Method for estimating temperature of electrically heated catalyst, control method for internal combustion engine , and control device for internal combustion engine

Abstract

An electrically heated catalyst (3) that generates heat as a result of being energized is provided in an exhaust passage (2) of an internal combustion engine (1). The temperature of the electrically heated catalyst (3) is raised up by feeding prescribed warmup electric energy prior to starting the internal combustion engine (1) after operation of a vehicle is initiated by turning on an ignition switch. The temperature of the electrically heated catalyst (3) is estimated using a relationship between the heat capacity of the electrically heated catalyst (3) and the warmup electric energy. The warmup electric energy is corrected according to the heat capacity of the electrically heated catalyst such that the catalyst temperature of the electrically heated catalyst (3) is raised to a prescribed starting catalyst temperature.

Description

Electrically heated catalyst temperature estimation method, internal combustion engine control method, and internal combustion engine control device

[0001] The present invention relates to a method for estimating the temperature of an electrically heated catalyst, a method for controlling an internal combustion engine, and a control device for an internal combustion engine.

[0002] For example, Patent Document 1 discloses a technique for calculating the power supply time required to heat the heater of a heated catalyst to a set temperature based on the known heat capacity of the heated catalyst. In Patent Document 1, power supply to the heated catalyst is terminated either when the power supply time has elapsed since the start of power supply, or when the temperature of the heated catalyst has reached the set temperature.

[0003] However, in Patent Document 1, the actual heat capacity of the heated catalyst may differ from the heat capacity used to calculate the power-on time of the heated catalyst due to product variations. Therefore, if the temperature of the heated catalyst cannot be detected due to a sensor failure or the like, the power-on time of the heated catalyst may be excessively long depending on the calculated power-on time, which may result in the heated catalyst overheating.

[0004] In other words, in electrically heated catalysts such as heated catalysts, there is room for further improvement in order to accurately raise the temperature of the electrically heated catalyst to the desired catalyst temperature, taking into account the variation in heat capacity of the electrically heated catalyst due to product variations.

[0005] Japanese Patent Application Publication No. 4-279718

[0006] In the present invention, the temperature of the electrically heated catalyst is estimated using the heat capacity of the electrically heated catalyst and the amount of power input to the electrically heated catalyst.

[0007] After the ignition switch is turned on to start the vehicle, a predetermined amount of warm-up electric power is input to the electrically heated catalyst before starting the internal combustion engine, and the internal combustion engine installed in the vehicle for power generation to raise the catalyst temperature of the electrically heated catalyst corrects the amount of warm-up electric power in accordance with the heat capacity of the electrically heated catalyst so that the catalyst temperature of the electrically heated catalyst rises to a predetermined starting catalyst temperature.

[0008] According to the present invention, the temperature of the electrically heated catalyst can be estimated with high accuracy, regardless of product variations in the electrically heated catalyst, and the temperature of the electrically heated catalyst can be raised with high accuracy to the desired temperature, that is, the starting catalyst temperature.

[0009] An explanatory diagram showing a schematic system configuration of an internal combustion engine 1 to which the present invention is applied. A characteristics diagram showing the correlation between the heat capacity of an electrically heated catalyst, the amount of power input to the electrically heated catalyst, and the amount of temperature rise of the electrically heated catalyst. A characteristics diagram showing the relationship between the heat capacity of an electrically heated catalyst and a heat capacity correction coefficient Ck. A flowchart showing an example of a control flow when warming up an electrically heated catalyst prior to starting an internal combustion engine. A flowchart showing an example of a control flow when warming up an electrically heated catalyst prior to starting an internal combustion engine.

[0010] An embodiment of the present invention will be described in detail below with reference to the drawings.

[0011] FIG. 1 is an explanatory diagram that schematically shows the system configuration of an internal combustion engine 1 to which the present invention is applied.

