JP7740197B2 - Hybrid vehicle control device - Google Patents

Description

The present invention relates to a control device for a hybrid vehicle.

Exhaust purification catalysts, such as three-way catalysts, oxidation catalysts, and NOx storage reduction catalysts, are used to purify the exhaust gases emitted by internal combustion engines. When exhaust gas containing hydrocarbons, carbon monoxide, and water flows into an exhaust purification catalyst, it generates hydrogen through catalytic action. Furthermore, when this hydrogen reacts with nitrogen oxides in the exhaust, ammonia is produced. Ammonia is likely to be produced in such exhaust purification catalysts immediately after the air-fuel ratio of an internal combustion engine changes from lean to rich.

A control device for an internal combustion engine described in Patent Document 1 is known as a technology for suppressing the release of ammonia generated by an exhaust gas purification catalyst into the outside air. The internal combustion engine controlled by the control device described in this document is equipped with an exhaust gas recirculation device that recirculates a portion of the exhaust gas flowing in the portion of the exhaust passage downstream of the exhaust gas purification catalyst into the intake air. In such an internal combustion engine, a portion of the ammonia generated by the exhaust gas purification catalyst is recirculated into the intake air together with the exhaust gas and burned in the combustion chamber. The control device for an internal combustion engine described in Patent Document 1 suppresses the release of ammonia into the outside air by increasing the amount of exhaust gas recirculated when switching from a lean to a rich air-fuel ratio, thereby increasing the amount of ammonia recirculated into the intake air together with the exhaust gas.

Japanese Patent Application Laid-Open No. 2022-100067

There is a limit to how much recirculated exhaust gas can be increased, which would result in a deterioration of combustion. Therefore, in the internal combustion engine described in Patent Document 1, if a large amount of ammonia is generated in the exhaust purification catalyst, it may not be possible to sufficiently prevent ammonia from being released into the outside air.

A hybrid vehicle control device that solves the above problem controls a hybrid vehicle equipped with an internal combustion engine with an exhaust purification catalyst installed in the exhaust passage and an electric motor as drive sources. This control device performs a determination process to determine whether the amount of ammonia produced in the exhaust purification catalyst exceeds an allowable amount, and if the determination process determines that the amount of ammonia produced exceeds the allowable amount, performs a leaning process to reduce the amount of intake air into the internal combustion engine and make the air-fuel ratio of the internal combustion engine leaner than the stoichiometric air-fuel ratio, and a torque increase process to increase the torque of the electric motor while the air-fuel ratio of the internal combustion engine is kept lean by the leaning process.

When the air-fuel ratio of an internal combustion engine is lean, the concentration of nitrogen oxides in the exhaust gas flowing into the exhaust purification catalyst increases. When nitrogen oxides and ammonia combine, they form nitrogen and water. Therefore, by supplying nitrogen oxides to the exhaust purification catalyst through lean processing, the ammonia generated in the exhaust purification catalyst can be purified. Furthermore, when the amount of intake air is reduced through lean processing, the amount of exhaust gas flowing into the exhaust purification catalyst decreases. This reduces the outflow of ammonia from the exhaust purification catalyst. Therefore, by performing lean processing, the release of ammonia generated in the exhaust purification catalyst into the outside air can be reduced.

However, when leaning is performed, the torque of the internal combustion engine decreases. The control device performs torque increase processing in conjunction with leaning to increase the torque of the electric motor. This reduces the decrease in drive torque of the hybrid vehicle while leaning is being performed.

1 is a diagram illustrating a schematic configuration of an embodiment of a control device for a hybrid vehicle; 4 is a flowchart of a combustion switching control routine executed by the control device of the embodiment.

An embodiment of a control device for a hybrid vehicle will be described in detail below with reference to FIGS. 1 and 2. FIG.
<Configuration of the control device for the hybrid vehicle>
First, the configuration of the drive system of a hybrid vehicle C to which the vehicle control device of this embodiment is applied will be described with reference to Fig. 1. As shown in Fig. 1, the hybrid vehicle C includes an internal combustion engine 10 and an electric motor 11 as drive sources for traveling.

