Control system for hybrid vehicles

Abstract

This suppresses the deterioration of drivability caused by the execution of a specific cylinder fuel cut process, which stops the fuel supply to some cylinders. [Solution] In a hybrid vehicle 10 equipped with an engine 11 having multiple cylinders 20 and motors (first generator motor 12, second generator motor 13) as a drive source for driving, a specific cylinder fuel cut process is performed to stop the fuel supply to some of the multiple cylinders 20 of the engine 11 and to supply fuel to the remaining cylinders. Prior to the execution of the specific cylinder fuel cut process, a vibration mitigation process is performed to adjust the engine torque to be below a predetermined value through coordinated control of the engine 11 and the motors.

Description

Technical Field

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

Background Art

[0002] Patent Document 1 describes a control device applied to an engine in which front-stage and rear-stage catalysts having oxygen storage capacity are installed in an exhaust passage. When it is determined that HC (hydrocarbon) poisoning has occurred in the rear-stage catalyst, this control device executes a specific cylinder fuel cut process for supplying oxygen to the rear-stage catalyst to recover the HC poisoning. The specific cylinder fuel cut process is a process of stopping the fuel supply to some of the plurality of cylinders of the engine and performing the fuel supply to the remaining cylinders.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] When the specific cylinder fuel cut process is executed, the vehicle body vibrates due to the torque difference between the cylinders where the fuel supply is performed and the combustion continues and the cylinders where the fuel supply is stopped and the combustion is suspended, so the drivability deteriorates.

Means for Solving the Problems

[0005] A control device for a hybrid vehicle that solves the above problems is a control device for a hybrid vehicle that has an engine with multiple cylinders and a motor as a drive source for driving, and is configured to perform a specific cylinder fuel cut process that stops the fuel supply to some of the multiple cylinders and supplies fuel to the remaining cylinders other than the aforementioned some cylinders, and prior to performing the specific cylinder fuel cut process, it is configured to perform a vibration mitigation process that adjusts the engine torque to be below a predetermined value through coordinated control of the engine and the motor. [Effects of the Invention]

[0006] The control device of the above-mentioned hybrid vehicle has the effect of suppressing the deterioration of drivability that occurs when a specific cylinder fuel cut-off process is performed, which stops the fuel supply to some cylinders. [Brief explanation of the drawing]

[0007] [Figure 1] Figure 1 is a schematic diagram showing the configuration of the drive system of a hybrid vehicle to which the control device of the first embodiment is applied. [Figure 2] Figure 2 is a schematic diagram showing the configuration of the control device for the hybrid vehicle according to the first embodiment. [Figure 3] Figure 3 is a flowchart of the process performed by the control device shown in Figure 2 for catalyst poisoning recovery control. [Figure 4] Figure 4 is a graph showing the relationship between vehicle longitudinal acceleration and engine torque during specific cylinder fuel cut-off processing. [Figure 5] Figure 5 is a graph showing the relationship between the longitudinal acceleration of the vehicle and the engine speed during specific cylinder fuel cut-off processing. [Modes for carrying out the invention]

[0008] (First Embodiment) A first embodiment of the control device for a hybrid vehicle will be described in detail below with reference to Figures 1 to 3.

[0009] <Hybrid vehicle configuration> First, with reference to Figure 1, the configuration of the hybrid vehicle 10 to which the control device of this embodiment is applied will be described. The hybrid vehicle 10 is equipped with an engine 11 and two motors, a first generator motor 12 and a second generator motor 13, as a drive source for driving. The first generator motor 12 and the second generator motor 13 each have the function of a motor that generates power by receiving an electrical supply, as well as the function of a generator that generates power by receiving power from an external source. The hybrid vehicle 10 is equipped with a power split mechanism 14. The power split mechanism 14 is a planetary gear having three rotating elements: a sun gear S, a ring gear R, and a planetary carrier C. The engine 11 is connected to the planetary carrier C of the power split mechanism 14, and the first generator motor 12 is connected to the sun gear S. Furthermore, the second generator motor 13 and the drive wheels 16 are connected to the ring gear R of the power split mechanism 14 via a reduction differential mechanism 15. Furthermore, the first generator-motor 12 and the second generator-motor 13 are electrically connected to the battery 18 via the inverter 17.

