Vehicle control system

Abstract

It suppresses the emission of both NOx and ammonia from the engine. [Solution] The electronic control unit, which is a control device for the hybrid vehicle, determines whether the ammonia emissions Amm from the three-way catalytic converter are above a certain value (S120). If the electronic control unit determines that the ammonia emissions Amm are above a certain value (S120: YES), it performs a combustion temperature reduction process to lower the combustion temperature of the engine (S130).

Description

Technical Field

[0001] The present invention relates to a control device for a vehicle.

Background Art

[0002] Patent Document 1 describes a control device for a hybrid vehicle including an engine provided with a three-way catalyst device as described above and a motor as drive sources. The hybrid vehicle to which this control device is applied is configured to switch between electric driving in which the engine is stopped and the motor is driven to travel and hybrid driving in which the engine is driven to travel according to the situation. And when switching from motor driving to hybrid driving, the control device suppresses the emission of NOx to the outside air by increasing the fuel injection amount of the engine.

Prior Art Document

Patent Document

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] When the inside of the three-way catalyst device is in a reducing atmosphere and at a high temperature, ammonia may be generated. Therefore, when the fuel injection amount is increased to reduce the NOx emission amount, there is a risk that the ammonia emission amount will increase.

Means for Solving the Problems

[0005] A vehicle control device that solves the above problem is a vehicle control device for a vehicle equipped with an engine having a three-way catalytic converter installed in the exhaust passage, and is configured to perform a determination process to determine whether or not the amount of ammonia emitted from the three-way catalytic converter is high, and, if the determination process determines that the amount of ammonia emitted is high, a combustion temperature reduction process to reduce the combustion temperature of the engine. [Effects of the Invention]

[0006] The control system in the above-mentioned vehicle has the effect of suppressing the emission of both NOx and ammonia from the engine. [Brief explanation of the drawing]

[0007] [Figure 1] Figure 1 is a schematic diagram showing the configuration of one embodiment of a vehicle control device. [Figure 2] Figure 2 is a flowchart of the process performed by the control device shown in Figure 1. [Modes for carrying out the invention]

[0008] The following describes in detail one embodiment of a vehicle control system. <Configuration of the vehicle's control system> The configuration of this embodiment will be described with reference to Figure 1. The vehicle to which the control device of this embodiment is applied is configured as a hybrid vehicle equipped with an engine 10 that generates driving force by the combustion of fuel and a motor 30 that generates driving force by power supplied from a battery 31 as the drive source for driving. The motor 30 is electrically connected to the battery 31 via an inverter 32.

[0009] First, let's describe the configuration of the engine 10. The engine 10 includes a combustion chamber 11 for burning the air-fuel mixture, an intake passage 12 which is the path for introducing intake air into the combustion chamber 11, and an exhaust passage 13 which is the path for discharging exhaust gas from the combustion chamber 11. The intake passage 12 is equipped with an air cleaner 14 for filtering out impurities such as dust from the intake air, an air flow meter 15 for detecting the intake air flow rate, and a throttle valve 16 for adjusting the intake air flow rate. The engine 10 also includes an injector 17 for injecting fuel into the intake air used for combustion in the combustion chamber 11, and an ignition device 18 for igniting the air-fuel mixture in the combustion chamber 11 by spark discharge. The exhaust passage 13 of the engine 10 is equipped with a three-way catalytic converter 19 that supports a three-way catalytic converter for purifying the exhaust gas. The three-way catalytic converter 19 has oxygen storage capacity. The exhaust passage 13 is equipped with 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 installed in the exhaust passage 13 upstream of the three-way catalytic converter 19. The rear air-fuel ratio sensor 21 is installed in the exhaust passage 13 downstream of the three-way catalytic converter 19. A NOx sensor 22 for detecting the amount of nitrogen oxides (NOx) in the exhaust is installed in the exhaust passage 13 downstream of the three-way catalytic converter 19. Furthermore, the engine 10 is equipped with an EGR (Exhaust Gas Recirculation) passage 23, which is a path for recirculating exhaust gas into the intake air. In the following description, the exhaust gas recirculated into the intake air through the EGR passage 23 will be referred to as EGR gas. The EGR passage 23 is equipped with an EGR cooler 24 for cooling the EGR gas and an EGR valve 25 for adjusting the flow rate of the EGR gas.

