Brake control system

Abstract

To suppress the pump operating noise when anti-lock brake control is performed. [Solution] The braking control device 35 controls the braking device 80 of the vehicle 90. The braking device 80 includes a pressure regulating reservoir 306 into which brake fluid discharged from wheel cylinders 11L, 11R, 12L, and 12R flows, and an electric pump 304 that draws brake fluid from the pressure regulating reservoir 306 and discharges it. When deceleration slip occurs in the wheels of the vehicle 90, the braking control device 35 starts a depressurization process that discharges brake fluid from the wheel cylinder corresponding to that wheel and drives the electric pump 304 at a first discharge speed. If the braking control device 35 starts a depressurization process in at least one of the front wheels while the required braking force for the vehicle 90 has not increased, it drives the electric pump 304 at a second discharge speed that is lower than the first discharge speed.

Description

Technical Field

[0001] The present invention relates to a braking control device.

Background Art

[0002] As a vehicle braking control device, there is one that performs antilock brake control to adjust the braking force and suppress wheel lock. In antilock brake control, when a wheel is about to lock during a braking operation, the wheel cylinder of that wheel is depressurized, and when the rotation of the wheel resumes, the wheel cylinder is pressurized again. The brake fluid discharged from the wheel cylinder for depressurization flows into a pressure regulating reservoir. When the pressure regulating reservoir becomes full, a bottoming state occurs where the brake fluid cannot be discharged from the wheel cylinder any more. Therefore, during antilock brake control, the electric pump sucks out the brake fluid in the pressure regulating reservoir to avoid the bottoming state.

[0003] Conventionally, as a braking control device that performs such antilock brake control, the device described in Patent Document 1 is known. The braking control device of Patent Document 1 detects or estimates the amount of brake fluid discharged from a wheel cylinder during depressurization. And the braking control device drives the electric pump at a rotational speed capable of sucking out the detected or estimated amount of brake fluid from the pressure regulating reservoir in a certain period of time, thereby suppressing the power consumption and operating noise of the electric pump.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0005] It is required to suppress the pump operating noise when performing antilock brake control. [Means for solving the problem]

[0006] A braking control device for solving the above problems is a braking control device for controlling a braking device mounted on a vehicle, wherein the braking device comprises a pressurizing source and a pressure regulating unit located in a fluid passage connecting the pressurizing source and the wheel cylinders of each wheel in the vehicle, the pressure regulating unit having a plurality of solenoid valves for adjusting the amount of brake fluid supplied to the wheel cylinders and the amount of brake fluid discharged from the wheel cylinders, a pressure regulating reservoir into which the brake fluid discharged from the wheel cylinders flows, and an electric pump for drawing brake fluid from the pressure regulating reservoir and discharging it, and the braking control device is The system includes a control unit that controls the solenoid valve to discharge brake fluid from the wheel cylinder corresponding to the wheel and to start a depressurization process that drives the electric pump at a first discharge speed when deceleration slip occurs in the wheels of the vehicle at a specified value or more due to the application of braking force to the vehicle, and the control unit drives the electric pump at a second discharge speed which is lower than the first discharge speed when the depressurization process is started in at least one of the leading wheels which are wheels located in the direction of travel of the vehicle, while the required braking force to the vehicle has not increased. [Effects of the Invention]

[0007] By considering whether the pressure regulating reservoir is likely to reach a bottoming state based on the status of the depressurization process, it is possible to suppress both the occurrence of the bottoming state and the reduction of pump operating noise. [Brief explanation of the drawing]

[0008] [Figure 1] Figure 1 is a schematic diagram showing one embodiment of a braking control device and the configuration of the braking device controlled by the braking control device. [Figure 2] Figure 2 is a block diagram of the braking control device shown in Figure 1. [Figure 3] Figure 3 is a flowchart showing the processing flow performed by the braking control device shown in Figure 1. [Figure 4] Figure 4 is a timing chart showing an example of the control mode by the braking control device in Figure 1. [Figure 5] Figure 5 is a timing chart showing another example of the control mode by the braking control device in Figure 1. [Modes for carrying out the invention]

[0009] An embodiment of the braking control device will be described below with reference to the drawings. Figure 1 illustrates an example of a braking control device 35, a braking device 80 controlled by the braking control device 35, and a vehicle 90 equipped with the braking control device 35 and the braking device 80. The vehicle 90 is equipped with the following wheels: left front wheel 91L, right front wheel 91R, left rear wheel 92L, and right rear wheel 92R.

[0010] <Brake device> The braking system 80 is a hydraulic friction braking system. As shown in Figure 1, the braking system 80 is equipped with wheel cylinders 11L, 11R, 12L, and 12R corresponding to each wheel 91L, 91R, 92L, and 92R of the vehicle 90. The braking system 80 can apply braking force to the wheels by pressing the friction parts against the rotating body. In the braking system 80, the higher the hydraulic pressure in the wheel cylinders, the greater the force pressing the friction parts against the rotating body that rotates together with the wheels. In other words, the higher the hydraulic pressure in the wheel cylinders, the greater the braking force applied to the wheels.

[0011] The braking system 80 includes a master cylinder 22 as a pressure source. The braking system 80 includes a pressure regulating unit 30 located in a fluid passage connecting the master cylinder 22 to each wheel cylinder 11L, 11R, 12L, and 12R. The braking system 80 includes a reserve tank 21. The reserve tank 21 is a tank that stores brake fluid, which is a liquid that acts as a medium for transmitting hydraulic pressure. The master cylinder 22 is a mechanical pressurizing device that generates hydraulic pressure in response to the depression of the brake pedal 20. The brake pedal 20 is provided as an operating member that can be operated by the driver of the vehicle 90. The braking system 80 in this embodiment includes a first fluid passage 13 connected to the wheel cylinders 11L and 11R of the left and right front wheels, and a second fluid passage 14 connected to the wheel cylinders 12L and 12R of the left and right rear wheels. The master cylinder 22 is connected to the wheel cylinders 11L and 11R of the left and right front wheels through the first fluid passage 13. Furthermore, the master cylinder 22 is connected to the wheel cylinders 12L and 12R of the left and right rear wheels via the second fluid passage 14.

