Internal combustion engine control method and control device

Abstract

An internal combustion engine (1) has an electrically heated catalyst (5) in an exhaust passage (2). If it is detected that a vehicle door is open, the electrically heated catalyst (5) is preheated. If power to an engine controller (8) is lost during preheating, information on an estimated temperature held by the engine controller (8) is lost. After power is restored, the engine controller (8) prohibits powering on the electrically heated catalyst (5) until a cooling period for lowering the temperature of the electrically heated catalyst (5) has passed. After the cooling period has passed, preheating is resumed.

Description

Technical Field

[0001] The present invention relates to a control method and a control device for an internal combustion engine having an electrically heated catalyst in an exhaust system. Background Art

[0002] It is known to use an electrically heated catalyst that can be forcibly heated by energizing the exhaust system to improve the exhaust performance of an internal combustion engine immediately after cold start. The electrically heated catalyst is preheated by energizing the catalyst before the internal combustion engine is started, thereby achieving an exhaust purification effect as soon as possible after starting.

[0003] Patent document 1 discloses that the electrically heated catalyst is energized until the total energization amount reaches the target energization amount. In addition, a structure is formed such that, when the energization is interrupted in response to a start request of the internal combustion engine, the energization amount after restarting the preheating is increased in consideration of the cooling amount during the preheating interruption.

[0004] It is usually difficult to directly detect the temperature of the electrically heated catalyst. For example, the temperature of the electrically heated catalyst during preheating is estimated sequentially by accumulating the amount of power supplied after the start of power supply. However, if the power supply of the engine controller is temporarily lost due to some unforeseen reason during preheating, the information of the estimated temperature will be lost. Therefore, when the power supply is restored, the same preheating as in the usual cold start is performed from the initial state. If the electrically heated catalyst is restarted to maintain a high temperature for preheating, the electrically heated catalyst may be overheated and cause a failure of the electrically heated catalyst. Patent Document 1 does not disclose this problem.

[0005] Patent Document 1: Japanese Patent Application Publication No. 2015-075068 Summary of the invention

[0006] According to the present invention, when the estimated temperature information is lost during preheating due to power failure of the engine controller, energization of the electrically heated catalyst is prohibited until a cooling period for lowering the temperature of the electrically heated catalyst has elapsed after power is restored to the engine controller.

[0007] By setting the cooling period in this way, the electrically heated catalyst can be reliably protected by prohibiting energization until the temperature of the electrically heated catalyst drops to a level that does not cause an excessive temperature increase even if normal warm-up is performed. BRIEF DESCRIPTION OF THE DRAWINGS

[0008] Figure 1 It is an explanatory diagram schematically showing the system configuration of the internal combustion engine according to the present invention.

[0009] Figure 2 This is a flowchart showing the processing flow of the first embodiment.

[0010] Figure 3 This is a flowchart showing the processing flow of the second embodiment.

[0011] Figure 4 It is a time chart showing changes in the temperature and SOC of the electrically heated catalyst as time passes during warm-up.

[0012] Figure 5 This is a characteristic diagram showing a state of temperature drop after the energization to the electrically heated catalyst is stopped.

[0013] Figure 6 ΔSOC is a characteristic diagram showing the relationship between the amount of change in SOC ΔSOC and the time tc2 serving as the cooling period.

[0014] Figure 7 It is an explanatory diagram showing the system configuration of an internal combustion engine corresponding to the third embodiment.

[0015] Figure 8 It is a flowchart showing the processing flow of the third embodiment.

[0016] Fig. 9 It is an explanatory diagram showing the system configuration of an internal combustion engine corresponding to the fourth embodiment.

