JP2011102553A - Control device of internal combustion engine - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To prevent driveability from being deteriorated due to an effect that an engine 10 is automatically stopped while a vehicle is driven although a driver has no intention to stop the vehicle during idle-stop control that permits the automatic stop of the engine 10 even while the vehicle is driven. <P>SOLUTION: A condition for stopping the engine 10 is set as a condition that a vehicle braking force which is a resultant of a force working in the direction to accelerate the vehicle and a force working in the direction to decelerate the vehicle, and a force that is positive in the direction to decelerate the vehicle should be greater than a first threshold value. The vehicle braking force is calculated on the basis of the generated torque of the engine 10, traveling resistance working on the vehicle, and a braking force of a brake. When the calculated vehicle braking force is determined to be larger than the first threshold value, processing for automatically stopping the engine 10 is performed. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a control device for an internal combustion engine including control means for performing a process of automatically stopping the internal combustion engine while a vehicle is traveling.

  Conventionally, as can be seen in, for example, Patent Document 1 below, when a predetermined stop condition is satisfied during idling of the internal combustion engine, the internal combustion engine is automatically stopped, and then when the predetermined restart condition is satisfied, the internal combustion engine is restarted. So-called idle stop control is known. According to the idle stop control, it is possible to obtain the fuel consumption reduction effect of the internal combustion engine.

  Here, as can be seen in Patent Document 2 below, a technique for permitting automatic stop of an internal combustion engine even when a vehicle is running is also known. As a result, the operating range in which the internal combustion engine is automatically stopped can be expanded, and the fuel consumption reduction effect can be further improved.

Japanese Patent No. 4096748 Japanese Patent No. 4237132

  By the way, in the technology that permits the automatic stop of the internal combustion engine even while the vehicle is traveling, the internal combustion engine may be automatically stopped while the vehicle is traveling, even though the driver does not intend to stop. In this case, the drivability may be lowered, for example, the vehicle traveling desired by the driver cannot be appropriately realized.

  The present invention has been made to solve the above-described problems, and an object thereof is to provide a control device for an internal combustion engine that can suitably suppress a decrease in drivability.

  Hereinafter, means for solving the above-described problems and the operation and effects thereof will be described.

  According to a first aspect of the present invention, there is provided a control device for an internal combustion engine comprising control means for performing a process of automatically stopping the internal combustion engine during traveling of the vehicle, wherein the force acting in the direction of accelerating the vehicle and the braking force of the brake are Vehicle braking force calculating means for calculating a vehicle braking force that is a resultant force with a force acting in a direction for decelerating the vehicle and that is positive in a direction for decelerating the vehicle, and the calculated vehicle control Prediction means for predicting whether or not the vehicle stops based on power and the traveling speed of the vehicle, and the control means automatically stops based on the prediction that the vehicle will stop It is characterized by performing processing.

  When stopping a running vehicle or adjusting the running speed of a vehicle by the driver's brake operation, the vehicle deceleration is usually between the start of the braking operation and the stop or speed adjustment. The braking force of the brake is adjusted by the brake operation so that the deceleration that the driver intends according to the traveling speed of the vehicle is achieved. Here, adjusting the braking force of the brake so as to achieve the deceleration intended by the driver means that the vehicle braking force is adjusted. For this reason, when the driver intends to stop the vehicle, the transition of the vehicle braking force from the start of the braking operation until the vehicle stops, for example, when the brake operation is performed to adjust the traveling speed of the vehicle, the driver is willing to stop. This is different from the transition of the vehicle braking force from when the brake operation is started until the speed adjustment is completed. Therefore, in the above invention, it is predicted whether or not the vehicle will stop based on the traveling speed of the vehicle and the vehicle braking force while the vehicle is traveling. Then, based on the fact that the vehicle is predicted to stop, a process for automatically stopping the internal combustion engine is performed. As a result, the internal combustion engine can be automatically stopped reflecting the driver's intention to stop, and as a result, a decrease in drivability can be suitably suppressed.

  According to a second aspect of the present invention, in the first aspect of the invention, the vehicle braking force calculating means includes a braking force of the brake, a running resistance acting on the vehicle including a gradient resistance acting on the vehicle, and the internal combustion engine. The vehicle braking force is calculated based on at least one of the torque generated by the engine.

  In the above invention, even if the generated torque or running resistance of the internal combustion engine changes due to changes in the running state of the vehicle or the operating state of the internal combustion engine, the vehicle braking force is calculated on the basis of the above parameters. A decrease in prediction accuracy can be suppressed. Thereby, the fall of the grasp accuracy of a driver's stop intention can be controlled suitably.