[0010] The engine 11 has multiple cylinders 20. Although four cylinders 20 are shown in Figure 1, the engine 11 can have two or more cylinders 20. The engine 11 is equipped with an injector 21 and an ignition device 22 for each cylinder 20. The engine 11 also has an intake passage 23, which is the path for introducing intake air to each cylinder 20, and an exhaust passage 25, which is the path for discharging exhaust gas from each cylinder 20. A throttle valve 24 is installed in the intake passage 23. A first catalyst 26 is installed in the exhaust passage 25. A second catalyst 27 is installed in the portion of the exhaust passage 25 downstream of the first catalyst 26. The first catalyst 26 and the second catalyst 27 are supported with a three-way catalyst and an oxygen storage agent. In other words, the first catalyst 26 and the second catalyst 27 are configured as exhaust gas purification catalysts with oxygen storage capacity. A front air-fuel ratio sensor 28 is installed in the exhaust passage 25 upstream of the first catalytic converter 26. Furthermore, a rear air-fuel ratio sensor 29 is installed in the exhaust passage 25 downstream of the first catalytic converter 26 and upstream of the second catalytic converter 27.

[0011] <Configuration of the control device for the hybrid vehicle 10> Figure 2 shows the configuration of the control device that controls the hybrid vehicle 10. In this embodiment, the control device is configured as an electronic control unit 30 comprising an arithmetic processing unit 31, a storage device 32, an input circuit 33, and an output circuit 34. The storage device 32 stores control programs and data. The electronic control unit 30 is configured to perform various processes for controlling the hybrid vehicle 10 by having the arithmetic processing unit 31 execute the programs stored in the storage device 32. In addition to the front air-fuel ratio sensor 28 and rear air-fuel ratio sensor 29 mentioned above, the input circuit 33 of the electronic control unit 30 is connected to an air flow meter 35, a crank angle sensor 36, an accelerator pedal sensor 37, and a vehicle speed sensor 38, etc. The air flow meter 35 is a sensor that detects the amount of intake air of the engine 11, and the crank angle sensor 36 is a sensor that detects the crank angle of the engine 11. The accelerator pedal sensor 37 is a sensor that detects the amount of accelerator pedal operation by the driver of the hybrid vehicle 10, and the vehicle speed sensor 38 is a sensor that detects the vehicle speed, which is the driving speed of the hybrid vehicle 10. Meanwhile, the output circuit 34 of the electronic control unit 30 is connected to actuators of the engine 11, such as the throttle valve 24, the injectors 21 for each cylinder 20, and the ignition system 22. An inverter 17 is also connected to the output circuit 34.

[0012] <Drive control of hybrid vehicles 10> This section outlines the drive control of the hybrid vehicle 10 performed by the electronic control unit 30. First, the electronic control unit 30 calculates the required driving force based on the accelerator pedal operation amount, vehicle speed, etc. The required driving force represents the driving force of the hybrid vehicle 10 requested by the driver. Next, the electronic control unit 30 calculates the charge / discharge required power based on the charge state of the battery 18, etc. The charge / discharge required power represents the driving force required for the traction / regeneration drive of the second generator motor 13 to bring the battery 18's charge state within an appropriate range. Then, the electronic control unit 30 calculates the required engine output, which is the requested value of the engine output, based on the required driving force and the charge / discharge required power. Subsequently, the electronic control unit 30 calculates the target rotational speed and target load factor of the engine 11 based on the required engine output. The target rotational speed and target load factor represent the rotational speed and load factor of the engine 11 that can efficiently generate an output equal to the required engine output. The electronic control unit 30 then adjusts the opening of the throttle valve 24 of the engine 11 so that the load factor of the engine 11 is equal to the target load factor. The electronic control unit 30 also adjusts the rotational speed of the first generator motor 12 so that the rotational speed of the engine 11 is equal to the target rotational speed. The adjustment of the rotational speed of the first generator motor 12 is performed by controlling the charging current of the first generator motor 12 to the battery 18 through the control of the inverter 17. The electronic control unit 30 also controls the inverter 17 so that the charge and discharge current of the second generator motor 13 to the battery 18 is a value corresponding to the charge and discharge power requirement.

