Electrically conductive heating type exhaust gas purification catalyst system and exhaust gas purification method

Abstract

Provided is an electrically heated exhaust gas purification catalyst system. The electrically heated exhaust gas purification catalyst system performs the following electric conduction control based on information on the temperature of a catalyst bed input from a temperature detection section of an electrically heated catalyst device: (1) electric conduction to a pair of electrodes when the temperature of the catalyst bed is below a first threshold temperature T1 set within a range of 350 ± 25°C; (2) no electric conduction to the pair of electrodes when the temperature of the catalyst bed is higher than the first threshold temperature T1 and below a second threshold temperature T2 set within a range of 450 ± 25°C; (3) electric conduction to the pair of electrodes when the temperature of the catalyst bed is higher than the second threshold temperature T2 and below a third threshold temperature T3 set at 550°C or higher; and (4) no electric conduction to the pair of electrodes when the temperature of the catalyst bed is higher than the third threshold temperature T3.

Description

Technical Field

[0001] This invention relates to an electrically heated exhaust gas purification catalyst system installed in the exhaust system of an internal combustion engine in a vehicle. Furthermore, this invention relates to an exhaust gas purification method using this electrically heated exhaust gas purification catalyst system. Additionally, this invention relates to a control program for the electrically heated exhaust gas purification catalyst system.

[0002] In addition, this application claims priority based on Japanese Patent Application No. 2021-019606, filed on February 10, 2021, the entire contents of which are incorporated herein by reference. Background Technology

[0003] Three-way catalysts (TWCs) are used as catalysts for removing harmful components such as hydrocarbons (HC), carbon monoxide (CO), and nitrogen oxides (NOx) from exhaust gases emitted by internal combustion engines such as vehicle engines through oxidation or reduction reactions. TWCs utilize metals (sometimes referred to as "catalyst metals") that function as oxidation and / or reduction catalysts, typically noble metals belonging to the platinum group such as palladium (Pd) and rhodium (Rh). For example, three-way catalysts in which Pd, as an oxidation catalyst, and Rh, as a reduction catalyst, are supported on a porous support are widely used.

[0004] This three-way catalytic converter exhibits high catalytic activity under specified high-temperature conditions. Therefore, in the case of a cold exhaust system during engine start-up, the activity of the three-way catalytic converter in the exhaust system is lower compared to the high-temperature conditions during long-term continuous engine operation. Therefore, a technology is needed to effectively purify exhaust gases even under such conditions.

[0005] In recent years, in particular, hybrid vehicles and so-called eco-friendly cars, including those with idle stop mechanisms and / or fuel cut-off mechanisms, have become increasingly popular. In these vehicles, the engine frequently stops during operation, and the exhaust system is prone to a cold state similar to that during engine start-up after operation begins. This necessitates the use of three-way catalytic converters to effectively purify exhaust gases even under such conditions.

[0006] To address this requirement, an electrically heated (also known as EHC) exhaust gas purification catalyst device has been developed. This device includes a carrier such as a honeycomb carrier and a three-way catalyst supported on the carrier. It also includes a pair of electrodes configured to supply electricity to the pair of electrodes to heat the catalytic metal.

[0007] As EHCs, there are known EHCs with structures that have an electric heater installed in the catalyst unit and EHCs with structures that support the catalyst on a conductive support and heat the support by applying electricity. For example, Patent Document 1 describes an EHC assembled with an electric heater for heating the catalyst metal. In addition, Patent Document 2 describes an EHC in which the support for supporting the catalyst component of the NOx adsorption reduction catalyst is made of a material that generates Joule heat by applying electricity.

[0008] Existing technical documents

[0009] Patent documents

[0010] Patent Document 1: Japanese Patent Application Publication No. 2004-176592

[0011] Patent Document 2: Japanese Patent Application Publication No. 2005-233066 Summary of the Invention

[0012] However, although EHC is used while heating the catalyst metal, it is more likely to be used in a lower temperature range compared to conventional exhaust gas purification catalytic converters. This tendency is particularly pronounced in hybrid vehicles and vehicles with fuel cut-off mechanisms.

[0013] Therefore, in order to use EHC for exhaust gas purification more effectively, it is important to correctly understand the temperature characteristics resulting from the catalytic activity of the catalyst metal and to perform more precise temperature control (heating control) of the catalyst metal in accordance with these temperature characteristics.

[0014] However, there is still room for improvement in accurately understanding the temperature characteristics of catalyst metals, especially three-way catalysts, in the relatively low-temperature region for effective EHC temperature control.

[0015] This invention was created with the aim of improving the temperature control of the three-way catalyst in an EHC, and in particular provides an electrically heated exhaust gas purification catalyst system and exhaust gas purification method capable of effectively controlling the temperature of exhaust gas in low-temperature regions. Furthermore, a control program for implementing this exhaust gas purification method is provided.

