JP5834608B2 - Automatic engine stop control device for vehicle - Google Patents

Description

  The present invention relates to an engine automatic stop control device that automatically stops an engine during traveling.

  As a vehicle engine automatic stop control device, a technique described in Patent Document 1 is disclosed. According to this publication, when the brake pedal operation amount is depressed more than the idling stop threshold while the vehicle is stopped, the engine is stopped. Even when the vehicle is running, the engine is stopped when the brake pedal operation amount is depressed more than a coast stop threshold value that is smaller than the idling stop threshold value, thereby improving fuel efficiency.

Japanese Patent No. 4374805

Here, if the engine is stopped carelessly, there is a concern about the influence on the control of the antilock brake system.

The present invention has been made paying attention to the above problems, and an object thereof is to provide a vehicle engine automatic stop control device capable of suppressing the influence on the control of the antilock brake system .

In order to achieve the above object, in the vehicle automatic engine stop control device of the present invention, when the driver operates the brake pedal more than a predetermined threshold during traveling, the engine is stopped before the operation of the antilock brake system. A predetermined threshold is set so as not to stop the engine .

Therefore, the above-mentioned influence can be suppressed by not stopping the engine before the operation of the antilock brake system .

1 is a system diagram illustrating a configuration of an automatic engine stop control device for a vehicle according to a first embodiment. 3 is a flowchart illustrating an engine automatic stop / restart control process according to the first embodiment. 6 is a flowchart illustrating a coast stop permission lower limit setting process according to the first embodiment. 3 is a gradient correction amount map according to the first embodiment. 2 is a vehicle weight map according to the first embodiment. 1 is a road surface μ map of Example 1. 2 is a vehicle speed map according to the first embodiment. It is a figure showing the relationship between the idling stop permission lower limit of Example 1, and a coast stop permission lower limit. It is a time chart showing the effect | action of the setting process of the coast stop permission lower limit at the time of the uphill driving | running | working of Example 1. FIG. It is a time chart showing the effect | action of the setting process of the coast stop permission lower limit at the time of the downhill driving | running | working of Example 1. FIG. It is a time chart showing the effect | action of the setting process of the coast stop permission lower limit at the time of the vehicle weight increasing at the time of the uphill driving | running | working of Example 1. FIG. It is a time chart showing the effect | action of the setting process of a coast stop permission lower limit when the vehicle weight increases at the time of the downhill driving | running | working of Example 1. FIG. 6 is a time chart illustrating a setting process of a coast stop permission lower limit value when traveling on a low μ road according to the first embodiment. It is a time chart showing the effect | action of the setting process of the coast stop permission lower limit at the time of correct | amending according to a vehicle speed at the time of the uphill driving | running | working of Example 1. FIG. It is a time chart showing the effect | action of the setting process of the coast stop permission lower limit at the time of correct | amending according to a vehicle speed at the time of the downhill driving | running | working of Example 1. FIG. 10 is a gradient correction amount map according to the second embodiment.

FIG. 1 is a system diagram illustrating a configuration of an automatic engine stop control device for a vehicle according to a first embodiment. The rotational driving force output from the engine 1 is input to the belt-type continuously variable transmission 3 via the torque converter 2, and is transmitted to the drive wheels 4 after being shifted by a desired gear ratio.
The engine 1 that is an internal combustion engine has a starter 1a that starts the engine. Specifically, a starter motor is provided, engine cranking is performed based on an engine start command, fuel is injected, and the starter motor is stopped when the engine 1 can rotate independently.

On the output side of the engine 1, there is provided a torque converter 2 having a lock-up clutch that performs torque amplification at a low vehicle speed and prohibits relative rotation at a predetermined vehicle speed (for example, about 14 km / h) or higher. A belt type continuously variable transmission 3 is connected to the output side of the torque converter 2.
The belt-type continuously variable transmission 3 includes a starting clutch, a primary pulley and a secondary pulley, and a belt stretched over these pulleys, and achieves a desired gear ratio by changing the pulley groove width by hydraulic control. . The belt-type continuously variable transmission 3 is provided with an oil pump driven by the engine 1, and when the engine is operated, the oil pump is used as a hydraulic source to supply the converter pressure of the torque converter 2 and the lockup clutch pressure. Also, the pulley pressure and clutch engagement pressure of the belt type continuously variable transmission 3 are supplied.

  Further, the belt-type continuously variable transmission 3 is provided with an electric oil pump 3a. When oil pressure cannot be supplied by the oil pump due to automatic engine stop, the electric oil pump 3a is activated and the required oil pressure is supplied to each actuator. It is configured to be able to supply. Therefore, even when the engine is stopped, a desired gear ratio can be achieved and the clutch engagement pressure can be maintained.

