Vehicle control method and vehicle control device

Abstract

To prevent a large amount of oxygen from flowing into a catalyst when an engine is stopped.SOLUTION: A vehicle V comprises an engine 1, a MG 2 connected to the engine 1 through a power transmission mechanism, and manifold catalyst 21 and a main catalyst 22 purifying exhaust gas of the engine 1. A controller 50 controlling the vehicle V assists rotation of the engine 1 with the MG 2 during a predetermined period when stopping the engine 1 and causes fuel in a cylinder 1a of the engine 1 to be continuously burned while making output torque smaller than the same required for enabling the engine 1 to autonomously rotate during a predetermined period.SELECTED DRAWING: Figure 3

Description

[Technical Field]

[0001] The present invention relates to a vehicle control method and a vehicle control device. [Background technology]

[0002] Patent Document 1 discloses a vehicle that runs by driving a generator with an engine to generate electricity, and then using the generated electricity to drive a motor. Although not shown in the figure, such vehicles generally have a catalyst that purifies exhaust gas from the engine. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Laid-Open No. 2015-67052 Summary of the Invention [Problem to be solved by the invention]

[0004] When the engine stops, the piston in the cylinder moves up and down until the engine stops completely. This causes the intake air to pass through the engine as it is, causing a large amount of oxygen to flow into the catalyst, which can cause the amount of oxygen adsorbed in the catalyst to become saturated.

[0005] If the engine is restarted in this state, there is a risk that the NOx emitted from the engine will not be purified (reduced).For this reason, immediately after the engine is restarted, the gas emitted from the engine (combustion chamber) is made rich to remove oxygen from the catalyst, but this consumes fuel.

[0006] The present invention has been made in view of these technical problems, and has as its object to suppress the inflow of a large amount of oxygen into the catalyst when the engine is stopped. [Means for solving the problem]

[0007] According to one aspect of the present invention, a vehicle includes an internal combustion engine, a rotating electric machine connected to the internal combustion engine via a power transmission mechanism, and a catalyst for purifying exhaust gas from the internal combustion engine. A control method for this vehicle includes, when the internal combustion engine is stopped, controlling the rotating electric machine to purify exhaust gas from the internal combustion engine for a predetermined time. of the internal combustion engine so that the rotational speed remains constant The rotation is assisted, and during the predetermined time, the output torque is set to be smaller than the output torque at which the internal combustion engine can rotate autonomously, thereby allowing the combustion of fuel in the cylinders of the internal combustion engine to continue. [Effects of the Invention]

[0008] According to the present invention, the amount of oxygen contained in the exhaust gas can be reduced as much as possible, and a large amount of oxygen can be prevented from flowing into the catalyst when the internal combustion engine is stopped. [Brief explanation of the drawings]

[0009] [Figure 1] FIG. 1 is a schematic diagram of a drive system for a vehicle according to this embodiment. [Figure 2] FIG. 2 is a schematic diagram of an engine system mounted on the vehicle of this embodiment. [Figure 3] FIG. 3 is a flowchart showing the flow of control when stopping the engine in this embodiment. [Figure 4] FIG. 4 is a flowchart showing the flow of engine stop control according to this embodiment. [Figure 5A] FIG. 5A is an example of a valve timing diagram during normal control according to an embodiment of the present invention. [Figure 5B] FIG. 5B is an example of a valve timing diagram during engine stop control according to the embodiment of the present invention. [Figure 6] FIG. 6 is a time chart showing an example of control when stopping the engine. DETAILED DESCRIPTION OF THE INVENTION

[0010] A vehicle V equipped with an engine system 100 according to an embodiment of the present invention will be described with reference to Figures 1 and 2. Figure 1 is a schematic configuration diagram of a drive system of the vehicle V according to this embodiment. Figure 2 is a schematic configuration diagram of the engine system 100 according to this embodiment.

