Control apparatus for electrically heated catalyst

Abstract

To suppress deterioration of a surface electrode of an electric heating type catalyst.SOLUTION: An electric control unit (17) for controlling electric power supplied to a EHC10 includes a carrier (12) carrying a catalytic material, a pair of electrodes (13) formed on outer surfaces of the carrier (12), and a pair of metallic wires (14) connected to the pair of electrodes (13), respectively. The electric control unit (17) sets a power limit based on a temperature of the pair of electrodes (13) and controls the electric power supplied to the EHC10 to be equal to or lower than the power limit.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a control device for an electrically heated catalyst. [Background technology]

[0002] Electrically heated catalysts are known as exhaust purification devices for internal combustion engines mounted on vehicles, etc. Electrically heated catalysts are configured so that a ceramic carrier carrying a catalytic material generates heat in response to the passage of electricity, thereby promoting the activation of the catalytic material. Patent Document 1 describes an electrically heated catalyst having a surface electrode formed on the outer surface of the carrier by thermal spraying or the like, and metal wiring connected to the carrier via the surface electrode. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Laid-Open No. 2013-136997 Summary of the Invention [Problem to be solved by the invention]

[0004] In the electrically heated catalyst described above, there is a risk that the surface electrodes may be deteriorated due to electromigration or the like. [Means for solving the problem]

[0005] The control device for an electrically heated catalyst that solves the above problem is a device that controls the supply power of an electrically heated catalyst that has a carrier on which a catalytic material is supported, a surface electrode formed on the outer surface of the carrier, and metal wiring connected to the surface electrode, and is configured to set a power limit value based on the electrode temperature, which is the temperature of the surface electrode, and to control the supply power of the electrically heated catalyst so that it is below the power limit value. [Effects of the Invention]

[0006] The control device of the above-described electric heating type catalyst has an effect of suppressing deterioration of the surface electrodes.

Brief Description of the Drawings

[0007] [Figure 1] It is a diagram schematically showing the configuration of an embodiment of a control device for an electric heating type catalyst. [Figure 2] It is a flowchart of a power control routine executed by the control device of FIG. 1. [Figure 3] It is a graph showing the relationship between the electrode temperature and the power limit value. [Figure 4] During electric heating control, (a) is a time chart showing the transition of the catalyst bed temperature, (b) is a time chart showing the transition of the supplied power, and (c) is a time chart showing the transition of the electrode temperature.

Modes for Carrying Out the Invention

[0008] Hereinafter, an embodiment of a control device for an electric heating type catalyst will be described in detail with reference to FIGS. 1 to 4. In the following description, the electric heating type catalyst is described as EHC (Electrically Heated Catalyst).

[0009] <Configuration of EHC and Its Control Device> As shown in FIG. 1, the EHC 10 is installed in the exhaust pipe 11 of an internal combustion engine. The EHC 10 includes a carrier 12. The carrier 12 is a porous member on which a catalyst substance such as platinum or palladium is supported. The carrier 12 is composed of a conductive ceramic base material such as silicon carbide. The inside of the carrier 12 has a honeycomb structure.

[0010] On the outer surface of the carrier 12, a pair of surface electrodes 13 are arranged so as to face each other. The surface electrode 13 is a metal-based sprayed coating formed on the outer surface of the carrier 12 and is composed of, for example, a Ni-Cr alloy, a MCrAlY alloy (M is one or more of Fe, Co, Ni).

[0011] Metal wiring 14 is connected to each of the surface electrodes 13. The metal wiring 14 is a ribbon-shaped thin metal plate made of a heat-resistant, oxidation-resistant alloy such as a stainless steel alloy, a Ni-based alloy, or a Co-based alloy.

[0012] The EHC 10 is electrically connected to a battery 16 via metal wiring 14. A power conversion circuit 15 for adjusting the power supplied to the EHC 10 is installed between the battery 16 and the EHC 10. In this embodiment, a voltage conversion circuit capable of adjusting the supply voltage of the EHC 10 is used as the power conversion circuit 15.

[0013] The power conversion circuit 15 is controlled by an electronic control unit 17. The electronic control unit 17 has a storage device 18 and a processing device 19. The storage device 18 stores programs and data used to control the power supply of the EHC 10. The processing device 19 reads and executes the programs from the storage device 18 to perform various processes for controlling the power supply of the EHC 10. The electronic control unit 17 acquires, from the power conversion circuit 15, the current value IC and the voltage value VC of the power to be supplied to the EHC 10. In this embodiment, the electronic control unit 17 corresponds to the control device of the EHC 10.

[0014] <Electric heating control> Next, the electric heating control of the EHC 10 executed by the electronic control unit 17 will be described with reference to Figures 2 and 3. Figure 2 shows the processing procedure of an electric heating control routine executed by the electronic control unit 17 for electric heating control. The electronic control unit 17 repeatedly executes this routine at predetermined control intervals while the internal combustion engine is operating.