  The operating state of the engine 1 is controlled by the engine control unit 10. The engine control unit 10 includes a brake signal from a brake switch 11 that outputs an ON signal by a driver's brake pedal operation, an accelerator signal from an accelerator pedal opening sensor 12 that detects a driver's accelerator pedal operation amount, A brake operation amount signal (master cylinder pressure) from the master cylinder pressure sensor 13 that detects the master cylinder pressure generated based on the brake pedal operation amount, and a wheel speed (from the wheel speed) from the wheel speed sensor 14 provided for each wheel. When detecting the vehicle speed, it is synonymous with the vehicle speed signal), the outside air temperature signal from the outside air temperature sensor 15 that detects the outside air temperature, the CVT state signal from the CVT control unit 20 described later, the engine water temperature, the crank angle, Input signals such as engine speed. The engine control unit 10 starts or automatically stops the engine 1 based on the various signals. In place of the master cylinder pressure sensor 13, a brake pedal stroke amount or a brake pedal depression force sensor or a wheel cylinder pressure sensor is used to detect the brake pedal operation amount. The operation intention may be detected and is not particularly limited.

  Further, in the engine control unit 10, a road surface gradient detecting unit 10a that detects a road surface gradient while the vehicle is traveling, a vehicle weight detecting unit 10b that detects the vehicle weight, and a road surface that estimates the road surface μ based on the outside air temperature. μ detector 10c (road surface friction coefficient detecting means). In the road surface gradient detection unit 10a, for example, the road surface gradient is determined based on the difference between the torque transmitted to the driving wheels, the actual vehicle acceleration detected from the wheel speed and the acceleration acting on the vehicle detected by the acceleration sensor. Is estimated. The vehicle weight detection unit 10b detects a suspension stroke or the like, and detects the vehicle weight based on how the vehicle sinks when the vehicle is stopped. Further, the road surface μ detection unit 10c detects the outside air temperature, and determines that the possibility of a frozen road surface is high and the road surface friction coefficient is small when the outside air temperature is 4 ° C. or less, for example. For example, when an ABS controller or the like that implements an anti-lock brake system (hereinafter referred to as ABS) that avoids locking of a wheel is performing an estimation calculation process of a road surface friction coefficient, these are not limited to the outside air temperature. The road surface μ information estimated in another controller may be used. The vehicle of the first embodiment is provided with an ABS controller, and when wheel lock tendency is detected, the wheel cylinder pressure is reduced, held and increased, and a cornering force is secured while avoiding wheel lock. . Note that a vehicle behavior stability control system or the like that causes the yaw rate of the vehicle to act in a stable direction by controlling wheel cylinder pressure, driving force control, or the like may be provided, and is not particularly limited.

  The CVT control unit 20 transmits / receives signals of the engine operating state and the CVT state to / from the engine control unit 10 and controls the gear ratio of the belt type continuously variable transmission 3 based on these signals. Specifically, when the travel range is selected, the start clutch is engaged, and the gear ratio is determined from the gear ratio map based on the accelerator pedal opening and the vehicle speed, and each pulley hydraulic pressure is controlled. Further, when the vehicle speed is lower than the predetermined vehicle speed, the lockup clutch is released, and when the vehicle speed is higher than the predetermined vehicle speed, the lockup clutch is engaged, and the engine 1 and the belt type continuously variable transmission 3 are brought into a direct connection state. Furthermore, when the engine is automatically stopped while the travel range is selected, the electric oil pump 3a is operated to ensure the necessary hydraulic pressure.

(Engine automatic stop control process)
Next, the engine automatic stop control process will be described. The automatic engine stop control device for a vehicle according to the first embodiment performs so-called idling stop control for stopping engine idling when a predetermined condition is satisfied when the vehicle is stopped. In addition, about idling stop control, since a known structure should just be implemented suitably, detailed description is abbreviate | omitted. In addition, even when the vehicle is running, when it is determined that the vehicle is decelerating and there is a high possibility that the vehicle will stop and shift to idling stop control, coast stop control for stopping the engine 1 is performed.

  In an idling stop vehicle that does not perform normal coast stop control, when the driver is coasting without operating the accelerator pedal (including a state in which the brake pedal is operated) The fuel injection is stopped, and the engine speed is maintained via the lock-up clutch by the coast torque transmitted from the drive wheel 4. However, when the vehicle is decelerated to a predetermined vehicle speed, the lockup clutch is released, so that the engine 1 stops unless fuel is injected. Therefore, fuel injection is resumed at the timing when the lockup clutch is released, and the engine self-sustaining rotation is maintained. Thereafter, after determining whether or not various conditions such as the vehicle is completely stopped and the brake pedal is sufficiently depressed, engine idling is stopped.

