JP2007112156A - Braking control device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To establish a compatibility between the stability of a vehicle and its comfortableness when the vehicle runs down a slope while maintaining the vehicle speed. <P>SOLUTION: The vehicle 10 has an ECU 100 which executes a braking control processing. The braking control processing executes two routines independently of each other, one which is to maintain the vehicle speed to the target value or below on the basis of the mean of the wheel speeds and the other which disengages locking of one wheel on the basis of the difference between the wheel speeds. The routine to maintain the vehicle speed to the target value or below works in a pressure boosting mode to control the braking forces of the wheels in a lump in accordance with the target differential pressure of a differential pressure valve 205. On the other hand, the routine to avoid locking works in a decompression mode to decompress the braking force given to that wheel which has a relatively lower wheel speed only in case the difference between the wheel speeds has exceeded the lock judging value Vdiff at the time of maintaining the vehicle speed as described. Therein if the difference between the wheel speeds lies at or below the lock judging value Vdiff, the wheel cylinder pressure is decompressed in the routine for maintaining the speed, and locking is disengaged. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a technical field of a braking control device that controls a braking system for braking a vehicle.

  In this type of technical field, a technique for maintaining a constant vehicle speed (hereinafter referred to as “vehicle speed” as appropriate) has been disclosed (for example, see Patent Document 1). According to the wheeled vehicle disclosed in Patent Document 1 (hereinafter referred to as “prior art” as appropriate), the electronic control unit has a braking force depending on the value at which the detected vehicle speed exceeds or falls below a threshold value. Since the hydraulic pressure control device is controlled to increase or decrease, the detected vehicle speed can be maintained below a threshold value. Further, when the wheel is locked in the process of maintaining the vehicle speed, a solenoid valve for reducing the hydraulic pressure on the locked wheel is opened, and it is possible to prevent the lock by reducing the braking force. Has been.

Japanese National Patent Publication No. 10-507145

  In the conventional technology, when avoiding wheel lock, the solenoid valve of the pressure increasing system is closed and the solenoid valve of the pressure reducing system is opened. May occur and the comfort of the vehicle may be impaired. In particular, when descending a steep slope, since the wheels are easily locked, such a problem occurs remarkably. That is, the conventional technique has a technical problem that comfort may be impaired if the stability of the vehicle is emphasized.

  The present invention has been made in view of the above-described problems, and an object of the present invention is to provide a braking control device that can achieve both vehicle stability and comfort when descending a slope while maintaining the vehicle speed.

  In order to solve the above-described problem, the braking control device according to the present invention has a hydraulic pressure transmission system for transmitting a hydraulic pressure of a braking fluid that defines a braking force to each of a plurality of braking target wheels. And a plurality of hydraulic pressure transmission systems are arranged in the main path connected to the master cylinder upstream (i), and the hydraulic pressure at the downstream end becomes the hydraulic pressure at the upstream end. A differential pressure valve that opens to maintain the differential pressure between the downstream end and the upstream end at the target differential pressure when greater than the target differential pressure, and (ii) the main pressure downstream of the differential pressure valve A pressure-increasing valve disposed on each of the plurality of pressure-increasing paths branching from the path to each of the plurality of wheels, and opening and closing according to the presence or absence of energization; and (iii) each of the plurality of pressure-increasing paths on the downstream side of the pressure-increasing valve. Placed in each of the multiple decompression paths branching from A braking control device for controlling the braking system in a vehicle including a braking system having a pressure reducing valve that opens and closes at the same time, and a wheel speed identifying unit that identifies a wheel speed corresponding to each of the braking target wheels, and descending a slope In order to maintain the speed of the vehicle below the target speed based on the wheel speed corresponding to each of the braking target wheels when an input indicating that the speed of the vehicle should be kept below the target speed is made. Setting means for setting the target differential pressure, and the braking system so that the hydraulic pressure corresponding to each of the braking target wheels becomes a hydraulic pressure corresponding to the set target differential pressure via the pressure increasing valve. When the difference between the first control means for controlling the wheel speed and the wheel speed corresponding to each of the braking target wheels exceeds the first reference value, the hydraulic pressure corresponding to the wheel having the relatively low wheel speed is It decreases through the pressure reducing valve Wherein characterized by comprising a second control means for controlling a braking system.

  The “hydraulic pressure transmission system” according to the present invention constitutes at least a part of a braking system that brakes a vehicle by applying a braking force to wheels, and the hydraulic pressure of the braking fluid that defines the braking force is a plurality of pressures. It is a concept that encompasses a mechanism, a device, a system, or the like that transmits to a wheel to be braked. By the action of the hydraulic pressure transmission system, the braking system can apply to the wheels a braking force that increases or decreases according to the increase or decrease of the hydraulic pressure. A plurality of hydraulic pressure transmission systems are provided for one braking system, and have mutually independent configurations. Here, “independent of each other” means that the hydraulic pressure can be normally transmitted to at least the brake target wheel of the other hydraulic pressure transmission system even if some trouble or inconvenience occurs in one hydraulic pressure transmission system. This is a concept representing a state in which independence is maintained, and a part of the hydraulic pressure transmission system may be common to each other as long as the concept is secured. Further, functional elements that can cause each of the hydraulic pressure transmission systems to function in the braking system may be shared between the hydraulic pressure transmission systems. Note that “transmitting the hydraulic pressure to the braking target wheel” does not represent only a form in which the hydraulic pressure transmission system directly transmits the hydraulic pressure to the braking target wheel, but a part of the braking system, for example, This is intended to include a mode in which hydraulic pressure is indirectly transmitted through a wheel cylinder or the like.