[0016] It is common knowledge in this field that the higher the temperature of the catalyst metal used in a three-way catalytic converter, or in other words, the higher the temperature of the exhaust gas supplied from the internal combustion engine to the catalyst bed (also known as the catalyst layer) in the catalyst unit through the exhaust pipe, the better the exhaust gas purification performance of the catalyst metal used in the three-way catalytic converter.

[0017] However, the inventors are interested in a more detailed relationship between the exhaust gas purification performance of the three-way catalyst and the temperature of the catalyst bed, particularly as... Figure 4The temperature characteristics are shown. Figure 4 The horizontal axis of the graph represents the temperature of the exhaust gas supplied to the catalyst bed (°C), and the vertical axis represents the purification rate of nitrogen oxides (NOx) in the exhaust gas, with the purification rate at an exhaust gas temperature of 400°C set as 100. The graph shows that the NOx purification performance consistently increases until the exhaust gas temperature supplied to the catalyst bed reaches 450°C. However, if the exhaust gas temperature supplied to the catalyst bed exceeds 450°C, the NOx purification performance decreases to the range of 500–550°C. Furthermore, when the exhaust gas temperature rises above the 500–550°C range, the NOx purification performance also increases.

[0018] The inventors created this invention in view of the reduced NOx purification performance of the three-way catalyst in the temperature range of approximately 450°C to 550°C.

[0019] According to the present invention, a technology is provided that even for electrically heated exhaust gas purification catalyst devices equipped in hybrid vehicles such as HV and PHEV, which emit relatively low-temperature exhaust gases at high frequency from the internal combustion engine to the exhaust system, the exhaust gas purification time can be actively reduced in the approximately 450°C to 550°C temperature range (hereinafter referred to as the "NOx purification reduction temperature range") where the NOx purification performance of the three-way catalyst is relatively reduced.

[0020] That is, the catalyst system for exhaust gas purification disclosed herein is an electrically heated exhaust gas purification catalyst system for purifying exhaust gas discharged from an internal combustion engine. The system includes: an electrically heated catalyst device disposed in the exhaust pipe of the internal combustion engine for purifying the exhaust gas discharged from the engine; the electrically heated catalyst device includes: an outer cylinder connected to the exhaust pipe; a pair of electrodes; a catalyst section including a catalyst bed that is in contact with the exhaust gas introduced into the outer cylinder and contains at least one catalyst metal that functions as a three-way catalyst; a heating element that heats up when the pair of electrodes is energized, thereby heating the catalyst bed; a temperature detection unit capable of detecting the temperature of the catalyst bed; and a control device that controls the energization of the pair of electrodes.

[0021] Furthermore, the control device of the electrically heated exhaust gas purification catalyst system disclosed herein performs the following power-on control (1) to (4) based on the information on the temperature of the catalyst bed input from the temperature detection unit:

[0022] (1) When the temperature of the catalyst bed is below the first threshold temperature T1 set in the range of 350±25℃, the pair of electrodes are energized.

[0023] (2) When the temperature of the catalyst bed is higher than the first threshold temperature T1 and lower than the second threshold temperature T2, which is set within the range of 450±25℃, the pair of electrodes shall not be energized.

[0024] (3) When the temperature of the catalyst bed is higher than the second threshold temperature T2 and lower than the third threshold temperature T3 which is set to be above 550°C, the pair of electrodes are energized.

[0025] (4) When the temperature of the catalyst bed exceeds the third threshold temperature T3, no current is applied to the pair of electrodes.

[0026] Furthermore, as another aspect of the present invention, a method for purifying exhaust gas using the system disclosed herein is provided. Specifically, the exhaust gas purification method disclosed herein utilizes an electrically heated catalyst device with the aforementioned configuration disposed in the exhaust pipe of an internal combustion engine to purify the exhaust gas discharged from the internal combustion engine.

[0027] Then, based on the information about the temperature of the catalyst bed obtained from the temperature detection unit, the above-mentioned power-on control (1) to (4) is performed.

[0028] In the electrically heated exhaust gas purification catalyst system and exhaust gas purification method with the above structure, the above-mentioned (1) to (4) energization control can be performed based on the temperature information of the catalyst bed from the temperature detection unit equipped with the above-mentioned catalyst device.

[0029] Specifically, in the operation of this system, when the catalyst bed temperature is below T1, the catalyst bed is heated by energizing a pair of electrodes. However, unlike existing technologies, when the catalyst bed temperature exceeds T1 but is below T2, the pair of electrodes are not energized. Therefore, for example, when purifying exhaust gas from an internal combustion engine that is not at a sufficiently high temperature, the temperature of the catalyst bed can be prevented from reaching the NOx purification reduction temperature range.

[0030] On the other hand, when the catalyst bed temperature tends to rise due to the continuous operation of the internal combustion engine, specifically, when the catalyst bed temperature exceeds T2, the aforementioned pair of electrodes are energized. This allows the catalyst bed temperature to quickly exceed the NOx purification reduction temperature range.

