Braking control device

Abstract

To improve stability of a vehicle that banks during steering.SOLUTION: A brake control device 10 is applicable to a vehicle 90 that enables a vehicle body and a wheel 91 to bank during steering. The brake control device 10 comprises a brake control part 20 that executes anti-lock brake control by which the wheel 91 is suppressed from being locked while braking the vehicle 90 and holding control by which magnitude of braking force to be applied to the wheel 91 during steering of the vehicle 90 is held. In a case where the anti-lock brake control is not executed during braking of the vehicle 90, when the vehicle 90 is steered and acceleration of the wheel is below an acceleration determination value which is a prescribed negative value and variations of the wheel acceleration in a prescribed period of time are variations thereof in a deceleration direction, the brake control part 20 starts to execute the holding control.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a braking control device for a vehicle in which the body and wheels can be tilted when turning. [Background technology]

[0002] In vehicles such as motorcycles, whose bodies and wheels can be tilted during cornering, the gyroscopic effect associated with wheel rotation contributes to vehicle stability. Therefore, if the wheels of such vehicles lock, the vehicle's stability is significantly reduced. In particular, if the front wheels lock due to a sudden increase in braking force while the body is tilted, there is a risk of the vehicle tipping over. Wheel lock due to a sudden increase in braking force during cornering is particularly likely to occur on low-friction roads, where the coefficient of friction between the road surface and the wheels is low.

[0003] Control that suppresses wheel slip by adjusting braking force is known, as disclosed in Patent Document 1. The control device disclosed in Patent Document 1 is configured to change the timing at which the reduction in braking force starts depending on wheel deceleration in order to improve stability when the vehicle turns as described above. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Laid-Open No. 2018-149979 Summary of the Invention [Problem to be solved by the invention]

[0005] To prevent wheels from locking during a vehicle turn, as described above, it is preferable to start reducing the braking force when the amount of slip is small. In the control device disclosed in Patent Document 1, the timing for starting the reduction of the braking force is determined by a threshold value of wheel deceleration. For example, it is conceivable to advance the timing for starting the reduction of the braking force by changing the threshold value of wheel deceleration. However, while the vehicle is traveling, there are cases where the wheel speed temporarily decreases relative to the vehicle speed but does not result in wheel lock. For example, when the vehicle is traveling on a high-μ road with a high road friction coefficient, even if the wheel speed temporarily decreases due to unevenness in the road surface, the decrease in wheel speed is easily resolved and the amount of slip is unlikely to increase. Simply advancing the timing for starting the reduction of the braking force may result in unnecessary reduction of the braking force in situations where the amount of slip is relatively unlikely to increase, such as when the vehicle is traveling on a high-μ road. [Means for solving the problem]

[0006] A braking control device for solving the above problem is applied to a vehicle that can bank the body and wheels when turning, and controls a braking device that applies braking force to the wheels. The braking control device includes a bank angle acquisition unit that acquires the inclination angle of the body due to banking as a bank angle, a wheel acceleration acquisition unit that acquires the acceleration of the wheels as wheel acceleration, a turning determination unit that determines whether the vehicle is turning based on the bank angle, anti-lock brake control that suppresses locking of the wheels while braking the vehicle, and a braking control unit that performs holding control that maintains the magnitude of the braking force applied to the wheels while the vehicle is turning.The gist of the braking control unit is that when the anti-lock brake control is not being performed while braking the vehicle, the vehicle is turning, the wheel acceleration is equal to or less than an acceleration determination value that is a specified negative value, and the change in the wheel acceleration over a specified period is a change in the direction of deceleration, the braking control unit starts the holding control.

[0007] According to the above configuration, by implementing the hold control, it is possible to reduce the amount of slippage while maintaining braking force during cornering. Because the amount of slippage is reduced by maintaining braking force, the duration of slippage is likely to be shorter than when antilock brake control (hereinafter also referred to as "ABS control") is implemented to reduce braking force. Furthermore, since the condition for initiating the hold control is that the change in wheel acceleration over a specified period is in the deceleration direction, hold control is less likely to be initiated if the decrease in wheel speed is temporary due to an external disturbance or the like. In other words, it is possible to prevent hold control from being initiated when no slippage is occurring. [Brief explanation of the drawings]