[0017] Fig.10 It is a flowchart showing the processing flow of the fourth embodiment. DETAILED DESCRIPTION

[0018] Figure 1 1 is an explanatory diagram schematically showing the system structure of the internal combustion engine 1 involved in the present invention. The internal combustion engine 1 is, for example, a spark ignition type internal combustion engine that uses gasoline as fuel. In a vehicle that is not a hybrid vehicle, the internal combustion engine 1 is mounted on the vehicle together with a transmission, and the vehicle is directly driven by the output of the internal combustion engine 1. In a so-called parallel hybrid vehicle, the internal combustion engine 1 is mounted on the vehicle together with an electric motor, and both the electric motor and the internal combustion engine 1 are used as a driving source for driving. In a so-called series hybrid vehicle, the internal combustion engine 1 is used to drive a generator, and the electric power generated is used for driving based on the electric motor.

[0019] The internal combustion engine 1 has an intake system (not shown) and an exhaust system. An exhaust passage 2 constituting the exhaust system extends from the internal combustion engine 1 to the rear end of the vehicle. In order to purify the exhaust gas discharged from the internal combustion engine 1, a catalyst device is provided in the exhaust system. As a catalyst device, in the example shown in the figure, it includes: a pre-catalyst 3 provided in the exhaust passage 2 near the outlet of the exhaust manifold 2a; and a main catalyst 4 located at a position further downstream than the pre-catalyst 3 and arranged under the floor of the vehicle.

[0020] The pre-catalyst 3 further includes: an electrically heated catalyst 5 constituting the upstream side portion of the pre-catalyst 3; and a catalyst 6 constituting the downstream side portion, both of which are accommodated in a shell. The electrically heated catalyst 5, for example, uses a heating element that generates heat by energizing as a catalyst carrier, and is formed into a structure in which a suitable catalyst metal of a three-way catalyst or an oxidation catalyst is applied as a slurry on its surface. Alternatively, it can be a structure in which an independent heater is combined with a catalyst carrier. The catalyst 6, for example, is coated with a suitable catalyst metal of a three-way catalyst or an oxidation catalyst as a slurry on the surface of a monolithic ceramic carrier formed with fine passages.

[0021] Similar to the catalyst 6 , the main catalyst 4 has a structure in which an appropriate catalyst metal of a three-way catalyst or an oxidation catalyst is applied as a slurry on the surface of a monolithic ceramic carrier having fine passages, for example.

[0022] Furthermore, a particulate filter for collecting exhaust particulates may be combined with the pre-catalyst 3 and part of the main catalyst 4 .

[0023] The energization of the electrically heated catalyst 5 is controlled by the engine controller 8. In addition, in the example shown in the figure, the engine controller 8 uses a 12-volt battery (not shown) that supplies power to general electrical components of the vehicle as a power source, while the electrically heated catalyst 5 uses a 48-volt battery (not shown) that can supply more power as a power source. The electrically heated catalyst 5 receives power supply from the 48-volt battery via a relay, a switching element, etc. In addition, a 12-volt battery can be used as a power source for the electrically heated catalyst 5.

[0024] The engine controller 8 performs various controls of the internal combustion engine 1, represented by the control of the fuel injection amount and injection timing based on the fuel injection valve (not shown) of the internal combustion engine 1, the control of the ignition timing based on the spark plug (not shown), the opening control of the throttle valve (not shown), etc. As one of the controls of the internal combustion engine 1, the energization of the electrically heated catalyst 5 for preheating during cold start is controlled. A plurality of detection signals are input to the engine controller 8 from various sensors and other controllers. For example, as representative sensors, detection signals of an air flow meter 11 for detecting the intake air amount of the internal combustion engine 1, a crank angle sensor 12 for detecting the rotation speed of the internal combustion engine 1, a water temperature sensor 13 for detecting the cooling water temperature, an oil temperature sensor 14 for detecting the lubricating oil temperature, and an air-fuel ratio sensor 15 for detecting the exhaust air-fuel ratio in the exhaust passage 2 for air-fuel ratio feedback control are input to the engine controller 8. In addition, the battery controller 16 that monitors the state of the 48V battery that supplies power to the electrically heated catalyst 5 supplies a signal indicating the charge level of the 48V battery, i.e., the SOC, to the engine controller 8. Furthermore, as a trigger condition for starting preheating before starting the internal combustion engine 1, a door switch 17 that detects the opening action of the driver's door of the vehicle is connected to the engine controller 8.