  The combination of the braking target wheels in each of the hydraulic pressure transmission systems may be arbitrary. For example, when a normal vehicle having four wheels is taken as an example, it may be a combination of left and right front wheels or left and right rear wheels. , A left front wheel and a right rear wheel, or a combination of a right front wheel and a left rear wheel. In the former case, each of the hydraulic pressure transmission systems adopts a so-called X-type pipe in which a part of the hydraulic pressure transmission path intersects with each other, and even if a malfunction occurs in one hydraulic pressure transmission system. It is preferable that the braking force of one of the front wheels and the rear wheel is secured by the action of the other hydraulic pressure transmission system.

  Each of the hydraulic pressure transmission systems includes a differential pressure valve, a pressure increasing valve, and a pressure reducing valve. The “differential pressure valve” according to the present invention is a concept including a valve, a valve mechanism or a valve system having a mechanism capable of maintaining a pressure difference (that is, a differential pressure) at both end portions at a target differential pressure. In particular, when the hydraulic pressure of the brake fluid at the downstream end (opposite to the master cylinder) is greater than the target differential pressure relative to the hydraulic pressure at the upstream end, which is disposed in the main path connected to the master cylinder upstream. Then, the valve is opened to maintain the differential pressure between the downstream end and the upstream end at the target differential pressure. Therefore, when the master cylinder pressure is low or small enough to be regarded as zero (typically when the brake pedal is not operated), the hydraulic pressure at the downstream end of the differential pressure valve basically does not exceed the target differential pressure. . As long as such a concept is secured, the differential pressure valve according to the present invention is the difference between the downstream side and the upstream side by the interaction of a plurality of valves or by the configuration of the main path in which the differential pressure valve is installed. The pressure may be maintained at a target differential pressure.

  At least one pressure increasing valve is installed in each pressure increasing path that branches from the main path where the differential pressure valve is arranged to each of the braking target wheels. The pressure increasing valve is a valve whose open / close state is controlled according to the presence or absence of energization, and takes the form of an electromagnetic open / close valve such as a solenoid valve, for example. The number of pressure increasing valves may be arbitrary as long as the operation of the hydraulic pressure transmission system is not hindered, and the pressure increasing path may further include a functional element different from the pressure increasing valve. On the other hand, the pressure reducing valve is a valve that is provided at least one in each pressure reducing path that branches from the pressure increasing path downstream of the pressure increasing valve, and typically takes the form of an electromagnetic on-off valve such as a solenoid valve, as with the pressure increasing valve. . As a general concept indicating the pressure increasing valve and the pressure reducing valve, the term “downstream valve” will be used as appropriate in the following description.

  According to the braking control device of the present invention, during the operation, the wheel speed corresponding to each brake target wheel is specified by the wheel speed specifying means. Here, the “specific” in the present invention is not only directly detected by, for example, physical, electrical, mechanical, mechanical, or chemical detection means, but also the detected result as an electrical signal. It is a concept that includes indirectly acquiring and further deriving from these detected or acquired values based on a predetermined algorithm or calculation formula. Therefore, the wheel speed specifying means may be a detecting means such as a wheel speed sensor arranged in the vicinity of each of the plurality of wheels, and the wheel speed detected by these detecting means can be acquired as an electric signal. It may be a processing unit such as an ECU (Electronic Control Unit) configured as described above.

  On the other hand, in the braking control device according to the present invention, the setting means is configured to maintain the vehicle speed below the target speed in response to an input indicating that the vehicle speed when descending the hill should be kept below the target speed. Set the target differential pressure of the differential pressure valve. At this time, the setting means sets the target differential pressure based on the wheel speed corresponding to each brake target wheel.

  The “slope” according to the present invention is a concept that includes a road surface having an inclination that causes the vehicle to start or continue to descend when at least no braking force is applied to the braking target wheel. In other words, the road surface can be maintained by controlling the braking force applied to each braking target wheel. Here, “input that the vehicle speed should be kept below the target speed” means, for example, by an artificial operation such as an operation button, an operation lever, or an operation dial by a vehicle occupant (driver, passenger, etc.) It is a concept that includes an electrical signal that is generated and an electrical signal that is output from a controller or other device without an operation of an occupant or the like when a certain condition determined to maintain the vehicle speed is satisfied. The input itself may be performed regardless of the road surface on which the vehicle is traveling. The target speed may be a fixed value, or may be a value that changes according to the traveling state of the vehicle, the traveling condition, or the slope condition. For example, the target speed may be determined in advance according to the slope of the slope.

  The mode of setting the target differential pressure is not particularly limited as long as it is made based on the wheel speed in order to maintain the vehicle speed below the target speed. For example, if the vehicle speed derived from the wheel speed, a value that defines the vehicle speed, or an index value that changes according to the vehicle speed exceeds a value corresponding to the target speed (which may be the target speed itself), the target difference A mode of feedback control in accordance with the running state may be adopted in which the pressure is increased and the target differential pressure is reduced if the pressure is lower than the value corresponding to the target speed. In view of the fact that each of the hydraulic transmission systems takes a mutually independent configuration, the target differential pressure can also be determined independently for each of the hydraulic transmission systems, but based on the wheel speeds corresponding to all wheels. One target differential pressure may be determined, and the target differential pressure of the differential pressure valve in each hydraulic pressure transmission system may be controlled to the determined value.

  When the target speed to be maintained is adopted as the threshold value, the target differential pressure is inevitably switched frequently, so that the target differential pressure is not increased or decreased in advance. A dead zone to be maintained may be provided. In this case, an upper limit value and a lower limit value that define the dead zone may be employed as threshold values for switching the target differential pressure, respectively.