The internal combustion engine 10 has multiple combustion chambers 12, an intake passage 13, and an exhaust passage 14. The intake passage 13 is a passage through which intake air is introduced into each combustion chamber 12. The exhaust passage 14 is a passage through which exhaust gas is discharged from each combustion chamber 12. The intake passage 13 is provided with a throttle valve 15, which is a valve that changes the flow area of the intake air. The exhaust passage 14 is provided with an exhaust purification catalyst 16. Examples of exhaust purification catalysts 16 include a three-way catalyst, an oxidation catalyst, and a NOx storage reduction catalyst. Each combustion chamber 12 is provided with an ignition device 17 that ignites the air-fuel mixture by spark discharge. Furthermore, the internal combustion engine 10 has an individual injector 18 for each combustion chamber 12. The injector 18 injects fuel such as gasoline or diesel into the intake air introduced into the combustion chamber 12 through the intake passage 13.

The crankshaft 19, which is the output shaft of the internal combustion engine 10, is mechanically connected to the rotating shaft 21 of the electric motor 11 via a clutch 20. Furthermore, the rotating shaft 21 of the electric motor 11 is mechanically connected to wheels 24 via a transmission 22 and a differential 23. Furthermore, the electric motor 11 is electrically connected to a battery 26 via an inverter 25.

The control device for the hybrid vehicle C includes an electronic control unit 30. The electronic control unit 30 includes a processing unit 31 and a storage unit 32. The storage unit 32 stores programs and data for vehicle control. The processing unit 31 reads and executes programs from the storage unit 32 to perform various processes for controlling the hybrid vehicle C. The electronic control unit 30 receives detection signals from sensors installed in various parts of the hybrid vehicle C. These sensors include an air flow meter 33, a crank angle sensor 34, a water temperature sensor 35, an accelerator pedal sensor 36, and a vehicle speed sensor 37. The air flow meter 33 detects the intake air volume GA, which is the flow rate of intake air flowing through the intake passage 13. The crank angle sensor 34 detects the rotation angle of the crankshaft 19. The water temperature sensor 35 detects the engine water temperature THW, which is the temperature of the coolant for the internal combustion engine 10. The accelerator pedal sensor 36 detects the accelerator pedal depression amount ACC, which is the driver's accelerator pedal depression amount. The vehicle speed sensor 37 is a sensor that detects the vehicle speed SPD, which is the traveling speed of the hybrid vehicle C. The electronic control unit 30 also obtains the engine speed NE, which is the rotational speed of the crankshaft 19, from the detection result of the crank angle sensor 34.

The electronic control unit 30 controls the internal combustion engine 10, electric motor 11, clutch 20, and transmission 22 based on the detection results of these sensors, thereby controlling the hybrid vehicle C. The electronic control unit 30 controls the internal combustion engine 10 by manipulating the throttle valve 15 opening, the ignition timing of the ignition device 17, the fuel injection amount of the injector 18, etc. The electronic control unit 30 also controls the torque of the electric motor 11 through operation of the inverter 25. The electronic control unit 30 also controls the gear ratio of the transmission 22 based on the accelerator pedal operation amount ACC and the vehicle speed SPD.

