Internal combustion engine control method and internal combustion engine control device

Abstract

An internal combustion engine (1) has an electrically heated catalyst (4) that is disposed in an exhaust passage (2) and that generates heat when energized. A fuel injection amount at the time of starting the internal combustion engine (1) is determined in accordance with an oxidizable oxygen storage amount that can be used for oxidation at the time of starting the internal combustion engine and that is stored in the electrically heated catalyst (4) on the basis of temperature information of the electrically heated catalyst (4). Thus, by predicting the oxygen storage amount that is stored in the electrically heated catalyst (4) before the internal combustion engine (1) is started and that can be used for oxidation of hydrocarbons and the like in the exhaust gas when the internal combustion engine (1) is started, deterioration of the exhaust performance when the internal combustion engine (1) is started can be suppressed, and the exhaust performance can be improved.

Description

Method for Controlling Internal Combustion Engine and Control Device for Internal Combustion Engine

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

[0002] For example, in Patent Document 1, a pre-stage catalyst that adsorbs hydrocarbons is disposed upstream of an electrically heated catalyst, and when starting the internal combustion engine, the air-fuel ratio is set to lean until the desorption of the hydrocarbons adsorbed on the pre-stage catalyst ends. A technique of operating is disclosed.

[0003] Here, since Patent Document 1 does not predict the amount of oxygen occluded in the electrically heated catalyst before starting the internal combustion engine or during the stop of the internal combustion engine, due to variations in the amount of hydrocarbons adsorbed on the pre-stage catalyst, the time for operating the internal combustion engine at a lean air-fuel ratio may become longer or shorter, and in that case, there is a risk that HC or NOx will increase. That is, in an internal combustion engine in which an electric heating catalyst is disposed in the exhaust passage, there is room for further improvement in improving the exhaust performance at the start of the internal combustion engine.

[0004] Japanese Patent Application Laid-Open No. 2017-14969

[0005] The internal combustion engine of the present invention has an electrically heated catalyst that is disposed in the exhaust passage and generates heat by being energized, and determines the fuel injection amount at the start of the internal combustion engine according to the amount of oxidizable oxygen occluded in the electrically heated catalyst that can be used for oxidation at the start of the internal combustion engine based on the temperature information of the electrically heated catalyst.

[0006] According to the present invention, by predicting the amount of oxygen occluded in the electrically heated catalyst before starting the internal combustion engine and available for oxidizing hydrocarbons and the like in the exhaust at the start of the internal combustion engine, deterioration of the exhaust performance at the start of the internal combustion engine can be suppressed, and the exhaust performance can be improved.

[0007] A schematic diagram illustrating the system configuration of an internal combustion engine to which the present invention is applied. A flowchart showing the control flow during startup of the internal combustion engine in the first embodiment. A characteristic diagram showing the correlation between the catalyst temperature of the electric heating catalyst and the amount of oxidizable oxygen stored. A timing chart showing an example of changes in various state quantities during startup of the internal combustion engine. A flowchart showing the control flow during startup of the internal combustion engine in the second embodiment. A characteristic diagram showing the correlation between the catalyst temperature of the electric heating catalyst and the oxidizable oxygen storage coefficient Kosa. A flowchart showing the calculation flow of the amount of oxidizable oxygen stored in the internal combustion engine of the third embodiment. A characteristic diagram showing the correlation between the integrated value of the change in the output signal of the second air-fuel ratio sensor (DAFR) and the oxidizable oxygen storage correction coefficient kaOS.

[0008] Hereinafter, an embodiment of the present invention will be described in detail with reference to the drawings. Figure 1 is a schematic diagram illustrating the system configuration of an internal combustion engine 1 to which the present invention is applied.

[0009] The internal combustion engine 1 is mounted in a so-called series hybrid vehicle (not shown) in which the drive wheels (not shown) are driven by an electric motor (not shown). That is, the internal combustion engine 1 is mounted in the vehicle for power generation, and is operated to generate electricity using an on-board generator (not shown) when the battery charge of the on-board battery (not shown) becomes low. The internal combustion engine 1 is, for example, a spark-ignition internal combustion engine that uses gasoline as fuel and is connected to the generator.