[0012] <Pressure Regulating Unit> The pressure regulating unit 30 is a device that can individually regulate the hydraulic pressure of the wheel cylinders 11L, 11R, 12L, and 12R of each wheel. In the following description, the hydraulic pressure of the wheel cylinders 11L, 11R, 12L, and 12R of each wheel will be referred to as the wheel pressure.

[0013] As shown in Figure 1, the pressure regulating unit 30 includes a first braking system 31 and a second braking system 32. In the pressure regulating unit 30 of this embodiment, the first braking system 31 is connected to the wheel cylinders 11L and 11R of the left front wheel 91L and the right front wheel 91R. The second braking system 32 is connected to the wheel cylinders 12L and 12R of the left rear wheel 92L and the right rear wheel 92R. In other words, the braking system for adjusting the braking force applied to the front wheels of the vehicle 90 and the braking system for adjusting the braking force applied to the rear wheels of the vehicle 90 are independent. The first braking system 31 and the second braking system 32 each include a pressure regulating reservoir 306.

[0014] First, the configuration of the hydraulic circuit for the wheel cylinder 11L in the first braking system 31 will be described. This hydraulic circuit includes a differential pressure control valve 301, a holding valve 302, a pressure reducing valve 303, an electric pump 304, a pressure regulating reservoir 306, and a return fluid passage 307.

[0015] The first fluid passage 13 is connected to the fluid passage 308 via a differential pressure control valve 301. The differential pressure control valve 301 is a normally open linear solenoid valve. By controlling the opening degree of the differential pressure control valve 301, a differential pressure can be generated between the first fluid passage 13 and the fluid passage 308. A check valve 309 is installed in parallel with the differential pressure control valve 301. The check valve 309 is a valve that allows the flow of brake fluid from the first fluid passage 13 to the fluid passage 308, while blocking the flow of brake fluid in the reverse direction.

[0016] The fluid passage 308 is connected to the wheel cylinder 11L via a retaining valve 302. The retaining valve 302 is a normally open solenoid valve that closes when energized and opens when energized. The retaining valve 302 is connected to the wheel cylinder 11L via a fluid passage 310. A check valve 311 is installed in parallel with the retaining valve 302 between the fluid passage 308 and the fluid passage 310. The check valve 311 allows the flow of brake fluid from the fluid passage 310 to the fluid passage 308, while blocking the flow of brake fluid from the fluid passage 308 to the fluid passage 310.

[0017] The liquid passage 310 is connected to the pressure regulating reservoir 306 via a pressure reducing valve 303. The pressure reducing valve 303 is a normally closed solenoid valve that opens when energized and closes when energized. The pressure reducing valve 303 and the pressure regulating reservoir 306 are connected via a liquid passage 312.

[0018] The liquid path 312 is connected to the liquid path 308 through the pump liquid path 313. An electric pump 304 is installed in the pump liquid path 313. The electric pump 304 operates upon receiving the rotation of the electric motor 305. Then, according to its operation, the electric pump 304 sucks the braking liquid in the pressure regulating reservoir 306 and discharges it into the liquid path 308. Note that a check valve 314 is installed in the portion between the electric pump 304 and the liquid path 308 in the pump liquid path 313. The check valve 314 is a valve that allows the flow of the braking liquid from the electric pump 304 toward the liquid path 308 while blocking the flow of the braking liquid from the liquid path 308 toward the electric pump 304.

[0019] The pressure regulating reservoir 306 is connected to the first liquid path 13 through the reflux liquid path 307. When there is a certain amount or more of braking liquid inside the pressure regulating reservoir 306, it is in a state of blocking the communication with the reflux liquid path 307. At this time, the electric pump 304 can suck the braking liquid in the pressure regulating reservoir 306. On the other hand, when the braking liquid inside the pressure regulating reservoir 306 decreases due to the suction of the electric pump 304, it becomes in a state of communicating with the reflux liquid path 307. As a result, the electric pump 304 can suck the braking liquid from the first liquid path 13 through the reflux liquid path 307.

[0020] Next, the configuration of the hydraulic circuit for the wheel cylinder 11R in the first braking system 31 will be described. The hydraulic circuit for the wheel cylinder 11R in the first braking system 31 has the same configuration as the hydraulic circuit for the wheel cylinder 11L. The hydraulic circuits for the wheel cylinder 11L and the wheel cylinder 11R share the differential pressure control valve 301, the electric pump 304, the pressure regulating reservoir 306, the reflux liquid path 307, the liquid paths 308, 312, the pump liquid path 313, and the check valves 309, 314. For the holding valve 302, the pressure reducing valve 303, the liquid path 310, and the check valve 311, the hydraulic circuit for the wheel cylinder 11L and the hydraulic circuit for the wheel cylinder 11R each have individual ones. The holding valve 302 and the pressure reducing valve 303 correspond to electromagnetic valves that adjust the supply amount of the braking liquid to the wheel cylinder and the discharge amount of the braking liquid from the wheel cylinder.

[0021] Next, the configuration of the hydraulic circuits for wheel cylinder 12L and wheel cylinder 12R in the second braking system 32 will be described. The hydraulic circuits for wheel cylinder 12L and wheel cylinder 12R in the second braking system 32 have the same configuration as the hydraulic circuits for wheel cylinder 11L and wheel cylinder 11R in the first braking system 31. The first braking system 31 and the second braking system 32 share an electric motor 305.

