Control device for electrically heated catalysts

Abstract

To provide a controller for electrically-heated catalysts that enables enhancement in purification performance and reduction in overheating and power consumption.SOLUTION: A controller for electrically-heated catalysts purifies exhaust from an internal combustion engine. The controller includes: a first acquisition unit that acquires the temperature of the electrically-heated catalyst; a second acquisition unit that acquires a purification rate of exhaust by the electrically-heated catalyst; and a control unit that controls power supplied to the electrically-heated catalyst on the basis of the temperature and the purification rate.SELECTED DRAWING: Figure 2

Description

Technical Field

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

Background Art

[0002] A catalyst for purifying the exhaust gas of an internal combustion engine is provided in an exhaust passage. An electrically heated catalyst (EHC, Electrically Heated Catalyst) is heated and activated by being energized (see Patent Document 1, etc.). When the catalyst is activated, the exhaust gas purification performance is improved.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] When the power increases, the generated heat also increases. The catalyst may be damaged by excessive heat. The power consumption also increases. Therefore, an object is to provide a control device for an electrically heated catalyst that can improve the purification performance and suppress overheating and power consumption.

Means for Solving the Problems

[0005] The above object can be achieved by a control device for an electrically heated catalyst that purifies the exhaust gas of an internal combustion engine, the control device including: a first acquisition unit that acquires the temperature of the electrically heated catalyst; a second acquisition unit that acquires the purification rate of the exhaust gas by the electrically heated catalyst; and a control unit that controls the power supplied to the electrically heated catalyst based on the temperature and the purification rate.

[0006] The control device may further include a third acquisition unit that acquires a target value of the purification rate, and the control unit may control the power so that the purification rate approaches the target value.

[0007] If the purification rate or the temperature is below a predetermined value, the control unit may supply power. [Effects of the Invention]

[0008] This invention provides a control device for an electrically heated catalyst that can improve exhaust gas purification performance while suppressing overheating and power consumption. [Brief explanation of the drawing]

[0009] [Figure 1] Figure 1 is a diagram illustrating an engine system according to the first embodiment. [Figure 2] Figure 2 is a flowchart illustrating the process in the first embodiment. [Figure 3] Figure 3 illustrates the purification rate. [Figure 4] Figure 4 is a flowchart illustrating the process in the second embodiment. [Figure 5] Figure 5 is an example of a time chart. [Modes for carrying out the invention]

[0010] <First Embodiment> The control device for the electrically heated catalyst of the first embodiment will now be described with reference to the drawings. Figure 1 is a diagram illustrating the engine system 100 according to the first embodiment.

[0011] The engine system 100 includes an internal combustion engine 10, an exhaust gas purification device 20, and an ECU (Electronic Control Unit) 40. The internal combustion engine 10 generates power by burning fuel such as gasoline. An intake passage 12 and an exhaust passage 14 are connected to the internal combustion engine 10. Air flows through the intake passage 12 and is introduced into the internal combustion engine 10. A throttle valve 16 and an airflow meter 18 are provided in the intake passage 12, arranged in this order from the upstream side. When the opening of the throttle valve 16 increases, the airflow rate in the intake passage increases. When the opening decreases, the airflow rate decreases. The airflow meter 18 detects the airflow rate.

[0012] A temperature sensor 15 and an exhaust gas purification device 20 are provided in the exhaust passage 14. The exhaust gas purification device 20 includes a heater 21, a catalyst 22, and a catalyst 24. The heater 21, catalyst 22, and catalyst 24 are installed in the exhaust passage 14 of the internal combustion engine 10, arranged in this order from the upstream side. The heater 21 and catalyst 22 are integrated on the same carrier to form an electrically heated catalyst 26. The temperature sensor 15 is installed, for example, downstream of the electrically heated catalyst 26 and upstream of the catalyst 24. Instead of installing a temperature sensor 15, the ECU 40 may estimate the temperature from the operating state of the internal combustion engine 10 and the energization state of the heater 21.

[0013] Catalysts 22 and 24 are, for example, three-way catalysts that purify substances such as carbon monoxide (CO) and nitrogen oxides (NOx). The exhaust gas purification device 20 may have a filter such as a GPF (Gasoline Particulate Filter). The heater 21 contains metal and has higher conductivity than the exhaust passage 14.

[0014] The power supply 30 includes, for example, a battery and a current-voltage source. The power supply 30 is electrically connected to the heater 21. A current sensor 32 and a voltage sensor 34 are provided in the wiring connecting the power supply 30 and the heater 21. The current sensor 32 is connected in series with the heater 21 and detects the current flowing through the heater 21. The voltage sensor 34 is connected in parallel with the heater 21 and detects the voltage applied to the heater 21.

