JP2018062295A - Vehicle braking control device - Google Patents

Abstract

[PROBLEMS] To ensure braking stability in a high speed range of a vehicle when left and right wheel independent control is performed so that the respective left and right rear wheel slip degrees approach the average value of the left and right front wheel slip degrees. Even when the low braking force characteristic is employed, it is possible to suppress an increase in the braking force of both the left and right rear wheels. In a vehicle having a brake device 20 capable of independently controlling the braking force of left and right rear wheels 10R, the respective slip ratios S of the left and right rear wheels 10R approach a common target slip ratio St. Executes left and right wheel independent control. The left and right wheel independent control is executed when the deceleration G is equal to or higher than the control start Gth2 lower than the control start Gth1 used in the low speed range in the high speed range of the vehicle 1. In the low speed range, the base value Stb that is the average value of the slip ratio S of the left and right front wheels 10F is used as the target slip ratio St. In the high speed range, a value obtained by multiplying the base value Stb by the correction coefficient K is used as the target slip ratio. Used as St. [Selection] Figure 6

Description

  The present invention relates to a vehicle braking control device, and more particularly to a braking control device suitable for controlling a vehicle in which left and right wheel independent control for independently controlling the braking force of left and right rear wheels is performed.

  Patent Document 1 discloses a vehicle braking force control device that can independently control the braking forces of the left and right rear wheels. According to this control device, the braking forces of the left and right rear wheels are individually controlled so that the rear wheel slip degree (for example, the slip ratio) becomes the target slip degree. This target slip degree is set to be lower by a predetermined amount than the front wheel slip degree. The target slip degree is corrected so that the target slip degree of the rear wheel on the contact load increasing side is higher than the target slip degree of the rear wheel on the contact load decreasing side.

JP 2012-096610 A

  In general, the center of gravity of a vehicle is often shifted in the left-right direction from the center of the vehicle, and also changes depending on changes in the number of passengers and the amount of cargo. When the center of gravity of the vehicle deviates in this way, a difference occurs in the ground contact load between the left and right wheels. If the left and right wheels have different ground loads, when the same braking force is applied to the left and right wheels, the vehicle tends to deflect toward the ground load reduction side even if the steered wheels are in the straight ahead position. This is because the degree of wheel slip during braking is proportional to the ground contact load, so if the left and right wheels have different ground contact loads due to a shift in the center of gravity of the vehicle from the vehicle center, the same braking force will be applied to the left and right wheels. This is because, when given, the wheel speed of the wheel on the ground load reduction side becomes lower than the wheel speed of the wheel on the opposite side.

  Therefore, the left and right rear wheel independent control is performed in such a manner that the braking forces of the left and right rear wheels are independently controlled so that the slip degrees (for example, slip ratio) of the left and right rear wheels are equal to the common target slip degree. Conceivable. According to such left and right wheel independent control, when braking is performed in a situation where the ground contact loads of the left and right wheels are different as described above, the braking force on the ground load increasing side becomes the braking force on the ground load decreasing side. The braking force of the left and right rear wheels can be controlled so as to be larger. As a result, a yaw moment (so-called anti-spin moment) for canceling the yaw moment of the vehicle to be deflected toward the contact load decreasing side can be applied to the left and right rear wheels. Thereby, the braking stability of the vehicle can be enhanced.

  It is conceivable to use an average value of the slip degree of the left and right front wheels as the target slip degree of the left and right wheel independent control. Here, when the braking force distribution of the front and rear wheels is near the ideal braking force distribution curve, it can be said that the braking force of the rear wheels is appropriately increased. For this reason, in this case, it can be said that the degree of slip of the rear wheel is likely to increase during braking. If the slip degree of the rear wheels is likely to increase, the target slip degree (that is, the slip degree of the left and right front wheels) is determined when braking is performed with the ground contact loads of the right and left wheels being different as described above. It is easy to form a state in which the average value) falls within the values of the respective slip degrees of the left and right rear wheels. According to the left and right wheel independent control, when this state is formed, the ground load increasing side (that is, the low slip degree side) is lowered while the braking force of the rear wheel is decreased while decreasing the ground load (that is, the high slip degree side). The braking force of the rear wheels is increased. Therefore, when the braking force distribution of the front and rear wheels is in the vicinity of the ideal braking force distribution curve, the antispin moment is easily applied to the left and right rear wheels.

  On the other hand, in order to ensure high braking stability in the high speed range of the vehicle, the characteristic that the braking force distribution of the rear wheels is reduced with a margin with respect to the ideal braking force distribution (for the sake of convenience, “rear wheel low It is conceivable to adopt a "braking force characteristic". Under this rear wheel low braking force characteristic, the slip degree of the rear wheel is less likely to increase during braking as compared with the case where the braking force distribution of the front and rear wheels is in the vicinity of the ideal braking force distribution curve. As a result, when the left and right rear wheel independent control is executed with the average value of the slip degree of the left and right front wheels as the target slip degree under the low braking force characteristic of the rear wheel, the slip degree of both the left and right rear wheels is lower than the target slip degree. A state is easily formed. According to the left and right wheel independent control, in such a state, in order to bring the slip degree of the left and right rear wheels closer to the target slip degree, not only the braking force of the rear wheel on the ground load increasing side but also the ground load decreasing side (high slip degree) The braking force of the rear wheel will be increased. If the braking forces of both the left and right rear wheels are increased in this way, it may be difficult to maintain the rear wheel low braking force characteristics that are employed with emphasis on braking stability in the high speed range.

