Control system for internal combustion engines

Abstract

This invention provides an internal combustion engine control system that can suppress fluctuations in engine output when the engine is restored from a fuel cut-off state. [Solution] The control system for an internal combustion engine comprises a cylinder, a fuel injection device that performs fuel injection, a heating device that raises the temperature inside the cylinder, and a control device that controls at least the fuel injection device and the heating device. The control device performs a fuel cut to stop the fuel injection from the fuel injection device during operation of the internal combustion engine, and when it returns from the fuel cut and performs fuel injection, if the temperature of the air flowing into the cylinder is below a predetermined temperature, or the pressure of the air flowing into the cylinder is below a predetermined pressure, it activates the heating device simultaneously with or after the fuel injection.

Description

Technical Field

[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 that raises the temperature inside a cylinder of the internal combustion engine by a glow plug has been known (for example, see Patent Document 1). The control system for the internal combustion engine of Patent Document 1 raises the temperature inside the cylinder using a glow plug to improve the warm-up performance of the internal combustion engine.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] Patent Document 1 discloses a technique for improving fuel ignition by using a glow plug to raise the temperature inside the cylinder when starting an internal combustion engine from a cold state. However, Patent Document 1 does not disclose a technique for improving fuel ignition after performing a fuel cut, which stops fuel injection during the operation of an internal combustion engine. When returning from a fuel cut, fuel ignition may be poor if the intake air temperature is low. Alternatively, if the vehicle is traveling at high altitude, fuel ignition may be poor if the intake air pressure is low. Thus, when the intake air temperature or intake air pressure is low, the inside of the cylinder becomes cold or low pressure, which worsens fuel ignition. Poor fuel ignition may lead to delayed ignition. Delayed ignition may cause fluctuations in the output of the internal combustion engine. Furthermore, compared to starting an internal combustion engine from a stopped state as described in Patent Document 1, the timing of fuel injection commencement is not clear when returning from a fuel cut, and it is not possible to delay the timing of fuel injection after receiving the fuel cut return command. Therefore, when the fuel cut-off is restored, the glow plugs cannot be activated before fuel injection begins, and the control system used when starting an internal combustion engine from a stopped state cannot be applied.

[0005] The objective of this disclosure is to provide an internal combustion engine control system that can suppress fluctuations in the engine's output when it recovers from a fuel cut-off. [Means for solving the problem]

[0006] The control system for an internal combustion engine according to this disclosure comprises a cylinder, a fuel injection device that performs fuel injection, a heating device that raises the temperature inside the cylinder, and a control device that controls at least the fuel injection device and the heating device, wherein the control device performs a fuel cut to stop the fuel injection from the fuel injection device during operation of the internal combustion engine, and when it returns from the fuel cut and performs fuel injection, if the temperature of the air flowing into the cylinder is below a predetermined temperature or the pressure of the air flowing into the cylinder is below a predetermined pressure, it activates the heating device simultaneously with or after the fuel injection. [Effects of the Invention]

[0007] According to this disclosure, when the inside of the cylinder is cold or under low pressure when fuel cut-off is restored, the temperature inside the cylinder is raised by a heating device. This suppresses the delay in fuel ignition. As a result, this internal combustion engine control system can suppress fluctuations in the output of the internal combustion engine. [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. [Figure 5] A timing chart showing the changes in the number of injection stages (upper stage) and output (lower stage) according to one embodiment of the present disclosure. [Figure 6] A diagram showing a map for operating a heating device according to another 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, a temperature riser 4, an intake air temperature detection device 6, an intake air pressure detection device 8, a control device 10, and an accelerator pedal 12. The control system 1 for the internal combustion engine E in this embodiment is mounted on a vehicle. 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 and a pressure accumulator such as a common rail. The fuel injector 2 is electrically connected to a control device 10, and the control device 10 controls the injection amount (fuel injection amount) and the injection stage (number of fuel injections in one cycle).

[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). The pilot injection (PiI) can further 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. The post-injection (PI) is performed, for example, to increase the temperature of an exhaust gas purification device (not shown).

[0014] The heating device 4 is a device that raises the temperature of the air inside the cylinder N. In this embodiment, the heating device 4 is a glow plug positioned facing the inside of the cylinder N. The glow plug has an electric heating coil, and the heating of the coil raises the temperature of the air inside the cylinder N. However, the heating device 4 may also be a heater positioned, for example, in the intake port 14, which heats the intake air to warm the air inside the cylinder N.

[0015] The intake air temperature detection device 6 is arranged in an intake pipe (such as an intake manifold) connected to the intake port 14, and is a device that detects the intake air temperature T (an example of air temperature), which is the temperature of the air flowing into the cylinder N. The intake air temperature detection device 6 is electrically connected to the control device 10.