[0025] In this embodiment, basically, when the driver's door of the vehicle is opened, the electric heating catalyst 5 starts to be energized, that is, the preheating of the electric heating catalyst 5 starts. In addition, when the cooling water temperature or the like indicates that the vehicle is in a warm-up state, the preheating is not performed. After the preheating starts, the temperature of the electric heating catalyst 5 is estimated successively by accumulating the amount of energization of the electric heating catalyst 5 or the like. If the estimated temperature reaches a predetermined temperature, it is determined that the preheating is completed and the energization of the electric heating catalyst 5 is terminated.

[0026] During this preheating process, if the power supply of the engine controller 8 is temporarily lost due to some unforeseen reason before the normal preheating is completed, the estimated temperature information will be lost. In this case, if the normal preheating is restarted when the power supply is restored, the temperature of the electrically heated catalyst 5 may be too high, which is not preferred. Examples of the power supply loss of the engine controller 8 include replacement of the 12-volt battery that is the power supply of the engine controller 8, disconnection of the power supply line, and instantaneous voltage drop.

[0027] In the present invention, in order to protect the electrically heated catalyst 5 from such a temporary power loss, the start of warm-up is permitted after the temperature of the electrically heated catalyst 5 is temporarily lowered.

[0028] Figure 21 is a flowchart showing the processing flow of the first embodiment. In addition, the flowchart is not a diagram showing the computer program itself, but an illustrative flowchart showing the processing flow in time series. First, if it is detected that the driver's door is open, the energization, i.e., preheating, of the electrically heated catalyst 5 (abbreviated as EHC in the flowchart, etc.) is started (step 1). Then, it is determined whether the power loss (cut-off) of the engine controller 8 (abbreviated as ECM in the flowchart, etc.) has occurred (step 2). If the power of the engine controller 8 is not lost until the preheating is completed, the energization is terminated by making the estimated temperature of the electrically heated catalyst 5 reach a predetermined temperature as described above.

[0029] When the power of the engine controller 8 is cut off, the power supply to the electrically heated catalyst 5 is stopped accordingly (step 3). Then, if the power of the engine controller 8 is restored (step 4), the engine controller 8 starts measuring the timer t that measures the elapsed time after the moment when the power is restored (step 5). Moreover, the value of the timer t is compared with a predetermined threshold value tc1 that is set in advance (step 6). During the period when the value of the timer t, i.e., the elapsed time after the power is restored, is less than or equal to the threshold value tc1, as shown in step 9, the power supply (preheating) to the electrically heated catalyst 5 is prohibited. In addition, if there is a request to start the internal combustion engine 1 during this period, as shown in step 10, the internal combustion engine 1 is started without preheating the electrically heated catalyst 5.

[0030] If the time t after the power supply is restored exceeds the threshold value tc1, the electrically heated catalyst 5 is energized, i.e., preheated, as usual, as shown in step 7. That is, the preheating after the initial stage when the electrically heated catalyst 5 is considered to be in a cold state is performed again. In addition, the internal combustion engine 1 is started according to the start request of the internal combustion engine 1 (step 8). In addition, the time required for preheating is, for example, about several seconds.

[0031] The threshold value tc1 corresponds to the cooling period of natural heat dissipation, and is set to a sufficient time for the electrically heated catalyst 5 (especially the heater part) to drop to a certain temperature (a temperature that will not cause any obstacles even if the preheating is restarted), assuming that the temperature of the electrically heated catalyst 5 has risen to the preheating completion temperature until the power supply of the engine controller 8 is lost. For example, it is about several tens of seconds to several minutes. That is, it is impossible to measure the time from the power loss to the power restoration, so the cooling period is fixedly set for the required time considering the possibility that the electrically heated catalyst 5 is near the preheating completion temperature when the power supply is restored.

