Control method for hybrid vehicle and control device for hybrid vehicle

Abstract

When switching the combustion mode of an internal combustion engine (10) from lean burn to stoichiometric burn, fuel supply to the internal combustion engine (10) is stopped, and the amount of intake air of the internal combustion engine (10) is reduced in the stop. Also, the internal combustion engine (10) is restarted with a target air-fuel ratio set to a theoretical air-fuel ratio or an air-fuel ratio richer than the theoretical air-fuel ratio. Thus, the vehicle (1) can suppress knocking of the internal combustion engine (10) when switching the combustion mode of the internal combustion engine (10) from lean burn to stoichiometric burn, and can alleviate the sense of discord of the driver.

Description

Technical Field

[0001] This invention relates to a control method and a control device for hybrid vehicles. Background Technology

[0002] For example, Patent Document 1 discloses an internal combustion engine that switches between stratified combustion, which stratifies the combustion chamber and controls the air-fuel ratio to be greater than the stoichiometric air-fuel ratio, and homogeneous combustion, which homogenizes the mixture in the combustion chamber and controls it to be less than the first air-fuel ratio (e.g., the stoichiometric air-fuel ratio).

[0003] The intake passage of the internal combustion engine in Patent Document 1 is connected to: a first bypass passage that connects the turbocharger and the intercooler in a manner that bypasses them; and a second bypass passage that is configured to bypass the throttle valve.

[0004] In this patent document 1, when the air-fuel ratio changes from the first air-fuel ratio to the second air-fuel ratio along with the switching of the combustion mode, in order to avoid torque shock, the amount of air is gradually reduced by using a first bypass control valve provided in the first bypass passage and a second bypass control valve provided in the second bypass passage, thereby suppressing the abrupt change in torque.

[0005] However, in Patent Document 1, if the control of air volume via the first bypass control valve and the second bypass control valve results in a response lag, the reduction of air volume during changes in air-fuel ratio will be delayed, potentially leading to detonation in the internal combustion engine.

[0006] In other words, there is room for further improvement regarding internal combustion engines that switch combustion modes by changing the air-fuel ratio, so as to prevent the engine from causing a sense of disharmony to the driver during the air-fuel ratio switching.

[0007] Patent Document 1: Japanese Patent Application Publication No. 4-362221 Summary of the Invention

[0008] The hybrid vehicle of the present invention can switch between stoichiometric combustion, which sets the target air-fuel ratio of the internal combustion engine to the stoichiometric air-fuel ratio, and lean combustion, which makes the target air-fuel ratio leaner than the stoichiometric air-fuel ratio. When switching the combustion mode from lean combustion to stoichiometric combustion, the fuel supply to the internal combustion engine is stopped. During this stop, the intake air volume of the internal combustion engine is reduced. With the intake air volume of the internal combustion engine reduced, the target air-fuel ratio of the internal combustion engine is set to the stoichiometric air-fuel ratio or a richer air-fuel ratio than the stoichiometric air-fuel ratio, thereby restarting the internal combustion engine.

[0009] According to the present invention, when a hybrid vehicle switches the combustion mode of the internal combustion engine from lean combustion to stoichiometric combustion, it can suppress the detonation of the internal combustion engine and alleviate the driver's sense of disharmony. Attached Figure Description

[0010] Figure 1 This is a schematic diagram illustrating a general outline of the drive system of a vehicle to which the present invention is applied.

[0011] Figure 2 It is an illustrative diagram that schematically represents the system structure of an internal combustion engine.

[0012] Figure 3 This is an explanatory diagram showing the relationship between equivalence ratio and NOx emissions from the engine.

[0013] Figure 4 This is an explanatory diagram showing the relationship between NOx emitted from the tailpipe and its equivalence ratio.

[0014] Figure 5 It is a dynamic time-series diagram showing the various parameters when switching combustion modes.

[0015] Figure 6 It is a dynamic time-series diagram showing the various parameters when switching combustion modes.

[0016] Figure 7 It is a dynamic time-series diagram showing the various parameters when switching combustion modes.

[0017] Figure 8 It is a dynamic time-series diagram showing the various parameters when switching combustion modes.

[0018] Figure 9 It is a dynamic time-series diagram showing the various parameters when switching combustion modes.

[0019] Figure 10 It is a dynamic time-series diagram showing the various parameters when switching combustion modes.

[0020] Figure 11 It is a dynamic time-series diagram showing the various parameters when switching combustion modes.

[0021] Figure 12 It is a dynamic time-series diagram showing the various parameters when switching combustion modes. Detailed Implementation

[0022] An embodiment of the present invention will now be described in detail with reference to the accompanying drawings.

[0023] Figure 1 This is an explanatory diagram schematically illustrating a drive system of a vehicle 1 to which the present invention is applied. The vehicle 1 includes: a drive unit 3 that drives drive wheels 2; and a power generation unit 4 that generates electricity to drive the drive wheels 2.

[0024] The drive unit 3 includes: a drive motor 5, which serves as a second electric motor and drives the drive wheel 2 to rotate; a first gear train 6 and a differential gear 7, which transmit the driving force of the drive motor 5 to the drive wheel 2. Power is supplied to the drive motor 5 from a battery 8 that has been charged with electricity generated by the power generation unit 4.