  According to a third aspect of the present invention, in the first or second aspect of the present invention, the first setting means for variably setting a first threshold value related to the vehicle braking force according to the traveling speed of the vehicle, and the vehicle braking force. And a second setting means for setting a second threshold value that is smaller than the first threshold value, and the predicting means has the vehicle braking force greater than the first threshold value. And the control means predicts that the vehicle will stop, and the control means is based on the fact that the vehicle braking force is less than or equal to the second threshold value during the automatic stop of the internal combustion engine. A process for restarting the internal combustion engine is performed.

  In the above invention, the vehicle is predicted to stop based on the vehicle braking force becoming greater than the first threshold value, and the internal combustion engine is automatically stopped. Here, the vehicle braking force may fluctuate due to the adjustment of the vehicle deceleration caused by the driver's braking operation or the like. In this case, for example, if the threshold value for performing the process of restarting the internal combustion engine is set to the same value as the first threshold value, the fuel consumption reduction effect or the Drivability may be reduced. In this regard, in the above invention, the first threshold value and the second threshold value for performing the process of automatically stopping and restarting the internal combustion engine are made different as described above. For this reason, even when the vehicle braking force varies due to the adjustment of the vehicle deceleration, it is possible to suppress the occurrence of a situation in which the automatic stop and restart of the internal combustion engine are frequently repeated. Thereby, the reduction in fuel consumption and drivability can be suitably suppressed.

  According to a fourth aspect of the present invention, in the third aspect of the invention, the execution of the restarting process is restricted for a predetermined time based on the fact that the vehicle is determined to be immediately before the internal combustion engine is automatically stopped. It is further characterized by further comprising a restart restriction means for imposing.

  Immediately before the vehicle stops, the brake operation may be performed so as to reduce the braking force of the brake operation for the purpose of alleviating the shock at the time of stopping caused by the brake operation. In this case, although the driver intends to stop, the internal combustion engine is restarted due to a decrease in the vehicle braking force, which may reduce drivability. In this regard, in the above-described invention, a predetermined time restriction is imposed on the execution of the process of restarting the internal combustion engine based on the determination that the vehicle is just before stopping. As a result, restart of the internal combustion engine unintended by the driver can be avoided, and as a result, a decrease in drivability can be suitably suppressed.

  The invention according to claim 5 is the invention according to claim 4, wherein the restart restriction means imposes a restriction on execution of the restarting process by reducing the second threshold value for the predetermined time. Features.

  In the above invention, it is possible to appropriately impose restrictions on the execution of the process for restarting the internal combustion engine.

  The invention according to claim 6 is the process according to any one of claims 3 to 5, wherein after the internal combustion engine is restarted, the automatic stop is performed until the traveling speed of the vehicle becomes equal to or higher than a predetermined value. It further comprises automatic stop restriction means for imposing a restriction on the execution of.

  Under circumstances where the driver tries to drive the vehicle at a low speed, the acceleration and deceleration of the vehicle may be repeated, for example, by the driver's accelerator operation and brake operation being alternately performed. In this case, the internal combustion engine may be automatically stopped despite the driver's intention to run the vehicle at a low speed due to the fluctuation of the vehicle braking force. In this regard, in the above-described invention, after the internal combustion engine is restarted, a restriction is imposed on the execution of the process of automatically stopping the internal combustion engine until the traveling speed of the vehicle becomes a predetermined speed or more. Thereby, although the driver intends to drive the vehicle at a low speed, it is possible to avoid the internal combustion engine from being automatically stopped, and accordingly, it is possible to favorably avoid a decrease in drivability.

  According to a seventh aspect of the invention, in the sixth aspect of the invention, the automatic stop restricting means increases the first threshold value until the traveling speed of the vehicle becomes equal to or higher than a predetermined value, so that the automatic stop processing is performed. It is characterized by imposing restrictions on the execution of.

  In the said invention, a restriction | limiting can be imposed appropriately to execution of the process which stops an internal combustion engine automatically.

The system block diagram concerning one Embodiment. The figure which shows the outline | summary of the stop condition of the engine concerning the embodiment. The figure which shows the outline | summary of the restart conditions of the engine concerning the embodiment. The flowchart which shows the idle stop control process concerning the embodiment. The figure which shows the outline | summary of the automatic stop restriction | limiting process concerning the embodiment. The time chart which shows the outline | summary of the restart restrictions process concerning the embodiment.

  Hereinafter, an embodiment of a control device for an internal combustion engine according to the present invention will be described with reference to the drawings.

  FIG. 1 shows a system configuration according to the present embodiment.