[0012] The internal combustion engine 1 is mounted on a so-called series hybrid vehicle (not shown) that drives drive wheels (not shown) with a motor (not shown). That is, the internal combustion engine 1 is mounted on the vehicle for generating electricity, and is operated to generate electricity using an on-board generator (not shown) when, for example, the remaining charge of an 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. Note that the internal combustion engine 1 may also be mounted on a so-called parallel hybrid vehicle, as long as the vehicle can run without transmitting the rotation of the crankshaft as driving force to the drive wheels of the vehicle.

[0013] An electrically heated catalyst (EHC) 3 is provided in an exhaust passage 2 of an internal combustion engine 1. The electrically heated catalyst 3 is provided, for example, near the outlet of an exhaust manifold in the exhaust passage 2. In other words, the electrically heated catalyst 3 is, for example, the first catalyst through which exhaust gas emitted from the internal combustion engine passes.

[0014] The electrically heated catalyst 3 is a catalyst that generates heat when electricity is passed through it, and is configured, for example, by using a ceramic heating element that generates heat when electricity is passed through it as a catalyst carrier, the surface of which is coated with a suitable catalytic metal slurry that can serve as a three-way catalyst or oxidation catalyst. The power supply to the electrically heated catalyst 3 is controlled by a control unit 4 that serves as a control section. In other words, the catalyst temperature of the electrically heated catalyst 3 can be controlled by the control unit 4.

[0015] The control unit 4 is a well-known digital computer equipped with a CPU, ROM, RAM, and an input / output interface. When a predetermined power generation request is received, the control unit 4 drives the internal combustion engine 1 to start power generation by the generator.

[0016] For various controls and calculations, the control unit 4 receives output signals from various sensors, such as a first exhaust gas temperature sensor 5 that detects the temperature or exhaust gas temperature upstream (inlet side) of the electrically heated catalyst 3, a second exhaust gas temperature sensor 6 that detects the temperature or exhaust gas temperature downstream (outlet side) of the electrically heated catalyst 3, an outside air temperature sensor 7 that detects the outside air temperature, a coolant temperature sensor 8 that detects the temperature of the coolant for the internal combustion engine 1, an ammeter 9 that detects the value of the current flowing through the electrically heated catalyst 3 when current is applied to the electrically heated catalyst 3, and a voltmeter 10 that detects the voltage applied to the electrically heated catalyst 3 when current is applied to the electrically heated catalyst 3.

[0017] Here, the catalyst temperature (EHC temperature) of the electrically heated catalyst 3 is correlated with the electrical resistance value (EHC resistance value) of the electrically heated catalyst 3, and the lower the catalyst temperature of the electrically heated catalyst 3, the larger the electrical resistance value of the electrically heated catalyst 3. In other words, the catalyst temperature of the electrically heated catalyst 3 can be estimated from the electrical resistance value of the electrically heated catalyst 3.

[0018] However, there is a risk that the catalyst temperature cannot be accurately estimated from the electrical resistance value of the electrically heated catalyst 3 due to factors such as large variations in electrical resistance value due to product variations, the higher the catalyst temperature, the less sensitive it becomes to electrical resistance, and changes in electrical resistance value due to deterioration.

[0019] Furthermore, for example, if the power input to the electrically heated catalyst 3 is kept constant and an attempt is made to compensate for variations in the temperature reached due to variations in the heat capacity of the electrically heated catalyst 3 by extending the power supply time, there is a risk of the electrically heated catalyst 3, which has a low heat capacity due to product variations, overheating.

[0020] The main variations in the electrically heated catalyst 3 are the heat capacity and electrical resistance. The power per unit time varies depending on the electrical resistance, but it can be kept constant using so-called PWM control. However, the rate at which the temperature of the electrically heated catalyst 3 rises and the temperature it reaches vary depending on the amount of power input due to variations in the heat capacity of each electrically heated catalyst 3.