[0011] 1, vehicle V includes an engine system 100 having engine 1, a first motor generator 2 (hereinafter referred to as MG2) as a rotating electric machine, a battery 3, a second motor generator 4 (hereinafter referred to as MG4) as a driving source for traveling, a controller 50 as a control device that controls the operation of these components, a gear mechanism 6 as a power transmission mechanism that transmits power between engine 1 and MG2, and a gear mechanism 7 as a power transmission mechanism that transmits power between MG4 and wheels 5. Vehicle V of this embodiment is a series-type hybrid vehicle in which engine 1 is used only for generating electricity and MG4 is used to drive wheels 5 and for regenerating electricity.

[0012] The MG2 is a three-phase AC permanent magnet synchronous motor mounted as both a generator and an electric motor. Specifically, the MG2 functions as a generator when it receives rotational power from the engine 1. Furthermore, when it receives power from the battery 3, the MG2 can function as a starter motor for the engine 1 and as a motoring motor that rotates and drives the engine 1.

[0013] The battery 3 is configured by, for example, a lithium ion battery. The battery 3 is charged with power generated by the MG2 and power regenerated by the MG4, and supplies the charged power to the MG4 or the MG2.

[0014] The SOC (state of charge) of the battery 3 is detected by an SOC sensor (not shown) and transmitted to the controller 50. The controller 50 controls the charging of the battery 3 based on the SOC (state of charge). When the SOC of the battery 3 drops to a lower limit value for charging control, the controller 50 drives the engine 1. This drives the MG2, and power generated by the MG2 is supplied to the battery 3, charging the battery 3. On the other hand, when the SOC of the battery 3 rises to an upper limit value for charging control, the controller 50 stops the engine 1. This stops the MG2, and power generation by the MG2 stops.

[0015] The MG4 is a three-phase AC permanent magnet synchronous motor powered by the battery 3. The MG4 is driven by power supplied from the battery 3 via an inverter (not shown). The rotational power of the MG4 is transmitted to the wheels 5 via a gear mechanism 7, causing the vehicle V to travel. The MG4 also has a regenerative function that receives rotational power from the wheels 5 when the vehicle V is decelerating or braking, and generates power to charge the battery 3.

[0016] Next, the engine system 100 will be described with reference to FIG.

[0017] 2, the engine system 100 includes an engine 1, an intake passage 10 that sends intake air to the engine 1, and an exhaust passage 20 that discharges combustion gas (exhaust gas) from the engine 1 to the outside. The operation of the entire engine system 100 is controlled by a controller 50.

[0018] The engine 1 is a gasoline-fueled internal combustion engine and has a plurality of cylinders 1a (for example, three).

[0019] The output shaft of the engine 1 is mechanically connected to the MG2 via a gear mechanism 6 (see FIG. 1). The power of the engine 1 is transmitted to the MG2 via the gear mechanism 6, and the MG2 rotates using the power of the engine 1 to generate electricity.

[0020] Arranged in the intake passage 10, in this order from the upstream side of the intake air flow, are an air cleaner 11, an air flow meter 12, an admission valve 13, a compressor 30A of a turbocharger 30, a water-cooled intercooler (WCAC) 14, a throttle valve 15, a collector tank 33, and a pressure sensor with a temperature sensor 16. Intake air is supplied into the cylinder 1a of the engine 1 through this intake passage 10.

[0021] Fresh air is drawn in through an air cleaner 11. The air cleaner 11 collects foreign matter in the fresh air. Note that the fresh air referred to here refers to air that is newly drawn into the engine system 100 from the atmosphere.

[0022] The air flow meter 12 detects the intake air flow rate (intake air flow rate Qin). The air flow meter 12 also has a built-in temperature sensor and is capable of detecting the intake air temperature. The intake air flow rate Qin and the intake air temperature detected by the air flow meter 12 are input to the controller 50.

[0023] The admission valve 13 is provided between the air flow meter 12 and a portion where an EGR passage 23 (described later) and the intake passage 10 are connected, and generates a pressure difference between the intake passage 10 and the exhaust passage 20. The admission valve 13 will be described in detail later.

[0024] The compressor 30A is provided coaxially with a turbine 30B of the turbocharger 30, which will be described later, and the compressor 30A rotates in conjunction with the rotation of the turbine 30B. The rotation of the compressor 30A pressurizes the intake air introduced into the cylinder 1a of the engine 1.

