Method and apparatus for shutting down an internal combustion engine in a hybrid vehicle

Abstract

After combustion stops, air is supplied to the three-way catalytic converter while the crankshaft rotates due to inertia, resulting in a higher oxygen storage capacity at restart. [Solution] In a series hybrid vehicle, when it is requested that the internal combustion engine 2 driving the power generation motor generator 1 be stopped, a rich combustion operation is performed with a target air-fuel ratio rich prior to stopping the combustion operation (times t0 to t2). After the start of this rich combustion operation, an intake throttling combustion operation is performed while the combustion operation continues, with the throttle valve opening reduced (times t1 to t4). With the intake negative pressure strengthened by this intake throttling combustion operation, when the rotational speed reaches the fuel cut rotational speed Fc, the fuel supply is stopped (time t4). At time t5, the rotation comes to a complete stop.

Description

Technical Field

[0001] The present invention relates to a method and an apparatus for stopping an internal combustion engine in a hybrid vehicle in which the internal combustion engine is stopped and restarted in response to a control request during vehicle operation.

Background Art

[0002] In a three-way catalyst for exhaust gas purification provided in an internal combustion engine, in order to achieve high-level coexistence of oxidation of CO and HC and reduction of NOx, a so-called oxygen storage capacity in which the catalyst stores and releases oxygen is important. When the internal combustion engine for a hybrid vehicle that repeats stop and restart stops the combustion operation in response to a control request, the crankshaft rotates by inertia even after the combustion operation stops, and during that time, only air flows through the three-way catalyst, so the oxygen storage amount of the three-way catalyst tends to become excessive.

[0003] Patent Document 1 describes a technique in which the oxygen storage amount of the catalyst is reduced by controlling the air-fuel ratio to the rich side immediately before the automatic stop of the internal combustion engine, and the oxygen storage amount is returned to the neutral state by controlling the air-fuel ratio to the lean side at the time of restart.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0005] Patent Document 1 assumes that the oxygen storage amount is sufficiently reduced by controlling the air-fuel ratio to the rich side immediately before the automatic stop of the internal combustion engine. However, actually, a large amount of air is supplied to the three-way catalyst while the crankshaft rotates by inertia after the combustion operation stops, so it is difficult to sufficiently lower the oxygen storage amount. Therefore, NOx at the time of restart cannot be sufficiently reduced. [Means for solving the problem]

[0006] This invention relates to a method for stopping an internal combustion engine in a hybrid vehicle in which the internal combustion engine is stopped and restarted in response to a control request while the vehicle is in operation. When the above-mentioned internal combustion engine is required to be stopped, a rich combustion operation is performed with a rich air-fuel ratio prior to stopping the combustion operation. After initiating this rich combustion operation, an intake-restricted combustion operation is performed while combustion is in progress, by reducing the throttle valve opening. This intake throttling combustion operation strengthens the intake negative pressure, at which point the fuel supply is stopped. [Effects of the Invention]

[0007] According to this invention, when the internal combustion engine is required to be stopped, in addition to the rich combustion operation performed before the combustion operation is stopped, the amount of air supplied to the three-way catalytic converter is reduced as the crankshaft rotates due to inertia after the combustion operation is stopped, thereby suppressing the increase in oxygen storage amount when the internal combustion engine is stopped. [Brief explanation of the drawing]

[0008] [Figure 1] A diagram illustrating the configuration of a series hybrid vehicle according to one embodiment. [Figure 2] A time chart showing the operation of an internal combustion engine when it is stopped. [Figure 3] A time chart showing the operation of an internal combustion engine when it stops from a motoring state. [Modes for carrying out the invention]

[0009] Hereinafter, an embodiment of this invention will be described in detail with reference to the drawings. Figure 1 schematically shows the configuration of a series hybrid vehicle as an example of a vehicle to which this invention is applied. The series hybrid vehicle is configured to include a power generation motor generator 1 that mainly operates as a generator, an internal combustion engine 2 used as a power generation internal combustion engine that drives the power generation motor generator 1 according to power demands, a drive motor generator 4 that mainly operates as a motor to drive the drive wheels 3, and a battery 5 that stores the generated electricity. The electricity obtained by the internal combustion engine 2 driving the power generation motor generator 1 is stored in the battery 5 via an inverter device (not shown). The drive motor generator 4 is driven and controlled using the power from the battery 5. The electricity generated during regeneration by the drive motor generator 4 is also stored in the battery 5 via an inverter device (not shown).