[0025] The power generation unit 4 includes: a generator 9 as a first electric motor that generates electricity to supply power to the drive motor 5; an internal combustion engine 10 that drives the generator 9; and a second gear train 11 that transmits the rotation of the internal combustion engine 10 to the generator 9.

[0026] Vehicle 1 is a so-called series hybrid vehicle that does not use the internal combustion engine 10 as a power source. For example, if the battery capacity of battery 8 decreases, the generator 9 generates electricity to drive the internal combustion engine 10 in order to charge battery 8.

[0027] The drive motor 5 is the direct drive source for the vehicle 1, for example, driven by AC power from the battery 8. Additionally, the drive motor 5 functions as a generator when the vehicle 1 decelerates.

[0028] The generator 9 converts the rotational energy generated in the internal combustion engine 10 into electrical energy, for example, to charge the battery 8. Additionally, the generator 9 also functions as an electric motor to drive the internal combustion engine 10, enabling its operation. The generator 9 can also function as a starter motor for the internal combustion engine 10. Furthermore, the electricity generated by the generator 9 can be supplied directly to the drive motor 5, depending on the operating conditions, for example, without charging the battery 8.

[0029] The internal combustion engine 10 can transmit the rotation of the crankshaft to the rotor of the generator 9. The internal combustion engine 10 can change the air-fuel ratio, switching between stoichiometric combustion (a first combustion mode) and lean combustion (a second combustion mode). Stoichiometric combustion is combustion where the target air-fuel ratio is set to the stoichiometric air-fuel ratio. Lean combustion is lean combustion where the target air-fuel ratio is set to a lean air-fuel ratio greater than the stoichiometric air-fuel ratio.

[0030] Figure 2 This is an illustrative diagram schematically representing the system structure of the internal combustion engine 10. An air-fuel ratio sensor 22, a first catalyst 23, and a second catalyst 24 are installed in the exhaust passage 21 of the internal combustion engine 10.

[0031] Air-fuel ratio sensor 22 detects the exhaust air-fuel ratio on the upstream side of the first catalyst 23. Air-fuel ratio sensor 22 is, for example, a so-called wide-range air-fuel ratio sensor with an output characteristic that is approximately linear with respect to the exhaust air-fuel ratio.

[0032] The first catalyst 23 is, for example, an exhaust gas purification catalyst composed of a three-way catalyst or the like. The second catalyst 24 is a NOx capture catalyst located downstream of the first catalyst 23.

[0033] The second catalyst 24 adsorbs NOx in the exhaust gas when the air-fuel ratio is leaner than the stoichiometric air-fuel ratio, and removes and reduces (purifies) NOx when the air-fuel ratio is richer than the stoichiometric air-fuel ratio. In other words, the second catalyst 24 adsorbs NOx in the exhaust gas when the exhaust air-fuel ratio is lean, and uses HC and CO in the exhaust gas as reducing agents to remove, reduce and purify the adsorbed NOx when the exhaust air-fuel ratio is rich.

[0034] The air-fuel ratio of the internal combustion engine 10 is controlled by the ECU (engine control unit) 31. The switching between stoichiometric combustion and lean combustion in the internal combustion engine 10 is controlled by the ECU 31. The combustion mode of the internal combustion engine 10 is determined based on the engine speed and torque (e.g., target torque) of the internal combustion engine 10.

[0035] ECU31 is a well-known electronic computer with a CPU, ROM, RAM, and input / output interfaces. Based on detection signals from various sensors, ECU31 optimizes the ignition timing and intake air volume of the internal combustion engine 10, and controls the air-fuel ratio of the internal combustion engine 10. In other words, ECU31 functions as both a first control unit and a second control unit that controls the operation of the internal combustion engine 10.

[0036] In addition to the detection signal from the air-fuel ratio sensor 22, detection signals from various sensors, such as the air flow meter 32 which detects the intake air volume and the crankshaft angle sensor 33 which detects the crankshaft angle of the internal combustion engine 10, are input to the ECU 31. The crankshaft angle sensor 33 can detect the internal combustion engine speed of the internal combustion engine 10.

[0037] For example, ECU 31 sets the internal combustion engine speed and fuel injection quantity of internal combustion engine 10 as parameters, and retrieves the amount of NOx captured per unit time from the prescribed data stored in the ROM of ECU 31 beforehand. By accumulating these data, it can calculate the amount of NOx captured by the second catalyst 24 (NOx adsorption amount). In addition, the amount of NOx captured by the second catalyst 24 can be calculated by various known methods other than those described above.

[0038] The ECU 31 is connected to the HCU (Hybrid Control Unit) 41, which performs comprehensive control of the vehicle 1, via the communication line 40 in a manner that allows for information exchange. The HCU 41 controls the operation of the drive motor 5 and the generator 9. In addition, the detection signal from the accelerator pedal opening sensor 34, which detects the amount of pressure applied to the accelerator pedal, is input to the HCU 41.

[0039] When the air-fuel ratio of the internal combustion engine 10 is switched from a lean air-fuel ratio (a leaner air-fuel ratio than the stoichiometric air-fuel ratio) to the stoichiometric air-fuel ratio, the throttle valve (not shown) is immediately closed. At this time, there is a response lag in the actual air volume, so if the fuel injection quantity is set to be constant in order to obtain the same torque before and after the air-fuel ratio switch, the equivalence ratio gradually increases.