[0008] [Figure 1] FIG. 1 is a schematic diagram showing an embodiment of a vehicle braking control device and a vehicle that is an object to be controlled by the braking control device. [Figure 2] FIG. 2 is a front view showing the vehicle. [Figure 3] FIG. 3 is a flowchart showing the flow of processing executed by the braking control device. [Figure 4] FIG. 4 is a flowchart showing the flow of processing executed by the braking control device. [Figure 5] FIG. 5 is a diagram showing changes in braking force and wheel speed when the brake control device performs holding control. [Figure 6] FIG. 6 is a diagram showing changes in braking force and wheel speed when the brake control device performs holding control. DETAILED DESCRIPTION OF THE INVENTION

[0009] An embodiment of a braking control device will be described below with reference to FIGS. FIG. 1 shows a braking control device 10 and a vehicle 90 to which the braking control device 10 is applied. <vehicle> The vehicle 90 is, for example, a motorcycle as shown in Fig. 2. A motorcycle is an example of a saddle-ride type vehicle in which a driver straddles a body 93 to ride. When a motorcycle turns a curve, the body 93 and wheels are banked, so that the body 93 and wheels lean from an upright state toward the inside of the curve, i.e., toward the center of the turn, around an axis in the fore-and-aft direction of the body 93. Terms used to describe the leaning of the body 93 and wheels when turning include bank, lean, and roll. In this embodiment, a description will be given using bank.

[0010] As shown in FIG. 1, a vehicle 90 has front wheels 91 and rear wheels 92. The front wheels 91 are steerable wheels that can be operated via a steering member such as a handlebar. The rear wheels 92 are drive wheels to which driving force is transmitted from a power source of the vehicle 90. An example of the power source of the vehicle 90 is an internal combustion engine. The power source is not limited to an internal combustion engine, and an electric motor or the like can also be used.

[0011] The vehicle 90 is equipped with a suspension that connects the wheels to a body 93. The vehicle 90 is equipped with, for example, a front fork that connects a front wheel 91 to the frame of the body 93. The vehicle 90 is equipped with, for example, a swing arm that connects a rear wheel 92 to the frame of the body 93.

[0012] <Brake device> As shown in Fig. 1, a vehicle 90 is provided with a braking device 70. One example of the braking device 70 is a friction braking device. Fig. 1 shows a hydraulic braking device as an example of a friction braking device.

[0013] The braking device 70 includes a front wheel braking mechanism 81 corresponding to the front wheel 91 and a rear wheel braking mechanism 82 corresponding to the rear wheel 92. The front wheel braking mechanism 81 is capable of applying a braking force to the front wheel 91. The rear wheel braking mechanism 82 is capable of applying a braking force to the rear wheel 92. Each braking mechanism 81, 82 is composed of a wheel cylinder, a rotating body that rotates integrally with the wheel, and a friction material that can be pressed against the rotating body. An example of the braking mechanisms 81, 82 is a disc brake. The braking mechanisms 81, 82 may also be drum brakes.

[0014] 1, braking device 70 includes a first master cylinder 71 and a second master cylinder 72. Braking device 70 includes a fluid pressure adjusting device 73 to which brake fluid is supplied from first master cylinder 71 and second master cylinder 72. Fluid pressure adjusting device 73 includes a fluid path connecting first master cylinder 71 and a wheel cylinder of a front wheel braking mechanism 81. Fluid pressure adjusting device 73 includes a fluid path connecting second master cylinder 72 and a wheel cylinder of a rear wheel braking mechanism 82.

[0015] The first master cylinder 71 is connected to a brake operating member for the front wheels 91 that can be operated by the driver of the vehicle 90. The first master cylinder 71 generates hydraulic pressure according to the amount of operation of the brake operating member for the front wheels 91. The hydraulic pressure generated by the first master cylinder 71 is called the front wheel MC pressure. An example of a brake operating member for the front wheels 91 is a brake lever. The brake lever is attached to the handlebar of the vehicle 90.

[0016] The second master cylinder 72 is connected to a brake operating member for the rear wheels 92 that can be operated by the driver of the vehicle 90. The second master cylinder 72 generates hydraulic pressure according to the amount of operation of the brake operating member for the rear wheels 92. The hydraulic pressure generated by the second master cylinder 72 is called rear wheel MC pressure. An example of a brake operating member for the rear wheels 92 is a brake pedal. The brake pedal is located near a step of the vehicle 90.

[0017] In the front wheel braking mechanism 81, brake fluid is supplied to the wheel cylinder from the first master cylinder 71. The front wheel braking mechanism 81 can generate a friction braking force on the front wheels 91 according to the fluid pressure in the wheel cylinder.

[0018] In the rear wheel braking mechanism 82, brake fluid is supplied to the wheel cylinder from the second master cylinder 72. The rear wheel braking mechanism 82 can generate a friction braking force on the rear wheel 92 according to the fluid pressure in the wheel cylinder.