[0013] <Air-fuel ratio control of engine 11> Next, an overview of the air-fuel ratio control of the engine 11 performed by the electronic control unit 30 will be described. The air-fuel ratio control of the engine 11 is performed through two types of feedback: main feedback based on the detection results of the front air-fuel ratio sensor 28, and sub-feedback based on the detection results of the rear air-fuel ratio sensor 29. The electronic control unit 30 detects the air-fuel ratio of the mixture burned in each cylinder 20 using the front air-fuel ratio sensor 28. In the main feedback, the electronic control unit 30 performs feedback correction of the fuel injection amount of the injector 21 so that the detected air-fuel ratio is equal to the target air-fuel ratio. In the sub-feedback, the electronic control unit 30 alternately switches the target air-fuel ratio between a rich air-fuel ratio that is richer than the stoichiometric air-fuel ratio and a lean air-fuel ratio that is leaner than the stoichiometric air-fuel ratio, based on the detection results of the rear air-fuel ratio sensor 29. Specifically, the electronic control unit 30 switches the target air-fuel ratio from a lean air-fuel ratio to a rich air-fuel ratio when the rear air-fuel ratio sensor 29 detects lean failure of the first catalyst 26. Furthermore, the electronic control unit 30 switches the target air-fuel ratio from a rich air-fuel ratio to a lean air-fuel ratio when the rear air-fuel ratio sensor 29 detects rich failure of the first catalyst 26. Lean failure indicates that the air-fuel ratio of the exhaust gas discharged from the first catalyst 26 has changed from the stoichiometric air-fuel ratio or a rich air-fuel ratio to a lean air-fuel ratio. Similarly, rich failure indicates that the air-fuel ratio of the exhaust gas discharged from the first catalyst 26 has changed from the stoichiometric air-fuel ratio or a lean air-fuel ratio to a rich air-fuel ratio.

[0014] The three-way catalyst supported on the first catalyst 26 and the second catalyst 27 purifies exhaust gas by oxidizing unburned fuel components (HC, CO) and simultaneously reducing nitrogen oxides (NOx). However, if the internal air surplus ratio λ of the first catalyst 26 and the second catalyst 27 is less than "1", they cannot completely oxidize the unburned fuel components in the exhaust gas, resulting in the emission of rich exhaust gas containing unburned fuel components. Also, if the internal air surplus ratio λ of the first catalyst 26 and the second catalyst 27 exceeds "1", they cannot completely reduce the NOx in the exhaust gas, resulting in the emission of lean exhaust gas containing NOx and excess oxygen. However, the first catalyst 26 and the second catalyst 27 are supported on the three-way catalyst along with an oxygen storage agent. The oxygen storage agent absorbs oxygen when the internal air surplus ratio λ of the first catalyst 26 and the second catalyst 27 exceeds "1", while releasing the absorbed oxygen when the air surplus ratio λ of the incoming exhaust gas is less than "1". Due to this oxygen absorption and release, even if the excess air ratio λ of the exhaust gas flowing into the first catalyst 26 and the second catalyst 27 deviates slightly from "1", the inside of the first catalyst 26 and the second catalyst 27 is maintained at an excess air ratio λ of "1".