[0016] The intake air pressure detection device 8 is arranged in an intake pipe connected to the intake port 14, and is a device that detects the intake air pressure P (an example of air pressure), which is the pressure of the air flowing into the cylinder N. The intake air pressure detection device 8 is electrically connected to the control device 10.

[0017] The control device 10 is electrically connected to the accelerator pedal 12 and acquires the opening degree of the accelerator pedal 12 depressed by the user of the vehicle. The control device 10 determines the required output Q required for the internal combustion engine E from the opening degree (depression amount) of the accelerator pedal 12. The control device 10 determines the injection amount and injection pattern of the fuel injection device 2 based on the required output Q, and injects the fuel.

[0018] More specifically, as shown in FIG. 3, the control device 10 stores a map that switches 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 also small, the control device 10 performs single injection of the main injection MI. As the required output Q increases, the control device 10 injects the pilot injection PiI to suppress combustion noise while suppressing the ignition delay of the main injection MI. When the required output Q further increases and the fuel injection amount increases, the control device 10 injects the pre-injection PrI to suppress combustion noise and suppress the generation of nitrogen oxides. When the rotational speed of the internal combustion engine E increases, the control device 10 injects the after-injection AF to suppress the generation of unburned hydrocarbons generated by the combustion residue. In the high load and high rotation region, the control device 10 injects all the required fuel injection amounts by the main injection MI. The control device 10 injects the post-injection PI during the regeneration or temperature rise of an exhaust purification device (not shown).

[0019] The control device 10 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 10 controls the control system 1 of the internal combustion engine E based on the maps and programs stored in the memory.

[0020] Next, the control procedure executed by the control device 10 will be described using FIG. 4.

[0021] In step S1, the control device 10 determines whether it is in a fuel cut return state. Fuel cut is a control to stop fuel injection from the fuel injection device 2 during the operation of the internal combustion engine E. For example, when the accelerator pedal 12 is turned off during the operation of the internal combustion engine E, the control device 10 executes fuel cut. When the accelerator pedal 12 is depressed again and the required output Q increases, the control device 10 executes fuel cut return control to start fuel injection again. When the control device 10 is executing fuel cut return control, it may determine that it is in a fuel cut return state. When the required output Q increases due to other factors such as an air conditioner (not shown), the control device 10 may execute fuel cut return control. If the control device 10 determines that it is in a fuel cut return state (step S1 YES), the process proceeds to step S2. If the control device 10 determines that it is not in a fuel cut return state (step S1 NO), it returns.

[0022] In step S2, the control device 10 determines whether the intake air temperature T is below a predetermined temperature Tt. The predetermined temperature Tt is, for example, an intake air temperature at which the ignition property of the fuel is poor. The predetermined temperature Tt is, for example, 0°C. If the control device 10 determines that the intake air temperature T is below the predetermined temperature Tt (step S2 YES), the process proceeds to step S4. If the control device 10 determines that the intake air temperature T is higher than the predetermined temperature Tt (step S2 NO), the process proceeds to step S3.

[0023] In step S3, the control device 10 determines whether the intake pressure P is less than or equal to a predetermined pressure Pt. The predetermined pressure Pt is, for example, the intake pressure at which fuel ignition is poor. The predetermined pressure Pt is, for example, 70 kPa. If the control device 10 determines that the intake pressure P is less than or equal to the predetermined pressure Pt (step S3 YES), it proceeds to step S4. If the control device 10 determines that the intake pressure P is higher than the predetermined pressure Pt (step S3 NO), it returns.

[0024] In step S4, the control device 10 performs fuel injection and then restarts fuel injection. Once the control device 10 restarts fuel injection, it proceeds to step S5.

[0025] In step S5, the control device 10 activates the heating device 4. The heating device 4 may be activated simultaneously with fuel injection, or it may be activated after fuel injection has started but before the number of injection stages increases. In this embodiment, the control device 10 activates the heating device 4 by turning on the glow plug. When the control device 10 turns on the glow plug, it proceeds to step S6. The control device 10 resumes fuel injection while activating the heating device 4 in this manner. When the intake air temperature T is low and / or the intake air pressure P is low, the fuel is difficult to ignite. In particular, during fuel cut-off, the intake air is discharged without combustion, so the internal temperature of the cylinder N tends to decrease. In the fuel cut-off recovery state, the accelerator pedal 12 may still be pressed, and the amount of fuel injected increases with the increase in the requested output Q. When combustion suddenly starts when the amount of fuel injected has increased, the output of the internal combustion engine E increases rapidly, and the vehicle user will feel a shock. To suppress such output fluctuations, the control device 10 ignites the fuel using the heating device 4 and starts combustion before the fuel injection amount becomes excessive.