  In addition, the amount of change or rate of change when increasing or decreasing the target differential pressure is preliminarily experimentally, empirically, or based on simulations, etc., due to vehicle behavior changes or braking force discontinuities. It may be determined so that the vehicle speed can be controlled naturally and accurately without causing discomfort. Further, the initial value of the target differential pressure may be stored in advance as a predetermined map in an appropriate storage unit in advance in association with the state of the slope such as a gradient, and the setting unit executes the feedback control as described above. In this case, a value corresponding to the state of the slope at that time may be set as an initial value.

  When the target differential pressure is set, the braking system is controlled by the first control means. The first control means adjusts the hydraulic pressure of the brake fluid corresponding to each wheel to be braked (hereinafter referred to as “braking pressure” as appropriate) to the set target differential pressure via a pressure increasing valve provided in the hydraulic pressure transmission system. The braking system is controlled so that the corresponding hydraulic pressure is obtained. The “hydraulic pressure corresponding to each braking target wheel” typically refers to the pressure of the wheel cylinder that brakes each braking target wheel, but it does not necessarily have to be the pressure of the wheel cylinder itself. It is a concept that encompasses pressures that define the braking force applied to each.

  On the other hand, the “hydraulic pressure corresponding to the target differential pressure” is a concept that includes the hydraulic pressure that has a one-to-one relationship with the target differential pressure, and each wheel to be braked (or alternatively, via the pressure increasing path from the differential pressure valve downstream) Needless to say, the target differential pressure itself may be used as long as no significant pressure change such as pressure loss occurs in a path until it is transmitted to a part of a braking system corresponding to each wheel to be braked such as a wheel cylinder.

  By the first control means controlling the braking system in this way, the vehicle speed can be maintained at or below the target vehicle speed. However, it is not necessary to maintain the vehicle speed below the target vehicle speed strictly in all time ranges. Macroscopically, the average vehicle speed is below the target vehicle speed within a finite and relatively large time range. Thus, the state where the vehicle speed is generally maintained below the target vehicle speed is also a category of the state where the vehicle speed is widely maintained below the target vehicle speed. During the execution of the control of the first control means for maintaining the vehicle speed below the target vehicle speed (hereinafter referred to as “speed maintenance control” as appropriate), the brake pedal is not normally operated. Can be transmitted as it is as a braking pressure, but when the master cylinder pressure becomes a significant value due to the operation of the brake pedal or the like (that is, when the master cylinder pressure becomes a significant pressure other than zero), the differential pressure valve The downstream hydraulic pressure can take a value larger than the target differential pressure. However, in this case as well, the function of the differential pressure valve itself does not change, so that the braking pressure itself can eventually become a hydraulic pressure corresponding to the target differential pressure.

  In order to maintain the downstream of the differential pressure valve at a hydraulic pressure corresponding to the target differential pressure, the hydraulic pressure on the inflow side (that is, the downstream side) of the braking fluid to the differential pressure valve needs to be equal to or higher than the target differential pressure. In view of such circumstances, it is common to each hydraulic pressure transmission system, or as a part of the braking system, to each of the hydraulic pressure transmission systems, to the main path, the pressure increasing path, or the pressure reducing path in each hydraulic pressure transmission system. It is desirable that some circulation means capable of forcibly circulating the brake fluid is provided. Such a circulation means may be, for example, a pump driven by a driving means such as a motor.

  In the speed maintenance control, the hydraulic pressure corresponding to the target differential pressure is transmitted to the braking target wheels (strictly, means for directly braking each braking target wheel, etc.) via the pressure increasing valve. The path needs to be closed. After all, the pressure increasing valve is opened and the pressure reducing valve is closed in a state where the downstream of the differential pressure valve is maintained at a fluid pressure corresponding to the target differential pressure. Such a driving mode of the downstream valve is hereinafter referred to as “pressure increasing mode” as appropriate. In the pressure increasing mode, the braking force applied to each brake target wheel is also increased or decreased according to the increase or decrease of the target differential pressure. Therefore, as the target differential pressure increases or decreases, the braking force applied to each brake target wheel increases or decreases in the same manner. That is, a factor that impedes comfort, such as noise or vibration, hardly occurs.

  In the braking control device according to the present invention, in view of the fact that the speed maintenance control is executed under the downstream valve driving mode corresponding to the pressure increasing mode, the pressure increasing valve and the pressure reducing valve are opened and closed when not energized, respectively. It is desirable that the valve be closed. In this case, during normal braking in which speed maintenance control is not executed, for example, even when braking pressure is transmitted via the master cylinder, the hydraulic pressure from the master cylinder is transmitted without energizing the downstream valve. It becomes possible to do.

  During braking in the pressure-increasing mode, it is possible to control the braking force applied to each braking target wheel according to the target differential pressure, but the road surface where each wheel contacts the ground, each braking target wheel, Various conditions such as a contact state with the road surface and a contact load on each brake target wheel may be different for each brake target wheel. Therefore, in the pressure increasing mode, one of the braking target wheels may be locked.

  From the viewpoint of preventing, avoiding, or eliminating such wheel locks, the hydraulic pressure transmission system according to the present invention discharges the brake fluid filled in the pressure increasing path through the pressure reducing valve and the pressure reducing path, and is subject to braking. It is possible to reduce the braking pressure of each wheel independently of each other. In this case, the pressure increasing valve is closed and the pressure reducing valve is opened. Hereinafter, such a driving mode of the downstream valve is appropriately referred to as a “pressure reduction mode”. In addition to the pressure increasing mode and the pressure reducing mode, for example, a mode in which both the pressure increasing valve and the pressure reducing valve are closed and the braking pressure at that time is held (hereinafter referred to as “holding mode” as appropriate) is prepared in advance. May be.

  In particular, during the period in which the pressure increasing mode is continued, vibration and noise are unlikely to occur as described above, but when the driving mode is switched from the pressure increasing mode to the pressure reducing mode or the holding mode, it is caused by the hydraulic pressure. Due to the impact, vibration and noise are generated in the hydraulic pressure transmission system. Therefore, if the decompression mode is always executed when the brake target wheel is locked, regardless of how the wheel is locked or not, the comfort of the vehicle may be greatly reduced. . Therefore, the braking control device according to the present invention suitably solves such a problem by including the second control means.

