Vehicle control method and vehicle

Abstract

To make it possible to smoothly start a vehicle without giving a driver feeling of rushing out when re-start condition is satisfied by a change of driver's intention after the automatic stop condition is satisfied and fuel cut is performed.SOLUTION: A control method of a vehicle comprises: performing an automatic stop control where an internal combustion engine is provided as driving source and the internal combustion engine is automatically stopped when a prescribed condition is established, and performing an automatic re-startup control where the internal combustion engine is re-started up when a prescribed re-start condition is established during execution of the automatic stop control; performing a brake holding control of applying brake force to wheels during the execution of the automatic stop control to keep the vehicle stop state; and automatically re-starting up the internal combustion engine when the re-start condition is established, and releasing the brake holding control after a lapse of a prescribed period of time from the establishment of the re-start condition. The prescribed period of time is varied according to the engine rotation speed at the time when the re-start condition is established.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to a vehicle control method and a vehicle.

Background Art

[0002] There is known a so-called idle stop vehicle that has a function of automatically stopping the engine when a predetermined automatic stop condition is satisfied during parking and automatically restarting the engine when a predetermined restart condition is satisfied. In Patent Document 1, as control of an idle stop vehicle, at least a brake pressure being less than a predetermined value is set as a restart condition, and when restarting the engine, the brake pedal is depressed, the brake pressure is less than a predetermined value, and if the engine rotation speed is equal to or higher than a predetermined rotation speed (a rotation speed at which sufficient creep force is generated), control is disclosed for continuing the application of the braking force for a predetermined period. When the brake pedal is depressed, it can be considered that the driver has no intention of starting. Also, if the engine rotation speed is equal to or higher than the predetermined rotation speed, there is a risk of a jump due to the creep force generated by the engine restart. That is, the above control is to continue the application of the braking force executed during idle stop when restarting the engine in a state where the driver has no intention of starting and there is a risk of a jump due to the engine restart. By this control, it is possible to prevent giving the driver a sense of jump associated with the engine restart. Further, in the control of the above document, when the brake pedal is depressed during automatic stop and then becomes not depressed, the application of the braking force is not continued. This is because releasing the depression of the brake pedal means that the driver intends to restart the engine, and it is considered that the driver will not feel a sense of jump, and priority is given to quick engine restart and starting.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

[0004] Incidentally, after the automatic stop condition is met and fuel is cut off to stop the engine, there are cases where, while the engine speed is decreasing, the driver may change their mind and switch from the brake pedal to the accelerator pedal, thus meeting the restart condition. In this case, according to the control described in the above-mentioned document, since the brake pedal is not pressed, it is assumed that the driver will not feel a sudden lurch, and the application of braking force is not continued. However, the engine speed at the time the restart condition is met will differ from the engine speed at the time the fuel cut off was performed. Therefore, depending on the engine speed, a creep force greater than the driver expects may be generated, potentially giving the driver a sudden lurch. On the other hand, if the application of braking force is continued for a predetermined period, as if the brake pedal were pressed, it will hinder a quick start.

[0005] Therefore, the present invention aims to enable a quick start without giving the driver a sudden feeling of abruptness when, after the automatic stop condition has been met and fuel cut-off has occurred, the restart condition is met due to a change in the driver's intention or the like. [Means for solving the problem]

[0006] According to one aspect of the present invention, a vehicle control method is provided which includes an internal combustion engine as a drive source, performs automatic stop control to automatically stop the internal combustion engine when predetermined stop conditions are met, performs automatic restart control to automatically restart the internal combustion engine when predetermined restart conditions are met during the execution of automatic stop control, performs brake hold control to maintain the vehicle in a stopped state by applying braking force to the wheels while the automatic stop control is being executed, automatically restarts the internal combustion engine when restart conditions are met, and releases the brake hold control when a predetermined period has elapsed since the restart conditions were met. In this control method, the predetermined period is changed according to the engine rotation speed at the time the restart conditions are met. [Effects of the Invention]

[0007] According to the above embodiment, if the restart condition is met due to a change in the driver's intention after the automatic stop condition has been met and fuel cut has been performed, it becomes possible to start quickly without giving the driver a sudden feeling of abruptness. [Brief explanation of the drawing]