[0021] Therefore, the control unit 4 estimates the catalyst temperature of the electrically heated catalyst 3 when the temperature of the electrically heated catalyst 3 is raised by passing current through it, based on the relationship between the heat capacity of the electrically heated catalyst 3 and the amount of electricity input to the electrically heated catalyst 3.

[0022] As shown in Figure 2, the amount of power input to the electrically heated catalyst 3 and the amount of temperature rise of the electrically heated catalyst 3 vary depending on the heat capacity of the electrically heated catalyst 3. Figure 2 is a characteristic diagram showing the correlation between the heat capacity of the electrically heated catalyst 3, the amount of power input to the electrically heated catalyst 3, and the amount of temperature rise of the electrically heated catalyst 3. Characteristic line L1 shows the case where the heat capacity of the electrically heated catalyst 3 is at its maximum value due to product variations. Characteristic line L2 shows the case where the product variations in the heat capacity of the electrically heated catalyst 3 are smaller than the maximum value. As shown in Figure 2, even if the amount of power input is the same, the smaller the heat capacity of the electrically heated catalyst 3, the greater the amount of temperature rise. In other words, even if the amount of power input is the same, the smaller the heat capacity of the electrically heated catalyst 3, the higher the temperature.

[0023] The amount of heat generated by the electrically heated catalyst 3 is the amount of power input to the electrically heated catalyst 3. Therefore, if the amount of heat generated is the same, the rate at which the temperature of the electrically heated catalyst 3 rises and the temperature that it reaches will depend on the heat capacity of each electrically heated catalyst 3. In other words, if the heat capacity of the electrically heated catalyst 3 and the catalyst temperature before power is supplied are known, it is possible to accurately estimate the catalyst temperature after power is supplied from the amount of power input.

[0024] Furthermore, by determining the amount of electricity input according to its own heat capacity, the electrically heated catalyst 3 can maintain a constant time to reach a specified target temperature and a constant rate of temperature rise until the specified target temperature is reached, regardless of product variations.

[0025] After the ignition switch is turned on to start the vehicle, the control unit 4 inputs a predetermined amount of warm-up electric power to the cold electrically heated catalyst 3 before starting the internal combustion engine 1, thereby raising the catalyst temperature of the electrically heated catalyst 3 to a predetermined starting catalyst temperature. The starting catalyst temperature is, for example, the temperature at which the electrically heated catalyst 3 is activated. Note that the starting catalyst temperature may be lower than the temperature at which the electrically heated catalyst 3 is activated.

[0026] At this time, the control unit 4 estimates the catalyst temperature of the electrically heated catalyst 3 when it is heated by passing current through it, using the relationship between the heat capacity of the electrically heated catalyst 3 and the amount of warm-up power, and corrects the amount of warm-up power in accordance with the heat capacity of the electrically heated catalyst 3 so that the catalyst temperature of the electrically heated catalyst 3 rises to the starting catalyst temperature.

[0027] The amount of warm-up electric power is set so that the catalyst temperature of the electrically heated catalyst 3 in a cold state reaches, for example, the startup catalyst temperature within a predetermined time. The amount of warm-up electric power may also be set so that the catalyst temperature of the electrically heated catalyst 3 in a cold state reaches the startup catalyst temperature at a predetermined temperature rise rate.

[0028] Here, the electrically heated catalyst 3 with the greatest product variation in heat capacity is defined as the reference electrically heated catalyst, and the amount of power required to raise this reference electrically heated catalyst from a cold state to the above-mentioned starting catalyst temperature is defined as the reference amount of power.

[0029] The warm-up electric energy is calculated by multiplying the reference electric energy by a predetermined heat capacity correction coefficient Ck calculated in accordance with the heat capacity of the electrically heated catalyst 3 .