[0032] Thus, in the first embodiment, when the information of the estimated temperature is lost during preheating due to power loss of the engine controller 8, power supply to the electrically heated catalyst 5 is prohibited until a cooling period for lowering the temperature of the electrically heated catalyst 5 has elapsed after power recovery of the engine controller 8. Therefore, excessive increase in the temperature of the electrically heated catalyst 5 due to re-preheating (power supply) is avoided.

[0033] Next, Figure 3 1 is a flowchart showing the processing flow of the second embodiment. Steps 11 to 15 are similar to steps 1 to 5 of the first embodiment. If it is detected that the driver's door is open, the electric heating catalyst 5 is energized, i.e., preheated (step 11). Then, it is determined whether the power supply of the engine controller 8 is lost (cut off) (step 12).

[0034] When the power supply of the engine controller 8 is cut off, the power supply to the electrically heated catalyst 5 is stopped (step 13). Then, if the power supply of the engine controller 8 is restored (step 14), the engine controller 8 starts measuring the timer t for measuring the elapsed time after the power supply is restored (step 15).

[0035] Here, in the second embodiment, as a parameter representing the amount of power supplied to the electrically heated catalyst 5 from the start of power supply to the electrically heated catalyst 5 until power supply is interrupted (power supply to the engine controller 8 is lost), the change ΔSOC of the SOC of the 48-volt battery is calculated, and based on the ΔSOC, a threshold value tc2 corresponding to the cooling period is determined (step 16).

[0036] The subsequent process is the same as that of the first embodiment. In step 17, the value of the timer t is compared with the threshold value tc2. During the period when the value of the timer t, i.e., the elapsed time after the power supply is restored, is less than or equal to the threshold value tc2, as shown in step 20, the energization (preheating) of the electrically heated catalyst 5 is prohibited. In addition, if there is a request to start the internal combustion engine 1 during this period, as shown in step 21, the internal combustion engine 1 is started without preheating the electrically heated catalyst 5.

[0037] If the time t after the power supply is restored exceeds the threshold value tc2, the electrically heated catalyst 5 is energized, i.e., preheated as usual, as shown in step 18. That is, the preheating after the initial stage when the electrically heated catalyst 5 is considered to be in a cold state is performed again. Then, the internal combustion engine 1 is started according to the start request of the internal combustion engine 1 (step 19).

[0038] In the second embodiment, the cooling period, which is the waiting time until the preheating is restarted, is set shorter than in the first embodiment. Figure 4The figure shows the change of SOC and the electrically heated catalyst 5 (particularly the heater part thereof) according to the time elapsed after the start of energization before the power supply is lost. As shown in the figure, as the preheating starts by the opening action of the driver's door, the temperature of the electrically heated catalyst 5 gradually increases, and the charge amount of the 48-volt battery, that is, the SOC, gradually decreases. If the power supply of the engine controller 8 is lost, the temperature (estimated temperature) of the electrically heated catalyst 5 thereafter is unknown. On the other hand, regarding SOC, the value SOC1 of SOC at the start of energization is stored in the non-volatile memory of the engine controller 8 or the battery controller 16. Moreover, the value SOC2 of SOC at the time of power recovery is estimated by the battery controller 16, for example, based on the voltage of the 48-volt battery. Therefore, the difference ΔSOC (= SOC1-SOC2) between the two can be obtained, and the change amount ΔSOC of the SOC is basically related to the amount of heat applied to the electrically heated catalyst 5 during the period from the start of preheating to the loss of power supply, and thus the temperature of the electrically heated catalyst 5 at the time of power loss.

[0039] The temperature of the electrically heated catalyst 5 at the time of power recovery cannot be accurately known, but at least it will not exceed the temperature at the time of power loss. Figure 5 The temperature at the time of power recovery of the electrically heated catalyst 5 and the temperature change accompanying the natural cooling time thereafter are shown. The higher the estimated temperature at the time of power recovery, the longer it takes to decrease to a certain temperature (a temperature that will not cause any hindrance even if preheating is restarted). The numerical values ​​in the figure are only examples.