[0015] When the target air-fuel ratio is set to a lean air-fuel ratio by subfeedback, lean combustion occurs in each cylinder 20 of the engine 11 at an air-fuel ratio leaner than the stoichiometric air-fuel ratio. At this time, lean exhaust with an air excess ratio λ exceeding "1" flows into the first catalyst 26, but the oxygen absorber absorbs oxygen, keeping the internal air excess ratio λ close to "1". However, there is a limit to the amount of oxygen that the first catalyst 26 can absorb. Therefore, if lean combustion continues, the first catalyst 26 will eventually be unable to absorb all the oxygen, and the emission of lean exhaust containing oxygen occurs, i.e., lean breakdown occurs. When the electronic control unit 30 detects lean breakdown of the first catalyst 26 by the rear air-fuel ratio sensor 29, it switches the target air-fuel ratio from a lean air-fuel ratio to a rich air-fuel ratio. As a result, rich combustion begins in each cylinder 20 of the engine 11 at an air-fuel ratio richer than the stoichiometric air-fuel ratio. At this time, rich exhaust gas with an air excess ratio λ of less than "1" flows into the first catalyst 26, but the oxygen absorber releases the oxygen it has absorbed, keeping the air excess ratio λ inside it close to "1". If rich combustion continues, the first catalyst 26 will release all the oxygen it has absorbed, resulting in the emission of rich exhaust gas containing unburned fuel components, i.e., rich breakdown. When the rear air-fuel ratio sensor 29 detects rich breakdown in the first catalyst 26, the electronic control unit 30 switches the target air-fuel ratio from a rich air-fuel ratio to a lean air-fuel ratio. In this way, lean combustion and rich combustion alternate in each cylinder 20 of the engine 11.

[0016] <Poisoning recovery control of the second catalyst 27> The first catalyst 26 and the second catalyst 27 may be poisoned by hydrocarbons (HC) in the exhaust gas, resulting in hydrocarbon poisoning (hereinafter referred to as HC poisoning) that reduces the exhaust gas purification ability. When sufficient oxygen is supplied, the HC adhering to the first catalyst 26 and the second catalyst 27 burns. Since oxygen is supplied to the first catalyst 26 every time lean combustion is performed by sub-feedback, HC poisoning is unlikely to progress. In contrast, the air excess ratio λ of the exhaust gas flowing into the second catalyst 27 is near "1" both during lean combustion and during rich combustion, so sufficient oxygen to eliminate HC poisoning is not supplied. However, when the fuel cut of the engine 11 is implemented during deceleration of the hybrid vehicle 10 or the like, the exhaust gas is replaced with fresh air, so sufficient oxygen is also supplied to the second catalyst 27. Therefore, if the fuel cut of the engine 11 is implemented, the progress of HC poisoning of the second catalyst 27 can be suppressed. However, if the hybrid vehicle 10 continues to travel steadily at high speed, the fuel cut is not implemented, so the second catalyst 27 may be poisoned by HC and the exhaust gas purification performance may deteriorate. When HC poisoning of the second catalyst 27 occurs, the electronic control unit 30 performs poisoning recovery control to eliminate it.

[0017] FIG. 3 shows a flowchart of the process executed by the electronic control unit 30 for poisoning recovery control. The electronic control unit 30 starts the process of FIG. 3 together with the start of the air-fuel ratio control of the engine 11.

[0018] When starting the process of FIG. 3, the electronic control unit 30 first determines whether HC poisoning of the second catalyst 27 has occurred (S100). In the case of this embodiment, the electronic control unit 30 determines that HC poisoning has occurred when the value of the catalyst poisoning counter indicating the progress of HC poisoning is greater than or equal to a predetermined poisoning determination value. The electronic control unit 30 increments the catalyst poisoning counter every predetermined time while the all-cylinder operation of the engine 11 continues, and clears the value of the catalyst poisoning counter when the all-cylinder operation is interrupted or ended. The all-cylinder operation represents a state where combustion is occurring in all the cylinders 20 of the engine 11. The interruption or end of the all-cylinder operation is performed, for example, by stopping the engine 11, fuel cut, or a specific cylinder fuel cut process described later. The electronic control unit 30 repeats the determination in step S100 every predetermined control cycle until it determines that HC poisoning has occurred. Then, when the electronic control unit 30 determines that HC poisoning has occurred, it proceeds to step S110 for processing.

[0019] In step S110, the electronic control unit 30 calculates the start time T1 of the specific cylinder fuel cut process. Note that in FIG. 3, the specific cylinder fuel cut (Fuel Cut) is described as "specific cylinder F / C". The electronic control unit 30 predicts the time when the oxygen storage amount OSA of the second catalyst 27 is within a predetermined range based on the switching cycle of the target air-fuel ratio by the sub-feedback of the air-fuel ratio control, and sets the predicted time as the start time T1. The predetermined range is set to be the range of the value of the oxygen storage amount OSA when the second catalyst 27 has sufficient margins for both oxygen storage and release.

