Vehicle control device

Abstract

Provided is a control device for a vehicle in which an engine is mounted. An engine is provided with a three-way catalyst device provided in an exhaust passage. The control device includes a processing circuit. The processing circuit is configured to implement: a determination process for determining whether or not there is a state in which a large amount of ammonia is discharged from the three-way catalytic device; and a combustion temperature reduction process for reducing the combustion temperature of the engine when it is determined in the determination process that the engine is in a state in which the discharge amount is large.

Description

Technical Field

[0001] This disclosure relates to vehicle control devices. Background Technology

[0002] Japanese Patent Application Publication No. 2015-124683 discloses a control device for a hybrid vehicle that uses an engine equipped with a three-way catalytic converter and an electric motor as drive sources. The hybrid vehicle using this control device is configured to switch between electric driving (where the engine is off and the electric motor is used for propulsion) and hybrid driving (where the engine is used for propulsion) depending on the situation. When switching from electric driving to hybrid driving, the control device suppresses NOx emissions into the atmosphere by increasing the amount of fuel injected into the engine. Summary of the Invention

[0003] The problem that the invention aims to solve

[0004] When the internal atmosphere of a three-way catalytic converter is reducing and the temperature is high, ammonia may be generated. Therefore, increasing the fuel injection rate to reduce NOx emissions may increase ammonia emissions.

[0005] Methods for solving problems

[0006] The vehicle control device disclosed herein is a control device for a vehicle equipped with an engine. The engine includes a three-way catalytic converter located in the exhaust passage. The control device includes a processing circuit. The processing circuit is configured to perform: a determination process to determine whether the ammonia emission from the three-way catalytic converter is excessive; and a combustion temperature reduction process, wherein when the determination process determines that the ammonia emission is excessive, the combustion temperature of the engine is reduced. Attached Figure Description

[0007] Figure 1 This is a diagram schematically illustrating the structure of one embodiment of the vehicle control device.

[0008] Figure 2 yes Figure 1 The flowchart shows the process executed by the control device. Detailed Implementation

[0009] The following describes in detail one embodiment of the vehicle control device.

[0010] <Structure of the vehicle's control device>

[0011] Reference Figure 1The structure of this embodiment will be explained below. The vehicle using the control device of this embodiment is a hybrid vehicle, which has an engine 10 that generates driving force through fuel combustion and an electric motor 30 that generates driving force through power supplied from a battery 31 as driving sources. The electric motor 30 is electrically connected to the battery 31 via an inverter 32.

[0012] Engine 10 includes: a combustion chamber 11 for burning a mixture of air and fuel, an intake passage 12 for introducing intake air into the combustion chamber 11, and an exhaust passage 13 for discharging exhaust gas from the combustion chamber 11. The intake passage 12 includes: an air filter 14 for filtering dust and other impurities in the intake air, an air flow meter 15 for detecting the intake airflow, and a throttle valve 16 for regulating the intake airflow. Engine 10 includes: an injector 17 for injecting fuel into the intake air for combustion in the combustion chamber 11, and an ignition device 18 for igniting the mixture in the combustion chamber 11 by spark discharge. The exhaust passage 13 of engine 10 includes a three-way catalytic converter 19 carrying a three-way catalytic converter for purifying the exhaust gas. The three-way catalytic converter 19 has oxygen storage capacity. The exhaust passage 13 includes two air-fuel ratio sensors: a front air-fuel ratio sensor 20 and a rear air-fuel ratio sensor 21. The front air-fuel ratio sensor 20 is located upstream of the three-way catalytic converter 19 in the exhaust passage 13. The rear air-fuel ratio sensor 21 is located downstream of the three-way catalytic converter 19 in the exhaust passage 13. A NOx sensor 22, which detects the amount of nitrogen oxides (NOx) in the exhaust gas, is also located downstream of the three-way catalytic converter 19 in the exhaust passage 13. Furthermore, the engine 10 includes an EGR (Exhaust Gas Recirculation) passage 23, which serves as a recirculation path for exhaust gas to the intake air. In the following description, the exhaust gas recirculated into the intake air through the EGR passage 23 is referred to as EGR gas. An EGR cooler 24 for cooling the EGR gas and an EGR valve 25 for regulating the EGR gas flow rate are provided in the EGR passage 23.