[0031] Furthermore, when the temperature of the catalyst bed exceeds the specified T3, it is determined that sufficient exhaust gas purification can be achieved even without further electric heating, and no further electric current is applied to the aforementioned pair of electrodes.

[0032] Thus, based on the electrically heated exhaust gas purification catalyst system and exhaust gas purification method disclosed herein, it is possible to effectively avoid the aforementioned reduction in the temperature range for NOx purification while purifying exhaust gases from internal combustion engines that generate exhaust gases in relatively low-temperature regions, such as those in hybrid vehicles and other economical cars.

[0033] In a preferred embodiment of the electrically heated exhaust gas purification catalyst system disclosed herein, the control device is configured to, during the energization control described in (3), also perform the following control: (3-1) not energize the pair of electrodes when combustion gases are not generated in the internal combustion engine. Furthermore, in a preferred embodiment of the exhaust gas purification method disclosed herein, the energization control described in (3) further includes the control (3-1).

[0034] The electrically heated exhaust gas purification catalyst system and exhaust gas purification method described herein can avoid unnecessary power supply when no exhaust gas to be purified is generated, thus achieving energy saving.

[0035] As a preferred example of a mode in which no combustion gases are produced in the internal combustion engine, idling stop and fuel cut-off can be cited.

[0036] In this so-called energy-saving mode of operation, no combustion gases are produced in the internal combustion engine, so it is preferable not to perform useless energizing on the aforementioned pair of electrodes.

[0037] In another preferred embodiment of the electrically heated exhaust gas purification catalyst system and exhaust gas purification method disclosed herein, the catalyst bed contains at least rhodium (Rh) as a catalyst metal.

[0038] The aforementioned energization control disclosed herein is highly effective for NOx reduction treatment by an electrically heated exhaust gas purification catalyst device, therefore rhodium is preferably included as a three-way catalyst.

[0039] Furthermore, the electrically heated exhaust gas purification catalyst system and exhaust gas purification method disclosed herein are particularly suitable for purifying exhaust gases from gasoline or diesel engines used in vehicles in the lower temperature range.

[0040] Furthermore, the present invention provides a control program for performing any of the exhaust gas purification methods disclosed herein. Additionally, the present invention provides a computer-readable, non-transitory recording medium storing a control program for performing any of the exhaust gas purification methods disclosed herein. The control program disclosed herein interprets the control device of the electrically heated exhaust gas purification catalyst system disclosed herein as a program for performing the electrical control described in (1) to (4) above. Attached Figure Description

[0041] Figure 1This is a schematic diagram illustrating the structure of an electrically heated exhaust gas purification catalyst system according to one embodiment.

[0042] Figure 2 This is a perspective view schematically illustrating one embodiment of an electrically heated catalyst device.

[0043] Figure 3 This is a schematic cross-sectional view of an electrically heated catalyst device according to another embodiment.

[0044] Figure 4 This is a graph showing the relationship between the NOx purification performance of a three-way catalyst and the temperature of the exhaust gas supplied to the catalyst bed.

[0045] Figure 5 This is a flowchart illustrating the power-on control process (main program) of one implementation method.

[0046] Figure 6 This is a flowchart illustrating an energy-saving mode power-on control process (subroutine) that may be included in the power-on control process of one implementation.

[0047] Figure 7 This is a flowchart illustrating other energy-saving mode power-on control processes (subroutines) that may be included in the power-on control process of one implementation.

[0048] Figure 8 This is a functional block diagram of a control device for one implementation method. Detailed Implementation

[0049] Hereinafter, with appropriate reference to the accompanying drawings, several preferred embodiments of the technology disclosed herein will be described. Matters necessary for implementing this technology, other than those specifically mentioned in this specification, can be understood by those skilled in the art as design considerations based on prior art. This technology can be implemented based on the disclosures in this specification and technical knowledge in the art. Furthermore, in this specification, A to B refers to A and below.

[0050] The general configuration of a preferred embodiment of the electrically heated exhaust gas purification catalyst system 10 disclosed herein is shown in Figure 1 .

[0051] The electrically heated exhaust gas purification catalyst system 10 of this embodiment is a system assembled in a vehicle such as an automobile, including an electrically heated catalyst device (EHC) 20 and a control device (ECU) 12.

[0052] As shown in the figure, the electrically heated catalyst device 20 is connected to a portion of the exhaust pipe 2, which is the exhaust system connected to the internal combustion engine (in this case, a gasoline engine for automobiles) 1. Furthermore, in this embodiment, the internal combustion engine 1 is a gasoline engine, but in other embodiments it could be a diesel engine.

[0053] The electrically heated catalyst device 20 includes: an outer cylinder 22 connected to an exhaust pipe 2 in a manner that forms part of an exhaust system; a catalyst section 30 and a temperature detection section 28 disposed inside the outer cylinder 22; and a pair of (positive and negative) electrodes 24 disposed in part of the outer cylinder 22 and connected to a substrate 26 of a structural heating element disposed inside the outer cylinder 22.