  Each cylinder of the illustrated engine 10 is provided with a fuel injection valve 12 for supplying fuel to the combustion chamber of the engine 10. The energy generated by the combustion of the mixture of the supplied fuel and intake air is taken out as the rotational force (engine generated torque) of the output shaft (crankshaft 14) of the engine 10. A crank angle sensor 16 that detects a rotation angle of the crankshaft 14 is provided in the vicinity of the crankshaft 14.

  A starter 18 is connected to the crankshaft 14. The starter 18 is started by turning on a starter switch (not shown), and applies initial rotation (cranking) to the crankshaft 14 to start the engine 10.

  The rotational force of the crankshaft 14 is transmitted to the transmission 20. In the transmission 20, the rotational speed of an input rotary shaft (not shown) to which the rotational force of the crankshaft 14 is transmitted is converted into the rotational speed of the output rotary shaft 22 according to the gear ratio corresponding to the shift position.

  The rotational force of the output rotary shaft 22 is transmitted to the drive wheels 26 via the differential gear 24. Here, the rotation speed of the output rotation shaft 22 is converted into the rotation speed of the drive wheel 26 according to the transmission gear ratio (difference ratio) of the differential gear 24. A wheel speed sensor 28 for detecting the traveling speed of the vehicle is provided in the vicinity of each of the drive wheels 26 and a steering wheel (wheel) (not shown).

  In the vicinity of each wheel, a brake actuator 32 is provided that applies a braking force to each wheel according to the amount of depression of the brake pedal 30. Specifically, as the amount of depression of the brake pedal 30 increases, the hydraulic pressure (brake hydraulic pressure) of the hydraulic system of the brake increases, so that the braking force (braking braking force) applied to the drive wheels 26 and the like by the brake actuator 32 is increased. growing. The brake hydraulic system is provided with a brake hydraulic pressure sensor 34 that detects brake hydraulic pressure (for example, master cylinder pressure).

  The brake pedal 30 is provided with a brake sensor 36 that detects the amount of depression of the pedal. On the other hand, the accelerator pedal 38 is provided with an accelerator sensor 40 that detects the amount of depression of the pedal (accelerator operation amount). Output signals from these various sensors, the shift position sensor 42 that detects the shift position, the crank angle sensor 16, the wheel speed sensor 28, the brake hydraulic pressure sensor 34, and the like are input to an electronic control unit (hereinafter, ECU 44).

  The ECU 44 is mainly composed of a microcomputer including a known CPU, ROM, RAM, and the like. The ECU 44 executes various control programs stored in the ROM based on the input signals from the sensors, thereby performing fuel injection control by the fuel injection valve 12, start control by the starter 18, and the like.

  In particular, the ECU 44 performs a process of automatically stopping the engine 10 when a predetermined stop condition is satisfied (automatic stop process), and a process of restarting the engine 10 when the predetermined restart condition is satisfied (restart process). So-called idle stop control is performed. Thereby, the fuel consumption reduction effect of the engine 10 can be obtained. In this embodiment, in order to further improve the fuel consumption reduction effect by the idle stop control, the execution of the automatic stop process is permitted even when the vehicle is traveling. Here, it is required to set the stop condition so that the driver's intention to stop can be grasped while the vehicle is running. Parameters for grasping the intention to stop include the traveling speed of the vehicle and the deceleration of the vehicle. That is, when stopping the running vehicle by adjusting the brake pedal 30 of the driver or adjusting the traveling speed of the vehicle, the stop or speed adjustment is usually completed from the start of the depression operation of the brake pedal 30. The braking force of the brake is adjusted by the stepping operation so that the deceleration of the vehicle in the period up to is the deceleration intended by the driver according to the traveling speed of the vehicle. Here, the transition of the deceleration of the vehicle due to the depression operation of the brake pedal 30 is different between the case where the driver does not intend to stop and the case where the driver intends to stop. For this reason, the traveling speed of the vehicle and the deceleration of the vehicle can be used as parameters for grasping the driver's intention to stop.

  By the way, the deceleration of the vehicle is normally calculated based on a differential operation value of an output of a sensor that detects the traveling speed of the vehicle such as the wheel speed sensor 28. However, if the vehicle deceleration calculated based on the differential calculation value is used as the parameter, the driver's intention to stop may not be properly grasped. That is, noise is usually mixed in the sensor output, and this noise can be amplified by differentiating the sensor output. In this case, there is a possibility that the vehicle deceleration cannot be appropriately calculated due to the influence of the amplified noise. For this reason, when the vehicle deceleration is used as a parameter for grasping the driver's intention to stop, the drivability is reduced because the engine 10 is automatically stopped while the vehicle is traveling even though the driver does not intend to stop. There is a risk. In particular, the sensor output for detecting the traveling speed of the vehicle is likely to be mixed with noise caused by vibrations that the vehicle receives from the road surface as the vehicle travels. For this reason, there is a possibility that noise amplification due to differential operation of the sensor output becomes significant. As a countermeasure for such a problem, it is conceivable to perform a filter process on the sensor output in order to remove noise mixed in the sensor output. However, in this case, since the filtered sensor output has a response delay, there is a possibility that the deceleration of the vehicle cannot be calculated appropriately depending on the sensor output with the response delay.