[0040] Furthermore, there exists an intermediate air-fuel ratio between the lean-burn air-fuel ratio and the stoichiometric air-fuel ratio, which increases the NOx concentration emitted from the internal combustion engine 10. Therefore, during the transition from lean-burn to stoichiometric combustion, the air-fuel ratio of the internal combustion engine 10 becomes the aforementioned intermediate air-fuel ratio, resulting in a decrease in the amount of NOx emitted from the internal combustion engine 10.

[0041] Figure 3 This is an explanatory diagram showing the relationship between equivalence ratio and NOx emissions from the engine. For example... Figure 3 As shown, if the equivalence ratio increases, the NOx emitted from the internal combustion engine 10 (engine NOx) increases. Regarding the NOx captured by the second catalyst (NOx trapping catalyst) 24 located in the exhaust passage 21, when the equivalence ratio increases to a certain extent, it can be treated by implementing so-called rich ignition. Rich ignition is achieved by temporarily changing the air-fuel ratio to a richer air-fuel ratio than the stoichiometric air-fuel ratio.

[0042] Figure 3 The time t1 in the equation is the timing at which the air-fuel ratio of the internal combustion engine 10 begins to gradually change from a lean air-fuel ratio to a stoichiometric air-fuel ratio. Figure 3 The time t2 in the equation is the timing at which the air-fuel ratio is immediately changed to initiate rich ignition. Rich ignition, for example, begins when the equivalence ratio reaches a specified value A. Figure 3 The time t3 in the equation is the timing for ending rich ignition. Figure 3 In this context, time t2 to t3 is the period during which rich ignition is carried out. Figure 3 In the process, the air-fuel ratio after time t3 becomes the stoichiometric air-fuel ratio.

[0043] Figure 4 This is an explanatory diagram showing the relationship between NOx emitted from the tailpipe and its equivalence ratio. For example... Figure 4 As shown, the smaller the equivalence ratio when the air-fuel ratio is immediately switched from a lean air-fuel ratio to a stoichiometric air-fuel ratio or a richer air-fuel ratio than the stoichiometric air-fuel ratio, i.e., the larger the air-fuel ratio (the leaner the air-fuel ratio), the more effectively NOx is suppressed from the tailpipe. This is because during the period when the air-fuel ratio gradually changes towards the stoichiometric air-fuel ratio ( Figure 3 During the time interval t1 to t2, the amount of NOx emitted from the internal combustion engine 10 can be reduced.

[0044] Therefore, when switching the combustion mode of the internal combustion engine 10 from lean combustion to stoichiometric combustion, the ECU 31 stops the fuel supply to the internal combustion engine 10, reducing the amount of air intake into the internal combustion engine 10 during this process. Furthermore, with the amount of air intake reduced compared to before the fuel supply to the internal combustion engine 10 was stopped, the ECU 31 restarts the internal combustion engine 10 by setting the target air-fuel ratio of the internal combustion engine 10 as the stoichiometric air-fuel ratio or a richer air-fuel ratio than the stoichiometric air-fuel ratio.

[0045] Therefore, when the vehicle 1 switches the combustion mode of the internal combustion engine 10 from lean combustion to stoichiometric combustion, it can suppress the knocking and sharp increase in torque of the internal combustion engine 10 without using the intermediate air-fuel ratio that produces high NOx from the engine, thus alleviating the driver's sense of disharmony.

[0046] When ECU31 switches the combustion mode from lean combustion to stoichiometric combustion, it stops the rotation of the internal combustion engine 10. When the internal combustion engine 10 is restarted, it switches the air-fuel ratio to the stoichiometric air-fuel ratio or a richer air-fuel ratio than the stoichiometric air-fuel ratio.

[0047] When the internal combustion engine 10 switches from lean combustion to stoichiometric combustion, the air-fuel ratio is switched to the stoichiometric air-fuel ratio while the engine 10 is stopped, thus preventing the air-fuel ratio from becoming an intermediate air-fuel ratio. Therefore, the vehicle 1 can avoid the deterioration of NOx performance when the internal combustion engine 10 switches from lean combustion to stoichiometric combustion.

[0048] In addition, instead of immediately switching the air-fuel ratio, the internal combustion engine 10 is temporarily stopped and then restarted, thus avoiding a sharp increase in torque during the switching process.

[0049] When switching the combustion mode from lean combustion to stoichiometric combustion, ECU31 cuts off the fuel supply to the internal combustion engine 10. When the fuel cut-off is restored to restart the fuel supply to the internal combustion engine 10 after the fuel cut-off, the air-fuel ratio can be switched to the stoichiometric air-fuel ratio or a richer air-fuel ratio than the stoichiometric air-fuel ratio.

[0050] Regarding vehicle 1, compared to the case where the rotation of the internal combustion engine 10 is temporarily stopped when switching the combustion mode of the internal combustion engine 10 from lean combustion to stoichiometric combustion, it is possible to suppress the sense of disharmony that may be caused to the driver.

[0051] If the amount of NOx captured by the second catalyst 24 is greater than or equal to a pre-set first threshold, the internal combustion engine 10 will switch the combustion mode from lean combustion to stoichiometric combustion.

[0052] The first threshold is, for example, the threshold at which NOx discharged from the tailpipe (tailpipe NOx) begins to deteriorate rapidly from the passage of the second catalyst 24. If the amount of NOx captured by the second catalyst 24 is greater than or equal to the second threshold, the NOx from the second catalyst 24 needs to be treated as soon as possible.