[0020] Next, the electronic control unit 30 calculates the start time T2 for the vibration mitigation process (S120). In this embodiment, the electronic control unit 30 performs a vibration mitigation process that reduces the engine torque to a predetermined value TE1 or less before the start of the specific cylinder fuel cut process. The electronic control unit 30 then determines the time ΔT required for the engine torque to decrease to the predetermined value TE1 based on the current engine torque, and sets the start time T2 for the vibration mitigation process to be earlier by that time ΔT than the start time T1 for the specific cylinder fuel cut process.

[0021] Subsequently, the electronic control unit 30 waits for the start time T2 to be reached (S130: YES) and then starts the vibration mitigation process (S140). Specifically, in the vibration mitigation process, the electronic control unit 30 adjusts the engine torque to be less than or equal to "TE1", and compensates for the resulting decrease in engine output by increasing the power torque of the second generator motor 13. Thus, in this embodiment, the electronic control unit 30 performs the vibration mitigation process by adjusting the engine torque to be less than or equal to a predetermined value TE1 through coordinated control of the engine 11 and the motor.

[0022] Subsequently, the electronic control unit 30 waits for the start time T1 to be reached (S150: YES) and then starts the specific cylinder fuel cut process (S160). The specific cylinder fuel cut process is a process that stops the fuel supply to some of the multiple cylinders 20 of the engine 11, while continuing to supply fuel to the remaining cylinders. For example, of the four cylinders 20 of the engine 11, the fuel supply to one cylinder is stopped, while the fuel supply to the remaining three cylinders is continued. Furthermore, the electronic control unit 30 increases the opening of the throttle valve 24 to increase the intake air filling rate of cylinder 20 in order to generate an output equal to the required engine output using only the three cylinders to which fuel is supplied.

[0023] Subsequently, when the electronic control unit 30 determines that the second catalyst 27 has recovered from HC poisoning (S170: YES), it terminates the vibration mitigation treatment and the specific cylinder fuel cut-off treatment (S180). After that, the electronic control unit 30 returns to step S100.

[0024] Furthermore, if the engine torque before the vibration mitigation process is less than or equal to "TE1", the specific cylinder fuel cut may be initiated without performing the vibration mitigation process. For example, if the engine torque at the point when the process proceeds to step S120 in Figure 3 is less than or equal to "TE1", the processes from step S120 to step S140 may be skipped, and the process may proceed to step S150.

[0025] <Operation of the First Embodiment> When a specific cylinder fuel cut-off process is executed, vibrations occur in the body of the hybrid vehicle 10 due to the torque difference between the cylinder 20 that stops fuel supply and ceases combustion, and the cylinder 20 that continues to receive fuel and perform combustion. These vibrations during the specific cylinder fuel cut-off process increase as the engine torque increases during the process. Prior to executing the specific cylinder fuel cut-off process, the electronic control unit 30 performs a vibration mitigation process that adjusts the engine torque to be less than or equal to a predetermined value TE1 through coordinated control of the engine 11 and the motor. Reducing the engine torque reduces the torque difference between the cylinder 20 that performs combustion and the cylinder 20 that stops combustion. Therefore, the vibrations generated by the specific cylinder fuel cut-off process are mitigated.

[0026] Figure 4 shows the relationship between engine torque and vehicle longitudinal acceleration during specific cylinder fuel cut-off processing. Vehicle longitudinal acceleration is an indicator of the magnitude of vibration generated by specific cylinder fuel cut-off processing. Vehicle longitudinal acceleration during specific cylinder fuel cut-off processing increases sharply when the engine torque exceeds a certain value. In this embodiment, the default value TE1 is set to a torque smaller than the engine torque at which vehicle longitudinal acceleration sharply increases.