[0025] The intake passage 10 is provided with a bypass path that branches off at the compressor 30A and joins at a position upstream of the compressor 30A, and this bypass path is provided with a recirculation valve 17. The recirculation valve 17 serves to recirculate (recirculate) the pressurized air trapped in the intake passage 10 from the throttle valve 15 to the compressor 30A to the upstream side of the compressor 30A when the throttle valve 15 is closed due to vehicle deceleration.

[0026] The water-cooled intercooler 14 is used to cool the air compressed by the compressor 30A using cooling water flowing through a cooling water passage. The air whose temperature has been increased by air compression by the compressor 30A is cooled by the intercooler 14, thereby improving supercharging efficiency. The strength of the cooling by the intercooler 14 (the temperature of the intercooler 14) is adjusted by the flow rate, water temperature, etc. of the cooling water flowing through the cooling water passage.

[0027] The throttle valve 15 is driven and controlled by a controller 50 to adjust the amount of intake air drawn into the cylinder 1a. The depression amount of the accelerator pedal is detected by an accelerator opening sensor (not shown), and the detected signal is input to the controller 50. The controller 50 controls the opening amount of the throttle valve 15 based on the depression amount of the accelerator pedal. The throttle valve 15 may be provided upstream of the intercooler 14.

[0028] The pressure sensor 16 with temperature sensor, which is an integrated temperature sensor and pressure sensor provided downstream of the throttle valve 15, is provided inside the collector tank 33 and detects the temperature (intercooler 14 outlet temperature) and pressure of the intake air introduced into the engine 1. The intake air temperature and intake pressure detected by the pressure sensor 16 with temperature sensor are input to the controller 50. Note that the pressure sensor 16 with temperature sensor may have a temperature sensor and a pressure sensor provided separately.

[0029] The engine 1 is provided with a fuel injector 18, a spark plug 19, an intake valve 31, and an exhaust valve 32. A controller 50 controls the fuel injector 18, the spark plug 19, the intake valve 31, and the exhaust valve 32 at predetermined timings to form an air-fuel mixture of intake air drawn into the cylinder 1a and fuel injected into the cylinder 1a by the fuel injector 18, and burns the air-fuel mixture based on a spark generated by the spark plug 19. The engine 1 is also provided with a knock sensor that detects knock, an in-cylinder pressure sensor that detects the pressure inside the cylinder 1a, and a crank angle sensor that detects the crank angle (none of which are shown), and signals detected by these sensors are input to the controller 50.

[0030] In this embodiment, the intake valve 31 and the exhaust valve 32 are opened and closed by a valve mechanism that operates based on commands from a controller 50. The valve mechanism may be, for example, a variable valve timing mechanism or a valve mechanism used for cylinder deactivation. Note that the valve mechanism may be any type, such as a mechanical type, a hydraulic type, an electric type, or a solenoid valve type.

[0031] Combustion gas (exhaust gas) from the engine 1 is discharged into an exhaust passage 20. In the exhaust passage 20, a turbine 30B of a turbocharger 30, a manifold catalyst 21, and a main catalyst 22 are arranged in this order from the upstream side of the exhaust flow. A muffler (not shown) for reducing exhaust noise is provided at the end of the exhaust passage 20. In addition, an air-fuel ratio sensor 27 for measuring the air-fuel ratio in the exhaust is provided in the exhaust passage 20, and the air-fuel ratio measured by the air-fuel ratio sensor 27 is input to a controller 50 as an electric signal.

[0032] The turbine 30B of the turbocharger 30 is rotated by the energy of the combustion gas (exhaust gas) discharged from the engine 1. As described above, the rotation of the turbine 30B rotates the compressor 30A provided coaxially with the turbine 30B, and the rotation of the compressor 30A pressurizes the intake air introduced into the cylinder 1a of the engine 1.

[0033] The exhaust passage 20 is provided with a bypass passage that bypasses the turbine 30B. The bypass passage is configured to be openable and closable by a wastegate valve 26. When the wastegate valve 26 opens, part of the exhaust gas flows bypassing the turbine 30B, causing the rotation speed of the turbine 30B to decrease compared to before the valve was opened, and also causing the rotation speed of the compressor 30A, which is coaxial with the turbine 30B, to decrease. Therefore, the boost pressure can be adjusted by controlling the opening of the wastegate valve 26.