[0053] If the amount of NOx captured by the second catalyst 24 is less than the first threshold and greater than or equal to a specified second threshold which is less than the first threshold, an air-fuel ratio switching request (exhaust-based stoichiometric request) caused by exhaust gas is established.

[0054] If the stoichiometric request based on the exhaust gas is met, ECU31 waits for the generation of a prescribed switching request and switches the combustion mode from lean combustion to stoichiometric combustion.

[0055] The second threshold is, for example, a threshold that indicates the gradual deterioration of NOx (tailpipe NOx) emitted from the tailpipe after passing through the second catalyst 24. If the amount of NOx captured by the second catalyst 24 is greater than or equal to the second threshold but less than the first threshold, it is not necessary to treat the NOx from the second catalyst 24 immediately, but it is necessary to treat the NOx from the second catalyst 24 as soon as possible.

[0056] A switching request refers to a request to set the air-fuel ratio to a lean air-fuel ratio or a stoichiometric air-fuel ratio. For example, in a lean-burn situation where it is necessary to ensure the braking negative pressure of vehicle 1, a request to set the air-fuel ratio to a stoichiometric air-fuel ratio is generated.

[0057] Regarding vehicle 1, if the amount of NOx captured by the second catalyst 24 remains in a lean air-fuel ratio and is within a range where the performance of the second catalyst 24 does not deteriorate significantly (when the amount of NOx captured by the second catalyst 24 is greater than or equal to the second threshold and less than the first threshold), then the switching conditions are awaited, and the number of times the internal combustion engine 10 stops rotating can be suppressed as the combustion mode is switched, and the improvement in fuel consumption can also be anticipated.

[0058] When the amount of NOx captured by the second catalyst 24 is greater than or equal to the second threshold and less than the first threshold, and the internal combustion engine 10 stops, the ECU 31 can wait for the specified internal combustion engine starting conditions to be met before restarting the internal combustion engine 10. The specified internal combustion engine stopping conditions include, for example, the state of charge (SOC) of the battery 8 being greater than or equal to a specified upper threshold, or the accelerator pedal being disengaged while driving. The specified internal combustion engine starting conditions include, for example, the SOC of the battery 8 being less than or equal to a specified lower threshold, or the accelerator pedal changing from a disengaged state to an engaged state while driving.

[0059] Therefore, vehicle 1 can suppress the number of times the internal combustion engine 10 stops rotating.

[0060] When the requested torque of the internal combustion engine 10 is greater than a preset value, the ECU 31 can switch the air-fuel ratio immediately without waiting for a reduction in the intake air volume when switching the combustion mode of the internal combustion engine 10 from lean combustion to stoichiometric combustion.

[0061] For vehicle 1, even if a sudden torque change occurs when the internal combustion engine 10 requests a large torque, the actual torque change is not felt. Therefore, the driver will not feel a large torque change, and the large output required at any moment can be ensured.

[0062] When switching the combustion mode from lean combustion to stoichiometric combustion, the ECU31 changes the opening of the throttle valve that controls the intake air volume of the internal combustion engine 10 to a position corresponding to the target air-fuel ratio during the rotation of the internal combustion engine 10 or the fuel cut-off of the internal combustion engine 10.

[0063] Regarding vehicle 1, when switching the combustion mode of internal combustion engine 10 from lean combustion to stoichiometric combustion, the opening degree of the throttle valve is changed during the rotation stop of internal combustion engine 10 or the fuel cut-off of internal combustion engine 10. Therefore, the torque variation during the switch from lean combustion to stoichiometric combustion can be converged to the range of torque variation during the restart of internal combustion engine 10 or the normal fuel cut-off recovery.

[0064] When the ECU31 switches the combustion mode from lean combustion to stoichiometric combustion, and the internal combustion engine 10 restarts after its rotation has stopped, the ECU31 changes the opening of the throttle valve that controls the intake air volume of the internal combustion engine 10 to a smaller opening than the opening corresponding to the target air-fuel ratio. Then, after maintaining this opening for a specified time, the ECU31 causes the opening of the throttle valve to change stepwise towards the opening corresponding to the target air-fuel ratio.

[0065] When the internal combustion engine 10 is restarted, the vehicle 1 reduces the opening of the throttle valve to reduce the amount of air during the regeneration of the second catalyst 24, thereby improving the exhaust performance during the regeneration of the second catalyst 24.

[0066] When switching the combustion mode from stoichiometric combustion to lean combustion, ECU31 can stop the fuel supply to the internal combustion engine 10, reduce the intake air volume of the internal combustion engine 10 during this stop, and restart the internal combustion engine 10 by setting the target air-fuel ratio of the internal combustion engine 10 to a leaner air-fuel ratio than the stoichiometric air-fuel ratio when the intake air volume of the internal combustion engine 10 is reduced compared to before the fuel supply to the internal combustion engine 10 is stopped.

[0067] ECU31 can stop the rotation of internal combustion engine 10 when switching the combustion mode from stoichiometric combustion to lean combustion, and when restarting internal combustion engine 10, switch the air-fuel ratio to a leaner air-fuel ratio than the stoichiometric air-fuel ratio.