[0010] Although not shown in detail, the above-mentioned power generation motor generator 1, internal combustion engine 2, and drive motor generator 4 are integrated into a single drive unit. This drive unit is supported by the vehicle body via multiple engine mounts, which are not shown.

[0011] The operation of motor generators 1 and 4, the charging and discharging of battery 5, and the operation of internal combustion engine 2 are controlled by controller 6. Controller 6 consists of multiple controllers connected to each other so that they can communicate with one another, including motor controller 7 which controls motor generators 1 and 4, engine controller 8 which controls internal combustion engine 2, and battery controller 9 which manages battery 5. Information such as the opening of the accelerator pedal (not shown) and vehicle speed is input to controller 6. Battery controller 9 also determines the state of charge (SOC) of battery 5 based on its voltage and current and manages its charging and discharging.

[0012] The driving modes of such a series hybrid vehicle include an EV driving mode in which the vehicle runs on the power of the battery 5 without combustion operation (i.e., power generation or charging) of the internal combustion engine 2, and an HEV driving mode in which the vehicle runs while generating power through combustion operation of the internal combustion engine 2. The battery controller 9 manages the charging and discharging of the battery 5 so that the State of Charge (SOC) of the battery 5 is maintained between a predetermined upper SOC target value and a lower SOC target value. For example, if the SOC decreases due to EV driving and falls below the lower SOC target value, the internal combustion engine 2 is started via the engine controller 8 and power generation is performed. This power generation by the internal combustion engine 2 ends, for example, when the SOC approaches the upper SOC target value. During this power generation, the internal combustion engine 2 is usually operated at several specific operating points (combinations of torque and rotational speed) that provide the best fuel efficiency.

[0013] Furthermore, when the vehicle's required driving force is high, the power supplied from the battery 5 is insufficient to meet the vehicle's driving force requirements, so the vehicle enters HEV driving mode and generates electricity using the internal combustion engine 2. In this case, in order to increase the power generation output, the internal combustion engine 2 is operated at several specific operating points, for example, at a rotational speed higher than the point of best fuel efficiency.

[0014] Therefore, while the vehicle's main switch is on, the internal combustion engine 2 will repeatedly cycle between combustion operation and combustion shutdown.

[0015] In one embodiment, the internal combustion engine 2 is a four-stroke spark-ignition internal combustion engine, also known as a gasoline engine. As shown in Figure 1, the crankshaft of the internal combustion engine 2 is always connected to the rotating shaft of the motor-generator 1, and the two rotate together. In Figure 1, the two are connected via a gear train, but the crankshaft of the internal combustion engine 2 and the rotating shaft of the motor-generator 1 may be directly connected.

[0016] Although not shown in detail, the internal combustion engine 2 includes a catalytic converter composed of a three-way catalyst for exhaust purification in its exhaust passage, and an upstream air-fuel ratio sensor and a downstream air-fuel ratio sensor are provided on the inlet side and the outlet side of this catalytic converter, respectively. These air-fuel ratio sensors are so-called wide-range air-fuel ratio sensors that can obtain an output according to the exhaust air-fuel ratio.

[0017] The operation including the start and stop of the internal combustion engine 2 is controlled by the engine controller 8. Various sensors generally required for the control of the internal combustion engine 2 (air flow meter, crank angle sensor, collector pressure sensor, upstream air-fuel ratio sensor, downstream air-fuel ratio sensor, coolant temperature sensor, atmospheric pressure sensor, outside air temperature sensor, etc.) are connected to the engine controller 8. And based on these detection signals, the engine controller 8 optimally controls the fuel injection timing, fuel injection amount (in other words, air-fuel ratio), ignition timing, EGR rate, etc. Since the crankshaft of the internal combustion engine 2 is connected to the rotating shaft of the motor generator 1, the rotational speed of the motor generator 1 and the rotational speed of the internal combustion engine 2 are substantially equivalent.

[0018] Next, the control when the internal combustion engine 2 stops will be described. This stop control basically targets the stop of the internal combustion engine 2 accompanying the transition from the HEV mode to the EV mode, but may also include the stop of the internal combustion engine 2 accompanying the key-off of the vehicle. Also, as will be described later, there may be a case where the internal combustion engine 2 is stopped from a state where the internal combustion engine 2 is motored by the power generation motor generator 1 for purposes such as surplus power consumption.