  Here, in the process of restarting fuel injection once from the running state where fuel injection was stopped and stopping the engine again, fuel consumption can be improved if the fuel at the time of restarting fuel injection can be further suppressed. It becomes. Therefore, during coasting where a predetermined condition is satisfied, coast stop control is performed so that the engine is stopped (fuel injection is not performed) without restarting fuel injection, and normal idling is performed after the vehicle stops. It was decided to move on to stop control.

  As one condition for performing the coast stop control, the brake pedal operation amount of the driver is within a predetermined range (that is, between the upper limit value and the lower limit value). The reason for setting the brake pedal operation amount as one of the conditions is that the start or end of the coast stop control should be performed based on the driver's braking intention. That is, when the brake pedal is strongly depressed, it is when the vehicle is decelerating rapidly, and it is considered that the time from the predetermined vehicle speed to the vehicle stop is short. At this time, it is necessary to shift the speed ratio of the belt type continuously variable transmission 3 to the lowest side when the vehicle is stopped. However, for this purpose, there is a limitation due to the speed change principle of the belt type continuously variable transmission 3, and the drive wheels 4 need to rotate. Therefore, in order to change speed quickly while the drive wheels 4 are rotating, it is necessary to secure the discharge amount of the oil pump, and engine stop is not preferable. It is also conceivable that ABS control or the like is performed to avoid wheel lock during sudden deceleration. At this time, in the ABS control logic, when increasing or decreasing the brake fluid pressure acting on the wheel, various gains are set in consideration of torque input from the engine side, and if the engine is stopped carelessly, There is also concern about the impact on these controls. Therefore, the coast stop permission upper limit value in consideration of these is set.

  On the other hand, at the time of slow deceleration where the brake pedal is gently depressed, there are a case where the vehicle is stopped as it is and a case where the brake pedal is released again and the vehicle restarts. For example, when driving in a traffic jam, it is conceivable to operate the brake pedal gently to continue the driving state. In this case, if the engine is stopped carelessly, the engine stop and restart are repeated, which may give the driver a feeling of strangeness. In addition, when the engine is restarted after the brake pedal is gently depressed after the engine is stopped, engine torque may be output to the drive wheels, giving a feeling of popping out. Therefore, the coast stop permission lower limit value in consideration of these is set.

[Engine automatic stop / restart control process]
FIG. 2 is a flowchart showing the engine automatic stop / restart control process according to the first embodiment. Note that other conditions that do not appear in this flowchart may be additionally set.
In step S101, the vehicle speed, master cylinder pressure, reference idling stop permission upper / lower limit values and coast stop permission upper / lower limit values are read. The vehicle speed may be an average value of wheel speeds detected by the wheel speed sensor 14 or an average value of driven wheel speeds, and is not particularly limited. The idling stop permission upper limit value and the coast stop permission upper limit value are values set in advance in the system, and are fixed values in the case of the first embodiment. The idling stop permission lower limit is set to a value larger than the coast stop permission lower limit. In this state, the idling stop is performed when the vehicle is stopped. When the engine is started in this state, the creep torque is output, but when the braking force by the brake is low, the vehicle is inadvertently caused by the creep torque. This is because it may move. In addition, the coast stop state is during vehicle deceleration (that is, during travel). In this state, the aim is to improve the fuel consumption by stopping the engine as much as possible, and the engine is restarted before the vehicle is stopped. However, it is because it is difficult for the driver to feel a sense of popping out due to creep torque while driving.

  In step S102, it is determined whether or not the vehicle speed is equal to or less than a predetermined value VSP1 representing the vehicle stop state. If it is equal to or less than VSP1, the process proceeds to step S103. Otherwise, the process proceeds to step S104. Here, the predetermined value VSP1 may be zero, may be an extremely low vehicle speed range of about 1 to 2 km / h, and may be a value that can be determined to be substantially a vehicle stop.

  In step S103, an idling stop permission upper limit value / lower limit value, which is an upper limit or a lower limit of the range of the brake pedal operation amount that permits idling stop control, is set. In the case of the first embodiment, the idling stop permission upper limit value is a fixed value, so the value read in step S101 is used as it is. On the other hand, the idling stop permission lower limit value is corrected. FIG. 4 is a gradient correction amount setting map of the first embodiment. A gradient correction amount ΔP1 is read according to the detected road surface gradient, and is added to the lower limit value, thereby setting the corrected idling stop permission lower limit value. This map is shared with the coast stop permission lower limit correction process, and the idling stop permission lower limit and the coast stop permission lower limit are offset in parallel by correction, and details will be described later. Moreover, you may correct | amend further based on the vehicle weight mentioned later.

  In step S104, a coast stop permission upper limit value / lower limit value, which is an upper limit or a lower limit of the range of the brake pedal operation amount permitting the coast stop control, is set. In the case of Example 1, since the coast stop permission upper limit is a fixed value, the value read in step S101 is used as it is. On the other hand, the coast stop permission lower limit value is corrected. The coast stop permission lower limit setting process will be described later.

