JP6454884B2 - 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 / restart control device, a technique disclosed in Patent Document 1 is disclosed. According to this publication, when a predetermined permission condition is satisfied, the engine is automatically stopped and the engine is stopped. When the predetermined permission condition is not satisfied, the engine is stopped and the engine is restarted. By doing so, fuel efficiency is improved. As the predetermined permission condition, it is determined that the predetermined permission condition is satisfied when the gradient is equal to or smaller than the predetermined threshold, and when the gradient is larger than the predetermined threshold, it is determined that the predetermined permission condition is not satisfied.

JP 2006-307866 JP

  By the way, in recent years, an increasing number of vehicles are equipped with a braking force control device capable of controlling the braking force of the vehicle according to the driving state. Some of these braking force control devices are equipped with a hill hold function that applies braking force to a vehicle so that the vehicle does not slide down when the vehicle starts from a state where the vehicle is stopped on an uphill road.

  Since the hill hold function generates a braking force according to the gradient of the road surface on which the vehicle is stopped, a larger braking force is applied as the gradient is steeper. The braking force by the hill hold function is realized by electric power from the battery, and large electric power is required to generate a large braking force. Therefore, in order to guarantee the hill hold function, the battery voltage needs to be equal to or higher than a voltage that guarantees the maximum power required for the hill hold function (hereinafter referred to as a hill hold guarantee voltage).

  However, the technique described in Patent Document 1 does not consider the combination of the hill hold function and the engine automatic stop / restart control, and leaves room for examination. For example, if the predetermined threshold value representing the gradient that is the predetermined permission condition is set to a value corresponding to a steep gradient, the permitted range for automatic engine stop can be expanded, but a large braking force must be generated by the hill hold function. Therefore, the hill hold guaranteed voltage becomes high. However, if a starter motor or the like is driven when the engine is restarted, a large current flows instantaneously, so that the battery voltage instantaneously drops to a low voltage. Therefore, the instantaneous low voltage becomes lower than the hill hold guaranteed voltage, and the There is a risk that the hold function may not work and the vehicle may slide down. In other words, the predetermined threshold value representing the gradient must be set in a range where the instantaneous voltage drop is equal to or higher than the hill hold guaranteed voltage. However, since the battery voltage changes slightly due to aging of the battery and low temperature, engine restart There was a possibility that the hill hold guaranteed voltage could not be secured at the start, and the vehicle could slip down.

  The present invention has been made paying attention to the above problems, and an object thereof is to provide an automatic engine stop control device for a vehicle that can achieve appropriate engine stop and restart even during traveling on a slope road.

In order to achieve the above object, the vehicle automatic engine stop control device of the present invention permits automatic engine stop when the road surface gradient is equal to or less than a predetermined threshold, and then automatically stops the engine when a predetermined condition is satisfied. When the predetermined condition is not satisfied, the motor is driven to restart the engine. Then, when starting from an automatic stop of the engine by restarting, hill hold control is performed to control the braking force control means to apply a braking force according to the gradient. The motor and the braking force control means are supplied with electric power from one battery. At this time, when the voltage of one battery is low, the predetermined threshold value of the road surface gradient is changed to a smaller value than when the voltage is high.

  Therefore, the engine can be stopped or restarted according to the gradient, and fuel efficiency and drivability can be improved. Moreover, even if the motor is driven and the engine is restarted while securing the brake fluid pressure by the hill hold control in order to change the predetermined threshold value at which the automatic stop of the engine is permitted according to the voltage, the battery voltage is instantaneously decreased. It is possible to prevent the vehicle from sliding down without causing a shortage of brake fluid pressure.

1 is a system diagram illustrating a configuration of an automatic engine stop control device for a vehicle according to a first embodiment. It is a flowchart showing the action | operation of the engine automatic stop control apparatus at the time of performing the threshold value setting control process of Example 1, and the action | operation of a brake fluid pressure control unit. It is a time chart showing the action | operation of the engine automatic stop control apparatus at the time of not performing the threshold value setting control process of Example 1 as a comparative example, and the action | operation of a brake fluid pressure control unit. It is a time chart showing the action | operation of the engine automatic stop control apparatus at the time of performing the threshold value setting control process of Example 1 in a small gradient, and the action | operation of a brake fluid pressure control unit. It is a time chart showing the action | operation of the engine automatic stop control apparatus and the action | operation of a brake fluid pressure control unit at the time of performing the threshold value setting control process of Example 1 in a big gradient.