[0034] The manifold catalyst 21 and the main catalyst 22 are configured, for example, as three-way catalysts, and purify harmful components such as HC, CO, and NOx contained in the exhaust gas.

[0035] An EGR passage 23 branches off from the exhaust passage 20 at a position between the manifold catalyst 21 and the main catalyst 22. The EGR passage 23 connects the exhaust passage 20 and the intake passage 10. An EGR cooler 24 and an EGR valve 25 are provided in the EGR passage 23. The opening of the EGR valve 25 is controlled by a controller 50 in accordance with the operating state of the engine 1. The operating state here refers to the rotation speed Ve of the engine 1 and the load on the engine 1.

[0036] As described above, the admission valve 13 is provided between the connection between the EGR passage 23 and the intake passage 10 and the air flow meter 12. The opening and closing of the admission valve 13 is controlled by the controller 50, and a pressure difference is created between the intake passage 10 and the exhaust passage 20. This pressure difference causes a portion of the exhaust gas to be recirculated from the exhaust passage 20 to the intake passage 10 as EGR gas.

[0037] The admission valve 13 is fully open in its default state, and is controlled by the controller 50 to be operated in the closing direction.

[0038] The admission valve 13 is used to control the intake passage 10 to create a negative pressure relative to the exhaust passage 20. On the other hand, the EGR valve 25 is used to control the introduction of EGR gas. The EGR valve 25 is controlled based on a map (EGR map) in which a target EGR rate is assigned for each operating state determined by the rotation speed Ve of the engine 1 and the load of the engine 1. That is, the controller 50 first determines a target EGR rate (target EGR rate on the EGR map) that is uniquely determined by the rotation speed Ve and load of the engine 1 with reference to the EGR map. Next, the controller 50 estimates the EGR rate (the ratio of EGR gas to the amount of air in the cylinder 1a of the engine 1) from the intake flow rate Qin detected by the air flow meter 12 and the rotation speed Ve of the engine 1, and controls the EGR valve 25 and the admission valve 13 so that the estimated EGR rate (estimated EGR rate) matches the target EGR rate.

[0039] It is preferable to provide the admission valve 13 to facilitate the introduction of EGR gas into the intake passage 10, but it is also possible to introduce EGR gas by simply controlling the opening and closing of the EGR valve 25.

[0040] The controller 50 is configured by a microcomputer equipped with a central processing unit (CPU), read-only memory (ROM), random access memory (RAM), and an input / output interface (I / O interface). The controller 50 may also be configured by multiple microcomputers. The controller 50 executes specific programs to perform processes for controlling the entire engine system 100.

[0041] The controller 50 receives input of detected values ​​such as the intake air flow rate Qin detected by the air flow meter 12, the intake air temperature and atmospheric temperature, and the intake air temperature (intercooler 14 outlet temperature) and intake air pressure detected by the temperature sensor-equipped pressure sensor 16. The controller 50 also receives input of detected values ​​from the air-fuel ratio sensor 27, crank angle sensor, in-cylinder pressure sensor, accelerator position sensor, etc. (none of which are shown). Based on these detected values, the controller 50 executes specific programs by controlling the opening of the throttle valve 15, fuel injection using the fuel injector 18, ignition timing using the spark plug 19, and opening of the EGR valve 25 and admission valve 13, thereby controlling the entire engine system 100.

[0042] In addition, the controller 50 receives inputs such as the charging rate of the battery 3 and the speed of the vehicle V, and controls the driving of the MG2 and MG4 and the charging of the battery 3 based on these signals.