<Drive control of hybrid vehicle C>
Next, the drive control of the hybrid vehicle C executed by the electronic control unit 30 will be described. When controlling the drive of the hybrid vehicle C, the electronic control unit 30 first calculates a required drive torque TR* based on the accelerator pedal depression amount ACC and the vehicle speed SPD. The required drive torque TR* is a required value of torque input from the rotating shaft 21 of the electric motor 11 to the transmission 22. Next, the electronic control unit 30 distributes the required drive torque TR* into a target engine torque TE* and a target motor torque TM*. The target engine torque TE* is a target value of torque to be generated in the internal combustion engine 10. The target motor torque TM* is a target value of torque to be generated in the electric motor 11. The electronic control unit 30 operates the inverter 25 so that the electric motor 11 generates a torque equal to the target motor torque TM*. The electronic control unit 30 also calculates the operation amounts of the internal combustion engine 10, such as the opening of the throttle valve 15, the ignition timing of the ignition device 17, and the amount of fuel injected by the injector 18, which are required to generate a torque equal to the target engine torque TE*.The electronic control unit 30 then operates the throttle valve 15, the ignition device 17, the injector 18, etc., in accordance with the calculated operation amounts.

The electronic control unit 30 adjusts the air-fuel ratio of the mixture combusted in the combustion chamber 12 depending on the operating conditions of the internal combustion engine 10. For example, when the hybrid vehicle C accelerates, the electronic control unit 30 adjusts the air-fuel ratio to a rich air-fuel ratio richer than the stoichiometric air-fuel ratio. Furthermore, when the hybrid vehicle C is operating under light load, the electronic control unit 30 adjusts the air-fuel ratio to a lean air-fuel ratio leaner than the stoichiometric air-fuel ratio. The electronic control unit 30 also adjusts the air-fuel ratio based on the warm-up status of the internal combustion engine 10 and the exhaust purification catalyst 16. The electronic control unit 30 adjusts the air-fuel ratio by manipulating the opening of the throttle valve 15 and the fuel injection amount of the injector 18. In the following description, combustion of a stoichiometric air-fuel ratio mixture is referred to as stoichiometric combustion, combustion of a rich air-fuel ratio mixture is referred to as rich combustion, and combustion of a lean air-fuel ratio mixture is referred to as lean combustion.

<Suppression and control of ammonia release>
Next, the suppression control executed by the electronic control unit 30 to suppress the release of ammonia generated in the exhaust purification catalyst 16 into the outside air will be described.

Figure 2 shows a flowchart of the suppression control routine executed by the electronic control unit 30 for such suppression control. The electronic control unit 30 repeatedly executes this routine at predetermined control intervals while the internal combustion engine 10 is operating.

When this routine starts, the electronic control unit 30 first determines in step S100 whether the lean processing flag F is set. The lean processing flag F is a flag that indicates whether the lean processing described below is being performed. If the lean processing flag F is set (YES), the electronic control unit 30 proceeds to step S160; if it is not set (NO), the electronic control unit 30 proceeds to step S110.

If the process proceeds to step S110, the electronic control unit 30 determines in step S110 whether the amount of ammonia produced in the exhaust purification catalyst 16 exceeds the allowable amount based on the operating state of the internal combustion engine 10. If the electronic control unit 30 determines that the amount of ammonia produced is equal to or less than the allowable amount (S110: NO), it ends the current processing of this routine. If the electronic control unit 30 determines that the amount of ammonia produced exceeds the allowable amount (S110: YES), it proceeds to step S120.

The amount of ammonia produced in the exhaust purification catalyst 16 increases when the air-fuel ratio changes from a lean air-fuel ratio to a rich air-fuel ratio. Such changes in the air-fuel ratio occur, for example, when the internal combustion engine 10 is started, when the hybrid vehicle C starts moving, and when transitioning from downhill driving to uphill driving. In these cases, the electronic control unit 30 determines that the amount of ammonia produced in the exhaust purification catalyst 16 exceeds the allowable amount.

When the process proceeds to step S120, the electronic control unit 30 sets the lean processing flag F in step S120. In the following step S130, the electronic control unit 30 resets the value of the cumulative intake air amount IGA to "0", and then proceeds to step S140.