[0008] [Figure 1] Figure 1 is a schematic diagram showing an example of a vehicle's system configuration. [Figure 2] Figure 2 is a timing chart for when the engine is automatically restarted after being automatically stopped. [Figure 3] Figure 3 is a flowchart of the control performed by the controller during automatic restart according to an embodiment of the present invention. [Figure 4] Figure 4 shows the first example of a timing chart when the control shown in Figure 3 is executed. [Figure 5] Figure 5 shows a second example of the timing chart when the control shown in Figure 3 is executed. [Figure 6] Figure 6 shows a third example of the timing chart when the control shown in Figure 3 is executed. [Figure 7] Figure 7 shows the timing chart when the rotation speed at the time of determination is fixed to the first rotation speed and the holding time is varied. [Figure 8] Figure 8 shows the timing chart when the rotation speed at the time of determination is fixed to the second rotation speed and the holding time is varied. [Modes for carrying out the invention]

[0009] Embodiments of the present invention will be described below with reference to the attached drawings.

[0010] Figure 1 is a schematic diagram showing an example of the system configuration of vehicle 1 according to this embodiment.

[0011] Vehicle 1 includes an internal combustion engine (hereinafter also simply referred to as "engine") 2 as a power source, a brake system 3 that applies braking force to the wheels 9, a controller 10 that controls the internal combustion engine 2 and the brake system 3, and sensors that acquire various information used for control by the controller 10.

[0012] Engine 2 may be either a gasoline engine or a diesel engine.

[0013] In addition to the function of applying braking force to the wheels 9 in response to the driver's brake pedal operation, the brake system 3 also has the function of applying braking force to the wheels 9 in response to instructions from the controller 10 for purposes such as collision avoidance, skidding prevention, and other driving assistance, even when the driver is not operating the brake pedal.

[0014] The controller 10 consists of a microcomputer equipped with a central processing unit (CPU), read-only memory (ROM), random access memory (RAM), and input / output interface (I / O interface). It is also possible to configure the controller 10 with multiple microcomputers.

[0015] Vehicle 1 is equipped with sensors including an accelerator pedal sensor 4 (not shown) that detects the opening degree of the accelerator pedal, a brake pedal sensor 5 (not shown) that detects whether or not the brake pedal is depressed, a vehicle speed sensor 6 that detects the vehicle speed, a gradient sensor 7 that detects the road surface gradient at the current position, and a crank angle sensor 8 that detects the rotational speed of the engine 2. The brake pedal sensor 5 only needs to be able to detect whether or not the brake pedal is depressed, but it may also detect the driver's pedal force. In addition to the above sensors, Vehicle 1 is also equipped with an airflow sensor (not shown) that detects the amount of intake air, a throttle position sensor (not shown) that detects the opening degree of the throttle valve, and the like.

[0016] The detection values of the above sensors are read into the controller 10 as detection signals. Based on these detection values, the controller 10 controls the engine 2 and the brake system 3.

[0017] The control performed by the controller 10 includes automatic stop control and automatic restart control of the engine 2. The automatic stop control is a control to automatically stop the engine 2 when a stop condition, for example, the brake pedal is depressed and the vehicle speed is below a predetermined vehicle speed, is satisfied. The automatic restart control is a control to automatically restart the engine 2 when a restart condition, for example, the brake pedal is released or the battery capacity becomes below a threshold value, is satisfied while the engine 2 is stopped by the automatic stop control. Note that since known conditions can be applied to the automatic stop condition and the restart condition, detailed descriptions thereof are omitted.

[0018] When the engine 2 is stopped and the vehicle is stationary due to the automatic stop control, the controller 10 executes brake holding control to apply braking force to the wheels 9 by the brake system 3 to maintain the vehicle stop state. The brake holding control can suppress an unintended start caused by torque generated by the automatic restart of the engine 2 when the battery capacity becomes below the threshold value during stationary operation according to a stop signal, for example.

[0019] Here, the brake holding control when automatically restarting the engine 2 according to the driver's intention to start becomes a problem.

[0020] If brake-holding control is not continued after the restart conditions are met, the driver may experience a sudden lurching sensation. This "sudden lurching sensation" refers to a general term encompassing abruptness that intensifies with increasing rate of change of acceleration, and a feeling of being pushed forward that intensifies with increasing initial acceleration peaks. On the other hand, continuing brake-holding control after the restart conditions are met can suppress the rollback that occurs when, for example, the driver releases the brake pedal to restart the engine while stopped on an uphill road, before the engine 2 generates torque. However, continuing brake-holding control may hinder a quick start.