  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 vehicle of the first embodiment supplies electric power to the engine 1, the starter motor 2, the automatic transmission 3, the brake fluid pressure control unit 7, the starter motor 2 and the brake fluid pressure control unit 7 through the power line 9a. And a battery 9 to be operated. The engine 1 which is an internal combustion engine is provided with a starter motor 2 for starting the engine, engine cranking is performed based on an engine start command from the engine controller 8, fuel is injected, and the engine 1 can rotate independently. Then, the starter motor 2 is stopped. The rotational driving force output from the engine 1 is input to the automatic transmission 3 and shifted by a desired gear ratio, and then transmitted to the drive wheels 5 via the drive shaft 4.

  The brake fluid pressure control unit 7 (braking force control means) includes a brake fluid pressure control actuator 7a having a built-in pump driven by various solenoid valves and motors, and a brake controller for controlling the operating state of the brake fluid pressure control actuator 7a. It consists of 7b. The brake fluid pressure control actuator 7a is connected to the master cylinder 6 and the wheel cylinder 7c via piping. The engine controller 8 and the brake controller 7b are connected via the CAN communication line 10, and are configured to be able to transmit and receive information. A power supply line 9 a for supplying power from the battery 9 is connected to the starter motor 2 and the brake fluid pressure control unit 7.

  A brake booster 1b that boosts the negative pressure of the intake air is connected to the air intake 1a for sucking air into the engine 1, and the master cylinder 6 has a master cylinder by boosting the brake pedal depression force. Generate pressure. The hydraulic pressure generated in the master cylinder 6 is supplied to the brake hydraulic pressure control actuator 7a, and is supplied to the wheel cylinder 7c via the control valve 7a1 in the brake hydraulic pressure control actuator 7a. The wheel cylinder 7c presses the brake pad against the brake rotor 4a that rotates together with the drive wheel 5 to generate a friction braking force.

The engine controller 8 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, an engine Signals such as water temperature, crank angle, and engine speed are input. The brake controller 7b also includes a brake fluid pressure signal from the brake fluid pressure sensor 13 that detects the master cylinder pressure, and a negative pressure signal from the brake negative pressure sensor 14 that detects the negative pressure supplied to the brake booster 1b. Then, the longitudinal acceleration signal from the acceleration sensor 15 for detecting the longitudinal acceleration of the vehicle is input. The engine controller 8 inputs the above various signals via the CAN communication line 10, and starts or automatically stops the engine 1 based on these signals.
In place of the brake fluid pressure sensor 13, a sensor for detecting the brake pedal stroke amount and the brake pedal depression force, or a sensor for detecting the wheel cylinder pressure, etc. is used to detect the brake pedal operation amount. The operation intention may be detected and is not particularly limited.

  Further, the engine controller 8 includes a road surface gradient detection unit 8a that detects a road surface gradient during travel of the vehicle. In the road surface gradient detection unit 8a, for example, the road surface gradient is determined based on the difference between the torque transmitted to the drive wheels, the actual vehicle acceleration detected from the wheel speed and the acceleration acting on the vehicle detected by the acceleration sensor. Is estimated.

(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, even if the vehicle is running, if 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. Note that the idling stop control and the coast stop control may be appropriately implemented with known configurations, and thus detailed description thereof is omitted.

  In the brake fluid pressure control unit 7, when idling stop control or coast stop control is performed on a slope road, hill hold control for applying a braking force to the vehicle is performed from the viewpoint of preventing the vehicle from sliding down when the engine is restarted. Specifically, the necessary braking force is calculated based on the road surface gradient detected by the road surface gradient detecting unit 8a, and the brake fluid pressure is generated by operating the pump by driving the motor. Supply the required brake fluid pressure.

  Here, the problem based on the said structure is demonstrated. Since the hill hold control generates a braking force according to the gradient of the road surface on which the vehicle is stopped, a larger braking force is applied as the gradient becomes steeper. The braking force by this hill hold control is realized by electric power from the battery 9, and large electric power is required to generate a large braking force. Therefore, in order to guarantee the operation of the hill hold control, it is necessary that the battery voltage be equal to or higher than the hill hold guaranteed voltage that guarantees the maximum power required for the hill hold control.