When the processing proceeds to step S140, the electronic control unit 30 performs a lean operation on the internal combustion engine 10 in step S140. The lean operation is a process of reducing the intake air amount GA of the internal combustion engine 10 and setting the air-fuel ratio of the internal combustion engine 10 to a lean air-fuel ratio. In this embodiment, the electronic control unit 30 commands the internal combustion engine 10 to perform lean idle operation during the lean operation. Lean idle operation is an idle operation of the internal combustion engine 10 in which the air-fuel ratio is set to a lean air-fuel ratio that is leaner than the stoichiometric air-fuel ratio. This command reduces the intake air amount GA of the internal combustion engine 10 to the minimum amount that allows the internal combustion engine 10 to operate autonomously with the air-fuel ratio set to a lean air-fuel ratio. The actual torque of the internal combustion engine 10 during lean idle operation becomes "0". In the following step S150, the electronic control unit 30 performs a torque increase process on the electric motor 11. In this embodiment, the electronic control unit 30 performs torque increase processing by resetting the target motor torque TM* so that it is equal to the required drive torque TR*. The electronic control unit 30 then ends the processing of this routine for the current control cycle.

On the other hand, if the processing proceeds to step S160, the electronic control unit 30 updates the value of the integrated intake air amount IGA based on the current intake air amount GA in step S160. Specifically, the electronic control unit 30 updates the value of the integrated intake air amount IGA by setting the updated value to the sum of the pre-update value and the current intake air amount GA. Note that the value of the integrated intake air amount IGA was reset to "0" when the lean processing flag F was set (S120). This value of the integrated intake air amount IGA represents the integrated value of the intake air amount GA after the lean processing began.

In the following step S170, the electronic control unit 30 determines whether the updated cumulative intake air amount IGA is equal to or greater than the predetermined lean adjustment completion determination value Y. If the cumulative intake air amount IGA is less than the lean adjustment completion determination value Y (NO), the electronic control unit 30 proceeds to step S140. On the other hand, if the cumulative intake air amount IGA is equal to or greater than the lean adjustment completion determination value Y (YES), the electronic control unit 30 clears the lean adjustment processing flag F in step S180 and then terminates the current processing of this routine.

<Actions and Effects of the Embodiment>
The operation and effects of the present embodiment configured as above will be described.
In step S110 of Fig. 2, the electronic control unit 30 performs a determination process to determine whether the amount of ammonia produced in the exhaust purification catalyst 16 exceeds the allowable amount. If the electronic control unit 30 determines in the determination process that the amount of ammonia produced exceeds the allowable amount, the electronic control unit 30 performs the following leaning process and torque increasing process. The leaning process is a process to reduce the intake air amount GA of the internal combustion engine 10 and to make the air-fuel ratio of the internal combustion engine 10 leaner than the stoichiometric air-fuel ratio. The torque increasing process is a process to increase the torque of the electric motor 11. In the case of Fig. 2, the process of step S140 corresponds to the leaning process, and the process of step S150 corresponds to the torque increasing process.

When the air-fuel ratio is made lean by the leaning process, the concentration of nitrogen oxides in the exhaust gas flowing into the exhaust purification catalyst 16 increases. When nitrogen oxides and ammonia combine, they become nitrogen and water. Therefore, by supplying nitrogen oxides to the exhaust purification catalyst 16 by the leaning process, the ammonia generated in the exhaust purification catalyst 16 can be purified. Furthermore, when the intake air amount GA is reduced by the leaning process, the amount of exhaust gas flowing into the exhaust purification catalyst 16 decreases. Therefore, the outflow of ammonia from the exhaust purification catalyst 16 is suppressed. Therefore, by performing the leaning process, the release of ammonia generated in the exhaust purification catalyst 16 into the outside air can be suppressed.

During the leaning process, the electronic control unit 30 causes the internal combustion engine 10 to idle with the air-fuel ratio set to a lean air-fuel ratio. That is, during the leaning process, the electronic control unit 30 reduces the intake air amount GA to the minimum amount that allows the internal combustion engine 10 to operate autonomously at a lean air-fuel ratio. This increases the effectiveness of the leaning process in suppressing the outflow of ammonia from the exhaust purification catalyst 16.