[0010] In the exhaust passage 2 of the internal combustion engine 1, a first catalyst 3, an electric heat-controlled catalyst (EHC) 4, and a second catalyst 5 are arranged from upstream in the direction of exhaust flow. The first catalyst 3 and the electric heat-controlled catalyst 4 constitute, for example, a manifold catalyst located near the outlet of the exhaust manifold in the exhaust passage 2. The second catalyst 5 is, for example, an underbody catalyst located under the floor of the vehicle.

[0011] The first catalyst 3 and the second catalyst 5 are, for example, three-way catalysts. A three-way catalyst can simultaneously purify NOx, HC, and CO in the exhaust gas with maximum conversion efficiency when the air-fuel ratio is within the so-called window centered around the stoichiometric air-fuel ratio.

[0012] The electrically heated catalyst 4 is a catalyst that generates heat when electricity is passed through it. For example, it has a structure in which a ceramic heating element that generates heat when electricity is passed through it is used as a catalyst support, and an appropriate catalytic metal that serves as a ternary catalyst or oxidation catalyst is coated onto its surface in a slurry.

[0013] Furthermore, in the exhaust passage 2, a first air-fuel ratio sensor 6 is provided upstream of the first catalyst 3 in the direction of exhaust flow, and a second air-fuel ratio sensor 7 is provided downstream of the electrically heated catalyst 4 in the direction of exhaust flow. The first air-fuel ratio sensor 6 is, for example, a so-called wide-range sensor having a nearly linear output characteristic according to the exhaust air-fuel ratio. The second air-fuel ratio sensor 7 is, for example, a sensor that detects only rich or lean air-fuel ratios by changing its output voltage ON / OFF (rich, lean) in a narrow range near the stoichiometric air-fuel ratio.

[0014] Here, the supply of power to the electrically heated catalyst 4 is controlled by the control unit 10, which acts as the control unit. In other words, the catalyst temperature of the electrically heated catalyst 4 can be controlled by the control unit 10.

[0015] The control unit 10 is a well-known digital computer equipped with a CPU, ROM, RAM, and an input / output interface. Furthermore, when a predetermined power generation request is received, the control unit 10 drives the internal combustion engine 1 to start power generation by the generator.

[0016] The control unit 10 receives input from various sensors for various control and calculation purposes, including the detection signals from the first air-fuel ratio sensor 6 and the second air-fuel ratio sensor 7 mentioned above, as well as output signals from various sensors such as an airflow meter 11 for detecting the intake air volume of the internal combustion engine 1, an outside air temperature sensor 12 for detecting the outside air temperature, and a vehicle speed sensor 13 for detecting the vehicle speed.

[0017] The control unit 10 then determines the fuel injection amount at the start of the internal combustion engine 1 based on the amount of oxidizable oxygen stored in the electric heating catalyst 4 that can be used for oxidation when the internal combustion engine 1 is started, based on the temperature information of the electric heating catalyst 4 (for example, the catalyst temperature of the electric heating catalyst 4).

[0018] In the first embodiment, as detailed below, if the temperature of the electric heating catalyst 4 at the time of starting the internal combustion engine 1 is lower than a predetermined temperature (for example, the activation temperature of the electric heating catalyst 4) based on the temperature information of the electric heating catalyst 4, the amount of oxidizable oxygen stored is considered to be small, and the air-fuel ratio at the time of starting the internal combustion engine 1 is set to the stoichiometric air-fuel ratio. Furthermore, in the first embodiment, if the temperature of the electric heating catalyst 4 at the time of starting the internal combustion engine 1 is above a predetermined temperature (for example, the activation temperature of the electric heating catalyst 4) based on the temperature information of the electric heating catalyst 4, the amount of fuel injected at the time of starting the internal combustion engine 1 is determined according to the amount of oxidizable oxygen stored in the electric heating catalyst 4 that can be used for oxidation at the time of starting the internal combustion engine 1.

[0019] Furthermore, after starting the internal combustion engine 1, the air-fuel ratio is controlled by air-fuel ratio feedback control based on the output signals from the first air-fuel ratio sensor 6 and the second air-fuel ratio sensor 7, for example, so that the exhaust air-fuel ratio becomes the stoichiometric air-fuel ratio.

[0020] Figure 2 is a flowchart showing the control flow during startup of the internal combustion engine 1 in the first embodiment.