[0030] 3 is a characteristic diagram showing the relationship between the heat capacity of the electrically heated catalyst 3 and the heat capacity correction coefficient Ck. The heat capacity correction coefficient Ck is "1", for example, when the heat capacity of the electrically heated catalyst 3 is at its maximum (reference heat capacity) due to product variations. Furthermore, the heat capacity correction coefficient Ck increases as the heat capacity of the electrically heated catalyst 3 increases. In other words, the heat capacity correction coefficient Ck is calculated, for example, based on the maximum value of the product variations in the heat capacity of the electrically heated catalyst 3, and is maximized when the heat capacity of the electrically heated catalyst 3 is at its maximum value of the product variations.

[0031] The heat capacity correction coefficient Ck is calculated, for example, using the catalyst temperature of the electrically heated catalyst 3 when the internal combustion engine 1 is started for the first time when the vehicle is driven for the first time, or the catalyst temperature of the electrically heated catalyst 3 when the internal combustion engine 1 is started for the first time after the vehicle has been driven by turning on the ignition switch. In other words, the heat capacity correction coefficient Ck is calculated using the temperature of the electrically heated catalyst 3 when the internal combustion engine 1 is started for the first time, or the temperature of the electrically heated catalyst 3 when the internal combustion engine is started for the first time after the ignition switch is turned on.

[0032] In other words, the heat capacity correction coefficient Ck is calculated based on a pre-calculated reference temperature rise rate, which is the temperature rise rate of the reference electrically heated catalyst when the reference amount of electric power is input to the reference electrically heated catalyst.

[0033] More specifically, the heat capacity correction coefficient Ck is calculated according to the ratio between the reference temperature rise rate and the temperature rise rate of the electrically heated catalyst 3 when a reference amount of electric power is input to the electrically heated catalyst 3 .

[0034] Specifically, for example, if the rate of temperature rise of the reference electrically heated catalyst when the reference amount of electric power is input to the reference electrically heated catalyst is ΔC_max, and the rate of temperature rise of the electrically heated catalyst 3 when the reference amount of electric power is input to the electrically heated catalyst 3 is ΔC_meas, the heat capacity correction coefficient Ck is calculated as ΔC_max / ΔC_meas. In other words, the heat capacity correction coefficient Ck is calculated according to the ratio between the slope of the characteristic line L1 in Figure 2 described above and the slope of the characteristic line L2 in Figure 2 described above.

[0035] The catalyst temperature of the electrically heated catalyst 3 before the warm-up electric energy is input can be set to either the coolant temperature, which is the environmental temperature of the internal combustion engine, the outside air temperature, or the temperature detected by the second exhaust temperature sensor 6, when the coolant temperature of the internal combustion engine 1 is below a predetermined first predetermined temperature, or when the difference between the coolant temperature of the internal combustion engine 1 and the outside air temperature is below a predetermined temperature threshold.

[0036] Furthermore, learning of the heat capacity correction coefficient Ck is permitted when, for example, the difference between the coolant temperature of the internal combustion engine 1 and the outside air temperature is equal to or less than a predetermined value during a cold start of the internal combustion engine 1.

[0037] FIG. 4 is a flowchart showing an example of a control flow when warming up the electrically heated catalyst 3 prior to starting the internal combustion engine 1 in the above-described embodiment.

[0038] In step S1, the current voltage (V_now) applied to the electrically heated catalyst 3 is detected. In step S2, the current resistance value (R_now) of the electrically heated catalyst 3 is detected.

[0039] In step S3, it is determined whether the heat capacity correction coefficient Ck has been calculated since the ignition switch was turned on. If it is determined in step S3 that the heat capacity correction coefficient Ck has been calculated, the process proceeds to step S4. If it is determined in step S3 that the heat capacity correction coefficient Ck has not been calculated, the process proceeds to step S9.

[0040] In step S4, a control output value (W_trg) is calculated to be used for controlling the power supplied when warming up the electrically heated catalyst 3. The control output value (W_trg) is calculated by multiplying the reference output (W_ref) by the heat capacity correction coefficient Ck. The reference output (W_ref) corresponds to the reference amount of power.