At this time, if the predetermined threshold value indicating the road surface gradient condition for permitting the idling stop control is set to a value corresponding to a steep gradient, the permitted range of the automatic engine stop can be expanded, but a large braking force is achieved by the hill hold control. Therefore, the hill hold guaranteed voltage becomes high. However, when a starter motor or the like is driven when the engine is restarted, a large current flows, and the battery voltage instantaneously drops to a low voltage (hereinafter referred to as “instantaneous low voltage”). If it becomes lower than that, the braking force by the hill hold control may not be ensured, and the vehicle may be lowered.
In other words, the predetermined threshold value indicating the road surface gradient condition must be set in a range where the instantaneous voltage drop is equal to or higher than the hill hold guaranteed voltage, but the battery voltage changes small due to aging and low temperature of the battery 9, Again, when the engine restarts, the hill hold guaranteed voltage may not be secured, and the vehicle may slip down. Thus, in the first embodiment, by changing the predetermined threshold according to the battery voltage, a threshold setting control process for setting an appropriate threshold according to the state of the battery 9 is executed, and the vehicle shear is improved while improving fuel efficiency. We decided to prevent the fall.

FIG. 2 is a flowchart showing the operation of the engine automatic stop control device and the operation of the brake fluid pressure control unit when executing the threshold setting control process of the first embodiment.
In step S1, the battery minimum voltage is detected. Here, the minimum battery voltage corresponds to a voltage when the battery voltage is reduced when the engine is started by the operation of the starter motor 2.
In step S2, it is determined whether or not the battery minimum voltage is equal to or lower than a predetermined voltage set in advance. On the other hand, when the voltage is less than the predetermined voltage, the process proceeds to step S4, and the predetermined threshold that is the gradient threshold is set to be large. The predetermined voltage is set to a value when the battery voltage decreases when the starter motor 2 is operated when the battery 9 is new. Thereby, it is possible to detect the case where the battery 9 is deteriorated or the voltage cannot be secured due to low temperature.

In step S5, it is determined whether other coast stop control or idling stop control start conditions other than the gradient are satisfied. If not, the process proceeds to step S8 and the engine 1 is not stopped. repeat. On the other hand, when it is established, the process proceeds to step S6.
In step S6, the road gradient is detected by the road gradient detector 8a.
In step S7, it is determined whether or not the detected gradient is less than the predetermined threshold set in step S3 or S4. If it is less than the predetermined threshold, the process proceeds to step S9. Otherwise, the process proceeds to step S8. The control flow is repeated without stopping the engine 1.

In step S9, the engine 1 is stopped.
In step S10, the brake fluid pressure control unit 7 is requested to apply a braking force by hill hold control corresponding to the gradient.
In step S11, it is determined whether or not there is a restart request for engine 1. If there is no restart request, the process returns to step S9 to continue the engine stop and hill hold control, and if there is a restart request, step S12. Proceed to
In step S12, the engine is restarted by cranking by the starter motor 2.
In step S13, a request for releasing the braking force by the hill hold control is output.

FIG. 3 is a time chart showing the operation of the engine automatic stop control device and the operation of the brake fluid pressure control unit when the threshold setting control process of the first embodiment is not executed as a comparative example. In this comparative example, the predetermined threshold value of the gradient is set as a relatively large value, and idling stop control and coast stop control are positively permitted.
When the driver releases the brake pedal at time t1, the idling stop control condition is not satisfied, and the engine cranking is performed by driving the starter motor 2. At this time, the battery voltage is greatly reduced. Thereafter, the driver depresses the accelerator pedal to start.

At time t2, the driver starts stepping on the brake pedal, the vehicle decelerates, and the vehicle stops. At time t3, the idling stop control is permitted because the slope is smaller than the predetermined threshold even on the slope road, and the brake fluid pressure control unit 7 pumps up by the hill hold control, and the wheel cylinder pressure is increased. Generate braking force. However, since sufficient battery voltage is not ensured, sufficient braking fluid pressure cannot be ensured.
At time t4, when the driver releases the brake pedal, the idling stop control permission condition is not satisfied, and engine cranking is started. Then, a current flows through the starter motor 2 and the voltage of the battery 9 falls below the hill hold guaranteed voltage. If it does so, wheel cylinder pressure will fall, the fluid pressure required in order to prevent vehicle sliding down cannot be secured, and vehicle sliding down will occur.