[0068] ECU31 can cut off the fuel supply to the internal combustion engine 10 when switching the combustion mode from stoichiometric combustion to lean combustion, and when the fuel cut-off resumes after the fuel cut-off, it can switch the air-fuel ratio to a leaner air-fuel ratio than the stoichiometric air-fuel ratio.

[0069] Figure 5 It is a dynamic timing diagram showing the various parameters when the internal combustion engine 10 is temporarily stopped and the combustion mode is switched from lean combustion to stoichiometric combustion. Figure 5 This indicates a situation where the amount of NOx captured by the second catalyst 24 does not reach the first threshold, and the combustion mode is switched from lean combustion to stoichiometric combustion.

[0070] Figure 5 Time t0 is the time at which the amount of NOx captured by the second catalyst 24 reaches the second threshold. Therefore, in Figure 5 At time t0, a stoichiometric request is generated due to the exhaust gas. Specifically, in... Figure 5 At time t0, the internal combustion engine 10 is not stopped or the combustion mode is not switched.

[0071] Figure 5 Time t1 is the timing at which a switching request to set the air-fuel ratio to a stoichiometric air-fuel ratio is generated, excluding exhaust gas. When a stoichiometric request is generated due to exhaust gas, and a switching request to set the air-fuel ratio to a stoichiometric air-fuel ratio is generated excluding exhaust gas, the internal combustion engine 10 is stopped even if the aforementioned engine shutdown condition is not met, and the combustion mode of the internal combustion engine 10 is switched from lean combustion to stoichiometric combustion. Figure 5 In the example, at time t1, to switch the combustion mode, the internal combustion engine 10 is stopped, and the throttle valve is closed to a position less than that required for stoichiometric combustion. For example, in Figure 5 At time t1, if the internal combustion engine 10 is not stopped, and the air-fuel ratio begins to change from a lean air-fuel ratio towards the stoichiometric air-fuel ratio (chemical stoichiometry) based on the air volume, then the aforementioned intermediate air-fuel ratio is used, and the NOx emitted from the internal combustion engine 10 (engine NOx emission) increases (refer to...). Figure 5 (thick dashed line in the middle).

[0072] Figure 5 The timing t2 is defined as follows: the internal combustion engine 10 stops rotating (engine speed is "0"), the throttle opening changes to a smaller opening than that used for stoichiometric combustion, and a predetermined time has elapsed. Figure 5 At time t2, the internal combustion engine 10, which had stopped rotating, is restarted, and the valve begins to open, causing the throttle opening to approach the throttle opening used for stoichiometric combustion. The throttle opening is at... Figure 5 After time t2, the throttling opening is increased stepwise in order to achieve stoichiometric combustion.

[0073] The internal combustion engine 10 starts at a low load during restart, and after starting, increases the load to the required load while preventing a sharp increase in torque, and improves NOx conversion efficiency by reducing the amount of air required for NOx treatment. Furthermore, in Figure 5 At time t2, rich ignition begins simultaneously with the restart of the internal combustion engine 10.

[0074] Figure 5 The time t3 is the time when the rich ignition ends. The amount of NOx captured by the second catalyst 24 is reset to "0" after the rich ignition ends.

[0075] Figure 6 It is a dynamic timing diagram showing the various parameters when the internal combustion engine 10 is temporarily stopped and the combustion mode is switched from lean combustion to stoichiometric combustion. Figure 6 This indicates the situation where the amount of NOx captured by the second catalyst 24 reaches the first threshold, and the combustion mode is switched from lean combustion to stoichiometric combustion.

[0076] Figure 6 Time t0 is the time at which the amount of NOx captured by the second catalyst 24 reaches the second threshold. Therefore, in Figure 6 At time t0, a stoichiometric request is generated due to the exhaust gas. Specifically, in... Figure 6 At time t0, the internal combustion engine 10 is not stopped or the combustion mode is not switched.

[0077] Figure 6 Time t1 is the time when the amount of NOx captured by the second catalyst 24 reaches the first threshold. If the amount of NOx captured by the second catalyst 24 exceeds the first threshold, even if the switching request other than the aforementioned exhaust gas and the engine shutdown condition are not met, the internal combustion engine 10 is stopped, and the combustion mode of the internal combustion engine 10 is switched from lean combustion to stoichiometric combustion. Figure 6 In the example, at time t1, in order to switch the combustion mode, the internal combustion engine 10 is stopped and the throttle valve is closed to a throttle opening less than that used for stoichiometric combustion.

[0078] Figure 6 The timing t2 is defined as follows: the internal combustion engine 10 stops rotating (engine speed is "0"), the throttle opening becomes less than the throttle opening used for stoichiometric combustion, and a predetermined time has elapsed. Figure 6At time t2, the internal combustion engine 10, which had stopped rotating, restarts and begins to open the valve, causing the throttle opening to approach the throttle opening for stoichiometric combustion. After time t2, the throttle opening increases stepwise in a manner that changes to the throttle opening for stoichiometric combustion.

[0079] The internal combustion engine 10 starts at a low load during restart, and after starting, increases the load to the required load while preventing a sharp increase in torque, and improves NOx conversion efficiency by reducing the amount of air required for NOx treatment. Furthermore, in Figure 6 At time t2, rich ignition begins simultaneously with the restart of the internal combustion engine 10.

