Method and apparatus for stopping the internal combustion engine in a series hybrid vehicle

Abstract

During reverse driving under high torque, the displacement of the engine mounts can increase rigidity, which can cause floor vibration due to resonance when the internal combustion engine stops. [Solution] The power generation motor generator, internal combustion engine, and drive motor generator are integrated as a single drive unit and supported by the vehicle body via multiple engine mounts. When the internal combustion engine is required to stop due to the completion of the power generation request, the fuel supply is stopped on the condition that the rotational speed drops to a predetermined fuel cut speed Fc. The fuel cut speed Fc is set relatively higher than when the torque transmitted by the drive shaft is below the threshold (T1) if the torque is negative and its absolute value is greater than the threshold (T1).

Description

Technical Field

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

Background Art

[0002] As is well known, when the internal combustion engine mounted on a vehicle stops, relatively large vehicle floor vibrations are likely to occur due to resonance. In particular, in a series hybrid vehicle that repeatedly stops and restarts the internal combustion engine during operation, the floor vibration at the time of stopping the internal combustion engine is not preferable in terms of vehicle quality.

[0003] On the other hand, in the three-way catalyst for exhaust purification provided in the internal combustion engine, in order to achieve high-level compatibility between the oxidation of CO and HC and the reduction of NOx, the so-called oxygen storage capacity in which the catalyst stores and releases oxygen is important. When the internal combustion engine stops, 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.

[0004] 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

[0005]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0006] In one configuration of a series hybrid vehicle, the generator, internal combustion engine, and traction motor are integrated into a single drive unit, which is supported by the vehicle body via engine mounts. In such a configuration, for example, when driving in reverse uphill, the engine mounts may be displaced (i.e., crushed) by a large torque reaction force, resulting in a higher resonant frequency that induces floor vibration. Therefore, if the fuel cut-off rotational speed, which stops fuel supply when the internal combustion engine stops, is low, the speed approaches the resonant frequency, making floor vibration more likely.

[0007] On the other hand, setting a higher fuel cut rotation speed increases the amount of air flowing to the three-way catalytic converter before the crankshaft stops rotating, resulting in a more pronounced increase in oxygen storage capacity during the stop.

[0008] Patent Document 1 does not contain any description of such problems. [Means for solving the problem]

[0009] This invention relates to a series hybrid vehicle in which a drive unit including a generator, an internal combustion engine that drives the generator, and a drive motor that drives the drive wheels via a drive shaft is supported on the vehicle body via an engine mount, When the internal combustion engine is stopped from combustion while the torque transmitted through the drive shaft is negative (the opposite of the torque transmitted during forward driving), if the absolute value of the transmitted torque is greater than a predetermined threshold, the fuel cut rotation speed at which fuel supply is stopped is set relatively higher than the fuel cut rotation speed at which the absolute value of the transmitted torque is less than or equal to the threshold.

[0010] If the torque transmitted through the driveshaft is negative (the opposite of that during forward driving) and its absolute value is greater than a certain threshold, the resonant frequency will increase due to the large displacement of the engine mount. In this case, the fuel cut speed is set higher, making floor vibration less likely to occur.

[0011] On the other hand, when the absolute value of the transmitted torque is below a threshold, the fuel cut rotation speed is set relatively low, thus suppressing the increase in oxygen storage capacity. [Effects of the Invention]

[0012] This invention makes it possible to avoid floor vibrations when the internal combustion engine is stopped and to suppress the increase in oxygen storage capacity. [Brief explanation of the drawing]

[0013] [Figure 1] A diagram illustrating the configuration of a series hybrid vehicle according to one embodiment. [Figure 2] An explanatory diagram showing an example of the arrangement of the drive unit within the vehicle body. [Figure 3] A characteristic diagram showing the correlation between the torque transmitted by the driveshaft during reverse driving and the displacement of the engine mount. [Figure 4] A characteristic diagram showing an example of setting the fuel cut rotation speed in relation to the torque transmitted by the drive shaft. [Figure 5] A time chart showing the operation of an internal combustion engine during shutdown and restart. [Figure 6] A time chart showing the operation during restart in the second embodiment. [Modes for carrying out the invention]

[0014] 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 in one embodiment to which this invention is applied. The series hybrid vehicle comprises 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 and drives the drive wheels 3 via a drive shaft 10, 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).