[0021] Furthermore, even if brake holding control is continued after the restart conditions are met, if the duration of this control is not appropriate, it may give the driver a feeling of sudden acceleration. This is because the engine speed at the time the restart conditions are met (also called the engine speed at the time of determination) varies depending on the situation, and if the engine speed at the time of determination is different, the engine speed and engine torque profile after restarting will also be different.

[0022] This will be explained with reference to Figure 2. Figure 2 is a timing chart of engine speed, brake input, and acceleration when engine 2 is automatically restarted after being automatically stopped. In this chart, the restart condition is met at timing T0, and then engine 2 is automatically restarted after a predetermined delay time.

[0023] If engine 2 has stopped rotating, the rotational speed at the time of determination is zero [rpm]. However, if the driver's intention changes and the brake pedal is released immediately after the vehicle has stopped due to the execution of fuel cut in accordance with the automatic stop condition, the engine rotational speed may not have decreased to zero when the restart condition is met. In Figure 2, the case where the rotational speed at the time of determination is zero is shown by a solid line, the case where the first rotational speed is higher than zero is shown by a dashed line, and the case where the second rotational speed is higher than the first rotational speed is shown by a dashed line.

[0024] Furthermore, the time during which brake holding control is continued after the restart condition is met, that is, the time during which the brake input is held constant (from timing T0 to timing T1), is called the holding time. The period during which the brake input gradually decreases to zero (from timing T1 to T2) is called the release time. In Figure 2, the holding time and release time are the same regardless of the rotational speed at the time of determination.

[0025] After the release time has elapsed (i.e., from timing T2 onward), if the rotational speed at the time of determination is the second rotational speed, the acceleration is the same as or less than when the rotational speed at the time of determination is zero [rpm] (hereinafter also referred to as the normal state). In contrast, if the rotational speed at the time of determination is the first rotational speed, the acceleration is greater in region A of Figure 2 compared to the normal state. In other words, when the rotational speed at the time of determination is the first rotational speed, the feeling of sudden acceleration is stronger than in the normal state. Furthermore, the appropriate holding time differs depending on whether the road on which the vehicle is stopped is flat or not. Therefore, in this embodiment, the control described below is performed in order to set a holding time that enables a quick start while suppressing the feeling of sudden acceleration.

[0026] Figure 3 is a flowchart of the control performed by the controller 10 when the restart conditions are met while the engine 2 has automatically stopped and the brake system 3 is performing brake hold control.

[0027] In step S10, the controller 10 acquires the gradient of the road surface while the vehicle is stationary based on the value detected by the gradient sensor 7. Alternatively, the gradient can be acquired from location information obtained by a navigation system (not shown) and pre-stored map data.

[0028] In step S20, the controller 10 determines whether there is a concern about sliding down based on the gradient obtained in step S10. If there is no concern, it executes the process in step S30; otherwise, it executes the process in step S40. Specifically, it determines that there is a concern if the gradient is above a predetermined threshold, and no concern if it is below the threshold. The threshold used here varies depending on the weight of vehicle 1, etc., and is set by simulation or the like for each specification of vehicle 1.

[0029] In step S30, the controller 10 obtains the rotational speed at the time of determination based on the value detected by the crank angle sensor 8, and then executes the process in step S70, which will be described later.

[0030] In step S40, the controller 10 obtains the rotation speed at the time of determination, similar to step S30.

[0031] In step S50, the controller 10 sets the timer start rotation speed based on the rotation speed at the time of determination. The count start rotation speed is the engine rotation speed at which the timer that counts the holding time starts counting. The count start rotation speed is also the engine rotation speed that can generate enough driving force to prevent the vehicle 1 from sliding backward, and the greater the gradient, the higher the value.

[0032] In step S60, the controller 10 determines whether the actual engine rotation speed has become equal to or greater than the count start rotation speed, and if it has become equal to or greater than the count start rotation speed, it executes the process in step S70.

[0033] In step S70, the controller 10 sets the hold time and starts counting on a timer that counts the hold time. Here, the higher the rotation speed at the time of determination, the shorter the hold time to be set.