[0021] In step S11, the amount of oxygen stored in the electrically heated catalyst 4 of the internal combustion engine 1 is detected. More specifically, if the internal combustion engine 1 is stopped, the amount of oxygen stored when the internal combustion engine 1 was stopped is detected. If the internal combustion engine 1 is running, the amount of oxygen stored is detected, for example, from the output signals of the air-fuel ratio sensors 6 and 7 before and after the electrically heated catalyst 4 and the intake air volume.

[0022] In step S12, the temperature of the electrically heated catalyst 4 after the vehicle's ignition switch is turned on is detected. If the catalyst temperature of the electrically heated catalyst 4 is low, preheating is performed by energizing it before starting the internal combustion engine 1. The temperature of the electrically heated catalyst 4 is estimated using, for example, the amount of electricity supplied to the electrically heated catalyst 4, the vehicle speed, the ambient temperature, etc.

[0023] In step S13, the amount of oxidizable oxygen stored is calculated. The amount of oxidizable oxygen stored changes depending on the catalyst temperature of the electric heating catalyst 4. Figure 3 is a characteristic diagram showing the correlation between the catalyst temperature of the electric heating catalyst 4 and the amount of oxidizable oxygen stored. The characteristic line shown as a solid line in Figure 3 shows the amount of oxidizable oxygen stored when a large amount of oxygen is stored in the electric heating catalyst 4 when the internal combustion engine 1 is stopped. The characteristic line shown as a dashed line in Figure 3 shows the amount of oxidizable oxygen stored when a small amount of oxygen is stored in the electric heating catalyst 4 when the internal combustion engine 1 is stopped.

[0024] The amount of oxidizable oxygen stored in the electrically heated catalyst 4 increases when the catalyst temperature of the electrically heated catalyst 4 exceeds its activation temperature. Furthermore, the amount of oxidizable oxygen stored in the electrically heated catalyst 4 increases with the amount of oxygen stored in the electrically heated catalyst 4 when the internal combustion engine 1 was stopped immediately beforehand.

[0025] In step S14, the target air-fuel ratio at the start of the internal combustion engine 1 is calculated as shown in equation (1) below.

[0026] [Equation 1] Target air-fuel ratio = 14.7 + min(Oxidizable oxygen storage, (Oxygen storage - Target oxygen storage amount)) × K ... (1) That is, the target air-fuel ratio in the first embodiment is obtained by comparing the value obtained by subtracting the target oxygen storage amount from the oxygen storage amount with the oxidizable oxygen storage amount, multiplying the smaller value (selectlow) by the coefficient K, and adding "14.7". Here, the oxidizable oxygen storage amount is calculated in step S13. The oxygen storage amount is detected in step S11. The target oxygen storage amount is a predetermined amount (predetermined value) set in advance. K is a coefficient for converting the oxygen amount to a value equivalent to the air-fuel ratio.

[0027] The amount of oxidizable oxygen stored becomes zero when the catalyst temperature of the electrically heated catalyst 4 is lower than its activation temperature. Therefore, the target air-fuel ratio becomes the stoichiometric air-fuel ratio when the catalyst temperature of the electrically heated catalyst 4 is lower than its activation temperature.

[0028] Figure 4 is a timing chart showing an example of changes in various state variables during the startup of the internal combustion engine 1. Time t1 in Figure 4 is the timing when the vehicle's ignition switch is turned on, and also the timing when preheating begins by energizing the electric heating catalyst 4. Time t2 in Figure 4 is the timing when the catalyst temperature of the electric heating catalyst 4 reaches the activation temperature, and the conditions for allowing the internal combustion engine 1 to start are met. Time t3 in Figure 4 is the timing when the operation of the internal combustion engine 1 begins in order to generate power in response to battery demand.

[0029] In Figure 4, the solid lines indicate the air-fuel ratio, oxygen storage capacity, and oxidizable oxygen storage capacity when the amount of oxygen absorbed by the electric heating catalyst 4 is high when the internal combustion engine 1 is stopped prior to ignition-on. In Figure 4, the dashed lines indicate the air-fuel ratio, oxygen storage capacity, and oxidizable oxygen storage capacity when the amount of oxygen absorbed by the electric heating catalyst 4 is low when the internal combustion engine 1 is stopped prior to ignition-on.