[0013] The control device in this embodiment is an electronic control unit 40 equipped with a processing circuit 41 and a storage device 42. The storage device 42 stores programs and data for vehicle control. The electronic control unit 40 executes the programs read from the storage device 42 through the processing circuit 41 to perform various processes for vehicle control. The detection results of various sensors installed in various parts of the vehicle are input to the electronic control unit 40. In addition to the air flow meter 15, front air-fuel ratio sensor 20, rear air-fuel ratio sensor 21, and NOx sensor 22 mentioned above, the sensors installed in the vehicle also include a crankshaft angle sensor 43, a rotary transformer 44, an accelerator pedal sensor 45, and a vehicle speed sensor 46. The crankshaft angle sensor 43 is a sensor that detects the crankshaft angle of the engine 10, and the rotary transformer 44 is a sensor that detects the rotation angle of the electric motor 30. The accelerator pedal sensor 45 is a sensor that detects the amount of time the driver has pressed the accelerator pedal, and the vehicle speed sensor 46 is a sensor that detects the vehicle speed. Based on the detection results of these sensors, the electronic control unit 40 performs vehicle control, including the control of the engine 10 and the electric motor 30. The electronic control unit 40 calculates the engine speed Ne based on the detection results of the crankshaft angle sensor 43. The electronic control unit 40 also calculates the engine load rate Kl based on the detection results of the air flow meter 15 and the calculated engine speed Ne. The engine load rate Kl represents the air filling rate of the combustion chamber 11.

[0014] The electronic control unit 40 performs intermittent operation control of the engine 10. In intermittent operation control, the electronic control unit 40 automatically stops and restarts the engine 10 based on the vehicle's driving conditions and the charging status of the battery 31. The purpose of intermittent operation control is to switch between electric driving and hybrid driving, as well as to stop idling. Electric driving involves stopping the engine 10 and using the electric motor 30 for driving, while hybrid driving involves using the engine 10 for driving.

[0015] <Air-fuel ratio control of engine 10>

[0016] The three-way catalytic converter 19, located in the exhaust passage 13 of the engine 10, carries a three-way catalyst and an oxygen storage agent. The three-way catalyst purifies the exhaust by oxidizing unburned fuel components (HC, CO) and reducing NOx. The three-way catalyst exerts its maximum exhaust purification capacity under a stoichiometric atmosphere. The oxygen storage agent stores oxygen in the exhaust in a lean atmosphere with excess oxygen, and releases the stored oxygen into the exhaust in a rich atmosphere with deficient oxygen.

[0017] As part of the engine 10 control system, the electronic control unit 40 controls the air-fuel ratio of the mixture burned in the combustion chamber 11 to enable the three-way catalytic converter 19 to effectively purify the exhaust. The electronic control unit 40 performs air-fuel ratio control through two feedback controls: a main feedback control based on the detection results of the front air-fuel ratio sensor 20 and a secondary feedback control based on the detection results of the rear air-fuel ratio sensor 21. In the following description, "feedback control" will be referred to as "F / B control". As the main F / B control, the electronic control unit 40 adjusts the fuel injection quantity to make the air-fuel ratio detected by the front air-fuel ratio sensor 20 equal to the target air-fuel ratio. As the secondary F / B control, the electronic control unit 40, based on the detection results of the rear air-fuel ratio sensor 21, alternately switches the target air-fuel ratio between a lean air-fuel ratio (lean than stoichiometric air-fuel ratio) and a rich air-fuel ratio (rich than stoichiometric air-fuel ratio). In detail, in the air-fuel ratio sub-F / B control, when the air-fuel ratio detection value of the rear air-fuel ratio sensor 21 becomes a value indicating a lean air-fuel ratio, the electronic control unit 40 switches the target air-fuel ratio from a lean air-fuel ratio to a rich air-fuel ratio. When the air-fuel ratio detection value of the rear air-fuel ratio sensor 21 becomes a value indicating a rich air-fuel ratio, the electronic control unit 40 switches the target air-fuel ratio from a rich air-fuel ratio to a lean air-fuel ratio.