[0019] The stop control of the internal combustion engine 2 includes two purposes. One is to suppress as much as possible the increase in the oxygen storage amount in the three-way catalyst generated with the combustion operation stop, so that the oxygen storage amount does not become saturated. The other is to suppress as much as possible the relatively large vehicle floor vibration caused by resonance that is likely to occur during the combustion operation stop. It is desirable to achieve both of these two at a high level.

[0020] Figure 2 is a time chart showing the operation of each part when the internal combustion engine 2 is operating for power generation and then stops when power generation is no longer needed. The latter half of this time chart shows the operation when the internal combustion engine 2 restarts after a power generation request is made. From top to bottom, the figures show the changes in (a) the rotational speed of the internal combustion engine 2, (b) the target torque of the internal combustion engine 2, (c) the intake air volume, (d) the target air-fuel ratio, (e) the air-fuel ratio feedback correction coefficient α, (f) the throttle valve opening, (g) the λ control permission flag, (h) the rich spike flag before stopping, and (i) the rich spike flag at restart. (d) The target air-fuel ratio is the target value of the exhaust air-fuel ratio detected by the upstream air-fuel ratio sensor, and is the stoichiometric air-fuel ratio while air-fuel ratio feedback control (λ control) is being performed. (e) The air-fuel ratio feedback correction coefficient α is a correction coefficient calculated, for example, by PID control during air-fuel ratio feedback control. (g) The λ control enable flag indicates whether or not to enable air-fuel ratio feedback control (λ control) with the stoichiometric air-fuel ratio as the target air-fuel ratio. When this flag is on, air-fuel ratio feedback control is enabled, and when it is off, the air-fuel ratio is controlled in open-loop mode (in other words, feedforward control). (h) The rich spike flag before stopping and (i) the rich spike flag at restart are flags that instruct a rich spike, i.e., enrichment of the air-fuel ratio.

[0021] Up to time t0 in Figure 2, the internal combustion engine 2 is operating in combustion mode, driving the power generation motor generator 1 to generate electricity. As mentioned above, the internal combustion engine 2 is operating at a predetermined operating point that provides the best fuel efficiency, and the air-fuel ratio is feedback-controlled with the stoichiometric air-fuel ratio as the target air-fuel ratio.

[0022] At time t0, the engine controller 8 commands the stop of power generation, that is, the stop of the internal combustion engine 2. In response to this, the pre-stop rich spike flag in column (h) is turned on, and the target air-fuel ratio becomes rich. That is, rich combustion operation is started prior to the stop of the combustion operation. The target air-fuel ratio can be set to about 12, for example. By this rich combustion operation, the exhaust air-fuel ratio becomes rich, and the oxygen storage amount of the three-way catalyst in the exhaust passage gradually decreases. It is desirable that the oxygen storage amount finally approaches 0 at the end of the rich combustion operation period. In a preferred embodiment, the rich combustion operation ends when the downstream exhaust air-fuel ratio detected by the downstream air-fuel ratio sensor reaches a rich-side threshold value, or when a predetermined time has elapsed.

[0023] Thereafter, at time t1, an intake throttle combustion operation with the throttle valve opening reduced is started. The throttle valve opening becomes, for example, the minimum opening near fully closed. By this intake throttle combustion operation, the intake negative pressure downstream of the throttle valve (the negative pressure in the collector) develops, and as shown in column (c), the intake air amount decreases.

[0024] Note that the target torque slightly increases between time t0 and time t1, which indicates that the operating point of the internal combustion engine 2 has been shifted to the operating point that gives the best fuel efficiency under a rich air-fuel ratio as the air-fuel ratio is made rich.

[0025] At time t2, the rich combustion operation ends, and the target air-fuel ratio returns to the theoretical air-fuel ratio. By the rich combustion operation from time t0 to time t2, the oxygen storage amount of the three-way catalyst approaches 0. At the end of this rich combustion operation, the intake throttle combustion operation is still continuing. That is, the intake throttle combustion operation is started during the period of the rich combustion operation, and the period of the rich combustion operation and the period of the intake throttle combustion operation partially overlap. Thereby, the total time required for the entire stop process sequence is shortened.

