Internal combustion engine control method and internal combustion engine control device

Abstract

An internal combustion engine (1) has a turbosupercharger (21) and is capable of introducing (recirculating) a portion of exhaust gas to an intake passage (2) via an EGR passage (35). The EGR passage (35) is connected to the intake passage (2) at the upstream side of a compressor (22) of the turbosupercharger (21). When there is an acceleration request during partial load operation and the internal combustion engine (1) operation state switches to high-torque operation, a control unit (41) temporarily fully closes an EGR valve (36) provided to the EGR passage (35). Thus, the internal combustion engine (1) is capable of temporarily introducing a larger amount of air and temporarily generating high torque.

Description

Control method for an internal combustion engine and control device for an internal combustion engine

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

[0002] For example, Patent Document 1 discloses a technique for lowering exhaust gas temperature by introducing EGR gas during high-torque operation (high-load operation).

[0003] In Patent Document 1, the target EGR rate is corrected for a certain period of time when acceleration is requested.

[0004] However, in Patent Document 1, the EGR valve is not fully closed when acceleration is requested, so there is a risk of a transient decrease in torque due to the amount of EGR gas being introduced. Also, in Patent Document 1, the target EGR rate is corrected for a fixed time when acceleration is requested, so depending on the setting of this fixed time, the exhaust temperature may rise transiently, and exhaust system components may be adversely affected by the high-temperature exhaust.

[0005] In other words, there is still room for further improvement in vehicle control when there is an acceleration request from an internal combustion engine that performs exhaust gas recirculation.

[0006] Japanese Patent Application Publication No. 7-317606

[0007] During high torque operation when the exhaust gas temperature becomes high, the internal combustion engine of the present invention introduces EGR gas into the intake passage to lower the exhaust gas temperature and introduce more air.

[0008] By introducing EGR gas into the intake passage during high-torque operation, the internal combustion engine can lower the temperature of the exhaust gas discharged from the combustion chamber of the internal combustion engine, preventing the temperature of exhaust system components from exceeding their heat-resistant temperature, while allowing more air to be introduced.

[0009] Therefore, internal combustion engines can generate high torque when the mixture ratio is stoichiometric, or in other words, theoretically optimal.

[0010] The present invention is applicable to an internal combustion engine having a high load operation mode, and the present invention is applicable to an internal combustion engine having a high load operation mode.

[0011] An embodiment of the present invention will be described in detail below with reference to the drawings.

[0012] 1 is an explanatory diagram showing a schematic system configuration of an internal combustion engine 1 to which the present invention is applied. The internal combustion engine 1 is mounted as a drive source in a vehicle such as an automobile, and has an intake passage 2 and an exhaust passage 3. The intake passage 2 is connected to a combustion chamber 5 of the internal combustion engine 1 via an intake valve 4. The exhaust passage 3 is connected to a combustion chamber 5 of the internal combustion engine 1 via an exhaust valve 6. The internal combustion engine 1 is, for example, of a direct injection type, and each cylinder is provided with a fuel injection valve (not shown) that injects fuel into the cylinder and a spark plug 7.

[0013] The intake passage 2 is provided with an air cleaner 11 for collecting foreign matter in the intake air, an air flow meter 12 for detecting the amount of intake air, an electric first throttle valve 13, and an electric second throttle valve 14 located upstream of the first throttle valve 13.

[0014] The air flow meter 12 is disposed upstream of the second throttle valve 14. The air cleaner 11 is disposed upstream of the air flow meter 12. The first throttle valve 13 controls the amount of intake air into the internal combustion engine 1 in accordance with the load. The second throttle valve 14 corresponds to a pressure control valve, and controls the intake pressure upstream of a compressor 22, which will be described later. The second throttle valve 14 is also disposed upstream in the flow direction of the intake air from the connection between the intake passage 2 and an EGR passage 35, which will be described later.

[0015] The exhaust passage 3 is equipped with an upstream exhaust purification device 17 and a downstream exhaust purification device 18. The upstream exhaust purification device 17 consists of, for example, a three-way catalytic converter. The downstream exhaust purification device 18 also consists of, for example, a three-way catalytic converter and is located downstream of the upstream exhaust purification device 17.

[0016] The internal combustion engine 1 also has a turbocharger 21 as a supercharger. The turbocharger 21 has a compressor 22 provided in the intake passage 2 and a turbine 23 provided in the exhaust passage 3. The compressor 22 and the turbine 23 are arranged coaxially and rotate integrally. The compressor 22 is arranged upstream of the first throttle valve 13 and downstream of the second throttle valve 14. The turbine 23 is arranged upstream of the upstream exhaust purification device 17.

[0017] Furthermore, an intercooler 24 is provided downstream of the first throttle valve 13 in the intake passage 2 to cool the intake air compressed (pressurized) by the compressor 22 and improve charging efficiency.