[0018] When combustion occurs in the combustion chamber 11 with a lean air-fuel ratio, lean exhaust gas containing unconsumed oxygen flows into the three-way catalytic converter 19. At this time, the three-way catalytic converter 19 stores oxygen from the exhaust gas using an oxygen storage agent, maintaining a stoichiometric air-fuel ratio atmosphere. Therefore, the air-fuel ratio detection value of the rear air-fuel ratio sensor 21 at this time represents the stoichiometric air-fuel ratio. However, there is an upper limit to the amount of oxygen that the three-way catalytic converter 19 can store. When the oxygen storage capacity of the three-way catalytic converter 19 reaches its upper limit, lean exhaust gas is discharged from the three-way catalytic converter 19. Therefore, the air-fuel ratio detection value of the rear air-fuel ratio sensor 21 changes from a value representing the stoichiometric air-fuel ratio to a value representing the lean air-fuel ratio. Correspondingly, the electronic control unit 40 switches the target air-fuel ratio from lean to rich in the air-fuel ratio sub-F / B control. When combustion occurs in the combustion chamber 11 with a rich air-fuel ratio, oxygen-deficient rich exhaust gas flows into the three-way catalytic converter 19. At this time, the three-way catalytic converter 19 releases the stored oxygen through the oxygen storage agent, maintaining a stoichiometric air-fuel ratio atmosphere. Therefore, the air-fuel ratio detection value of the rear air-fuel ratio sensor 21 represents the stoichiometric air-fuel ratio. Afterwards, when the three-way catalytic converter 19 releases all the stored oxygen, rich exhaust gas is discharged from the three-way catalytic converter 19. Therefore, the air-fuel ratio detection value of the rear air-fuel ratio sensor 21 changes from a value representing the stoichiometric air-fuel ratio to a value representing the rich air-fuel ratio. Correspondingly, the electronic control unit 40 switches the target air-fuel ratio from rich to lean in the air-fuel ratio sub-F / B control. Thus, the electronic control unit 40 alternately switches the target air-fuel ratio to lean and rich in the air-fuel ratio sub-F / B control.

[0019] <Ammonia Excretion Inhibition Control>

[0020] In the three-way catalytic converter 19, ammonia may sometimes be generated when the internal environment is hot and oxygen-deficient. The conditions for ammonia generation in the three-way catalytic converter 19 may occur during the catalyst preheating process after a cold start of the engine 10, immediately after fuel cut-off recovery, and immediately after recovery from intermittent shutdown. The conditions for ammonia generation may also occur during sulfur poisoning recovery control of the three-way catalytic converter 19. When ammonia is generated in the three-way catalytic converter 19, it may be released into the atmosphere in excess of the permissible amount. In this embodiment, the electronic control unit 40 performs control to suppress ammonia emissions.

[0021] Figure 2 The diagram illustrates the process executed by the electronic control unit 40 for ammonia emission suppression control. During engine 10 operation, the electronic control unit 40 repeatedly executes this process at predetermined control cycles. Figure 2 The processing.

[0022] exist Figure 2 In step S100, the electronic control unit 40 acquires a state quantity representing the operating state of the engine 10. Figure 2 In the illustrated process, in step S100, the electronic control unit 40 obtains the engine speed Ne, engine load rate Kl, air-fuel ratio AbyF, catalyst temperature Thc, and NOx emission amount Nox. In the subsequent step S110, the electronic control unit 40 calculates the ammonia emission amount Amm from the three-way catalytic converter 19 based on the obtained state variables of the engine 10. The electronic control unit 40 uses a physical model representing the relationship between the state variables of the engine 10 and the ammonia emission amount Amm to calculate the ammonia emission amount Amm.