[0027] The electronic control unit 30 determines the period from the start of vibration mitigation processing to the start of specific cylinder fuel cut processing based on the engine torque before the start of vibration mitigation processing. The time required for the engine torque to decrease to the default value TE1 during vibration mitigation processing varies depending on the engine torque before the start of vibration mitigation processing. Therefore, by using the engine torque before the start of vibration mitigation processing, the start times T1 and T2 for specific cylinder fuel cut processing and vibration mitigation processing can be set so that the specific cylinder fuel cut processing starts at an appropriate time when the engine torque has decreased to a point where vibration can be mitigated.

[0028] <Effects of the First Embodiment> The control device for the hybrid vehicle 10 of this embodiment provides the following effects. (1) Prior to executing the specific cylinder fuel cut process, the electronic control unit 30 performs vibration mitigation processing to adjust the engine torque to a predetermined value TE1 or less through coordinated control of the engine 11 and the motors (first generator motor 12 and second generator motor 13). This vibration mitigation processing suppresses the increase in torque steps between cylinders during the specific cylinder fuel cut process. Therefore, the control device of the hybrid vehicle 10 in this embodiment has the effect of suppressing the deterioration of drivability that occurs when executing the specific cylinder fuel cut process, which stops the fuel supply to some cylinders.

[0029] (2) If the deterioration of drivability associated with the implementation of specific cylinder fuel cut-off processing is not suppressed, then specific cylinder fuel cut-off processing can only be implemented in specific situations where the deterioration of drivability is acceptable. In this respect, since the deterioration of drivability associated with the implementation is suppressed, opportunities to implement specific cylinder fuel cut-off processing become easier to obtain.

[0030] (3) The electronic control unit 30 determines the period from the start of the vibration reduction process to the start of the specific cylinder fuel cut process based on the engine torque before the vibration reduction process begins. Therefore, the start times T1 and T2 for the specific cylinder fuel cut process and the vibration reduction process can be set so that the specific cylinder fuel cut process starts at an appropriate time when the engine torque has decreased to a point where vibration can be reduced.

[0031] (4) The engine 11 to which the electronic control unit 30 is applied has a first catalyst 26 installed in the exhaust passage 25 and a second catalyst 27 installed in the exhaust passage 25 downstream of the first catalyst 26. Both the first catalyst 26 and the second catalyst 27 are exhaust gas purification catalysts that have oxygen storage capacity. The engine 11 is configured to alternate between lean combustion, which is combustion at an air-fuel ratio leaner than the stoichiometric air-fuel ratio, and rich combustion, which is combustion at an air-fuel ratio richer than the stoichiometric air-fuel ratio. In such an engine 11, the electronic control unit 30 is configured to perform a specific cylinder fuel cut-off treatment when it is determined that HC poisoning of the second catalyst 27 has occurred. This makes it possible to suppress the decrease in the exhaust gas purification capacity of the second catalyst 27 due to HC poisoning while mitigating the deterioration of drivability.

[0032] (5) The electronic control unit 30 predicts the time when the oxygen storage amount OSA of the second catalyst 27 will be within a predetermined range based on the target air-fuel ratio switching cycle by subfeedback of the air-fuel ratio control, and sets this predicted time as the start time T1. If the exhaust inside the second catalyst 27 is too rich during the fuel cut-off treatment of a specific cylinder, much of the oxygen supplied to the second catalyst 27 will be used to oxidize CO in the exhaust, thus reducing the amount of oxygen available to eliminate HC poisoning. On the other hand, if the exhaust inside the second catalyst 27 is too lean during the fuel cut-off treatment of a specific cylinder, lean failure will occur in the second catalyst 27, and NOx emissions will increase. The air-fuel ratio inside the second catalyst 27 changes with the oxygen storage amount OSA, and the future trend of the oxygen storage amount OSA can be predicted from the target air-fuel ratio switching cycle by subfeedback of the air-fuel ratio control. Therefore, by using the target air-fuel ratio switching cycle based on subfeedback of the air-fuel ratio control, the time when the inside of the second catalyst 27 has an appropriate air-fuel ratio can be set as the start time T1 for the fuel cut-off treatment of a specific cylinder.