  The present invention has been made in view of the above-described problems, and the left and right rear wheels are arranged so that the respective slip degrees of the left and right rear wheels approach a common target slip degree that is an average value of the slip degrees of the left and right front wheels. When the left and right wheel independent control that controls the braking force independently is performed, even if the rear wheel low braking force characteristic is adopted to ensure the braking stability in the high speed range of the vehicle, both the left and right rear wheels are controlled. An object of the present invention is to provide a vehicle braking control device that can suppress an increase in braking force.

  The vehicle braking control device according to the present invention is a vehicle braking control device including a braking device capable of independently controlling the braking force of the left and right rear wheels. The braking force control performed by the braking control device includes left and right wheel independent control for independently controlling the braking force of the left and right rear wheels so that the slip degrees of the left and right rear wheels approach a common target slip degree. The braking control device performs the left and right wheel independent control when the deceleration of the vehicle is equal to or higher than a first predetermined value in the low speed range of the vehicle, and in the high speed range higher than the low speed range, The left and right wheel independent control is executed when the deceleration is equal to or greater than a second predetermined value that is smaller than the first predetermined value. The left and right wheel independent control is executed using the average value of the slip degree of the left and right front wheels as the target slip degree in the low speed range, and is corrected to be lower than the average value in the high speed range. Is used as the target slip degree.

  The correction value may be a value corrected so that the degree of decrease with respect to the average value is higher when the deceleration during execution of the left and right wheel independent control is higher than when the deceleration is low. .

  The correction value is a decrease relative to the average value when the deceleration value at the start of the left and right wheel independent control is low when compared with a high value when the correction values for the same deceleration are compared. You may correct | amend so that a degree may become high.

  The correction value is a value corrected so that the degree of decrease with respect to the average value is higher when the yaw rate index value of the vehicle during execution of the left and right wheel independent control is higher than when it is low. May be.

  According to the present invention, in the high speed range of the vehicle, when a deceleration (second predetermined value) lower than the deceleration (first predetermined value) of the vehicle when the left and right wheel independent control is started in the low speed range is reached. The left and right wheel independent control is started. As a result, it is possible to create an environment in which the rear wheel low braking force characteristics (characteristics in which the braking force distribution of the rear wheels is reduced with a margin with respect to the ideal braking force distribution) can be realized. In addition, according to the present invention, the left and right wheel independent control is executed using the average value of the slip degree of the left and right front wheels as the target slip degree in the low speed range, whereas it is lower than the above average value in the high speed range. This is executed using the correction value corrected to the target slip degree. Thus, in the high speed range, the left and right wheel independent control is executed so that the rear wheel slip degree is lower than the front wheel slip degree. As a result, it is possible to suppress an increase in the braking force of both the left and right rear wheels even if the rear wheel low braking force characteristic is employed to ensure braking stability in a high speed range.

It is the schematic showing an example of the composition of vehicles to which the braking control device of Embodiment 1 of the present invention is applied. It is a conceptual diagram for demonstrating the left-right wheel independent control which concerns on Embodiment 1 of this invention. It is a figure for demonstrating an example of the adjustment of the braking force of the right-and-left rear wheel by the left-right wheel independent control which concerns on Embodiment 1 of this invention. It is a figure showing the relationship between the braking force of a front wheel and the braking force of a rear wheel. In Embodiment 1 of this invention, it is a figure for demonstrating the setting of the correction coefficient K used for the left-right wheel independent control accompanying the setting for high speeds. It is a flowchart which shows the routine performed by ECU in order to implement | achieve the braking control which concerns on Embodiment 1 of this invention. It is a figure showing an example of the operation | movement of the left-right wheel independent control when the routine shown in FIG. 6 is performed. In Embodiment 2 of this invention, it is a figure for demonstrating the setting of the correction coefficient K 'used for right-and-left wheel independent control with the setting for high speed. It is a flowchart which shows the routine performed by ECU in order to implement | achieve the braking control which concerns on Embodiment 2 of this invention.

Embodiment 1 FIG.
[Configuration of Embodiment 1]
FIG. 1 is a schematic diagram illustrating an example of a configuration of a vehicle 1 to which the braking control device according to the first embodiment of the present invention is applied. As shown in FIG. 1, the vehicle 1 of the present embodiment includes four wheels 10. In the following description, the left front wheel, the right front wheel, the left rear wheel, and the right rear wheel are referred to as 10FL, 10FR, 10RL, and 10RR, respectively. Further, the front wheels may be collectively referred to as 10F, and the rear wheels may be collectively referred to as 10R.

  The vehicle 1 includes a steering device 12 having a steering wheel 12a. The steering device 12 is configured to change the direction of the front wheels 10F that are the steering wheels of the vehicle 1 in accordance with the operation of the steering wheel 12a by the driver.

  The vehicle 1 includes a brake device 20. The brake device 20 includes a brake pedal 22, a master cylinder 24, a brake actuator 26, a brake mechanism 28, and a hydraulic pipe 30. The master cylinder 24 generates a hydraulic pressure corresponding to the depression force of the brake pedal 22 and supplies the generated hydraulic pressure to the brake actuator 26.

  The brake actuator 26 has a hydraulic circuit (not shown) interposed between the master cylinder 24 and the brake mechanism 28. The hydraulic circuit includes a pump for increasing the brake hydraulic pressure without relying on the master cylinder pressure, a reservoir for storing brake fluid, and a plurality of electromagnetic valves.