[0015] 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.

[0016] As driving modes of such a series hybrid vehicle, there are an EV driving mode in which the vehicle runs using the power of the battery 5 without combustion operation (i.e., power generation or charging) of the internal combustion engine 2, and a HEV driving mode in which the vehicle runs while generating power by the combustion operation of the internal combustion engine 2. The battery controller 9 manages the charge and discharge of the battery 5 so that the SOC of the battery 5 is maintained between a predetermined SOC upper limit target value and a SOC lower limit target value. For example, if the SOC decreases due to EV driving and falls below the SOC lower limit target value, the internal combustion engine 2 is started via the engine controller 8 and power generation is performed. The power generation by this internal combustion engine 2 ends, for example, when the SOC approaches the SOC upper limit target value. During this power generation, usually, the internal combustion engine 2 is operated at some specific operating points (combinations of torque and rotational speed) at which the fuel consumption is the best.

[0017] Also, when the required driving force of the vehicle is high, since the required driving force of the vehicle cannot be covered with the power that can be supplied from the battery 5, the HEV driving mode is entered and power generation is performed by the internal combustion engine 2. At this time, in order to increase the power generation output, for example, the internal combustion engine 2 is operated at some specific operating points at a rotational speed higher than the best fuel consumption point.

[0018] Therefore, the internal combustion engine 2 repeats combustion operation and combustion operation stop while the main switch of the vehicle is on.

[0019] In one embodiment, the internal combustion engine 2 is a four-stroke cycle spark ignition internal combustion engine, a so-called gasoline engine. As shown in FIG. 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 integrally. Although the two are connected via a gear train in FIG. 1, a configuration in which the crankshaft of the internal combustion engine 2 and the rotating shaft of the motor generator 1 are directly connected, so-called, may be employed.

[0020] 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.

[0021] The operation including the start / stop of the internal combustion engine 2 is controlled by the engine controller 8. Various sensors generally necessary for controlling 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. 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 and the rotating shaft of the motor generator 1 are connected, the rotational speed of the motor generator 1 and the rotational speed of the internal combustion engine 2 are substantially equivalent.

[0022] Also, in the series hybrid vehicle of one embodiment, as schematically shown in FIG. 2, the above-described power generation motor generator 1, internal combustion engine 2, and driving motor generator 4 are integrated as one drive unit 11. And this drive unit 11 is supported at the front part of the vehicle body 12 via a plurality of engine mounts not shown. The engine mount has a general configuration using rubber having elasticity. The internal combustion engine 2 is mounted in a so-called horizontal posture with respect to the vehicle body, and the rotation center lines of the driving motor generator 4 and the power generation motor generator 1 extend along the width direction of the vehicle body, similar to the crankshaft of the internal combustion engine 2.

[0023] Next, we will explain the fuel cut rotation speed when the combustion operation of the internal combustion engine 2 stops. When power generation is no longer needed and the internal combustion engine 2 stops, a predetermined control sequence is executed as described later, and finally, fuel supply is stopped, with one of the conditions being that the rotation speed of the internal combustion engine 2 has decreased to a predetermined fuel cut rotation speed. The level of this fuel cut rotation speed is related to the vibration of the vehicle floor due to resonance during stopping and the increase in the oxygen storage amount of the three-way catalytic converter, as mentioned above. And, basically, there is a trade-off relationship between the two.

[0024] In other words, setting a low fuel cut rotation speed means that combustion continues down to an even lower rotation speed during the process of reducing rotation speed to shut down the engine, and floor vibrations are more easily induced by the combustion torque at low rotation speeds. On the other hand, setting a high fuel cut rotation speed is advantageous in terms of suppressing floor vibrations, but disadvantageous in terms of increasing oxygen storage capacity.