[0019] Each braking mechanism 81, 82 is configured so that the higher the hydraulic pressure in the wheel cylinder, the greater the force pressing the friction material against the rotating body. In other words, each braking mechanism 81, 82 can apply a greater braking force to the wheel as the hydraulic pressure in the wheel cylinder increases. The hydraulic pressure in the wheel cylinder is an example of a value that indicates the pressing force pressing the friction material against the rotating body.

[0020] The hydraulic pressure adjusting device 73 can adjust the hydraulic pressure supplied to the wheel cylinders of each of the braking mechanisms 81, 82. For example, the hydraulic pressure adjusting device 73 includes a pump, a motor for driving the pump, and a solenoid valve. The hydraulic pressure is adjusted by controlling the motor and the solenoid valve. The hydraulic pressure adjusting device 73 may be configured as a device having a hydraulic passage connected to the first master cylinder 71 and a device having a hydraulic passage connected to the second master cylinder 72.

[0021] Sensor The vehicle 90 is equipped with various sensors. Illustrated in Fig. 1 as examples of the various sensors are a first wheel speed sensor SE1, a second wheel speed sensor SE2, and a behavior detection sensor SE3. Detection signals from the various sensors are input to the braking control device 10.

[0022] The first wheel speed sensor SE1 and the second wheel speed sensor SE2 are sensors that detect the wheel speeds VW of the wheels. The brake control device 10 can calculate the wheel speed VW of the front wheels 91 based on the detection signal from the first wheel speed sensor SE1. The brake control device 10 can calculate the wheel speed VW of the rear wheels 92 based on the detection signal from the second wheel speed sensor SE2. The brake control device 10 can calculate the vehicle speed VS based on the wheel speeds VW. The vehicle speed VS indicates the traveling speed of the vehicle 90.

[0023] The behavior detection sensor SE3 is an inertial sensor that detects the behavior of the vehicle 90. The behavior detection sensor SE3 is attached to the body 93 of the vehicle 90. The behavior detection sensor SE3 is a sensor unit that includes, for example, an acceleration sensor and a gyro sensor. The braking control device 10 can calculate the longitudinal acceleration, lateral acceleration, vertical acceleration, pitch rate, roll rate, and yaw rate based on the detection signals from the behavior detection sensor SE3.

[0024] Braking control device The braking control device 10 is a processing circuit made up of multiple functional units that execute various types of control. Fig. 1 shows, as examples of the functional units, a bank angle acquisition unit 11, a wheel acceleration acquisition unit 12, and a braking control unit 20. The braking control unit 20 includes an ABS control unit 21 and a holding control unit 22. The functional units included in the braking control device 10 can send and receive information to and from each other.

[0025] The bank angle acquisition unit 11 acquires the inclination angle of the vehicle body 93 as a bank angle θ. For example, the bank angle acquisition unit 11 can calculate the bank angle θ based on the lateral acceleration and the roll rate.

[0026] The bank angle θ will be explained using Figure 2. Figure 2 shows a vehicle 90 in an upright position with the body 93 and wheels perpendicular to a horizontal road surface RD, as viewed from the front. The vehicle 90 can lean to the left or right, as indicated by the white arrows in Figure 2. The angle of inclination of the body 93 at this time is the bank angle θ. The bank angle θ is set to "0" when the vehicle 90 is upright, i.e., when the vehicle 90 is perpendicular to the horizontal plane. The bank angle θ is calculated as a positive value when the body 93 is leaning to one side. In this case, the more the body 93 is leaning, the larger the bank angle θ. The bank angle θ is calculated as a negative value when the body 93 is leaning to the other side. In this case, the more the body 93 is leaning, the smaller the bank angle θ. In other words, the larger the absolute value of the bank angle θ, the more the body 93 is leaning. In this embodiment, the road surface is assumed to be horizontal.

[0027] The wheel acceleration acquisition unit 12 acquires the wheel acceleration DVW of the front wheels 91 and the wheel acceleration DVW of the rear wheels 92. The wheel acceleration acquisition unit 12 can calculate the wheel acceleration DVW, for example, by differentiating the wheel speed VW with respect to time. If the wheel acceleration DVW is a positive value, it indicates that the wheel speed VW is changing in an accelerating direction. If the wheel acceleration DVW is a negative value, it indicates that the wheel speed VW is changing in a decelerating direction.

[0028] The braking control unit 20 has a function of controlling the hydraulic pressure adjusting device 73. By controlling the hydraulic pressure adjusting device 73, the braking control unit 20 can adjust the braking force applied to the front wheels 91 and the braking force applied to the rear wheels 92, respectively.