  In step S105, it is determined whether or not the master cylinder pressure is within the range of the upper limit value and the lower limit value. If it is determined that the master cylinder pressure is within the range, the process proceeds to step S106 and the engine is automatically stopped. On the other hand, when it is determined that it is out of the range, the process proceeds to step S107 to determine whether or not the engine is stopped. If the engine is in a stopped state, the process proceeds to step S108 and the engine is restarted. If the engine is in an operating state, the engine operating state is continued as it is.

(Coast stop permission lower limit setting process)
Next, the setting process of the coast stop permission lower limit value mentioned above is demonstrated. FIG. 3 is a flowchart showing a coast stop permission lower limit setting process according to the first embodiment.
In step S201, the road gradient is detected by the road gradient detector 10a.
In step S202, the vehicle weight is detected by the vehicle weight detection unit 10b.
In step S203, the road surface μ is detected by the road surface μ detector 10c.

  In step S204, a gradient correction amount ΔP1 is calculated based on the gradient correction amount map of FIG. 4 (corresponding to a threshold setting unit). FIG. 4 is a gradient correction amount map of the first embodiment. Specifically, the gradient correction amount ΔP1 is increased as the absolute value of the detected gradient increases. For example, if the coast stop is permitted even at a low master cylinder pressure on an ascending slope, the engine restart timing will be delayed if the driver intends to continue running near the vehicle stop and loosens the brake pedal. This is because the vehicle may roll back due to the upward slope.

  On the other hand, if the coast stop is permitted even at a low master cylinder pressure on a downward slope, the engine restart timing will be delayed if the driver intends to continue running near the vehicle stop and loosens the brake pedal. This is because, since the brake braking force is also low, the vehicle is likely to move, and because it is a downward slope, there is a possibility of giving a feeling of popping out due to creep torque when the engine is restarted.

  In addition, ΔP1 is set larger in the case of the upward gradient than in the case of the downward gradient. This is because it is important to avoid movement in a direction unintended by the driver, that is, rollback. In other words, the coast stop is actively performed on the down slope to improve fuel efficiency, and the coast stop is performed on the up slope while avoiding the rollback.

  In step S205, a vehicle weight correction amount ΔP2 is calculated based on the vehicle weight map of FIG. Specifically, the vehicle weight correction amount ΔP2 is increased as the detected vehicle weight is heavier. For example, if the coast stop is permitted even on a flat road even with a low master cylinder pressure, the engine restart timing will be delayed if the driver intends to continue running near the vehicle stop and loosens the brake pedal. This is because, since the vehicle weight is large, the inertia of the vehicle is large, and the responsiveness when starting the vehicle may not be ensured. On the uphill, if the vehicle weight is heavy, the risk of rolling back increases. On the downhill, the heavy vehicle weight increases the risk of unintended start.

  In step S206, the road surface μ correction amount ΔP3 is calculated based on the road surface μ map of FIG. Specifically, the road surface μ correction amount ΔP3 is increased as the detected road surface μ is lower. In particular, in a region where the road surface is likely to freeze (for example, in a state where the outside air temperature is lower than 4 ° C.), the road surface μ may be decreased at a stretch. Therefore, the road surface μ correction amount ΔP3 is increased at a stretch. As a result, when there is a high possibility that ABS control or the like will be performed due to a decrease in road surface μ, the coast stop permission lower limit value is high even if the driver depresses the brake pedal strongly, so that coast stop is substantially prohibited. It is.

  In step S207, a vehicle speed correction amount ΔP4 is calculated based on the vehicle speed map of FIG. Specifically, the vehicle speed correction amount ΔP4 is increased as the detected vehicle speed is lower. In other words, when the vehicle speed is high to some extent, the coastal stop is allowed as much as possible to improve fuel efficiency, and when the vehicle is close to the stop state, the driver's intention to re-start can be detected quickly so Avoids rollback and suppresses popping feeling on downhills.

  In step S208, a final coast stop permission lower limit is calculated based on the gradient correction amount ΔP1, the vehicle weight correction amount ΔP2, the road surface μ correction amount ΔP3, and the vehicle speed correction amount ΔP4. Specifically, these correction amounts may be added or may be multiplied by setting an appropriate gain. FIG. 8 is a diagram illustrating the relationship between the idling stop permission lower limit value and the coast stop permission lower limit value of the first embodiment. The idling stop permission lower limit value is set to be larger as the gradient increases, and when it is set according to the vehicle weight, the idling stop permission lower limit value is set to be larger as the vehicle weight increases. On the other hand, the coast stop permission lower limit value is smaller than the idling stop permission lower limit value, and is set larger as the gradient increases, is set larger as the vehicle weight increases, and is set larger as the vehicle speed is lower.