[0018] An exhaust bypass passage 31 is connected to the exhaust passage 3, bypassing the turbine 23 and connecting the upstream side and downstream side of the turbine 23. The downstream end of the exhaust bypass passage 31 is connected to the exhaust passage 3 at a position upstream of the upstream exhaust purification device 17. An electric wastegate valve 32 is arranged in the exhaust bypass passage 31 to control the exhaust flow rate in the exhaust bypass passage 31. Reference numeral 33 in FIG. 1 denotes an intake collector.

[0019] The internal combustion engine 1 is capable of exhaust gas recirculation (EGR), which introduces (recirculates) a portion of the exhaust gas from the exhaust passage 3 into the intake passage 2 as EGR gas, and has an EGR passage 35 as an exhaust gas recirculation passage branched from the exhaust passage 3 and connected to the intake passage 2. One end of the EGR passage 35 is connected to the exhaust passage 3 at a position between the upstream exhaust gas purification device 17 and the downstream exhaust gas purification device 18, and the other end is connected to the intake passage 2 at a position downstream of the second throttle valve 14 and upstream of the compressor 22. The EGR passage 35 is provided with an electric EGR valve 36 that adjusts (controls) the flow rate of EGR gas introduced into the intake passage 2, and an EGR cooler 37 that can cool the EGR gas.

[0020] The internal combustion engine 1 is configured such that the EGR rate during high-torque operation (high-load operation), when high torque can be obtained, is smaller than the EGR rate during partial-load operation.

[0021] The EGR valve 36 is controlled by a control unit 41 of the internal combustion engine 1 so as to have a target valve opening.

[0022] The control unit 41 corresponds to the control unit and is a well-known digital computer equipped with a CPU, ROM, RAM, and input / output interface. In addition to the airflow meter 12 described above, the control unit 41 receives detection signals (detected values) from various sensors, such as a crank angle sensor 42 that can detect the engine speed along with the crank angle of the crankshaft of the internal combustion engine 1, and an accelerator opening sensor 43 that detects the amount of accelerator pedal depression (accelerator opening APO) that represents the required load state of the internal combustion engine 1.

[0023] The control unit 41 then optimally controls the opening degree of the EGR valve 36, as well as the fuel injection amount and timing of the fuel injection valve (not shown), the ignition timing of the spark plug 7, the opening degree of the first throttle valve 13, the opening degree of the second throttle valve 14, the opening degree of the wastegate valve 32, and the opening degree of the EGR valve 36, based on detection signals from various sensors.

[0024] Furthermore, the control unit 41 is capable of estimating the temperature of the exhaust gas discharged from the combustion chamber 5 using the engine speed of the internal combustion engine 1, the required load, the ignition timing, the EGR rate, the vehicle speed, etc. In other words, the control unit 41 is capable of estimating the exhaust gas temperature of the internal combustion engine 1 based on the operating conditions of the vehicle and the internal combustion engine 1. Here, the estimated exhaust gas temperature is the exhaust gas temperature at the highest temperature point in the exhaust passage 3, for example, the exhaust gas temperature in the exhaust passage 3 at a position upstream of the turbine 23 in the exhaust passage 3.

[0025] FIG. 2 is a timing chart showing changes in various state quantities when the internal combustion engine 1 switches from partial load operation to high load operation.

[0026] 2 is the timing when the operating state of the internal combustion engine 1 switches from partial load operation to high torque operation and the acceleration request is turned on. In this specification, turning on the acceleration request means that a command to generate high torque is issued to the internal combustion engine 1.

[0027] An acceleration request is determined to exist when, for example, the difference between the current torque command value and the previous torque command value of the internal combustion engine 1 is equal to or greater than a predetermined acceleration request determination threshold. The acceleration request determination threshold is set, for example, according to the vehicle speed of the vehicle equipped with the internal combustion engine 1. The torque command value is calculated, for example, to be a value corresponding to the depression amount of the accelerator pedal, and becomes larger as the depression amount of the accelerator pedal increases.

[0028] When the operating state of the internal combustion engine 1 is switched at time t1 in FIG. 2 , the command torque to the internal combustion engine 1 becomes larger than that during partial load operation, as shown by characteristic line A. The dashed characteristic line A in FIG. 2 shows the change in the command torque to the internal combustion engine 1 of this embodiment. As shown by characteristic line A, the command torque to the internal combustion engine 1 is switched in a stepwise manner at time t1 from the torque during partial load operation to the torque during high torque operation in response to an acceleration request. The actual torque of the internal combustion engine 1 of this embodiment gradually increases from time t1, approaching characteristic line A, as shown by characteristic line B in FIG. 2 , shown by a solid line. Characteristic line B shows the case where the EGR rate is controlled to zero and the second throttle valve 14 is fully opened from time t1. Note that the EGR rate and the valve opening of the second throttle valve 14 are not switched in a stepwise manner at time t1. Therefore, in Fig. 2, the EGR rate changes toward 0% at a constant rate (constant gradient) from time t1. Similarly, in Fig. 2, the valve opening of the second throttle valve 14 changes toward full open at a constant rate (constant gradient) from time t1. Characteristic line C shown by a thin dashed line in Fig. 2 indicates the change in torque in the comparative example, and indicates the change in torque when the EGR rate is zero at time t1 and the second throttle valve 14 is not fully open.