[0029] The following describes control for the front wheels 91 of the wheels of the vehicle 90. In the following description, detected values ​​or calculated values ​​such as the wheel speed VW, the wheel acceleration DVW, and values ​​calculated based on the wheel acceleration DVW are values ​​related to the front wheels 91 that are the object of control. Note that the braking control unit 20 can also perform control for the rear wheels 92 in the same manner as the control for the front wheels 91.

[0030] The ABS control unit 21 can implement antilock brake control to prevent wheels from locking during braking of the vehicle 90. The ABS control unit 21 starts ABS control when an ABS initiation condition is met. The ABS initiation condition is determined to be met, for example, when the amount of wheel slip is equal to or greater than a threshold value. The amount of wheel slip can be calculated based on the vehicle speed VS and the wheel speed VW. When the ABS control unit 21 starts ABS control, it operates the braking device 70 to adjust the braking force according to the amount of slip. The ABS control reduces the amount of slip by switching between a pressure reduction mode, which reduces the braking force or maintains the braking force constant, and a pressure increase mode, which increases the braking force, according to the amount of slip. Note that pressure increase means increasing the pressure, which corresponds to increasing the hydraulic pressure in the wheel cylinder. Pressure decrease means decreasing the pressure, which corresponds to decreasing the hydraulic pressure in the wheel cylinder.

[0031] The hold control unit 22 can perform hold control to maintain the magnitude of the braking force applied to the wheels while the vehicle 90 is turning. When the hold control starts, the hold control unit 22 operates the brake device 70 to maintain the braking force constant. For example, the hold control unit 22 maintains the braking force applied to the wheels by maintaining the hydraulic pressure in the wheel cylinders without increasing or decreasing the hydraulic pressure. When a hold end condition for terminating the hold control is met, the braking control unit 20 increases the braking force. Note that if an ABS start condition is met while the hold control is being executed, control is shifted from the hold control to the ABS control. In other words, the braking force that was maintained constant by the hold control is adjusted by the ABS control.

[0032] <Retention Control> The process when the holding control is performed will be described in detail with reference to FIGS. 3 shows the flow of processing executed by the braking control unit 20. This processing routine is repeatedly executed at predetermined intervals while the vehicle 90 is braking.

[0033] When this processing routine is started, first, in step S101, the braking control unit 20 determines whether or not ABS control is being performed. If ABS control is being performed (S101: YES), the braking control unit 20 temporarily ends this processing routine.

[0034] On the other hand, if ABS control is not being performed (S101: NO), the braking control unit 20 proceeds to step S102. In step S102, the braking control unit 20 determines whether the vehicle 90 is turning.

[0035] The braking control unit 20 determines that the vehicle 90 is turning, for example, when the absolute value of the bank angle θ is equal to or greater than a lean determination value. The lean determination value is a preset threshold value for determining whether the vehicle 90 is traveling straight or turning, depending on the bank angle θ. The braking control unit 20 corresponds to a turning determination unit that determines whether the vehicle 90 is turning based on the bank angle θ. Note that because this determination is made based on the bank angle θ, if the vehicle 90 is turning by operating the steering wheel while the vehicle body 93 is upright or nearly upright, such as when turning at low speed, it is not determined that the vehicle is turning.

[0036] If the vehicle 90 is not turning (S102: NO), the braking control unit 20 temporarily ends this processing routine. On the other hand, if the vehicle 90 is turning (S102: YES), the braking control unit 20 proceeds to step S103.

[0037] In step S103, the braking control unit 20 determines whether the wheel acceleration DVW is smaller than a wheel acceleration determination value DVWth. The wheel acceleration determination value DVWth is a preset threshold value for determining whether the wheel speed VW is rapidly decreasing. The wheel acceleration determination value DVWth may be, for example, -1.0 G, but is not limited to this. The wheel acceleration determination value DVWth corresponds to an acceleration determination value that is a specified negative value.

[0038] If the wheel acceleration DVW is equal to or greater than the wheel acceleration determination value DVWth (S103: NO), the braking control unit 20 temporarily ends this processing routine. On the other hand, if the wheel acceleration DVW is smaller than the wheel acceleration determination value DVWth (S103: YES), the braking control unit 20 proceeds to step S104.