[0034] In step S80, the controller 10 repeatedly checks whether the holding time has elapsed until the holding time has elapsed. Once the holding time has elapsed, in step S90, the controller 10 reduces the braking force of the brake system 3 and terminates this control routine.

[0035] In addition, a separate brake system controller for controlling the brake system 3 may be provided in addition to the controller 10. In that case, after the controller 10 has processed steps S10 to S80, it sends a brake release request to the brake system controller in step S90.

[0036] Figures 4 to 6 show the timing charts when the above control is performed while the vehicle is stopped on a flat road. Figure 4 shows the case where the rotational speed at the time of determination is zero [rpm] (i.e., normal), Figure 5 shows the case where the rotational speed at the time of determination is the first rotational speed, and Figure 6 shows the case where the rotational speed at the time of determination is the second rotational speed. Note that zero < first rotational speed < second rotational speed.

[0037] Furthermore, in all of Figures 4 to 6, the brake pedal is released at timing T1, the restart condition is met at timing T2, and then the engine 2 starting operation is disclosed. Note that the time between timing T1 and timing T2 is a control delay time. Similarly, there is a delay time between the time the restart condition is met and the actual start operation of engine 2.

[0038] In the normal operation shown in Figure 4, the rotational speed at the time of determination is zero [rpm], and the brake holding control ends at timing T3, when a predetermined holding time has elapsed since the restart condition was met, and the braking force begins to decrease.

[0039] If the rotational speed at the time of determination shown in Figure 5 is a first rotational speed that is higher than zero, a shorter holding time is set than under normal circumstances, and the brake holding control ends at a timing T4 earlier than timing T3.

[0040] If the rotational speed at the time of determination, as shown in Figure 6, is higher than the first rotational speed (second rotational speed), an even shorter holding time is set, and the brake holding control ends at a timing T5 that is earlier than timing T4.

[0041] As described above, by shortening the holding time of the brake holding control as the rotational speed at the time of judgment increases, it is possible to achieve an acceleration profile that is almost the same as under normal conditions, whether the rotational speed at the time of judgment is the first rotational speed or the second rotational speed. In other words, by setting the holding time according to the rotational speed at the time of judgment, the feeling of sudden acceleration can be kept at the level of under normal conditions.

[0042] Figure 7 shows the timing chart when the rotation speed at the time of determination is fixed to the first rotation speed and the holding time is varied. In Figure 7, the solid line shows the case where the holding time is the same as normal, the dashed line shows the case where the holding time is shorter than normal, and the dashed line shows the case where the holding time is longer than normal.

[0043] When the holding time is shortened compared to the normal holding time, the timing of the first acceleration peak is earlier and the initial peak is lower compared to the case with the normal holding time (see region B in Figure 7). In other words, by shortening the holding time compared to the normal time, it is possible to start more quickly and suppress the feeling of being pushed forward, in particular, when the holding time is the same as the normal time.

[0044] Furthermore, even if the holding time is extended beyond the normal duration, the initial peak of acceleration will be lower compared to when the holding time is the same as normal, thus suppressing the feeling of sudden acceleration. However, since the timing of the acceleration increase will be later than normal, it will not be possible to achieve a rapid start.

[0045] Figure 8 shows the timing chart when the rotation speed at the time of determination is fixed to the second rotation speed and the holding time is varied. The solid line in Figure 8 shows the case where the holding time is the same as the normal case, and the dashed line shows the case where the holding time is shorter than the normal case. Note that the timing T5 when the holding time ends is earlier than the timing T4 when the rotation speed at the time of determination is the first rotation speed.

[0046] By shortening the holding time, the time required from when engine 2 automatically restarts until acceleration builds up is reduced (see region C in Figure 8). In other words, rapid starting is possible.