[0043] In the vehicle V configured as described above, when stopping the engine 1, the supply of fuel to the engine 1 by the fuel injector 18 is stopped, and ignition timing control by the spark plug 19 is stopped. After the supply of fuel to the engine 1 and ignition are stopped in this manner, the rotation speed of the engine 1 is subsequently reduced for a predetermined period of time while being controlled by the MG2, and the engine 1 is finally stopped. At this time, the piston 1b of the engine 1 moves up and down, so that fresh air drawn into the cylinder 1a of the engine 1 is discharged directly into the exhaust passage 20. When unburned fresh air flows into the manifold catalyst 21 and the main catalyst 22 in this manner, the amount of oxygen adsorbed in the manifold catalyst 21 and the main catalyst 22 increases.

[0044] If the engine 1 is restarted in a state where the amount of oxygen adsorbed in the manifold catalyst 21 and the main catalyst 22 has increased, the NOx reduction reaction may be inhibited, and the amount of NOx emitted outside the vehicle may increase. For this reason, when starting the engine 1, it is necessary to supply a larger amount of fuel so that the air-fuel ratio becomes rich. However, supplying a larger amount of fuel may result in a deterioration in fuel economy.

[0045] Therefore, in the vehicle V of this embodiment, when the engine 1 is stopped, control is performed to suppress the supply of oxygen to the manifold catalyst 21 and the main catalyst 22 (hereinafter, the control performed when stopping the engine 1 is also referred to as "engine stop control"). This will be specifically described below with reference to the flowcharts shown in FIGS. 3 and 4.

[0046] In step S1, it is determined whether or not there is a command to stop the engine 1. Specifically, a situation in which a command to stop the engine 1 is issued occurs, for example, when the SOC of the battery 3 rises to the upper limit value of the charge control. When the controller 50 detects such a state in which it is necessary to stop the engine 1, it determines that there is a command to stop the engine 1. When the controller 50 determines that there is a command to stop the engine 1, the process proceeds to step S2, and when the controller 50 determines that there is no command to stop the engine 1, the process proceeds to END.

[0047] In step S2, engine stop control is executed. The engine stop control of this embodiment will now be described in detail with reference to the flowchart shown in Fig. 4. Note that the controls from step S21 to step S23 in Fig. 4 are ordered for the sake of explanation, but in reality, the controller 50 executes these controls simultaneously.

[0048] In step S21, the opening of the throttle valve 15 is reduced. Specifically, the controller 50 sets the opening of the throttle valve 15 to a predetermined opening S, thereby reducing the intake air flow rate Qin into the cylinder 1a of the engine 1. In this embodiment, the opening S of the throttle valve 15 is smaller than the opening when the engine 1 can rotate autonomously.

[0049] In step S22, the excess air ratio λ is set to 1. Specifically, the controller 50 controls the fuel injected from the fuel injector 18 based on the detection signal of the air-fuel ratio sensor 27 so that the excess air ratio λ becomes 1, and then continues combustion.

[0050] In step S23, the valve timing is retarded. Specifically, for example, from the valve timing during normal operation (e.g., operation at the best fuel-efficient operating point) shown in FIG. 5A, the opening timing of the intake valve 31 is retarded as shown in FIG. 5B, so that the intake valve 31 opens (IVO) in the region from approximately the middle to the first half of the intake stroke (in FIG. 5B, the crank angle is approximately 45° from the top dead center) and closes (IVC) in the region from approximately the middle to the second half of the compression stroke. Note that the exhaust valve 32 opens (EVO) just before the expansion bottom dead center and closes (EVC) near the exhaust top dead center, as in normal control. Such a change in the valve timing of the intake valve 31 is performed by controlling the valve train. By retarding the valve timing of the intake valve 31 in this way, the amount of air intake into the cylinder 1a can be reduced and the in-cylinder pressure at maximum compression can be reduced. In step S23, the valve timing of the intake valve 31 may be advanced, for example, the IVC may be set in the first half of the intake stroke. In this case, the same effect as in the case of retarding the valve timing can be obtained.

[0051] When executing the control of step S23, if the configuration allows adjustment of the lift amount of the intake valve 31, it is preferable to control the lift amount of the intake valve 31 to be as small as possible. By reducing the lift amount of the intake valve 31, the amount of air taken into the cylinder 1a when the intake valve 31 opens can be reduced.