[0010] The control device of this embodiment is configured as an electronic control unit 40 comprising a processing circuit 41 and a storage device 42. The storage device 42 stores programs and data for controlling the vehicle. The electronic control unit 40 performs various processes for controlling the vehicle by having the processing circuit 41 execute the programs read from the storage device 42. The electronic control unit 40 receives detection results from various sensors installed in various parts of the vehicle. Sensors installed in the vehicle include the air flow meter 15, front air-fuel ratio sensor 20, rear air-fuel ratio sensor 21, NOx sensor 22 mentioned above, as well as a crank angle sensor 43, resolver 44, accelerator pedal sensor 45, and vehicle speed sensor 46. The crank angle sensor 43 is a sensor that detects the crank angle of the engine 10, and the resolver 44 is a sensor that detects the rotation angle of the motor 30. The accelerator pedal sensor 45 is a sensor that detects the amount the driver depresses the accelerator pedal, and the vehicle speed sensor 46 is a sensor that detects the vehicle speed. The electronic control unit 40 controls the vehicle, including the engine 10 and motor 30, based on the detection results of these sensors. The electronic control unit 40 also calculates the engine speed Ne based on the detection results of the crank angle sensor 43. Furthermore, the electronic control unit 40 calculates the engine load ratio Kl based on the detection results of the airflow meter 15, the calculated engine speed Ne, etc. The engine load ratio Kl represents the air filling rate of the combustion chamber 11.

[0011] 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 according to the vehicle's driving conditions and the battery 31's charge status. Intermittent operation control is performed for purposes such as switching between electric driving, where the engine 10 is stopped and the motor 30 is driven, and hybrid driving, where the engine 10 is driven, as well as for idling stop.

[0012] <Air-fuel ratio control for engine 10> A three-way catalytic converter 19, installed in the exhaust passage 13 of the engine 10, supports a three-way catalytic converter and an oxygen storage agent. The three-way catalytic converter purifies the exhaust gas through the oxidation of unburned fuel components (HC, CO) and the reduction of NOx. The three-way catalytic converter exhibits its maximum exhaust gas purification capacity under a stoichiometric atmosphere. The oxygen storage agent absorbs oxygen from the exhaust gas under a lean atmosphere with excess oxygen, while releasing the absorbed oxygen into the exhaust gas under a rich atmosphere with deficient oxygen.

[0013] As part of the control of the engine 10, the electronic control unit 40 controls the air-fuel ratio of the air-fuel mixture burned in the combustion chamber 11 so that the three-way catalytic converter 19 can effectively purify the exhaust gases. The electronic control unit 40 controls the air-fuel ratio through two types of feedback control: main air-fuel ratio feedback control based on the detection results of the front air-fuel ratio sensor 20, and sub-air-fuel ratio 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 air-fuel ratio F / B control, the electronic control unit 40 controls the fuel injection amount so that the air-fuel ratio detected by the front air-fuel ratio sensor 20 is equal to the target air-fuel ratio. In addition, as the sub-air-fuel ratio F / B control, the electronic control unit 40 controls the target air-fuel ratio by alternately switching between a lean air-fuel ratio that is richer than the stoichiometric air-fuel ratio and a rich air-fuel ratio that is richer than the stoichiometric air-fuel ratio, based on the detection results of the rear air-fuel ratio sensor 21. In detail, in air-fuel ratio sub-F / B control, 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 detected by the rear air-fuel ratio sensor 21 becomes a value indicating a lean air-fuel ratio. Furthermore, the electronic control unit 40 switches the target air-fuel ratio from a rich air-fuel ratio to a lean air-fuel ratio when the air-fuel ratio detected by the rear air-fuel ratio sensor 21 becomes a value indicating a rich air-fuel ratio.