  A brake mechanism 28 is connected to the brake actuator 26 via a hydraulic pipe 30. The brake mechanism 28 is disposed on each wheel 10. The brake actuator 26 distributes the brake hydraulic pressure to the brake mechanism 28 of each wheel 10. More specifically, the brake actuator 26 can supply brake hydraulic pressure to the brake mechanism 28 of each wheel 10 using the master cylinder 24 or the pump as a pressure source. The brake mechanism 28 has a wheel cylinder 28a that operates according to the supplied brake hydraulic pressure.

  Furthermore, the brake actuator 26 can independently adjust the brake hydraulic pressure applied to each wheel 10 by controlling various electromagnetic valves provided in the hydraulic circuit. More specifically, the brake actuator 26 has a pressure increasing mode for increasing the pressure, a holding mode for holding the pressure, and a pressure reducing mode for decreasing the pressure as the control mode of the brake hydraulic pressure. The brake actuator 26 can vary the control mode of the brake hydraulic pressure for each wheel 10 by controlling ON / OFF of various electromagnetic valves. The braking force applied to each wheel 10 is determined according to the brake hydraulic pressure supplied to each wheel cylinder 28a. Therefore, the brake actuator 26 can independently control the braking force of each wheel 10 by changing the control mode.

  The braking control device of this embodiment includes an electronic control unit (ECU) 40 on the vehicle 1. Various sensors and the brake actuator 26 are electrically connected to the ECU 40. The various sensors herein include a wheel speed sensor 42, a vehicle speed sensor 44, an acceleration sensor 46, a brake pedaling force sensor 48, and a yaw rate sensor 50. The wheel speed sensor 42 is disposed on each wheel 10 and outputs a wheel speed signal corresponding to the rotational speed of the wheel 10. The vehicle speed sensor 44 outputs a vehicle speed signal corresponding to the vehicle speed (vehicle speed). The acceleration sensor 46 outputs an acceleration signal corresponding to the longitudinal acceleration of the vehicle 1. The brake pedal force sensor 48 outputs a brake pedal force signal corresponding to the pedal force of the brake pedal 22. The yaw rate sensor 50 outputs a yaw rate signal corresponding to the yaw rate of the vehicle 1.

  The ECU 40 includes a processor, a memory, and an input / output interface. The input / output interface takes in sensor signals from various sensors attached to the vehicle 1 and outputs an operation signal to the brake actuator 26. In the memory, various control programs and maps for controlling the brake actuator 26 are stored. The processor reads the control program from the memory and executes it, thereby realizing the function of the braking control device.

[Brake Control of Embodiment 1]
(Outline of independent left and right wheel independent control)
FIG. 2 is a conceptual diagram for explaining the left and right wheel independent control according to the first embodiment of the present invention. FIG. 3 is a diagram for explaining an example of adjusting the braking force of the left and right rear wheels 10RL and 10RR by the left and right wheel independent control according to the first embodiment of the present invention, in which the left and right rear wheels 10RL and 10RR are adjusted during braking. The relationship between the longitudinal force (that is, braking force) and the slip ratio S is shown.

  In the present embodiment, “right and left wheel independent control” is used for the left and right rear wheels 10RL and 10RR in order to ensure the braking stability of the vehicle 1. In the left and right wheel independent control, the braking forces of the left and right rear wheels 10RL and 10RR are independently controlled so that the slip ratios S of the left and right rear wheels 10RL and 10RR are equal to the common target slip ratio St. . The target slip ratio St used in the present embodiment has a base value Stb. As the base value Stb, the average value of the slip ratio S of the left and right front wheels 10FL, 10FR is used. In addition, the target slip ratio St is corrected from the base value Stb as described later in the high speed range of the vehicle 1.

The slip ratio S of the wheel 10 can be calculated according to the following equation (1) based on the wheel speed Vw detected by the wheel speed sensor 42 and the vehicle body speed V detected by the vehicle speed sensor 44, for example. Note that the vehicle body speed V is replaced with the vehicle speed sensor 44 by using a known method based on, for example, the wheel speed Vw detected by the wheel speed sensor 42 and the deceleration of the vehicle 1 detected by the acceleration sensor 46. May be estimated.

In general, the center of gravity of the vehicle is often shifted in the left-right direction from the center of the vehicle as in the example shown in FIG. FIG. 2 shows a situation where braking is performed in a state where the center of gravity of the vehicle 1 is shifted in the left-right direction. Thus, when the center of gravity of the vehicle 1 is deviated, the ground loads of the left and right wheels 10 are different. If the ground loads on the left and right wheels 10 are different, when the same braking force is applied to the left and right wheels 10, the ground load reducing wheel 10 (in the example shown in FIG. 2, the right front wheel 10FR and the right rear wheel 10RR). Is lower than the wheel speeds of the opposite wheels (the left front wheel 10FL and the left rear wheel 10RL). As a result, as shown by the dashed line in FIG. 3, the same braking force F1 is the left and right rear wheels 10RL, when a given 10RR, vertical load than the slip ratio S _RL of the left rear wheel 10RL of vertical load increasing side decreasing side towards the slip ratio _{S RR} of the right rear wheel 10RR increases of. FIG. 3 shows the characteristics of the left and right rear wheels 10RL and 10RR. The relationship between the left front wheel 10FL and the right front wheel 10FR is the same as that in FIG.