[0023] Next, in the next step S120, the electronic control unit 40 determines whether the ammonia discharge amount Amm is above the threshold. Specifically, in this step S120, the electronic control unit 40 determines whether the ammonia discharge amount Amm calculated in step S110 is above a predetermined threshold. When the electronic control unit 40 determines that the ammonia discharge amount Amm is below the threshold (No), it ends the current control cycle. Figure 2 The processing is as follows. In contrast, when it is determined that the ammonia discharge Amm is above the determination value (yes), the electronic control unit 40 will proceed the processing to step S130.

[0024] In step S130, the electronic control unit 40 performs a combustion temperature reduction process to lower the combustion temperature in the combustion chamber 11. Examples of combustion temperature reduction processes include an EGR increase process that increases the amount of exhaust gas recirculation to the intake air and an ignition delay process that delays ignition timing. Either the EGR increase process or the ignition delay process can be performed as a combustion temperature reduction process, or both can be performed.

[0025] Next, in step S140, the electronic control unit 40 determines whether the engine torque has decreased due to the combustion temperature reduction process. The electronic control unit 40 estimates the engine torque based on the detection results from the rotary transformer 44 located in the electric motor 30. Based on the estimated engine torque, the electronic control unit 40 performs the determination in step S140. If it is determined that the engine torque has not decreased (No), the electronic control unit 40 ends the current control cycle. Figure 2 In contrast, when the electronic control unit 40 determines that the engine torque has decreased (yes), the process is advanced to step S150.

[0026] In step S150, the electronic control unit 40 performs torque compensation processing to compensate for the decrease in engine torque by increasing the electric motor torque. Then, the electronic control unit 40 ends the current control cycle. Figure 2 The processing.

[0027] <The Role of the Implementation Method>

[0028] In the three-way catalytic converter 19, ammonia may be generated when the interior is in a high-temperature, oxygen-deficient state. Such ammonia generation conditions are likely to occur when the engine 10 restarts, such as during catalyst preheating after a cold start, during recovery from an intermittent stop, or during recovery from a fuel cut-off. This is based on the following reasons.

[0029] During engine 10 shutdown, exhaust gas in exhaust passage 13 is replaced with air. Therefore, the three-way catalytic converter 19 stores a large amount of oxygen when engine 10 restarts. Thus, when air-fuel ratio sub-F / B control is initiated immediately after engine 10 restarts, the target air-fuel ratio is set to a rich air-fuel ratio. As a result, rich combustion occurs in combustion chamber 11, and rich exhaust gas flows into the three-way catalytic converter 19. Therefore, immediately after engine 10 restarts, the interior of the three-way catalytic converter 19 is in a high-temperature, oxygen-deficient state, which easily leads to ammonia formation.

[0030] In this embodiment, the electronic control unit 40 performs a determination process to determine whether the ammonia emission from the three-way catalytic converter 19 is excessive (S120). When the electronic control unit 40 determines in the determination process that the ammonia emission is excessive (S120: Yes), it performs a combustion temperature reduction process to lower the combustion temperature of the engine 10 (S130). When the combustion temperature decreases, the temperature of the exhaust gas flowing through the exhaust passage 13 decreases, and therefore the temperature inside the three-way catalytic converter 19 also decreases. As mentioned above, ammonia is easily generated when the inside of the three-way catalytic converter 19 is in a high-temperature, oxygen-deficient state. Therefore, when the combustion temperature reduction process is performed, the generation of ammonia in the three-way catalytic converter 19 is suppressed. As a result, the ammonia emitted from the engine 10 to the atmosphere is suppressed.

