on the required output Q, the control device 12 determines the injection amount and injection mode of the fuel injector 2 and injects the fuel.

[0019] More specifically, as shown in FIG. 3, the control device 12 stores a map for switching from single injection to multi-injection according to the required output Q. For example, in a region where the required output Q is small and the rotational speed of the internal combustion engine E is also small, since the fuel injection amount is small, the control device 12 performs single injection for the main injection MI. As the required output Q increases, the control device 12 injects the pilot injection PiI to suppress the combustion noise while suppressing the ignition delay of the main injection MI. Further, when the required output Q further increases and the fuel injection amount increases, the control device 12 injects the pre-injection PrI to suppress the combustion noise and the generation of nitrogen oxides. When the rotational speed of the internal combustion engine E increases, the control device 12 injects the after-injection AI to suppress the generation of unburned hydrocarbons generated by the combustion residue. In the high load and high rotation region, the control device 12 injects all the required fuel injection amounts by the main injection MI. The control device 12 injects the post-injection PI during the regeneration or temperature increase of the exhaust purification device 4.

[0020] The control device 12 further determines the necessity of increasing the temperature of the exhaust purification device 4. For example, the control device 12 may obtain the temperature ET of the exhaust purification device 4 from the exhaust temperature sensor 20 and determine the necessity of increasing the temperature of the exhaust purification device 4. Further, when the exhaust purification device 4 is a urea selective reduction type catalyst system, the control device 12 may determine that it is necessary to increase the temperature of the exhaust purification device 4 when injecting urea. When it is necessary to increase the temperature of the exhaust purification device 4, the control device 12 may execute the post-injection PI.

[0021] The control device 12 further determines the necessity of regenerating the exhaust purification device 4. For example, when the exhaust purification device 4 is a diesel particulate filter, if the soot deposited on the diesel particulate filter exceeds a predetermined value, the control device 12 may determine that regeneration of the exhaust purification device 4 is necessary. Further, when the exhaust purification device 4 is a NOx trap, the control device 12 may determine that regeneration is necessary when the NOx trap stores a predetermined amount or more of NOx. When it is necessary to regenerate the exhaust purification device 4, the control device 12 may execute the post-injection PI.

[0022] The control device 12 executes either the first control or the second control according to the operating state of the internal combustion engine E. The first control is the control to close the opening / closing device 6. The first control closes the opening / closing device 6 and closes the exhaust passage, thereby increasing the exhaust gas (also referred to as internal EGR) flowing back into the cylinder N. As a result, the internal temperature of the cylinder N rises and the exhaust gas is re-burned. Thereby, the emission of unburned hydrocarbons is reduced. Note that "closing the opening / closing device 6" and "closing the exhaust passage" do not only refer to the state where the exhaust passage is completely closed, but also include the state where the opening / closing device 6 is closed (half-open state) to such an extent that the exhaust resistance increases as the internal EGR sufficiently increases. In the first control, the degree to which the opening / closing device 6 should be closed may be appropriately set in consideration of the degree of temperature rise of the cylinder N due to the increase in internal EGR by experiments or the like.

[0023] The second control is the control to execute the post-injection PI. The second control is the control to burn the unburned hydrocarbons discharged from the cylinder N by heating the exhaust gas by the post-injection PI. Thereby, the emission of unburned hydrocarbons is reduced. In the second control, the control device 12 increases the difference between the injection end timing of the pre-injection PrI and the injection start timing of the main injection MI, or the difference between the injection end timing of the pilot injection PiI and the injection start timing of the main injection MI. As a result, the fuel is more likely to be converted into heat and the temperature inside the cylinder N rises. As a result, the ignition property of the main injection MI is improved. Note that the injection timing of the post-injection PI in the second control is the same as that of the post-injection PI in the normal control of FIG. 2.

[0024] The control device 12 is actually an ECU (Electronic Control Unit) composed of a microcomputer including an arithmetic unit, a memory, an input / output buffer, etc. The control device 12 controls the control system 1 of the internal combustion engine E based on the maps and programs stored in the memory.

[0025] Next, the control procedure executed by the control device 12 will be described using FIG. 4.

[0026] In step S1, the control device 12 determines whether the intake air is cold or not. In this embodiment, the control device 12 determines whether the intake air temperature T obtained from the intake air temperature detection device 8 is below a predetermined intake air temperature Tt. The predetermined intake air temperature Tt is, for example, minus 10°C. At such an intake air temperature T, ignition performance tends to deteriorate. If the control device 12 determines that the intake air temperature T is below the predetermined intake air temperature Tt (step S1 YES), it proceeds to step S2.

[0027] In step S2, the control device 12 determines whether the pressure is low or not. In this embodiment, the control device 12 determines whether the intake pressure P obtained from the intake pressure detection device 10 is less than a predetermined intake pressure Pt. The predetermined intake pressure Pt is a pressure below atmospheric pressure (for example, about 0.7 atmospheres). At such an intake pressure P, ignition performance tends to deteriorate. If the control device 12 determines that the intake pressure P is less than the predetermined intake pressure Pt (step S2 YES), it proceeds to step S3.