[0029] A characteristic line F shown by a solid line in Fig. 2 indicates the change in the EGR rate in this embodiment. A characteristic line G shown by a dashed line in Fig. 2 indicates the change in the EGR rate in a comparative example. A characteristic line H shown by a solid line in Fig. 2 indicates the change in the valve opening of the second throttle valve 14 in this embodiment. A characteristic line G shown by a dashed line in Fig. 2 indicates the change in the second throttle valve 14 in a comparative example. In the comparative example, EGR gas is introduced even during a transient state when an acceleration request is turned on, so the opening of the second throttle valve 14 is controlled to an opening that generates a negative pressure for stable introduction of EGR gas even during a transient state.

[0030] The charging efficiency increases from time t1. A characteristic line D shown by a solid line in Fig. 2 indicates the change in charging efficiency of the internal combustion engine 1 of this embodiment. A characteristic line E shown by a dashed line in Fig. 2 indicates the change in charging efficiency of the internal combustion engine 1 of the comparative example.

[0031] The exhaust gas temperature starts to rise at time t1. A solid characteristic line J in Fig. 2 shows the change in the exhaust gas temperature of the internal combustion engine 1 of this embodiment. A dashed characteristic line K in Fig. 2 shows the change in the exhaust gas temperature of the internal combustion engine 1 of the comparative example.

[0032] At time t2 in FIG. 2, the exhaust temperature of the internal combustion engine 1 reaches a predetermined temperature threshold value that has been set in advance, and the acceleration request is switched from ON to OFF.

[0033] The acceleration request may be switched from on to off when any of the following conditions is met: the difference between the torque command value of the internal combustion engine 1 and the torque estimate value of the internal combustion engine 1 is smaller than a predetermined value; the difference between the current torque command value of the internal combustion engine 1 and the previous torque command value is smaller than a predetermined value; or a predetermined time has elapsed since the acceleration request was determined to be on.

[0034] The EGR rate is controlled at time t2 from 0% to a predetermined non-zero low EGR rate corresponding to high torque operation of the internal combustion engine 1. During partial load operation of the internal combustion engine 1, the EGR rate is controlled to a predetermined high EGR rate that is higher than the low EGR rate set during high torque operation. Note that the EGR rate is not switched in a stepwise manner at time t2. Therefore, in FIG. 2 , the EGR rate changes from time t2 toward the predetermined low EGR rate at a constant rate of change (constant gradient).

[0035] Since the introduction of EGR gas into the internal combustion engine 1 is resumed at time t2, the exhaust temperature of the internal combustion engine 1 does not exceed a predetermined heat resistance temperature threshold. The heat resistance temperature threshold is a value set in consideration of the heat resistance temperatures of the exhaust system components, for example, the heat resistance temperature of the exhaust system components. The heat resistance temperature threshold may be a value obtained by adding a margin to the heat resistance temperature of the exhaust system components.

[0036] If the acceleration request is not turned off at time t2 and the recirculation of EGR gas is stopped until the torque of the internal combustion engine 1 matches (matches) the command torque, the exhaust temperature of the internal combustion engine 1 may exceed the flame-resistant temperature threshold, as shown by the dashed-dotted characteristic line N in Fig. 2, which may adversely affect exhaust system components. The dashed-dotted characteristic line L in Fig. 2 shows the case where the acceleration request is turned on at the timing when the torque of the internal combustion engine 1 matches (matches) the command torque. The dashed-dotted characteristic line M in Fig. 2 shows the change in the EGR rate when the introduction of EGR gas is resumed at the timing when the torque of the internal combustion engine 1 matches (matches) the command torque.

[0037] In the above-described embodiment, the control unit 41 of the internal combustion engine 1 controls the opening of the EGR valve 36 during high-torque operation in which the torque is higher than a predetermined value, and introduces EGR gas into the intake passage 2 to lower the exhaust temperature and introduce more air. The exhaust temperature becomes high during high-torque operation of the internal combustion engine 1.

[0038] The internal combustion engine 1 introduces EGR gas into the intake passage 2, thereby lowering the exhaust gas temperature discharged from the combustion chamber 5, preventing the temperature of exhaust system components from exceeding their heat resistance temperature, while also enabling the introduction of more air.