[0031] When the combustion temperature decreases, combustion efficiency deteriorates, and engine torque decreases. Conversely, when engine torque decreases due to the combustion temperature reduction process (S140), the electronic control unit 40 performs torque compensation processing, increasing the electric motor torque to compensate for the decrease in engine torque. Therefore, even if engine torque decreases due to the combustion temperature reduction process, the vehicle's driving force can be maintained.

[0032] <Effects of the Implementation Method>

[0033] The vehicle control device of this embodiment described above has the following effects.

[0034] (1) The electronic control unit 40 is a control device for a vehicle equipped with engine 10. Engine 10 includes a three-way catalytic converter 19 located in exhaust passage 13. The electronic control unit 40 performs a determination process to determine whether the ammonia emission Amm from the three-way catalytic converter 19 is excessive. When the determination process determines that the ammonia emission Amm is excessive, the electronic control unit 40 performs a combustion temperature reduction process to lower the combustion temperature of engine 10. Ammonia is generated when the three-way catalytic converter 19 is in a high-temperature, oxygen-deficient state. Therefore, when the combustion temperature of engine 10 is lowered, the temperature of the three-way catalytic converter 19 decreases, making it difficult for ammonia to be generated. Even if the three-way catalytic converter 19 is made into an oxygen-rich state by performing lean combustion, the generation of ammonia in the three-way catalytic converter 19 can be suppressed. However, if lean combustion is performed in a state where a large amount of oxygen is stored in the three-way catalytic converter 19, the NOx emission Nox from engine 10 will increase. In this respect, in this embodiment, ammonia generation is suppressed by performing rich combustion and lowering the combustion temperature. Therefore, the vehicle control device of this embodiment has the effect of suppressing the emission of both NOx and ammonia from the engine 10.

[0035] (2) The electronic control unit 40 implements air-fuel ratio sub-F / B control based on the detection results of the rear air-fuel ratio sensor 21 located downstream of the three-way catalytic converter 19 in the exhaust passage 13. When air-fuel ratio sub-F / B control is started, rich combustion occurs immediately after the engine 1 restarts, and ammonia is easily generated in the three-way catalytic converter 19. In this embodiment, even under such conditions where ammonia is easily generated, ammonia emission from the engine 10 can be suppressed by lowering the combustion temperature.

[0036] (3) The electronic control unit 40 implements one or both of the following processes to reduce combustion temperature: increasing the amount of exhaust gas recirculated into the intake air and delaying ignition timing. Based on these processes, the combustion temperature can be reduced under rich combustion conditions. Therefore, ammonia emissions can be suppressed without increasing NOx emissions.

[0037] (4) The electronic control unit 40 implements torque compensation processing to compensate for the decrease in engine torque caused by the reduction in combustion temperature. Therefore, it is possible to suppress the decrease in vehicle driving force caused by the reduction in combustion temperature.

[0038] <Other Implementation Methods>

[0039] The above-described embodiments can be implemented by modifications as follows. The above-described embodiments and the following modifications can be combined with each other to the extent that they do not contradict each other technically.

[0040] When the engine 10 is equipped with a variable valve timing mechanism, a process can be implemented to increase the valve overlap by driving the variable valve timing mechanism as a combustion temperature reduction process. When the valve overlap is increased, the amount of exhaust gas returning from the exhaust passage 13 to the combustion chamber 11, i.e., the so-called internal EGR amount, increases, thereby reducing the combustion temperature of the engine 10. As long as the process involves rich combustion and reduces the combustion temperature, any process other than ignition delay or EGR increase can be implemented as a combustion temperature reduction process.

[0041] An ammonia sensor for detecting the amount of ammonia in the exhaust gas can be installed in the portion of the exhaust passage 13 downstream of the three-way catalytic converter 19, and the detection results can be used for... Figure 2 The determination in step S120.