  When the difference between the wheel speeds corresponding to each of the braking target wheels exceeds the first reference value, the second control means reduces the braking pressure corresponding to the wheel having a relatively low wheel speed via the pressure reducing valve. The braking system is controlled as follows. That is, according to the braking control device of the present invention, when a difference exceeding the first reference value occurs in the wheel speed corresponding to each of the braking target wheels during the period in which the speed maintaining control is performed using the pressure increasing mode. The decompression mode is executed at the same time. Therefore, the pressure reduction mode is not executed in at least a part of the case where the difference in wheel speed corresponding to each brake target wheel is equal to or less than the first reference value.

  On the other hand, a decrease in the stability of the vehicle due to the second control unit executing the pressure reduction mode in a limited situation is compensated within the control range of the speed maintenance control by the first control unit. That is, the first control means performs speed maintenance control independently of the second control means at least in terms of control, and the target differential pressure is set based on the wheel speed as described above. Therefore, if the wheel speed of each brake target wheel decreases to zero or close to zero due to the occurrence of a lock, the braking pressure corresponding to each brake target wheel is inevitably reduced according to the pressure increasing mode, and the braking is performed. The lock of the target wheel is released. Thus, according to the braking control device according to the present invention, the pressure reduction mode is executed only during a period during which it can be determined that it is difficult to avoid or prevent lock in the target differential pressure control under the pressure increase mode. The opportunity to perform decompression mode with vibration or noise is clearly reduced. That is, it is possible to achieve both the stability and comfort of the vehicle when descending the slope while maintaining the vehicle speed.

  Note that the first reference value is a concept representing a difference in wheel speed that can be determined that it is necessary to individually depressurize each braking target wheel, and is experimentally, empirically, or based on simulation, for example. It may be set. The first control means and the second control means may have the same hardware configuration or at least partly the same as long as the above-described braking system control can be performed independently of each other. Good.

  In one aspect of the braking control apparatus according to the present invention, the setting means sets the target differential pressure based on an average value of wheel speeds corresponding to each of the braking target wheels.

  According to this aspect, the target differential pressure is set based on the average value of the wheel speeds of the respective braking target wheels, so that the deceleration and stability of the vehicle are realized with a good balance. Also, the average wheel speed is zero or close to it if both wheels are locked in the same manner, and is higher than that if only one wheel is locked. When the target differential pressure is set, it is possible to reflect the state of each brake target wheel on the setting of the target differential pressure relatively accurately, which is preferable.

  In this aspect, the setting means (i) relatively increases the target differential pressure when the average value is equal to or higher than an upper limit value defined as a value equal to or higher than the target speed, and (ii) the The target differential pressure may be set relatively small when the average value is equal to or lower than a lower limit value defined as a value equal to or lower than the target speed.

  In this case, the above-described dead zone can be defined by the upper limit value and the lower limit value. Therefore, when the target differential pressure is set based on the comparison between the upper limit value and the lower limit value in this way, the target differential pressure is not easily switched frequently, which is effective from the viewpoint of maintaining comfort.

  In another aspect of the braking control apparatus according to the present invention, the setting means sets the target differential pressure based on a smaller wheel speed among wheel speeds corresponding to the respective braking target wheels.

  According to this aspect, since the target differential pressure is set based on the smaller wheel speed among the wheel speeds corresponding to the braking target wheel, it is difficult for the braking target wheel to be locked, and the stability of the vehicle is improved. Since it can improve, it is effective.

  In another aspect of the braking control apparatus according to the present invention, the setting means sets the target differential pressure based on a larger wheel speed among wheel speeds corresponding to each of the braking target wheels.

  According to this aspect, since the target differential pressure is set based on the larger wheel speed among the wheel speeds corresponding to the braking target wheel, the deceleration of the vehicle in the speed maintenance control is improved, and the vehicle speed is set to the target vehicle speed. Since it becomes easy to maintain below, it is effective.

  The setting means can select one of the average value of the wheel speeds, the relatively smaller wheel speed, the relatively larger wheel speed, or other index values different from these. It may be configured. In this case, the setting unit may select one index as appropriate based on the state of the vehicle, the traveling condition, the road surface condition, or the like. Alternatively, the occupant may be configured to be able to select one of these indices through some input means.

  In another aspect of the braking control device according to the present invention, the braking target wheel includes one side front wheel and the other side rear wheel in the vehicle, and the braking control device is provided on a road surface on which the vehicle travels. And further comprising: a slope specifying means for specifying a slope; and a traveling direction specifying means for specifying a traveling direction of the vehicle, wherein the second control means comprises (i) the slope is equal to or greater than a predetermined value, and (ii) the When the difference exceeds a second reference value that is smaller than the first reference value in the traveling condition in which the traveling direction is the reverse direction, the hydraulic pressure corresponding to the wheel with the relatively low wheel speed is The braking system is controlled so as to decrease through a pressure reducing valve.

  Here, the slope specifying means according to the present invention may be any means as long as the slope of the slope can be specified. For example, a processing unit such as an ECU configured to be able to calculate a gradient based on an acceleration value acquired as an electric signal from an acceleration sensor that detects acceleration in the front-rear direction of the vehicle or the acceleration sensor may be used. The gradient specified by the gradient specifying means may not be a strict physical value. That is, as long as it is possible to determine whether or not the gradient is such that the front wheels are likely to be locked in the speed maintaining control during the reverse descent, the specific accuracy and the specific mode of the gradient are not particularly limited.

