JP2011127696A - Control device of vehicle - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a control device of a vehicle controlling the generation of an engine stall that might be caused when the combustion state of a gaseous mixture is unstable upon returning from a fuel cut. <P>SOLUTION: An output shaft 10a of an internal combustion engine 10 is connected with a CVT 12 through a torque converter 11 provided with a lockup clutch mechanism 14. An ECU 18 controls a gear ratio of CVT 12 so that an engine rotation speed in the execution of the fuel cut is maintained at a constant speed near and higher than a return rotational speed. The ECU 18 changes the engine rotational speed in the execution of the fuel cut and the return rotational speed so that they become higher as engine water temperature is low. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a control device for a vehicle equipped with a continuously variable transmission.

  As an in-vehicle transmission, a continuously variable transmission (CVT) capable of continuously changing a gear ratio continuously and continuously has been put into practical use. As such an in-vehicle CVT, Patent Document 1 discloses a belt-type CVT that uses a metal belt and changes speed by changing the diameters of pulleys on the input side (engine side) and output side (drive shaft side). Are listed. There are also toroidal CVTs that use rollers and disks instead of belts and pulleys. In a vehicle equipped with such a CVT, the fuel efficiency characteristics and driving performance of the vehicle are optimized by cooperatively controlling the engine torque and the CVT gear ratio in accordance with the traveling state of the vehicle.

Japanese Patent Laid-Open No. 10-184834

  On the other hand, in an internal combustion engine mounted on a vehicle, when the engine speed is not less than a predetermined value when the accelerator pedal is not depressed, a process of temporarily stopping fuel injection from the fuel injection valve, so-called fuel cut is performed. Done. This fuel cut is stopped when the engine rotational speed becomes equal to or lower than the return rotational speed, and fuel injection is started again. The fuel cut is preferably performed over as long a period as possible in order to improve fuel consumption.

  Therefore, in a vehicle equipped with a continuously variable transmission as described above, the fuel cut is controlled as much as possible by controlling the gear ratio so that the engine rotation speed during fuel cut exceeds the return rotation speed for as long as possible. Can be continued for a long time.

  More specifically, the return rotational speed is set as low as possible, and the engine rotational speed is set to a constant target rotational speed that is slightly higher than the return rotational speed. During the fuel cut, the engine rotational speed also decreases as the vehicle speed decreases. When the engine rotational speed reaches the target rotational speed in the process of decreasing the engine rotational speed, the engine rotational speed becomes the target rotational speed. The gear ratio of the continuously variable transmission is controlled so that the speed is maintained. More specifically, the gear ratio (the rotational speed of the input shaft of the continuously variable transmission / the rotational speed of the output shaft of the continuously variable transmission) is increased so as to suppress a decrease in the engine rotational speed accompanying a decrease in the vehicle speed. .

  In this way, if the control is performed to maintain the engine speed during fuel cut at a speed near the return speed and slightly higher than the return speed, the fuel cut execution period can be lengthened. Can do. In addition, when the accelerator pedal is depressed during fuel cut and an acceleration request is made, the speed ratio of the continuously variable transmission is already set to a relatively large value. Can be quickly changed to a large gear ratio). Therefore, it is possible to suppress the driving condition from deviating from the optimum condition in terms of fuel consumption characteristics and acceleration characteristics until the speed is changed to a desired gear ratio.

  By the way, as described above, when the engine rotation speed is maintained in the vicinity of the return rotation speed, the engine rotation speed during the fuel cut is maintained at a relatively low rotation speed. Is done.

  For example, when the combustion state of the air-fuel mixture becomes unstable, such as when the engine temperature is low, even if the fuel cut is stopped and the fuel injection is restarted, sufficient engine output is resumed from the restart of the fuel injection. It takes a certain amount of time until this occurs, and the engine speed decreases within this time. Therefore, when the engine speed during the fuel cut is maintained at a relatively low speed, the engine speed immediately after returning from the fuel cut is also low, and the engine speed decreases from this low speed state. Will do. In this case, there is a possibility that the engine rotational speed is greatly reduced before the engine output is sufficiently generated, resulting in an engine stall.

  The present invention has been made in view of such circumstances, and its object is to suppress the occurrence of engine stall that may occur when the combustion state of the air-fuel mixture is unstable when returning from a fuel cut. It is an object of the present invention to provide a vehicle control device that can handle the above-described problem.

In the following, means for achieving the above object and its effects are described.
According to a first aspect of the present invention, there is provided a vehicle including an internal combustion engine in which the fuel cut is stopped when the engine speed during execution of the fuel cut is lower than the return rotational speed, and a continuously variable transmission connected to the internal combustion engine. Applied to the internal combustion engine and the continuously variable transmission, wherein the engine speed during execution of the fuel cut is a speed in the vicinity of the return rotational speed and from the return rotational speed. A speed ratio control means for controlling the speed ratio of the continuously variable transmission so that the constant speed is maintained at a high constant, and the engine speed during the fuel cut and the return speed are determined by the mixture of the internal combustion engine. And a changing means for changing to a higher rotational speed as the degree of instability of the combustion state is higher.

  In the present invention, during the fuel cut, the engine speed is maintained at a slightly higher speed than the return speed of the fuel cut by controlling the gear ratio of the continuously variable transmission. The execution period of is made as long as possible.

  Here, in the present invention, the engine rotational speed and the return rotational speed during fuel cut execution are set to higher rotational speeds when the instability of the combustion state of the air-fuel mixture is higher. Therefore, the engine speed immediately after the fuel cut is stopped and the fuel injection is restarted increases as the combustion state of the air-fuel mixture becomes unstable, and the engine speed immediately after the fuel injection is restarted becomes an engine stall. The time required for the reduction to the extent becomes longer as the combustion state of the air-fuel mixture becomes unstable. Accordingly, it is possible to appropriately secure a time until sufficient engine output is generated after the fuel injection is restarted. As a result, the combustion state of the air-fuel mixture becomes unstable when returning from the fuel cut. It is possible to suppress the occurrence of engine stall that may occur at any time.

  In addition, when changing the engine rotation speed and the return rotation speed during the fuel cut according to the instability of the combustion state, for example, the engine rotation speed during the fuel cut is directly A mode in which the return rotational speed is set or the engine rotational speed during fuel cut execution is set based on the degree of instability, and a value lower than the set engine rotational speed by a predetermined value is set as the return rotational speed. It is possible to adopt such a mode.

The invention according to claim 2 is characterized in that, in the invention according to claim 1, the speed ratio control means increases the speed ratio as the vehicle speed decreases.
When the vehicle speed decreases, the engine speed also decreases through the continuously variable transmission. Here, when the transmission ratio of the continuously variable transmission is increased, the rotational speed of the input shaft of the continuously variable transmission can be increased with respect to the output shaft of the continuously variable transmission connected to the wheel side. The rotational speed of the output shaft of the internal combustion engine connected to the engine, that is, the engine rotational speed can be increased.

  Therefore, according to the invention described in claim 2, the speed change ratio control means adopts a configuration in which the speed change ratio of the continuously variable transmission is increased as the vehicle speed decreases, whereby the engine during fuel cut is being executed. The rotation speed can be maintained at a constant speed that is near the return rotation speed and higher than the return rotation speed.

  According to a third aspect of the present invention, in the first or second aspect of the present invention, the changing unit detects a parameter correlated with the engine temperature, and the engine that is executing the fuel cut is detected based on the detection result. The gist is to set the rotational speed and the return rotational speed to values according to the degree of instability.