[0030] If a large amount of oxygen is absorbed by the electrically heated catalyst 4 when the internal combustion engine 1 is stopped prior to ignition-on, the air-fuel ratio at startup (immediately after startup) is controlled to be richer than the stoichiometric air-fuel ratio. Conversely, if a small amount of oxygen is absorbed by the electrically heated catalyst 4 when the internal combustion engine 1 is stopped prior to ignition-on, the air-fuel ratio at startup (immediately after startup) is controlled to be leaner than the stoichiometric air-fuel ratio.

[0031] Furthermore, if the amount of oxygen absorbed by the electrically heated catalyst 4 when the internal combustion engine 1 is stopped prior to ignition-on is uncertain, the air-fuel ratio at startup (immediately after startup) is controlled to be leaner than the stoichiometric air-fuel ratio.

[0032] In the internal combustion engine 1 of this first embodiment, by predicting the amount of oxygen that is absorbed into the electrically heated catalyst 4 before starting the internal combustion engine 1 and can be used for the oxidation of hydrocarbons in the exhaust gas when the internal combustion engine 1 starts up, it is possible to suppress the deterioration of exhaust performance when the internal combustion engine 1 starts up and improve exhaust performance.

[0033] Furthermore, if the temperature of the electrically heated catalyst 4 at the time of starting the internal combustion engine 1 is lower than a predetermined temperature (for example, the activation temperature of the electrically heated catalyst 4), the internal combustion engine 1 sets the air-fuel ratio at the time of starting the internal combustion engine 1 to the stoichiometric air-fuel ratio.

[0034] When the amount of oxidizable oxygen stored in the electrically heated catalyst 4 is low, i.e., when the electrically heated catalyst 4 is not activated, the internal combustion engine 1 sets the air-fuel ratio to the stoichiometric air-fuel ratio. This allows the internal combustion engine 1 to suppress HC and CO emissions downstream of the electrically heated catalyst 4 and improve exhaust performance.

[0035] The internal combustion engine 1 determines the amount of fuel injected at startup based on the temperature information of the electric heating catalyst 4 (for example, the catalyst temperature of the electric heating catalyst 4) if the temperature of the electric heating catalyst 4 at startup is above a predetermined temperature (for example, the activation temperature of the electric heating catalyst 4). This determines the amount of fuel injected at startup based on the amount of oxidizable oxygen stored in the electric heating catalyst 4 that can be used for oxidation at startup. As a result, the internal combustion engine 1 can set the air-fuel ratio at startup based on the amount of oxidizable oxygen stored in the electric heating catalyst 4, thereby suppressing the emission of HC and CO from the internal combustion engine 1 and improving exhaust performance.

[0036] Other embodiments of the present invention will be described below. Note that components identical to those in the first embodiment described above are denoted by the same reference numerals, and redundant descriptions are omitted.

[0037] A second embodiment of the present invention will be described using Figures 5 and 6. The internal combustion engine 1 of the second embodiment has substantially the same configuration as the internal combustion engine 1 of the first embodiment described above, but in calculating the target air-fuel ratio at startup, the target air-fuel ratio at startup is calculated using the oxidizable oxygen storage coefficient Kosa, rather than the amount of oxidizable oxygen storage that can be used for oxidation at the time of startup of the internal combustion engine 1.

[0038] Figure 5 is a flowchart showing the control flow during startup of the internal combustion engine 1 in the second embodiment.

[0039] In step S21, the oxygen storage amount stored in the electric heating catalyst 4 of the internal combustion engine 1 is detected. Specifically, if the internal combustion engine 1 is stopped, the oxygen storage amount stored when the internal combustion engine 1 is stopped is detected. If the internal combustion engine 1 is in operation, for example, the oxygen storage amount is detected from the output signals of the air-fuel ratio sensors 6 and 7 before and after the electric heating catalyst 4 and the intake air amount.

[0040] In step S22, the temperature of the electric heating catalyst 4 after the ignition switch of the vehicle is turned on is detected. The temperature of the electric heating catalyst 4 is estimated using, for example, the amount of electric power input to the electric heating catalyst 4, the vehicle speed, the outside air temperature, etc.

[0041] In step S23, the oxidizable oxygen storage amount coefficient Kosa is calculated. The oxidizable oxygen storage amount coefficient Kosa varies depending on the catalyst temperature of the electric heating catalyst 4. FIG. 6 is a characteristic diagram showing the correlation between the catalyst temperature of the electric heating catalyst 4 and the oxidizable oxygen storage amount coefficient Kosa.