[0039] In step S104, the braking control unit 20 determines whether the wheel G decrease amount ΔDVW is greater than the start determination value ΔDVWth. The wheel G decrease amount ΔDVW is a value indicating a change in the wheel acceleration DVW over a specified period. For example, the braking control unit 20 calculates the wheel G decrease amount ΔDVW as a value obtained by subtracting the wheel acceleration DVW at the current time from the wheel acceleration DVW at a specified time period before the current time. Here, the specified period is not particularly limited, but may be, for example, 24 ms. The start determination value ΔDVWth is set in advance as a threshold value for determining whether the change in the wheel acceleration DVW over the specified period is a change in the deceleration direction. For example, the start determination value ΔDVWth may be, but is not limited to, 1.0 G.

[0040] If the wheel G decrease amount ΔDVW is equal to or less than the start determination value ΔDVWth (S104: NO), the braking control unit 20 temporarily ends this processing routine. On the other hand, if the wheel G decrease amount ΔDVW is greater than the start determination value ΔDVWth (S104: YES), the braking control unit 20 proceeds to step S105.

[0041] In step S105, the braking control unit 20 causes the hold control unit 22 to start the hold control. As a result, the hold control unit 22 operates the braking device 70 so as to maintain a constant braking force. After causing the hold control unit 22 to start the hold control, the braking control unit 20 ends this processing routine. The hold start conditions for starting the hold control include that the wheel acceleration DVW is smaller than the wheel acceleration determination value DVWth and that the wheel G decrease amount ΔDVW is larger than the start determination value ΔDVWth.

[0042] 4 shows the flow of processing executed by the braking control unit 20. This processing routine is repeatedly executed at predetermined intervals while the holding control is being carried out. When this processing routine is started, first, in step S201, the braking control unit 20 determines whether the elapsed time TM is equal to or greater than the determination time TMth.

[0043] The elapsed time TM is the time that has elapsed since the braking control was initiated. When the braking control is initiated, the elapsed time TM is counted, for example, by the braking control unit 20. The determination time TMth is set as a time during which the driver of the vehicle 90 cannot perceive that the magnitude of the braking force is being maintained if the elapsed time TM is shorter than the determination time TMth. In other words, the determination time TMth is the shortest time during which the driver can perceive that the braking force is being maintained despite the driver's own operation. The determination time TMth is set to a value that is calculated in advance through experiments, etc. Note that the driver's perception may include the driver's perception of the speed, acceleration, and behavior of the vehicle 90, and the driver's perception of vibrations transmitted to the brake operating member via the master cylinder as the braking force is adjusted by the braking control.

[0044] If the elapsed time TM is shorter than the determination time TMth (S201: NO), the braking control unit 20 proceeds to step S202. In step S202, the braking control unit 20 determines whether the wheel acceleration change amount DDVW is greater than the change amount determination value DDVWth.

[0045] The wheel acceleration change amount DDVW is calculated to be a positive value if the wheel acceleration DVW is changing in the accelerating direction. For example, the wheel acceleration change amount DDVW is a value obtained by subtracting the previous wheel acceleration DVW from the current wheel acceleration DVW. The change amount determination value DDVWth is a threshold value set for determining whether the wheel acceleration DVW is changing in the accelerating direction. For example, the change amount determination value DDVWth is "0." In this case, if the current wheel acceleration DVW is greater than the previous wheel acceleration DVW, the braking control unit 20 determines that the wheel acceleration change amount DDVW is greater than the change amount determination value DDVWth. That is, in step S202, the braking control unit 20 determines whether the wheel acceleration DVW is further changing in the decelerating direction.

[0046] The wheel acceleration change amount DDVW is the change amount judgment value DDVWth below If so (S202: NO), the braking control unit 20 temporarily ends this processing routine. On the other hand, if the wheel acceleration change amount DDVW is greater than the change amount determination value DDVWth (S202: YES), the processing proceeds to step S203.

[0047] In step S203, the braking control unit 20 causes the hold control unit 22 to end the hold control. After that, the braking control unit 20 ends this processing routine. When the elapsed time TM is shorter than the judgment time TMth, the wheel acceleration change amount DDVW is greater than the change amount judgment value DDVWth, which is one of the hold end conditions for ending the hold control.

[0048] On the other hand, in the process of step S201, if the elapsed time TM is equal to or greater than the determination time TMth (S201: YES), the braking control unit 20 proceeds to step S204. In step S204, the braking control unit 20 determines whether the wheel acceleration DVW is greater than "0".

[0049] If the wheel acceleration DVW is equal to or less than "0" (S204: NO), the braking control unit 20 proceeds to step S206. In step S206, the braking control unit 20 determines whether the holding period has ended. For example, the braking control unit 20 determines that the holding period has ended when the elapsed time TM reaches a specified maximum time. The maximum time can be set to be longer than the determination time TMth. The end of the holding period is one of the holding end conditions for ending the holding control.