[0042] In the above embodiment, when the ammonia discharge amount Amm calculated in step S110 is above a predetermined judgment value, the electronic control unit 40 determines that the ammonia discharge amount Amm is high. However, the electronic control unit 40 may also determine that the ammonia discharge amount Amm is high when more ammonia is generated than in a certain state, for example, when more ammonia is generated than in a state where no ammonia is generated or almost no ammonia is generated. In the case of such determination, the electronic control unit 40 may not perform estimation or detection of the ammonia discharge amount Amm, but rather determine whether the ammonia discharge amount Amm is high based on the operating conditions of the engine 10. Specifically, the ammonia generation conditions in the three-way catalytic converter 19 can be determined based on the operating conditions of the engine 10, and when the generation conditions are met, the ammonia discharge amount Amm is high. For example, the ammonia discharge amount Amm can be high during catalyst preheating during engine cold start, during recovery from intermittent stop, or during recovery from fuel cut-off. Alternatively, based on the state parameters of the engine 10, such as the air-fuel ratio AbyF of the engine 10 or the temperature of the three-way catalytic converter 19, it can be determined whether the ammonia generation conditions in the three-way catalytic converter 19 are met, thereby determining whether the ammonia emission Amm is in a state of high levels.

[0043] When the effect of engine torque reduction caused by the combustion temperature reduction treatment is negligible, or when the vehicle is not capable of torque compensation based on the electric motor 30, the torque compensation treatment can be omitted, and ammonia emission suppression control can be implemented instead. For example, the torque compensation treatment can be omitted. Figure 2 The processes in steps S140 and S150 are performed to suppress ammonia emissions. With this configuration, the control device described in the above embodiment can also be applied to engine vehicles that use only an engine as the driving source.

[0044] The target air-fuel ratio can be switched between rich and lean air-fuel ratios without using the rear air-fuel ratio sensor 21. For example, the oxygen storage capacity of the three-way catalytic converter 19 can be estimated based on state parameters of the engine 10, such as intake air volume or air-fuel ratio, and the target air-fuel ratio can be switched based on the estimated result.

[0045] The control device is not limited to an electronic control unit 40 having a processing circuit 41 and a storage device 42. For example, the control device may have dedicated hardware circuitry (e.g., an ASIC) for performing at least a portion of the processing performed in the above embodiments. That is, the control device may simply include a processing circuit having any of the structures in (a) to (c) below.

[0046] (a) A processing circuit having one or more processing devices that perform all of the above-described processes according to a program and one or more program storage devices such as a ROM that stores the program.

[0047] (b) A processing circuit having one or more processing devices that perform a portion of the above-described processing according to a program, one or more program storage devices, and one or more dedicated hardware circuits that perform the remaining processing.

[0048] (c) A processing circuit having one or more dedicated hardware circuits that perform all of the above processes.

Claims

1. A vehicle control device, specifically for a vehicle equipped with an engine, said engine having a three-way catalytic converter located in the exhaust passage. The control device includes a processing circuit. The processing circuit is configured to implement: The determination process includes determining whether the ammonia discharge from the three-way catalytic converter is high; and... The combustion temperature reduction process involves lowering the engine's combustion temperature when the engine is determined to be in a state of high exhaust volume during the determination process.

2. The vehicle control device according to claim 1, wherein, The engine also includes an air-fuel ratio sensor located downstream of the three-way catalytic converter in the exhaust passage. The processing circuit is configured to implement air-fuel ratio sub-feedback control based on the detection results of the air-fuel ratio sensor.

3. The vehicle control device according to claim 1, wherein, The combustion temperature reduction treatment includes increasing the amount of exhaust gas recirculated into the intake air.

4. The vehicle control device according to claim 1, wherein, The combustion temperature reduction process includes delaying the ignition timing.

5. The vehicle control device according to claim 1, wherein, The vehicle is a hybrid vehicle equipped with both an engine and an electric motor as driving sources. The processing circuit is configured to perform torque compensation processing to compensate for the decrease in engine torque caused by the combustion temperature reduction processing with motor torque.

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