  The combustion state of the air-fuel mixture tends to become unstable as the engine temperature is lower. Accordingly, as in the third aspect of the invention, a parameter correlated with the engine temperature is detected, and the engine rotational speed and the return rotational speed during execution of the fuel cut are determined according to the degree of instability based on the detection result. It is possible to adopt a configuration such as setting to a different value. In this configuration, the lower the engine temperature, the higher the instability of the combustion state. Therefore, the lower the engine temperature, the higher the engine speed and return speed during the fuel cut are set. It is desirable.

  The parameters correlated with the engine temperature include the engine coolant temperature, the engine oil temperature, the elapsed time since the engine start, and the like. Therefore, according to a fourth aspect of the present invention, the changing means detects the engine coolant temperature as the parameter, and the engine speed and the return engine speed during the fuel cut as the coolant temperature decreases. It is also possible to adopt a configuration in which is set to a high rotational speed. By the way, the combustion state becomes unstable even when the intake air temperature is low. Therefore, the intake air temperature may be detected, and the engine rotation speed and the return rotation speed during the fuel cut may be set to values corresponding to the instability based on the detection result.

  The invention according to claim 5 is the invention according to any one of claims 1 to 4, wherein the output shaft is provided between the output shaft of the internal combustion engine and the input shaft of the continuously variable transmission. A connection mechanism for switching the input shaft between a connected state and a disconnected state is provided, and when the vehicle speed becomes a predetermined value or less, the output shaft and the input shaft are disconnected. The gist is that the operating state is controlled.

  According to this invention, when the vehicle speed falls below a predetermined value, the connection between the output shaft of the internal combustion engine and the input shaft of the continuously variable transmission is released. If such connection of each shaft is released while the fuel cut is being performed, the engine rotation speed decreases and becomes lower than the return rotation speed, so that fuel injection is resumed. Further, when the fuel injection is restarted, the connection between the output shaft of the internal combustion engine and the input shaft of the continuously variable transmission is released, so the load of the vehicle drive system on the internal combustion engine is very small, and the fuel The return from the cut is made promptly.

  Therefore, even if the engine speed during the fuel cut is maintained at a constant speed that is close to the return speed and higher than the return speed, the fuel cut must be stopped without fail. In addition, it is possible to quickly return from the fuel cut.

  According to a sixth aspect of the present invention, in the fifth aspect of the present invention, when the control command value is output so that the operating state of the connection mechanism becomes the connected state, the actual operating state becomes the connected state. And the fuel cut that maintains the return rotational speed at a constant speed when it is determined by the determination means that the actual operating state is not connected. The gist of the present invention is to provide second changing means for changing the engine speed so that the engine speed becomes higher as the instability of the combustion state is higher than the engine speed being executed.

  If the operating state of the connection mechanism is changed from the connected state to the disconnected state, or when the operating state is switched rapidly from the disconnected state to the connected state, a shock may occur in the power transmission system of the vehicle. is there. Therefore, normally, when the operating state of the connection mechanism is switched, the control command value for the connection mechanism is adjusted so that the switching is gradually performed.

  On the other hand, when the control command value is output so that the operation state of the connection mechanism becomes the connection state, the connection mechanism operates against the control command value due to a disturbance or the like acting on the connection mechanism. When the state becomes a disconnected state, the engine speed rapidly decreases. In this way, even if the engine rotation speed decreases, the fuel injection is resumed if the engine rotation speed falls below the return rotation speed. However, the engine rotation speed decrease speed at this time is a decrease during normal time when the connection state is gradually switched. Since it is faster than the speed, the amount of decrease in the rotational speed after falling below the return rotational speed increases. For this reason, there is a possibility that the engine speed will not be restored after the fuel injection is restarted, resulting in an engine stall. In particular, when the combustion state of the air-fuel mixture is unstable, there is a possibility that engine stall is likely to occur for the reasons described above.

  Therefore, in the above invention, when it is determined that the connection is released when the connection mechanism is supposed to be in a connected state, the engine whose return rotational speed is maintained at a constant rotational speed during the fuel cut is performed. The rotation speed is changed to a higher rotation speed. For this reason, if it is determined that the connection mechanism is in an operating state different from the control command value, the engine speed at that time is equal to or lower than the changed return speed, so the fuel cut is immediately stopped. The fuel injection is resumed. Accordingly, the fuel injection is resumed before the engine rotational speed decreases to the return rotational speed before the change, and the fuel injection is performed at a higher engine rotational speed than when the return rotational speed is not changed. It will be resumed. Therefore, even when the amount of decrease in engine speed after restarting fuel injection increases, the occurrence of engine stall can be suppressed. In the second changing means, the return rotational speed to be changed is changed so that the higher the instability of the combustion state, the higher the rotational speed becomes. Therefore, the return rotational speed after the change can be changed according to the degree of instability of the combustion state of the air-fuel mixture, and the above action can be obtained appropriately.

  According to a seventh aspect of the present invention, in the invention according to the fifth or sixth aspect, a torque converter is connected to an input shaft of the continuously variable transmission, and the connection mechanism is provided in the torque converter. The gist is that it is a lock-up clutch mechanism.

    As the connection mechanism, a lock-up clutch mechanism provided in the torque converter can be employed as in the invention described in claim 6.

1 is a schematic configuration diagram of a vehicle to which the embodiment of a vehicle control device according to the present invention is applied. The graph which shows the relationship of lockup ON / OFF based on the amount of accelerator operation, and a vehicle speed. The graph which shows the gear ratio of the continuously variable transmission based on lockup and a fuel cut execution state. The flowchart which shows the procedure of a target rotational speed setting process. The graph which shows the relationship between engine water temperature and target input rotation speed. The flowchart which shows the procedure of a return rotational speed setting process. The graph which shows the relationship between engine water temperature and a return rotational speed. The timing chart which shows an example of transition of each parameter when an engine water temperature is high when performing a target rotational speed setting process and a return rotational speed setting process. The timing chart which shows an example of transition of each parameter when an engine water temperature is low, when performing a target rotational speed setting process and a return rotational speed setting process. The timing chart which shows the mode of a return from a fuel cut when the lockup by a lockup clutch mechanism is cancelled | released in the state in which the lockup ON signal is output during fuel cut execution.

Hereinafter, an embodiment embodying the present invention will be described with reference to FIGS.
As shown in FIG. 1, a torque converter 11 that transmits torque via a working fluid is connected to an output shaft 10 a of the internal combustion engine 10. An input shaft 12 a of a continuously variable transmission (hereinafter referred to as CVT) 12 is connected to the torque converter 11, and an output shaft 12 b of the CVT 12 is connected to drive wheels 13.

  The torque converter 11 is provided with a lockup clutch mechanism 14 as a connection mechanism for mechanically connecting the output shaft 10a of the internal combustion engine 10 and the input shaft 12a of the CVT 12.

  Through the operation of the lockup clutch mechanism 14, the “connected state” in which the output shaft 10a of the internal combustion engine 10 and the input shaft 12a of the CVT 12 are directly connected and the connection between the output shaft 10a and the input shaft 12a are released. The “unconnected state” is switched.

  The CVT 12 is a transmission that can change the gear ratio continuously and continuously. Specifically, the CVT 12 includes an output pulley 15 to which an output shaft 12b (drive wheel 13 side) is connected, an input pulley 16 to which an input shaft 12a (torque converter 11 side) is connected, and pulleys 15 and 16 And a belt 17 wound around. Both pulleys 15 and 16 can be freely changed in groove width by using, for example, hydraulic pressure as a drive source, and the winding radius of the belt 17 is adjusted according to the change in the groove width.