[0080] Figure 6 The time t3 is the time when the rich ignition ends. The amount of NOx captured by the second catalyst 24 is reset to "0" after the rich ignition ends.

[0081] Figure 7 It is a dynamic timing diagram showing the various parameters when the internal combustion engine 10 is temporarily stopped and the combustion mode is switched from lean combustion to stoichiometric combustion. Figure 7 This indicates the condition under which the above-mentioned internal combustion engine shutdown condition is met when a stoichiometric request caused by exhaust gas is generated.

[0082] Figure 7 Time t0 is the time at which the amount of NOx captured by the second catalyst 24 reaches the second threshold. Therefore, in Figure 7 At time t0, a stoichiometric request is generated due to the exhaust gas. Specifically, in... Figure 7 At time t0, the internal combustion engine 10 is not stopped or the combustion mode is not switched.

[0083] Figure 7 Time t1 is the timing at which the internal combustion engine stopping conditions, other than those mentioned above, are met. When the internal combustion engine stopping condition is met due to a stoichiometric request caused by exhaust, the internal combustion engine 10 is stopped even if no switching condition other than the exhaust is generated, and the combustion mode of the internal combustion engine 10 is switched from lean combustion to stoichiometric combustion. Figure 7 In the example, at time t1, in order to switch the combustion mode, the internal combustion engine 10 is stopped and the throttle valve is closed to a throttle opening less than that used for stoichiometric combustion.

[0084] Figure 7Time t2 is the timing at which the aforementioned internal combustion engine starting conditions are met. When the internal combustion engine stops due to the occurrence of a stoichiometric request caused by exhaust gas, the engine 10 stops rotating (engine speed is "0"), not after a predetermined time period of throttle valve closure, but at the timing when the aforementioned internal combustion engine starting conditions are met, causing the engine 10 to restart. Figure 7 At time t2, the internal combustion engine 10, which had stopped rotating, is restarted, and the valve begins to open, causing the throttle opening to approach the throttle opening required for stoichiometric combustion. After time t2, the throttle opening increases stepwise in order to reach the throttle opening required for stoichiometric combustion.

[0085] The internal combustion engine 10 starts at a low load during restart, and after starting, increases the load to the required load while preventing a sharp increase in torque, thus improving NOx conversion efficiency by reducing the amount of air required for NOx treatment. Furthermore, in Figure 7 At time t2, rich ignition begins simultaneously with the restart of the internal combustion engine 10.

[0086] Figure 7 The time t3 is the time when the rich ignition ends. The amount of NOx captured by the second catalyst 24 is reset to "0" after the rich ignition ends.

[0087] Figure 8 It is a time-series diagram showing the dynamics of various parameters when the fuel supply to the internal combustion engine 10 is stopped and the combustion mode is switched from lean combustion to stoichiometric combustion.

[0088] Figure 8 The time t1 is the timing at which a combustion switching request (a stoichiometric request or switching request caused by exhaust gas) is generated. That is, Figure 8 The time t1 is the time when a stoichiometric request is generated due to exhaust gas or a request to change the air-fuel ratio from a lean air-fuel ratio to a stoichiometric air-fuel ratio due to a switching request.

[0089] exist Figure 8 At time t1, fuel cutoff begins, and the throttle valve opening is switched to the throttle opening for stoichiometric combustion. The internal combustion engine 10 switches to the throttle opening for stoichiometric combustion during fuel cutoff, thus suppressing the increase in NOx (tailpipe NOx) gas volume emitted from the tailpipe during the switching of combustion modes, as it passes through the second catalyst 24. Furthermore, in Figure 8 In the example, during the period from time t1 to time t2, the generator 9 is driven so that the speed of the internal combustion engine 10 does not decrease. Figure 8 The time t2 is the time when the intake air volume reaches the target value for stoichiometric combustion. Figure 8At time t2, rich ignition begins simultaneously with the release (end) of fuel cutoff. Figure 8 The time t3 is the timing of the end of rich ignition.

[0090] Figure 9 It is a time-series diagram showing the dynamics of various parameters when the fuel supply to the internal combustion engine 10 is stopped and the combustion mode is switched from lean combustion to stoichiometric combustion. Figure 9 This indicates that the valve is closed during fuel cutoff so that the throttling opening is less than the throttling opening used for stoichiometric combustion.

[0091] Figure 9 The time t1 is the timing at which a combustion switching request (a stoichiometric request or switching request caused by exhaust gas) is generated. That is, Figure 9 Time t1 is the timing at which a stoichiometric request is generated due to exhaust gas or a request to change the air-fuel ratio from a lean air-fuel ratio to a stoichiometric air-fuel ratio due to a switching request. Figure 9 At time t1, fuel cutoff begins, and the throttle valve opening is switched to a level lower than that used for stoichiometric combustion. The internal combustion engine 10 switches to a throttle opening during fuel cutoff, thus suppressing the increase in NOx (tailpipe NOx) gas volume emitted from the tailpipe during combustion mode switching, as this occurs when the second catalyst 24 passes through it. Furthermore, in Figure 9 In the example, during the period from time t1 to time t2, the generator 9 is driven so that the speed of the internal combustion engine 10 does not decrease.