[0054] The outer cylinder 22 is made of a material with excellent heat resistance, durability, and machinability. Examples of suitable materials include stainless steel (a conductive material) and ceramic materials. The outer cylinder 22 may also be made of the same material as the exhaust pipe 2. The outer cylinder 22 can be any cylindrical shape with an internal space; besides a cylindrical shape, it can also be a square shape, etc.

[0055] The temperature detection unit 28 only needs to be able to measure the temperature of the exhaust gas flowing out of the catalyst section 30 (the exhaust gas immediately after passing through the catalyst bed), and its structure is not particularly limited. For example, a temperature sensor made of a thermocouple can be used as the temperature detection unit 28.

[0056] The catalyst section 30 of the electrically heated catalyst device (EHC) 20 in this embodiment may be... Figure 2 The structure shown. Specifically, as Figure 2 As shown, it includes a cylindrical substrate 26 with an internal honeycomb structure, and a pair of electrode layers 25 and electrodes (terminals) 24 formed on the outer peripheral surface of the substrate 26 in a manner that sandwiches the substrate 26 and faces each other. The electrode layers 25 have the function of diffusing current on the surface of the substrate 26 so as to efficiently heat the heating element (in this case, the substrate 26). The shape and size of the electrode layers 25 can be appropriately set.

[0057] The substrate 26 in this embodiment is made of a material that functions as a heating element capable of generating heat through Joule heating when an electric current is applied to the pair of electrodes 24. For example, it can be made of a non-metallic or metallic material capable of generating heat when an electric current is applied.

[0058] As preferred non-metallic heating elements, examples include porous materials (e.g., monolithic honeycomb structures) with regular unit structures composed of silicon carbide, molybdenum disilicide, etc., which are capable of conducting electricity due to doping with impurities (such as nitrogen (N)). Alternatively, as preferred metallic heating elements, porous metallic materials (typically honeycomb structures) composed of metals such as Ni-Cr or Fe-Cr-Al can be used. By configuring the substrate 26 as a component that functions as a heating element that generates heat through Joule heating when the pair of electrodes 24 are energized, a separate heating element is not required. Therefore, it is not necessary to ensure space for heating elements of other components inside the outer cylinder 22, allowing for more efficient arrangement of the catalyst bed.

[0059] Alternatively, as in other implementations, such as Figure 3 As shown, the heating element 46 can also be disposed separately from the substrate 51 constituting the catalyst section 50. Specifically, in Figure 3 In the electrically heated catalyst unit (EHC) 40 shown, a heating element 46, consisting of an annular heater connected to a pair of electrodes 44, is arranged adjacent to the upstream side of the catalyst section 50 in the direction of exhaust gas flow within the outer cylinder 42. Thus, by heating the annular heater (heating element) 46 inside the outer cylinder 22, the temperature of the catalyst bed can be increased.

[0060] like Figure 2 As shown, the substrate 26 is a honeycomb structure with multiple cells 32 having two end openings on the exhaust gas inflow side and the exhaust gas outflow side, and partition walls 34 separating adjacent cells 32. However, the shape of the cells 32 is not particularly limited, and is not limited to square, rectangular or other quadrilateral shapes. For example, it can also be a polygonal shape such as a triangle, hexagon, or octagon, or a circle.

[0061] The substrate 26 is not limited to a regular honeycomb structure composed of cells 32 and partition walls 34 as described above. For example, it can also be a sponge-like porous material with irregular pores, as long as the exhaust gas flows smoothly in the pores.

[0062] Furthermore, the substrate 26 is not limited to a so-called direct-flow type where exhaust gas introduced into the chamber 32 from the inlet side is directly discharged from the outlet side through the chamber 32. For example, it can also be a so-called wall-through type substrate where exhaust gas introduced from a chamber with only an inlet side opening moves through a porous partition wall to an adjacent chamber with only an outlet side opening and is discharged from the outlet side of the chamber 32.

[0063] Within this chamber 32, specifically, a catalyst bed (not shown) is formed on the surface and / or within the partition wall 34. The catalyst bed (also referred to as a catalyst layer) can be formed from existing catalyst devices without requiring a special structure.

[0064] That is, the catalyst bed provided in the catalyst section 30 of this embodiment includes at least catalyst metal particles that function as a three-way catalyst and a carrier that supports the metal particles.

[0065] Examples of catalyst metals include palladium (Pd), rhodium (Rh), and platinum (Pt), which belong to the platinum group elements, or other metals that function as oxidation or reduction catalysts. Pd and Pt exhibit excellent purification performance (oxidation purification capacity) for carbon monoxide and hydrocarbons, while Rh demonstrates excellent purification performance (reduction purification capacity) for NOx, making them particularly preferred catalyst metals for three-way catalysts. In addition, metals composed of alkali metals, alkaline earth metals, transition metals, etc., can also be used. The average particle size of the catalyst metal, based on electron microscopy observation, is preferably 0.5 nm or more and 50 nm or less, more preferably 1 nm or more and 20 nm or less, but is not particularly limited.

