JP7533130B2 - Vehicle control device - Google Patents

Description

The present invention relates to a vehicle control device.

Driving assistance technologies that automatically maintain the actual vehicle speed at a target vehicle speed, such as ACC (Adaptive Cruise Control), ASL (Adjustable Speed Limiter), and CRC (Cruise Control System), are known. In such driving assistance, the braking force by the powertrain and the braking force by the brakes are controlled to maintain the actual vehicle speed at the target vehicle speed. For example, when a vehicle is traveling downhill, if the required braking force to maintain the target vehicle speed is lower than the braking force by the powertrain when the engine fuel is cut off at a specified gear stage, the brakes are operated so that the sum of the braking force by the powertrain and the braking force by the brakes becomes the required braking force. In addition, if the required braking force is predicted to further decrease and become lower than the braking force by fuel cut at a gear stage downshifted from the current gear stage, the gear stage is downshifted while continuing the fuel cut.

JP 2020-121679 A

As described above, when the vehicle is traveling downhill, the brakes continue to be applied to maintain the actual vehicle speed at the target vehicle speed. However, if the required braking/driving force does not fall below the braking/driving force caused by fuel cut in the gear after the downshift, the downshift will not be performed and the brakes will remain applied for a long period of time. This can cause vibrations.

The present invention aims to provide a vehicle control device that prevents the brakes from remaining applied for long periods of time during driving assistance that automatically maintains the actual vehicle speed at the target vehicle speed.

The object of the present invention is to provide a vehicle control device that performs driving assistance by controlling a powertrain including an engine and a stepped transmission and a brake, and that automatically maintains an actual vehicle speed at a target vehicle speed, and in this case, when a gear stage of the stepped transmission is controlled to a predetermined gear stage to execute fuel cut of the engine and generate braking force by the brake so that the sum of the braking/driving force by the powertrain and the braking force by the brake becomes a required braking/driving force, if it is predicted that the braking/driving force of the powertrain due to the execution of fuel cut at a gear stage after a downshift from the predetermined gear stage is lower than the required braking/driving force, the predetermined gear stage is controlled to execute fuel cut of the engine and generate braking force by the brake. This can be achieved by a vehicle control device which, when the time during which the brake continues to be activated in a gear stage reaches or exceeds a predetermined upper limit time, downshifts from the specified gear stage to the gear stage after the downshift and resumes fuel injection without activating the brake, wherein the upper limit time is set to a time that is shorter by a predetermined margin than the time during which vibration occurs when braking force is generated by the brake while fuel cut is being performed in the specified gear stage, and which is specified so that the upper limit time becomes gradually or stepwise shorter as the braking force by the brake increases while the brake continues to be activated in the specified gear stage.

The present invention provides a vehicle control device that prevents the brakes from remaining applied for a long period of time during driving assistance that maintains the actual vehicle speed at the target vehicle speed.

FIG. 1 is a functional block diagram of a vehicle according to this embodiment. FIG. 2 is an example of a flowchart showing the braking/driving force control executed by the vehicle control device. FIG. 3 is an example of a flowchart showing the braking/driving force control executed by the vehicle control device. FIG. 4 is a map that defines upper limit times corresponding to braking forces. FIG. 5 is an example of a timing chart for a case where a downshift is executed because the required braking/driving force is lower than the fuel cut braking/driving force after a downshift. FIG. 6 is an example of a timing chart for a case where a downshift is executed because the braking duration exceeds the upper limit time.

[General configuration of the vehicle]
1 is a functional block diagram of a vehicle according to this embodiment. The vehicle is equipped with a vehicle control device 1, a powertrain 50, and a brake 60. The powertrain 50 includes a stepped transmission 51 and an engine 52. The stepped transmission 51 is a stepped automatic transmission that selectively switches between a plurality of gear stages, and for example, one of eight forward stages, one reverse stage, and neutral is selected, and speed conversion is performed according to the gear ratio of each gear stage. The engine 52 is an internal combustion engine that uses gasoline or the like as fuel, and is the power source of the vehicle that generates braking and driving forces by burning fuel.