[0014] When combustion occurs at a lean air-fuel ratio, lean exhaust containing excess oxygen that is not consumed during combustion flows into the three-way catalytic converter 19. At this time, the inside of the three-way catalytic converter 19 is maintained in a stoichiometric atmosphere by the oxygen storage agent absorbing oxygen from the exhaust. Therefore, the air-fuel ratio detected by the rear air-fuel ratio sensor 21 at this time will be a value indicating the stoichiometric air-fuel ratio. However, there is an upper limit to the amount of oxygen that the three-way catalytic converter 19 can absorb. When the oxygen storage capacity of the three-way catalytic converter 19 reaches its upper limit, lean exhaust is discharged from the three-way catalytic converter 19, and the air-fuel ratio detected by the rear air-fuel ratio sensor 21 changes from a value indicating the stoichiometric air-fuel ratio to a value indicating the lean air-fuel ratio. Accordingly, the electronic control unit 40 switches the target air-fuel ratio from a lean air-fuel ratio to a rich air-fuel ratio in the air-fuel ratio sub-F / B control. When combustion occurs at a rich air-fuel ratio, oxygen-deficient rich exhaust flows into the three-way catalytic converter 19. At this time, the inside of the three-way catalytic converter 19 is maintained in a stoichiometric atmosphere as the oxygen absorber releases the absorbed oxygen. Therefore, the air-fuel ratio detected by the rear air-fuel ratio sensor 21 is a value indicating the stoichiometric air-fuel ratio. Subsequently, when the three-way catalytic converter 19 releases all the absorbed oxygen, rich exhaust is discharged from the three-way catalytic converter 19, and the air-fuel ratio detected by the rear air-fuel ratio sensor 21 changes from a value indicating the stoichiometric air-fuel ratio to a value indicating the rich air-fuel ratio. Accordingly, the electronic control unit 40 switches the target air-fuel ratio from the rich air-fuel ratio to the lean air-fuel ratio in the air-fuel ratio sub-F / B control. In this way, the electronic control unit 40 alternately switches the target air-fuel ratio between the lean air-fuel ratio and the rich air-fuel ratio in the air-fuel ratio sub-F / B control.

[0015] <Ammonia emission control> In the three-way catalytic converter 19, ammonia may be generated when the inside is in a high-temperature, oxygen-deficient state. Conditions for ammonia generation in the three-way catalytic converter 19 may be met during the catalyst warm-up process after a cold start of the engine 10, immediately after fuel cut-off is restored, and immediately after restoring from intermittent stopping. Conditions for ammonia generation may also be met during sulfur poisoning recovery control of the three-way catalytic converter 19. If ammonia is generated in the three-way catalytic converter 19, there is a risk that ammonia exceeding an acceptable amount will be discharged into the outside air. In this embodiment, the electronic control unit 40 performs control to suppress ammonia emission.

[0016] Figure 2 shows the processing flow performed by the electronic control unit 40 for ammonia emission suppression control. The electronic control unit 40 repeatedly performs the processing shown in Figure 2 at predetermined control cycles while the engine 10 is running.

[0017] In step S100 of Figure 2, the electronic control unit 40 acquires state variables indicating the operating state of the engine 10. In Figure 2, in step S100, the electronic control unit 40 acquires the engine rotational speed Ne, engine load ratio Kl, air-fuel ratio AbyF, catalyst temperature Thc, and NOx emission Nox. Then, in the subsequent step S110, the electronic control unit 40 calculates the ammonia emission Amm from the three-way catalytic converter 19 based on the acquired state variables of the engine 10. The electronic control unit 40 calculates the ammonia emission Amm using a physical model that shows the relationship between the state variables of the engine 10 and the ammonia emission Amm.

[0018] Subsequently, in the next step S120, the electronic control unit 40 determines whether the ammonia emission amount Amm is large. Specifically, in this step S120, the electronic control unit 40 determines whether the ammonia emission amount Amm calculated in step S110 is greater than or equal to a predetermined determination value. If the electronic control unit 40 determines that the ammonia emission amount Amm is less than the determination value (NO), it ends the process of FIG. 2 in the current control cycle. On the other hand, if the electronic control unit 40 determines that the ammonia emission amount Amm is greater than or equal to the determination value (YES), it proceeds to step S130.

[0019] In step S130, the electronic control unit 40 executes a combustion temperature reduction process for reducing the combustion temperature in the combustion chamber 11. Examples of the combustion temperature reduction process include an EGR increase process for increasing the recirculation amount of exhaust gas to the intake air, and an ignition retard process for retarding the ignition timing. As the combustion temperature reduction process, either one of the EGR increase process and the ignition retard process may be executed, or both may be executed.

[0020] Subsequently, in step S140, the electronic control unit 40 determines whether the engine torque has decreased due to the execution of the combustion temperature reduction process. The electronic control unit 40 estimates the engine torque based on the detection result of the resolver 44 installed in the motor 30. Then, the electronic control unit 40 makes the determination in step S140 based on the estimated engine torque. If the electronic control unit 40 determines that the engine torque has not decreased (NO), it ends the process of FIG. 2 in the current control cycle. On the other hand, if the electronic control unit 40 determines that the engine torque has decreased (YES), it proceeds to step S150.