[0025] Figure 3 shows the correlation between the torque transmitted by the drive shaft 10 during reverse driving and the displacement of the engine mount. If the direction of the torque transmitted by the drive shaft 10 during forward driving powered by the drive motor generator 4 is considered positive, then the torque transmitted by the drive shaft 10 during reverse driving is negative. The vertical axis in Figure 3 represents the absolute value of the negative transmitted torque. As shown in Figure 3, the larger the absolute value of the transmitted torque, the greater the displacement of the engine mount, and therefore the higher the rigidity of the engine mount that elastically supports the drive unit 11. Furthermore, the higher the rigidity of the engine mount, the higher the resonance frequency (in other words, the rotational speed of the internal combustion engine 2) that induces floor vibration. For example, in the initial state where the engine mount is not displaced, the rotational speed of the internal combustion engine 2 that induces floor vibration is about 600 to 1000 rpm, but as the engine mount is displaced and its rigidity increases, resonance occurs at higher rotational speeds.

[0026] On the other hand, if the fuel cut rotation speed is set high, as mentioned above, the amount of oxygen stored when the engine stops will increase significantly.

[0027] Figure 4 shows an example of setting the fuel cut rotation speed Fc in one embodiment. The horizontal axis shows the transmitted torque of the drive shaft 10, and the range greater than 0 is the transmitted torque during forward driving. The range greater than 0 is the transmitted torque during reverse driving. The transmitted torque is negative when the drive motor generator 4 is performing regenerative operation while the vehicle is moving forward, just as it is when driving in reverse. Note that the transmitted torque of the drive shaft 10 shown on the horizontal axis is proportional to the torque of the drive motor generator 4, so it is possible to determine the transmitted torque of the drive shaft 10 from the torque of the drive motor generator 4. In the range where the absolute value of the negative transmitted torque is less than or equal to a predetermined threshold (T1), the fuel cut rotation speed Fc becomes a basic fuel cut rotation speed Fc0 that is appropriately higher than the rotation speed of 600 to 1000 rpm, which is the rotation speed at which the above-mentioned resonance can occur. This basic fuel cut rotation speed Fc0 is, for example, about 1400 rpm.

[0028] In contrast, if the absolute value of the negative transmitted torque is greater than a predetermined threshold (T1), the fuel cut rotational speed Fc becomes the high-torque fuel cut rotational speed FcH, which is relatively higher than the basic fuel cut rotational speed Fc0. This high-torque fuel cut rotational speed FcH is, for example, around 1500 rpm near the threshold (T1), and furthermore, it has the characteristic of becoming a higher rotational speed as the absolute value of the transmitted torque increases. The threshold (T1) corresponds to the magnitude of the transmitted torque at which vibrations associated with the combustion operation of the internal combustion engine 2 are easily transmitted to the vehicle body due to the displacement of the engine mount. In other words, it corresponds to the magnitude of the transmitted torque (i.e., the rigidity of the engine mount) at which floor vibrations may be induced when combustion operation is performed at the basic fuel cut rotational speed Fc0. Similarly, the characteristics of the high-torque fuel cut rotational speed FcH are set considering the change in engine mount rigidity and, consequently, the rise in the resonant frequency, which corresponds to the magnitude of the transmitted torque.

[0029] If the fuel cut rotational speed, which is also the limit rotational speed at which combustion operation can occur, is sufficiently higher than the rotational speed range in which resonance can occur, floor vibration due to resonance with combustion torque as the excitation force can be avoided. After the combustion operation of the internal combustion engine 2 stops at the fuel cut rotational speed, the crankshaft continues to rotate by inertia, crossing the rotational speed range in which resonance can occur and coming to a complete stop. However, at this time, no combustion torque is generated in the internal combustion engine 2, and the time spent passing through the rotational speed range in which resonance can occur is very short, so floor vibration does not become a problem.

[0030] Therefore, under conditions where the rigidity of the engine mount is high, increasing the fuel cut rotation speed as shown in Figure 4 reliably prevents floor vibration due to resonance. Furthermore, in the range below the threshold (T1) where the engine mount can block vibrations with its initial characteristics, the basic fuel cut rotation speed Fc0 becomes relatively low, thus suppressing the increase in the amount of oxygen stored in the three-way catalytic converter that occurs during stopping.

[0031] In one embodiment, in the region where the transmitted torque is positive, the fuel cut rotation speed is the basic fuel cut rotation speed Fc0.