  As described above, even when the braking force of the left and right wheels 10 is the same during braking, a difference occurs in the slip ratio S between the left wheels 10FL, 10RL and the right wheels 10FR, 10RR, and the moment ( The clockwise moment shown in FIG. As a result, as in the example shown in FIG. 2, even when the steered wheel (front wheel 10F) is in the straight traveling position, the vehicle 1 tends to deflect toward the ground load reduction side (right side in the example shown in FIG. 2). .

As described above, when braking is performed in a situation where the ground loads of the left and right wheels 10 are different, the following effects can be obtained by applying the left and right wheel independent control of the present embodiment. Here, as an example of the target slip ratio St of the left and right wheels independently controlled left and right rear wheels 10RL, as shown in FIG. 3, each of the slip ratio _S RL of _10RR, for example a value St1 is used in between _{S RR} Description To do.

In the example shown in FIG. 2 and FIG. 3, the left and right rear wheels 10RL are set so that the left and right rear wheels 10RL and 10RR have the same slip ratio S equal to the common target slip ratio St1 by executing the left and right wheel independent control. The braking force of 10RR is controlled independently. As a result, the braking force of the left rear wheel 10RL, which is the wheel on the contact load increasing side (that is, the outside of the turn due to the moment based on the gravity offset), is increased from F1 to _FRL in order to increase the slip ratio S. On the other hand, the ground contact load decreases side (i.e., inside of the turn) braking force of the right rear wheel 10RR is a wheel is reduced to F _RR from F1 to reduce the slip ratio S.

  According to the left and right wheel independent control, as described above, the braking force of the left rear wheel 10RL on the contact load increasing side is increased more than the braking force of the right rear wheel 10RR on the contact load decreasing side. A difference is given to the braking force of 10RR. As a result, a moment (a counterclockwise moment shown in FIG. 2) is generated in the vehicle 1 due to the left-right difference in the braking force. This moment acts as a yaw moment (so-called anti-spin moment) for canceling the moment due to the gravity offset. Thereby, the braking stability of the vehicle 1 can be improved. The left and right wheel independent control described above corresponds to one of EBD (Electronic Brake force Distribution) which appropriately controls the braking force distribution to each wheel 10 according to the situation of the vehicle 1.

As can be seen from the characteristics shown in FIG. 3, the braking force of the wheel (10RL) on the ground load increasing side is reduced on the ground load decreasing side even when compared with any slip ratio S other than the target slip ratio St1. It becomes larger than the braking force of the wheel (10RR). Therefore, when the difference between the left and right given to the braking force of the rear wheel 10R during right and left wheels independently control run, the slip ratio S _RL as target slip ratio St is _St1, anti-spin not be a value between S _RR A moment is about to occur in the vehicle 1. However, the target slip ratio St is the left and right rear wheels 10RL as in the example shown in FIG. 3, the slip ratio _S RL of _10RR, when is between _{S RR,} the ground load increase side (i.e., outside of the turning vehicle 1 ) Since the braking force of the rear wheel 10R on the contact load increasing side (inside of the turning) is reduced while increasing the braking force of the rear wheel 10R, the antispin moment can be generated more effectively.

(Issues for independent control of left and right wheels at high speed)
FIG. 4 is a diagram showing the relationship between the braking force of the front wheel 10F and the braking force of the rear wheel 10R. The parabolic curve in FIG. 4 is an ideal braking force distribution curve that represents an ideal distribution of the braking force of the front and rear wheels 10. The braking performance of the vehicle 1 can be improved by bringing the actual braking force distribution closer to the ideal braking force distribution curve. A line other than the ideal braking force distribution curve in FIG. 4 represents an actual braking force distribution line.

  A straight line L0 connecting the origin P0 and the point P1 in FIG. 4 is an actual braking force distribution line used when the left and right wheel independent control is not performed. The point P1 corresponds to a point where the deceleration G of the vehicle 1 becomes Gth1 on the actual braking force distribution line L0. In the present embodiment, when the vehicle speed (vehicle speed) V is in the low speed range, the left and right wheel independent control is started when the deceleration G reaches Gth1 (hereinafter referred to as “low speed setting”). Is used. Hereinafter, the deceleration G when the left and right wheel independent control with the low speed setting is started is simply referred to as “control start Gth1”. According to the left and right wheel independent control, when the slip ratio S of the left and right rear wheels 10RL and 10RR becomes equal to the target slip ratio St, the braking force applied to the left and right rear wheels 10RL and 10RR is maintained. The straight line L1 corresponds to an actual braking force distribution line when the braking force of the left and right rear wheels 10RL, 10RR is held in a situation where the deceleration G increases beyond G1 under the low speed setting.

The point P1 is located near the ideal braking force distribution curve. For this reason, according to the low speed setting, it can be said that the left and right wheel independent control can be performed in a state where the braking force of the rear wheel 10R is appropriately increased. If the braking force of the rear wheel 10R is increased, it can be said that the slip ratio S of the rear wheel 10R is likely to increase during braking. If the slip ratio S of the rear wheel 10 is likely to increase due to the use of the low speed setting, the target slip ratio is obtained when braking is performed in a situation where the ground contact loads of the left and right wheels 10R are different as described above. St (i.e., left and right front wheels 10FL, the average value of the slip ratio S of the 10FR) easily left and right rear wheels 10RL, respectively of the slip ratio _S (S _{RL, S RR)} of 10RR state C1 to fit in between the values of the form .