[0041] In step S5, a control target current value (I_trg) is calculated. The control target current value (I_trg) is the value obtained by dividing the control output value (W_trg) calculated in step S4 by the voltage (V_now) detected in step S1.

[0042] In step S6, the maximum current value (I_max) is calculated by dividing the voltage (V_now) detected in step S1 by the resistance value (R_now) detected in step S2.

[0043] In step S7, a control duty ratio is calculated, which is the value obtained by dividing the control target current value (I_trg) calculated in step S5 by the maximum current value (I_max) calculated in step S6.

[0044] In step S8, the control duty ratio calculated in step S7 is used to control the output of electric power when electric power is supplied to the electrically heated catalyst 3.

[0045] In step S9, the coolant temperature of the internal combustion engine 1, the outside air temperature, and the outlet side temperature of the electrically heated catalyst 3 are detected.

[0046] In step S10, the temperature of the electrically heated catalyst 3 before it is warmed up is calculated.

[0047] In step S11, the reference amount of electric power is input to the electrically heated catalyst 3 to warm up the electrically heated catalyst 3.

[0048] In step S12, it is determined whether the electric power input to the electrically heated catalyst 3 has reached the reference electric power amount. If it is determined in step S12 that the electric power input to the electrically heated catalyst 3 has reached the reference electric power amount, the process proceeds to step S113. If it is not determined in step S12 that the electric power input to the electrically heated catalyst 3 has reached the reference electric power amount, the process proceeds to step S11.

[0049] In step S13, the time (arrival time) from when the supply of electric power to the electrically heated catalyst 3 starts until the amount of electric power reaches the reference amount of electric power is calculated.

[0050] In step S14, the internal combustion engine 1 is started.

[0051] In step S15, the catalyst temperature of the electrically heated catalyst 3 is detected. That is, in step S15, the catalyst temperature of the electrically heated catalyst 3 after the reference amount of electric power is input is detected. When the internal combustion engine 1 is started, an exhaust flow occurs, and the catalyst temperature of the electrically heated catalyst 3 can be detected from the detection value of the second exhaust gas temperature sensor 6. Note that the catalyst temperature may be estimated using not only the detection value of the second exhaust gas temperature sensor 6, but also the detection values ​​of the first exhaust gas temperature sensor 5 and the outside air temperature sensor 7.

[0052] In step S16, a heat capacity correction coefficient Ck is calculated. The heat capacity correction coefficient Ck is calculated by dividing the predetermined reference temperature rise rate (ΔC_max) by the temperature rise rate (ΔC_meas) of the electrically heated catalyst 3. The temperature rise rate (ΔC_meas) of the electrically heated catalyst 3 is calculated, for example, using the catalyst temperature before warming up the electrically heated catalyst 3, the catalyst temperature after warming up the electrically heated catalyst 3 detected in step S15, and the arrival time calculated in step S13. The reference temperature rise rate (ΔC_max) is, for example, the temperature rise rate of the reference electrically heated catalyst when the reference amount of electric power is input to the reference electrically heated catalyst for the arrival time calculated in step S13.

[0053] In step S17, the heat capacity correction coefficient Ck calculated in step S16 is stored (recorded) in the control unit 4 and learned.

[0054] In FIG. 4, the flow from step S3 to step S4 is a flow in which control is performed to warm up the electrically heated catalyst 3 using the learned heat capacity correction coefficient Ck, and the flow from step S3 to step S9 is a flow in which control is performed to warm up the electrically heated catalyst 3 for the first time after the ignition switch is turned on and to learn the heat capacity correction coefficient Ck.

[0055] In the above-described embodiment, the relationship between the heat capacity of the electrically heated catalyst 3 and the amount of power input to the electrically heated catalyst 3 is utilized to estimate the temperature of the electrically heated catalyst 3 when it is heated by energization.