  Further, the traveling direction specifying means according to the present invention may be any means as long as the traveling direction of the vehicle can be specified. For example, a shift position sensor that detects a shift position of a shift lever that selects a gear ratio of a vehicle transmission, or a processing unit such as an ECU configured to be able to acquire a shift position detection value as an electrical signal from the shift position sensor. May be. Alternatively, the traveling direction may be detected by a wheel speed sensor that can detect the rotation direction of the wheel in addition to the wheel speed.

  According to this aspect, since the front and rear wheels are included in the braking target wheels in the individual hydraulic pressure transmission systems, even if a malfunction occurs in one hydraulic pressure transmission system, the other hydraulic pressure transmission system causes the front wheels and The braking force of the rear wheel can be ensured. However, when the vehicle moves backward and down a steep slope, the gravity component applied to the front part of the traveling direction (that is, the rear part of the vehicle) relatively increases, so that the balance between the ground load applied to the front and rear wheels and the braking force is balanced. Easy to collapse. As a result, when the speed maintenance control is executed (that is, when braking is performed in the pressure increasing mode), there is a high possibility that the wheel at the rear in the traveling direction (that is, the front of the vehicle), that is, the front wheel is locked.

  According to this aspect, in the traveling condition in which the gradient is equal to or greater than the predetermined value and the traveling direction of the vehicle is the backward traveling direction, that is, the traveling condition in which the vehicle moves backward and down the steep slope, the second control means performs the first control. Since the decompression mode is executed based on the comparison with the second reference value that is smaller than the reference value (that is, when the difference exceeds the second reference value), the control range of the decompression mode is expanded and the wheel is locked. Locking can be reliably prevented under easy driving conditions.

  The second reference value is not limited as long as it is smaller than the first reference value, and may be set in advance experimentally, empirically, or based on simulations, for example.

  Such an operation and other advantages of the present invention will become apparent from the embodiments described below.

<Embodiment of the Invention>
Preferred embodiments of the present invention will be described below with reference to the drawings as appropriate.
<First Embodiment>
<Configuration of Embodiment>
<Vehicle configuration>
First, the configuration of the vehicle according to the first embodiment of the present invention will be described with reference to FIG. Here, FIG. 1 is a schematic view of the vehicle 10.

  In FIG. 1, a vehicle 10 is an example of a “vehicle” according to the present invention, and is a four-wheel drive vehicle. The vehicle 10 includes an engine 11 that is a power source. The engine 11 is, for example, a gasoline engine. The engine 11 transmits a rotational driving force output from the engine 11 to a driving shaft 14F and a driving shaft 14R, which will be described later, and a transmission 12 and a transfer (sub-motor) for decelerating (shifting) the rotation of the rotational driving force. A transmission 13 is connected.

  The transmission 12 is configured such that the driver can select one gear from among a plurality of gears having mutually different gear ratios by operating a shift lever (not shown). Is an automatic transmission (AT) configured to be automatically performed.

  The transfer 13 is an auxiliary transmission that distributes the driving force transmitted from the transmission 12 to the front wheel side drive shaft 14F and the rear wheel side drive shaft 14R. The transfer 13 includes a differential device (center differential) therein, and absorbs a rotation difference generated between the front wheels and the rear wheels when the vehicle 10 turns.

  The front wheel side drive shaft 14F is connected to the left and right drive shafts 16FL and 16FR via a front differential 15F, and the drive shafts 16FL and 16FR are connected to wheels FL (left front wheel) and FR (right front wheel), respectively. Yes. The rear wheel side drive shaft 14R is connected to the left and right drive shafts 16RL and 16RR via a rear differential 15R. The drive shafts 16RL and 16RR include a wheel RL (left rear wheel) and a wheel RR (right rear wheel), respectively. ) Are connected. In the vehicle 10, the driving torque of the engine 11 is transmitted to each wheel through these mechanisms.

  The wheels FL, FR, RL and RR are provided with braking devices 17FL, 17FR, 17RL and 17RR, respectively. Each brake device is provided with wheel cylinders 18FL, 18FR, 18RL and 18RR, respectively, and a mechanism for braking the vehicle 10 by driving a brake member (not shown) according to the hydraulic pressure of the brake fluid. Yes. Each aspect of the braking device may have any aspect as long as the vehicle 10 can be braked, and preferably adopts an aspect such as a disc brake or a drum brake.

  The wheels FL, FR, RL and RR are provided with wheel speed sensors 19FL, 19FR, 19RL and 19RR, respectively. Each wheel speed sensor is configured to be able to detect the wheel speed and rotation direction of each wheel.

  Each wheel cylinder is configured so that the hydraulic pressure of the brake fluid is transmitted via the master cylinder 20, and the hydraulic pressure in the master cylinder 20 increases or decreases according to the amount of depression of the brake pedal 21 by the driver. It has a configuration. Therefore, normally, the braking force of each braking device is controlled by the driver's brake pedal operation.

  On the other hand, a brake actuator 200 is interposed between each wheel cylinder and the master cylinder 20. The brake actuator 200 is configured to be able to increase or decrease the hydraulic pressure of each wheel cylinder regardless of the operation of the brake pedal 21 by the driver. The brake actuator 200, the master cylinder 20, each braking device, and each wheel cylinder are configured to function as an example of the “braking system” according to the present invention.

  The start switch 22 is disposed at a predetermined position of the vehicle 10 such as a console panel so that the operation by the driving vehicle is possible. When the activation switch 22 is pressed, an activation signal as an example of “an input indicating that the vehicle speed should be maintained below the target vehicle speed” according to the present invention is output.

  The front-rear G sensor 23 is a sensor configured to be able to detect acceleration generated in the traveling direction of the vehicle (that is, the front-rear direction).