[0022] <Various Sensors> As shown in Figure 1, the vehicle 90 is equipped with various sensors, including a stroke sensor 280, a hydraulic pressure sensor 33, and wheel speed sensors 36-39. The various sensors output their detection results to the braking control device 35.

[0023] The stroke sensor 280 is a sensor that detects the pedal stroke S. The pedal stroke S represents the amount the brake pedal 20 is pressed. The hydraulic pressure sensor 33 is a sensor that detects the master pressure. The master pressure represents the hydraulic pressure supplied by the master cylinder 22 to the first fluid passage 13.

[0024] Wheel speed sensors 36, 37, 38, and 39 are provided for each of the wheels 91L, 91R, 92L, and 92R of the vehicle 90. Each of the wheel speed sensors 36, 37, 38, and 39 is a sensor that detects the wheel speed of the corresponding wheel.

[0025] <Braking control device> As shown in Figure 2, the braking control device 35 includes a processing circuit 351. An example of the processing circuit 351 is an electronic control device. In this case, the processing circuit 351 has a CPU 352, a first memory 353, and a second memory 354. The first memory 353 stores the control program executed by the CPU 352. The second memory 354 stores the calculation results of the CPU 352, etc. By the CPU 352 executing the control program, the processing circuit 351 can control the braking device 80.

[0026] <Functional configuration of the processing circuit> Referring to Figure 2, the functional configuration of the processing circuit 351 will be described. The CPU 352 executes a control program for the first memory 353, causing the processing circuit 351 to function as multiple functional units. These multiple functional units include, for example, an acquisition unit M11, an ABS determination unit M12, and a control unit M21.

[0027] [Acquisition Department] The acquisition unit M11 can acquire detection results from various sensors. Based on the detection results from each wheel speed sensor 36 to 39, the acquisition unit M11 can calculate the vehicle speed VS, which is the vehicle's running speed, and the acceleration / deceleration of the vehicle 90. Based on the detection results from the hydraulic pressure sensor 33 and the control status of the first braking system 31 and the second braking system 32, the acquisition unit M11 can calculate the hydraulic pressure of each wheel cylinder 11L, 11R, 12L, and 12R.

[0028] [Control Unit] The control unit M21 can adjust the braking force applied to each wheel of the vehicle 90 by controlling the braking device 80. The control unit M21 can perform anti-lock brake control through individual pressure adjustment of the wheel pressure of each wheel. In the following description, anti-lock brake control will be referred to as ABS control.

[0029] The ABS control performed by the control unit M21 will be explained with reference to Figure 1. During braking of the vehicle 90, the braking control device 35 checks whether deceleration slip is occurring in the wheels at a specified value or higher based on the detection results of the wheel speed sensors 36-39 for each wheel. When the braking control device 35 confirms that deceleration slip is occurring at a specified value or higher, it starts ABS control. For example, when the slip ratio of a wheel exceeds a predetermined threshold, ABS control is started for that wheel. When ABS control is started, the braking control device 35 first performs a pressure reduction process. The pressure reduction process is a process that controls the first braking system 31 and the second braking system 32 to reduce the wheel pressure of the wheel at which deceleration slip has been confirmed. Specifically, the braking control device 35 performs the pressure reduction process by closing the retaining valve 302 and opening the pressure reducing valve 303. As a result, the brake fluid from the wheel cylinder corresponding to the wheel at which deceleration slip has occurred is discharged to the pressure regulating reservoir 306, and the wheel pressure decreases. After confirming that the deceleration slip of the wheels has been eliminated, the braking control device 35 performs a pressure boosting process. The pressure boosting process controls the first braking system 31 and the second braking system 32 to increase the wheel pressure of the wheels whose deceleration slip has been eliminated. Specifically, the braking control device 35 closes the pressure reducing valve 303 and opens the holding valve 302 as the pressure boosting process. As a result, the discharge of brake fluid from the wheel cylinders 11L, 11R, 12L, and 12R stops, and the wheel pressure of the wheels whose deceleration slip has been confirmed to have been eliminated increases. During ABS control, the braking control device 35 repeatedly performs these pressure reducing and pressure boosting processes alternately. In addition, the control unit M21 drives the electric pump 304 during the execution of ABS control. Details of the process for controlling the electric pump 304 will be described later.

[0030] [ABS judgment section] The ABS determination unit M12 can determine whether the ABS control being performed is an instantaneous ABS control. Hereafter, an instantaneous ABS control will be referred to as instantaneous ABS control. Also, an ABS control that does not fall under instantaneous ABS control will be referred to as normal ABS control.

[0031] Instantaneous ABS control refers to ABS control where the duration from start to finish is extremely short. For example, when the wheels of vehicle 90 pass over a manhole cover, if the slip ratio of the wheels increases momentarily between the time the wheels ride over the cover and the time the wheels have finished passing over the cover, the ABS control may activate. In such short-duration ABS control, which ends when the wheels have finished passing over the manhole cover, the amount of brake fluid discharged from the wheel cylinder due to the depressurization process and flowing into the pressure regulating reservoir 306 is less than in normal ABS control. Therefore, even with instantaneous ABS control, it is unlikely to reach a bottoming-out state.

[0032] The same phenomenon as described above can occur not only on manhole covers, but also in areas on the road where the μ value is partially low. In this specification, areas on the road where the μ value is partially low are referred to as low-μ areas to distinguish them from low-μ roads. Examples of low-μ areas include areas where metal is exposed. Examples of this type of metal include manhole covers, gratings, and expansion joints. Expansion joints are devices installed between bridge girders or between bridge girders and abutments in bridges, elevated roads, etc. Also, when the wheels cross a bump in the road, ABS control may activate instantaneously in the same way as described above. Note that the slip ratio is particularly likely to increase when low-μ areas and bumps are wet due to rain, etc., but the slip ratio may also increase even when low-μ areas and bumps are not wet. As described above, ABS control that is activated in response to the partial condition of the road surface on which the vehicle 90 is traveling mainly corresponds to instantaneous ABS control.