[0056] This allows the catalyst temperature of the electrically heated catalyst 3 to be estimated with high accuracy, regardless of product variations in the electrically heated catalyst 3. Furthermore, because the catalyst temperature of the electrically heated catalyst 3 can be estimated with high accuracy, the electrically heated catalyst 3 can be accurately raised to the desired starting catalyst temperature prior to starting the internal combustion engine 1, thereby preventing deterioration in the exhaust performance of the internal combustion engine 1.

[0057] In the internal combustion engine 1, the amount of warm-up electric power is set so that the temperature of the electrically heated catalyst 3 in a cold state reaches the starting catalyst temperature in a predetermined time, and therefore, the robustness of exhaust performance and fuel economy can be improved by keeping constant the time required to warm up the electrically heated catalyst 3 to the starting catalyst temperature regardless of product variations in the electrically heated catalyst 3. Furthermore, in the internal combustion engine 1, when the amount of warm-up electric power is set so that the temperature of the electrically heated catalyst 3 in a cold state reaches the starting catalyst temperature at a predetermined temperature rise rate, the robustness of exhaust performance and fuel economy can be improved by keeping constant the temperature rise rate required to warm up the electrically heated catalyst 3 to the starting catalyst temperature regardless of product variations in the electrically heated catalyst 3.

[0058] The heat capacity correction coefficient Ck may be calculated based on a reference temperature rise amount, which is the amount of temperature rise of the reference electrically heated catalyst when the reference amount of electric power is input to the reference electrically heated catalyst 3. More specifically, the heat capacity correction coefficient Ck may be calculated based on the ratio between the reference temperature rise amount and the amount of temperature rise of the electrically heated catalyst 3 when the reference amount of electric power is input to the electrically heated catalyst 3.

[0059] Specifically, for example, if the temperature rise of the reference electrically heated catalyst when the reference amount of power is input to the reference electrically heated catalyst is C_max, and the temperature rise of the electrically heated catalyst 3 when the reference amount of power is input to the electrically heated catalyst 3 is C_meas, the heat capacity correction coefficient Ck may be calculated as C_max / C_meas.

[0060] FIG. 5 is a flowchart showing an example of a control flow for calculating the heat capacity correction coefficient Ck based on the temperature rise amount (C_max) of the reference electrically heated catalyst when warming up the electrically heated catalyst 3 prior to starting the internal combustion engine 1 in the above-described embodiment.

[0061] In step S21, the current voltage (V_now) applied to the electrically heated catalyst 3 is detected. In step S22, the current resistance value (R_now) of the electrically heated catalyst 3 is detected.

[0062] In step S23, it is determined whether the heat capacity correction coefficient Ck has been calculated since the ignition switch was turned on. If it is determined in step S23 that the heat capacity correction coefficient Ck has been calculated, the process proceeds to step S24. If it is determined in step S23 that the heat capacity correction coefficient Ck has not been calculated, the process proceeds to step S29.

[0063] Steps S24 to S28 are the same as steps S4 to S8 in Fig. 4. Therefore, the individual explanations of steps S24 to S28 will be omitted because they overlap with steps S4 to S8 in Fig. 4.

[0064] In step S29, the reference amount of electric power is input to the electrically heated catalyst 3 to warm up the electrically heated catalyst 3.

[0065] In step S30, it is determined whether the electric power input to the electrically heated catalyst 3 has reached the reference electric power amount. If it is determined in step S30 that the electric power input to the electrically heated catalyst 3 has reached the reference electric power amount, the process proceeds to step S31. If it is not determined in step S30 that the electric power input to the electrically heated catalyst 3 has reached the reference electric power amount, the process proceeds to step S29.

[0066] In step S31, the internal combustion engine 1 is started.

[0067] In step S32, the catalyst temperature of the electrically heated catalyst 3 is detected. That is, in step S32, the catalyst temperature of the electrically heated catalyst 3 after the reference amount of electric power is input is detected.