The internal combustion engine 10, the CVT 12, the lockup clutch mechanism 14, etc. are controlled by an electronic control unit (hereinafter referred to as ECU) 18.
The ECU 18 is composed of a plurality of microcomputer units specializing in engine control, transmission control, etc., and performs various controls of the vehicle based on information detected by sensors provided in each part of the vehicle.

  For example, the vehicle detects a vehicle speed sensor 19 that detects the vehicle speed SPD, an accelerator sensor 20 that detects the accelerator pedal operation amount ACCP, and a rotational speed of the input shaft 12a that rotates together with the input pulley 16 (input shaft rotational speed Nin). An input shaft rotation speed sensor 21 is provided. Also provided are a shift position sensor 22 for detecting the position of the shift lever, a travel mode selection switch 23 for selecting either a normal mode or a sport mode as the travel mode. The internal combustion engine 10 includes an engine speed sensor 25 that detects the engine speed NE, a water temperature sensor 24 that detects the engine water temperature Thw, an intake pressure sensor 26 that detects the pressure PM of the intake system, and an airflow that detects the intake air amount. A meter or the like is provided.

  The ECU 18 controls the gear ratio of the CVT 12 and the operation of the lockup clutch mechanism 14 through hydraulic control by a hydraulic control circuit (not shown). The ECU 18 performs various engine controls such as fuel injection control of the internal combustion engine 10 based on the detection results of the various sensors.

  As shown in FIG. 2, the operation of the lockup clutch mechanism 14 is controlled by the ECU 18 based on the vehicle speed SPD and the accelerator operation amount ACCP. More specifically, when the vehicle speed is higher than a certain high vehicle speed H2, the ECU 18 outputs a lock-up ON signal that is a control command value regardless of the accelerator operation amount ACCP, and lock-up is executed (lock-up ON). Thus, the driving force loss in the torque converter 11 is suppressed.

  Further, when the vehicle speed is a certain low lockup release speed H1 or less (H1 <H2), a lockup OFF signal that is a control command value is output from the ECU 18 regardless of the accelerator operation amount ACCP, and the lockup is released. (Lock-up OFF). This is because the output shaft 10a of the internal combustion engine 10 and the input shaft 12a of the CVT 12 are directly connected in a state where lockup is being executed. For this reason, the engine rotational speed also decreases as the vehicle speed decreases. However, if the lockup is continued until the vehicle stops, the engine rotational speed decreases too much and engine stall occurs. Therefore, when the vehicle speed becomes equal to or lower than the lockup release speed H1, the lockup is released and the output shaft 10a of the internal combustion engine 10 and the input shaft 12a of the CVT 12 are disconnected, thereby avoiding the occurrence of the engine stall. Is done.

  When the vehicle speed is between the lockup release speed H1 and the vehicle speed H2, the lockup state is switched based on the vehicle speed SPD and the accelerator operation amount ACCP. More specifically, when the accelerator operation amount ACCP is equal to or greater than a predetermined value A, a lockup OFF signal is output from the ECU 18 and the lockup is released. When the accelerator operation amount ACCP is less than the predetermined value A, a lockup ON signal is output from the ECU 18 and lockup is executed. The predetermined value A is variably set so as to increase as the vehicle speed increases. As a result, as the vehicle speed is lower, the lock-up is released with a smaller accelerator operation amount ACCP, and the torque increasing action by the torque converter 11 can be suitably obtained in the low speed range.

  When the operation state of the lock-up clutch mechanism 14 is changed from the connected state (lock-up ON) to the non-connected state (lock-up OFF), or from the non-connected state (lock-up OFF) to the connected state (lock-up ON). If the operating state is switched rapidly, a shock or the like may occur in the power transmission system of the vehicle. Therefore, when the operating state of the lockup clutch mechanism 14 is switched, the control command value for the lockup clutch mechanism 14 is adjusted so that the switching is gradually performed. More specifically, the lockup clutch mechanism 14 is configured to be in a lockup ON state by supplying hydraulic pressure, and to be in a lockup OFF state by stopping the hydraulic supply, and when the operation state is switched, the hydraulic pressure gradually increases. It is hydraulically controlled to change to

  Further, the ECU 18 performs a so-called fuel cut at deceleration, which stops fuel injection of the internal combustion engine 10 when the vehicle is decelerated. This fuel cut is executed on condition that the accelerator pedal is not depressed and that the engine rotational speed NE exceeds a predetermined return rotational speed. When the engine rotational speed becomes equal to or lower than the return rotational speed, or when the accelerator pedal is depressed, the fuel cut is stopped and fuel injection is resumed.

  In order to improve fuel efficiency, the fuel cut is desirably performed over a period as long as possible. Therefore, the vehicle control apparatus according to the present embodiment controls the gear ratio of the CVT 12 so that the engine rotational speed NE during fuel cut exceeds the return rotational speed for as long as possible, and continues the fuel cut for as long as possible. I try to let them.

  More specifically, the lowest possible rotation speed is set for the return rotation speed Nrtlu. Further, as shown in FIG. 3, the engine rotational speed NE is controlled to be a constant target speed NEp that is slightly higher than the return rotational speed Nrtlu. Here, since the vehicle speed is at a certain level during fuel cut during deceleration, the lock-up clutch mechanism 14 is in a lock-up state, and the engine rotation speed NE and the rotation speed of the input shaft 12a of the CVT 12 are the same. . Further, during the fuel cut, it is impossible to adjust the engine rotational speed by the fuel injection control, but it is possible to adjust the engine rotational speed through the rotational speed control of the input shaft 12a by the gear ratio control of the CVT 12. Therefore, when controlling the engine rotational speed NE to be maintained at the target speed NEp, the target rotational speed Nint of the input shaft 12a is set so that the rotational speed of the input shaft 12a becomes the target rotational speed Nint. The transmission ratio of CVT 12 is adjusted.

  As indicated by the solid line in FIG. 3, until the engine rotational speed NE (= the rotational speed of the input shaft 12a) decreases to the target speed NEp (= the target rotational speed Nint), the transmission ratio of the CVT 12 is the minimum speed change. Maintained in ratio. When the engine rotational speed NE (= the rotational speed of the input shaft 12a) reaches the target speed NEp (= the target rotational speed Nint), the engine rotational speed NE (= the rotational speed of the input shaft 12a) is changed to the target speed as described above. The gear ratio of the CVT 12 is controlled so as to maintain NEp (= target rotational speed Nint). More specifically, the gear ratio (the rotational speed of the input shaft 12a of the CVT 12 / the rotational speed of the output shaft 12b of the CVT 12) is increased so as to suppress a decrease in the engine rotational speed NE accompanying a decrease in the vehicle speed. Note that the difference between the return rotational speed Nrtlu and the target rotational speed Nint is as small as possible while providing the difference to some extent so that the engine rotational speed does not temporarily fall below the return rotational speed Nrtlu due to fluctuations or the like. It is desirable to make it a value.

  Incidentally, a process for controlling the speed ratio of the CVT 12 so that the engine speed NE is maintained at the target speed NEp is performed by the ECU 18, and the ECU 18 that executes this process constitutes the speed ratio control means.

  In this way, the fuel cut execution period is controlled by maintaining the engine speed NE during the fuel cut at a constant target speed NEp that is near the return speed Nrtlu and slightly higher than the return speed Nrtlu. Becomes longer. Further, when the accelerator pedal is depressed and an acceleration request is made when the engine speed NE is maintained at the target speed NEp while the fuel is being cut, the gear ratio of the CVT is already set to a relatively large value. Therefore, it is possible to quickly change toward a desired gear ratio (generally a large gear ratio) that satisfies the acceleration request. Therefore, it is possible to suppress the driving condition from deviating from the optimum condition in terms of fuel consumption characteristics and acceleration characteristics until the speed is changed to a desired gear ratio.