[0033] The ABS determination unit M12 determines whether the following conditions (A1) and (A2) are met during the execution of ABS control. If both conditions (A1) and (A2) are met, the ABS determination unit M12 determines that the ABS control is instantaneous ABS control.

[0034] (A1) The required braking force for vehicle 90 has not increased. (A2) Depressurization was initiated on at least one of the leading wheels, which are the wheels located in the direction of travel of the vehicle.

[0035] Regarding the above condition (A1), "the required braking force has not increased" means that the required braking force is constant during the period from before the predetermined time until the determination time, or that the required braking force has decreased during the period from before the predetermined time until the determination time. The above required braking force corresponds to, for example, the pedal stroke S. The above predetermined time can be set appropriately as long as it is long enough to determine that no request for an increase in braking force has been made during the period from before the predetermined time until the determination time. Note that if ABS control is executed when the required braking force is increasing but condition (A1) is not met, it is possible that ABS control has been initiated mainly because the braking force has been excessively increased. If ABS control is executed when condition (A1) is met, it is possible that ABS control is operating in a situation where the braking force is not excessively large.

[0036] Under the above condition (A2), when vehicle 90 is moving forward, the front wheels of vehicle 90, namely the left front wheel 91L and the right front wheel 91R, correspond to the leading wheels. On the other hand, when vehicle 90 is moving backward, the rear wheels of vehicle 90, namely the left rear wheel 92L and the right rear wheel 92R, correspond to the leading wheels. The fact that the depressurization process targeting the leading wheels is initiated when the required braking force has not increased may be the result of the leading wheels running over the low-friction area or step mentioned above.

[0037] While the ABS determination unit M12 determines that the ABS control currently being performed is instantaneous ABS control, it repeatedly determines at predetermined control cycles whether the following conditions (B1) and (B2) are met. The ABS determination unit M12 determines that the ABS control is normal ABS control if at least one of conditions (B1) and (B2) is met.

[0038] (B1) A specified time T1 has elapsed since it was determined that instantaneous ABS control was in operation. (B2) ABS control is being performed on at least one of the leading wheels, and deceleration slip occurs on a trailing wheel, which is not a leading wheel of the vehicle 90.

[0039] Regarding the above condition (B1), the specified time T1 can be set as appropriate, but for example, the specified time T1 is the value obtained by dividing the length of the expected low-μ area by the vehicle speed VS. An example of the length of the expected low-μ area is the diameter of a typical manhole cover. If the ABS control continues even after the specified time T1 has elapsed since it was determined that instantaneous ABS control is in operation, it is possible that the cause is not that the leading wheel has driven over a low-μ area or a step. Therefore, when the specified time T1 has elapsed since it was determined that instantaneous ABS control is in operation, the ABS determination unit M12 determines that the ABS control is normal ABS control.

[0040] Furthermore, the ABS determination unit M12 may set the specified time T1 to be longer when the depressurization process is started on only one of the leading wheels than when the depressurization process is started on both leading wheels. For example, when the depressurization process is started on only one of the leading wheels, the ABS determination unit M12 may set the pre-correction specified time T0 to the value obtained by dividing the length of the low-μ area by the vehicle speed VS, and set the specified time T1 to the value obtained by multiplying the pre-correction specified time T0 by the correction value X1. Here, the correction value X1 is a value greater than 1. The correction value X1 is, for example, a value of 2 or less. On the other hand, when the depressurization process is started on both leading wheels, the ABS determination unit M12 sets the specified time T1 to the value obtained by dividing the length of the low-μ area by the vehicle speed VS.

[0041] Regarding the above condition (B2), when vehicle 90 is moving forward, the rear wheels of vehicle 90, namely the left rear wheel 92L and the right rear wheel 92R, correspond to the following wheels. On the other hand, when vehicle 90 is moving backward, the front wheels of vehicle 90, namely the left front wheel 91L and the right front wheel 91R, correspond to the following wheels. In addition, instead of the condition that ABS control is performed on at least one of the leading wheels, the condition may be that ABS control is performed on both leading wheels. If deceleration slip occurs in the following wheels in addition to the leading wheels, the road surface conditions on which vehicle 90 is traveling may be large puddles, snow, icy roads, etc. In other words, the deceleration slip of the leading wheels may not be caused by the leading wheels riding over a low-friction area or a step. Therefore, when deceleration slip occurs in the following wheels in addition to the leading wheels, the ABS determination unit M12 determines that the ABS control is normal ABS control.

[0042] <Control of electric pumps> During ABS control, the braking control device 35 drives the electric pump 304 to draw out the brake fluid that has flowed from the wheel cylinders 11L, 11R, 12L, and 12R into the pressure regulating reservoir 306. The braking control device 35 controls the pump speed when driving the electric pump 304 during ABS control. The pump speed is the discharge speed of the electric pump 304. In this embodiment, the braking control device 35 controls the pump speed by adjusting the drive current supplied to the electric motor 305.

[0043] Referring to Figure 3, the processing flow executed by the processing circuit 351 of the braking control device 35 when controlling the pump speed will be explained. During the execution of ABS control, the processing circuit 351 repeatedly executes the process shown in Figure 3 at predetermined control cycles.

[0044] In step S101, the processing circuit 351, based on the determination made by the processing circuit 351 functioning as the ABS determination unit M12, proceeds to step S103 if instantaneous ABS control is being performed (S101: YES). On the other hand, if instantaneous ABS control is not being performed, i.e., if normal ABS control is being performed (S101: NO), the processing circuit 351 proceeds to step S102.