[0015] When the electronic control unit 17 starts the processing of this routine, first in step S100, it determines whether or not electric heating of the EHC 10 is required. Whether or not electric heating is required is determined, for example, based on whether or not the catalyst bed temperature THC of the EHC 10 is lower than a target temperature. The electronic control unit 17 estimates the catalyst bed temperature THC based on the operating conditions of the internal combustion engine. If the electronic control unit 17 determines that electric heating is required (YES), the processing proceeds to step S105. On the other hand, if the electronic control unit 17 determines that electric heating is not required (NO), the processing of this routine for the current control cycle ends.

[0016] When the process proceeds to step S105, the electronic control unit 17 calculates the reference electric power PTRG in step S105. The reference electric power PTRG is a value that serves as a base for calculating the electric power supplied to the EHC 10. The reference electric power PTRG may be a fixed value, or may be calculated based on, for example, the catalyst bed temperature THC.

[0017] Next, in step S110, the electronic control unit 17 determines whether or not the supply of electricity to the EHC 10 is continuing. Here, it is determined that the supply of electricity is not continuing when the EHC 10 starts electric heating.

[0018] If the electronic control unit 17 determines that the current supply is not continuing (NO), in step S115, it sets the catalyst bed temperature THC as the value of the electrode temperature THS, and then proceeds to step S130. The electrode temperature THS represents the temperature of the surface electrode 13. The setting of the electrode temperature THS here reflects the fact that the temperature of the surface electrode 13 before the start of electric heating is approximately the same as that of the support 12.

[0019] On the other hand, if the electronic control unit 17 determines that the power supply is continuing (S110: YES), then in step S120, the electronic control unit 17 calculates the temperature change amount ΔT of the surface electrode 13 based on the current value IC and voltage value VC of the power currently being supplied to the EHC 10. The amount of heat generated by the surface electrode 13 due to the power supply can be estimated from the current value IC and voltage value VC, and the temperature change amount ΔT of the surface electrode 13 can be calculated from the amount of heat generated. In this embodiment, the relationship between the current value IC and voltage value VC and the temperature change amount ΔT is determined in advance through experiments or the like, and this relationship is stored in the storage device 18 of the electronic control unit 17 in the form of a calculation map MAP1. The electronic control unit 17 then calculates the temperature change amount ΔT using the calculation map MAP1. In the next step S125, the electronic control unit 17 updates the value of the electrode temperature THS based on the temperature change amount ΔT. Specifically, the electronic control unit 17 adds the temperature change amount ΔT to the value before the update, and updates the value of the electrode temperature THS so that the added value becomes the updated value. After that, the electronic control unit 17 proceeds to step S130.

[0020] In step S130, the electronic control unit 17 calculates the power limit value PLMT based on the electrode temperature THS. In this embodiment, the electronic control unit 17 calculates the power limit value PLMT using a calculation map MAP2 stored in advance in the storage device 18.

[0021] The solid line L1 in the graph of FIG. 3 indicates the relationship between the electrode temperature THS and the power limit value PLMT in the calculation map MAP2. "PMAX" in FIG. 3 indicates the allowable upper limit of the power supply of the EHC 10, which is determined based on the specifications of the EHC 10 and the power conversion circuit 15. Temperature TH2 in FIG. 3 indicates the upper limit of the range of electrode temperatures THS at which the progression of deterioration of the surface electrode 13 due to electromigration or the like can be suppressed to an allowable range. In this embodiment, the value of the power limit value PLMT is fixed to "PMAX" when the electrode temperature THS is below temperature TH1. Furthermore, the value of the power limit value PLMT is fixed to "0" when the electrode temperature THS is above temperature TH2. Within the range from temperature TH1 to temperature TH2, the value of the power limit value PLMT is calculated so that it decreases continuously as the electrode temperature THS increases, from "PMAX" at temperature TH1 to "0" at temperature TH2.

[0022] After calculating the power limit value PLMT in step S130, the electronic control unit 17 proceeds to step S135. In step S135, the electronic control unit 17 sets the smaller of the reference power PTRG and the power limit value PLMT as the value of the required power PREQ.

[0023] Next, in step S140, electronic control unit 17 calculates an electrical resistance value RC of EHC 10 from current value IC and voltage value VC (RC = VC / IC). Then, in the following step S145, electronic control unit 17 calculates, based on electrical resistance value RC, the voltage of EHC 10 required to supply power equal to the value of requested power PREQ, as the value of requested voltage VREQ. Then, in step S150, electronic control unit 17 adjusts the voltage supplied to EHC 10 by power conversion circuit 15 so that the voltage is equal to requested voltage VREQ, and then ends the processing of this routine for the current control cycle.