FIG. 4 is a time chart showing the operation of the engine automatic stop control device and the operation of the brake fluid pressure control unit when the threshold setting control process of the first embodiment is executed with a small gradient.
When the driver releases the brake pedal at time t1, the idling stop control condition is not satisfied, and the engine cranking is performed by driving the starter motor 2. At this time, since the battery voltage is lower than the predetermined voltage, the predetermined threshold value of the gradient is changed to a small value.
At time t2, the driver starts stepping on the brake pedal, the vehicle decelerates, and the vehicle stops. At time t3, idling stop control is permitted because the slope is smaller than the predetermined threshold value that has been changed to a small value at time t1 even on a slope road, and the brake fluid pressure control unit 7 pumps up by hill hold control. The wheel cylinder pressure is increased and braking force is generated.
At time t4, when the driver releases the brake pedal, the idling stop control permission condition is not satisfied, and engine cranking is started. At this time, although the battery voltage is reduced, the gradient is small, so that a large voltage drop does not occur and the brake fluid pressure can be secured, and the vehicle does not slide down.

FIG. 5 is a time chart showing the operation of the engine automatic stop control device and the operation of the brake fluid pressure control unit when the threshold value setting control process of the first embodiment is executed at a large gradient.
When the driver releases the brake pedal at time t1, the idling stop control condition is not satisfied, and the engine cranking is performed by driving the starter motor 2. At this time, since the battery voltage is lower than the predetermined voltage, the predetermined threshold value of the gradient is changed to a small value.
At time t2, the driver starts stepping on the brake pedal, the vehicle decelerates, and the vehicle stops. At time t3, since the gradient is larger than a predetermined threshold value changed to a small value at time t1, idling stop control is not permitted, engine automatic stop control is not performed, and hill hold control is performed. Is not implemented. Therefore, the problem of insufficient brake fluid pressure due to cranking of the starter motor 2 during hill hold control does not occur, and the vehicle does not slide down.

  As described above, in the first embodiment, when the minimum voltage of the battery 9 is lower than the predetermined voltage, the predetermined threshold value representing the gradient is changed to be small, and only when the power required for the hill hold control is small, the idling stop control or Since coast stop control is permitted, the brake fluid pressure is not insufficient due to a voltage drop when the engine is restarted. Therefore, the vehicle can be prevented from sliding down.

As described above, in the first embodiment, the following operational effects can be obtained.
(1) Engine 1, starter motor 2 (motor) for starting engine 1, brake fluid pressure control unit 7 (braking force control means) capable of generating an arbitrary braking force, starter motor 2 and brake fluid A battery 9 for supplying electric power to the pressure control unit 7, and an automatic stop of the engine 1 is permitted when the road surface gradient is equal to or less than a predetermined threshold, and then the engine 1 is automatically stopped when a predetermined condition is satisfied, When this condition is no longer satisfied, the engine automatic stop control (engine control means) that drives the starter motor 2 to restart the engine 1 and the brake hydraulic pressure control unit 7 Step S10 (hill hold control means) for applying a braking force according to the gradient by controlling, and when the voltage of the battery 9 is low, the predetermined threshold is changed to a smaller value than when the voltage is high Step S2, S3 and (threshold setting unit), with a.
Therefore, the engine 1 can be stopped or restarted according to the gradient, and fuel efficiency and drivability can be improved. In addition, in order to change the predetermined threshold at which automatic engine stop is permitted according to the voltage, even if the starter motor 2 is driven and the engine 1 is restarted while the brake fluid pressure is secured by the hill hold control, the battery voltage It is possible to prevent the vehicle from sliding down without causing insufficient brake fluid pressure due to a momentary drop.