[0033] (Second Embodiment) A second embodiment of the control device for a hybrid vehicle will be described in detail with reference to Figure 5. In this embodiment, components common to the above embodiment are denoted by the same reference numerals, and their detailed description is omitted. The control device of this embodiment is configured to perform a vibration mitigation process different from that of the first embodiment.

[0034] Figure 5 shows the relationship between engine speed and vehicle longitudinal acceleration during specific cylinder fuel cut-off processing. When vibrations of a specific frequency band occur in engine 11, the vehicle body resonates, and the vehicle longitudinal acceleration increases. On the other hand, the frequency of vibrations generated by specific cylinder fuel cut-off processing is determined by the engine speed. Therefore, if specific cylinder fuel cut-off processing is performed when the engine speed is within a specific range, the vibrations may be amplified by resonance, potentially significantly worsening drivability. In the following explanation, the range of engine speeds in which resonance occurs will be referred to as the resonance region. In Figure 5, the range of engine speeds from "NE1" to "NE2" corresponds to the resonance region. Therefore, if specific cylinder fuel cut-off processing is performed only when the engine speed is below "NE1" or above "NE2", the deterioration of drivability can be suppressed.

[0035] In this embodiment as well, the electronic control unit 30 performs poisoning recovery control in the procedure shown in Figure 3. However, in this embodiment, in step S140 of Figure 3, the electronic control unit 30 performs a vibration mitigation process to adjust the engine rotation speed so that it is outside a predetermined range. More specifically, if the engine rotation speed before the start of the vibration mitigation process is within the resonance region, the electronic control unit 30 performs a vibration mitigation process to adjust the engine rotation speed so that it is outside the resonance region. For example, the electronic control unit 30 modifies the target rotation speed of the engine 11 so that it is outside the resonance region, and also modifies the target load ratio so that the load ratio obtains the required engine output for the modified target rotation speed. When the target rotation speed and target load ratio are modified, the rotation speed of the first generator motor 12, the opening degree of the throttle valve 24 of the engine 11, etc. are changed. Thus, in this embodiment, the process of adjusting the engine rotation speed so that it is outside a predetermined range is performed as a vibration mitigation process through coordinated control of the engine 11 and the motor.

[0036] Furthermore, in this embodiment, the electronic control unit 30 calculates the start time T2 in step S120 of Figure 3 based on the engine speed at that time, that is, the engine speed before the start of the vibration mitigation process. From the engine speed before the start of the vibration mitigation process, the amount of adjustment required to bring the engine speed outside the resonance region, and consequently the time required to adjust the engine speed to a speed outside the resonance region, can be determined. The electronic control unit 30 calculates the time ΔT required to adjust the engine speed to be outside the resonance region from the engine speed before the start of the vibration mitigation process. The electronic control unit 30 then calculates the start time T2 of the vibration mitigation process to be earlier by that time ΔT than the start time T1 of the specific cylinder fuel cut process.

[0037] In this embodiment configured as described above, the electronic control unit 30 performs vibration mitigation processing to adjust the engine speed to be outside a predetermined range through coordinated control of the engine 11 and the motor, prior to executing the specific cylinder fuel cut-off process. Through this vibration mitigation processing, the engine speed is adjusted so that the frequency of vibrations generated by the specific cylinder fuel cut-off process falls outside the vehicle body's resonant frequency band. By performing vibration mitigation processing in advance and adjusting the engine speed to a rotational speed that can mitigate resonance before starting the specific cylinder fuel cut-off process, the deterioration of drivability associated with the execution of the specific cylinder fuel cut-off process can be suppressed.

[0038] Furthermore, the electronic control unit 30 determines the period from the start of vibration mitigation processing to the start of specific cylinder fuel cut processing based on the engine speed before the start of vibration mitigation processing. The time required to adjust the engine speed to be outside the resonance region during vibration mitigation processing is determined by the engine speed at the start of vibration mitigation processing. Therefore, the start times T1 and T2 for specific cylinder fuel cut processing and vibration mitigation processing can be set so that the specific cylinder fuel cut processing is started at an appropriate time when the engine speed is outside the resonance region.