[0045] In step S102, the processing circuit 351 sets the first discharge speed V1 as the pump speed. As a result, the processing circuit 351 functions as a control unit M21, driving the electric pump 304 at the first discharge speed V1. Once the first discharge speed V1 is set as the pump speed, the processing circuit 351 completes the series of processes shown in Figure 3.

[0046] The first discharge speed V1 is set as a pump speed value that can maintain an increase in the amount of brake fluid remaining in the pressure regulating reservoir 306 close to "0" while ABS control is being performed. More specifically, the first discharge speed V1 is set to a pump speed such that the flow rate of brake fluid drawn out of the pressure regulating reservoir 306 by the electric pump 304 driven at the first discharge speed V1 is approximately the same as the maximum flow rate of brake fluid flowing into the pressure regulating reservoir 306 during ABS control. Alternatively, the first discharge speed V1 may be set to a pump speed such that the flow rate of brake fluid drawn out of the pressure regulating reservoir 306 by the electric pump 304 driven at the first discharge speed V1 is greater than the maximum flow rate of brake fluid flowing into the pressure regulating reservoir 306 during ABS control.

[0047] In step S103, the processing circuit 351 sets the second discharge speed V2 as the pump speed. As a result, the processing circuit 351 functions as a control unit M21, driving the electric pump 304 at the second discharge speed V2. Once the second discharge speed V2 is set as the pump speed, the processing circuit 351 completes the series of processes shown in Figure 3.

[0048] The second discharge speed V2 is set as a fixed value smaller than the first discharge speed V1. In this embodiment, if the time during which ABS control targeting both leading wheels continues is less than the specified time T1, the amount of brake fluid in the pressure regulating reservoir 306 will not reach the maximum storage amount Max, even if the pump speed is set to the second discharge speed V2.

[0049] <Operation and Effects of This Embodiment> When ABS control is initiated, brake fluid discharged from the wheel cylinder corresponding to the target wheel flows into the pressure regulating reservoir 306. When the pressure regulating reservoir 306 becomes full, it becomes impossible to discharge any more brake fluid from the wheel cylinder, and thus ABS control cannot be continued. The braking control device 35 drives the electric pump 304 during ABS control to discharge the brake fluid that has flowed from the wheel cylinder into the pressure regulating reservoir 306.

[0050] The braking control device 35 sets the pump speed of the electric pump 304 during ABS control to either a first discharge speed V1 or a second discharge speed V2. The first discharge speed V1 is set to a speed that can maintain the amount of brake fluid remaining in the pressure regulating reservoir 306 close to "0" during ABS control. In contrast, the second discharge speed V2 is set to a speed lower than the first discharge speed V1. If ABS control is continued while maintaining the pump speed at the second discharge speed V2, the operating noise of the electric pump 304 is suppressed, but the amount of brake fluid remaining in the pressure regulating reservoir 306 may gradually increase.

[0051] Figure 4 shows an example of an embodiment of ABS control by the braking control device 35 of this embodiment. In the example in Figure 4, the vehicle 90 moving forward is decelerating due to the application of braking force. Also, the required braking force remains constant throughout the period shown in Figure 4.

[0052] Figure 4(a) shows the change in wheel speed VWFr1 of one of the front wheels, 91R, as a solid line. Figure 4(a) also shows the change in vehicle speed VS as a dashed line. Wheel speeds for wheels where there is no difference from vehicle speed VS are omitted.

[0053] Figure 4(b) shows the progression of the determination made by the ABS determination unit M12. In Figure 4(b), "instantaneous" indicates that instantaneous ABS control has been determined, and "off" indicates that ABS control is not being performed.

[0054] Figure 4(c) shows the change in pump speed. Figure 4(d) shows the change in the residual amount of brake fluid in the pressure regulating reservoir 306. Here, the pressure regulating reservoir 306 is the pressure regulating reservoir 306 provided in the first braking system 31 connected to the wheel cylinders 11L and 11R corresponding to the front wheels 91R and 91L of the vehicle 90. Figure 4(d) also shows the maximum storage amount Max, which is the upper limit of the amount of brake fluid that the pressure regulating reservoir 306 can store.

[0055] As shown in Figure 4(a), deceleration slip occurs in wheel 91R, one of the front wheels of the braking vehicle 90, causing the wheel speed VWFr1 to begin to decrease. Accordingly, the processing circuit 351 starts ABS control at timing t11. Once the deceleration slip of the front wheel is resolved, the processing circuit 351 terminates ABS control at timing t12.

[0056] When ABS control is started at timing t11, the processing circuit 351 determines whether the ABS control is instantaneous ABS control or normal ABS control. Here, based on the fact that the required braking force is constant and that the pressure reduction process has started only on one of the front wheels, the processing circuit 351 determines that it is instantaneous ABS control, as shown in Figure 4(b).

[0057] Based on the determination that instantaneous ABS control is being performed, the processing circuit 351 sets the second discharge speed V2 as the pump speed, as shown in Figure 4(c). As a result, the electric pump 304 is driven at the second discharge speed V2 from timing t11.

[0058] When ABS control is initiated at timing t11, the brake fluid discharged from the wheel cylinder by the depressurization process first begins to flow into the pressure regulating reservoir 306. Here, since the pump speed is the second discharge speed V2, which is lower than the first discharge speed V1, the amount of brake fluid discharged from the pressure regulating reservoir 306 per unit time is less than the amount of brake fluid flowing into the pressure regulating reservoir 306 per unit time. For this reason, as shown in Figure 4(d), the amount of brake fluid remaining in the pressure regulating reservoir 306 increases after timing t11.