[0066] As a support for the catalyst bed, there are no particular limitations as long as it can support the catalyst metal particles, and existing known supports can be used. Examples include inorganic materials with oxygen adsorption capacity (OSC) such as cerium oxide (CeO2) and composite oxides containing cerium oxide (e.g., cerium oxide-zirconia composite oxides (CZ or ZC composite oxides)); oxides such as alumina (Al2O3), titanium dioxide (TiO2), zirconium oxide (ZrO2), and silicon dioxide (SiO2). One type can be used alone or two or more can be used in combination. Since OSC materials can function as co-catalysts for waste gas purification, supports containing OSC materials are more preferred. The catalyst bed may also contain components other than the catalyst component and the support (e.g., binders, additives, etc.).

[0067] There is no particular limitation on the content of catalyst metal (three-way catalyst) in the catalyst bed. For example, relative to the total mass of the support contained in the catalyst bed, it can be more than 0.01% by mass and less than 10% by mass, preferably more than 0.1% by mass and less than 5% by mass.

[0068] The catalyst bed can be a simple single-layer structure or a multi-layer structure comprising two or more layers with different types and proportions of catalyst metals. In the electrically heated exhaust gas purification catalyst system 10 disclosed herein, particularly for effectively achieving NOx purification performance in low-temperature regions, the catalyst bed (catalyst layer) has a multi-layer structure, and the types of metals contained in each layer can be the same or different. Furthermore, the thickness and length of the catalyst bed can be appropriately determined based on the size of the chamber 32 of the substrate 26 and the flow rate of the exhaust gas supplied to the electrically heated catalyst device 20. For example, the thickness of the catalyst bed can be 1 μm or more and 500 μm or less.

[0069] On the other hand, the control device 12 in this embodiment is a device comprised of a computer that constitutes an ECU (engine control unit; also called an electronic control unit) for various controls of the operating state of the internal combustion engine 1. The structure of the ECU itself can be the same as that used in existing automobiles. The ECU is, for example, a microcomputer, including an interface (I / F), a central processing unit (CPU) that executes commands for the control program, a ROM (read-only memory) that stores the control program executed by the CPU, RAM (random access memory) used as the working area for deploying the program, and a storage unit such as a memory that stores the program and various data.

[0070] In the control device 12, a program for controlling the energization of the pair of electrodes 24 disclosed herein is pre-installed in the ECU. The control device 12 is electrically connected to a temperature detection unit 28 to obtain information about the catalyst bed temperature from the temperature detection unit 28. Additionally, the control device 12 is electrically connected to a power supply unit (not shown) (e.g., a generator linked to the vehicle battery and internal combustion engine), and can control the on / off energization of the pair of electrodes 24 from the power supply unit based on the catalyst bed temperature information obtained from the temperature detection unit 28. Furthermore, this on / off control itself can be the same as the energization on / off control in existing EHC systems, and further detailed description is omitted.

[0071] Next, refer to Figure 5 The flowchart shown illustrates the execution of the power-on control program in the electrically heated exhaust gas purification catalyst system 10 of this embodiment.

[0072] The control device 12 initiates control by recognizing the start of vehicle operation and the commencement of operation of the internal combustion engine (the vehicle's gasoline engine) 1. Specifically, control is initiated when the ECU determines that the internal combustion engine 1 is running based on a signal input from a crankshaft position sensor separately installed on the internal combustion engine 1. However, control can also be initiated at times other than those described above. For example, hybrid vehicles, also known as so-called powerful hybrid vehicles, can operate even when the engine is stopped by the drive battery and electric motor. Therefore, in the case of such vehicles, in order to preheat the EHC in an operating mode where the engine is not started at startup, the energization control in the electrically heated exhaust gas purification catalyst system 10 of this embodiment can be initiated by the driver's IG-ON (the main switch is turned on at the start of operation).

[0073] like Figure 5As shown, the control device 12 first sets the first threshold temperature T1, the second threshold temperature T2, and the third threshold temperature T3 (step S1). At this time, T1 is set to any temperature within the range of 350±25℃, T2 is set to any temperature within the range of 450±25℃, and T3 is set to any temperature above 550℃.

[0074] Next, while the control device 12 is operating (typically during the operation of the internal combustion engine 1), it inputs temperature data from the temperature detection unit 28 at predetermined intervals (step S2). Then, based on the input temperature data (catalyst bed temperature information), it determines whether the catalyst bed temperature Tx is below the first threshold temperature T1 (step S3). Here, if it is determined that the catalyst bed temperature Tx is below the first threshold temperature T1, energizing a pair of electrodes 24 is performed (step S4). Then, the process from step S1 onwards is returned.