[0047] As described above, this embodiment provides a vehicle 1 equipped with an internal combustion engine 2 as a drive source, in which a controller 10 performs automatic stop control to automatically stop the internal combustion engine 2 when predetermined stop conditions are met, and performs automatic restart control to automatically restart the internal combustion engine 2 when predetermined restart conditions are met during the execution of automatic stop control. While the automatic stop control is being executed, the controller 10 also performs brake hold control to maintain the vehicle in a stopped state by applying braking force to the wheels 9. Furthermore, when the restart conditions are met, the controller 10 automatically restarts the internal combustion engine 2 and releases the brake hold control when a predetermined period has elapsed since the restart conditions were met. The controller 10 changes the predetermined period according to the engine rotation speed (determination rotation speed) at the time the restart conditions are met. More specifically, the controller 10 shortens the predetermined period the higher the engine rotation speed at the time the restart conditions are met. The driving force profile generated after engine 2 automatically restarts varies depending on the rotational speed at the time of determination. However, according to this embodiment, it is possible to set a holding time that matches the generated driving force profile, and as a result, it becomes possible to start quickly without giving the driver a sudden jolt.

[0048] In this embodiment, the controller 10 changes a predetermined period (holding time) not only based on the engine speed at the time the restart condition is met, but also based on the gradient of the road surface on which the vehicle 1 is stopped. Since the gradient also affects the generated driving force profile, similar to the rotation speed at the time of determination, changing the holding time according to the gradient can suppress sudden acceleration and other such issues.

[0049] In this embodiment, the controller 10 continues brake holding control until at least a predetermined engine speed is reached, if the road surface gradient is above a threshold determined according to the specifications of the vehicle 1. When automatically restarting on an uphill road, there is a concern that the vehicle 1 may roll backward, but according to this embodiment, rolling backward can be prevented. The predetermined engine speed is set to an engine speed that can generate enough driving force to prevent the vehicle 1 from rolling backward.

[0050] In this embodiment, the controller 10 changes a predetermined engine rotation speed according to the engine rotation speed at the time the restart condition is met (determination rotation speed). In other words, the timing for releasing the brake holding control is set according to the driving force profile generated after automatic restart, which differs depending on the determination rotation speed. This suppresses the feeling of sudden acceleration after automatic restart and prevents the vehicle 1 from sliding backward.

[0051] It goes without saying that the present invention is not limited to the embodiments described above, and various modifications can be made within the scope of the technical idea described in the claims. [Explanation of symbols]

[0052] 1. Vehicle, 2. Internal combustion engine, 3. Brake system, 4. Accelerator pedal sensor, 5. Brake pedal sensor, 6. Vehicle speed sensor, 7. Gradient sensor, 8. Crank angle sensor, 9. Wheels, 10. Controller

Claims

1. The system is equipped with an internal combustion engine as a power source, and the controller performs automatic stop control to automatically stop the internal combustion engine when predetermined stop conditions are met, and performs automatic restart control to automatically restart the internal combustion engine when predetermined restart conditions are met during the execution of the automatic stop control. During the execution of the aforementioned automatic stop control, brake holding control is also performed, which applies braking force to the wheels to maintain the vehicle in a stopped state. In a vehicle control method, when the restart condition is met, the internal combustion engine is automatically restarted, and when a predetermined period of time has elapsed since the restart condition was met, the brake holding control is released. A vehicle control method characterized in that the controller changes the predetermined period according to the engine speed at the time the restart condition is met and the gradient of the road surface on which the vehicle is stopped.

2. In the vehicle control method described in claim 1, A vehicle control method that shortens the predetermined period as the engine speed at the time the restart condition is met increases.

3. In the vehicle control method described in Claim 1, A vehicle control method that, when the gradient of the road surface is greater than or equal to a threshold determined according to the specifications of the vehicle, continues the brake holding control until at least a predetermined engine speed is reached.

4. In the vehicle control method described in Claim 3, A vehicle control method that changes the predetermined engine rotation speed according to the engine rotation speed at the time the restart condition is met.

5. An internal combustion engine as a power source, A braking system that applies braking force to the wheels, A controller that controls the internal combustion engine and the brake system, Equipped with, In a vehicle, the controller performs automatic stop control to automatically stop the internal combustion engine when predetermined stop conditions are met, performs automatic restart control to automatically restart the internal combustion engine when predetermined restart conditions are met during the execution of the automatic stop control, simultaneously performs brake hold control to maintain the vehicle in a stopped state by applying braking force to the wheels during the execution of the automatic stop control, automatically restarts the internal combustion engine when the restart conditions are met, and releases the brake hold control when a predetermined period has elapsed since the restart conditions were met, A vehicle characterized in that the controller changes the predetermined period according to the engine speed at the time the restart condition is met and the gradient of the road surface on which the vehicle is stopped.

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