[0021] In step S150, the electronic control unit 40 executes a torque compensation process for compensating for the decrease in engine torque by increasing the motor torque. Then, the electronic control unit 40 ends the process of FIG. 2 in the current control cycle.

[0022] <Function of Embodiment> In the three-way catalyst device 19, ammonia may be generated when its interior is in a high-temperature oxygen-deficient state. Such ammonia generation conditions are likely to be established when the engine 10 resumes operation, such as during catalyst warm-up after cold start, when resuming from an intermittent stop, or when resuming from fuel cut-off. This is due to the following reasons.

[0023] During the stop of the engine 10, the exhaust gas in the exhaust passage 13 is replaced by air. Therefore, the three-way catalyst device 19 at the time of resuming the operation of the engine 10 stores a large amount of oxygen. Thus, when the air-fuel ratio sub F / B control is started immediately after the resumption of the engine 10 operation, a rich air-fuel ratio is set as the target air-fuel ratio. As a result, rich combustion occurs in the combustion chamber 11, and rich exhaust gas flows into the three-way catalyst device 19. Therefore, immediately after the resumption of the engine 10 operation, the interior of the three-way catalyst device 19 becomes a high-temperature oxygen-deficient state, making it easier for ammonia to be generated.

[0024] In the case of this embodiment, the electronic control unit 40 performs a determination process to determine whether or not the ammonia emission amount Amm from the three-way catalyst device 19 is large (S120). And when the electronic control unit 40 determines in the determination process that the ammonia emission amount Amm is large (S120: YES), it executes a combustion temperature reduction process for reducing 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, so the temperature inside the three-way catalyst device 19 also decreases. As described above, ammonia is likely to be generated when the interior of the three-way catalyst device 19 is in a high-temperature oxygen-deficient state. Therefore, when the combustion temperature reduction process is executed, the generation of ammonia in the three-way catalyst device 19 is suppressed. And as a result, the emission of ammonia from the engine 10 to the outside air is suppressed.

[0025] Furthermore, a decrease in combustion temperature leads to a decrease in combustion efficiency and a reduction in engine torque. In response to this, the electronic control unit 40 performs torque compensation processing when the engine torque decreases due to the combustion temperature reduction process (S140), compensating for the decrease in engine torque by increasing the motor torque. Therefore, even if the engine torque decreases due to the combustion temperature reduction process, the vehicle's driving force is maintained.

[0026] <Effects of the Embodiment> The vehicle control device of this embodiment described above provides the following effects. (1) The electronic control unit 40 is configured as a control device for a vehicle equipped with an engine 10 having a three-way catalytic converter 19 installed in the exhaust passage 13. The electronic control unit 40 performs a determination process to determine whether or not the ammonia emission Amm from the three-way catalytic converter 19 is high. If the electronic control unit 40 determines in the determination process that the ammonia emission Amm is high, it performs a combustion temperature reduction process to lower the combustion temperature of the engine 10. Since ammonia is generated in the three-way catalytic converter 19 when its interior is in a high-temperature, oxygen-deficient state, lowering the combustion temperature of the engine 10 lowers the temperature of the three-way catalytic converter 19, making it less likely for ammonia to be generated. Note that ammonia generation in the three-way catalytic converter 19 can also be suppressed by performing lean combustion to create an oxygen-rich state inside the three-way catalytic converter 19. However, if lean combustion is performed with the three-way catalytic converter 19 having absorbed a lot of oxygen, the NOx emission NOx from the engine 10 will increase. In this embodiment, however, ammonia generation is suppressed by performing rich combustion while 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.

[0027] (2) The electronic control unit 40 performs air-fuel ratio sub-F / B control based on the detection result of the rear air-fuel ratio sensor 21 installed in the downstream portion 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 10 restarts, making it easier for ammonia to be generated in the three-way catalytic converter 19. In this embodiment, even in such a situation where ammonia is easily generated, the emission of ammonia from the engine 10 can be suppressed by lowering the combustion temperature.

[0028] (3) The electronic control unit 40 performs one or both of the following as combustion temperature reduction treatments: increasing the amount of exhaust gas recirculated into the intake, or retarding the ignition timing. These treatments make it possible to lower the combustion temperature while maintaining rich combustion. As a result, ammonia emissions can be suppressed without increasing NOx emissions.