  By the way, as described above, when the engine rotational speed NE is maintained in the vicinity of the return rotational speed Nrtlu, the engine rotational speed NE during the fuel cut is maintained at a relatively low rotational speed. There is concern about the occurrence of

  For example, when the combustion state of the air-fuel mixture becomes unstable, such as when the engine temperature is low, even if the fuel cut is stopped and the fuel injection is restarted, sufficient engine output is resumed from the restart of the fuel injection. It takes a certain amount of time for the engine to occur, and the engine speed NE falls within this time. Therefore, when the engine rotational speed NE during the fuel cut is maintained at a relatively low rotational speed, the engine rotational speed NE immediately after returning from the fuel cut is also low. NE will decrease. In this case, there is a possibility that the engine rotation speed NE is greatly reduced before the engine output is sufficiently generated, resulting in an engine stall.

  Therefore, in the present embodiment, by executing the following target rotation speed setting process for setting the target rotation speed Nint and the following return rotation speed setting process for setting the return rotation speed, such an engine stall is performed. I try to suppress the occurrence of.

FIG. 4 shows the procedure of the target rotational speed setting process. The target rotation speed setting process is repeatedly executed by the ECU 18 at predetermined control cycles.
In this process, first, in step S11, based on the engine water temperature Thw, the target rotational speed Nint is calculated with reference to the target rotational speed calculation map. As shown in FIG. 5, a target rotational speed Nint corresponding to the engine coolant temperature Thw is set in the target rotational speed calculation map. In this target rotational speed calculation map, the target rotational speed Nint is set to a constant minimum value A in an area where it can be determined that the engine water temperature Thw is equal to or higher than a predetermined value T and the internal combustion engine 10 is in a warm-up completion state. . On the other hand, in a region where the engine coolant temperature Thw is lower than the predetermined value T and it can be determined that the internal combustion engine 10 is not warmed up, the target rotational speed Nint is set higher as the engine coolant temperature Thw decreases. The target rotational speed Nint is thus changed according to the engine coolant temperature Thw. However, at any engine coolant temperature Thw, the target rotational speed Nint is a speed in the vicinity of the return rotational speed Nrtlu and the same return rotational speed Nrtlu. A slightly higher rotational speed is set (see FIG. 7).

  The reason for setting the target rotational speed Nint based on the engine water temperature Thw as described above is as follows. That is, the combustion state of the air-fuel mixture tends to become unstable as the engine temperature is lower. Therefore, as a method of detecting the degree of instability of the combustion state of the air-fuel mixture, there is a method of detecting a parameter correlated with the engine temperature and detecting the degree of instability of the combustion state based on the detection result. Here, examples of the parameter correlated with the engine temperature include the engine coolant temperature. Therefore, in this embodiment, the degree of instability of the air-fuel mixture combustion state is estimated based on the engine water temperature Thw, and the lower the engine water temperature Thw, that is, the higher the degree of instability of the combustion state, the more the target rotational speed Nint becomes. High value is set.

  When the target rotational speed Nint is calculated in step S11, next, the process proceeds to step S12, and various parameters indicating the pressure PM of the intake system of the internal combustion engine 10, the type of travel mode, and the like are detected. Based on this, various required rotational speeds of the input shaft 12a are calculated. Examples of these various required rotational speeds include the following.

  In a vehicle, the negative pressure of the intake system is used to obtain a boosting action by a brake booster or to introduce evaporated fuel in a fuel tank into the intake system. Depending on the engine operating condition, this negative pressure may be insufficient. In this case, it is necessary to reduce the internal pressure of the intake system by increasing the engine speed. Therefore, when it is determined that the pressure PM of the intake system is equal to or higher than a predetermined value when there is a request that negative pressure is required, and it is determined that the required negative pressure cannot be ensured, the engine speed NE. The required rotational speed required to increase the pressure and secure the negative pressure is calculated.

Further, when the vehicle travel mode is the sport mode, a required rotational speed for increasing the engine rotational speed is calculated as compared to the normal mode.
When the various required rotational speeds are calculated in this way, in step S13, the highest rotational speed among the target rotational speed Nint calculated in step S11 and the various required rotational speeds calculated in step S12 is the maximum target rotational speed. The speed Nintmax is selected and the process is temporarily terminated. If the target rotational speed Nint is the highest rotational speed as a result of the processing in step S13, the target rotational speed Nint is set to the maximum target rotational speed Nintmax. On the other hand, when the various requested rotational speeds are higher than the target rotational speed Nint, the highest rotational speed among the various requested rotational speeds is set as the maximum target rotational speed Nintmax. In this case, since the rotational speed higher than at least the target rotational speed Nint is set as the maximum target rotational speed Nintmax, the set maximum target rotational speed Nintmax does not fall below a return rotational speed Nrtlu described later.

  When the maximum target rotation speed Nintmax is set in this way, the ECU 18 controls the gear ratio of the CVT 12 so that the rotation speed of the input shaft 12a becomes the maximum target rotation speed Nintmax. For example, the ECU 18 changes the gear ratio of the CVT 12 so that the input shaft rotational speed Nin is maintained at the maximum target rotational speed Nintmax when the input shaft rotational speed Nin of the CVT 12 decreases to the maximum target rotational speed Nintmax during the fuel cut. To control.

  Next, the return rotation speed setting process will be described with reference to the flowchart shown in FIG. This return rotation speed setting process is also repeatedly executed by the ECU 18 at predetermined control cycles.

  In this process, first, in step S21, it is determined whether or not the actual operation state is the lockup ON state in a state where the lockup ON signal is output. Here, if the deviation between the engine rotational speed NE and the input shaft rotational speed Nin of the input shaft 12a is within a predetermined value, it is determined that the actual operating state of the lockup clutch mechanism 14 is in the lockup ON state. The Note that the difference between the target rotation speed Nint and the return rotation speed Nrtlu is set to be larger than the predetermined value for determining the deviation. In other words, the predetermined value for determining the deviation is smaller than the difference between the target rotational speed Nint and the return rotational speed Nrtlu.

  On the other hand, when the deviation between the engine rotational speed NE and the input shaft rotational speed Nin exceeds a predetermined value, the actual lockup clutch mechanism 14 is operated even though the lockup ON signal is output as the control command value. It is determined that the operating state is the lock-up OFF state. The reason why the operating state of the lockup clutch mechanism 14 becomes the lockup OFF state contrary to the control command value of the ECU 18 as described above is that, for example, a disturbance acts on the lockup clutch mechanism 14 (the lockup clutch For example, an action of a physical force for releasing the mechanism 14 or a temporary decrease in hydraulic pressure). Incidentally, the process of step S21 constitutes the determination means.

If it is determined that the actual operating state is the lock-up ON state (S21: YES), the process proceeds to step S22.
In step S22, with reference to the return rotation speed calculation map, the return rotation speed Nrtlu at the time of lockup ON is calculated based on the engine water temperature Thw, and this process is temporarily ended.

On the other hand, when it is determined in step S21 that the actual operating state is the lock-up OFF state (S21: YES), the process proceeds to step S24.
In step S24, with reference to the return rotation speed calculation map, the second return rotation speed Nrtluoff at the time of lock-up OFF is calculated based on the engine water temperature Thw, and this process is temporarily ended.