In order to solve such a problem, the present inventor paid attention to the force applied in the traveling direction of the vehicle as a parameter capable of grasping the driver's intention to stop while the vehicle is traveling. Here, the force applied in the traveling direction of the vehicle is the resultant force of the force acting in the direction of accelerating the vehicle and the force acting in the direction of decelerating the vehicle including the braking force of the brake, and this resultant force decelerates the vehicle. The case of acting in the direction is positive, and this is called the vehicle braking force FC. Hereinafter, a method for setting the stop condition and the restart condition based on the vehicle braking force FC will be described in detail.
<1. Stop condition setting method>
In the present embodiment, the vehicle braking force FC is defined by the following equation (1).

FC = Fbk + Fv−Feg (1)
(A) Engine driving force Feg: The engine driving force Feg is the engine-generated torque transmitted to the drive wheels 26. Specifically, the engine driving force Feg is calculated based on a value obtained by multiplying the engine generated torque by the speed ratio and the differential ratio of the transmission 20, and the engine generated torque is calculated from the torque generated by the combustion of the air-fuel mixture. The torque corresponding to the loss (friction loss) caused by the friction of the sliding portion (piston or the like) inside the engine 10 or the pumping loss is subtracted. Here, the engine driving force Feg increases as the required torque for the engine 10 increases as the accelerator operation amount increases. The speed ratio may be calculated based on the output value of the shift position sensor 42. Further, the engine generated torque may be calculated from the accelerator operation amount based on the output value of the accelerator sensor 40 and the engine rotation speed based on the output value of the crank angle sensor 16.

  (B) Brake braking force Fbk: The brake braking force Fbk may be calculated from the brake hydraulic pressure based on the output value of the brake hydraulic pressure sensor 34.

  (C) Running resistance Fv acting on the vehicle: The running resistance Fv is an added value of the rolling resistance of the wheel, the air resistance acting on the vehicle, and the gradient resistance. Here, the rolling resistance of the wheel increases as the weight of the vehicle increases, and the air resistance increases as the traveling speed of the vehicle increases. In addition, the gradient resistance increases as the gradient of the road surface on which the vehicle travels increases toward the uphill side. In this embodiment, the rolling resistance of the wheel is calculated based on a predetermined rolling resistance coefficient corresponding to a road surface condition that is assumed to be high in the traveling frequency of the vehicle and the weight of the vehicle, and the air resistance is calculated based on the wheel speed. This is calculated based on the traveling speed of the vehicle calculated from the output value of the sensor 28. The gradient resistance is calculated based on the road surface gradient and the weight of the vehicle. Here, for example, when the vehicle is assumed to travel on a flat road (the road surface gradient is 0), the vehicle surface speed is assumed to change from the current engine driving force Feg and the braking force Fbk of the brake. (Speed) and an actual acceleration / deceleration may be used for estimation. Here, in view of the fact that the ratio of the air resistance to the vehicle braking force FC is small because the traveling speed range of the vehicle in which the idle stop control is performed is low, the air resistance is ignored when calculating the assumed acceleration / deceleration. May be. Here, the actual acceleration / deceleration may be calculated by filtering the differential operation value of the output value of the wheel speed sensor 28. This is based on the fact that it is assumed that there are few situations in which the road gradient changes suddenly while the vehicle is running, and that the response delay of the filtered sensor output has little influence on the estimation accuracy of the road gradient. Is.

  The vehicle braking force FC calculated in the above mode is mixed with the sensor output in comparison with the vehicle braking force calculated by multiplying the vehicle deceleration calculated as a differential operation value of the sensor output by the vehicle weight. The effect of noise is significantly reduced. That is, the vehicle braking force FC can be used as a parameter for accurately grasping the driver's intention to stop.