[0026] In step S6, the control device 10 determines whether the fuel injection amount has increased. In a diesel engine, the fuel injection amount increases with increasing demand output Q. Therefore, the control device 10 may determine that the fuel injection amount has increased if the demand output Q has increased. Alternatively, the control device 10 may count the actual fuel injection amount and determine that the fuel injection amount has increased if the fuel injection amount is equal to or greater than the first reference amount. If the control device 10 determines that the fuel injection amount has increased (step S6 YES), it proceeds to step S7. If the control device 10 determines that the fuel injection amount has not increased (step S6 NO), it proceeds to step S2, and injects fuel with the heating device 4 activated until the intake air temperature T is greater than a predetermined temperature Tt and the intake air pressure P is greater than a predetermined pressure Pt.

[0027] In step S7, the control device 10 reduces the output of the heating device 4. That is, the control device 10 reduces the output of the heating device 4 to less than when the heating device 4 started in step S4. In this embodiment, the control device 10 reduces the output (power supplied) of the glow plug. From the start to the stop of operation of the heating device 4, the control device 10 reduces the output of the heating device 4 as the fuel injection amount increases. As the required output Q increases and the fuel injection amount increases, ignition becomes easier and the combustion energy at the time of ignition increases. If the heating device 4 heats the air temperature of the cylinder N too much, the combustion energy at the time of ignition may become too large. For this reason, the control device 10 suppresses the output of the heating device 4 in accordance with the increase in fuel injection amount to protect the internal combustion engine E. Furthermore, the control device 10 suppresses the output of the heating device 4 as the fuel injection amount per cycle increases. This adjusts the system so that the combustion energy at the time of ignition does not become too large. After reducing the output of the heating device 4, the control device 10 proceeds to step S8.

[0028] In step S8, the control device 10 determines whether the number of injection stages is greater than 2 stages (an example of a predetermined number of stages). As shown in Figure 3, in this embodiment, as the requested output Q and fuel injection amount increase, the number of injection stages increases in the following order: 1-stage injection of main injection MI, 2-stage injection of pre-injection PrI and main injection MI, 3-stage injection of pre-injection PrI, pilot injection PiI and main injection MI, or 3-stage injection of pre-injection PrI, main injection MI and after-injection AI. If the number of injection stages becomes 3 or more, the control device 10 determines that the number of injection stages is greater than 2 stages. If the control device 10 determines that the number of injection stages is greater than 2 stages (step S8 YES), it proceeds to step S9. If the control device 10 determines that the number of injection stages is 2 stages or less (step S8 NO), it proceeds to step S2, and fuel is injected with the heating device 4 activated until the intake air temperature T is greater than a predetermined temperature Tt and the intake air pressure P is greater than a predetermined pressure Pt.

[0029] In step S9, the control device 10 determines that the fuel injection amount is equal to or greater than a predetermined amount. The predetermined amount is, for example, the amount of fuel injected that could damage the internal combustion engine E due to abnormal combustion (e.g., knocking) when the fuel is ignited using the heating device 4. In this embodiment, as the amount the accelerator pedal 12 is pressed increases, the requested output Q increases, and the fuel injection amount also increases. As the fuel injection amount increases, the number of injection stages also increases. Therefore, the control device 10 can determine that the amount is equal to or greater than a predetermined amount when the number of injection stages is greater than two. Furthermore, when the fuel cut is restored, ignition is difficult at the first injection stage. However, if the number of injection stages is greater than two, there is a high probability that ignition has already been completed. For this reason, stopping the heating device 4 based on the increase in the number of injection stages is a more reliable way to protect the internal combustion engine E than actually counting the fuel injection amount. When the control device 10 determines that the fuel injection amount is equal to or greater than a predetermined amount, it proceeds to step S10.

[0030] In step S10, the control device 10 stops the heating device 4. In this way, the control device 10 protects the internal combustion engine E by stopping the heating device 4 when the fuel injection amount is above a predetermined amount. After stopping the heating device 4, the control device 10 returns to its original position.

[0031] As described above, the control system 1 of the internal combustion engine E of this disclosure raises the temperature inside the cylinder N using the heating device 4 when the intake air temperature T is low or the intake air pressure P is low. This suppresses the delay in fuel ignition. As a result, the control system 1 of the internal combustion engine E can suppress fluctuations in the output of the internal combustion engine E.