[0040] Therefore, according to this relationship, Figure 6 As shown, the time serving as the threshold value tc2 can be set according to the amount of change ΔSOC in SOC, and a larger threshold value tc2 is set as the amount of change ΔSOC increases.

[0041] Thus, in the second embodiment described above, the temperature of the electrically heated catalyst 5 at the time of power failure is estimated and set as the threshold value tc2 for the cooling period. Therefore, the cooling period as the waiting time until the preheating is restarted is shorter than that of the first embodiment based on the preheating completion temperature, and the preheating can be restarted as early as possible.

[0042] Next, Figure 8 A flowchart showing the third embodiment, in addition, Figure 7 The system configuration of the internal combustion engine 1 corresponding to the third embodiment is shown.

[0043] like Figure 7 As shown, the third embodiment is applied to an internal combustion engine 1 driving a generator 21 as a so-called series hybrid vehicle. In the series hybrid vehicle, the driving wheels are driven by a running motor (not shown), and the internal combustion engine 1 is used to generate electricity.

[0044] In the third embodiment, as described later, the internal combustion engine 1 is electrically operated (motoring) using the generator 21 composed of a motor / generator as a driving source during the cooling of the electrically heated catalyst 5. The electrically operated motoring causes gas to flow from the intake system to the exhaust system of the internal combustion engine 1, thereby forcibly cooling the electrically heated catalyst 5.

[0045] In addition, in this embodiment, a temperature sensor 22 for detecting the temperature of the gas passing through the electrically heated catalyst 5 is arranged on the downstream side (exit side) of the electrically heated catalyst 5. In a preferred embodiment, the temperature sensor 22 is arranged in the housing of the pre-catalyst 3 near the boundary between the electrically heated catalyst 5 on the upstream side and the catalyst 6 on the downstream side. If the gas flows through the pre-catalyst 3 by electric operation, the detection value corresponding to the temperature of the electrically heated catalyst 5 is measured by the temperature sensor 22. Therefore, during the period of gas circulation, the temperature of the electrically heated catalyst 5 can be substantially detected by the temperature sensor 22.

[0046] exist Figure 8 In the flowchart, steps 31 to 35 are the same as steps 1 to 5 of the first embodiment. If it is detected that the driver's door is open, the electric heating catalyst 5 is energized, i.e., preheated (step 31). Then, it is determined whether the power supply of the engine controller 8 is lost (cut off) (step 32).

[0047] When the power supply of the engine controller 8 is cut off, the power supply to the electrically heated catalyst 5 is stopped (step 33). Then, if the power supply of the engine controller 8 is restored (step 34), the engine controller 8 starts measuring the timer t for measuring the elapsed time after the power supply is restored (step 35).

[0048] Here, in the third embodiment, the internal combustion engine 1 is powered by the generator 21 (step 36). By the power running, the gas is caused to flow through the electrically heated catalyst 5 as described above, and forced cooling is performed.

[0049] In the next step 37, the value of the timer t is compared with the threshold value tc3. The threshold value tc3 is appropriately set based on the premise of forced cooling based on power operation. During the period when the value of the timer t, i.e., the elapsed time after the power supply is restored, is less than or equal to the threshold value tc3, as shown in step 41, the energization (preheating) of the electrically heated catalyst 5 is prohibited. In addition, if there is a start request for the internal combustion engine 1 during this period, as shown in step 42, the internal combustion engine 1 is started without preheating the electrically heated catalyst 5.

[0050] If the time t after the power supply is restored exceeds the threshold value tc3, the electrically heated catalyst 5 is energized, i.e., preheated as usual, as shown in step 38. That is, the preheating after the initial stage when the electrically heated catalyst 5 is considered to be in a cold state is performed again. Then, the internal combustion engine 1 is started according to the start request of the internal combustion engine 1 (step 39).

[0051] Here, in the third embodiment, the temperature Tec of the electrically heated catalyst 5 detected by the temperature sensor 22 is further compared with the threshold temperature T1 in step 40, and when the temperature Tec of the electrically heated catalyst 5 is less than or equal to the threshold temperature T1 during the period when the elapsed time t is less than or equal to the threshold temperature tc3, the restart of preheating is permitted.