  FIG. 2 shows an example of the vehicle braking force FC. The broken line in the figure indicates the vehicle braking force FC when the braking force Fbk of the brake is constant. Here, since the air resistance increases as the traveling speed V of the vehicle increases, the vehicle braking force FC increases as the traveling speed V of the vehicle increases. The vehicle braking force FC is changed not only by the air resistance but also when the gradient resistance changes due to a change in the running state of the vehicle or the engine driving force Feg changes due to a change in the operating state of the engine 10. However, under the situation where the running state of the vehicle and the driving state of the engine 10 change, the braking force Fbk of the brake is adjusted so that the deceleration of the vehicle becomes the deceleration intended by the driver.

Here, in the present embodiment, in view of the fact that the deceleration of the vehicle is different between the case where the driver intends to stop and the case where the driver intends to stop as described above, the transition of the vehicle braking force FC when the driver intends to stop (see FIG. The first threshold value Sth (> 0, diagram), which is a threshold value for discriminating the transition of the vehicle braking force FC when there is no intention to stop (illustrated by a dotted line). The middle solid line) is variably set according to the traveling speed V of the vehicle. The first threshold value Sth can be set by measuring the transition of the vehicle braking force FC when there is a driver's intention to stop and when there is no intention to stop. Then, the stop condition of the engine 10 is set as a condition that the vehicle braking force FC is larger than the first threshold value Sth. Accordingly, it is possible to predict whether or not the vehicle will stop based on the vehicle braking force FC calculated each time and the first threshold value Sth variably set according to the traveling speed V of each vehicle. Become. Then, the automatic stop process is performed based on the prediction that the vehicle will stop. Note that there is a travel speed range in which the vehicle braking force FC is substantially constant regardless of the travel speed V of the vehicle when the driver intends to stop the vehicle indicated by the one-dot chain line in FIG. This limits the braking force Fbk of the brake so that the inertial force acting on the driver when the vehicle is decelerated does not increase transiently, rather than increasing the braking force Fbk of the brake so as to stop the vehicle quickly. This is because the driver performs the brake operation in preference to the operation. In the present embodiment, when the traveling speed V of the vehicle exceeds a predetermined speed V1 (> 0), the automatic stop process and restart process of the engine 10 are prohibited.
<2. Method for setting restart conditions>
In the present embodiment, as indicated by the one-dot chain line in FIG. 3, a second threshold value Rth (Rth <Sth) that is smaller than the first threshold value Sth is set. The restart condition of the engine 10 is a condition that the vehicle braking force FC is equal to or less than the second threshold value Rth. This is a condition for avoiding a situation where the fuel consumption reduction effect and drivability are reduced. That is, when the driver has an intention to accelerate the vehicle (acceleration intention), usually, the depression operation of the brake pedal 30 is released or the depression operation of the accelerator pedal 38 is performed, so that the vehicle braking force FC is reduced. Become. When the vehicle braking force FC becomes smaller than the second threshold value Rth, the engine 10 is restarted by the restart process. On the other hand, in the period from when the depression operation of the brake pedal 30 is started until the vehicle stops, the vehicle deceleration is slightly adjusted by the depression operation of the accelerator pedal 38 or the brake pedal 30 of the driver. The braking force FC may fluctuate. In this case, for example, if the second threshold value Rth is set to the same value as the first threshold value Sth, the fuel consumption reduction effect and drivability may decrease due to frequent repeated automatic stop and restart of the engine 10. There is. For this reason, the situation where a fuel consumption reduction effect and drivability fall is avoided by setting restart conditions as mentioned above and giving a hysteresis to the threshold value for performing an automatic stop process and a restart process.

  FIG. 4 shows a procedure of idle stop control processing according to the present embodiment. This process is repeatedly executed by the ECU 44 at a predetermined cycle, for example.

  In this series of processes, first, in step S10, the vehicle traveling speed V, the accelerator operation amount ACCP, the engine rotational speed NE, and the brake hydraulic pressure BP are acquired.

  In the subsequent step S12, the vehicle braking force FC is calculated based on the acquired parameter. Here, the vehicle braking force FC may be calculated based on the above equation (1). The engine driving force Feg during the automatic stop of the engine 10 may be calculated as, for example, an engine driving force Feg assumed during idling operation, triggered by the accelerator operation amount ACCP becoming greater than or equal to a predetermined value.