[Example 2]
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. In the first embodiment, in step S2, when the voltage of the battery 9 decreases when the starter motor 2 is operated as a predetermined voltage that is a threshold value for determining whether or not the voltage of the battery 9 has decreased. The battery voltage value was set. That is, the case where the voltage drops below the predetermined voltage is synonymous with the detection of a state where the battery 9 starts to deteriorate or a state where a sufficient voltage cannot be secured at a low temperature.
In contrast, the second embodiment is different in that the hill hold guarantee voltage required for the hill hold control is set as a predetermined voltage. That is, by setting the hill hold guaranteed voltage as a predetermined voltage, even if the voltage is lowered due to deterioration of the battery 9 or low temperature, if the hill hold guaranteed voltage can be secured, idling stop control and coast stop control The fuel consumption can be improved.

As described above, in the second embodiment, the following operational effects can be obtained.
(2) Engine 1, starter motor 2 (motor) for starting engine 1, brake fluid pressure control unit 7 (braking force control means) capable of generating an arbitrary braking force, starter motor 2 and brake fluid A battery 9 for supplying electric power to the pressure control unit 7, and an automatic stop of the engine 1 is permitted when the road surface gradient is equal to or less than a predetermined threshold, and then the engine 1 is automatically stopped when a predetermined condition is satisfied, When this condition is no longer satisfied, the engine automatic stop control (engine control means) that drives the starter motor 2 to restart the engine 1 and the brake hydraulic pressure control unit 7 Step S10 (hill hold control means) for applying a braking force according to the gradient by controlling, and a hill hold guarantee voltage in which the voltage of the battery 9 guarantees the operation of the brake fluid pressure control unit 7 When guarantee voltage) lower than was provided with a step S2, S3 (threshold value setting means) for changing the predetermined threshold value to a smaller value.
Therefore, the engine 1 can be stopped or restarted according to the gradient, and fuel efficiency and drivability can be improved. In addition, when the minimum voltage is lower than the hill hold guaranteed voltage, the idling stop can be performed on flat roads that are considered to be a lot of scenes as general driving conditions, or on small slope roads that conform to them by changing the predetermined threshold value to a small value. By permitting the control and the coast stop control, the fuel consumption can be improved while preventing the vehicle from sliding down.

  As mentioned above, although this invention has been demonstrated based on the Example, it is not restricted to the said Example but another structure is also included in this invention. For example, in Example 1, although the example which employ | adopted the general starter motor was shown, the starting device other than this may be sufficient. For example, an alternator coupled to the engine crankshaft via a belt can be used as a motor, and the engine can be started and restarted with this alternator. The initial start is performed with a starter motor. Only the restart may be performed by the alternator. In a hybrid vehicle, the engine may be restarted by a motor generator that performs power running and regeneration.

DESCRIPTION OF SYMBOLS 1 Engine 2 Starter motor 3 Automatic transmission 4 Drive shaft 5 Drive wheel 6 Master cylinder 7 Brake fluid pressure control unit 8 Engine control unit 8a Road surface gradient detection part 9 Battery

Claims (2)

Engine,
A motor for starting the engine;
Braking force control means capable of generating an arbitrary braking force;
One battery for supplying electric power to the motor and the braking force control means;
When the road surface gradient is below a predetermined threshold, the engine is allowed to stop automatically. Thereafter, when a predetermined condition is satisfied, the engine is automatically stopped, and when the predetermined condition is not satisfied, the motor is driven. Engine control means for restarting the engine;
A hill hold control means for controlling the braking force control means to apply a braking force according to a gradient at the start from the automatic stop of the engine;
When the minimum voltage of the one battery when driving the motor and restarting the engine is equal to or lower than a predetermined voltage, the predetermined threshold is changed to a smaller value than when the minimum voltage is higher than the predetermined voltage. Threshold setting means;
An automatic engine stop control device for a vehicle, comprising: Engine,
A motor for starting the engine;
Braking force control means capable of generating an arbitrary braking force;
One battery for supplying electric power to the motor and the braking force control means;
When the road surface gradient is below a predetermined threshold, the engine is allowed to stop automatically. Thereafter, when a predetermined condition is satisfied, the engine is automatically stopped, and when the predetermined condition is not satisfied, the motor is driven. Engine control means for restarting the engine;
A hill hold control means for controlling the braking force control means to apply a braking force according to a gradient at the start from the automatic stop of the engine;
A threshold value for changing the predetermined threshold value to a smaller value when the minimum voltage of the one battery when the motor is driven and the engine is restarted is lower than a guaranteed voltage that guarantees the operation of the braking force control means. Setting means;
An automatic engine stop control device for a vehicle, comprising:

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