[0092] Figure 9 Time t2 is the time elapsed after the throttling opening has reached the target opening, which is smaller than the throttling opening used for stoichiometric combustion. Figure 9 At time t2, rich ignition begins simultaneously with the release (end) of fuel cutoff. Additionally, at... Figure 9 At time t2, the valve begins to open, causing the throttling opening to approach the throttling opening used for stoichiometric combustion. Figure 9 After time t2, the throttling opening gradually increases in a manner that becomes the throttling opening used for stoichiometric combustion. Figure 9 The time t3 is the timing of the end of rich ignition.

[0093] Figure 10 It is a dynamic timing diagram showing the various parameters when the combustion mode is switched from lean combustion to stoichiometric combustion when the requested torque of the internal combustion engine 10 is greater than a specified value (when a large torque request is generated).

[0094] Figure 10 The time t1 is the timing at which a combustion switching request (a stoichiometric request or switching request caused by exhaust gas) is generated. That is, Figure 9Time t1 is the timing at which a stoichiometric request is generated due to exhaust gas or a request to change the air-fuel ratio from a lean air-fuel ratio to a stoichiometric air-fuel ratio due to a switching request. Figure 10 At time t1, the requested torque of the internal combustion engine 10 is greater than the specified value. Therefore, the throttle valve opening is switched to the throttle opening for stoichiometric combustion, and the air-fuel ratio is immediately switched to initiate rich ignition. Figure 10 As shown by the thick dashed line in the image, if from... Figure 10 When the engine load gradually increases from the time t1, it can suppress torque shock. However, even if the torque requested by the internal combustion engine 10 exceeds the specified value due to rapid acceleration, the torque shock will not cause a significant sense of disharmony to the driver. Therefore, at the time t1, the combustion mode is immediately switched from lean combustion to stoichiometric combustion. Figure 10 The time t2 is the timing of the end of rich ignition.

[0095] Figure 11 It is a dynamic timing diagram showing the various parameters when the internal combustion engine 10 is temporarily stopped and the combustion mode is switched from stoichiometric combustion to lean combustion.

[0096] Figure 11 Time t1 is the timing at which a combustion switching request (e.g., a switching request) is generated to change the air-fuel ratio from a stoichiometric air-fuel ratio to a lean air-fuel ratio. Specifically, in... Figure 11 At time t1, the internal combustion engine 10 is not stopped or the combustion mode is not switched.

[0097] Figure 11 The time t2 is the time at which the above-mentioned internal combustion engine stopping condition is met.

[0098] If a request is generated to switch the combustion mode of the internal combustion engine 10 from stoichiometric combustion to lean combustion, the combustion mode is switched while waiting for the engine shutdown condition to be met during a predetermined constant time period after the request is generated. That is, if the engine shutdown condition is not met during the predetermined constant time period after the request is generated, the internal combustion engine 10 is stopped after a predetermined constant time period following the request. Figure 11 In the example, at time t2, in order to switch the combustion mode, the internal combustion engine 10 is stopped and the throttle valve is closed to a throttle opening less than that used for stoichiometric combustion.

[0099] Figure 11 Time t3 is the point at which the internal combustion engine speed of internal combustion engine 10 reaches "0". The air-fuel ratio is... Figure 11 The timing of t3 is switched to an air-fuel ratio greater than the lean air-fuel ratio.

[0100] Figure 11Time t4 is the timing at which the aforementioned internal combustion engine starting conditions are met. Figure 11 At time t4, the internal combustion engine 10, which had stopped rotating, is restarted, and the valve begins to open, causing the throttle opening to tend towards the throttle opening required for lean combustion. After time t4, the throttle opening increases stepwise in a manner that achieves the throttle opening required for lean combustion.

[0101] Figure 12 It is a dynamic timing diagram showing the various parameters when the fuel supply to the internal combustion engine 10 is stopped and the combustion mode is switched from stoichiometric combustion to lean combustion.

[0102] Figure 12 The time t1 is the timing at which a combustion switching request (e.g., a switching request) is generated to change the air-fuel ratio from a stoichiometric air-fuel ratio to a lean air-fuel ratio. Figure 12 At time t1, fuel cutoff begins, and the throttle valve opening is switched to the lean-burn setting. Additionally, at... Figure 12 In the example, during the period from time t1 to time t2, the generator 9 is driven so that the speed of the internal combustion engine 10 does not decrease.

[0103] Figure 12 The time t2 is the time at which the intake air volume reaches the target value for lean combustion. Figure 12 At time t2, the fuel cutoff is lifted (ended).

[0104] The specific embodiments of the present invention have been described above. The present invention is not limited to the above embodiments, and various modifications can be made without departing from its spirit.

[0105] For example, the present invention can be applied to hybrid vehicles other than series hybrid vehicles.

[0106] The above embodiments relate to a control method and a control device for hybrid vehicles.

Claims

1. A control method for a hybrid vehicle, the hybrid vehicle comprising: a first electric motor capable of supplying electricity generated by a battery; a second electric motor capable of driving drive wheels using electricity from the battery or electricity generated by the first electric motor; and an internal combustion engine capable of driving the first electric motor. It can switch between stoichiometric combustion, which sets the target air-fuel ratio of the aforementioned internal combustion engine to the stoichiometric air-fuel ratio, and lean combustion, which makes the target air-fuel ratio leaner than the stoichiometric air-fuel ratio. When switching the combustion mode from lean combustion to stoichiometric combustion, the fuel supply to the internal combustion engine is stopped, and the intake air volume of the internal combustion engine is reduced during this stop. With the intake air volume of the internal combustion engine reduced, the target air-fuel ratio of the internal combustion engine is set to the stoichiometric air-fuel ratio or a richer air-fuel ratio than the stoichiometric air-fuel ratio, and the internal combustion engine is restarted. If the requested torque of the internal combustion engine is greater than a specified value, when switching the combustion mode of the internal combustion engine from lean combustion to stoichiometric combustion, the air-fuel ratio is switched while the fuel supply continues.