[0052] In step S24, the controller 50 drives the MG2. Specifically, the controller 50 drives the MG2 and assists the rotation of the engine 1 with the power of the MG2 so that the rotation speed Ve of the engine 1 becomes a predetermined rotation speed V1. In this embodiment, the predetermined rotation speed V1 is set to a value equal to or lower than the optimal fuel-efficient rotation speed Vb of the engine 1.

[0053] In this way, in the engine stop control of this embodiment, when an engine stop command is issued, the opening of the throttle valve 15 is reduced, thereby reducing the intake air flow rate Qin into the cylinder 1a.

[0054] Furthermore, when the opening of the throttle valve 15 is reduced to the predetermined opening S in this manner, the output torque of the engine 1 becomes smaller than the output torque at which the engine 1 can rotate autonomously. However, in this embodiment, the rotation of the engine 1 is assisted by driving the MG2. This allows combustion to continue without stopping the rotation of the engine 1. Furthermore, as described above, by continuing combustion at an excess air ratio λ of 1, that is, at the stoichiometric air-fuel ratio, the amount of oxygen contained in the exhaust gas from the cylinder 1a is reduced as much as possible, and the amount of oxygen flowing into the manifold catalyst 21 and the main catalyst 22 is reduced. This makes it possible to suppress an increase in the amount of oxygen adsorbed in the manifold catalyst 21 and the main catalyst 22, thereby preventing the NOx reduction reaction from being hindered when the engine 1 is restarted.

[0055] When such engine stop control (step S2) is started, the process proceeds to step S3.

[0056] In step S3, it is determined whether a predetermined time T has elapsed. Specifically, the controller 50 determines whether the predetermined time T has elapsed since the start of engine stop control. If the predetermined time T has elapsed, the process proceeds to step S4. If the predetermined time T has not elapsed, the determination in step S3 is repeated until the predetermined time T has elapsed. Note that the predetermined time T is, for example, the time until the target negative pressure is generated in the intake passage 10. By generating the target negative pressure in the intake passage 10, it is possible to suppress the occurrence of engine rotational vibration when the engine is stopped in the subsequent step S4.

[0057] In step S4, the engine is stopped. Specifically, the controller 50 ends the engine stop control. More specifically, the MG2 is stopped, and the control of the fuel injector 18 and the spark plug 19 is stopped. This causes the engine 1 to completely stop. At this time, compared to when the engine stop control is not performed, the amount of intake air into the engine 1 is very small, and the rotation of the engine 1 stops immediately, so the increase in the amount of oxygen adsorbed in the manifold catalyst 21 and the main catalyst 22 is very small.

[0058] Next, referring to the time chart shown in FIG. 6, the changes in the rotation speed Ve of the engine 1 and the changes in the oxygen adsorption rate (oxygen adsorption amount) in the manifold catalyst 21 and the main catalyst 22 during control (engine stop control) when stopping the engine 1 according to this embodiment will be explained in chronological order.

[0059] When the controller 50 determines that there is an engine stop command (time t1), the opening of the throttle valve 15 is set to a predetermined opening S, and combustion continues at an excess air ratio λ=1. By reducing the opening of the throttle valve 15, the rotation speed Ve of the engine 1 decreases. Therefore, the controller 50 drives the MG2 to assist the rotation of the engine 1 so that the rotation speed Ve of the engine 1 becomes the predetermined rotation speed V1 (time t2). As a result, the rotation speed Ve of the engine 1 is maintained at the predetermined rotation speed V1.

[0060] Then, when a predetermined time T has elapsed (time t3) since the controller 50 determined that an engine stop command has been issued (time t1), the controller 50 stops the MG2 and stops control of the fuel injector 18 and the spark plug 19. This causes the engine 1 to stop.

[0061] If the engine stop control of this embodiment is not executed when the engine 1 is stopped, the amount of oxygen adsorbed in the manifold catalyst 21 and the main catalyst 22 increases significantly and becomes saturated (the oxygen adsorption rate reaches 100%), as shown by the thick dotted line in Figure 6. Therefore, when the engine 1 is restarted (at time t4), if the lambda control is performed with an increase in fuel amount, which is generally performed at the time of engine start, the reduction reaction of NOx is inhibited, and the amount of NOx emitted outside the vehicle increases. In other words, the purification performance of the manifold catalyst 21 and the main catalyst 22 at the time of restart is deteriorated. Furthermore, if fuel is supplied to make the air-fuel ratio rich in order to remove oxygen from the manifold catalyst 21 and the main catalyst 22, fuel economy deteriorates.