[0059] During the period from timing t11 to timing t12, the process transitions from depressurization to pressure boosting. Once the process transitions to pressure boosting, the discharge of brake fluid from the wheel cylinder stops. As a result, the electric pump 304 continues to discharge brake fluid from the pressure regulating reservoir 306, causing the amount of brake fluid remaining in the pressure regulating reservoir 306 to begin decreasing even at the second discharge speed V2. In the example shown in Figure 4, since the inflow of brake fluid is due to a temporary depressurization process associated with instantaneous ABS control, the amount of brake fluid remaining in the pressure regulating reservoir 306 begins to decrease before reaching the maximum storage capacity Max, as shown in Figure 4(d).

[0060] When ABS control ends at timing t12, the drive of the electric pump 304 is also stopped. Note that the period from timing t11 to timing t12 is shorter than the specified time T1 when depressurization is started on only one of the leading wheels.

[0061] Next, another example of an embodiment of ABS control by the braking control device 35 of this embodiment will be described using Figure 5. In the example in Figure 5, the vehicle 90 moving forward is decelerating due to the application of braking force. Also, the required braking force remains constant throughout the period shown in Figure 5.

[0062] Figure 5(a) shows the change in wheel speed VWFr1 of one of the front wheels, 91R, as a solid line. Figure 5(a) shows the change in wheel speed VWRr1 of one of the rear wheels, 92R, as a dashed line. Figure 5(a) shows the change in vehicle speed VS as a dashed line. Wheel speeds for wheels where there is no difference from vehicle speed VS are omitted.

[0063] Figure 5(b) shows the progression of the determination made by the ABS determination unit M12. In Figure 5(b), "instantaneous" indicates that instantaneous ABS control has been determined, "normal" indicates that normal ABS control has been determined, and "off" indicates that ABS control is not being performed.

[0064] Figure 5(c) shows the change in pump speed. Figure 5(d) shows the change in the residual amount of brake fluid in the pressure regulating reservoir 306. Here, the pressure regulating reservoir 306 is the pressure regulating reservoir 306 provided in the first braking system 31 connected to the wheel cylinders 11L and 11R corresponding to the front wheels 91R and 91L of the vehicle 90. Figure 5(d) also shows the maximum storage amount Max, which is the upper limit of the amount of brake fluid that the pressure regulating reservoir 306 can store.

[0065] As shown in Figure 5(a), deceleration slip occurs in wheel 91R, one of the front wheels of the braking vehicle 90, and the wheel speed VWFr1 begins to decrease. Accordingly, the processing circuit 351 starts ABS control for that front wheel at timing t21. Subsequently, deceleration slip also occurs in wheel 92R, one of the rear wheels, and the wheel speed VWRr1 begins to decrease. Accordingly, the processing circuit 351 starts ABS control for that rear wheel at timing t22. The ABS control started for each wheel is continuously performed from the time of start for the period shown in Figure 5.

[0066] When ABS control is initiated for the front wheels at timing t21, the processing circuit 351 determines whether the ABS control is instantaneous ABS control or normal ABS control. Here, based on the fact that the required braking force is constant and that pressure reduction processing has been initiated for only one of the front wheels, the processing circuit 351 determines that it is instantaneous ABS control, as shown in Figure 5(b).

[0067] Based on the determination that instantaneous ABS control is being performed, the processing circuit 351 sets the second discharge speed V2 as the pump speed, as shown in Figure 5(c). As a result, the electric pump 304 is driven at the second discharge speed V2 from timing t21.

[0068] At timing t21, ABS control is initiated for the front wheels, and first, the brake fluid discharged from the wheel cylinders by the depressurization process begins to flow into the pressure regulating reservoir 306. Here, since the pump speed is the second discharge speed V2, which is lower than the first discharge speed V1, the amount of brake fluid discharged from the pressure regulating reservoir 306 per unit time is less than the amount of brake fluid flowing into the pressure regulating reservoir 306 per unit time. For this reason, as shown in Figure 5(d), the amount of brake fluid remaining in the pressure regulating reservoir 306 increases after timing t21.

[0069] At timing t21 or later, the process transitions from depressurization to pressure boosting. Once the process transitions to pressure boosting, the discharge of brake fluid from the wheel cylinder stops. As a result, the electric pump 304 continues to discharge brake fluid from the pressure regulating reservoir 306, causing the amount of brake fluid remaining in the pressure regulating reservoir 306 to begin decreasing even at the second discharge speed V2.

[0070] When ABS control is initiated for the rear wheels at timing t22, the processing circuit 351 determines that the ABS control is normal ABS control. Specifically, based on the fact that ABS control is being performed on one of the front wheels and that deceleration slip has occurred on one of the rear wheels, the processing circuit 351 determines that it is normal ABS control, as shown in Figure 5(b). Note that the period from timing t21 to timing t22 is shorter than the specified time T1 when depressurization is initiated on only one of the leading wheels. For this reason, in the example shown in Figure 5, which involves the inflow of brake fluid due to depressurization targeting one of the front wheels, the residual amount of brake fluid in the pressure regulating reservoir 306 does not reach the maximum storage amount Max during the period from timing t21 to timing t22, as shown in Figure 5(d).

[0071] Based on the determination that normal ABS control is being performed, the processing circuit 351 changes the pump speed to the first discharge speed V1 at timing t22, as shown in Figure 5(c). As a result, from timing t22 onward, the electric pump 304 is driven at the first discharge speed V1.

[0072] From timing t22 onward, the pump speed is changed to the first discharge speed V1, resulting in more brake fluid being discharged from the pressure regulating reservoir 306 compared to the period from timing t21 to timing t22 when the pump speed was set to the second discharge speed V2. Therefore, as shown in Figure 5(d), even from timing t22 onward, the amount of brake fluid remaining in the pressure regulating reservoir 306 of the first brake system 31 has not reached its maximum storage capacity Max. Similarly, although not shown in the figure, the amount of brake fluid remaining in the pressure regulating reservoir 306 of the second brake system 32 has also not reached its maximum storage capacity Max.