[0068] In step S33, a heat capacity correction coefficient Ck is calculated. The heat capacity correction coefficient Ck is calculated by dividing the pre-stored C_max by the temperature increase (C_meas) calculated using the catalyst temperature detected in step S32. Here, the temperature increase (C_meas) is calculated by subtracting the catalyst temperature immediately before the reference amount of electric power is supplied to the electrically heated catalyst 3 in step S29 from the catalyst temperature of the electrically heated catalyst 3 detected in step S32. The catalyst temperature immediately before the reference amount of electric power is supplied to the electrically heated catalyst 3 in step S29 is set to, for example, the outside air temperature or the coolant temperature immediately before the reference amount of electric power is supplied to the electrically heated catalyst 3, because the internal combustion engine 1 has not yet started since the ignition switch was turned on.

[0069] In step S34, the heat capacity correction coefficient Ck calculated in step S33 is stored (recorded) in the control unit 4 and learned.

[0070] In FIG. 5, the flow from step S23 to step S24 is a flow for controlling the warming up of the electrically heated catalyst 3 using the learned heat capacity correction coefficient Ck, and the flow from step S23 to step S29 is a flow for warming up the electrically heated catalyst 3 for the first time after the ignition switch is turned on and learning the heat capacity correction coefficient Ck.

[0071] 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.

[0072] For example, the heat capacity correction coefficient Ck may be calculated by dividing the weight of the electrically heated catalyst 3 by the weight (reference weight) when the heat capacity of the electrically heated catalyst 3 is at its maximum due to product variations. That is, the heat capacity correction coefficient Ck may be calculated based on the ratio of a pre-measured weight of the electrically heated catalyst 3 to the above-mentioned reference weight. In this case, the heat capacity correction coefficient Ck is calculated (learned) using the pre-measured weight of the electrically heated catalyst 3. Therefore, the heat capacity correction coefficient Ck can be calculated without using the detection signal of the second exhaust gas temperature sensor 6.

[0073] For example, the temperature before the electrically heated catalyst 3 is warmed up may be the average value of the detected water temperature and outside air temperature.

[0074] For example, the heat capacity correction coefficient Ck may continue to use the value that was initially calculated and learned when the vehicle was first driven.

[0075] The above-described embodiments relate to a method for estimating the temperature of the electrically heated catalyst 3, a method for controlling the internal combustion engine 1, and a control device for the internal combustion engine 1.

Claims

1. A method for estimating the temperature of an electrically heated catalyst that is provided in the exhaust passage of an internal combustion engine and generates heat when electricity is applied, the method estimating the temperature of the electrically heated catalyst using the heat capacity of the electrically heated catalyst and the amount of electricity input to the electrically heated catalyst.

2. A control method for an internal combustion engine mounted on a vehicle for power generation, which has an electrically heated catalyst that is provided in an exhaust passage and generates heat when current is applied, and which supplies a predetermined amount of warm-up electric power to the electrically heated catalyst before starting the internal combustion engine after the vehicle has started operating by turning on the ignition switch, thereby raising the catalyst temperature of the electrically heated catalyst, the control method for an internal combustion engine estimating the temperature of the electrically heated catalyst using the relationship between the heat capacity of the electrically heated catalyst and the amount of warm-up electric power, and correcting the amount of warm-up electric power in accordance with the heat capacity of the electrically heated catalyst so that the catalyst temperature of the electrically heated catalyst rises to the predetermined starting catalyst temperature.

3. A method for controlling an internal combustion engine according to claim 2, wherein the amount of electric power for warm-up is set so that the temperature of the electrically heated catalyst reaches the temperature of the starting catalyst within a predetermined time.

4. A method for controlling an internal combustion engine according to claim 2, wherein the amount of electric power for warm-up is set so that the temperature of the electrically heated catalyst reaches the starting catalyst temperature at a predetermined temperature rise rate.