[0075] On the other hand, if it is determined in step S3 that the temperature Tx of the catalyst bed is not below the first threshold temperature T1, i.e., above T1, then it is determined whether the temperature Tx of the catalyst bed is below the second threshold temperature T2 (step S5). Here, if it is determined that the temperature Tx of the catalyst bed is below the second threshold temperature T2 (i.e., T1 < Tx ≤ T2), no current is applied to the pair of electrodes 24 (step S6). Then, the process from step S1 is returned.

[0076] If, in step S5, it is determined that the temperature Tx of the catalyst bed is not below the second threshold temperature T2 (i.e., above T2), then it is determined whether the temperature Tx of the catalyst bed is below the third threshold temperature T3 (step S7). Here, if it is determined that the temperature Tx of the catalyst bed is below the third threshold temperature T3 (i.e., T2 < Tx ≤ T3), energizing a pair of electrodes 24 is performed (step S8). Then, the process from step S1 is returned.

[0077] At this point, regarding the operation of internal combustion engine 1, there is an option to execute other subroutine processing when the specified energy-saving mode is in operation. This subroutine processing will be described later.

[0078] If, in step S7, it is determined that the temperature Tx of the catalyst bed is not below the third threshold temperature T3, i.e., above T3, then since the temperature of the catalyst bed has been sufficiently heated, no current is applied to the pair of electrodes 24 (step S9). Then, the process returns to that from step S1.

[0079] By executing the power-on control program of this embodiment, which includes the steps S1 to S9 described above, the aforementioned NOx purification temperature range can be effectively avoided, and the exhaust gas from internal combustion engines 1, which frequently produce exhaust gas in relatively low-temperature regions, such as those in hybrid vehicles or vehicles equipped with so-called energy-saving modes (called energy-saving cars), can be purified efficiently.

[0080] Next, refer to Figure 6 The flowchart illustrates the execution of the energy-saving mode power-on control process (subroutine) that can accompany the above-mentioned power-on control process (main program).

[0081] Furthermore, in this embodiment, a subroutine is set for the case where both an idle stop mechanism and a fuel cut-off mechanism are included in the internal combustion engine 1 as a mode in which no combustion gases are generated. However, depending on the type of environmentally friendly vehicle (e.g., a mild hybrid vehicle with a smaller motor and a smaller capacity drive battery compared to a strong hybrid vehicle, or an environmentally friendly vehicle specification for a pure engine vehicle), only the idle stop mechanism and the fuel cut-off mechanism may be set for processing.

[0082] like Figure 6 As shown, in step S7 (refer to...) Figure 5 If the temperature Tx of the catalyst bed is determined to be below the third threshold temperature T3 (i.e., T2 < Tx ≤ T3), then step S8 is followed to start the energy-saving mode power-on control process (subroutine).

[0083] Specifically, the operating mode of the internal combustion engine 1 controlled by the ECU at that moment is determined. First, it is determined whether the current operating mode is in the process of idling stop (step S11).

[0084] Here, when the operating mode is determined to be idling stop operation, the power supply to the pair of electrodes 24 is cut off to avoid unnecessary power consumption (step S12).

[0085] On the other hand, if it is determined in step S11 that the operation is not in an idle speed cut-off operation, then it is determined whether the current operating mode is in a fuel cut-off operation (step S13). Here, if it is determined that the operating mode is in a fuel cut-off operation, the power supply to the pair of electrodes 24 is also cut off to avoid unnecessary power consumption (step S12). On the other hand, if it is determined in step S13 that the operation is not in a fuel cut-off operation, the power supply to the pair of electrodes 24 is not cut off, and the power supply control process for this energy-saving mode ends (subroutine).

[0086] Alternatively, as another preferred method for the energy-saving mode power-on control processing (subroutine) program, it can also be as follows: Figure 7As shown, the subroutine processing is set up in a prescribed manner to take into account the temporary shutdown of the internal combustion engine 1. For example, in the vehicles referred to above as hybrid electric vehicles (HEVs) and plug-in hybrid electric vehicles (PHEVs), the mode of temporary engine shutdown may occur frequently during operation, so it is preferable to incorporate such energy-saving mode power-on control processing into the system.

[0087] like Figure 7 As shown, in step S7 (refer to...) Figure 5 If the temperature Tx of the catalyst bed is determined to be below the third threshold temperature T3 (i.e., T2 < Tx ≤ T3), then step S8 is followed to start the power-on control processing (subroutine) program of this method in energy-saving mode.

[0088] Specifically, the operating mode of the internal combustion engine 1 controlled by the ECU at that moment is determined. That is, it is determined whether the current operating mode is that the engine is stopped (step S21). Here, if it is determined that the operating mode is that the engine is stopped, the power supply to the pair of electrodes 24 is cut off (step S22). On the other hand, if it is determined in step S21 that the engine is not stopped (i.e., the engine is running), the power supply to the pair of electrodes 24 is not cut off, and the energy-saving mode power supply control process (subroutine) ends.