The vehicle control device 1 includes a required acceleration calculation unit 10, a braking/driving force control unit 20, a powertrain control unit 30, and a brake control unit 40. The vehicle control device 1 is an ECU (Electronic Control Unit) that has a built-in memory and a microcomputer that stores programs and various maps, and the functions of the control blocks are realized by this ECU. The required acceleration calculation unit 10, braking/driving force control unit 20, powertrain control unit 30, and brake control unit 40 may be realized by separate ECUs, but the boundaries between them are not limited to this. The required acceleration calculation unit 10, braking/driving force control unit 20, powertrain control unit 30, and brake control unit 40 may be realized by one or more ECUs having boundaries different from those in FIG. 1.

The required acceleration calculation unit 10 is provided in a driving assistance device that has a function of achieving and maintaining a target vehicle speed such as ACC. The required acceleration calculation unit 10 sets a target vehicle speed based on information indicating the state of the vehicle and its surroundings obtained from a vehicle speed sensor, a camera, etc., and on previously set information, and calculates a required acceleration, which is the acceleration to be generated by the vehicle, as control information for maintaining the actual vehicle speed at the target vehicle speed.

The braking/driving force control unit 20 receives the above-mentioned required acceleration as a request from the required acceleration calculation unit 10, and converts the required acceleration into a force to be generated in the vehicle to calculate the required braking/driving force. The required braking/driving force is expressed, for example, as a value with the vehicle's traveling direction as the positive direction. The required braking/driving force can be calculated, for example, based on the required acceleration and a preset vehicle weight. In addition, when calculating, calculations such as feedback based on the actual vehicle speed obtained from a vehicle speed sensor or correction based on the inclination of the road surface obtained from various sensors may be performed. Furthermore, based on the required braking/driving force, the braking/driving force control unit 20 requests the powertrain control unit 30 to provide a braking force or a driving force, or further requests braking force from the brake control unit 40.

The powertrain control unit 30 can control the powertrain 50 to generate a braking/driving force. When generating a braking force, the powertrain control unit 30 can execute a fuel cut for the engine 52 according to various states of the powertrain 50, such as the temperature of the engine 52 and the gear stage of the stepped transmission 51, and the value of the braking force.

The powertrain control unit 30 monitors various states of the powertrain 50, and based on this, calculates the fuel cut braking/driving force, which is the braking/driving force that the powertrain 50 generates when cutting fuel to the engine 52, for the current gear of the stepped transmission 51 and for a gear downshifted from the current gear. In addition, the powertrain control unit 30 determines the control content of the powertrain 50, such as whether to change the gear of the stepped transmission 51 or cut fuel to the engine 52, according to the requested braking/driving force, and generates the braking/driving force.

The brake control unit 40 controls the brakes 60 installed in the vehicle to generate braking force on the wheels.

[Braking/driving force control]
Figures 2 and 3 are examples of flowcharts showing the braking/driving force control executed by the vehicle control device 1. The flowcharts shown in Figures 2 and 3 are repeatedly executed when, during driving assistance such as ACC, the vehicle travels, for example, on a downhill road and the braking/driving force generated in the vehicle gradually decreases in order to maintain a target vehicle speed. First, the flowchart shown in Figure 2 will be described.

The required acceleration calculation unit 10 calculates the required acceleration as described above (step S1). The braking/driving force control unit 20 calculates the required braking/driving force as described above based on the required acceleration (step S2). The powertrain control unit 30 calculates the fuel-cut braking/driving force in the current gear stage of the stepped transmission 51 (step S3). The fuel-cut braking/driving force is the minimum value of the braking/driving force of the engine 52 when fuel cut is executed.