[0026] Immediately after the target air-fuel ratio changes to the stoichiometric air-fuel ratio at time t2, air-fuel ratio control is performed in the form of feedforward control, not air-fuel ratio feedback control. This is to avoid overshoot of the air-fuel ratio feedback control due to a large change in the exhaust air-fuel ratio. Therefore, at time t3, slightly delayed from time t2, the λ control permission flag in column (g) is turned on, and the system switches to air-fuel ratio feedback control (see the air-fuel ratio feedback correction coefficient α in column (e)). During operation at the stoichiometric air-fuel ratio, the oxygen storage amount of the three-way catalytic converter does not increase in principle.

[0027] Meanwhile, the rotational speed of the internal combustion engine 2 gradually decreases from time t1, when the target torque has decreased. Time t4 is the timing when the rotational speed has decreased to a predetermined fuel cut rotational speed Fc, and in the illustrated example, fuel supply is stopped at this time t4. More specifically, fuel supply is stopped when both of the following two conditions are met: the intake negative pressure has reached a predetermined negative pressure level due to intake throttling combustion operation, and the rotational speed has decreased to a predetermined fuel cut rotational speed Fc. In the example in Figure 2, the intake negative pressure has reached the predetermined negative pressure level before time t4. In reality, the above two conditions are set to be met almost simultaneously. After the combustion operation ends at time t4, the rotational speed of the crankshaft, which continues to rotate due to inertia, rapidly decreases and comes to a complete stop at time t5. Between time t4 and time t5, air is supplied to the three-way catalytic converter, resulting in an increase in oxygen storage capacity.

[0028] The restricted combustion operation ends when the fuel supply is stopped at time t4, but the throttle valve opening remains at the minimum opening during restricted combustion operation until time t5, when the rotation of the internal combustion engine 2 comes to a complete stop, as shown in column (f). Therefore, as is clear from the intake air volume in column (c), the amount of air flowing through the three-way catalyst during rotation due to inertia is minimized, and the increase in oxygen storage volume is suppressed.

[0029] Furthermore, since fuel supply is stopped while the intake negative pressure is strengthened by reducing the throttle valve opening, vibrations of the internal combustion engine 2 associated with engine cessation are suppressed, and vehicle floor vibrations induced via the engine mounts are reduced. In other words, by strengthening the negative pressure when fuel supply is stopped, the amount of air in the cylinder is reduced, and vibrations caused by the reaction force applied to the piston are reduced.

[0030] As described above, by performing rich combustion operation when the internal combustion engine 2 is required to stop, the oxygen storage level at time t4 is kept at a sufficiently low level. Furthermore, since the amount of air passing through between times t4 and t5 is limited by the reduction in throttle valve opening, the oxygen storage level at time t5 does not ultimately become excessively high. Note that the actual time from time t0, when the stopping of the internal combustion engine 2 is requested, to time t4, when the combustion operation stops, is a relatively short time of less than 1 second.

[0031] Time t11 in Figure 2 indicates the timing when a power generation request is given to the engine controller 8 while the internal combustion engine 2 is stopped. At this time t11, the process for restarting begins. First, the internal combustion engine 2 is motorized using the power generation motor generator 1 for restarting. Then, once it has reached an appropriate rotational speed, fuel supply and ignition begin at time t12. Immediately after starting at time t12, the restart rich spike flag shown in column (i) is turned on, and rich combustion is performed with a target air-fuel ratio of rich (for example, around 12). This suppresses NOx emissions immediately after restarting and returns the oxygen storage amount of the three-way catalyst to an appropriate intermediate level. In one preferred embodiment, the period during which the restart rich spike flag is on, i.e., the rich combustion operation during restarting, ends when the downstream exhaust air-fuel ratio detected by the downstream air-fuel ratio sensor reaches the rich threshold, or when a predetermined time has elapsed. At time t13, the restart rich spike flag is turned off, and the target air-fuel ratio returns to the stoichiometric air-fuel ratio. Similar to the time intervals t2-t3 mentioned above, immediately after transitioning to the stoichiometric air-fuel ratio at time t13, air-fuel ratio control is performed in the form of feedforward control, and then at time t14, air-fuel ratio feedback control (λ control) begins.

[0032] Next, the time chart in Figure 3 will be explained. This time chart shows the process when the rotation of the internal combustion engine 2 is stopped from a state in which the internal combustion engine 2 is being motored by the power generation motor generator 1, for example, to consume excess power from the battery 5. Even when stopping from such motoring, it is preferable to suppress the amount of oxygen stored in the three-way catalytic converter in order to restart the engine.