[Effects of climbing slope]
Next, the operation based on the control process will be described. FIG. 9 is a time chart illustrating the operation of the coast stop permission lower limit value setting process during uphill traveling according to the first embodiment. In FIG. 9, the dotted line represents the state before correction according to the gradient, and the solid line represents the state after correction according to the gradient. The precondition of the traveling state at the first time in the time chart is that the driver releases his / her foot from the accelerator pedal while traveling on an uphill road surface and is in a coasting traveling state.

(Without gradient correction)
When the driver starts to depress the brake pedal at time t1, deceleration is started.
When the master cylinder pressure exceeds the coast stop permission lower limit before correction at time t11, the engine speed starts to decrease toward the stop because coast stop is started.
At time t3, the driver starts to depress the brake pedal. At time t44, when the master cylinder pressure sufficiently decreases and falls below the coast stop permission lower limit before correction, the coast stop is terminated and the engine is restarted. At this time, since the master cylinder pressure is too low, the force to stop the vehicle becomes insufficient and rollback occurs. In addition, since the engine restart timing is late, the timing at which torque is transmitted to the drive wheels is also delayed.

(With slope correction)
When the driver starts to depress the brake pedal at time t1, deceleration is started.
When the master cylinder pressure exceeds the corrected coast stop permission lower limit value at time t2, the engine speed starts to decrease toward the stop because the coast stop is started.
At time t3, the driver starts to depress the brake pedal. Then, at time t4, when the master cylinder pressure slightly decreases, the corrected coast stop permission lower limit value is exceeded, the coast stop is terminated, and the engine is restarted. At this time, since the master cylinder pressure does not decrease too much, a force for stopping the vehicle can be secured, and rollback can be avoided. In addition, since the engine restart timing is early, the timing at which torque is transmitted to the drive wheels can also be advanced, and a traveling state according to the driver's intention can be achieved.

[Effects on downward slope]
FIG. 10 is a time chart illustrating the operation of the coast stop permission lower limit value setting process during downhill traveling according to the first embodiment. In FIG. 10, the dotted line represents the state before correction according to the gradient, and the solid line represents the state after correction according to the gradient. The precondition of the traveling state at the first time in the time chart is that the driver releases his / her foot from the accelerator pedal while traveling on a downhill road surface and is in a coasting traveling state.

(Without gradient correction)
When the driver starts to depress the brake pedal at time t1, deceleration is started.
When the master cylinder pressure exceeds the coast stop permission lower limit before correction at time t11, the engine speed starts to decrease toward the stop because coast stop is started.
At time t3, the driver starts to depress the brake pedal. At time t44, when the master cylinder pressure sufficiently decreases and falls below the coast stop permission lower limit before correction, the coast stop is terminated and the engine is restarted. At this time, since the master cylinder pressure is too low, the force to stop the vehicle becomes insufficient, and a feeling of popping out accompanying engine restart occurs.

(With slope correction)
When the driver starts to depress the brake pedal at time t1, deceleration is started.
When the master cylinder pressure exceeds the corrected coast stop permission lower limit value at time t2, the engine speed starts to decrease toward the stop because the coast stop is started.
At time t3, the driver starts to depress the brake pedal. Then, at time t4, when the master cylinder pressure slightly decreases, the corrected coast stop permission lower limit value is exceeded, the coast stop is terminated, and the engine is restarted. At this time, since the master cylinder pressure has not decreased too much, it is possible to secure a force for stopping the vehicle, and to avoid a feeling of popping out accompanying engine restart.

[Effect when vehicle weight increases on an ascending slope]
FIG. 11 is a time chart illustrating the operation of the coast stop permission lower limit setting process when the vehicle weight increases during uphill traveling according to the first embodiment. In FIG. 11, a dotted line represents a state before correction according to the gradient and the vehicle weight, and a solid line represents a state after correction according to the gradient and the vehicle weight. The precondition that is the running state at the first time of this time chart is that the driver releases the accelerator pedal and is on the coast running state while traveling on an uphill road surface with a large number of passengers and on-board luggage. To do.

(Without gradient correction)
When the driver starts to depress the brake pedal at time t1, deceleration is started.
When the master cylinder pressure exceeds the coast stop permission lower limit before correction at time t11, the engine speed starts to decrease toward the stop because coast stop is started.
At time t3, the driver starts to depress the brake pedal. At time t44, when the master cylinder pressure sufficiently decreases and falls below the coast stop permission lower limit before correction, the coast stop is terminated and the engine is restarted. At this time, since the master cylinder pressure is too low, the force for stopping the vehicle is insufficient, and particularly the weight of the vehicle is increased, so that the force to move backward becomes stronger and rollback occurs. In addition, since the engine restart timing is late, the timing at which torque is transmitted to the drive wheels is also delayed.