The powertrain control unit 30 determines whether the required braking/driving force is lower than the fuel cut braking/driving force calculated in step S3 (step S4). If the answer is Yes in step S4, the brake control unit 40 calculates the brake braking force so that the sum of the fuel cut braking/driving force and the brake braking force is the required braking/driving force (step S5). Next, the powertrain control unit 30 cuts fuel to the engine 52, and the brake control unit 40 generates a brake braking force in the brake 60 (step S6). Next, the brake control unit 40 starts counting the duration since the brake braking force was generated in the brake 60 (step S7), which will be described in detail later.

If step S4 is No, the powertrain control unit 30 causes the powertrain 50 to generate a required braking/driving force (step S8). In this case, if the required braking/driving force and the fuel cut braking/driving force are approximately the same, the powertrain control unit 30 causes the engine 52 to perform fuel cut, and if the required braking/driving force is greater than the fuel cut braking/driving force, the powertrain control unit 30 causes the engine 52 to start fuel injection and drive the engine 52. In either case, if step S4 is No, the brake control unit 40 does not operate the brake 60.

In this way, the vehicle's braking/driving force can be made to follow the required braking/driving force, and the vehicle speed can be maintained at the target vehicle speed.

Next, as shown in FIG. 3, the powertrain control unit 30 calculates the fuel cut braking/driving force for the gear stage after downshifting from the current gear stage of the stepped transmission 51 (step S11).

The powertrain control unit 30 determines whether the required braking/driving force is lower than the fuel cut braking/driving force at the gear stage after the downshift calculated in step S11 minus a predetermined braking/driving force α (step S12). Here, the predetermined braking/driving force α is a value greater than zero, but it may be zero. In addition, the predetermined braking/driving force α may be a constant value regardless of the gear stage after the downshift, or may be a different value depending on the gear stage after the downshift. If the answer is Yes in step S12, the powertrain control unit 30 downshifts the gear stage of the stepped transmission 51 (step S13).

If the answer is No in step S12, the brake control unit 40 judges whether the brake duration that was started to be counted in step S7 is equal to or longer than the upper limit time β (step S14). Here, the upper limit time β differs depending on the brake braking force. FIG. 4 is a map that specifies the upper limit time β corresponding to the brake braking force. The horizontal axis indicates the brake braking force [N], and the vertical axis indicates the upper limit time β [ms]. In the example of FIG. 4, the upper limit time β is specified to the longest constant value from 0 to a predetermined value of the brake braking force, and the upper limit time β is specified to be shorter as the brake braking force increases, and the upper limit time β is specified to be the shortest constant value even if the brake braking force increases thereafter. The upper limit time β is set to a time that is shorter by a predetermined margin than the time at which vibration occurs when the brake 60 generates a brake braking force during the execution of the fuel cut. The map in FIG. 4 is obtained in advance by experiment and stored in the memory of the brake control unit 40. The upper limit time β is not limited to the map in FIG. 4, and may be specified so that, for example, the upper limit time β is shortened gradually or in stages as the braking force increases. Also, instead of using such a map, the upper limit time β may be calculated using an arithmetic formula that uses the braking force as an argument.

If step S14 is No, this control ends. Note that if step S4 is determined as No and step S8 is executed, and step S7 is not executed and the braking duration time has not been counted, step S14 is determined as No.

If the answer is Yes in step S14, it is assumed that continued operation of the brake 60 is likely to cause vibrations, and the powertrain control unit 30 causes the stepped transmission 51 to downshift (step S13).

Here, the case where step S12 is No includes a case where the required braking/driving force is greater than the fuel cut braking/driving force after the downshift and a case where the required braking/driving force is smaller than the fuel cut braking/driving force after the downshift by a value equal to or less than the predetermined braking/driving force α. If the required braking/driving force is greater than the fuel cut braking/driving force after the downshift, the engine 52 returns from the fuel cut and combustion starts after the downshift, and the operation of the brake 60 is released. If the required braking/driving force is smaller than the fuel cut braking/driving force after the downshift by a value equal to or less than the predetermined braking/driving force α, the fuel cut continues after the downshift, the brake braking force is controlled to a value smaller than before the downshift, and the operation of the brake 60 continues. In this case, the count of the brake duration continues, and a downshift may be performed again based on the upper limit time β corresponding to the brake braking force controlled to a smaller value again.