[0039] (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.

[0040] • The fuel cut-off treatment for specific cylinders may be performed for purposes other than eliminating HC poisoning of the second catalyst 27. For example, the control device of the hybrid vehicle 10 may be configured to perform the fuel cut-off treatment for specific cylinders for purposes such as warming up the catalyst, recovering from sulfur poisoning, or increasing the oxygen storage amount OSA.

[0041] The number of cylinders whose fuel supply is stopped during the specific cylinder fuel cut-off process may be changed. Alternatively, the cylinders whose fuel supply is stopped during the specific cylinder fuel cut-off process may not be fixed, but changed for each combustion cycle.

[0042] The start times T1 and T2 for the specific cylinder fuel cut-off process and the vibration mitigation process may be set in a manner different from that of the above embodiment. For example, the period from the start of the vibration mitigation process to the start of the specific cylinder fuel cut-off process may be fixed, regardless of the engine torque or engine speed before the start of the vibration mitigation process. Alternatively, the engine torque or engine speed after the start of the vibration mitigation process may be monitored, and the specific cylinder fuel cut-off process may be started when it is confirmed that the engine torque has fallen below a predetermined value TE1 or that the engine speed has moved outside the resonance region.

[0043] The control method for the air-fuel ratio control of engine 11 may be changed, such as performing air-fuel ratio control using only main feedback and without sub-feedback. The configuration of the engine 11, for example, the type and number of catalysts installed in the exhaust passage 25, may be different from that shown in Figure 1. [Explanation of symbols]

[0044] 10 Hybrid Vehicles 11 Engine 12. First Generator / Motor 13. Second Generator / Motor 17 Inverter 18 batteries 20 cylinders 21 Injectors 26 First Catalyst 27 Second Catalyst 28 Front air-fuel ratio sensor 29 Rear air-fuel ratio sensor 30 Electronic control unit 31 Arithmetic Processing Unit 32 Storage device

Claims

1. A control device for a hybrid vehicle equipped with an engine having multiple cylinders and an electric motor as a drive source for driving, A specific cylinder fuel cut process is performed, which involves stopping the fuel supply to some of the aforementioned cylinders and supplying fuel to the remaining cylinders other than those mentioned above. Prior to executing the fuel cut-off process for the specific cylinder, a vibration mitigation process is performed to adjust the engine torque to a value below a predetermined value through coordinated control of the engine and the motor. Control system for hybrid vehicles.

2. A control device for a hybrid vehicle according to claim 1, which determines the period from the start of the vibration mitigation treatment to the start of the specific cylinder fuel cut treatment based on the engine torque before the start of the vibration mitigation treatment.

3. A control device for a hybrid vehicle that runs using the driving force generated by an engine having multiple cylinders and the driving force generated by an electric motor, A specific cylinder fuel cut process is performed, which involves stopping the fuel supply to some of the aforementioned cylinders and supplying fuel to the remaining cylinders other than those mentioned above. Prior to executing the fuel cut-off process for the specific cylinder, a vibration mitigation process is performed to adjust the engine speed so that it is outside a predetermined range through coordinated control of the engine and the motor. Control system for hybrid vehicles.

4. The control device for a hybrid vehicle according to claim 3, which determines the period from the start of the vibration mitigation treatment to the start of the specific cylinder fuel cut treatment based on the engine rotation speed before the start of the vibration mitigation treatment.

5. The engine comprises a first catalyst, which is an exhaust gas purification catalyst having oxygen storage capacity and installed in the exhaust passage, and a second catalyst, which is an exhaust gas purification catalyst having oxygen storage capacity and installed in the exhaust passage downstream of the first catalyst, and is configured to alternately perform lean combustion, which is combustion at an air-fuel ratio leaner than the stoichiometric air-fuel ratio, and rich combustion, which is combustion at an air-fuel ratio richer than the stoichiometric air-fuel ratio. The control device is configured to execute the specific cylinder fuel cut-off process when it determines that hydrocarbon poisoning of the second catalyst is occurring. A control device for a hybrid vehicle according to claim 1 or claim 2.

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