[0050] If the holding period has not ended (S206: NO), the braking control unit 20 temporarily ends this processing routine. If the holding period has ended (S206: YES), the braking control unit 20 proceeds to step S205.

[0051] In step S205, the braking control unit 20 performs a pressure increase adjustment process. The pressure increase adjustment process is a process for gradually increasing the braking force. After that, the braking control unit 20 proceeds to step S203 and ends the holding control.

[0052] In the process of step S204, if the wheel acceleration DVW is greater than "0" (S204: YES), the braking control unit 20 proceeds to step S205 and step S203. That is, the brake control unit 20 performs the pressure increase adjustment process and then ends the holding control. When the elapsed time TM is equal to or greater than the determination time TMth, the wheel acceleration DVW being greater than "0" is one of the holding end conditions for ending the holding control.

[0053] Here, if the pressure increase adjustment process is not performed when the holding control is terminated, the braking force is increased at the maximum gradient that the brake device 70 can achieve. That is, if the pressure increase adjustment process is not performed, the braking force increases at a faster rate than when the pressure increase adjustment process is performed. In the processing flow described with reference to FIG. 4, if the holding control is terminated as a result of a negative determination in the processing of step S201 and a positive determination in the processing of step S202, the pressure increase adjustment process is not performed. That is, if the brake control unit 20 terminates the holding control and increases the braking force when the elapsed time TM is shorter than the determination time TMth, the brake control unit 20 increases the rate at which the braking force increases. More specifically, the brake control unit 20 increases the rate at which the braking force increases compared to when the holding control is terminated and the braking force is increased when the elapsed time TM is equal to or greater than the determination time TMth.

[0054] <Action and Effects> The operation and effects of this embodiment will be described. An example of a case where holding control is performed when the vehicle body 93 is tilted and turning will be described using FIG. 5. In the example shown in FIG. 5, braking is initiated by the driver of the vehicle 90 at timing t11. In FIG. 5(a), the solid line shows the transition of braking force when holding control is performed. The dashed line in FIG. 5(a) corresponds to the front wheel MC pressure. In FIG. 5(b), the dashed line shows the vehicle body speed VS. In FIG. 5(b), the solid line shows the wheel speed VW.

[0055] As shown by the solid line in Figure 5(a), the braking force increases after time t11. As shown in Figure 5(b), after time t11, the vehicle speed VS and the wheel speed VW gradually deviate from each other. The difference between the vehicle speed VS and the wheel speed VW corresponds to the amount of slip.

[0056] At timing t12, the wheel acceleration DVW is smaller than the wheel acceleration determination value DVWth (S103: YES), and the wheel G decrease amount ΔDVW is larger than the start determination value ΔDVWth (S104: YES), so the braking force holding control is started (S105). Therefore, as shown by the solid line in Figure 5(a), the braking force is held constant from timing t12.

[0057] Thereafter, as shown in (b) of Figure 5, the wheel speed VW continues to decrease and the amount of slip increases, causing ABS control to be initiated at time t14. After time t14, the control mode shifts from holding control to ABS control, causing the braking force to begin to decrease, as shown by the solid line in (a) of Figure 5. Thereafter, the control mode is switched, and the braking force is adjusted.

[0058] 5A shows, as a comparative example, a two-dot chain line illustrating the transition of braking force when ABS control is started at timing t13, which is later than timing t12. In FIG. 5B, the wheel speed VW in the comparative example is shown by a two-dot chain line. In the comparative example in which ABS control is started at timing t13, as shown in FIG. 5B, the wheel speed VW is reduced more than in the example in which holding control is performed, which is shown by the solid line.

[0059] The brake control device 10 starts the holding control based on the wheel acceleration DVW and the wheel G-force decrease amount ΔDVW. Specifically, the conditions for starting the holding control include that the wheel G-force decrease amount ΔDVW is greater than the start determination value ΔDVWth, i.e., that the change in the wheel acceleration DVW over a specified period is a change in the deceleration direction. Therefore, if the decrease in wheel acceleration is due to an external disturbance, the holding control is unlikely to be started. An example of such a disturbance is the effect of noise in the detection signal from the wheel speed sensor due to rotor eccentricity. In other words, the brake control device 10 can prevent the holding control from being started when slippage is not occurring.