As described above, if step S12 returns No, fuel cut continues, ensuring improved fuel economy, but the brake 60 continues to operate, which may cause vibration. For this reason, in this embodiment, a downshift is performed when the braking duration exceeds the upper limit time β, thereby achieving both improved fuel economy and suppressed vibration.

Figure 5 is an example of a timing chart for when a downshift is performed because the required braking/driving force is lower than the fuel cut braking/driving force after the downshift. Figure 5 shows the gradient of the road on which the vehicle is traveling, the actual vehicle speed, the target vehicle speed, the required braking/driving force, the fuel cut braking/driving force, and the gear stage of the stepped transmission 51. The actual vehicle speed is shown by a solid line, the target vehicle speed is shown by a dotted line, the required braking/driving force is shown by a thick line, and the fuel cut braking/driving force is shown by a thin line.

In the example shown in Figure 5, at time T0, the road on which the vehicle is traveling becomes a downhill road, and thereafter, the gradient, with the uphill portion expressed as positive, gradually decreases (the downhill portion becomes steeper), and the required braking/driving force for maintaining the actual vehicle speed at the target vehicle speed gradually decreases. Note that, although Figure 5 shows these as constant values as an example, in reality they may fluctuate depending on the operation of the driving assistance device and the state of the powertrain 50. Similar processing is possible even when these values fluctuate.

At time T0, the gear of the stepped transmission 51 is controlled to 7th gear, for example. Before time T1, the powertrain control unit 30 keeps the gear of the stepped transmission 51 at the current gear (7th gear), generates a required braking/driving force in the powertrain 50 without cutting fuel from the engine 52, and the brake control unit 40 does not generate a braking force in the brake 60 (step S8).

At time T1, the powertrain control unit 30 cuts fuel from the engine 52 while keeping the gear stage of the stepped transmission 51 at the current gear stage (seventh gear), and generates a fuel cut braking/driving force for the current gear stage (seventh gear) in the powertrain 50, and the brake control unit 40 does not generate a braking force in the brake 60 (step S8).

When the required braking/driving force becomes equal to or lower than the fuel cut braking/driving force when the gear is in the seventh gear after time T1, the powertrain control unit 30 continues to cut fuel in the engine 52, while the brake control unit 40 causes the brakes 60 to generate a braking force equivalent to the difference between the required braking/driving force and the fuel cut braking/driving force of the current gear (seventh gear) (step S6). In Fig. 5, the hatched area where the required braking/driving force is lower than the fuel cut braking/driving force corresponds to the brake braking force.
The brake 60 continues to be applied.

After time T2, the required braking/driving force becomes lower than the fuel cut braking/driving force when the gear is in sixth gear minus the predetermined braking/driving force α (Yes in step S12), and the powertrain control unit 30 downshifts the stepped transmission 51 (step S13).

Furthermore, from time T2 onwards, as long as the required braking/driving force is equal to or greater than the fuel cut braking/driving force of the gear (5th gear) downshifted from the current gear (6th gear) minus a predetermined braking/driving force α (No in step S12), the powertrain control unit 30 will keep the gear of the stepped transmission 51 at the current gear (6th gear) and execute a fuel cut in the engine 52 to generate a fuel cut braking/driving force for the current gear (6th gear), and the brake control unit 40 will cause the brake 60 to generate a braking force equivalent to the difference between the required braking/driving force and the fuel cut braking/driving force of the current gear (step S6).

If the required braking/driving force continues to decrease thereafter, downshifts may be repeated while fuel cut continues, and fuel cut and brake 60 operation may continue.

The powertrain control unit 30 is also configured to calculate the fuel cut braking/driving force at a gear stage that is downshifted two or more stages from the current gear stage, and if the required braking/driving force is abruptly reduced, the step-variable transmission 51 may be downshifted two or more stages if the execution of the fuel cut can be continued and the braking force of the brake 60 can be generated so that the actual braking/driving force, which is the sum of the fuel cut braking/driving force generated by the powertrain 50 and the braking force of the brake 60, matches the required braking/driving force.