(With slope correction)
When the driver starts to depress the brake pedal at time t1, deceleration is started.
When the master cylinder pressure exceeds the corrected coast stop permission lower limit value at time t2, the engine speed starts to decrease toward the stop because the coast stop is started.
At time t3, the driver starts to depress the brake pedal. Then, at time t4, when the master cylinder pressure slightly decreases, the corrected coast stop permission lower limit value is exceeded, the coast stop is terminated, and the engine is restarted. At this time, the master cylinder pressure has not decreased too much (that is, the coast stop permission lower limit value is set higher according to the vehicle weight), so that the force for stopping the vehicle can be secured and the vehicle weight is heavy. Even in cases, rollback can be avoided. In addition, since the engine restart timing is early, the timing at which torque is transmitted to the drive wheels can also be advanced, and the driver can achieve a traveling state as intended.

[Effects on downward slope]
FIG. 12 is a time chart showing the operation of the setting process of the coast stop permission lower limit value when the vehicle weight increases during downhill traveling of the first embodiment. In FIG. 12, a dotted line represents a state before correction according to the gradient and the vehicle weight, and a solid line represents a state after correction according to the gradient and the vehicle weight. The precondition that is the running state at the first time of this time chart is that the driver releases the accelerator pedal and is on the coast running state while traveling on a downhill road surface with a large number of passengers and vehicle-mounted luggage To do.

(Without gradient correction)
When the driver starts to depress the brake pedal at time t1, deceleration is started.
When the master cylinder pressure exceeds the coast stop permission lower limit before correction at time t11, the engine speed starts to decrease toward the stop because coast stop is started.
At time t3, the driver starts to depress the brake pedal. At time t44, when the master cylinder pressure sufficiently decreases and falls below the coast stop permission lower limit before correction, the coast stop is terminated and the engine is restarted. At this time, since the master cylinder pressure is too low, the force for stopping the vehicle is insufficient, and particularly the vehicle weight is increased, so that the force to move further forward becomes stronger and accompanying the engine restart. A feeling of popping out occurs.

(With slope correction)
When the driver starts to depress the brake pedal at time t1, deceleration is started.
When the master cylinder pressure exceeds the corrected coast stop permission lower limit value at time t2, the engine speed starts to decrease toward the stop because the coast stop is started.
At time t3, the driver starts to depress the brake pedal. Then, at time t4, when the master cylinder pressure slightly decreases, the corrected coast stop permission lower limit value is exceeded, the coast stop is terminated, and the engine is restarted. At this time, the master cylinder pressure has not decreased too much (that is, the coast stop permission lower limit value is set higher according to the vehicle weight), so that the force for stopping the vehicle can be secured and the vehicle weight is heavy. Even in this case, it is possible to avoid the feeling of popping out due to the engine restart.

[Operation on low μ roads]
FIG. 13 is a time chart showing the setting process of the coast stop permission lower limit value when traveling on a low μ road according to the first embodiment. In FIG. 13, a dotted line represents a state before correction according to the road surface μ, and a solid line represents a state after correction according to the road surface μ. The precondition that is the running state at the first time in the time chart is that the driver releases his / her foot from the accelerator pedal while running on a low μ road and is in a coasting running state.

(With no road surface μ correction)
When the driver starts to depress the brake pedal at time t1, deceleration is started.
When the master cylinder pressure exceeds the coast stop permission lower limit before correction at time t2, the engine speed starts to decrease toward the stop because coast stop is started. At this time, because the road surface is low μ, when the ABS control is started, the wheel cylinder pressure of the wheel which tends to be locked on the ABS control side is reduced, held and increased so that the optimum braking force and cornering force can be obtained. Control. At this time, since various control gains and the like are set on the ABS control side on the premise that torque is applied from the engine side, appropriate ABS control cannot be executed without the engine torque (for example, the wheel speed is reduced). As a result, the vehicle speed cannot be lowered sufficiently, resulting in a longer distance to the stop state, which is not preferable for safety.

  At time t3 after the engine is stopped, the driver starts to depress the brake pedal. When the master cylinder pressure falls below the pre-correction coast stop permission lower limit at time t31, the engine is restarted. At this time, because of the low μ road, a slip occurs between the drive wheels and the road surface due to torque fluctuations due to engine restart, and a stagnation state where the vehicle speed does not increase is caused because sufficient traction cannot be transmitted. Further, when the slip amount is large, there is a possibility that a traction control system or the like that suppresses the engine torque is activated, and the vehicle is still in a stagnation state. Then, after the brake pedal is completely released at time t5, the vehicle speed finally starts to be generated at time t6, and there is a concern that the responsiveness at the time of start-up due to engine restart may be reduced.