[0015] The ECU40 is a control device for the electrically heated catalyst 26, and is equipped with memory devices such as a CPU (Central Processing Unit), RAM (Random Access Memory), and ROM (Read Only Memory). It performs various controls by executing programs stored in the ROM and other memory devices.

[0016] The ECU 40 controls the opening degree of the throttle valve 16. The ECU 40 obtains the airflow rate (intake volume) from the airflow meter 18 and estimates the exhaust flow rate based on the intake volume. The ECU 40 obtains the temperature of the exhaust passage 14 from the temperature sensor 15. The ECU 40 obtains the current detected by the current sensor 32 and the voltage detected by the voltage sensor 34.

[0017] The ECU 40 functions as a first acquisition unit that acquires the temperature of catalyst 22 and catalyst 24 based on, for example, current, voltage, exhaust temperature, and operating conditions of the internal combustion engine 10. Operating conditions include, for example, intake air volume, rotational speed, and ignition timing. The ECU 40 functions as a second acquisition unit that acquires the purification rate of the electrically heated catalyst 26 and catalyst 24 based on the temperature and operating conditions of the internal combustion engine 10. The ECU 40 functions as a third acquisition unit that acquires a target value for the purification rate.

[0018] The ECU 40 functions as a control unit that controls the power supply 30. The ECU 40 controls the power input from the power supply 30 to the heater 21 by controlling the current and voltage. The heater 21 generates heat when energized. The heat of the heater 21 is transmitted to the catalyst 22 and the catalyst 24 by exhaust gas or the like, so that the temperatures of the catalyst 22 and the catalyst 24 increase. The catalyst 22 and the catalyst 24 are activated by the temperature increase, and the purification rate increases. The ECU 40 adjusts the temperature of the electric heating type catalyst 26 and the temperature of the catalyst 24 by controlling the power, and controls the purification rate of the electric heating type catalyst 26 and the purification rate of the catalyst 24. The ECU 40 can bring the purification rate of the electric heating type catalyst 26 and the purification rate of the catalyst 24 closer to their respective target values by changing the temperature.

[0019] Figure 2 is a flowchart illustrating the processing in the first embodiment. The ECU 40 acquires the temperature and purification rate of the electric heating type catalyst 26 (step S10). The ECU 40 acquires the temperature and purification rate of the catalyst 24 (step S12). The ECU 40 acquires the target value of the purification rate of the electric heating type catalyst 26 and the target value of the purification rate of the catalyst 24 based on, for example, the operating conditions of the internal combustion engine 10 (step S14). The ECU 40 calculates the power to be input to the heater 21 (step S16) and energizes it with the calculated power (step S18). The heater 21 generates heat when energized. The catalysts 22 and 24 are activated by the temperature increase. The purification rate approaches the target value. The processing of Figure 2 ends here.

[0020] Figure 3 is a diagram illustrating the purification rate. The horizontal axis represents the temperature of the catalyst. The vertical axis represents the purification rate. The purification rate in Figure 3 is, for example, the sum of the purification rate of the electric heating type catalyst 26 and the purification rate of the catalyst 24. G1 and G2 represent the exhaust gas flow rate. G2 is greater than G1. A1 and A2 represent the purification rate. A1 is the purification rate before heating. A2 is within the target purification rate.

[0021] Assume that the flow rate is G1, the temperature is T1, and the purification rate is A1. The ECU 40 obtains the target value A2 through the process shown in FIG. 2 and conducts energization. The temperature rises from T1 to T2. The catalysts 22 and 24 are activated due to the temperature rise. The purification rate rises from A1 to the target value A2.

[0022] Assume that the flow rate is G2, the temperature is T3, and the purification rate is A1. The ECU 40 conducts energization. The temperature rises from T3 to T4. The purification rate rises from A1 to the target value A2.

[0023] According to the first embodiment, the ECU 40 acquires the temperatures and purification rate of the electric heating type catalyst 26 and the catalyst 24 (steps S10 and S12 in FIG. 2). Based on the temperature and purification rate, the ECU 40 determines the electric power and energizes the heater 21 (steps S16 and S18). The heater 21 generates heat, and the temperatures of the catalysts 22 and 24 rise. The catalysts 22 and 24 are activated, and the purification rate increases. The exhaust purification performance can be enhanced.

[0024] By continuously applying excessive electric power, the electric heating type catalyst 26 may be damaged. Also, the power consumption increases. According to the first embodiment, the ECU 40 controls the electric power according to the temperature and purification rate, for example, controls the magnitude of the electric power and the time for which the electric power is applied. Overheating of the electric heating type catalyst 26 can be suppressed, and the power consumption can be suppressed.