[0033] In the example shown in Figure 3, the internal combustion engine 2 is motorized until time t21, at which time t21, the internal combustion engine 2 is commanded to stop. During motoring, the throttle valve opening is kept at a relatively small opening, close to the minimum opening, as shown in column (f).

[0034] At time t21, the power generation motor generator 1 ceases to operate, and the rotational speed of the motorized internal combustion engine 2 rapidly decreases. At time t22, when the rotational speed of the internal combustion engine 2 has decreased to a predetermined fuel cut rotational speed Fc, fuel supply and ignition are started. In other words, combustion operation is restarted prior to rotational cessation in order to perform the rich combustion operation and intake throttle combustion operation described above. The subsequent processing is basically the same as the example in Figure 2.

[0035] Immediately after the start of combustion at time t22, rich combustion is performed with a rich target air-fuel ratio. Subsequently, at time t23, intake-restricted combustion is started with a reduced throttle valve opening. The throttle valve opening becomes, for example, the minimum opening near fully closed. This intake-restricted combustion develops the intake negative pressure downstream of the throttle valve (negative pressure in the collector), and as shown in column (c), the intake air volume decreases.

[0036] At time t24, the rich combustion operation ends, and the target air-fuel ratio returns to the stoichiometric air-fuel ratio. The rich combustion operation period from time t22 to time t24 (i.e., the period when the pre-stop rich spike flag is on) is set so that the oxygen storage amount approaches zero. In a preferred embodiment, the rich combustion operation ends when the downstream exhaust air-fuel ratio detected by the downstream air-fuel ratio sensor reaches a rich threshold, or when a predetermined time has elapsed. At the end of this rich combustion operation, the intake throttle combustion operation is still in progress. In other words, the intake throttle combustion operation starts in the middle of the rich combustion operation period, and the rich combustion operation period and the intake throttle combustion operation period partially overlap. This shortens the time required for the entire shutdown sequence.

[0037] Immediately after the target air-fuel ratio changes to the stoichiometric air-fuel ratio at time t24, air-fuel ratio control is performed in the form of feedforward control, not air-fuel ratio feedback control. Then, at time t25, slightly later than time t24, the λ control permission flag in column (g) is turned on, and the system switches to air-fuel ratio feedback control (see the air-fuel ratio feedback correction coefficient α in column (e)). During operation at the stoichiometric air-fuel ratio, the oxygen storage amount of the three-way catalytic converter does not increase in principle.

[0038] Meanwhile, the rotational speed of the internal combustion engine 2 is maintained at the fuel cut rotational speed Fc during combustion operation. Time t26 is the timing when the intake negative pressure reaches a predetermined negative pressure level due to intake throttling combustion operation, and in the illustrated example, fuel supply is stopped at this time t26. As mentioned above, fuel supply is stopped when both of the following conditions are met: the intake negative pressure reaches a predetermined negative pressure level due to intake throttling combustion operation, and the rotational speed has decreased to a predetermined fuel cut rotational speed Fc. In the example of Figure 3, the rotational speed has decreased to the fuel cut rotational speed Fc before time t26, so fuel supply is stopped when the intake negative pressure reaches the predetermined negative pressure level. After the combustion operation ends at time t26, the rotational speed of the crankshaft, which continues to rotate due to inertia, rapidly decreases and comes to a complete stop at time t27. Between time t26 and time t27, air is supplied to the three-way catalytic converter, resulting in an increase in oxygen storage amount.

[0039] The throttled combustion operation ends when the fuel supply is stopped at time t26, but the throttle valve opening remains at the minimum opening until a timing slightly later than time t26, as shown in column (f). Therefore, as is clear from the intake air volume in column (c), the amount of air flowing through the three-way catalyst during rotation due to inertia is minimized, and the increase in oxygen storage volume is suppressed.

[0040] Furthermore, since fuel supply is stopped while the intake negative pressure is strengthened by reducing the throttle valve opening, vibrations of the internal combustion engine 2 associated with engine cessation are suppressed, and vehicle floor vibrations induced via the engine mounts are reduced. In other words, by strengthening the negative pressure when fuel supply is stopped, the amount of air in the cylinder is reduced, and vibrations caused by the reaction force applied to the piston are reduced.