  FIG. 7 shows how the return rotation speed calculation map is set. In FIG. 7, the solid line shows the setting mode of the target rotational speed Nint described above, the one-dot chain line shows the setting mode of the return rotational speed Nrtlu when the lockup is ON, and the two-dot chain line shows the setting mode when the lockup is OFF. 2 shows how the return rotational speed Nrtluoff is set.

  As indicated by the alternate long and short dash line in FIG. 7, regarding the return rotational speed Nrtlu at the time of lock-up ON, it can be determined that the engine water temperature Thw is equal to or higher than a predetermined value T and the warm-up of the internal combustion engine 10 is completed. It is set to a certain minimum value B in the region. On the other hand, in a region where the engine water temperature Thw is lower than the predetermined value T, the return rotational speed Nrtlu is set to be higher as the engine water temperature Thw is lower. The return rotational speed Nrtlu is thus changed according to the engine coolant temperature Thw. However, at any engine coolant temperature Thw, the return rotational speed Nrtlu is a speed in the vicinity of the target rotational speed Nint. The rotational speed is set slightly lower than the target rotational speed Nint.

  Further, as indicated by a two-dot chain line in FIG. 7, the engine water temperature Thw is equal to or higher than a predetermined value T and the warm-up of the internal combustion engine 10 is completed for the second return rotational speed Nrtluoff when the lockup is OFF. Is set to a certain minimum value C in an area where it can be determined that the On the other hand, in a region where the engine water temperature Thw is lower than the predetermined value T, the second return rotational speed Nrtluoff is set to be higher as the engine water temperature Thw is lower. In this way, the second return rotational speed Nrtluoff at the time of lockup OFF is also changed according to the engine water temperature Thw. However, the second return rotational speed Nrtluoff is the target value at any engine water temperature Thw. The rotation speed is set near the rotation speed Nint and is slightly higher than the target rotation speed Nint.

  Thus, in the return rotation speed setting process, the return rotation speed is set based on the engine water temperature Thw, but a different value is set according to the operating state of the lockup clutch mechanism 14. More specifically, when the lockup ON signal is output and the actual operation state is the lockup ON state, and the lockup clutch mechanism 14 is operating normally, the target rotational speed Nint Also, a low return rotational speed Nrtlu is set. On the other hand, when the lock-up ON signal is output and the actual operating state is the lock-up OFF state, and the lock-up clutch mechanism 14 is not operating normally, the second higher than the target rotational speed Nint. The return rotational speed Nrtluoff is set.

The ECU 18 that executes the target rotational speed setting process and the return rotational speed setting process constitutes the changing means and the second changing means.
Next, the effect | action by the said target speed setting process and the said return rotation speed setting process is demonstrated with reference to FIGS. 8 to 10 exemplify a case where the maximum target rotation speed Nintmax is set to the target rotation speed Nint.

  FIG. 8 shows the operation when the fuel cut is performed when the internal combustion engine 10 is in the warm-up completion state. FIG. 9 shows the operation when the fuel cut is performed when the internal combustion engine 10 is in a cold state. FIG. 10 shows the operation when the lockup is released due to a disturbance or the like during execution of the fuel cut.

  As shown in FIG. 8, the lock-up ON signal is output before time t1, and the actual operating state of the lock-up clutch mechanism 14 is the lock-up ON state. When the accelerator pedal is no longer depressed while the vehicle is traveling (time t1), fuel cut is executed and the vehicle speed SPD gradually decreases. As the vehicle speed SPD decreases, the input shaft rotation speed Nin and the engine rotation speed NE also gradually decrease.

  Here, since the internal combustion engine 10 is in the warm-up completed state and the degree of instability regarding the combustion state of the air-fuel mixture is low, the target rotational speed Nint is set to the minimum value A, and the return rotational speed Nrtlu is the minimum value B. Set to

  When the input shaft rotational speed Nin decreases to the target rotational speed Nint (time t2), gear ratio control for maintaining the input shaft rotational speed Nin at the target rotational speed Nint is started, and the engine rotational speed NE is set to the target rotational speed Nint. The speed NEp is maintained.

  When the vehicle speed SPD decreases to the lockup release speed H1 (time t3), a lockup OFF signal is output and the lockup is released. When releasing this lockup, the release is gradually performed as described above. Then, as the unlocking progresses, the engine speed NE decreases, and when the engine speed NE falls below the return speed Nrtlu (time t4), the fuel cut is stopped and fuel injection is resumed. . In this case, since the air-fuel mixture burns stably, the period from when the fuel injection is restarted until sufficient engine output is generated is short. For this reason, even if the target rotation speed Nint and the return rotation speed Nrtlu are set to the minimum values, the decrease in the engine rotation speed NE is settled at an early stage and maintained at a predetermined rotation speed (for example, an idle rotation speed).

  Since the fuel injection is resumed after the lock-up OFF signal is output, the fuel injection is resumed in a state where the load of the vehicle drive system on the internal combustion engine 10 is very small. Therefore, the recovery from the fuel cut, that is, the recovery of the engine rotation speed is made promptly.

  Incidentally, in this embodiment, the gear ratio control for maintaining the input shaft rotational speed Nin at the target rotational speed Nint is stopped after the fuel cut is stopped. Therefore, when the fuel cut is stopped, the input shaft rotational speed Nin decreases as the vehicle speed decreases. The speed ratio control may be stopped at another timing, for example, when the lockup signal is switched from ON to OFF.

On the other hand, when the internal combustion engine 10 is in a cold state, the action shown in FIG. 9 is obtained.
As shown in FIG. 9, the lock-up ON signal is output before time t6, and the actual operation state of the lock-up clutch mechanism 14 is the lock-up ON state. When the accelerator pedal is no longer depressed while the vehicle is traveling (time t6), fuel cut is executed and the vehicle speed SPD gradually decreases. As the vehicle speed SPD decreases, the input shaft rotation speed Nin and the engine rotation speed NE also gradually decrease.

  Here, when the internal combustion engine 10 is in a cold state, the degree of instability in the combustion state of the air-fuel mixture is high. Therefore, based on the engine water temperature Thw correlated with the instability of the combustion state, the target rotational speed Nint and the return rotational speed Nrtlu are set to higher values as the engine water temperature Thw is lower.

  When the input shaft rotational speed Nin decreases to the target rotational speed Nint (time t7), gear ratio control for maintaining the input shaft rotational speed Nin at the target rotational speed Nint is started, and the engine rotational speed NE is set to the target rotational speed Nint. The speed NEp is maintained. At this time, since the target rotational speed Nint is higher than the target rotational speed Nint set when the warm-up is completed, the engine rotational speed NE maintained by the speed ratio control when the engine is cold is: It is higher than the engine speed NE maintained when the warm-up is completed.

  When the vehicle speed SPD decreases to the lockup release speed H1 (time t8), a lockup OFF signal is output and the lockup is released. When releasing this lockup, the release is gradually performed as described above. Then, as the release of the lockup proceeds, the engine rotational speed NE decreases, and when the engine rotational speed NE falls below the return rotational speed Nrtlu (time t9), the fuel cut is stopped and fuel injection is resumed. . As described above, the return rotation speed Nrtlu set in the cold state is higher than the return rotation speed Nrtlu set in the warm-up completion state.