[0052] As described above, in the third embodiment, the electrically heated catalyst 5 can be forcedly cooled by powering the internal combustion engine 1. Therefore, the cooling period as the waiting time until the warm-up is resumed can be shortened compared to the case of natural cooling.

[0053] Furthermore, by generating a gas flow in the exhaust passage 2 by electric operation, the temperature of the electrically heated catalyst 5 can be detected by the downstream temperature sensor 22. Therefore, it is actually possible to detect that the electrically heated catalyst 5 has dropped to the threshold temperature T1 and that warm-up has been resumed.

[0054] In the third embodiment, the threshold value tc3 of the elapsed time t is fixedly set as in the first embodiment, but the threshold value tc3 may be variably set based on the amount of change ΔSOC in SOC as in the second embodiment.

[0055] The third embodiment is not limited to a series hybrid vehicle, but can be applied to any configuration as long as the internal combustion engine 1 can be driven by some external drive source.

[0056] Next, Fig.10 A flowchart showing the fourth embodiment, in addition, Fig. 9 The system configuration of the internal combustion engine 1 corresponding to the fourth embodiment is shown.

[0057] like Fig. 9 As shown, the fourth embodiment is configured to include a secondary air pump 31 capable of supplying secondary air to the electrically heated catalyst 5 in the exhaust passage 2. The secondary air pump 31 is connected to the exhaust passage 2 on the upstream side of the electrically heated catalyst 5 via a secondary air passage 31a.

[0058] In the fourth embodiment, as described later, during the cooling period of the electrically heated catalyst 5 , the secondary air pump 31 is driven, and forced cooling of the electrically heated catalyst 5 is performed based on the circulation of secondary air.

[0059] In addition, in this embodiment, similarly to the third embodiment, a temperature sensor 22 for detecting the temperature of the gas passing through the electrically heated catalyst 5 is arranged on the downstream side (exit side) of the electrically heated catalyst 5. In a preferred embodiment, the temperature sensor 22 is arranged in the housing of the pre-catalyst 3 near the boundary between the electrically heated catalyst 5 on the upstream side and the catalyst 6 on the downstream side. The secondary air flows through the pre-catalyst 3, and similarly to the third embodiment, the temperature of the electrically heated catalyst 5 can be substantially detected by the temperature sensor 22.

[0060] In addition to step 56, Fig.10 Flowchart and Figure 8 That is, if it is detected that the driver's door is open, the electric heating catalyst 5 is energized, i.e., preheated (step 51). Then, it is determined whether the power supply of the engine controller 8 is lost (cut off) (step 52).

[0061] When the power supply of the engine controller 8 is cut off, the power supply to the electrically heated catalyst 5 is stopped (step 53). Then, if the power supply of the engine controller 8 is restored (step 54), the engine controller 8 starts measuring the timer t for measuring the elapsed time after the power supply is restored (step 55).

[0062] Here, in the fourth embodiment, the secondary air pump 31 is operated instead of the electric power operation in the third embodiment (step 56). The supply of the secondary air causes the gas to flow through the electrically heated catalyst 5, thereby forcibly cooling the gas.

[0063] In the next step 57, the value of the timer t is compared with the threshold value tc4. The threshold value tc4 is appropriately set based on the premise of forced cooling based on the secondary air supply. During the period when the value of the timer t, i.e., the elapsed time after the power supply is restored, is less than or equal to the threshold value tc4, as shown in step 51, the energization (preheating) of the electrically heated catalyst 5 is prohibited. In addition, if there is a start request for the internal combustion engine 1 during this period, as shown in step 52, the internal combustion engine 1 is started without preheating the electrically heated catalyst 5.

[0064] If the time t after the power supply is restored exceeds the threshold value tc4, the electrically heated catalyst 5 is energized, i.e., preheated as usual, as shown in step 58. That is, the preheating after the initial stage when the electrically heated catalyst 5 is considered to be in a cold state is performed again. In addition, the internal combustion engine 1 is started according to the start request of the internal combustion engine 1 (step 59).