[0062] In contrast, when the engine stop control of this embodiment is executed, combustion continues while suppressing the intake air flow rate Qin to the cylinder 1a so that the excess air ratio λ becomes 1, thereby reducing the amount of oxygen in the exhaust gas. This makes it possible to suppress an increase in the amount of oxygen adsorbed in the manifold catalyst 21 and the main catalyst 22. As a result, when the engine 1 is restarted, oxygen can be adsorbed in the manifold catalyst 21 and the main catalyst 22, thereby suppressing a deterioration in purification performance at the time of restart. Furthermore, since oxygen is removed from the manifold catalyst 21 and the main catalyst 22 when the engine 1 is restarted, the number of times and amount of fuel are supplied can be reduced so that the air-fuel ratio becomes rich, thereby suppressing a deterioration in fuel economy.

[0063] In the above embodiment, when the engine stop control is executed, the rotation speed Ve of the engine 1 (internal combustion engine) is set to a rotation speed lower than the best fuel-efficient rotation speed Vb of the engine 1 (internal combustion engine). However, this is not limited to this, and the best fuel-efficient rotation speed Vb of the engine 1 (internal combustion engine) or the rotation speed Ve at the time when the engine stop command is issued may be maintained.

[0064] Furthermore, in the above embodiment, the valve timing of the intake valve 31 is changed when the engine stop control is executed. However, the valve timing of the intake valve 31 does not have to be changed.

[0065] In the above embodiment, the vehicle V is described as a series hybrid type vehicle, but the engine stop control can also be applied to other hybrid type vehicles, such as a one-motor, two-clutch parallel hybrid type vehicle.

[0066] In the above embodiment, the case where two catalysts, the manifold catalyst 21 and the main catalyst 22, are provided has been described as an example, but the present invention is not limited to this. The number of catalysts may be one, or three or more.

[0067] The configuration, operation, and effects of the embodiment of the present invention configured as above will be described below.

[0068] The vehicle V includes an engine 1 (internal combustion engine), an MG2 (rotating electric machine) connected to the engine 1 (internal combustion engine) via a gear mechanism 6 (power transmission mechanism), and a manifold catalyst 21 and a main catalyst 22 that purify exhaust gas from the engine 1 (internal combustion engine). When stopping the engine 1 (internal combustion engine), a controller 50 (control device) that controls the vehicle V assists the rotation of the engine 1 (internal combustion engine) with the MG2 (rotating electric machine) for a predetermined time T, and continues combustion of fuel in cylinders 1a (inside cylinders) of the engine 1 (internal combustion engine) for the predetermined time T by setting the output torque to be smaller than the output torque at which the engine 1 (internal combustion engine) can rotate autonomously.

[0069] In this configuration, the rotation of the engine 1 (internal combustion engine) is assisted by the MG2 (rotating electric machine) for a predetermined time T, and the output torque is set to a value lower than the output torque at which the engine 1 (internal combustion engine) can autonomously rotate, thereby continuing fuel combustion in the cylinder 1a of the engine 1 (internal combustion engine). This reduces the intake air flow rate Qin into the cylinder 1a of the engine 1 and allows combustion to continue without stopping the rotation of the engine 1. Furthermore, by setting the excess air ratio λ to 1, i.e., the stoichiometric air-fuel ratio, the amount of oxygen contained in the exhaust gas from the cylinder 1a can be more reliably reduced, thereby preventing a large amount of oxygen from flowing into the manifold catalyst 21 and the main catalyst 22 when the engine 1 is stopped. This prevents the oxygen adsorption capacity of the manifold catalyst 21 and the main catalyst 22 from saturating, allowing oxygen to be adsorbed into the manifold catalyst 21 and the main catalyst 22 even when the engine 1 is restarted. This prevents deterioration of purification performance when the engine 1 is restarted. Furthermore, when the engine 1 is restarted, oxygen is removed from the manifold catalyst 21 and the main catalyst 22, so the number of times and amount of fuel to be supplied can be reduced so that the air-fuel ratio becomes rich, thereby suppressing deterioration in fuel efficiency.