Figure 6 is an example of a timing chart for when a downshift is performed because the braking duration exceeds the upper limit time β. Like Figure 5, Figure 6 shows the gradient of the road on which the vehicle is traveling, the actual vehicle speed, the target vehicle speed, the required braking/driving force, the fuel cut braking/driving force, and the gear stage of the stepped transmission 51.

In the example shown in FIG. 6, at time T01, the road on which the vehicle is traveling becomes a downhill road, and thereafter, the gradient, with the uphill portion being positive, gradually decreases (the downhill portion becomes steeper), and the required braking/driving force to achieve the target vehicle speed gradually decreases. At time T01, the gear stage of the stepped transmission 51 is, for example, seventh gear. At time T11, the required braking/driving force becomes equal to the fuel cut braking/driving force when the gear stage is seventh gear. After that, at time T21, the duration from time T11 becomes the upper limit time β, and the powertrain control unit 30 downshifts the stepped transmission 51. In FIG. 6, these are shown as constant values as an example, but similar processing is possible even if these values fluctuate.

At time T11 and during the period from time T11 to time T21, the same processing is carried out as at time T1 and during the period from time T1 to time T2 shown in FIG. 5.

Unlike the time T2 shown in FIG. 5, the gradient does not become smaller around time T21. Therefore, at time T21, the required braking/driving force is not lower than the fuel-cut braking/driving force after the downshift (No in step S12), but the duration from time T11 when the brake 60 started to operate exceeds the upper limit time β (Yes in step S14), and the powertrain control unit 30 executes a downshift of the stepped transmission 51 (step S13).

In addition, after time T21, the fuel cut braking/driving force becomes lower than the required braking/driving force (No in step S4), so the powertrain control unit 30 resumes fuel injection in the engine 52 to return from the fuel cut, and the brake control unit 40 does not operate the brake 60 (step S8). As a result, it is possible to suppress the occurrence of vibrations caused by the brake 60 operating continuously for a long period of time.

In the above embodiment, the powertrain control unit 30 determines the braking/driving force to be generated in the powertrain 50, but this is not limited thereto, and the braking/driving force control unit 20 may determine the braking/driving force to be generated in the powertrain 50.

Although the embodiments of the present invention have been described in detail above, the present invention is not limited to these specific embodiments, and various modifications and variations are possible within the scope of the gist of the present invention as described in the claims.

REFERENCE SIGNS LIST 1 vehicle control device 10 required acceleration calculation unit 20 braking/driving force control unit 30 powertrain control unit 40 brake control unit 50 powertrain 51 stepped transmission 52 engine 60 brake

Claims (1)

A vehicle control device that performs driving assistance by automatically maintaining an actual vehicle speed at a target vehicle speed by controlling a power train including an engine and a stepped transmission and a brake,
When the gear stage of the stepped transmission is controlled to a predetermined gear stage to execute fuel cut of the engine and generate braking force by the brake so that the sum of the braking/driving force by the powertrain and the braking force by the brake becomes the required braking/driving force, if it is predicted that the braking/driving force of the powertrain due to the execution of fuel cut at a gear stage after downshifting from the predetermined gear stage is lower than the required braking/driving force, when the time during which the operation of the brake at the predetermined gear stage continues is equal to or exceeds a predetermined upper limit time, a downshift is performed from the predetermined gear stage to the gear stage after downshift, and fuel injection is resumed without operating the brake,
the upper limit time is set to a time that is shorter by a predetermined margin than a time during which vibration occurs when a braking force is generated by the brake during execution of a fuel cut at the predetermined gear stage,
A vehicle control device , wherein the upper limit time is specified to be gradually or stepwise shorter as the braking force by the brake increases in a state in which the brake continues to be applied in the specified gear stage .

Images