  According to the left and right wheel independent control, when the state C1 described above is formed, the outer ring (that is, the rear wheel on the ground load increasing side) 10R while reducing the braking force of the inner ring (that is, the rear wheel on the ground load decreasing side) 10R. The braking force of can be increased. Therefore, when the braking force distribution of the front and rear wheels 10 is in the vicinity of the ideal braking force distribution curve, the anti-spin moment is easily applied to the left and right rear wheels 10RL and 10RR. FIG. 4 shows an example of adjusting the braking force of the left and right rear wheels 10RL and 10RR, that is, increasing the braking force of the outer wheel 10R with respect to the actual braking force distribution line L1 and decreasing the braking force of the inner wheel 10R. An example is shown in which a left-right difference is given to the braking force.

  In the present embodiment, when the vehicle speed V is in the high speed range higher than the low speed range where the low speed setting is used, the deceleration Gth2 is lower than Gth1 (hereinafter simply referred to as “control start Gth2”). The setting (hereinafter referred to as “high-speed setting”) is used in which independent control of the left and right wheels is started when the vehicle reaches (referred to as “high speed setting”). A point P2 in FIG. 4 corresponds to a point at which the deceleration G of the vehicle 1 becomes G2 on the actual braking force distribution line L0. This G2 corresponds to an example of the control start Gth2 used under the high speed setting. More specifically, in the present embodiment, a different value according to the vehicle speed V (more specifically, a lower value as the vehicle speed V is higher) is used as the control start Gth2 used under the high speed setting. . G2 corresponds to one of such a plurality of control start Gth2.

  The straight line L2 is an actual braking force distribution line when the braking force applied to the left and right rear wheels 10RL, 10RR is held in a situation where the deceleration G increases beyond the control start Gth2 under the high speed setting. It corresponds to. As described above, the control start Gth2 used under the high speed setting is lower than the control start Gth1 used under the low speed setting. As shown in FIG. 4, according to the actual braking force distribution line L2, compared with the actual braking force distribution line L1 for low speed, the braking force distribution of the rear wheel 10R has a margin with respect to the ideal braking force distribution. A reduced characteristic (hereinafter referred to as “rear wheel low braking force characteristic”) can be realized. According to this rear wheel low braking force characteristic, it is possible to suppress a decrease in the cornering power of the rear wheel 10R, so that the braking stability of the vehicle 1 can be improved.

  Under the above-described rear wheel low braking force characteristic, the slip ratio S of the rear wheel 10R is less likely to increase during braking as compared with the case where the braking force distribution of the front and rear wheels 10 is in the vicinity of the ideal braking force distribution curve. As a result, when the left and right rear wheel independent control is executed with the average value of the slip ratio S of the left and right front wheels 10FL and 10FR as the target slip ratio St under the rear wheel low braking force characteristics, both the left and right rear wheels 10RL and 10RR are controlled. A state C2 in which the slip rate S is lower than the target slip rate St is easily formed.

  According to the left and right wheel independent control, in the above-described state C2, the outer wheel (increase in ground load) is increased as shown in an example shown in FIG. 4 in order to bring the slip ratio S of the left and right rear wheels 10RL and 10RR closer to the common target slip ratio St. In addition to the braking force of the rear wheel 10R on the side, the braking force of the inner wheel (rear wheel on the ground contact load reducing side) 10R is increased. When the braking forces of both the left and right rear wheels 10RL and 10RR are increased in this way, it becomes difficult to maintain the rear wheel low braking force characteristics that are employed with emphasis on braking stability in a high speed range. Further, when the braking force of both the left and right rear wheels 10RL and 10RR is increased, an effective anti-spin moment is applied to the vehicle 1 even if the left and right rear wheels 10RL and 10RR have a left-right difference in braking force. It becomes difficult.

(Characteristic control of Embodiment 1)
In the present embodiment, in view of the above-described problem in the high speed range, the target slip ratio St is changed as follows according to the vehicle speed V when the left and right wheel independent control is executed. That is, in the low speed range, the above-described base value Stb is used as it is as the target slip ratio St. On the other hand, in the high speed range, a correction value corrected to be lower than the base value Stb according to the method described below with reference to FIG. 5 is used as the target slip ratio St. Thereby, in the high speed region, the left and right wheel independent control is executed so that the slip ratio S of the rear wheel 10R is lower than the slip ratio S of the front wheel 10F.

FIG. 5 is a diagram for explaining the setting of the correction coefficient K used in the left and right wheel independent control with the setting for high speed in the first embodiment of the present invention. In the present embodiment, the target slip ratio St when using the high speed setting is calculated as a value obtained by multiplying the base value Stb by the correction coefficient K according to the following equation (2).
St = Stb × K (2)

  As shown in FIG. 5, the correction coefficient K (0 <K <1) is a deceleration G during execution of the left and right wheel independent control accompanied by the setting for high speed, and a deceleration G at the start of the left and right wheel independent control. It is changed according to the control start Gth2. More specifically, under the same control start Gth2, the correction coefficient K is set so as to decrease as the deceleration G during execution of the left and right wheel independent control increases. Further, when the control start Gth2 is low, the correction coefficient K at the same deceleration G is set to be smaller than when the control start Gth2 is high. Note that the numerical values of the correction coefficient K, the deceleration G, and the control start Gth2 shown in FIG. 4 are examples. And these numerical values differ according to the specification (for example, braking force distribution of the front and rear wheels) of the application target vehicle.