  When the fuel injection is resumed and the target rotational speed Nint and the return rotational speed Nrtlu are not increased according to the engine coolant temperature Thw (shown in FIG. 9 (NEp = Nint), (Ntrlu)), As shown by the broken line L1 in FIG. 9, the engine speed NE changes. That is, the combustion state of the air-fuel mixture becomes unstable when the engine is cold. For this reason, even if the fuel cut is stopped and the fuel injection is restarted, it takes a certain amount of time until the sufficient engine output is generated after the restart of the fuel injection, and the engine speed NE is within this time. Will fall. Therefore, when the target rotational speed Nint is not increased according to the engine water temperature Thw and the engine rotational speed NE during the fuel cut is maintained at a relatively low rotational speed, the engine immediately after the return from the fuel cut is performed. The rotational speed NE is also low, and the engine rotational speed NE is reduced from this low rotational state. In this case, before the fuel injection is restarted and sufficient engine output is generated, the engine speed NE may be greatly reduced, leading to engine stall.

  In this respect, in the present embodiment, the return rotational speed Nrtlu is increased according to the engine water temperature Thw. The target rotational speed Nint is also increased according to the engine water temperature Thw in accordance with the increase of the return rotational speed Nrtlu. Therefore, the engine speed NE immediately after the fuel cut is stopped and the fuel injection is restarted increases as the combustion state of the air-fuel mixture becomes unstable, and the engine speed NE immediately after the fuel injection is restarted is the engine speed NE. The time required to decrease to the stall becomes longer as the combustion state of the air-fuel mixture becomes unstable. Accordingly, the time required from when the fuel injection is restarted until sufficient engine output is generated can be appropriately ensured according to the degree of instability of the combustion state. When the engine is restored, the engine stall that may occur when the combustion state of the air-fuel mixture is unstable can be suppressed.

When the fuel injection is resumed in this way, thereafter, the decrease in the engine rotational speed NE is stopped and maintained at a predetermined rotational speed (for example, an idle rotational speed).
On the other hand, when the lockup is released due to a disturbance or the like during the fuel cut, the operation shown in FIG. 10 is obtained.

  When the vehicle passes through a step or suddenly brakes, the lockup clutch mechanism 14 may be disturbed. In such a case, even if the lockup ON signal is output, the actual operation state of the lockup clutch mechanism 14 may be in the lockup OFF state. As described above, when the lockup ON signal is output, the actual operation state is the lockup OFF state, and a state where the lockup clutch mechanism 14 is not operating normally occurs during the fuel cut. Since the connection between the output shaft 10a of the internal combustion engine 10 and the input shaft 12a of the CVT 12 is rapidly released, the engine speed NE decreases rapidly.

  For example, as shown in FIG. 10, in the state where the fuel cut is being executed and the engine speed NE is maintained at the target speed NEp, the actual operating state is locked even though the lock-up ON signal is output. When the engine is in the up-off state (time t13), the engine speed NE is rapidly reduced.

  As indicated by the broken line L2, when the engine speed NE decreases rapidly and falls below the return rotational speed Nrtlu, fuel injection is resumed (time t15). However, the decrease speed of the engine rotational speed NE before resuming the fuel injection is the normal decrease speed at which the lockup state is gradually switched, that is, the control command value for controlling the lockup state is changed from “ON” to “OFF”. It is faster than the decrease speed of the engine rotational speed NE when it is switched to. For this reason, the amount of decrease in the rotational speed after the return rotational speed Nrtlu is lowered is also increased. Therefore, there is a possibility that engine stall may occur because the engine speed NE cannot be returned in time after the fuel injection is resumed. In particular, when the combustion state of the air-fuel mixture is unstable, there is a possibility that engine stall is likely to occur for the reasons described above.

  In this regard, in this embodiment, when the lock-up clutch mechanism 14 is released when the lock-up ON signal is output and the lock-up clutch mechanism 14 is supposed to be in the connected state (time t13). ) The deviation between the engine rotational speed NE and the input shaft rotational speed Nin increases. If it is determined that the lock-up is OFF based on the deviation (time t14), the return rotational speed is changed from the return rotational speed Nrtlu at the time of lock-up ON to the second return rotational speed Nrtluoff (time). t14). Since the second return rotational speed Nrtluoff is set to a rotational speed higher than the target rotational speed Nint, the engine rotational speed NE when the return rotational speed is changed in this way is equal to or lower than the second return rotational speed Nrtluoff. The rotation speed becomes. Therefore, the fuel cut is immediately stopped and fuel injection is resumed (time t14).

  Accordingly, the fuel injection is resumed before the engine speed NE decreases to the return speed Nrtlu before the change, and the return speed from the return speed Nrtlu at the time of lock-up ON to the second return speed. Compared with the case where the engine speed is not changed to Nrtluoff, the fuel injection is resumed with the engine speed NE being higher. Therefore, even when the amount of decrease in the engine speed NE after the fuel injection is resumed tends to increase, the rate of decrease in the engine speed NE can be suppressed as shown by the solid line. Can be suppressed. Further, since the time from when the lockup is released until the fuel injection is restarted is shortened, the fuel injection can be restarted while the decrease acceleration of the engine rotational speed NE is smaller. Therefore, the amount of decrease in the engine rotational speed NE after restarting the fuel injection can be reduced, and the engine stall can also be suppressed.

  As described above, the predetermined value for determining whether or not the actual operation state of the lockup clutch mechanism 14 is the lockup ON state is based on the difference between the target rotation speed Nint and the return rotation speed Nrtlu. It is also small. Therefore, after the lockup clutch mechanism 14 is disconnected at the time t13, it can be determined that the lockup OFF state is present before the engine rotational speed NE decreases to the return rotational speed Nrtlu. Therefore, before the engine rotation speed NE decreases to the return rotation speed Nrtlu, the return rotation speed can be reliably changed to the second return rotation speed Nrtluoff, and the fuel injection restart timing can be surely advanced.

  Further, the second return rotation speed Nrtluoff is changed so as to be higher as the engine coolant temperature Thw is lower. Accordingly, the second return rotational speed Nrtluoff is changed to a higher rotational speed as the instability of the combustion state is higher. Therefore, the return rotational speed after change (second return rotational speed Nrtluoff) can be changed according to the degree of instability of the combustion state of the air-fuel mixture, and the above action can be obtained appropriately.

  Incidentally, FIG. 10 shows an example in which the lockup is released when the engine speed NE is maintained at the target speed NEp. In addition, even when the lockup is released in the middle of the fuel cut being started and the engine rotational speed NE is reduced to the target speed NEp (between time t11 and time t12 in FIG. 10), the return rotational speed is The return rotational speed Nrtlu at the time of lockup ON is changed to the second return rotational speed Nrtluoff. In this case, if the engine speed NE at the time when the return rotational speed is changed is equal to or lower than the second return rotational speed Nrtluoff, the fuel cut is immediately stopped and fuel injection is resumed. On the other hand, when the engine rotational speed NE at the time when the return rotational speed is changed exceeds the second return rotational speed Nrtluoff, the fuel cut is performed when the engine rotational speed NE decreases to the second return rotational speed Nrtluoff. It is stopped and fuel injection is resumed. In any of these cases, the return rotational speed is changed from the return rotational speed Nrtlu at the time of lock-up ON to the second return rotational speed Nrtluoff, so that the fuel is earlier than when the return rotational speed is not changed in this way. The injection is resumed. Accordingly, even when the lockup is released in the middle of the fuel cut being started and the engine speed NE is reduced to the target speed NEp, the lockup is not performed when the engine speed NE is maintained at the target speed NEp. The same effect as when it is released can be obtained.