  In a succeeding step S14, it is determined whether or not the engine 10 is in operation. If it is determined in step S14 that the engine 10 is in operation, it is determined in step S16 whether or not the restart flag F is set to “1”. Here, the restart flag F is set to “1” for a predetermined period after the engine 10 is restarted. In the subsequent step S18, it is determined whether or not the traveling speed V of the vehicle is equal to or higher than a first specified speed α (0 <α <V1). The processes in steps S16 and S18 are for determining whether or not the automatic stop restriction process is executed. Here, the automatic stop restriction process will be described with reference to FIG. This process is a process of increasing the first threshold value Sth until the vehicle traveling speed V becomes equal to or higher than the first specified speed α after the engine 10 is restarted, and suppresses a decrease in drivability. belongs to. That is, under a situation where the driver tries to drive the vehicle at a low speed, the accelerator pedal 38 and the brake pedal 30 are alternately depressed, whereby the acceleration and deceleration of the vehicle may be repeated. In this case, as illustrated by γ in the figure, the vehicle braking force FC fluctuates, and automatic drivability and restart of the engine 10 are repeated, which may reduce drivability. As a countermeasure for such a problem, it is conceivable to set the second threshold value Rth sufficiently smaller than the first threshold value Sth. However, in this case, even when the driver depresses the accelerator pedal 38 to accelerate the vehicle, the time until the vehicle braking force FC reaches the second threshold value Rth is increased. The time until the restart condition is satisfied can be lengthened. In this case, the engine 10 cannot be restarted quickly reflecting the driver's acceleration intention, and drivability may be reduced. For this reason, after the engine 10 is restarted, the first threshold value Sth is set to be greater than the value during normal idle stop control (the dotted line in the figure) until the vehicle traveling speed V becomes equal to or higher than the first specified speed α. By setting a large value at the time of the automatic stop restriction process (solid line in the figure), it is possible to realize low-speed driving of the vehicle and quick restart of the engine 10 reflecting the driver's acceleration intention, thereby improving drivability. Avoid degradation.

  Returning to the description of FIG. 4, when it is determined in step S <b> 16 that the restart flag F is set to “1” and it is determined in step S <b> 18 that the vehicle traveling speed V is less than the first specified speed α. Therefore, it is determined that the situation where the driver tries to drive the vehicle at a low speed is continued, and in step S20, the first threshold value Sth is set to a value at the time of the automatic stop restriction process according to the traveling speed V of the vehicle. . Here, the first threshold value Sth is set to a larger value as the traveling speed V of the vehicle is higher.

  On the other hand, if an affirmative determination is made in step S18, it is determined that the situation for running at a low speed has ended, and a restart flag F is set to “0” in step S22.

  When a negative determination is made in step S16 or when the process of step S22 is completed, the first threshold value Sth is set to a value at the time of normal idle stop control according to the traveling speed V of the vehicle in step S24. . The setting process of the first threshold value Sth at the time of the automatic stop restriction process or the normal idle stop control is specifically performed by inputting the vehicle traveling speed V and storing the storage means of the ECU 44 (an EEPROM which is a nonvolatile memory). The first threshold value Sth is variably set using a map or a mathematical expression in which the first threshold value Sth and the traveling speed V of the vehicle stored in advance are associated with each other.

  After completion of the processes of steps S20 and S24, the process proceeds to step S26, and it is determined whether or not a stop condition for the engine 10 is satisfied. This process is a process for predicting whether or not the vehicle will stop. Here, the stop condition is a condition that the vehicle braking force FC becomes larger than the first threshold value Sth as described above.

  If it is determined in step S26 that the engine 10 stop condition is satisfied, the engine 10 is automatically stopped in step S28. Here, the automatic stop process is a process of stopping the engine 10 by stopping the fuel injection from the fuel injection valve 12.

  When the process of step S28 is completed, or when it is determined in step S14 that the engine 10 is stopped, a restart restriction process is performed in steps S30 and S32. Here, the restart restriction process will be described with reference to FIG. Specifically, FIG. 6A shows the transition of the vehicle running speed V, and FIG. 6B shows the transition of the second threshold Rth. The restart restriction process is a process for reducing the second threshold Rth by a predetermined time (t1 to t2) when it is determined that the vehicle is immediately before stopping, and is for suppressing a decrease in drivability. That is, immediately before the vehicle stops, the amount of depression of the brake pedal 30 may be reduced so as to reduce the braking force Fbk of the brake for the purpose of alleviating the shock at the time of stopping caused by the depression operation of the brake pedal 30. In this case, although the driver intends to stop, the restart condition is satisfied when the vehicle braking force FC is reduced, and the drivability may be reduced when the engine 10 is restarted. For this reason, the restart restriction process makes it difficult to satisfy the restart condition for a predetermined time immediately before the vehicle stops, thereby avoiding restart of the engine 10 unintended by the driver and suppressing a decrease in drivability.

  Returning to the description of FIG. 4, in step S <b> 30, it is determined whether or not the traveling speed V of the vehicle is higher than 0 and equal to or lower than the second specified speed β (0 <β <α). This process is a process for determining whether or not the vehicle is just before stopping.