(With road surface μ correction)
When the driver starts to depress the brake pedal at time t1, deceleration is started.
Basically, the coast stop permission lower limit is corrected to a high value on low μ roads. In this case, the master cylinder pressure does not exceed the corrected coast stop permission lower limit, and coast stop is not performed. . At this time, because the road surface is low μ, when the ABS control is started, the wheel cylinder pressure of the wheel which tends to be locked on the ABS control side is reduced, held and increased so that the optimum braking force and cornering force can be obtained. Control. Since the ABS control side sets various control gains and the like on the premise that torque is applied from the engine side, the distance to the stop state does not become long, and the vehicle behavior can be stabilized. This is preferable for safety.

  In addition, since the engine idling state continues, when the driver starts to depress the brake pedal at time t3, the torque transmitted from the engine side starts to exceed the braking force smoothly at time t4. start. That is, it is possible to start with better responsiveness than in the case of no road surface μ correction.

[Effects of vehicle speed correction when climbing uphill]
FIG. 14 is a time chart showing the operation of the coast stop permission lower limit value setting process in the case of correction according to the vehicle speed during uphill traveling according to the first embodiment. In FIG. 14, the dotted line represents the state before correction according to the vehicle speed, and the solid line represents the state after correction according to the vehicle speed. The precondition of the traveling state at the first time in the time chart is that the driver releases his / her foot from the accelerator pedal while traveling on an uphill road surface and is in a coasting traveling state.

(Without gradient correction)
When the driver starts to depress the brake pedal at time t1, deceleration is started.
When the master cylinder pressure exceeds the coast stop permission lower limit before correction at time t22, the engine speed starts to decrease toward the stop because coast stop is started.
At time t3, the driver starts to depress the brake pedal. At time t44, when the master cylinder pressure sufficiently decreases and falls below the coast stop permission lower limit before correction, the coast stop is terminated and the engine is restarted. At this time, since the master cylinder pressure is too low, the force to stop the vehicle becomes insufficient and rollback occurs. In addition, since the engine restart timing is late, the timing at which torque is transmitted to the drive wheels is also delayed.

(With slope correction)
When the driver starts to depress the brake pedal at time t1, deceleration is started.
When the master cylinder pressure exceeds the corrected coast stop permission lower limit value at time t2, the engine speed starts to decrease toward the stop because the coast stop is started. At this time, since the vehicle speed correction amount is set to be small when the vehicle speed is high, the coast stop permission lower limit value is exceeded even at a relatively low master cylinder pressure, so coast stop can be started earlier and fuel economy can be improved. .
At time t3, the driver starts to depress the brake pedal. Then, at time t4, when the master cylinder pressure slightly decreases, the corrected coast stop permission lower limit value is exceeded, the coast stop is terminated, and the engine is restarted. At this time, the master cylinder pressure has not decreased too much (that is, the coast stop permission lower limit is set higher according to the vehicle speed), so that it is possible to secure a force for stopping the vehicle and avoid rollback. . In addition, since the engine restart timing is early, the timing at which torque is transmitted to the drive wheels can also be advanced, and the driver can achieve a traveling state as intended.

[Operation at the time of vehicle speed correction on a downward slope]
FIG. 15 is a time chart illustrating the operation of the coast stop permission lower limit value setting process when correction is made according to the vehicle speed during downhill traveling according to the first embodiment. In FIG. 15, the dotted line represents the state before correction according to the vehicle speed, and the solid line represents the state after correction according to the vehicle speed. The precondition of the traveling state at the first time in the time chart is that the driver releases his / her foot from the accelerator pedal while traveling on a downhill road surface and is in a coasting traveling state.

(Without gradient correction)
When the driver starts to depress the brake pedal at time t1, deceleration is started.
When the master cylinder pressure exceeds the coast stop permission lower limit before correction at time t11, the engine speed starts to decrease toward the stop because coast stop is started.
At time t3, the driver starts to depress the brake pedal. At time t44, when the master cylinder pressure sufficiently decreases and falls below the coast stop permission lower limit before correction, the coast stop is terminated and the engine is restarted. At this time, since the master cylinder pressure is too low, the force to stop the vehicle becomes insufficient, the force to move further forward becomes stronger, and a feeling of popping out accompanying engine restart occurs.

(With slope correction)
When the driver starts to depress the brake pedal at time t1, deceleration is started.
When the master cylinder pressure exceeds the corrected coast stop permission lower limit value at time t2, the engine speed starts to decrease toward the stop because the coast stop is started. At this time, since the vehicle speed correction amount is set to be small when the vehicle speed is high, the coast stop permission lower limit value is exceeded even at a relatively low master cylinder pressure, so coast stop can be started earlier and fuel economy can be improved. .
At time t3, the driver starts to depress the brake pedal. Then, at time t4, when the master cylinder pressure slightly decreases, the corrected coast stop permission lower limit value is exceeded, the coast stop is terminated, and the engine is restarted. At this time, the master cylinder pressure has not decreased too much (that is, the coast stop permission lower limit is set higher depending on the vehicle speed), so that the force for stopping the vehicle can be secured, and the engine restart is accompanied. A feeling of popping out can be avoided.