  According to the setting of the correction coefficient K described above, when the deceleration G during execution of the left and right wheel independent control is high, the target slip ratio St is set so that the degree of decrease with respect to the base value Stb is higher than when the deceleration G is low. Can be corrected. Further, according to this setting, when the target slip ratio St at the same deceleration G is compared, when the control start Gth2 is low, the degree of decrease with respect to the base value is higher than when the control start Gth2 is high. The target slip ratio St can be corrected.

(Processing by ECU)
FIG. 6 is a flowchart showing a routine that is executed by the ECU 40 in order to realize the braking control according to the first embodiment of the present invention. Note that this routine is repeatedly executed at a predetermined cycle after the vehicle 1 is started.

  In the routine shown in FIG. 6, the ECU 40 first obtains the deceleration G, the wheel speed Vw, and the vehicle speed V using the acceleration sensor 46, the wheel speed sensor 42, and the vehicle speed sensor 44 (step 100).

  Next, the ECU 40 calculates the slip rate S for each wheel 10 using the wheel speed Vw, the vehicle speed (body speed) V acquired in step 100, and the above equation (1) (step 102). Next, the ECU 40 calculates the average value of the slip ratios S of the left and right front wheels 10FL, 10FR acquired in step 100 as the base value Stb of the target slip ratio St (step 104).

  Next, the ECU 40 determines whether or not a predetermined start condition A for the left and right wheel independent control is satisfied (step 106). The start condition A is determined in advance based on the deceleration G and the vehicle speed V acquired in step 100 as described below. The start condition A is determined to be satisfied when the deceleration G is a predetermined threshold value. The threshold value is set to be different depending on the vehicle speed V. More specifically, in the low speed range where the vehicle speed V is less than the predetermined value Vth, the control start Gth1 described above is used as the threshold value (setting for low speed). On the other hand, in a high speed range where the vehicle speed V is equal to or higher than the predetermined value Vth, a control start Gth2 smaller than Gth1 is used as the threshold value. In the high speed range, the higher the vehicle speed V, the lower the control start Gth2 is used as the threshold value (high speed setting).

  If the ECU 40 determines in step 106 that the start condition A is not satisfied, the ECU 40 immediately ends the current processing cycle. In this case, the brake hydraulic pressure corresponding to the depression force of the brake pedal 22 is supplied to the wheel cylinders 28 a of the wheels 10. More specifically, the wheel cylinder 28a of each wheel 10 is provided with the same braking force with respect to the left and right directions of the front wheel 10F and the rear wheel 10R so as to obtain a braking force according to a predetermined front-rear distribution. Thus, the brake hydraulic pressure adjusted by the brake actuator 26 is supplied.

  On the other hand, when it is determined in step 106 that the start condition A is satisfied, the ECU 40 determines whether or not the current vehicle speed range is the high speed range based on the comparison result between the current vehicle speed V and the predetermined value Vth. (Step 108). As a result, when the ECU 40 determines that the current vehicle speed range is the low speed range, the ECU 40 proceeds to step 110. In step 110, the left and right wheel independent control is executed while using the base value Stb calculated in step 104 as it is as the target slip ratio St.

  If the ECU 40 determines in step 108 that the current vehicle speed range is the high speed range, the ECU 40 proceeds to step 112. The ECU 40 stores a map (not shown) that defines the relationship between the deceleration G and control start Gth2 and the correction coefficient K (the relationship as shown in FIG. 5). In step 112, referring to such a map, a correction coefficient K corresponding to the deceleration G acquired in step 100 and the control start Gth2 used in step 106 is acquired. In addition, a correction value obtained by multiplying the acquired correction coefficient K by the base value Stb calculated in step 104 is calculated as the target slip ratio St. In this step 112, the left and right wheel independent control is executed using the target slip ratio St thus calculated.

  FIG. 7 is a diagram showing an example of the left and right wheel independent control operation when the routine shown in FIG. 6 is executed. According to the routine shown in FIG. 6 described above, in the left and right wheel independent control performed in the low speed range, the “low speed setting” using the relatively high control start Gth1 is used. In the low speed range, the base value Stb (that is, the average value of the slip ratio S of the left and right front wheels 10FL and FR) is used as it is as the target slip ratio St. Accordingly, as shown in FIG. 7 (as in the example shown in FIG. 4), the left and right wheel independent control is performed with the braking force distribution of the rear wheel 10R appropriately increased so as to approach the ideal braking force distribution curve. Can be implemented. As a result, the left and right wheel independent control is executed in such a manner that the braking force of the inner wheel (that is, the rear wheel on the ground load reduction side) 10R is reduced while the braking force of the outer wheel (that is, the rear wheel on the ground load increasing side) 10R is increased. It becomes easy. For this reason, the anti-spin moment can be appropriately applied to the left and right rear wheels 10RL, 10RR, so that high braking stability of the vehicle 1 can be ensured. In addition, according to the left and right wheel independent control for the low speed region described above, the rear wheel is moved to the vicinity of the ideal braking force distribution curve in the low speed region where the braking stability of the vehicle 1 is relatively easily secured as compared with the high speed region. By actively using the braking force of 10R, the braking performance of the vehicle 1 can be improved and the braking stability can be ensured high.