[0028] In step S3, the control device 12 determines whether the load is low or not. In this embodiment, the control device 12 determines whether the acquired requested output Q is less than or equal to a predetermined output Qt. The predetermined output Qt is, for example, 10kW. At such a requested output Q, ignition performance tends to deteriorate. If the control device 12 determines that the requested output Q is less than or equal to the predetermined output Qt (step S3 YES), it proceeds to step S4.

[0029] In step S4, the control device 12 determines whether the vehicle C is in an accelerating state. In this embodiment, the control device 12 determines that the vehicle is in an accelerating state if, for example, the requested output Q continues to increase. If the control device 12 determines that the vehicle is in an accelerating state (step S4 YES), it proceeds to step S5.

[0030] In step S5, the control device 12 performs a second control. When vehicle C is accelerating, closing the opening / closing device 6 creates exhaust resistance, worsening the acceleration of vehicle C. Therefore, the control device 12 opens the opening / closing device 6 and performs post-injection PI. This reduces the emission of unburned hydrocarbons without worsening acceleration performance. After performing the second control, the control device 12 proceeds to step S6. In this embodiment, "opening the opening / closing device 6" is not limited to fully opening the opening / closing device 6, but also includes closing it to an opening degree that minimizes the increase in exhaust resistance. An opening degree that minimizes the increase in exhaust resistance is an opening degree greater than the opening degree at which the exhaust resistance increases to a sufficient extent that internal EGR increases.

[0031] In step S6, the control device 12 determines whether or not to terminate the second control. The control device 12 may terminate the second control if, for example, a predetermined time has elapsed since the execution of the second control. In addition, the control device 12 may terminate the second control according to the temperature ET of the exhaust gas purification device 4. If the control device 12 determines to terminate the second control (step S6 YES), it proceeds to step S7. If the control device 12 determines to continue the second control (step S6 NO), it proceeds to step S5 and continues the second control.

[0032] In step S7, the control device 12 terminates the post-injection PI and returns.

[0033] If in step S1 the intake air temperature T is determined to be greater than a predetermined intake air temperature Tt (step S1 NO), if in step S2 the intake air pressure P is determined to be greater than or equal to a predetermined intake air pressure Pt (step S2 NO), and if in step S3 the requested output Q is determined to be greater than a predetermined output Qt (step S3 NO), the control device 12 proceeds to step S8.

[0034] In step S8, the control device 12 disables the first and second controls and performs normal control. The control device 12 performs injection mode according to the rotational speed of the internal combustion engine E and the required output Q (required torque). The control device 12 returns after performing normal control.

[0035] If the control device 12 determines in step S4 that the acceleration state is not being maintained (step S4 NO), the process proceeds to step S9.

[0036] In step S9, the control device 12 determines whether or not to restart the internal combustion engine E. If the control device 12 determines that it is not a restart (step S9 NO), it proceeds to step S10. In step S10, the control device 12 executes the first control. After executing the first control, the control device 12 proceeds to step S11. Note that whether or not to restart the internal combustion engine E refers to whether or not a predetermined time has elapsed since the internal combustion engine E was restarted. The predetermined time is, for example, 10 seconds.

[0037] In step S11, the control device 12 determines whether or not to terminate the first control. The control device 12 may terminate the first control if, for example, a predetermined time has elapsed since the first control was executed. In addition, the control device 12 may terminate the first control according to the temperature ET of the exhaust gas purification device 4. If the control device 12 determines to terminate the first control (step S11 YES), it proceeds to step S12. If the control device 12 determines to continue the first control (step S11 NO), it proceeds to step S10 and continues the first control.

[0038] In step S12, the control device 12 executes an advanced post-injection PIa. As shown by the dashed line in Figure 2, the advanced post-injection PIa is injected at a time that is advanced toward the main injection MI than the post-injection PI. The advanced post-injection PIa may be injected at a timing that overlaps with, for example, the after-injection AI. The control device 12 executes the advanced post-injection PIa when the first control is completed. In this embodiment, when the control device 12 determines that the first control is complete, it executes the advanced post-injection PIa and then closes the switchgear 6 to complete the first control. When the switchgear 6 is closed, unburned hydrocarbons may remain in the exhaust pipe 16. Thus, by executing the advanced post-injection PIa, the control device 12 can ensure that the unburned hydrocarbons remaining in the exhaust pipe 16 are burned. After executing the advanced post-injection PIa, the control device 12 returns.

[0039] If the control device 12 determines in step S9 that the internal combustion engine E is being restarted (step S9 YES), the control device 12 proceeds to step S14. In step S14, the control device 12 executes the second control. Even in low temperature, low pressure, and low load conditions, the internal combustion engine E may already be warm after being restarted. For this reason, post-injection PI by the second control is more effective in reducing the emission of unburned hydrocarbons than increasing internal EGR by the first control. After executing the second control, the control device 12 proceeds to step S15.