[0032] More specifically, as shown in Figure 5, when the intake air temperature T is low or the intake air pressure P is low, when fuel cut-off is initiated at time t1, the internal combustion engine control system 1 starts fuel injection. At time t1, the internal combustion engine control system 1 performs a single-stage injection (main injection MI) and activates the heating device 4. As the required output Q increases, at time t2, the internal combustion engine control system 1 performs a second-stage injection (pilot injection PiI and main injection MI). If the heating device 4 is not operating at this time, the output (torque) will drop due to ignition delay, as shown by the dashed line in Figure 5, and ignition will occur at time t3, when, for example, a third-stage injection is performed, causing a rapid increase in torque. This will result in fluctuations in output. However, as shown by the solid line in Figure 5, if the heating device 4 is operating, the output can be increased while suppressing abrupt changes in output. At time t3, when the internal combustion engine control system 1 performs a third-stage injection (pilot injection PiI, pre-injection PrI, and main injection MI), it stops the heating device 4. In order to prevent ignition at an unexpected timing caused by the heating device 4, and to reduce the energy consumption required to operate the heating device 4, it is preferable to stop the heating device 4 when it is no longer needed, i.e., after the internal combustion engine E has fully combusted (after it has started to operate stably). In this way, the control system 1 for the internal combustion engine E can suppress fluctuations in the output of the internal combustion engine E.

[0033] <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.

[0034] In the above embodiment, an example was described in which the requested output Q and fuel injection amount increase according to the amount the accelerator pedal 12 is pressed, and the number of injection stages increases in accordance with these increases, but the disclosure is not limited thereto. For example, when the requested output Q increases, the number of injection stages may be temporarily reduced from two-stage injection to one-stage injection, or from three-stage injection to two-stage injection, and then the number of injection stages may be increased thereafter.

[0035] Furthermore, although the above embodiment was described using an example in which the heating device 4 is stopped when the number of injection stages is greater than two, the disclosure is not limited thereto. The control device 10 may stop the heating device 4 when the number of injection stages is greater than one. In addition, the control device 10 may, for example, count the actual fuel injection amount and determine that it is greater than or equal to a predetermined amount and stop the heating device 4, or it may count the operating time of the heating device 4 and stop the heating device 4 when the operating time exceeds a predetermined time.

[0036] Furthermore, although the above embodiment describes an example in which an intake air temperature detection device 6 is placed in the intake pipe connected to the intake port 14 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 10 may estimate the intake air temperature T inside the cylinder N from the values ​​obtained by these sensors.

[0037] Furthermore, although the above embodiment describes an example in which an intake pressure detection device 8 is placed in the intake pipe connected to the intake port 14 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 10 may estimate the intake pressure P inside the cylinder N from the values ​​obtained by these sensors.

[0038] Furthermore, in the above embodiment, an example was described in which the control device 10 operates the heating device 4 when the intake air temperature T is less than or equal to a predetermined temperature Tt (see step S2 YES) or the intake air pressure P is less than or equal to a predetermined pressure Pt (see step S3 YES), but this disclosure is not limited thereto. The control device 10 may store a map recording the coefficients for operating the heating device 4 shown in Figure 6, and operate the heating device 4 by fitting the detected intake air temperature and intake air pressure to this map. In the map, the coefficient is set to 1 when the temperature is less than or equal to a predetermined temperature Tt (0°C in Figure 6) and the pressure is less than or equal to a predetermined pressure Pt. The control device 10 may operate the heating device 4 when the coefficient is 1. [Explanation of Symbols]

[0039] 1: Control system, 2: Fuel injection system, 4: Temperature riser, 10: Control device 12: Accelerator pedal E: Internal combustion engine T: Intake air temperature, Tt: Predetermined temperature P: Intake pressure, Pt: Predetermined pressure

Claims

1. Cylinder and A fuel injection system that performs fuel injection, A heating device for raising the temperature inside the cylinder, A control device that controls at least the fuel injection device and the heating device, Equipped with, The control device performs a fuel cut-off to stop fuel injection from the fuel injector during the operation of the internal combustion engine, and when it resumes fuel injection after the fuel cut-off, if the temperature of the air flowing into the cylinder is below a predetermined temperature, or the pressure of the air flowing into the cylinder is below a predetermined pressure, it activates the heating device simultaneously with or after the fuel injection. Control system for internal combustion engines.

2. The control device suppresses the output of the heating device as the amount of fuel injection increases. The control system for an internal combustion engine according to claim 1.

3. The control device activates the heating device simultaneously with or after the fuel injection, and stops the heating device when the amount of fuel injected exceeds a predetermined amount. The control system for an internal combustion engine according to claim 1.

4. It also has an accelerator pedal, The control device increases the number of fuel injection stages according to the amount the accelerator pedal is pressed. If the number of injection stages exceeds a predetermined number, the system determines that the amount of fuel injected is greater than or equal to a predetermined amount and stops the heating device. The control system for an internal combustion engine according to claim 1.

5. The control device reduces the output of the heating device as the amount of fuel injection increases during the period from the start to the stop of operation of the heating device. A control system for an internal combustion engine according to any one of claims 1 to 4.

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