[0041] The restart process shown on the right side of Figure 3 is the same as the process described in Figure 2. Motoring is started in response to the restart request (time t31), and fuel injection and ignition are started when the rotational speed has increased appropriately (time t32). The target air-fuel ratio is rich until time t33 in order to reduce the amount of oxygen stored, and at time t33, the target air-fuel ratio shifts to the stoichiometric air-fuel ratio. The air-fuel ratio is controlled in a feedforward manner until time t34, and at time t34, air-fuel ratio feedback control is started.

[0042] Thus, when stopping the rotation of the internal combustion engine 2 from motoring, the internal combustion engine 2 is temporarily operated to perform rich combustion operation and intake-restricted combustion operation. This makes it possible to keep the amount of oxygen stored after the rotation of the internal combustion engine 2 has stopped, i.e., the amount of oxygen stored at the restart stage, at a relatively low level, and thus avoid the deterioration of NOx during restart.

[0043] Although one embodiment of the present invention has been described in detail above, the present invention is not limited to the above embodiment, and various modifications are possible. For example, although the above embodiment described an example in which the present invention is applied to a series hybrid vehicle, the present invention is not necessarily limited to the power generation internal combustion engine of a series hybrid vehicle, but can also be applied to the internal combustion engine of other types of hybrid vehicles in which the internal combustion engine is stopped and restarted in response to control requests during vehicle operation. [Explanation of Symbols]

[0044] 1…Power generation motor generator 2…Internal combustion engine 4…Drive motor generator 5… Battery 8…Engine controller

Claims

1. A method for stopping an internal combustion engine in a hybrid vehicle in which the internal combustion engine is stopped and restarted in response to a control request while the vehicle is in operation, When the above-mentioned internal combustion engine is required to be stopped, a rich combustion operation is performed with a rich air-fuel ratio prior to stopping the combustion operation. After initiating this rich combustion operation, an intake-restricted combustion operation is performed while combustion is in progress, by reducing the throttle valve opening. This intake restriction combustion operation strengthens the intake negative pressure, at which point the fuel supply is stopped. A method for shutting down the internal combustion engine in a hybrid vehicle.

2. As part of intake throttling combustion operation, the reduced throttle valve opening is maintained while the fuel supply is stopped. A method for stopping an internal combustion engine in a hybrid vehicle according to claim 1.

3. Prior to stopping the fuel supply as described above, the rotational speed will be reduced. Fuel supply is stopped when the engine speed drops to a predetermined fuel cut-off speed. A method for stopping an internal combustion engine in a hybrid vehicle according to claim 1.

4. Furthermore, fuel supply is stopped, with the intake negative pressure reaching a predetermined negative pressure level as one of the conditions for the above-mentioned intake throttling combustion operation. A method for stopping an internal combustion engine in a hybrid vehicle according to claim 3.

5. During the period of the rich combustion operation described above, the intake restriction combustion operation described above is initiated. A method for stopping an internal combustion engine in a hybrid vehicle according to claim 1.

6. The period of the rich combustion operation described above and the period of the intake throttled combustion operation described above partially overlap. A method for stopping an internal combustion engine in a hybrid vehicle according to claim 5.

7. The intake throttle combustion operation after the rich combustion operation is performed with the air-fuel ratio set to the stoichiometric air-fuel ratio. A method for stopping an internal combustion engine in a hybrid vehicle according to claim 1.

8. When the internal combustion engine is being motorized by a motor generator and a shutdown of the internal combustion engine is requested, the combustion operation is restarted, and the rich combustion operation and intake throttle combustion operation are performed as described above. A method for stopping an internal combustion engine in a hybrid vehicle according to claim 1.

9. At least the motoring immediately before restarting the combustion operation described above should be performed with the throttle valve opening reduced. A method for stopping an internal combustion engine in a hybrid vehicle according to claim 8.

10. An internal combustion engine stop device for a hybrid vehicle in which the internal combustion engine is stopped and restarted in response to a control request while the vehicle is in operation, When the above-mentioned internal combustion engine is required to be stopped, a rich combustion operation is performed with a rich air-fuel ratio prior to stopping the combustion operation. After initiating this rich combustion operation, an intake-restricted combustion operation is performed while combustion is in progress, by reducing the throttle valve opening. This intake restriction combustion operation strengthens the intake negative pressure, at which point the fuel supply is stopped. A device for stopping the internal combustion engine in a hybrid vehicle.

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