[0040] In step S15, the control device 12 determines whether the temperature ET of the exhaust gas purification device 4 is above a predetermined temperature ETt. The predetermined temperature ETt is, for example, the temperature at which the catalyst of the exhaust gas purification device 4 may melt. That is, if post-injection PI is performed during restart, the temperature of the exhaust gas purification device 4 may rise too high. If the control device 12 determines that the temperature ET of the exhaust gas purification device 4 is above the predetermined temperature ETt (step S15 YES), it proceeds to step S10 and switches from the second control to the first control. On the other hand, if the control device 12 determines that the temperature ET of the exhaust gas purification device 4 is below the predetermined temperature ETt (step S15 NO), it proceeds to step S6 and continues the second control until the termination condition for the second control is met.

[0041] As described above, this disclosure provides a control system 1 for an internal combustion engine E that can perform appropriate control to suppress the emission of unburned hydrocarbons depending on the operating conditions of the internal combustion engine E.

[0042] <Other Embodiments> Although embodiments of the present disclosure have been described above, the present disclosure is not limited to the embodiments described above, and various modifications are possible without departing from the spirit of the invention. In particular, the various modifications described herein can be combined as needed.

[0043] Furthermore, although the above embodiment describes an example in which an intake air temperature detection device 8 is placed in the intake pipe connected to the intake port 18 to detect the intake air temperature T, this disclosure is not limited to this. The intake air temperature T may also be detected using, for example, an airflow sensor placed upstream of the air cleaner. Moreover, the control device 12 may estimate the intake air temperature T inside the cylinder N from the values ​​obtained by these sensors.

[0044] Furthermore, although the above embodiment describes an example in which an intake pressure detection device 10 is placed in the intake pipe connected to the intake port 18 to detect the intake pressure P, this disclosure is not limited to this. The intake pressure P may also be detected using, for example, an airflow sensor placed upstream of the air cleaner. Moreover, the control device 12 may estimate the intake pressure P inside the cylinder N from the values ​​obtained by these sensors.

[0045] Furthermore, although the above embodiment described an example in which the control device 12 determines that an acceleration state is occurring when, for example, the requested output Q continues to increase, the disclosure is not limited thereto. The control device 12 may also determine the acceleration state using a G sensor (not shown) that detects the acceleration state of the vehicle C. [Explanation of symbols]

[0046] 1: Control system, 2: Fuel injection system, 4: Exhaust gas purification system 6: Switching device, 8: Intake air temperature detection device, 10: Intake pressure detection device 12: Control device, 14: Accelerator pedal 16: Exhaust pipe, 18: Intake port, 20: Exhaust temperature sensor C: Vehicle, E: Internal combustion engine, ET: Temperature, ETT: Specified temperature, MI: Main injection PI: Post-injection, PIa: Advance-injection post-injection, PiI: Pilot injection PrI: Pre-injection, Pt: Predetermined intake pressure Q: Requested output, Qt: Specific output T: Intake temperature, Tt: Predetermined intake temperature

Claims

1. A control system for an internal combustion engine that performs post-injection capable of heating exhaust gases, A switching device for opening and closing the exhaust pipe of an internal combustion engine, A control device for controlling the opening and closing device, Equipped with, The control device, when the intake air of the internal combustion engine is at a low temperature and low pressure, and the load on the internal combustion engine is low, executes either a first control that closes the switchgear or a second control that opens the switchgear and performs post-injection, depending on the operating state of the internal combustion engine. Control system for internal combustion engines.

2. The internal combustion engine is mounted on the vehicle, and the control device executes the second control when the vehicle is in an accelerating state. The control system for an internal combustion engine according to claim 1.

3. The system further includes an exhaust gas purification device for purifying the exhaust gas of the internal combustion engine, The switchgear is located downstream of the exhaust purifier. The control device executes the second control when restarting the internal combustion engine, and executes the first control when restarting the internal combustion engine if the temperature of the exhaust gas purification device is above a predetermined temperature. The control system for an internal combustion engine according to claim 1.

4. The control device is capable of performing advanced-angle post-injection, which is injected at a time more advanced than the post-injection, and performs the advanced-angle post-injection when terminating the first control. The control system for an internal combustion engine according to claim 1.

5. The system further comprises an intake pipe for introducing intake air into the internal combustion engine, The control device prohibits the first control and the second control when the intake air temperature of the intake pipe is above a predetermined intake air temperature. The control system for an internal combustion engine according to claim 1.

6. The control device is capable of performing a main injection that is injected at a timing advanced compared to the post-injection, and a pre-injection or pilot injection that is injected at a timing advanced compared to the main injection, and when performing the second control, it increases the difference between the end time of the pre-injection and the start time of the main injection, or the difference between the end time of the pilot injection and the start time of the main injection. A control system for an internal combustion engine according to any one of claims 1 to 5.

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