[0089] Figure 8 This is a functional block diagram of a control device 12 according to one embodiment. The control device 12 is communicatively connected to a pair of electrodes 24 and a temperature detection unit 28 included in the electrically heated catalyst device 40, and is configured to control them. The control device 12 includes a temperature setting unit 12a, a temperature input unit 12b, a first temperature determination unit 12c, a second temperature determination unit 12d, a third temperature determination unit 12e, a first power-on control unit 12f, a mode determination unit 12g, and a second power-on control unit 12h. The various parts of the control device 12 are configured to communicate with each other. The functions of each part of the control device 12 are implemented, for example, by a processor and / or circuitry.

[0090] Temperature setting unit 12a, temperature input unit 12b, first temperature determination unit 12c, second temperature determination unit 12d, third temperature determination unit 12e, and first power-on control unit 12f constitute the main program for performing the above (see reference). Figure 5 The temperature setting unit 12a is a control unit that sets the first threshold temperature T1, the second threshold temperature T2, and the third threshold temperature T3. The temperature setting unit 12a is configured to execute step S1 (see reference). Figure 5 The temperature input unit 12b is a control unit that obtains information about the temperature Tx of the catalyst bed from the temperature detection unit 28. The temperature input unit 12b is configured to execute step S2 (see reference). Figure 5 (The action of ).

[0091] The first temperature determination unit 12c is a control unit that compares the catalyst bed temperature Tx obtained from the temperature detection unit 28 with the first threshold temperature T1 set by the temperature setting unit 12a to determine the magnitude relationship. Figure 5 The second temperature determination unit 12d is a control unit that compares the catalyst bed temperature Tx obtained from the temperature detection unit 28 with the second threshold temperature T2 set by the temperature setting unit 12a to determine the magnitude relationship. The temperature determination unit 12c is configured to execute step S5 (see reference). Figure 5 The third temperature determination unit 12e is a control unit that compares the catalyst bed temperature Tx obtained from the temperature detection unit 28 with the third threshold temperature T3 set by the temperature setting unit 12a to determine the magnitude relationship. Figure 5 (The action of ).

[0092] The first energization control unit 12f is a control unit that controls the energization of a pair of electrodes 24 based on the results obtained from the first temperature determination unit 12c, the second temperature determination unit 12d, and the third temperature determination unit 12e. The first energization control unit 12f is configured to execute steps S4, S6, S8, and S9 (see...). Figure 5 (The action of ).

[0093] The mode determination unit 12g and the second power-on control unit 12h perform the above-mentioned subroutines (see reference). Figure 6 The mode determination unit 12g is a control unit that determines the operating mode of the internal combustion engine 1. The mode determination unit 12g is configured to execute steps S11 and S13 (see reference). Figure 6 The second power-on control unit 12h is a control unit that controls the on / off state of the pair of electrodes 24 based on the result obtained by the mode determination unit 12g. The second power-on control unit 12h is configured to execute step S12 (see...). Figure 6 (The action of ).

[0094] The functions of each part of the control device 12 can also be implemented by a computer program. This computer program can be read from a non-transitory recording medium or downloaded via the Internet. In this case, a program for causing the computer to execute the aforementioned exhaust gas purification method is also an aspect of the invention disclosed herein. Furthermore, a recording medium on which the operation of each part of the control device 12 is written and can be read by a computer is also an aspect of the invention disclosed herein. Examples of non-transitory recording media include semiconductor recording media such as ROM and non-volatile memory cards; optical recording media such as DVD, MD, and CD; and magnetic recording media such as magnetic tape.

[0095] The above provides detailed examples of the technology disclosed herein, but these are merely illustrative and do not limit the scope of the claims. The technology described in the claims includes technologies obtained by various modifications and alterations to the above-illustrated examples.

[0096] For example, in the power-on control program of the electrically heated exhaust gas purification catalyst system 10 of the above embodiment, in step S1, the predetermined temperatures are set as the first threshold temperature T1, the second threshold temperature T2 and the third threshold temperature T3. However, each threshold temperature does not need to be constant and can be appropriately changed during repeated main program processing.

[0097] For example, since the rate of temperature rise and the frequency of temperature rise / fall of the catalyst bed vary depending on the driver's driving mode, a feedback mechanism corresponding to the rate of temperature rise / fall and the frequency of temperature rise / fall of the catalyst bed can be set up, and the first threshold temperature T1 and the second threshold temperature T2 can be appropriately changed, so that the time during driving when the temperature of the catalyst bed is within the NOx purification reduction temperature range can be reduced.