[0070] When stopping the engine 1 (internal combustion engine), the controller 50 (control device) sets the rotation speed Ve of the engine 1 (internal combustion engine) to a rotation speed lower than the best fuel-efficient rotation speed Vb of the engine 1 (internal combustion engine) when assisting the rotation of the engine 1 (internal combustion engine) with the MG2 (rotating electric machine).

[0071] When engine stop control is executed, the rotation speed Ve of the engine 1 (internal combustion engine) is reduced, thereby reducing the intake air flow rate Qin into the cylinder 1a. This reduces the flow rate of exhaust gas from the cylinder 1a, thereby further reducing the amount of oxygen flowing into the manifold catalyst 21 and the main catalyst 22. This makes it possible to suppress an increase in the amount of oxygen adsorbed in the manifold catalyst 21 and the main catalyst 22, thereby more reliably preventing the NOx reduction reaction from being hindered when the engine 1 is restarted.

[0072] When stopping the engine 1 (internal combustion engine), the controller 50 (control device) retards the valve timing of the intake valve 31 of the engine 1 (internal combustion engine) while assisting the rotation of the engine 1 (internal combustion engine) with the MG2 (rotating electric machine).

[0073] By retarding the valve timing of the intake valve 31, it is possible to reduce the amount of air taken into the cylinder 1a of the engine 1 and also to lower the pressure during recompression. This makes it possible to suppress the rise in pressure inside the cylinder 1a (in-cylinder pressure) during the compression stroke, thereby reducing the impact of compression reaction force on noise and vibration.

[0074] Although the embodiments of the present invention have been described above, the above embodiments merely illustrate some of the application examples of the present invention, and it is not intended that the technical scope of the present invention be limited to the specific configurations of the above embodiments. [Explanation of symbols]

[0075] V···vehicle, 100··engine system, 1···engine, 1a···cylinder, 2···first motor generator (MG), 4···second motor generator (MG), 10···intake passage, 15···throttle valve, 18···fuel injector, 20···exhaust passage, 21···manifold catalyst, 22···main catalyst, 31···intake valve, 32···exhaust valve, 50···controller (control device)

Claims

1. an internal combustion engine; a rotating electric machine connected to the internal combustion engine via a power transmission mechanism; a catalyst for purifying exhaust gas from the internal combustion engine, A vehicle control method comprising, when stopping the internal combustion engine, assisting the rotation of the internal combustion engine by the rotating electric machine so that the rotational speed of the internal combustion engine remains constant for a predetermined time, and setting an output torque that is smaller than the output torque at which the internal combustion engine can rotate autonomously for the predetermined time, thereby continuing fuel combustion in the cylinders of the internal combustion engine.

2. 2. A vehicle control method according to claim 1, comprising: A vehicle control method comprising: when the internal combustion engine is stopped and the rotation of the internal combustion engine is assisted by the rotating electric machine, setting the rotation speed of the internal combustion engine to a rotation speed lower than the best fuel-efficient rotation speed of the internal combustion engine.

3. 3. A vehicle control method according to claim 2, comprising: a control method for a vehicle, the method comprising: when stopping the internal combustion engine, retarding valve timing of an intake valve of the internal combustion engine while the rotating electric machine is assisting rotation of the internal combustion engine;

4. an internal combustion engine; a rotating electric machine connected to the internal combustion engine via a power transmission mechanism; a catalyst for purifying exhaust gas from the internal combustion engine, A vehicle control device in which, when the internal combustion engine is stopped, the control device assists the rotation of the internal combustion engine by using the rotating electric machine to maintain a constant rotational speed for a predetermined time, and continues combustion of fuel in the cylinders of the internal combustion engine by setting an output torque that is smaller than the output torque at which the internal combustion engine can rotate autonomously for the predetermined time.

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