  The ECU 100 is an electronic control unit that includes a CPU (Central Processing Unit), a ROM (Read Only Memory), a RAM (Random Access Memory), and the like and controls the entire operation of the vehicle 10, and is a “braking control device” according to the present invention. It is an example. The ECU 100 is electrically connected to the start switch 22 and the front / rear G sensor 23, and acquires the start signal output from the start switch 22 and the electrical signal representing the vehicle longitudinal acceleration detected by the front / rear G sensor 23. Is possible. In addition, when acquiring a starting signal, ECU100 is comprised so that the braking control process mentioned later can be performed. The ECU 100 is also electrically connected to each wheel speed sensor (a control line is not shown), and an electric signal indicating the wheel speed and the rotation direction of each wheel detected by each wheel speed sensor is always transmitted by the ECU 100. Is being monitored.

  The ECU 100 is also electrically connected to the brake actuator 200, and controls the braking force applied to each wheel in the braking control process via the break actuator 200 by controlling the brake actuator 200 to the upper level.

<Configuration of brake actuator>
Next, a part of the configuration of the brake actuator 200 will be described with reference to FIG. FIG. 2 is a schematic diagram of the brake actuator 200. In FIG. 2, the same portions as those in FIG. The brake hydraulic pressure transmission system in the brake actuator 200 includes a hydraulic pressure transmission system in which the front left wheel FL and the right rear wheel RR are braked wheels, a right front wheel FR and a left rear wheel. It is divided into a hydraulic pressure transmission system that uses RL as a braking target wheel, and each is configured to be able to transmit the hydraulic pressure of the braking fluid to the braking target wheel without being affected by the other transmission system. ing. In FIG. 2, only the hydraulic pressure transmission system using the right front wheel FR and the left rear wheel RL as the braking target wheels is shown for simplification of description.

  In FIG. 2, the brake actuator 200 includes a motor 201. The motor 201 is a drive source for driving the pump 202, and the pump 202 supplied with the driving force from the motor 201 pumps the brake fluid from the reservoir 203 and supplies it to the pipe line 217 via the check valve 204. It is configured to be possible.

  A differential pressure valve 205 is disposed in a pipe line 211 connected to the master cylinder 20 (that is, an example of a “main path” according to the present invention). The differential pressure valve 205 is an open valve that allows the brake fluid to pass in both directions when not energized, and more specifically, the downstream side (what is the master cylinder) so that the differential pressure at both ends is maintained at the target differential pressure when energized. This is a valve that functions as a pressure regulating valve that opens and closes so that the pressure on the different side is higher than the upstream side by the target differential pressure. The target differential pressure is set by the ECU 100 electrically connected to the brake actuator 200. Further, a check valve 206 is disposed in a pipe line that bypasses the differential pressure valve 205 in the pipe line 211.

  The pipe 211 is branched downstream of the differential pressure valve 205 into pipes 213 and 214 (that is, an example of the “pressure increasing path” according to the present invention) corresponding to the wheels FR and RL as the braking target wheels. . The pipe line 217 described above is disposed so as to join the position where the pipe line 211 branches into the pipe lines 213 and 214. Incidentally, at the upstream position of the differential pressure valve 205, the pipe line 212 is connected to the reservoir 203, and braking fluid is supplied from the reservoir 203.

  A pressure increasing valve 209 is disposed in the pipe line 213. The pressure increasing valve 209 is an electromagnetic valve whose open / close state is switched under the control of the ECU 100. Further, the pressure increasing valve 209 is configured to open when not energized. Further, the pipe line 213 further branches into the pipe line 215 at the downstream position of the pressure increasing valve 209. The pipe line 215 is an example of the “pressure reducing path” according to the present invention, and the pressure reducing valve 210 is disposed on the pipe line 215. The pressure reducing valve 210 is an electromagnetic valve whose open / closed state is switched under the control of the ECU 100. Further, the pressure reducing valve 210 is configured to close when not energized. On the other hand, the pipe line 214 has the same configuration as the pipe line 213, a pressure increasing valve 207 is installed on the pipe line 214, and a pressure reducing valve 208 is provided on the pressure reducing path 216 branched from the pipe line 214. The pipe lines 214 and 215 are connected to the downstream positions of the pump 202, respectively.

<Operation of Embodiment>
<Details of braking mode>
In the vehicle 10, a plurality of braking modes for braking the vehicle 10 are realized by the ECU 100 controlling the brake actuator 200. The details of a plurality of braking modes provided in the vehicle 10 will be described with reference to FIG.

<Normal braking mode>
The normal braking mode is a mode in which a braking force corresponding to the depression amount of the brake pedal 21 is applied to each wheel, in other words, a braking mode that directly reflects the driver's braking intention. When executing the normal braking mode (in this embodiment, the normal braking mode is selected by default), the ECU 100 deenergizes the differential pressure valve 205 and stops the operation of the motor 201 and the pump 202. Accordingly, the differential pressure valve 205 is simply opened, and the master cylinder pressure of the master cylinder 20 is transmitted to each wheel cylinder via the differential pressure valve 205, the pressure increasing valve 207, and the pressure increasing valve 209.

<Pressure increase mode>
The pressure increasing mode is one of the braking modes executed in a braking control process described later. In the present embodiment, for simplification of description, it is assumed that each of the pressure increasing mode, the holding mode, and the pressure reducing mode is executed when the brake pedal 21 is not operated.

  In the pressure increasing mode, the ECU 100 energizes the differential pressure valve 205 and further operates the motor 201 and the pump 202. At this time, the pump 202 is driven such that a hydraulic pressure higher than a target differential pressure described later is applied to the differential pressure valve 205. On the other hand, since the differential pressure valve 205 opens and closes so as to maintain the differential pressure between the upstream end and the downstream end at the target differential pressure, the valve opens when the hydraulic pressure applied to the downstream side is equal to or higher than the target differential pressure. Then, the brake fluid is passed through the upstream side, which is the low pressure side. On the other hand, when the hydraulic pressure applied to the downstream side is less than the target differential pressure, the differential pressure valve 205 is closed, so that the hydraulic pressure downstream of the differential pressure valve 205 eventually becomes the target difference by repeatedly opening and closing the differential pressure valve 205. Maintained at pressure.