[0032] Next, we will explain the restart of the internal combustion engine 2 after it has been stopped as described above. As mentioned above, when the internal combustion engine 2 is stopped, the amount of oxygen stored in the three-way catalytic converter increases. When restarting, a rich combustion operation is performed with a rich air-fuel ratio in order to quickly return the amount of oxygen stored in the three-way catalytic converter to an appropriate intermediate level and to suppress transient NOx emissions. In one embodiment, as described above, the fuel cut rotation speed is variably controlled, and a rich combustion operation is performed to provide reducing components that match the amount of oxygen stored at the time of restart. That is, if the fuel cut rotation speed is high, the amount of air supplied to the three-way catalytic converter between the stop of combustion operation and the stop of crankshaft rotation becomes large, and the amount of oxygen stored while the internal combustion engine 2 is stopped, that is, immediately before restarting, becomes large. Conversely, if the fuel cut rotation speed is low, the amount of oxygen stored becomes relatively small.

[0033] Therefore, in the first embodiment of restart control, the air-fuel ratio in rich combustion operation is set according to the fuel cut rotation speed at the time of the previous shutdown. Specifically, the higher the fuel cut rotation speed, the richer the mixture is made.

[0034] In the second embodiment of the restart control, the period of rich combustion operation is set according to the fuel cut rotation speed at the time of the previous shutdown. Specifically, the higher the fuel cut rotation speed, the longer the period of rich combustion operation.

[0035] Figure 5 is a time chart showing the operation of each part when the internal combustion engine 2 is running for power generation, stops running when power generation is no longer needed, and then restarts in response to a power generation request. This includes the restart control of the first embodiment.

[0036] The figures, from top to bottom, 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 downstream exhaust air-fuel ratio detected by the downstream air-fuel ratio sensor, (f) the target equivalence ratio (TFBYA), and (g) a timer indicating the elapsed time since the start of rich combustion operation during 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 basically the stoichiometric air-fuel ratio. (f) The target equivalence ratio (TFBYA) is this target air-fuel ratio expressed as an equivalence ratio. (e) For the downstream exhaust air-fuel ratio, only the characteristics during restart control are shown, and the characteristics during the stop process are omitted from the illustration.

[0037] Up to time t0 in Figure 5, 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 controlled (e.g., by feedback control) with the stoichiometric air-fuel ratio as the target air-fuel ratio.

[0038] At time t0, the engine controller 8 is instructed to stop power generation, i.e., to stop the internal combustion engine 2. In response, the target air-fuel ratio becomes rich, as shown in columns (d) and (f). In other words, rich combustion operation is started prior to the cessation of combustion operation. The target air-fuel ratio can be set to, for example, around 12. This rich combustion operation makes the exhaust air-fuel ratio rich, and the amount of oxygen stored in the three-way catalyst in the exhaust passage gradually decreases. It is desirable that the amount of oxygen stored approaches 0 at the end of the rich combustion operation period.

[0039] Subsequently, at time t1, intake throttling combustion operation is initiated with a reduced throttle valve opening. The throttle valve opening becomes, for example, the minimum opening near fully closed. This intake throttling combustion operation causes the intake negative pressure downstream of the throttle valve (negative pressure in the collector) to develop, and the intake air volume decreases as shown in column (c).

[0040] Furthermore, the target torque is slightly higher between time t0 and time t1. This indicates that, due to the enrichment of the air-fuel ratio, the operating point of the internal combustion engine 2 was shifted to the operating point that provides the best fuel efficiency under a rich air-fuel ratio.

[0041] At time t2, 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 t0 to time t2 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 restriction combustion operation is still in progress. In other words, the intake restriction combustion operation starts in the middle of the rich combustion operation period, and the rich combustion operation period and the intake restriction combustion operation period partially overlap. This shortens the time required for the entire shutdown sequence.

[0042] During operation at the stoichiometric air-fuel ratio after time t2, the oxygen storage capacity of the three-way catalytic converter does not increase in principle.