As described above, the following operational effects can be obtained in the first embodiment.
(1) When the driver operates the brake pedal more than the coast stop permission lower limit (predetermined threshold) during traveling, step S106 (coast stop control means) for stopping the engine and road mu (road friction coefficient) are performed. The road surface friction coefficient detecting unit 10c (road surface friction coefficient detecting means) to be detected, and step S206 (threshold setting means) for increasing the coast stop permission lower limit value as the detected road surface friction coefficient decreases.
Therefore, coast stop control is less likely to be performed on low μ road surfaces, and drivability can be improved by avoiding torque fluctuations associated with engine restart.

(2) An ABS (anti-lock brake system) that avoids locking of the wheels is included, and step S206 (threshold setting means) is a coast stop permission lower limit so that the engine is not stopped by the coast stop control before the operation of the ABS. The value was increased. In other words, coast stop control is prohibited when there is a possibility that the ABS operates on a low μ road.
Therefore, it is possible to maintain a state in which torque is applied to the drive wheels from the engine side during the ABS control, and it is possible to stabilize the vehicle behavior without increasing the distance until shifting to the stop state.

(3) The road surface friction coefficient detection unit 10c (road surface friction coefficient detection means) detects the outside air temperature, and detects the road surface friction coefficient as a small value when the outside air temperature is below a predetermined temperature.
That is, when the outside air temperature is 4 ° C. or less, for example, the possibility of a frozen road surface is high, so it can be determined that the road surface friction coefficient is small, and the road surface friction coefficient can be detected with a simple configuration.

  Next, Example 2 will be described. Since the basic configuration is the same as that of the first embodiment, only different points will be described. FIG. 16 is a gradient correction amount map of the second embodiment. In the first embodiment, the slope correction amount ΔP1 is set larger when the slope is upward than when the slope is downward. On the other hand, in the second embodiment, the gradient correction amount ΔP1 is made smaller in the case of the upward gradient than in the case of the downward gradient. In other words, on a downward slope, a propulsive force based on the vehicle weight always acts on the front of the vehicle. Therefore, when coasting is stopped with a gentle brake pedal operation, the driver further loosens the brake pedal and tries to accelerate again. In this case, unnecessary torque is output to the drive wheels when the engine is started, and the braking force is small, which may cause a feeling of popping out. Thus, in the second embodiment, the feeling of popping out when the engine is restarted is suppressed by making it difficult to enter the coast stop when the vehicle is going downhill.

  As described above, the present invention has been described based on the first and second embodiments. However, the present invention is not limited to the above-described embodiments, and other configurations are also included in the present invention. For example, in the first and second embodiments, the example in which the belt-type continuously variable transmission is adopted is shown, but a configuration including another stepped automatic transmission, a manual transmission, or the like may be used. Moreover, although the example provided with the torque converter was shown, even if it is a vehicle which is not provided with the torque converter, it is applicable.

  Moreover, although the example which calculated | required various correction amount from the map was shown, you may obtain | require by calculation etc., and when calculating a correction amount, it is the structure which correct | amends the map gradient of a certain correction amount based on another correction amount. It does not matter.

DESCRIPTION OF SYMBOLS 1 Engine 1a Starter 2 Torque converter 3 Belt type continuously variable transmission 3a Electric oil pump 4 Drive wheel 10 Engine control unit 10a Road surface gradient detection unit 10b Vehicle weight detection unit 10c Road surface μ detection unit 11 Brake switch 12 Accelerator pedal opening sensor 13 Master cylinder pressure sensor 14 Wheel speed sensor 15 Outside air temperature sensor 20 Control unit

Claims (3)

Coast stop control means for stopping the engine when the driver operates the brake pedal more than a predetermined threshold during traveling;
Threshold setting means for setting the predetermined threshold so as not to stop the engine by the coast stop control means before the operation of the anti-lock brake system for avoiding wheel locking ;
An automatic engine stop control device for a vehicle, comprising: The automatic engine stop control device for a vehicle according to claim 1,
A road surface friction coefficient detecting means for detecting a road surface friction coefficient;
The threshold value setting means increases the predetermined threshold value as the detected road friction coefficient is smaller . The automatic engine stop control device for a vehicle according to claim 2 ,
The road engine friction coefficient detecting means detects an outside air temperature, and detects the road surface friction coefficient as a small value when the outside air temperature is equal to or lower than a predetermined temperature.

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