  In this state, the ECU 100 opens the pressure increasing valves 207 and 209 and closes the pressure reducing valves 208 and 210 while the hydraulic pressure downstream of the differential pressure valve 205 is maintained at the target differential pressure. As described above, since each pressure increasing valve is an electromagnetic valve that opens when not energized, and each pressure reducing valve is an electromagnetic valve that closes when not energized, the ECU 100 eventually energizes these downstream valves in the pressure increasing mode. Do not do. The target differential pressure, which is the hydraulic pressure downstream of the differential pressure valve 205, is transmitted to each wheel cylinder via each pressure increasing valve, and the braking force applied to each wheel increases or decreases as the target differential pressure increases or decreases, respectively. Centrally controlled by differential pressure.

<Pressure reduction mode>
The decompression mode is one of the braking modes executed during the braking control process. In the pressure reducing mode, the ECU 100 closes the pressure increasing valve 207 or the pressure increasing valve 209 and opens the pressure reducing valve 208 or the pressure reducing valve 210. In a state where the open / close state of the downstream valve is controlled in this way, the ECU 100 further drives the motor 201 and the pump 202, and causes the brake fluid in the pipe 213 or the pipe 214 to pass through the pipe 215 or the pipe 216. Suctioning, the wheel cylinder pressure in one of the wheel cylinders (ie, an example of the aforementioned “braking pressure”) is reduced. That is, in the decompression mode, it is possible to reduce only the braking force applied to one of the wheels. Note that which wheel cylinder pressure is reduced (that is, which braking force of which wheel is reduced) is determined by a braking control process.

<Retention mode>
The holding mode is one of the braking modes executed during the braking control process. In the holding mode, the ECU 100 closes the pressure increasing valve 207, the pressure increasing valve 209, the pressure reducing valve 208, and the pressure reducing valve 210. In this state, the hydraulic pressure applied to each wheel cylinder at the present time is maintained. The holding mode is selected, for example, to hold the reduced pressure state for a certain period after the reduced pressure mode is executed.

<Details of braking control processing>
The vehicle 10 is configured to be able to maintain the vehicle speed below the target vehicle speed when the ECU 100 executes a braking control process in accordance with a control program stored in the ROM when the slope is descending. The braking control process is executed when a start signal is output from the start switch 22. Here, the details of the braking control process will be described with reference to FIG. FIG. 3 is a flowchart of the braking control process. FIG. 3 shows control of one hydraulic pressure transmission system in the brake actuator 200 (that is, control of one front wheel and one rear wheel).

  In FIG. 3, when the braking control process is started, the ECU 100 first executes initial setting (step A10). Here, the initial setting refers to the selection of the braking mode and the setting of the initial value of the target differential pressure. In the initial setting, the ECU 100 selects the braking mode as the above-described pressure increasing mode, that is, the braking mode for centrally controlling the braking force of each wheel according to the target differential pressure maintained by the differential pressure valve 205.

  On the other hand, the initial value Pt0 of the target differential pressure Pt is determined by referring to the initial value setting map 101 stored in advance in the ROM. Here, the initial value Pt0 of the target differential pressure Pt in the braking control process will be described with reference to FIG. FIG. 5 is a schematic diagram of the initial value setting map 101.

  In FIG. 4, an initial value setting map 102 is a map showing an initial value Pt0 of the target differential pressure with respect to the slope of the slope. In the present embodiment, the initial value Pt0 of the target differential pressure is set in advance with an upper limit value Pt0H and a lower limit value Pt0L (Pt0L <Pt0H). (A2> A1) The target differential pressure Pt0H is set in each of the above gradient regions. Further, in the gradient region that is greater than or equal to the gradient A1 and less than the gradient A2, the initial value Pt0 of the target differential pressure is set to increase linearly from the target differential pressure Pt0L to the target differential pressure Pt0H. In the initial setting in FIG. 3 step A10, the ECU 100 calculates the gradient of the road surface on which the vehicle 10 is in contact with the ground based on the acceleration in the longitudinal direction of the vehicle 10 detected by the longitudinal G sensor 23, and the calculated gradient Is read from the initial value setting map 101 and temporarily stored in the RAM.

  Returning to FIG. 3, accompanying the initial setting, the ECU 100 sets the initial value Pt0 of the target differential pressure stored in the RAM as the target differential pressure Pt of the differential pressure valve 205, and starts braking in the pressure increasing mode.

  When braking is started, the ECU 100 sets the target vehicle speed Vt (step A11). The target vehicle speed Vt is determined by referring to the target vehicle speed setting map 102 stored in advance in the ROM. Here, the target vehicle speed setting map will be described with reference to FIG. FIG. 5 is a schematic diagram of the target vehicle speed setting map 102.

  In FIG. 5, a target vehicle speed setting map 102 is a map that represents a target vehicle speed Vt with respect to a road surface gradient. In the present embodiment, the target vehicle speed VH on the high speed side and the target vehicle speed VL on the low speed side (VL <VH) are determined in advance as the target vehicle speed Vt, and the target vehicle speed VH is the gradient A4 in the gradient region below the gradient A3. (A4> A3) The target vehicle speed VL is set in each of the above gradient regions. Further, in the gradient region that is greater than or equal to the gradient A3 and less than the gradient A4, the target vehicle speed Vt is set to linearly attenuate from the target vehicle speed VH to the target vehicle speed VL.