  If it is determined in step S30 that the vehicle is just before stopping, the process proceeds to step S32, and the second threshold Rth is decreased for a predetermined time after an affirmative determination is made in step S30.

  When the process of step S32 is completed or when a negative determination is made in step S30, the process proceeds to step S34 to determine whether or not a restart condition for the engine 10 is satisfied. Here, as described above, the restart condition is a condition that the vehicle braking force FC is equal to or less than the second threshold value Rth.

  When it is determined in step S34 that the restart condition of the engine 10 is satisfied, the process proceeds to step S36 and the restart process of the engine 10 is performed. Here, the restart process is a process of performing cranking by starting the starter 18 and restarting the engine 10 that is automatically stopped by operating the fuel injection valve 12. Then, after confirming that the engine 10 has started, the restart flag F is set to “1”.

  If a negative determination is made in steps S26 and S34, or if the process of step S36 is completed, this series of processes is temporarily terminated.

  According to the embodiment described in detail above, the following effects can be obtained.

  (1) The vehicle braking force FC was calculated based on the engine driving force Feg, the wheel rolling resistance, the air resistance acting on the vehicle, the gradient resistance, and the braking force Fbk of the brake. The vehicle braking force FC is significantly influenced by noise mixed in the sensor output as compared with the vehicle braking force calculated by multiplying the vehicle deceleration calculated as the differential operation value of the sensor output by the vehicle weight. It will be small. For this reason, the situation where the grasping | ascertaining precision of the driver's stop intention resulting from noise falls can be avoided suitably. Furthermore, according to the vehicle braking force FC, it is possible to favorably maintain the accuracy of grasping the driver's intention to stop even when the running state of the vehicle or the driving state of the engine 10 changes.

  (2) The stop condition of the engine 10 is a condition that the vehicle braking force FC is larger than the first threshold value Sth that is variably set according to the traveling speed V of the vehicle. As a result, the driver's intention to stop can be reflected, and the engine 10 can be automatically stopped while the vehicle is running, so that a decrease in drivability can be suitably suppressed.

  (3) The restart condition of the engine 10 is a condition that the vehicle braking force FC is equal to or less than the second threshold value Rth, which is a value smaller than the first threshold value Sth. Thereby, generation | occurrence | production of the situation where the automatic stop and restart of the engine 10 are repeated frequently can be suppressed, and the fuel consumption reduction effect and the fall of drivability can be suppressed suitably.

  (4) After restarting the engine 10, a process (automatic stop restriction process) for increasing the first threshold value Sth is performed until the traveling speed V of the vehicle becomes equal to or higher than the first specified speed α. As a result, it is possible to realize low-speed traveling of the vehicle and quick restart of the engine 10 reflecting the driver's intention to accelerate, and it is possible to favorably avoid a decrease in drivability.

  (5) When it is determined that the vehicle is immediately before stopping while the engine 10 is automatically stopped, a process (restart restriction process) is performed to reduce the second threshold Rth for a predetermined time after it is determined that the vehicle is immediately before stopping. It was. As a result, restart of the engine 10 not intended by the driver can be avoided, and as a result, a decrease in drivability can be suitably suppressed.

(Other embodiments)
The above embodiment may be modified as follows.

  The method for estimating the road surface gradient is not limited to the method exemplified in the above embodiment, and may be estimated by the following method. That is, for example, the vehicle weight is perpendicular to the road surface based on the detection value of a means (for example, a vehicle height sensor) that detects a load in the direction perpendicular to the road surface of the suspension mechanically connected to each of the wheels or information correlated therewith. The load of the directional component is calculated, and the absolute value of the road surface gradient is estimated as an inverse cosine value obtained by dividing the vehicle weight by this load. When it is assumed that the vehicle travels on a flat road, the acceleration / deceleration of the vehicle assumed from the current engine driving force Feg and the braking force Fbk of the brake and the differential operation value of the output value of the wheel speed sensor 28 are filtered. The road surface gradient is estimated by determining the sign of the absolute value based on the deviation from the actual acceleration / deceleration calculated in this way. This is based on the fact that the load of the vertical component becomes smaller with respect to the vehicle weight as the road surface gradient increases. Thereby, when the vehicle is accelerated or decelerated, the influence exerted on the calculation of the road surface gradient by the inertial force acting on the vehicle can be minimized. Further, for example, when an acceleration sensor that detects vehicle acceleration in a direction perpendicular to the traveling direction of the vehicle and the road surface is provided, an inverse cosine of a value obtained by dividing the vehicle acceleration in the traveling direction by the detected vehicle acceleration in the vertical direction. The road surface gradient may be estimated as a value.