  Further, according to the above routine, in the left and right wheel independent control performed in the high speed range, the “high speed setting” using the control start Gth2 lower than the control start Gth1 is used. In the high speed range, a correction value corrected so as to be lower than the base value Stb is used as the target slip ratio St. According to such left and right wheel independent control, since the control start Gth2 is set lower than the control start Gth1, the above-mentioned “rear wheel low braking force characteristics” (rear braking force distribution line L1 for low speed is compared with It is possible to create an environment in which the braking force distribution of the wheel 10R can be realized with a characteristic that is reduced with a margin with respect to the ideal braking force distribution. In addition, by reducing the target slip ratio St, it is possible to make it difficult to make an adjustment that increases the braking force of both the left and right rear wheels 10RL and 10RR during the execution of the left and right wheel independent control. In other words, the left and right wheel independent control can be easily performed in such a manner that the braking force of the inner wheel 10R is decreased while the braking force of the outer wheel 10R is increased. As a result, as shown in FIG. 7, the anti-spin moment can be appropriately applied to the left and right rear wheels 10RL and 10RR while maintaining the rear wheel low braking force characteristics well during the left and right wheel independent control. . In other words, it is possible to obtain the braking stability improvement effect by the left and right wheel independent control while maintaining the rear wheel low braking force characteristic that emphasizes the braking stability in the high speed range.

  Further, according to the correction of the target slip ratio St based on the correction coefficient K, when the deceleration G during execution of the left and right wheel independent control accompanied with the setting for high speed is high, the base value Stb is compared with the case where the deceleration G is low. The target slip ratio St is corrected so as to increase the degree of decrease. When the deceleration G increases, the load on the rear wheel 10R decreases, so that the behavior of the vehicle 1 is likely to be disturbed. According to the above-described correction setting, when the deceleration G is high, it is possible to suppress an increase in the braking force of the rear wheel 10R due to the execution of the left and right wheel independent control as compared with the case where the deceleration G is low. Therefore, the target slip ratio St can be corrected so that the braking stability of the vehicle 1 can be appropriately ensured regardless of the change in the deceleration G during execution of the left and right wheel independent control.

  Further, according to the correction of the target slip ratio St based on the correction coefficient K, when the target slip ratio St at the same deceleration G is compared, the base start is lower when the control start Gth2 is low than when it is high. The target slip ratio St is corrected so that the degree of decrease with respect to the value Stb is increased. The setting for lowering the control start Gth2 is used to more effectively obtain the above-described rear wheel low braking force characteristic for suppressing the braking force of the rear wheel 10R. Therefore, according to the correction setting based on the control start Gth2, when the control start Gth2 is lower, that is, when it is desired to further suppress the braking force of the rear wheel 10R, the control of the rear wheel 10R is performed by executing the left and right wheel independent control. A setting that makes it difficult to increase power is obtained.

Embodiment 2. FIG.
Next, a second embodiment of the present invention will be described with reference to FIGS. In the following description, the configuration shown in FIG. 1 is used as an example of the system configuration of the second embodiment.

[Brake Control of Embodiment 2]
In the first embodiment described above, the correction coefficient K is set based on the deceleration G and the control start Gth2 during execution of the left and right wheel independent control accompanied by the setting for high speed. On the other hand, the braking control of the present embodiment is different from the braking control of the first embodiment in that a correction coefficient K ′ for correcting the target slip ratio St is set based on the yaw rate YR of the vehicle 1. It is different.

  FIG. 8 is a diagram for explaining the setting of the correction coefficient K ′ used for the left and right wheel independent control with the high speed setting in the second embodiment of the present invention. The correction coefficient K ′ of the present embodiment is multiplied by the base value Stb, similarly to the correction coefficient K of the first embodiment. In the present embodiment, as an example, the yaw rate signal output from the yaw rate sensor 50 is used to acquire the yaw rate index value.

  As shown in FIG. 8, the correction coefficient K ′ is set to 1.0 in the minute region of the yaw rate YR. For this reason, this minute region functions as a dead zone in which correction by the correction coefficient K ′ does not act. In the setting shown in FIG. 8, the correction coefficient K ′ is set so as to decrease as the yaw rate YR during the left and right wheel independent control is higher in the region on the higher yaw rate side than the minute region.

  According to the setting of the correction coefficient K ′ described above, when the yaw rate YR during execution of the left and right wheel independent control is high, the target slip ratio St is set so that the degree of decrease with respect to the base value Stb is higher than when the yaw rate YR is low. Can be corrected.

(Processing by ECU)
FIG. 9 is a flowchart showing a routine executed by the ECU 40 in order to realize the braking control according to the second embodiment of the present invention. The processing in steps 100 to 110 in the routine shown in FIG. 9 is as described in the first embodiment.

  In this routine, following the process of step 100, the ECU 40 acquires the yaw rate YR using the yaw rate sensor 50 (step 200). The yaw rate index value used for correcting the target slip ratio St is not limited to the yaw rate YR acquired using the yaw rate sensor 50 in this way. That is, for example, the yaw rate index value may be acquired as a larger value as the difference between the wheel speeds of the left and right front wheels 10FL and 10FR increases.

  In this routine, if the ECU 40 determines in step 108 that the current vehicle speed range is the high speed range, the ECU 40 proceeds to step 202. The ECU 40 stores a map (not shown) that defines the relationship (the relationship as shown in FIG. 8) between the yaw rate YR and the correction coefficient K ′. In step 202, referring to such a map, a correction coefficient K corresponding to the yaw rate YR acquired in step 200 is acquired. Then, a correction value obtained by multiplying the acquired correction coefficient K ′ by the base value Stb calculated in step 104 is calculated as the target slip ratio St. In this step 202, the left and right wheel independent control is executed while using the target slip ratio St thus calculated.