[0043] Meanwhile, the rotational speed of the internal combustion engine 2 gradually decreases from time t1, when the target torque has decreased. Time t3 is the timing when the rotational speed has decreased to the fuel cut rotational speed Fc mentioned above, and in the illustrated example, fuel supply is stopped at this time t3. 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 the fuel cut rotational speed Fc. In the example in Figure 5, the intake negative pressure has reached the predetermined negative pressure level before time t3. Here, as mentioned above, the fuel cut rotational speed Fc is set according to the characteristics in Figure 4. After the combustion operation ends at time t3, the rotational speed of the crankshaft, which continues to rotate due to inertia, rapidly decreases and comes to a complete stop at time t4. Between time t3 and time t4, air is supplied to the three-way catalytic converter, resulting in an increase in oxygen storage amount. Preferably, the throttle valve opening remains at the minimum opening during intake-restricted combustion operation even after time t3, until time t4 when the rotation of the internal combustion engine 2 comes to a complete stop. Therefore, the amount of air flowing through the three-way catalytic converter is minimized during rotation due to inertia, and the increase in oxygen storage volume is suppressed.

[0044] In the illustrated example, fuel supply is stopped when the intake negative pressure is strengthened by reducing the throttle valve opening. This suppresses vibrations of the internal combustion engine 2 associated with engine cessation, which is advantageous in reducing vehicle floor vibrations induced via the engine mounts. 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 on the piston are reduced.

[0045] As described above, by performing rich combustion operation when the internal combustion engine 2 is required to stop, the oxygen storage level at time t3 is kept at a sufficiently low level. Furthermore, since the amount of air passing through between times t3 and t4 is limited by the reduction in throttle valve opening, the oxygen storage level at time t4 will not ultimately be excessively high. Note that the actual time from time t0, when the stopping of the internal combustion engine 2 is requested, to time t3, when the combustion operation stops, is a relatively short time of less than 1 second.

[0046] Time t11 in Figure 5 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 target air-fuel ratio becomes rich, as shown in columns (d) and (f). In other words, rich combustion operation begins simultaneously with the restart of combustion operation. Rich combustion operation ends at time t13, and the target air-fuel ratio returns to the stoichiometric air-fuel ratio. The end of rich combustion operation is conditional on either of the following two conditions being met: "the downstream exhaust air-fuel ratio in column (e) is below a predetermined threshold (set to a value smaller than the stoichiometric air-fuel ratio of 14.7)" and "the timer value shown in column (g) is above a predetermined threshold."

[0047] Here, the target air-fuel ratio during rich combustion operation is set according to the fuel cut rotation speed Fc at the time of the previous shutdown, with the higher the fuel cut rotation speed Fc, the richer the setting. More specifically, the engine controller 8 has a target equivalent ratio map that assigns corresponding target equivalent ratio (TFBYA) values ​​to the intake air volume and fuel cut rotation speed as parameters, and the target equivalent ratio, i.e., the target air-fuel ratio during rich combustion operation is set based on this target equivalent ratio map. The target equivalent ratio becomes smaller (closer to 1) as the intake air volume increases, and larger as the fuel cut rotation speed Fc increases. This allows for appropriate rich combustion operation in a way that offsets the effect of the fuel cut rotation speed.

[0048] Next, Figure 6 is a time chart showing a second embodiment of restart control. Column (h) shows the integrated value of "target equivalent ratio × intake air amount" after the start of rich combustion operation. As shown in the figure, this integrated value is compared with the rich spike termination timing threshold RSS.

[0049] In this second embodiment, the target air-fuel ratio during rich combustion operation can be a constant value (for example, around 12), and the duration of this rich combustion operation is set according to the fuel cut rotation speed Fc at the time of the previous shutdown. The higher the fuel cut rotation speed Fc, the longer the rich combustion operation period.

[0050] In a specific example, rich combustion operation terminates when any of the following three conditions are met: "the cumulative value in column (h) becomes equal to or greater than the rich spike termination timing threshold RSS," "the downstream exhaust air-fuel ratio in column (e) becomes less than or equal to a predetermined threshold (set to a value smaller than the stoichiometric air-fuel ratio of 14.7)," and "the timer value shown in column (g) becomes equal to or greater than the predetermined threshold." Note that termination based on the downstream exhaust air-fuel ratio and termination based on the timer are preliminary and can be omitted.