[0065] In addition, in step 50, the temperature Tec of the electrically heated catalyst 5 detected by the temperature sensor 22 is compared with the threshold temperature T1. During the period when the elapsed time t is less than or equal to the threshold temperature tc4, if the temperature Tec of the electrically heated catalyst 5 is less than or equal to the threshold temperature T1, the restart of preheating is permitted.

[0066] As described above, in the fourth embodiment, the electrically heated catalyst 5 can be forcedly cooled by the secondary air supply. Therefore, the cooling period, which is the waiting time until the warm-up is resumed, can be shortened compared to the case of natural cooling.

[0067] Also, similarly to the third embodiment, the gas flow in the exhaust passage 2 is generated so that the temperature of the electrically heated catalyst 5 can be detected by the downstream temperature sensor 22. Therefore, it is actually possible to detect that the electrically heated catalyst 5 has dropped to the threshold temperature T1 and that warm-up has been resumed.

[0068] In the fourth embodiment, the threshold value tc4 of the elapsed time t is fixedly set as in the first embodiment, but the threshold value tc4 may be variably set based on the amount of change ΔSOC in SOC as in the second embodiment.

Claims

1. A control method for an internal combustion engine, wherein the internal combustion engine has an electrically heated catalyst in an exhaust system, and the electrically heated catalyst is energized to start preheating before the internal combustion engine is started, and the preheating is performed until the estimated temperature of the electrically heated catalyst estimated successively reaches a predetermined temperature, wherein: If the estimated temperature information is lost during warm-up due to power failure of the engine controller, After the power supply of the engine controller is restored, energization of the electrically heated catalyst is prohibited until a cooling period has elapsed for lowering the temperature of the electrically heated catalyst to a level that does not cause an excessive temperature increase even with normal warm-up.

2. The internal combustion engine control method according to claim 1, wherein: The cooling period is fixedly set to a predetermined time required to determine that the electrically heated catalyst is at the predetermined temperature when power is restored.

3. The control method of the internal combustion engine according to claim 1, wherein: The amount of energization of the electrically heated catalyst until power failure is determined based on the battery charge at the start of preheating and the battery charge when power is restored, and the cooling period is variably set to a longer time as the amount of energization increases.

4. The control method of an internal combustion engine according to any one of claims 1 to 3, wherein: During the cooling period, the internal combustion engine is electrically operated by an external driving source to allow air to flow through the electrically heated catalyst.

5. The control method of an internal combustion engine according to any one of claims 1 to 3, wherein: During the cooling period, secondary air is supplied from the upstream side of the electrically heated catalyst in the exhaust system by a secondary air pump.

6. The control method of the internal combustion engine according to claim 4, wherein: A temperature sensor is provided on the downstream side of the electrically heated catalyst, and when it is determined based on the temperature detected by the temperature sensor that the temperature of the electrically heated catalyst has dropped, the cooling period is ended.

7. The control method of the internal combustion engine according to claim 5, wherein: A temperature sensor is provided on the downstream side of the electrically heated catalyst, and when it is determined based on the temperature detected by the temperature sensor that the temperature of the electrically heated catalyst has dropped, the cooling period is ended.

8. A control device for an internal combustion engine, comprising: An internal combustion engine having an electrically heated catalyst in the exhaust system; and An engine controller that energizes an electrically heated catalyst to start preheating before starting an internal combustion engine, and preheats the electrically heated catalyst until an estimated temperature of the electrically heated catalyst estimated successively reaches a predetermined temperature, wherein: The above-mentioned engine controller is constructed as follows, that is, when the information of the estimated temperature is lost during preheating due to the loss of power supply of the engine controller, after the power supply is restored, the power supply to the electrically heated catalyst is prohibited until a cooling period has passed for reducing the temperature of the electrically heated catalyst to a temperature that will not cause an excessive increase in temperature even if normal preheating is performed.

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