[0024] <Operation of the embodiment> When controlling the electric heating of the EHC 10, the electronic control unit 17 estimates the electrode temperature THS, which is the temperature of the surface electrode 13, and sets the power limit value PLMT based on the estimated electrode temperature THS. The electronic control unit 17 then controls the power supply of the EHC 10 so that the power supply is equal to or less than the power limit value PLMT.

[0025] FIG. 4 shows an example of such a control mode of electric heating control. FIG. 4(a) shows the transition of the catalyst bed temperature THC during electric heating control, FIG. 4(b) shows the transition of the power supply to the EHC 10 during electric heating control, and FIG. 4(c) shows the transition of the electrode temperature THS during electric heating control. In addition, FIGS. 4(a) to 4(c) also show, with dashed lines, the transitions of the catalyst bed temperature THC, the power supply, and the electrode temperature THS during electric heating control in a control device that is a comparative example of this embodiment. The control device of the comparative example is configured to perform electric heating control without setting the power limit value PLMT based on the electrode temperature THS or limiting the power supply to the EHC 10 based on the power limit value PLMT. Here, in both this embodiment and the comparative example, the reference power PTRG is set to a fixed value.

[0026] 4, in both the present embodiment and the comparative example, at time t0, the supply power is set to the reference power PTRG and the EHC 10 begins to be energized. In the comparative example, the supply power to the EHC 10 is maintained at the reference power PTRG until the catalyst bed temperature THC reaches the target temperature at time t2 and the EHC 10 stops being energized. In the comparative example, during energization, the electrode temperature THS exceeds the upper limit temperature TH2 at which degradation of the front surface electrode 13 due to electromigration can be suppressed.

[0027] In contrast, in this embodiment, the limitation of the supplied power by the power limit value PLMT begins at time t1 when the electrode temperature THS exceeds temperature TH1. This limitation suppresses the increase in the electrode temperature THS after time t1. As a result, the catalyst bed temperature THC reaches the target temperature at time t3, which is later than in the comparative example, but the electrode temperature THS during current flow does not increase until it exceeds temperature TH2.

[0028] <Effects of the embodiment> The electrically heated catalyst control device of this embodiment has the following advantages. (1) The electronic control unit 17 sets the power limit value PLMT based on the electrode temperature THS and controls the power supplied to the EHC 10 so that the power is equal to or less than the power limit value PLMT. This prevents the electrode temperature THS from increasing while the EHC 10 is energized. Therefore, the control device of this embodiment is effective in preventing deterioration of the surface electrode EHC 10.

[0029] (2) The electronic control unit 17 estimates the electrode temperature THS based on the power supplied to the EHC 10, more specifically, based on the current value IC and voltage value VC of the supplied power. Therefore, the electric heating control of the EHC 10 can be performed based on the electrode temperature THS without installing an additional sensor for detecting the electrode temperature THS.

[0030] (Other embodiments) The above embodiment can be modified as follows: The above embodiment and the following modifications can be combined with each other within the scope of technical compatibility.

[0031] The manner in which the power limit value PLMT is set in step S130 in Fig. 2 may be changed. For example, as shown by the dashed line L2 in Fig. 3, the power limit value PLMT may be set so as to decrease in stages within the range of the electrode temperature THS from temperature TH1 to temperature TH2. Furthermore, as shown by the dashed line L3 in Fig. 3, the power limit value PLMT may be set to "PMAX" when the electrode temperature THS is below temperature TH2, and to "0" when the electrode temperature THS is equal to or higher than TH2.

[0032] The method of calculating the electrode temperature THS may be changed in steps S110 to S125 in Fig. 2. For example, a sensor for detecting the electrode temperature THS may be installed in the EHC 10, and the electrode temperature THS may be calculated from the detection result.

[0033] The contents of the processes relating to the determination of whether or not electrical heating is necessary in step S100 of FIG. 2, the calculation of the reference power PTRG in step S105, and the adjustment of the supplied power in steps S140 to S150 may be changed. [Explanation of symbols]

[0034] 10...electrically heated catalyst (EHC), 12...support, 13...surface electrode, 14...metal wiring, 17...electronic control unit (control device).

Claims

1. An apparatus for controlling the supply power of an electrically heated catalyst, the apparatus comprising: a carrier on which a catalytic material is supported; a surface electrode formed on the outer surface of the carrier; and metal wiring connected to the surface electrode, A power limit value is set based on the electrode temperature, which is the temperature of the surface electrode, and the power supplied to the electrically heated catalyst is controlled so that the power limit value is equal to or less than the power limit value. Control device for electrically heated catalyst.

2. 2. The control device for an electrically heated catalyst according to claim 1, wherein the electrode temperature is estimated based on the power supplied to the surface electrode.

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