[0029] (4) The electronic control unit 40 performs torque compensation processing to compensate for the decrease in engine torque caused by the combustion temperature reduction process with motor torque. As a result, the decrease in vehicle driving force caused by the combustion temperature reduction process can be suppressed.

[0030] <Other Embodiments> The above embodiment can be implemented with the following modifications. The above embodiment and the following modifications can be combined with each other to the extent that they do not contradict each other technically.

[0031] If the engine 10 is equipped with a variable valve timing mechanism, it is possible to perform a combustion temperature reduction process by driving the variable valve timing mechanism to increase the valve overlap amount. Increasing the valve overlap amount increases the amount of exhaust gas blown back from the exhaust passage 13 to the combustion chamber 11, the so-called internal EGR amount, which lowers the combustion temperature of the engine 10. In addition, any process that lowers the combustion temperature while performing rich combustion, other than ignition retardation and increasing the EGR amount, may be performed as a combustion temperature reduction process.

[0032] Alternatively, an ammonia sensor for detecting the amount of ammonia in the exhaust gas may be installed in the exhaust passage 13 downstream of the three-way catalytic converter 19, and the determination in step S120 of Figure 2 may be made based on the detection result.

[0033] - Instead of estimating or detecting ammonia emissions (Amm), it is also possible to determine whether or not the ammonia emissions (Amm) are high based on the operating conditions of the engine 10. Specifically, it is determined from the operating conditions of the engine 10 whether or not the conditions for ammonia generation in the three-way catalytic converter 19 are met, and if the generation conditions are met, it is determined that the ammonia emissions (Amm) are high. For example, it is possible to determine that the ammonia emissions (Amm) are high during catalyst warm-up when the engine 10 is cold-started, when recovering from intermittent stop, when recovering from fuel cut, etc. Alternatively, it is also possible to determine whether or not the ammonia emissions (Amm) are high by determining whether or not the conditions for ammonia generation in the three-way catalytic converter 19 are met based on the state variables of the engine 10, such as the air-fuel ratio (AbyF) and the temperature of the three-way catalytic converter 19.

[0034] If the effect of the reduction in engine torque due to the combustion temperature reduction process is negligible, or if the vehicle is configured in a way that prevents torque compensation by the motor 30, the ammonia emission suppression control may be performed without the torque compensation process. For example, the processes in steps S140 and S150 in Figure 2 may be omitted, and the ammonia emission suppression control may be performed. In such cases, the control device of the above embodiment can also be provided to engine vehicles that are equipped with only an engine as a drive source for driving.

[0035] • The target air-fuel ratio may be switched between a rich air-fuel ratio and a lean air-fuel ratio without using the rear air-fuel ratio sensor 21. For example, the oxygen storage amount of the three-way catalytic converter 19 may be estimated based on the state quantities of the engine 10, such as the intake air amount and air-fuel ratio, and the target air-fuel ratio may be switched based on the estimation result. [Explanation of Symbols]

[0036] 10 Engines 11 Combustion chamber 12 Intake passage 13 Exhaust passage 14. Air cleaner 15. Airflow meter 16 Throttle valve 17 Injectors 18 Ignition system 19 Three-way catalyst device 20 Front air-fuel ratio sensor 21 Rear air-fuel ratio sensor 22 NOx Sensors 23 EGR passage 24 EGR cooler 25 EGR valve 30 motors 31 batteries 32 Inverters 40 Electronic control unit 41 Processing Circuit 42 Storage device 43 Crank angle sensor 44 resolvers 45. Accelerator pedal sensor 46. ​​Vehicle speed sensor

Claims

1. A control device for a vehicle equipped with an engine having a three-way catalytic converter installed in the exhaust passage, A determination process for determining whether or not the amount of ammonia emitted from the three-way catalytic converter is high, If the determination process determines that the emissions are high, a combustion temperature reduction process is performed to lower the combustion temperature of the engine. A control device for a vehicle that performs this task.

2. The vehicle control device according to claim 1, which performs air-fuel ratio subfeedback control based on the detection result of an air-fuel ratio sensor installed in the downstream portion of the three-way catalytic converter in the exhaust passage.

3. The vehicle control device according to claim 1, wherein the combustion temperature reduction treatment is a treatment that increases 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 is a process of retarding the ignition timing.

5. The vehicle is a hybrid vehicle equipped with the engine and motor as drive sources for driving, and the control device performs a torque compensation process to compensate for the decrease in engine torque due to the execution of the combustion temperature reduction process with motor torque, as described in claim 1.

Images