5. The method for controlling an internal combustion engine according to claim 2, wherein the correction of the amount of warm-up electric power in accordance with the heat capacity of the electrically heated catalyst is performed using a predetermined heat capacity correction coefficient.

6. A method for controlling an internal combustion engine as set forth in claim 5, wherein the heat capacity correction coefficient is calculated using the temperature of the electrically heated catalyst at the initial start of the internal combustion engine or the temperature of the electrically heated catalyst at the first start of the internal combustion engine after the ignition switch is turned on.

7. The method for controlling an internal combustion engine according to claim 5, wherein the heat capacity correction coefficient is learned using a weight of the electrically heated catalyst that has been measured in advance.

8. The method for controlling an internal combustion engine according to claim 7, wherein the heat capacity correction coefficient is a value obtained according to the ratio of a weight of the electrically heated catalyst measured in advance to a predetermined reference weight.

9. A method for controlling an internal combustion engine as described in claim 6, wherein the heat capacity correction coefficient is calculated based on the rate of temperature rise of a reference electrically heated catalyst when a predetermined reference amount of electric power is input to the reference electrically heated catalyst, the heat capacity of which becomes a predetermined reference heat capacity.

10. A control method for an internal combustion engine as described in claim 9, wherein the heat capacity correction coefficient is calculated as a value corresponding to the ratio of the rate of temperature rise of the electrically heated catalyst caused by inputting the reference amount of electric power to the rate of temperature rise of the reference electrically heated catalyst when the reference amount of electric power is input to the reference electrically heated catalyst.

11. A method for controlling an internal combustion engine as described in claim 6, wherein the heat capacity correction coefficient is calculated based on the amount of temperature rise of a reference electrically heated catalyst when a predetermined reference amount of electric power is input to the reference electrically heated catalyst, the heat capacity of which becomes a predetermined reference heat capacity.

12. A method for controlling an internal combustion engine as described in claim 11, wherein the heat capacity correction coefficient is calculated as a value corresponding to the ratio between the amount of temperature rise of the electrically heated catalyst caused by inputting the reference amount of electric power and the amount of temperature rise of the reference electrically heated catalyst when the reference amount of electric power is input to the reference electrically heated catalyst.

13. A control method for an internal combustion engine as described in claim 10 or claim 12, wherein when the coolant temperature of the internal combustion engine is below a predetermined first predetermined temperature, or when the difference between the coolant temperature of the internal combustion engine and the outside air temperature is below a predetermined temperature threshold, either the coolant temperature of the internal combustion engine, the outside air temperature, or a temperature detected by an exhaust temperature sensor arranged downstream of the electrically heated catalyst is regarded as the catalyst temperature of the electrically heated catalyst before the input of the reference amount of electric power.

14. A method for controlling an internal combustion engine as described in claim 5, wherein the heat capacity correction coefficient is calculated based on the maximum value of the product variation in the heat capacity of the electrically heated catalyst, and is set so as to be maximum when the heat capacity of the electrically heated catalyst is at the maximum value of the product variation.

15. A method for controlling an internal combustion engine according to claim 5, wherein learning of the heat capacity correction coefficient is permitted when the difference between the engine coolant temperature and the outside air temperature is equal to or less than a predetermined value during a cold start of the internal combustion engine.

16. A control device for an internal combustion engine mounted on a vehicle for power generation, the control device having: an electrically heated catalyst that is provided in an exhaust passage and generates heat when current is applied; and a control unit that inputs a predetermined amount of warm-up electric power to the electrically heated catalyst and raises the catalyst temperature of the electrically heated catalyst before starting the internal combustion engine after the vehicle has started operating with the ignition switch turned on, wherein the control unit estimates the temperature of the electrically heated catalyst using the relationship between the heat capacity of the electrically heated catalyst and the amount of warm-up electric power, and corrects the amount of warm-up electric power in accordance with the heat capacity of the electrically heated catalyst so that the catalyst temperature of the electrically heated catalyst rises to a predetermined starting catalyst temperature.

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