Note that when leaning is performed, the torque of the internal combustion engine 10 decreases. Therefore, simply performing leaning would result in a lack of drive torque for the hybrid vehicle C. In response to this, the electronic control unit 30 performs a torque increase process, which increases the torque of the electric motor 11, in addition to the leaning process. As a result, the electronic control unit 30 compensates for the decrease in torque of the internal combustion engine 10 that occurs during leaning by increasing the torque of the electric motor 11. This makes it possible to suppress a decrease in drive torque for the hybrid vehicle C that would occur when leaning is performed.

<Other Embodiments>
This embodiment can be modified as follows: This embodiment and the following modifications can be combined and implemented within the scope of technical compatibility.

- The amount of ammonia produced in the exhaust purification catalyst 16 may be estimated, and a determination process may be performed based on the estimated result. The amount of ammonia produced may be estimated based on, for example, the air-fuel ratio of the internal combustion engine 10, the intake air amount GA, the temperature of the exhaust purification catalyst 16, etc.

- An ammonia sensor that detects the concentration or amount of ammonia in the exhaust gas may be installed inside the exhaust purification catalyst 16 or downstream of the exhaust purification catalyst 16 in the exhaust passage 14. The determination process may then be performed based on the detection results of the ammonia sensor.

- In the above embodiment, the intake air amount GA was reduced in the leaning process to an amount that would cause the internal combustion engine 10 to operate in lean idle mode. The intake air amount GA after reduction in the leaning process may be set to an amount greater than the amount that would cause the internal combustion engine 10 to operate in lean idle mode. The torque increase amount of the electric motor 11 in the torque increase process may be set to an amount equal to the amount of torque reduction of the internal combustion engine 10 due to the leaning process.

- In the above embodiment, the period during which the leaning process and torque increase process are performed is determined based on the cumulative intake air amount IGA from the start of the process. The period during which the leaning process and torque increase process are performed may also be determined based on parameters other than the cumulative intake air amount IGA, such as the elapsed time from the start of the process.

- The control device of the above embodiment can also be applied to hybrid vehicles with a configuration different from that shown in Figure 1, such as hybrid vehicles equipped with an internal combustion engine and an electric motor as drive sources, such as hybrid vehicles equipped with multiple electric motors.

10...internal combustion engine, 11...electric motor, 12...combustion chamber, 13...intake passage, 14...exhaust passage, 15...throttle valve, 16...exhaust purification catalyst, 17...ignition device, 18...injector, 19...crankshaft, 20...clutch, 21...rotating shaft, 22...transmission, 23...differential, 24...wheels, 25...inverter, 26...battery, 30...electronic control unit, 31...processing device, 32...storage device, 33...air flow meter, 34...crank angle sensor, 35...water temperature sensor, 36...accelerator pedal sensor, 37...vehicle speed sensor

Claims (3)

A device for controlling a hybrid vehicle having an internal combustion engine with an exhaust purification catalyst installed in an exhaust passage and an electric motor as drive sources,
A determination process is carried out to determine whether or not the amount of ammonia produced in the exhaust purification catalyst exceeds an allowable amount,
a leaning process for reducing an intake air amount of the internal combustion engine and making the air-fuel ratio of the internal combustion engine leaner than a stoichiometric air-fuel ratio, and a torque increasing process for increasing the torque of the electric motor, when it is determined in the determination process that the amount of ammonia produced will exceed an allowable amount. The control device for a hybrid vehicle described in claim 1, wherein the leaning process is a process of idling the internal combustion engine with the air-fuel ratio set to a lean air-fuel ratio. A control device for a hybrid vehicle as described in claim 1, which terminates the leaning process when the cumulative intake air volume after the start of the leaning process reaches or exceeds a predetermined judgment value.