According to this embodiment described above, the following effects can be obtained.
(1) The gear ratio of the CVT 12 so that the engine rotational speed NE during the fuel cut is maintained at a constant speed (target speed NEp) that is near the return rotational speed Nrtlu and higher than the return rotational speed Nrtlu. To control. The engine rotational speed NE and the return rotational speed Nrtlu during the fuel cut are changed to higher rotational speeds as the degree of instability in the combustion state of the air-fuel mixture of the internal combustion engine 10 increases. Therefore, the engine speed NE immediately after the fuel cut is stopped and the fuel injection is restarted increases as the combustion state of the air-fuel mixture becomes unstable, and the engine speed NE immediately after the fuel injection is restarted is the engine speed NE. The time required to decrease to the stall becomes longer as the combustion state of the air-fuel mixture becomes unstable. Accordingly, it is possible to appropriately secure a time until sufficient engine output is generated after the fuel injection is restarted. As a result, the combustion state of the air-fuel mixture becomes unstable when returning from the fuel cut. It is possible to suppress the occurrence of engine stall that may occur at any time.

  (2) When the vehicle speed decreases, the engine speed NE also decreases through the CVT 12. Here, if the transmission ratio of the CVT 12 is increased, the rotational speed of the input shaft 12a of the CVT 12 can be increased with respect to the output shaft 12b of the CVT 12 connected to the drive wheel 13, and the CVT 12 is connected to the input shaft 12a. The rotational speed of the output shaft 10a of the internal combustion engine 10, that is, the engine rotational speed NE can be increased.

  Therefore, the gear ratio of the CVT 12 is increased as the vehicle speed decreases, so that the engine rotation speed NE during fuel cut is a speed near the return rotation speed Nrtlu and higher than the return rotation speed Nrtlu. Will be able to keep up with the speed.

  (3) The combustion state of the air-fuel mixture tends to become unstable as the engine temperature is lower. Therefore, the engine water temperature Thw, which is a parameter correlated with the engine temperature, is detected, and the target speed NEp and the return rotational speed Nrtlu of the engine speed NE during the fuel cut are set based on the detection result. Therefore, it becomes possible to appropriately set the target speed NEp and the return rotational speed Nrtlu of the engine speed NE during fuel cut according to the instability of the combustion state of the air-fuel mixture.

  (4) Control the operation state of the lockup clutch mechanism 14 so that the output shaft 10a of the internal combustion engine 10 and the input shaft 12a of the CVT 12 are disconnected when the vehicle speed SPD becomes equal to or lower than the lockup release speed H1. Like to do. If the connection between the output shaft 10a and the input shaft 12a is released during the fuel cut in this way, the engine rotational speed NE decreases and becomes lower than the return rotational speed Nrtlu, so that fuel injection is resumed. The Further, when the fuel injection is restarted, the connection between the output shaft 10a of the internal combustion engine 10 and the input shaft 12a of the CVT 12 is released, so that the load of the vehicle drive system on the internal combustion engine 10 is very small. The return from the fuel cut is made promptly.

  Accordingly, even when the engine speed NE during the fuel cut is maintained at a constant speed that is near the return speed Nrtlu and higher than the return speed Nrtlu, the fuel cut is surely stopped. In addition, it is possible to quickly return from the fuel cut.

  (5) When the lock-up ON signal is output so that the operating state of the lock-up clutch mechanism 14 is in the connected state, it is determined whether or not the actual operating state is in the connected state.

  When it is determined that the actual operating state is not in the connected state based on the determination result, the return rotational speed is changed from the return rotational speed Nrtlu at the time of lockup ON to the second return rotational speed Nrtluoff. I have to. The second return rotational speed Nrtluoff is higher than the engine rotational speed NE (target speed NEp) during the fuel cut that is maintained at a constant speed, and the instability of the combustion state of the air-fuel mixture is high. It is changed so that the rotation speed becomes higher as occasion demands.

  Therefore, if it is determined that the lockup clutch mechanism 14 is in an operating state different from the control command value, the engine rotational speed NE at that time becomes a rotational speed equal to or lower than the second return rotational speed Nrtluoff. The cut is stopped and fuel injection is resumed. Therefore, fuel injection is resumed before the engine speed NE decreases to the return speed Nrtlu before the change, and the engine speed NE is higher than when the return speed is not changed. Fuel injection is resumed. Therefore, even if the amount of decrease in the engine speed NE after the fuel injection is resumed increases, the occurrence of engine stall can be suppressed. Further, the second return rotation speed Nrtluoff is changed so that the higher the instability of the combustion state, the higher the rotation speed becomes. Therefore, the second return rotational speed Nrtluoff can be changed according to the degree of instability of the combustion state of the air-fuel mixture, and the above action can be obtained appropriately.

In addition, embodiment mentioned above can also be implemented with the following forms which changed this suitably.
The internal combustion engine 10 and the CVT 12 may be connected via an electromagnetic clutch instead of being connected via the torque converter 11 with the lockup clutch mechanism 14. In the case of an electromagnetic clutch, its operation is electrically controlled, so that responsiveness is improved with respect to a control command value for controlling the connection state between the internal combustion engine 10 and the CVT 12.

  -In the target rotational speed calculation map, when the engine water temperature Thw is in the region of the predetermined value T or more, the constant minimum value A is set as the target rotational speed Nint. In this way, the target rotational speed Nint is constant. It does not have to be a value of. For example, the relationship between the target rotation speed Nint and the engine water temperature Thw may be set so that the target rotation speed Nint increases as the engine water temperature Thw decreases in the entire region of the engine water temperature Thw.

  In the return rotation speed calculation map, when the engine water temperature Thw is in the region of the predetermined value T or more, a fixed minimum value B is set as the return rotation speed Nrtlu, and a fixed minimum value C is set as the second return rotation speed Nrtluoff. However, the return rotational speed may not be set to a constant value in this way. For example, in the entire region of the engine water temperature Thw, the relationship between the return rotation speed and the engine water temperature Thw may be set so that the return rotation speed Nrtlu and the second return rotation speed Nrtluoff increase as the engine water temperature Thw decreases.

  Although the target rotation speed Nint, the return rotation speed Nrtlu, and the second return rotation speed Nrtluoff are calculated based on the map, they may be calculated in other manners. For example, it may be calculated using a function formula. The target rotational speed Nint is set based on the engine water temperature Thw, and the return rotational speed is obtained by subtracting a predetermined value from the target rotational speed Nint or multiplying by a predetermined value (a value between 1 and 0). Nrtlu may be calculated. Similarly, the target rotation speed Nint is set based on the engine coolant temperature Thw, and a second value is added by adding a predetermined value to the target rotation speed Nint or multiplying the target rotation speed Nint by a predetermined value (a value greater than 1). The return rotational speed Nrtluoff may be calculated.

  When changing the return rotation speed from the return rotation speed Nrtlu at the time of lockup ON to the second return rotation speed Nrtluoff, at the time when the fuel cut is stopped (time t14 in FIG. 10), or the actual operation state It is desirable to switch the lockup signal from the ON state to the OFF state, for example, when it is determined that is in the lockup OFF state (time t13 in FIG. 10). In this case, since the lockup clutch mechanism 14 that has been in the lockup OFF state due to disturbance or the like attempts to return to the lockup ON state again after the fuel injection is resumed, the lockup OFF signal is output. The actual operating state of the lockup clutch mechanism 14 is set to the lockup OFF state. Therefore, when fuel injection is performed by stopping the fuel cut, the load on the vehicle drive system with respect to the internal combustion engine 10 is very small, so that the recovery from the fuel cut, that is, the recovery of the engine speed is quick. And will be made surely.

  A parameter different from the engine water temperature Thw may be used as a parameter correlated with the engine temperature. For example, since the oil temperature of the engine, the elapsed time from the start of the engine, and the like are correlated with the engine temperature, these parameters may be used.