[0039] Therefore, the internal combustion engine 1 is capable of generating high torque in a stoichiometric mixture ratio state. In other words, the internal combustion engine 1 is capable of generating high torque in a stoichiometric mixture ratio state.

[0040] When the control unit 41 receives an acceleration request during partial load operation and the operating state of the internal combustion engine 1 switches to high torque operation, it transiently (temporarily) fully closes the EGR valve 36 located in the EGR passage 35.

[0041] This allows the internal combustion engine 1 to transiently introduce more air and generate transiently (temporarily) high torque.

[0042] Furthermore, the control unit 41 controls the EGR valve 36 to open when the exhaust temperature exceeds a predetermined temperature during operation in response to the acceleration request.

[0043] The internal combustion engine 1 introduces EGR gas into the intake passage 2 in such a way that it satisfies the heat resistance requirements of the exhaust system components, even during transitions from transient states. This ensures the heat resistance of the exhaust system components while generating high torque at the stoichiometric mixture ratio (stoichiometric air-fuel ratio).

[0044] The control unit 41 closes the second throttle valve 14 to generate negative pressure in the intake passage 2 during partial load operation, which is an operating state of the internal combustion engine 1 where the exhaust pressure is low.

[0045] As a result, the internal combustion engine 1 can stably introduce EGR gas from the exhaust passage 3 to the intake passage 2 even when operating at low rotational speeds or low torque conditions where exhaust pressure is low.

[0046] During operation in response to the acceleration request, the control unit 41 controls the second throttle valve 14 to be fully open.

[0047] This allows the internal combustion engine 1 to generate high torque when acceleration is required.

[0048] During operation in response to the acceleration request, the control unit 41 controls the EGR valve 36 to open when the exhaust temperature reaches a predetermined temperature or higher, and controls the second throttle valve 14 to close when the exhaust pressure drops.

[0049] As a result, the internal combustion engine 1 can stably introduce EG gas from the exhaust passage 3 to the intake passage 2, even during transitions from transient states.

[0050] Although specific embodiments of the present invention have been described above, the present invention is not limited to the above-described embodiments, and various modifications are possible within the scope of the invention.

[0051] For example, the exhaust temperature of the internal combustion engine 1 may be detected using a temperature sensor separately disposed in the exhaust passage 3, rather than being estimated based on the operating states of the vehicle and the internal combustion engine 1. In this case, the temperature sensor is disposed, for example, at a position upstream of the turbine 23 and downstream of the exhaust manifold.

[0052] The above-described embodiment relates to a control method for an internal combustion engine and a control device for an internal combustion engine.

Claims

1. A control method for an internal combustion engine having an EGR passage connected to an intake passage for recirculating a portion of the exhaust gas to the intake passage as EGR gas, wherein the control method introduces EGR gas into the intake passage during high torque operation when the exhaust gas temperature becomes high, thereby lowering the exhaust gas temperature and introducing more air.

2. A control method for an internal combustion engine according to claim 1, wherein the internal combustion engine has a supercharger disposed in the intake passage, and the EGR passage is connected to the intake passage upstream of the supercharger.

3. A control method for an internal combustion engine as set forth in claim 1, wherein, when a request for acceleration is made while a predetermined condition is met, an EGR valve disposed in the EGR passage is fully closed.

4. The control method for an internal combustion engine according to claim 3, wherein the predetermined condition includes a partial load operation in which EGR gas is introduced at a higher EGR rate than during high torque operation.

5. The control method for an internal combustion engine according to claim 3, wherein the EGR valve is opened when the exhaust temperature reaches or exceeds a predetermined temperature during operation in response to the acceleration request.

6. A control method for an internal combustion engine as set forth in claim 2, wherein a pressure control valve for controlling intake pressure is disposed in the intake passage upstream of the connection between the EGR passage and the intake passage, and when the exhaust pressure is low, the pressure control valve is closed to generate negative pressure in the intake passage.

7. A control method for an internal combustion engine according to claim 4, wherein the pressure control valve is fully opened during operation when a request for acceleration is received while a predetermined condition is met.

8. A control method for an internal combustion engine as described in claim 3, wherein a pressure control valve for controlling intake pressure is arranged in the intake passage upstream of the connection between the EGR passage and the intake passage, and when the exhaust temperature reaches or exceeds a predetermined temperature during operation in response to the acceleration request, the EGR valve opens, and when the exhaust pressure drops, the pressure control valve closes.

9. A control device for an internal combustion engine having an EGR passage connected to an intake passage for recirculating a portion of the exhaust gas to the intake passage as EGR gas, and a control unit for introducing EGR gas into the intake passage during high torque operation when the exhaust gas temperature becomes high, thereby lowering the exhaust gas temperature and introducing more air.

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