[0042] The oxidizable oxygen storage amount coefficient Kosa increases when the catalyst temperature of the electric heating catalyst 4 exceeds the activation temperature. The minimum value of the oxidizable oxygen storage amount coefficient Kosa of the electric heating catalyst 4 is "0", and the maximum value is "1".

[0043] In step S24, the target air-fuel ratio at the start of the internal combustion engine 1 is calculated as follows in the following formula (2).

[0044] [Equation 2] Target air-fuel ratio = 14.7 + (oxygen storage amount - target stored oxygen amount) × oxidizable oxygen storage amount coefficient Kosa × K... (2) That is, the target air-fuel ratio of the second embodiment is obtained by subtracting the target stored oxygen amount from the oxygen storage amount, multiplying by the oxidizable oxygen storage amount coefficient Kosa and the coefficient K, and adding "14.7". Here, the oxidizable oxygen storage amount coefficient Kosa is calculated in step S23. The oxygen storage amount is detected in step S21. The target stored oxygen amount is a predetermined amount (predetermined value) set in advance. K is a coefficient for converting the amount of oxygen into a value equivalent to the air-fuel ratio.

[0045] The oxygen storage coefficient Kos of oxidizable oxygen becomes zero when the catalyst temperature of the electric heating catalyst 4 is lower than the activation temperature. Therefore, the target air-fuel ratio becomes the theoretical air-fuel ratio when the catalyst temperature of the electric heating catalyst 4 is lower than the activation temperature.

[0046] Such an internal combustion engine 1 of the second embodiment can exhibit substantially the same operational effects as the internal combustion engine 1 of the first embodiment described above.

[0047] A third embodiment of the present invention will be described with reference to FIGS. 7 to 8. The internal combustion engine 1 of the third embodiment has substantially the same configuration as the internal combustion engine 1 of the first embodiment described above, but when calculating the target air-fuel ratio at startup, the amount of oxidizable oxygen that can be used for oxidation at startup of the internal combustion engine 1 is calculated using the change amount of the output signal of the second air-fuel ratio sensor 7. That is, the control flow of the internal combustion engine 1 at startup in the third embodiment is substantially the same as that of the first embodiment described above, but the content of step S13 in FIG. 2 is different from that of the first embodiment.

[0048] FIGS. The flowchart which shows the flow of calculation of the oxygen storage amount of the oxidizable oxygen of the internal combustion engine 1 in a 3rd Example.

[0049] In step S31, it is determined whether or not the electric heating catalyst 4 is being preheated. In step S31, if the electric heating catalyst 4 is not being preheated, the process proceeds to step S32, and if the electric heating catalyst 4 is being preheated, the process proceeds to step S By step S37, the oxidizable oxygen storage amount correction coefficient kaOS is set to "1", and the process proceeds to step S38.

[0050] In step S32, it is determined whether or not the temperature of the electric heating catalyst 4 is higher than a preset predetermined temperature (for example, the activation temperature of the electric heating catalyst 4). In step S32, if the temperature of the electric heating catalyst 4 is not higher than the predetermined temperature, the process proceeds to step S33, and if the temperature of the electric heating catalyst 4 is higher than the predetermined temperature, the process proceeds to step S38.

[0051] In step S33, the output signal (AFR) of the second air-fuel ratio sensor 7 is detected.

[0052] In step S34, it is determined whether the output signal of the second air-fuel ratio sensor 7 detected this time is smaller than the output signal of the second air-fuel ratio sensor 7 detected last time. If, in step S34, the output signal of the second air-fuel ratio sensor 7 detected this time is smaller than the output signal of the second air-fuel ratio sensor 7 detected last time, the process proceeds to step S35.

[0053] In step S35, DAFR, which is the integrated value of the change in the output signal of the second air-fuel ratio sensor 7, is calculated. DAFR is calculated by subtracting the output signal of the second air-fuel ratio sensor 7 detected this time from the previous value of the output signal of the second air-fuel ratio sensor 7, and adding the previous value of DAFR.

[0054] In step S36, the oxidizable oxygen storage correction coefficient kaOS is calculated using the integrated value (DAFR) of the change in the output signal of the second air-fuel ratio sensor 7. The oxidizable oxygen storage correction coefficient kaOS changes depending on the integrated value (DAFR) of the change in the output signal of the second air-fuel ratio sensor 7.