[0060] This makes it possible to prevent the holding control from being initiated when no slip has occurred, even if a positive determination is made more likely in step S103 from the stage when the wheel speed VW has started to decrease and the amount of slip is small. For example, if the wheel acceleration determination value DVWth is set to a negative value close to "0," a positive determination is more likely to be made in step S103 from the stage when the wheel speed VW has started to decrease and the amount of slip is small. In this way, the brake control device 10 makes it easier to initiate the holding control when slip has occurred, while preventing the holding control from being initiated at the wrong time.

[0061] For example, if sudden braking is applied while the vehicle 90 is turning on a low-μ road with a relatively low road friction coefficient, the amount of slippage may suddenly increase. The brake control device 10, which can easily start holding control when slippage occurs while preventing the holding control from being started at the wrong time, can prevent the wheels from locking by holding control even on a low-μ road before the amount of slippage increases.

[0062] By performing braking force holding control, the braking control device 10 maintains the braking force to ensure braking force and reduce the amount of slip. Therefore, the braking control device 10 can more easily suppress a decrease in the wheel speed VW and keep the amount of slip small compared to the comparative example illustrated by the two-dot chain line in FIG. 5. Furthermore, compared to the comparative example, the time during which slip occurs is more likely to be shorter. This can improve the stability of the vehicle 90.

[0063] The case where the holding control is ended will be described with reference to FIG. In the example shown in Figure 6, braking is initiated by the driver of the vehicle 90 at timing t21. Figure 6(a) shows the transition of braking force when brake holding control is performed using a solid line. The dashed line in Figure 6(a) corresponds to the front wheel MC pressure. Figure 6(b) shows the vehicle speed VS using a dashed line. Figure 6(b) shows the wheel speed VW using a solid line.

[0064] As shown in FIG. 6(b), after timing t21, the vehicle speed VS and the wheel speed VW begin to diverge. At timing t22, the start condition for the hold control is met, and the hold control is started. As shown in FIG. 6(b), after timing t22, the wheel speed VW changes from a locking tendency to a return to a grip state. Therefore, at timing t23, when the change in the wheel acceleration DVW from a deceleration direction to an acceleration direction changes, it is determined that the hold end condition is met, and the hold control is ended (S203). In the example shown in FIG. 6, the period from timing t22 to timing t23 is shorter than the determination time TMth. When the hold control is ended at timing t23, the braking force is rapidly increased, as shown in FIG. 6(a).

[0065] According to the brake control device 10, when the holding control is ended when the elapsed time TM is shorter than the judgment time TMth, the braking force can be increased promptly as shown after timing t23 in (a) of Fig. 6. This makes it less likely that the driver of the vehicle 90 will feel uncomfortable if the holding control is ended before the elapsed time TM reaches the judgment time TMth, even if the holding control is started and the braking force is temporarily held.

[0066] When the load on the wheels is light, the friction circle is smaller than when the load is heavy, making slippage more likely to occur. For this reason, even if the wheel speed VW begins to deviate from the vehicle speed VS when the load is light, slippage may be eliminated when the friction circle becomes larger due to the increased load on the wheels as the vehicle turns. If control to limit the braking force, such as braking force holding control, is performed in such a case, the braking force will be unnecessarily limited.

[0067] In this regard, the brake control device 10 terminates the holding control on the condition that the wheel acceleration change amount DDVW is greater than the change amount judgment value DDVWth when the elapsed time TM is shorter than the judgment time TMth. This makes it possible to prevent the braking force from being unnecessarily limited when the amount of slip does not tend to increase, even when the holding control is configured to start early.

[0068] Furthermore, even if the wheel speed VW temporarily decreases due to a disturbance, for example, and the wheel speed holding control is initiated, the brake control device 10 can terminate the wheel speed holding control without continuing it. An example of the disturbance is the effect of road surface irregularities. When the vehicle 90 is traveling on a high-μ road with a relatively high road friction coefficient, even if the wheel speed VW temporarily decreases due to road surface irregularities, the decrease in wheel speed VW may be resolved in a short time.

[0069] In a motorcycle in which the front wheel 91 is the steering wheel, such as vehicle 90, if the front wheel 91 locks while turning, the vehicle is likely to lose its balance and fall over. For this reason, it is particularly effective to apply holding control to the front wheel 91, which has the effect of making it easier to keep the amount of slip small and shortening the time that slip occurs.

[0070] (Example of change) This embodiment can be modified as follows: This embodiment and the following modifications can be combined and implemented within the scope of technical compatibility.