[0025] The ECU 40 acquires the target value of the purification rate (step S14). The ECU 40 controls the electric power so that the purification rate approaches the target value. As shown in FIG. 3, the purification rate rises toward the target value A2 due to the temperature rise. The purification performance improves. Since energization is performed so that the purification rate becomes the target value, it is difficult for the electric power to become excessively large. Overheating of the electric heating type catalyst 26 can be suppressed, and the power consumption can be suppressed.

[0026] The exhaust passage 14 is equipped with an electrically heated catalyst 26 and a catalyst 24. Catalyst 24 is located downstream of the electrically heated catalyst 26. Heat generated by the heater 21 of the electrically heated catalyst 26 is transferred to catalyst 24 by the exhaust gas. This activates both the electrically heated catalyst 26 and catalyst 24, improving purification performance. Two or more catalysts may be provided downstream of the electrically heated catalyst 26. Catalyst 24 may not be provided.

[0027] <Second Embodiment> The configuration shown in Figure 1 also applies to the second embodiment. The same configuration as in the first embodiment will not be described.

[0028] Figure 4 is a flowchart illustrating the process in the second embodiment. At the start of the process in Figure 4, power from the power supply 30 is assumed to be off. The ECU 40 performs steps S10, S12, and S14. The ECU 40 determines whether or not power is required (step S15). For example, if the purification rate is above the target value, power is not required, and a negative determination (No) is made in step S15. The process in Figure 4 is completed.

[0029] If the purification rate is below the target value, a positive judgment (Yes) is made in step S15. The ECU 40 calculates the power and energizes the unit (steps S16 and S18). This completes the process shown in Figure 4.

[0030] Figure 5 is an example of a time chart. From top to bottom, it shows the current flow, purification performance, catalyst temperature, and vehicle speed. In the example in Figure 5, the vehicle repeatedly accelerates and decelerates. The vehicle speed repeatedly increases and decreases.

[0031] Between times t1 and t2, power is supplied (turned on). Heater 21 generates heat, causing the temperature to rise above T0. Purification performance increases and reaches the target value A2 or higher. After power is supplied (turned off), purification performance and temperature decrease. At time t3, purification performance falls below the target value A2. The temperature falls below T0. Between times t3 and t4, power is supplied (step S18 in Figure 4). The temperature rises above T0. Purification performance increases and reaches the target value A2 or higher.

[0032] According to the second embodiment, when the purification rate is less than or equal to the target value A2, the ECU 40 energizes (step S18). The purification rate increases from less than or equal to the target value A2 toward the target value A2. When the purification rate is greater than or equal to the target value A2, the energization is stopped. The ECU 40 monitors the purification rate and controls the power. The exhaust gas purification performance can be improved. Overheating and power consumption of the electrically heated catalyst 26 can be suppressed. The ECU 40 may acquire the temperature detected by the temperature sensor 15 and start energizing when the temperature falls below T0.

[0033] Although preferred embodiments of the present invention have been described in detail above, the present invention is not limited to these specific embodiments, and various modifications and changes are possible within the scope of the gist of the present invention as described in the claims. [Explanation of Symbols]

[0034] 10 Internal combustion engine, 12 Intake passage, 14 Exhaust passage, 15 Temperature sensor, 16 Throttle valve, 18 Airflow meter, 20 Exhaust purification device, 21 Heater, 22, 24 Catalytic converter, 26 Electrically heated catalytic converter, 30 Power supply, 32 Current sensor, 34 Voltage sensor, 40 ECU, 100 Engine system

Claims

1. A control device for an electrically heated catalyst that purifies the exhaust gas of an internal combustion engine, A first acquisition unit for acquiring the temperature of the electrically heated catalyst, A second acquisition unit that acquires the exhaust gas purification rate by the electrically heated catalyst based on the temperature, A third acquisition unit for acquiring the target value of the purification rate, The system comprises a control unit that controls the power supplied to the electrically heated catalyst so that the purification rate approaches the target value, based on the temperature, the exhaust flow rate of the internal combustion engine, and the purification rate. A control device for an electric heating catalyst, wherein the control unit controls the power so that the purification rate approaches the target value, and so that the temperature of the electric heating catalyst when the exhaust flow rate is high is higher than the temperature of the electric heating catalyst when the exhaust flow rate is low.

2. The control device for an electrically heated catalyst according to claim 1, wherein the control unit supplies power when the purification rate or the temperature is below a predetermined value.

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