[0055] Figure 8 is a characteristic diagram showing the correlation between the integrated value of the change in the output signal of the second air-fuel ratio sensor 7 (DAFR) and the oxidizable oxygen storage correction coefficient kaOS. The oxidizable oxygen storage correction coefficient KaOS increases as the integrated value of the change in the output signal of the second air-fuel ratio sensor 7 (DAFR) increases. The minimum value of the oxidizable oxygen storage correction coefficient kaOS is "0" and the maximum value is "1".

[0056] If the process does not proceed from step S34 to step S35, in step S36, the oxidizable oxygen storage correction coefficient kaOS is calculated using the previous value of the integrated value (DAFR) of the change in the output signal of the second air-fuel ratio sensor 7.

[0057] In step S38, the amount of oxygen stored is calculated by multiplying the amount of oxygen stored detected in step S11 in Figure 2 by the oxidizable oxygen storage correction coefficient kaOS.

[0058] The internal combustion engine 1 of this third embodiment can achieve substantially the same effects as the internal combustion engine 1 of the first embodiment described above.

[0059] The internal combustion engine 1 starts only after the temperature of the electrically heated catalyst 4 reaches a temperature that evaporates condensed water. Therefore, by using the output signal of the second air-fuel ratio sensor 7 before the internal combustion engine 1 starts and after the temperature of the electrically heated catalyst 4 reaches a predetermined temperature (for example, the activation temperature of the electrically heated catalyst 4), the amount of oxidizable oxygen stored in the electrically heated catalyst 4 can be predicted before the internal combustion engine 1 starts, and the predicted amount of oxidizable oxygen stored can be used for air-fuel ratio control when the internal combustion engine 1 starts (immediately after starting).

[0060] Furthermore, oxygen surrounding the electro-heated catalyst 4 and the first and second air-fuel ratio sensors 6 and 7 adjacent to the electro-heated catalyst 4 is adsorbed onto the electro-heated catalyst 4 when its temperature rises and it becomes activated. As a result, when the temperature of the electro-heated catalyst 4 rises and it becomes activated, the output signals of the first and second air-fuel ratio sensors 6 and 7 change from a state where they remain unchanged to a state where they change.

[0061] As a result, the amount of oxidizable oxygen stored in the electric heating catalyst 4 that can be used for oxidation when starting the internal combustion engine 1 can be predicted by utilizing the change in the output signal of at least one of the first air-fuel ratio sensor 6 and the second air-fuel ratio sensor 7.

[0062] The amount of oxidizable oxygen stored in the electric heating catalyst 4 that can be used for oxidation when the internal combustion engine 1 is started is predicted to be large, for example, when the internal combustion engine 1 is stopped or the electric heating catalyst 4 is energized, and the greater the amount of change to the lean side, or the greater the cumulative value of the change to the lean side, if the output signals of the first air-fuel ratio sensor 6 and the second air-fuel ratio sensor 7 change to the lean side.

[0063] Although specific embodiments of the present invention have been described above, the present invention is not limited to the embodiments described above, and various modifications are possible without departing from the spirit of the invention.

[0064] For example, the temperature of the electric heating catalyst 4 may be estimated using the heat capacity of the electric heating catalyst 4 and the amount of electricity supplied to the electric heating catalyst 4, or the electrical resistance of the electric heating catalyst 4 may also be estimated.

[0065] For example, when the temperature of the electrically heated catalyst 4 at the time of starting the internal combustion engine 1 is lower than a predetermined temperature (for example, the activation temperature of the electrically heated catalyst 4), the air-fuel ratio at the time of starting the internal combustion engine 1 may be set to be leaner than the stoichiometric air-fuel ratio. In other words, when the amount of oxidizable oxygen stored in the electrically heated catalyst 4 is small, that is, when the electrically heated catalyst 4 is not activated, the air-fuel ratio may be set to be leaner than the stoichiometric air-fuel ratio.

[0066] For example, the second air-fuel ratio sensor 7 may be a so-called wide-range sensor having an output characteristic that is almost linear according to the exhaust air-fuel ratio.

[0067] For example, the amount of oxidizable oxygen stored may be calculated using at least one of the following: the change in the output signal of at least one of the first air-fuel ratio sensor 6 and the second air-fuel ratio sensor 7, or the integral value of the change in the output signal of at least one of the first air-fuel ratio sensor 6 and the second air-fuel ratio sensor 7.