  -Stop conditions of the engine 10 are not limited to those exemplified in the above embodiment. For example, a condition that the storage amount of the in-vehicle storage battery that supplies power to the in-vehicle device is greater than or equal to a predetermined value may be added to the stop condition.

  The method for calculating the vehicle braking force FC is not limited to that exemplified in the above embodiment. For example, air resistance may be excluded from the calculation of the vehicle braking force FC. This is based on the fact that the ratio of the air resistance to the vehicle braking force FC is reduced in view of the fact that the running speed range of the vehicle in which the idle stop control is performed is a low speed range. Further, for example, wheel rolling resistance, gradient resistance, and engine driving force Feg may be excluded from the calculation of the vehicle braking force FC. Further, for example, in the calculation process of the vehicle braking force FC, a process of selectively removing a force or resistance that is a small proportion of the vehicle braking force FC according to the traveling state of the vehicle or the road surface gradient may be performed.

  The method for setting the second threshold value Rth is not limited to the one exemplified in the above embodiment. For example, the second threshold Rth may be the same as the first threshold Sth.

  In the above embodiment, the second threshold value Rth is set as the value in the direction (negative) for accelerating the vehicle only in the low speed range of the vehicle traveling speed V. However, the present invention is not limited to this. For example, the second threshold value Rth may be set as a positive value smaller than the first threshold value Sth in the travel speed range (0 ≦ V ≦ V1) in which the idle stop control is performed. In this case, the second threshold value Rth may be set so that the restart process is executed when the depression operation of the brake pedal 30 is released. In this case, the second threshold value Rth that is reduced by the restart restriction process may be maintained at a positive value.

  The automatic stop restriction process is not limited to that exemplified in the above embodiment. For example, the automatic stop process may be prohibited until the traveling speed V of the vehicle reaches the first specified speed α.

  The restart restriction process is not limited to the process exemplified in the above embodiment. For example, the restart process may be prohibited for a predetermined time after it is determined that the vehicle is just before stopping.

  DESCRIPTION OF SYMBOLS 10 ... Engine, 18 ... Starter, 20 ... Transmission, 24 ... Differential gear, 28 ... Wheel speed sensor, 30 ... Brake pedal, 44 ... ECU (one Embodiment of the control apparatus of an internal combustion engine).

Claims (7)

In a control device for an internal combustion engine comprising control means for performing a process of automatically stopping the internal combustion engine while the vehicle is running,
Vehicle control that is a resultant force of a force acting in the direction of accelerating the vehicle and a force acting in a direction of decelerating the vehicle including a braking force of a brake, and a force that makes the direction of decelerating the vehicle positive. Vehicle braking force calculation means for calculating power;
Prediction means for predicting whether or not the vehicle stops based on the calculated vehicle braking force and the traveling speed of the vehicle;
The control device of the internal combustion engine, wherein the control means performs the automatic stop processing based on the prediction that the vehicle is stopped.   The vehicle braking force calculation means is based on the braking force of the brake and at least one of a running resistance acting on the vehicle including a gradient resistance acting on the vehicle and a torque generated by the internal combustion engine. The control apparatus for an internal combustion engine according to claim 1, wherein: First setting means for variably setting a first threshold value related to the vehicle braking force according to the traveling speed of the vehicle;
A second setting means for setting a second threshold value that is a threshold value related to the vehicle braking force and that is smaller than the first threshold value;
The predicting means predicts that the vehicle stops based on the vehicle braking force becoming larger than the first threshold value.
The said control means performs the process which restarts the said internal combustion engine based on the said vehicle braking force becoming below the said 2nd threshold value during the automatic stop of the said internal combustion engine. Item 3. The control device for an internal combustion engine according to Item 1 or 2.   The apparatus further comprises restart restriction means for imposing a predetermined time restriction on the execution of the restarting process based on the fact that the vehicle is determined to be immediately before the internal combustion engine is automatically stopped. 3. The control device for an internal combustion engine according to 3.   5. The control apparatus for an internal combustion engine according to claim 4, wherein the restart restriction means imposes a restriction on execution of the restarting process by reducing the second threshold value for the predetermined time.   6. The automatic stop restricting means for imposing a restriction on execution of the automatic stop processing until the traveling speed of the vehicle becomes equal to or higher than a predetermined speed after the internal combustion engine is restarted. The control apparatus for an internal combustion engine according to any one of the preceding claims.   7. The automatic stop restriction means imposes a restriction on the execution of the automatic stop process by increasing the first threshold until a traveling speed of the vehicle becomes equal to or higher than a predetermined value. Control device for internal combustion engine.

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