[0073] As explained with reference to Figure 4, if the required braking force for the vehicle 90 has not increased, and depressurization is initiated on at least one of the leading wheels, which are the wheels located in the direction of travel of the vehicle 90, it is determined that instantaneous ABS control is being performed. When the ABS control performed is instantaneous ABS control, the pump speed is maintained at the second discharge speed V2 while the ABS control is being performed. This suppresses the operating noise of the electric pump 304 compared to when the pump speed is set to the first discharge speed V1. By suppressing the operating noise of the electric pump 304, it is possible to prevent the operating noise of the electric pump 304 from causing discomfort to the occupants of the vehicle 90. It is also possible to reduce the power consumption of the electric pump 304. In the case of instantaneous ABS control, that is, when ABS control is activated instantaneously, the amount of brake fluid flowing into the pressure regulating reservoir 306 is small. For this reason, even if the pump speed is maintained at the second discharge speed V2, it is unlikely to reach a bottoming state. In other words, if instantaneous ABS control is detected, that is, if the pressure reduction process for the leading wheel is performed while the required braking force is not increasing, then even if the pump speed is maintained at the second discharge speed V2, it is unlikely to reach a bottoming-out state.

[0074] On the other hand, as explained with reference to Figure 5, if deceleration slip occurs in the trailing wheel in addition to the leading wheel, in other words, if deceleration slip occurs in the trailing wheel while the electric pump 304 is being driven at the second discharge speed V2, it is determined that normal ABS control is in operation. For this reason, if deceleration slip occurs in the trailing wheel while the electric pump 304 is being driven at the second discharge speed V2, the speed of the electric pump 304 is changed to the first discharge speed V1. If deceleration slip occurs in the trailing wheel in addition to the leading wheel, it may not be instantaneous ABS control. In normal ABS control, more brake fluid flows into the pressure regulating reservoir 306 compared to instantaneous ABS control. According to this embodiment, if there is a possibility that normal ABS control is being performed, changing the pump speed to the first discharge speed V1 can suppress the bottoming out of the pressure regulating reservoir 306 even if a large amount of brake fluid flows in.

[0075] Furthermore, in this embodiment, if a specified time T1 has elapsed since it was determined that the ABS control is instantaneous ABS control, in other words, if the electric pump 304 is driven at the second discharge speed V2 for a specified time T1, it is determined that the ABS control is normal ABS control. For this reason, if the electric pump 304 is driven at the second discharge speed V2 for a specified time T1, the speed of the electric pump 304 is changed to the first discharge speed V1. In this way, if the execution of the ABS control continues for a long time, that is, if the ABS control is not instantaneously activated ABS control, changing the pump speed to the first discharge speed V1 can suppress the occurrence of a bottoming-out state.

[0076] In this embodiment, as with the first braking system 31 and second braking system 32, when the braking system for adjusting the braking force applied to the front wheels of the vehicle 90 and the braking system for adjusting the braking force applied to the rear wheels of the vehicle 90 are independent, the following can be said: The amount of brake fluid flowing into a single pressure regulating reservoir 306 differs depending on whether the depressurization process is started on only one of the leading wheels or on both leading wheels. Specifically, when the depressurization process is started on only one of the leading wheels, the amount of brake fluid flowing into a single pressure regulating reservoir 306 is less than when the depressurization process is started on both leading wheels. Therefore, when the depressurization process is started on only one of the leading wheels, it is less likely to reach a bottoming state compared to when the depressurization process is started on both leading wheels. Accordingly, in this embodiment, when the depressurization process is started on only one of the leading wheels, the specified time T1 is set longer than when the depressurization process is started on both leading wheels, so that the pump speed can be set to the second discharge speed V2 for a longer period of time. This allows for a longer period during which the operating noise of the electric pump 304 can be suppressed.

[0077] As described above, according to this embodiment, by considering whether or not a bottoming state is likely to occur based on the status of the depressurization process, it is possible to suppress both the occurrence of a bottoming state and the suppression of pump operating noise.

[0078] Furthermore, according to this embodiment, if the depressurization process targeting the leading wheel is started while the required braking force has not increased, the pump speed of the electric pump 304 can be set to the second discharge speed V2 from the time the depressurization process starts. This makes it possible to suppress the operating noise of the electric pump 304 from the time the depressurization process starts. For this reason, even if it is ultimately determined to be normal ABS control as in the example in Figure 5, the pump operating noise can be suppressed during the period from timing t21 to timing t22, that is, immediately after the start of ABS control.

[0079] Here, as a comparative example, consider a configuration that predicts the amount of brake fluid flowing into the pressure regulating reservoir during ABS control. For example, it is conceivable to predict the amount of brake fluid flowing into the pressure regulating reservoir before the vehicle comes to a stop based on the vehicle speed and the vehicle's deceleration. In such a comparative example, by adjusting the pump speed based on the predicted inflow amount so that the remaining amount of brake fluid in the pressure regulating reservoir does not reach the maximum storage capacity, it is possible to suppress the bottoming out state. If the predicted inflow amount is small, the pump speed can be reduced, thereby suppressing the operating noise of the electric pump. On the other hand, if the predicted inflow amount is large, the pump speed cannot be reduced. In the comparative example configured as described above, when the vehicle speed is high, the deceleration is small, etc., it is thought that the predicted amount of brake fluid flowing into the pressure regulating reservoir will be large. For this reason, when the instantaneous ABS control described in this embodiment is activated when the vehicle speed is high, the deceleration is small, etc., the pump speed will be set relatively high based on the predicted inflow amount. Thus, there is a problem that the pump speed cannot be reduced when the vehicle speed is high, the deceleration is small, etc.