  Also in the routine shown in FIG. 9 described above, as in the first embodiment, the correction value corrected so as to be lower than the base value Stb is used as the target slip ratio St in the high speed range. Thereby, in the high speed range, the braking stability improvement effect by the left and right wheel independent control can be obtained while maintaining the rear wheel low braking force characteristic that emphasizes the braking stability.

  In addition, according to the above routine, the target slip ratio St is corrected so that the degree of decrease relative to the base value Stb is higher when the yaw rate YR during execution of the left and right wheel independent control is higher than when the yaw rate YR is low. . When braking is performed in a situation where the ground loads on the left and right wheels 10 are different, if a large moment due to gravity offset acts on the vehicle 1, the yaw rate YR increases. According to the yaw rate YR, the disturbance of the behavior of the vehicle 1 can be appropriately grasped, and when the yaw rate YR is large, it can be determined that the disturbance of the behavior due to the moment is large. For this reason, according to the correction of the target slip ratio St based on the correction coefficient K ′, the target slip is ensured so that the braking stability of the vehicle 1 can be appropriately ensured regardless of the change in the yaw rate YR during the execution of the left and right wheel independent control. The rate St can be corrected.

  By the way, in the first embodiment described above, the yaw rate YR during the execution of the left and right wheel independent control is achieved in the degree of decrease according to the deceleration G and the control start Gth2 during the execution of the left and right wheel independent control. The target slip ratio St in the high speed range is corrected so as to be lower than the base value Stb with a degree of decrease corresponding to. However, the target slip degree in the high speed range in the present invention may be corrected so as to be lower than the average value of the slip degree of the left and right front wheels (the base value Stb is equivalent to this). That is, the correction of the target slip degree in the high speed range does not necessarily have to be performed with the degree of decrease according to the above-described deceleration G or the like, and may be performed based on a predetermined fixed value, for example. Further, the target slip degree in the low speed range in the present invention is not strictly limited to the average value of the slip degree of the left and right front wheels (the base value Stb corresponds to this), and may be a value in the vicinity of the average value.

  Further, in the left and right wheel independent control of the first and second embodiments described above, the slip ratio S is used as an example of the slip degree. However, the left and right wheel independent control according to the present invention may be any control that independently controls the braking force of the left and right rear wheels so that the respective slip degrees of the left and right rear wheels are equal to the target slip degree. Instead, for example, a slip amount (that is, a difference obtained by subtracting the wheel speed Vw from the vehicle body speed V) may be used as the slip degree.

  Moreover, in Embodiment 1 and 2 mentioned above, the brake device 20 which can control the braking force of the four wheels 10 of the vehicle 1 independently was mentioned as an example. However, the braking control according to the present invention can be applied to a vehicle including a braking device that can independently control at least the braking forces of the left and right rear wheels.

  In the first and second embodiments described above, the control start Gth1 used under the low speed setting corresponds to the “first predetermined value” in the present invention, and the control start Gth2 used under the high speed setting is This corresponds to the “second predetermined value” in the present invention.

1 Vehicle 10 Wheel 10F Front Wheel 10FL Left Front Wheel 10FR Right Front Wheel 10R Rear Wheel 10RL Left Rear Wheel 10RR Right Rear Wheel 12 Steering Device 12a Steering Wheel 20 Brake Device 22 Brake Pedal 24 Master Cylinder 26 Brake Actuator 28 Brake Mechanism 28a Wheel Cylinder 30 Hydraulic Piping 40 Electronic Control Unit (ECU)
42 Wheel speed sensor 44 Vehicle speed sensor 46 Acceleration sensor 48 Brake pedal force sensor 50 Yaw rate sensor

Claims (4)

A vehicle braking control device including a braking device capable of independently controlling the braking force of the left and right rear wheels,
The braking force control performed by the braking control device includes left and right wheel independent control for independently controlling the braking force of the left and right rear wheels so that the respective slip degrees of the left and right rear wheels approach a common target slip degree,
The braking control device performs the left and right wheel independent control when the deceleration of the vehicle is equal to or higher than a first predetermined value in the low speed range of the vehicle, and in the high speed range higher than the low speed range, Executing the left and right wheel independent control when the deceleration is equal to or greater than a second predetermined value smaller than the first predetermined value;
The left and right wheel independent control is executed using the average value of the slip degree of the left and right front wheels as the target slip degree in the low speed range, and is corrected to be lower than the average value in the high speed range. The braking control device for a vehicle is executed by using as a target slip degree.   The correction value is a value corrected so that the degree of decrease with respect to the average value is higher when the deceleration during execution of the left and right wheel independent control is higher than when the deceleration is low. The vehicle braking control device according to claim 1.   The correction value is a decrease relative to the average value when the deceleration value at the start of the left and right wheel independent control is low when compared with a high value when the correction values for the same deceleration are compared. The vehicle braking control device according to claim 1, wherein the braking control device is corrected so as to increase the degree.   The correction value is a value corrected so that the degree of decrease relative to the average value is higher when the yaw rate index value of the vehicle during execution of the left and right wheel independent control is higher than when the vehicle is low. The vehicle braking control apparatus according to claim 1.

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