[0071] The braking control device 10, which is a processing circuit, may have any of the following configurations [a] to [c]. [a] A circuit having one or more processors that execute various processes according to a computer program. The processor includes a processing device. Examples of the processing device include a CPU, a DSP, and a GPU. The processor includes a memory. Examples of the memory include a RAM, a ROM, and a flash memory. The memory stores program code or instructions configured to cause the processing device to execute a process. The memory, i.e., a computer-readable medium, includes any available medium that can be accessed by a general-purpose or special-purpose computer. [b] A circuit having one or more hardware circuits that execute various processes. Examples of hardware circuits include an ASIC (Application Specific Integrated Circuit), a CPLD (Complex Programmable Logic Device), and an FPGA (Field Programmable Gate Array). [c] A circuit having a processor that executes some of the various processes according to a computer program and a hardware circuit that executes the remaining processes.

[0072] Some of the functions implemented by the braking control device 10 may be implemented by another processing circuit connected to the braking control device 10. For example, the vehicle may be equipped with another control device having a function of calculating longitudinal acceleration, lateral acceleration, vertical acceleration, pitch rate, roll rate, yaw rate, etc. based on the detection signal from the behavior detection sensor SE3.

[0073] In the above embodiment, a hydraulic braking device is used as an example of a friction braking device. However, the friction braking device is not limited to a hydraulic braking device, and may be a mechanical friction braking device that presses a friction material against a rotating body by mechanically transmitting the drive force of an electric motor.

[0074] The brake control device 10 may be applied to a vehicle that can apply braking forces to the front wheels and rear wheels based on the operation of a single brake operating member. The vehicle 90 to which the brake control device 10 is applied is not limited to a motorcycle, but may be a three-wheeled vehicle or a four-wheeled vehicle as long as the vehicle body and wheels can bank when turning. A three-wheeled vehicle may be a vehicle with two front wheels or a vehicle with two rear wheels. The vehicle 90 may be a vehicle in which only one of the front and rear wheels bank. Furthermore, the vehicle 90 is not limited to a saddle-ride type vehicle.

[0075] In the above embodiment, the bank angle is detected based on the vertical direction, but the bank angle may also be detected based on the direction perpendicular to the road surface. The following methods, for example, can be used to detect the bank angle based on the direction perpendicular to the road surface. Note that the bank angle detection method is not limited to the exemplified methods.

[0076] One example is a method of installing a sensor such as an ultrasonic distance sensor at the banking portion of the vehicle and detecting the bank angle based on the distance between a predetermined position and the road surface. Another example is a method in which, for example, in the case of a three-wheeled vehicle described above that has a banking section and a non-banking section, a sensor such as a rotation angle sensor or displacement sensor is installed at the junction between the banking and non-banking sections to detect the angle between the two sections. An example of a banking section is a section of the vehicle that includes the front wheels, and an example of a non-banking section is a section of the vehicle that includes the rear wheels. [Explanation of symbols]

[0077] 10...Brake control device 11...Bank angle acquisition section 12...Wheel acceleration acquisition section 20...Braking control unit 70...braking device 81...Front wheel braking mechanism 82...Rear wheel braking mechanism 90...Vehicle 91...Front wheel 92...rear wheel 93...Body SE1: First wheel speed sensor SE2: Second wheel speed sensor SE3...Behavior detection sensor

Claims

1. 1. A braking control device that is applied to a vehicle that can bank a vehicle body and wheels when turning, and controls a braking device that applies braking force to the wheels, a bank angle acquisition unit that acquires a bank angle that is a tilt angle of the vehicle body due to banking; a wheel acceleration acquisition unit that acquires the acceleration of the wheel as a wheel acceleration; a turning determination unit that determines whether the vehicle is turning based on the bank angle; a braking control unit that performs antilock brake control to prevent the wheels from locking while braking the vehicle, and a braking force holding control to hold the magnitude of the braking force applied to the wheels while the vehicle is turning, The braking control unit the holding control is started when the antilock brake control is not being performed during braking of the vehicle, the vehicle is turning, the wheel acceleration is equal to or less than an acceleration determination value that is a specified negative value, and the change in the wheel acceleration during a specified period is a change in the deceleration direction, When the braking control unit terminates the holding control and increases the braking force when the elapsed time since the start of the holding control is less than a specified judgment time, the braking control unit increases the rate of increase of the braking force more than when the holding control is terminated and the braking force is increased when the elapsed time is equal to or greater than the judgment time. Braking control device.

2. When the elapsed time is within the determination time, the braking control unit terminates the holding control when the wheel acceleration changes in an accelerating direction. The braking control device according to claim 1 .

3. The determination time is set as a time during which the driver of the vehicle cannot perceive that the magnitude of the braking force is being maintained if the elapsed time is shorter than the determination time. The braking control device according to claim 1 or 2.

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