2. The control method for a hybrid vehicle according to claim 1, wherein, When switching the combustion mode from lean combustion to stoichiometric combustion, the rotation of the aforementioned internal combustion engine stops. When restarting the aforementioned internal combustion engine, the air-fuel ratio is switched to the stoichiometric air-fuel ratio or an air-fuel ratio richer than the stoichiometric air-fuel ratio.

3. The control method for a hybrid vehicle according to claim 1, wherein, When switching the combustion mode from lean combustion to stoichiometric combustion, a fuel cut-off is performed to stop the fuel supply to the internal combustion engine. When the fuel cut-off is restored to resume the fuel supply to the internal combustion engine, the air-fuel ratio is switched to the stoichiometric air-fuel ratio or an air-fuel ratio richer than the stoichiometric air-fuel ratio.

4. The control method for a hybrid vehicle according to claim 2, wherein, It has a NOx capture catalyst that captures NOx in exhaust gas. If the amount of NOx captured by the aforementioned NOx-capturing catalyst is greater than or equal to a pre-set first threshold, the combustion mode will be switched from lean combustion to stoichiometric combustion. If the amount of NOx captured by the NOx-capturing catalyst is less than the first threshold and greater than or equal to a second threshold that is smaller than the first threshold, the combustion mode is switched from lean combustion to stoichiometric combustion while waiting for a specified switching request to be fulfilled.

5. The control method for a hybrid vehicle according to claim 4, wherein, When the amount of NOx captured by the NOx-capturing catalyst is less than the first threshold and greater than or equal to the second threshold, and the internal combustion engine stops due to the specified engine stop condition, the internal combustion engine will restart after the specified engine start condition is met.

6. The control method for a hybrid vehicle according to any one of claims 2 to 5, wherein, When switching the combustion mode from lean combustion to stoichiometric combustion, during the shutdown of the internal combustion engine or the fuel cut-off of the internal combustion engine, the opening of the throttle valve that controls the intake air volume of the internal combustion engine is changed to a position corresponding to the target air-fuel ratio.

7. The control method for a hybrid vehicle according to any one of claims 2 to 5, wherein, When switching the combustion mode from lean combustion to stoichiometric combustion, during the restart of the internal combustion engine after it has stopped rotating, or when the fuel cut-off of the internal combustion engine is restored, the opening of the throttle valve that controls the intake air volume of the internal combustion engine is changed to a degree less than the opening corresponding to the target air-fuel ratio, and then the opening of the throttle valve is changed to the opening corresponding to the target air-fuel ratio.

8. The control method for a hybrid vehicle according to any one of claims 1 to 5, wherein, When switching the combustion mode from stoichiometric combustion to lean combustion, the fuel supply to the internal combustion engine is stopped, and then the internal combustion engine is restarted by setting the target air-fuel ratio as a leaner air-fuel ratio than the stoichiometric air-fuel ratio.

9. The control method for a hybrid vehicle according to claim 8, wherein, When switching the combustion mode from stoichiometric combustion to lean combustion, the rotation of the aforementioned internal combustion engine stops. When the aforementioned internal combustion engine is restarted, the air-fuel ratio is switched to an air-fuel ratio that is leaner than the stoichiometric air-fuel ratio.

10. The control method for a hybrid vehicle according to claim 8, wherein, When switching the combustion mode from stoichiometric combustion to lean combustion, a fuel cut-off is performed to stop the fuel supply to the internal combustion engine. When the fuel cut-off is restored to restart the fuel supply to the internal combustion engine, the air-fuel ratio is switched to an air-fuel ratio that is leaner than the stoichiometric air-fuel ratio.

11. A control device for a hybrid vehicle, wherein, This hybrid vehicle features: The first electric motor is capable of supplying the electricity generated by the battery; The second electric motor drives the drive wheel using power from the battery or power generated by the first electric motor. An internal combustion engine that drives the aforementioned first electric motor; The first control unit is capable of switching between stoichiometric combustion, which sets the target air-fuel ratio of the aforementioned internal combustion engine to the stoichiometric air-fuel ratio, and lean combustion, which makes the target air-fuel ratio leaner than the stoichiometric air-fuel ratio; and The second control unit stops the fuel supply to the internal combustion engine when switching the combustion mode from lean combustion to stoichiometric combustion. During this stop, it reduces the intake air volume of the internal combustion engine. With the intake air volume of the internal combustion engine reduced, it sets the target air-fuel ratio of the internal combustion engine to the stoichiometric air-fuel ratio or a richer air-fuel ratio than the stoichiometric air-fuel ratio and restarts the internal combustion engine. If the requested torque of the internal combustion engine is greater than a predetermined value, it switches the air-fuel ratio while continuing the fuel supply when switching the combustion mode of the internal combustion engine from lean combustion to stoichiometric combustion.

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