[0051] Here, the rich spike termination timing threshold RSS is set according to the fuel cut rotation speed Fc at the time of the most recent shutdown, and the higher the fuel cut rotation speed Fc, the larger the value set. More specifically, the engine controller 8 has a termination timing threshold map that assigns corresponding rich spike termination timing threshold RSS values ​​to the intake air volume and fuel cut rotation speed as parameters, and the rich spike termination timing threshold RSS is set based on this termination timing threshold map. The rich spike termination timing threshold RSS becomes smaller as the intake air volume increases, and larger as the fuel cut rotation speed Fc increases. As a result, the higher the fuel cut rotation speed Fc, the longer the rich combustion operation will be performed, and appropriate rich combustion operation can be performed in a way that cancels out the effect of the fuel cut rotation speed Fc.

[0052] In the second embodiment shown in Figure 6, the target equivalent ratio (target air-fuel ratio) may be changed according to the fuel cut rotation speed Fc, similar to the first embodiment. In this case, the cumulative value of "target equivalent ratio × intake air volume" in column (h) will be a different value.

[0053] 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, in the above embodiment, rich combustion operation and intake throttle combustion operation are performed when the internal combustion engine is stopped, but these processes are not necessarily essential in the present invention. [Explanation of symbols]

[0054] 1…Power generation motor generator 2…Internal combustion engine 4…Drive motor generator 5… Battery 8…Engine controller

Claims

1. In a series hybrid vehicle in which a drive unit including a generator, an internal combustion engine that drives the generator, and a drive motor that drives the drive wheels via a drive shaft is supported on the vehicle body via an engine mount, When the internal combustion engine is shut down while the torque transmitted through the drive shaft is negative (the opposite of the torque transmitted during forward driving), if the absolute value of the transmitted torque is greater than a predetermined threshold, the fuel cut rotation speed at which fuel supply is stopped is set relatively higher than the fuel cut rotation speed at which the absolute value of the transmitted torque is less than or equal to the threshold. A method for shutting down the internal combustion engine in a series hybrid vehicle.

2. When the absolute value of the transmitted torque is greater than the threshold, the fuel cut rotation speed is set higher as the absolute value of the transmitted torque increases. A method for stopping an internal combustion engine in a series hybrid vehicle according to claim 1.

3. If the absolute value of the transmitted torque is less than or equal to the threshold, the fuel cut rotation speed is a constant value regardless of the absolute value of the transmitted torque. A method for stopping an internal combustion engine in a series hybrid vehicle according to claim 2.

4. When restarting the internal combustion engine after the above-mentioned combustion operation has stopped, the air-fuel ratio is controlled to be rich, The duration of this rich control is increased as the fuel cut rotation speed increases. A method for stopping an internal combustion engine in a series hybrid vehicle according to claim 1.

5. When restarting the internal combustion engine after the above-mentioned combustion operation has stopped, the air-fuel ratio is controlled to be rich, In this rich control, the air-fuel ratio is made richer as the fuel cut rotation speed increases. A method for stopping an internal combustion engine in a series hybrid vehicle according to claim 1.

6. The above threshold is set to correspond to the magnitude of the transmitted torque at which vibrations associated with the combustion operation of the internal combustion engine are more easily transmitted to the vehicle body due to the displacement of the engine mount caused by the reaction force of the transmitted torque. A method for stopping an internal combustion engine in a series hybrid vehicle according to claim 1.

7. A device for stopping an internal combustion engine in a series hybrid vehicle, wherein the drive unit, which includes a generator, an internal combustion engine that drives the generator, and a drive motor that drives the drive wheels via a drive shaft, is supported in the vehicle body via an engine mount, When the internal combustion engine is shut down while the torque transmitted through the drive shaft is negative (the opposite of the torque transmitted during forward driving), if the absolute value of the transmitted torque is greater than a predetermined threshold, the fuel cut rotation speed at which fuel supply is stopped is set relatively higher than the fuel cut rotation speed at which the absolute value of the transmitted torque is less than or equal to the threshold. A device for stopping the internal combustion engine in a series hybrid vehicle.

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