  -The instability of the combustion state of the air-fuel mixture is detected based on a parameter that correlates with the engine temperature. In addition, for example, since the combustion state becomes unstable even when the intake air temperature is low, the degree of instability of the combustion state may be detected based on the intake air temperature.

  By the way, the combustion state becomes unstable even when the intake air temperature is low. Therefore, the intake air temperature may be detected, and the target rotation speed Nint, the return rotation speed Nrtlu, and the second return rotation speed Nrtluoff may be set to values according to the instability of the combustion state based on the detection result. .

The target rotation speed setting process and the return rotation speed setting process may be executed only during the fuel cut.
In the state where the engine speed NE has not reached the target speed NEp during fuel cut, control is performed so that the gear ratio of the CVT 12 becomes the minimum gear ratio. In addition, for example, control may be performed so that the transmission ratio of the CVT 12 is larger than the minimum transmission ratio.

  In the target rotational speed setting process shown in FIG. 4, various required rotational speeds are calculated (S12), and the highest rotational speed is selected from the target rotational speed Nint and various required rotational speeds (S13). ). In addition, the process of step S12 and step S13 may be abbreviate | omitted and only the target rotational speed Nint based on the engine water temperature Thw may be calculated.

  In the return rotational speed setting process shown in FIG. 6, the second return rotational speed Nrtluoff is calculated. However, the processes of steps S21 and S24 are omitted, and the second return rotational speed Nrtluoff is calculated. It may not be performed. Even in this case, the effects described in the above (1) to (4) can be obtained.

  In the above embodiment, the transmission ratio control of the CVT 12 is performed in order to maintain the engine speed NE at the target speed NEp. Here, when the vehicle speed greatly decreases, it becomes impossible to maintain the engine speed NE at the target speed NEp even with the maximum gear ratio of the CVT 12. Therefore, the engine speed NE decreases as the vehicle speed decreases. Accordingly, the engine rotational speed NE becomes lower than the return rotational speed Nrtlu. Therefore, in the above embodiment, the lockup is released by the output of the lockup OFF signal and the engine speed NE is decreased, so that the engine speed NE is lower than the return speed Nrtlu. It is not necessary that the engine rotational speed NE be lower than the return rotational speed Nrtlu by canceling up.

  By setting the target rotational speed Nint for the rotational speed of the input shaft 12a of the CVT 12, and controlling the gear ratio so that the actual rotational speed of the input shaft 12a (input shaft rotational speed Nin) becomes the target rotational speed Nint. The engine rotational speed NE is maintained at the target speed NEp in the vicinity of the return rotational speed Nrtlu. That is, the engine rotational speed NE is indirectly maintained at the target speed NEp through maintaining the rotational speed of the input shaft 12a at the target rotational speed Nint. Here, as described above, in the lock-up ON state, the output shaft 10a of the internal combustion engine 10 and the input shaft 12a of the CVT 12 have the same rotational speed. Accordingly, the setting of the target rotational speed Nint may be omitted, and the gear ratio control of the CVT 12 may be directly performed based on the target speed NEp.

  Whether or not the actual operating state of the lockup clutch mechanism 14 is in the lockup ON state is determined based on the deviation between the engine rotational speed NE and the input shaft rotational speed Nin of the input shaft 12a. You may make it determine in this other aspect. For example, the lock-up clutch mechanism 14 may be provided with a sensor or a switch for detecting the operating state, and the actual operating state may be determined based on the detection result of the sensor or the switch.

  When determining the actual lockup state based on the deviation between the engine rotation speed NE and the input shaft rotation speed Nin of the input shaft 12a, until the deviation reaches a predetermined value after the lockup state changes. It takes some time between. Therefore, only the time (from time t13 to time t14 shown in FIG. 10) until the return rotational speed is changed to the second return rotational speed Nrtluoff after the actual lockup state is turned off. It takes time in between. In this regard, if the operation state of the lockup clutch mechanism 14 can be detected earlier by the sensor, the switch, or the like, the time required for the determination as described above can be further shortened. Therefore, it is possible to shorten the time from when the actual lockup state is turned off to when the return rotational speed is changed to the second return rotational speed Nrtluoff, and in a state where the engine rotational speed NE is higher, Specifically, fuel injection can be resumed in a state closer to the target speed NEp.

-Although the case where belt type CVT12 was applied as an example of a continuously variable transmission was mentioned as an example, other continuously variable transmissions may be used. For example, a toroidal continuously variable transmission may be used.
Although the case where the lock-up clutch mechanism 14 is applied as an example of the connection mechanism that switches the output shaft 10a of the internal combustion engine 10 and the input shaft 12a of the CVT 12 between the connected state and the non-connected state has been described, other mechanisms may be used. . For example, the electromagnetic clutch mentioned above may be used.

  DESCRIPTION OF SYMBOLS 10 ... Internal combustion engine, 10a ... Output shaft, 11 ... Torque converter, 12 ... Continuously variable transmission (CVT), 12a ... Input shaft, 12b ... Output shaft, 13 ... Drive wheel, 14 ... Lock-up clutch mechanism, 15 ... Output Pulley, 16 ... input pulley, 17 ... belt, 18 ... speed ratio control means, changing means, and electronic control unit (ECU) as second changing means, 19 ... vehicle speed sensor, 20 ... accelerator sensor, 21 ... input shaft Rotational speed sensor, 22 ... shift position sensor, 23 ... travel mode selection switch, 24 ... water temperature sensor, 25 ... engine rotational speed sensor, 26 ... intake pressure sensor.

Claims (7)

And applied to a vehicle including an internal combustion engine in which fuel cut is stopped when the engine rotational speed during fuel cut is lower than a return rotational speed and a continuously variable transmission connected to the internal combustion engine, and A control device for controlling the continuously variable transmission,
A speed ratio for controlling the speed ratio of the continuously variable transmission so that the engine speed during the fuel cut is maintained at a constant speed near the return speed and higher than the return speed. Control means;
Changing means for changing the engine rotational speed during the fuel cut and the return rotational speed to a higher rotational speed as the degree of instability in the combustion state of the air-fuel mixture of the internal combustion engine is higher. Vehicle control device. The vehicle control device according to claim 1, wherein the speed ratio control unit increases the speed ratio as the vehicle speed decreases. The change means detects a parameter correlated with the engine temperature, and sets the engine rotation speed and the return rotation speed during execution of the fuel cut to values according to the degree of instability based on the detection result. Or the control apparatus of the vehicle of 2. The said change means detects the engine coolant temperature as the parameter, and sets the engine rotational speed and the return rotational speed during the fuel cut to a higher rotational speed as the coolant temperature is lower. Vehicle control device. A connection mechanism is provided between the output shaft of the internal combustion engine and the input shaft of the continuously variable transmission to switch the output shaft and the input shaft between a connected state and a disconnected state, and the vehicle speed is a predetermined value. The vehicle control device according to any one of claims 1 to 4, wherein an operation state of the connection mechanism is controlled so that the output shaft and the input shaft are disconnected when the following conditions are satisfied. Determination means for determining whether or not the actual operation state is a connection state when a control command value is output so that the operation state of the connection mechanism is a connection state;
When it is determined by the determination means that the actual operating state is not in the connected state, the return rotational speed is maintained at a constant speed and is higher than the engine rotational speed during execution of the fuel cut. The vehicle control device according to claim 5, further comprising: a second changing unit configured to change the rotational speed so that the higher the instability of the combustion state is, the higher the rotational speed is. The vehicle control device according to claim 5 or 6, wherein a torque converter is connected to an input shaft of the continuously variable transmission, and the connection mechanism is a lock-up clutch mechanism provided in the torque converter.

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