[0098] Explanation of reference numerals in the attached figures

[0099] 1. Internal combustion engine (engine)

[0100] 2 exhaust pipes

[0101] 10. Electrically heated exhaust gas purification catalyst system

[0102] 12 Control Units (ECUs)

[0103] 20, 40 Electrically heated catalyst unit (EHC)

[0104] 22, 42 outer cylinder

[0105] 24, 44 electrodes

[0106] 25 Electrode Layers

[0107] 26. Substrate (Heating Element)

[0108] 28 Temperature Detection Section (Thermocouples)

[0109] 30, 50 Catalyst Section

[0110] 32 cabins

[0111] 34. Partition wall

[0112] 46. ​​Heating element

[0113] 51. Substrate.

Claims

1. An electrically heated exhaust gas purification catalyst system for purifying exhaust gas from an internal combustion engine, characterized in that, include: An electrically heated catalyst device, disposed in the exhaust pipe of an internal combustion engine, purifies the exhaust gas discharged from the internal combustion engine. The electrically heated catalyst device includes: The outer cylinder connected to the exhaust pipe; A pair of electrodes; The catalyst section includes a catalyst bed that is capable of contacting the exhaust gas introduced into the outer cylinder and contains at least one catalyst metal that functions as a three-way catalyst. A heating element that generates heat when the pair of electrodes is energized, thereby heating the catalyst bed; and A temperature detection unit capable of detecting the temperature of the catalyst bed, and A control device that controls the energizing of the pair of electrodes. The control device is configured to perform the following power-on control steps 1 to 4 based on the temperature information of the catalyst bed input from the temperature detection unit: Step 1: When the temperature of the catalyst bed is below the first threshold temperature T1 set within the range of 350±25℃, energize the pair of electrodes; Step 2: When the temperature of the catalyst bed is higher than the first threshold temperature T1 and lower than the second threshold temperature T2 set within the range of 450±25℃, the pair of electrodes are not energized; Step 3: When the temperature of the catalyst bed is higher than the second threshold temperature T2 and lower than the third threshold temperature T3, which is set to be above 550°C, energize the pair of electrodes; Step 4: When the temperature of the catalyst bed exceeds the third threshold temperature T3, do not energize the pair of electrodes.

2. The electrically heated waste gas purification catalyst system as described in claim 1, characterized in that: When performing the power-on control in step 3, the control device is configured to also perform the following control: Step 3-1: When no combustion gases are produced in the internal combustion engine, the pair of electrodes are not energized.

3. The electrically heated waste gas purification catalyst system as described in claim 2, characterized in that: The mode in which no combustion gases are produced in the internal combustion engine is idling stop or fuel cut-off.

4. The electrically heated waste gas purification catalyst system as described in any one of claims 1 to 3, characterized in that: The catalyst bed contains at least rhodium as the catalyst metal.

5. The electrically heated waste gas purification catalyst system as described in any one of claims 1 to 3, characterized in that: The internal combustion engine is a gasoline engine or a diesel engine used in vehicles.

6. A method for purifying exhaust gas discharged from an internal combustion engine using an electrically heated catalyst device disposed in the exhaust pipe of the internal combustion engine, characterized in that: The electrically heated catalyst device includes: an outer cylinder connected to the exhaust pipe; a pair of electrodes; a catalyst section including a catalyst bed that is in contact with the exhaust gas introduced into the outer cylinder and contains at least one catalyst metal that functions as a three-way catalyst; a heating element that heats up when the pair of electrodes are energized, thereby heating the catalyst bed; and a temperature detection unit capable of detecting the temperature of the catalyst bed. The exhaust gas purification method performs the following power-on control steps 1 to 4 based on the temperature information of the catalyst bed obtained from the temperature detection unit: Step 1: When the temperature of the catalyst bed is below the first threshold temperature T1 set within the range of 350±25℃, energize the pair of electrodes; Step 2: When the temperature of the catalyst bed is higher than the first threshold temperature T1 and lower than the second threshold temperature T2 set within the range of 450±25℃, the pair of electrodes are not energized; Step 3: When the temperature of the catalyst bed is higher than the second threshold temperature T2 and lower than the third threshold temperature T3, which is set to be above 550°C, energize the pair of electrodes; Step 4: When the temperature of the catalyst bed exceeds the third threshold temperature T3, do not energize the pair of electrodes.

7. The waste gas purification method as described in claim 6, characterized in that: The power-on control in step 3 also includes the following controls: Step 3-1: When no combustion gases are produced in the internal combustion engine, the pair of electrodes are not energized.

8. The waste gas purification method as described in claim 7, characterized in that: The mode in which no combustion gases are produced in the internal combustion engine is idling stop or fuel cut-off.

9. The waste gas purification method according to any one of claims 6 to 8, characterized in that: The catalyst bed contains at least rhodium as the catalyst metal.

10. The waste gas purification method according to any one of claims 6 to 8, characterized in that: The internal combustion engine is a gasoline engine or a diesel engine used in vehicles.

11. A control program product, characterized in that: The control program product includes a control program for causing a computer to execute the exhaust gas purification method according to any one of claims 6 to 10.

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