[0080] In this respect, this embodiment does not involve predicting the amount of brake fluid flowing into the pressure regulating reservoir 306 when setting the pump speed of the electric pump 304. According to this embodiment, even if instantaneous ABS control is activated when the speed is high or the deceleration is small, it is expected that the operating noise of the electric pump 304 will be suppressed.

[0081] (Example of change) This embodiment can be implemented with the following modifications. This embodiment and the following modifications can be combined with each other to the extent that they do not contradict each other technically.

[0082] In the above embodiment, a braking device 80 with so-called front and rear piping was illustrated, which includes a first braking system 31 that adjusts the braking force applied to the left front wheel 91L and the right front wheel 91R, and a second braking system 32 that adjusts the braking force applied to the left rear wheel 92L and the right rear wheel 92R. The piping connection in the braking device may be a cross-piping configuration in which the front wheels and rear wheels are arranged in the first and second braking systems, respectively.

[0083] In the above embodiment, the master cylinder 22 was given as an example of a pressure source provided by the braking device 80. However, the pressure source is not limited to this, and may also be a device that generates hydraulic pressure using an electric cylinder, for example.

[0084] In the above embodiment, the pedal stroke S was used as an example of the required braking force. If the vehicle 90 is a vehicle that can automatically brake regardless of the driver's operation of the brake pedal 20, the determination may be made using the required braking force calculated in the process related to automatic braking.

[0085] In the above embodiment, the second discharge speed V2 was set as a fixed value smaller than the first discharge speed V1. Alternatively, the second discharge speed V2 may be set as a variable value within a range smaller than the first discharge speed V1. In this case, the second discharge speed V2 can be changed based on, for example, the vehicle speed VS, the deceleration of the vehicle 90, or the predicted amount of liquid flowing into the pressure regulating reservoir 306 during the depressurization process.

[0086] In the above embodiment, when the depressurization process is started on only one of the leading wheels, the specified time T1 is set to be longer than the value obtained by dividing the length of the low-μ area by the vehicle speed VS. Alternatively, the specified time T1 may be set as follows: When the depressurization process is started on only one of the leading wheels, the ABS determination unit M12 sets the specified time T1 to the value obtained by dividing the length of the low-μ area by the vehicle speed VS. On the other hand, when the depressurization process is started on both leading wheels, the ABS determination unit M12 sets the pre-correction specified time T0 to the value obtained by dividing the length of the low-μ area by the vehicle speed VS, and sets the pre-correction specified time T0 multiplied by the correction value X2 to be the specified time T1. Here, the correction value X2 is a value greater than 0 and less than 1. With the above configuration as well, when the depressurization process is started on only one of the leading wheels, the specified time T1 can be set to be longer than when the depressurization process is started on both leading wheels.

[0087] The processing circuit 351 may be configured as a circuit including one or more processors that operate according to a computer program, one or more dedicated hardware circuits such as dedicated hardware that performs at least some of the various processes, or a combination thereof. Examples of dedicated hardware include application-specific integrated circuits (ASICs). The processor includes a CPU and memory such as RAM and ROM, where the memory stores program code or instructions configured to cause the CPU to perform the processes. Memory, i.e., storage media, includes any available media that can be accessed by a general-purpose or dedicated computer.

[0088] As used herein, the expression "at least one" means "one or more" of the desired options. More specifically, as used herein, the expression "at least one" means "only one option" or "both of the two options" if there are two options. As another example, as used herein, the expression "at least one" means "only one option" or "any combination of two or more options" if there are three or more options. [Explanation of Symbols]

[0089] 11L, 11R, 12L, 12R… Wheel Cylinder 20...Brake pedal 21…Reserve tank 22…Master cylinder (pressure source) 30... Pressure regulating unit 31...1st braking system 32…Second braking system 35... Brake control device 80...braking device 90... Vehicles 91L, 91R, 92L, 92R…wheels 302... Holding valve (solenoid valve) 303... Pressure reducing valve (solenoid valve) 304... Electric pump 306... Pressure regulating reservoir

Claims

1. A braking control device that controls the braking system mounted on a vehicle, The braking device comprises a pressure source and a pressure regulating unit located in a fluid passage connecting the pressure source and the wheel cylinders of each wheel in the vehicle. The pressure regulating unit comprises a plurality of solenoid valves that adjust the amount of brake fluid supplied to the wheel cylinder and the amount of brake fluid discharged from the wheel cylinder, a pressure regulating reservoir into which the brake fluid discharged from the wheel cylinder flows, and an electric pump that draws out brake fluid from the pressure regulating reservoir and discharges it. The aforementioned braking control device is The system includes a control unit that, when a braking force is applied to the vehicle, causes deceleration slip to occur in the vehicle's wheels exceeding a specified value, controls the solenoid valve to discharge brake fluid from the wheel cylinder corresponding to the wheel, and initiates a depressurization process that drives the electric pump at a first discharge speed. If the control unit starts the depressurization process on at least one of the leading wheels, which are wheels located in the direction of travel of the vehicle, while the required braking force for the vehicle has not increased, it drives the electric pump at a second discharge speed that is lower than the first discharge speed. Brake control device.

2. The control unit changes the speed of the electric pump to the first discharge speed when the electric pump has been driven at the second discharge speed for a specified time. The braking control device according to claim 1.

3. The control unit sets the specified time to be longer when the depressurization process is started on only one of the leading wheels than when the depressurization process is started on both leading wheels. The braking control device according to claim 2.

4. If, while the control unit continues to drive the electric pump at the second discharge speed, a deceleration slip exceeding the specified value occurs in the trailing wheel (which is not the leading wheel), the control unit changes the speed of the electric pump to the first discharge speed. A braking control device according to any one of claims 1 to 3.

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