[0068] For example, if the output signals of the first air-fuel ratio sensor 6 and the second air-fuel ratio sensor 7 do not change even when the temperature of the electric heating catalyst 4 reaches a predetermined temperature (e.g., the activation temperature of the electric heating catalyst 4), it may be determined that there is a large amount of oxidizable oxygen stored in the electric heating catalyst 4 that can be used for oxidation when the internal combustion engine 1 is started, and the amount of oxidizable oxygen stored in the electric heating catalyst 4 may be estimated based on the temperature of the electric heating catalyst 4. In this case, it is estimated that the amount of oxidizable oxygen stored in the electric heating catalyst 4 is greater as the catalyst temperature of the electric heating catalyst 4 increases. This makes it possible to suppress the increase in NOx due to insufficient supply of reducing agent.

[0069] For example, the internal combustion engine 1 may be installed in a so-called parallel hybrid vehicle. Alternatively, the internal combustion engine 1 may be installed in a non-hybrid vehicle that is in a state where the rotation of the crankshaft can always be transmitted as driving force to the vehicle's drive wheels while it is in motion.

[0070] 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, comprising an electrically heated catalyst placed in the exhaust passage of the internal combustion engine that generates heat when an electric current is passed through it, wherein the amount of fuel injected at the time of starting the internal combustion engine is determined according to the amount of oxidizable oxygen stored in the electrically heated catalyst that can be used for oxidation at the time of starting the internal combustion engine, based on the temperature information of the electrically heated catalyst.

2. The method for controlling an internal combustion engine according to claim 1, wherein, based on the temperature information of the electric heating catalyst, when the temperature of the electric heating catalyst at the time of starting the internal combustion engine is lower than a predetermined temperature, the air-fuel ratio at the time of starting the internal combustion engine is set to the stoichiometric air-fuel ratio or leaner than the stoichiometric air-fuel ratio.

3. The method for controlling an internal combustion engine according to claim 2, wherein, based on the temperature information of the electric heating catalyst, when the temperature of the electric heating catalyst at the time of starting the internal combustion engine is above a predetermined temperature, the amount of fuel injected at the time of starting the internal combustion engine is determined according to the amount of oxidizable oxygen stored in the electric heating catalyst that can be used for oxidation at the time of starting the internal combustion engine.

4. A method for controlling an internal combustion engine according to claim 1, comprising: a first air-fuel ratio sensor located upstream of the electric heating catalyst in the exhaust flow direction for detecting the air-fuel ratio of the exhaust; and a second air-fuel ratio sensor located downstream of the electric heating catalyst in the exhaust flow direction for detecting the air-fuel ratio of the exhaust, wherein the amount of oxidizable oxygen stored in the electric heating catalyst that can be used for oxidation when starting the internal combustion engine is estimated using at least one of the change in the output signal of at least one of the first air-fuel ratio sensor and the second air-fuel ratio sensor, or the integral value of the change in the output signal of at least one of the first air-fuel ratio sensor and the second air-fuel ratio sensor.

5. The method for controlling an internal combustion engine according to claim 4, wherein if the output signals of the first air-fuel ratio sensor and the second air-fuel ratio sensor do not change even when the temperature of the electric heating catalyst reaches a predetermined temperature or higher, it is determined that there is a large amount of oxidizable oxygen stored in the electric heating catalyst that can be used for oxidation when starting the internal combustion engine, and the amount of oxidizable oxygen stored in the electric heating catalyst is estimated based on the temperature of the electric heating catalyst.

6. A method for controlling an internal combustion engine according to claim 4, wherein the amount of oxidizable oxygen stored in the electric heating catalyst is estimated using at least one of the amount of change in the output signal of the second air-fuel ratio sensor or the integral value of the amount of change in the output signal of the second air-fuel ratio sensor.

7. The method for controlling an internal combustion engine according to any one of claims 1 to 6, wherein the internal combustion engine is mounted on a vehicle for power generation.

8. A control device for an internal combustion engine, comprising: an electrically heated catalyst placed in the exhaust passage of the internal combustion engine and generating heat when an electric current is passed through it; and a control unit that determines the amount of fuel injected at the start of the internal combustion engine according to the amount of oxidizable oxygen stored in the electrically heated catalyst that can be used for oxidation at the start of the internal combustion engine, based on the temperature information of the electrically heated catalyst.

Images