  On the other hand, an upper limit value Vt1 (Vt1> Vt) and a lower limit value Vt2 (Vt> Vt2) as control threshold values are set for the target vehicle speed Vt (shown solid line) (respectively indicated by chain lines). These upper limit value Vt1 and lower limit value Vt2 are obtained by giving a certain difference as an offset to the target vehicle speed Vt. In the process according to step A11 in FIG. 3, the ECU 100 temporarily stores the target vehicle speed Vt, the target vehicle speed upper limit value Vt1, and the target vehicle speed lower limit value Vt2 corresponding to the current gradient in the RAM.

  Returning to FIG. 3, when the setting of the target vehicle speed Vt is completed, the ECU 100 calculates an average value Mean of the wheel speeds of the front and rear wheels detected by the respective wheel speed sensors, and the average value Mean is stored in the RAM. It is determined whether or not the vehicle speed upper limit value Vt1 or higher (step A12).

  When the average value Mean of the wheel speed is equal to or higher than the target vehicle speed upper limit value Vt1 (step A12: YES), the ECU 100 increases the target differential pressure Pt from the previous value (step A13). At this time, the pressure increase amount of the target differential pressure Pt is stored in the ROM in advance. The previous value refers to the initial value Pt0 of the target differential pressure, that is, the process related to step A14 that is first executed at the start of the braking control process.

  If the average value Mean of the wheel speed is less than the target vehicle speed upper limit value Vt1 (step A12: NO) or the target differential pressure Pt is increased by the processing according to step A13, the ECU 100 determines that the average value of the wheel speed Mean Is less than the target vehicle speed lower limit value Vt2 (step A14).

  When the average value Mean of the wheel speed is less than the target vehicle speed lower limit value Vt2 (step A14: YES), the ECU 100 reduces the target differential pressure Pt from the previous value (step A15). At this time, the amount of reduction in the target differential pressure Pt is stored in advance in the ROM.

  A series of processing routines from step A11 to step A15 is a speed maintenance routine for maintaining the vehicle speed at or below the target vehicle speed Vt in the braking control process. In the speed maintenance routine, the target differential pressure Pt is maintained in a speed region where the average wheel speed value Mean is greater than or equal to the target vehicle speed lower limit value Vt2 and less than the target vehicle speed upper limit value Vt1. As described above, in the present embodiment, a dead zone in which the target differential pressure Pt is not switched is provided, and frequent switching of the target differential pressure is prevented. On the other hand, the vehicle speed of the vehicle 10 is not always maintained below the target vehicle speed Vt by such control, but the vehicle speed of the vehicle 10 is maintained below the target vehicle speed Vt macroscopically or a finite number of vehicles. In the time range, the average vehicle speed of the vehicle 10 is maintained below the target vehicle speed Vt. In such a strict sense, the case where the vehicle speed is not maintained below the target vehicle speed is also within the category of “maintaining the vehicle speed below the target vehicle speed” according to the present invention.

  When the processing related to step A15 ends, the ECU 100 determines that the front wheel lock index value defined as a value obtained by subtracting the wheel speed Vf of the front wheel from the wheel speed Vr of the rear wheel (that is, Vr−Vf) is a predetermined lock determination value. It is determined whether or not it is larger than Vdiff (that is, an example of the “first reference value” according to the present invention) (step A16).

  When the front wheel lock index value is larger than the lock determination value Vdiff (step A16: YES), the ECU 100 shifts the front wheel braking mode to the pressure reduction mode and reduces the wheel cylinder pressure on the front wheel side (step A17). The lock determination value Vdiff is stored in advance in the ROM as a difference value of the wheel speed at which the pressure reduction mode should be executed, and is set to 3 km / h in this embodiment. In the process according to step A17, the ECU 100 closes the pressure reducing valve 210 after depressurizing the front wheels, and shifts the braking mode to the holding mode.

  On the other hand, when the front wheel lock index value is equal to or less than the lock determination value Vdiff (step A16: NO), the ECU 100 continues the pressure increasing mode (step A18). However, at this time, if the previous braking mode is the holding mode and the predetermined holding period has not elapsed, the holding mode is continued.

  When the processing according to step A17 or step A18 is executed, the ECU 100 determines that the rear wheel lock index value defined as a value obtained by subtracting the wheel speed Vr of the rear wheel from the wheel speed Vf of the front wheel (that is, Vf−Vr). Then, it is determined whether or not it is larger than the lock determination value Vdiff (step A19).

  When the rear wheel lock index value is larger than the lock determination value Vdiff (step A19: YES), the ECU 100 shifts the rear wheel braking mode to the pressure reducing mode and reduces the wheel cylinder pressure on the rear wheel (step A20). ). At this time, as in the case of the front wheels, the pressure reducing valve 208 is closed after the rear wheel is depressurized, and the braking mode is shifted to the holding mode.

  On the other hand, when the rear wheel lock index value is equal to or less than the lock determination value Vdiff (step A19: NO), the ECU 100 continues the pressure increasing mode (step A21). However, as in the case of the front wheels, when the previous braking mode is the holding mode and the predetermined holding period has not elapsed, the holding mode is continued. When the process related to step A20 or step A21 is executed, the process returns to step A11, and the speed maintenance routine is executed again.

  A series of processes from step A16 to step A21 is a lock avoidance routine for releasing the lock of one wheel in the braking control process. In the lock avoidance routine, when the wheel speed difference is equal to or less than the lock determination value Vdiff, the decompression mode is not executed. That is, when both front and rear wheels are locked to the same degree, the pressure reduction independent of each wheel by the pressure reduction mode is not executed. However, if both the front and rear wheels are locked in the speed maintenance routine, the average value of the wheel speed is inevitably less than the target vehicle speed lower limit value Vt2, so the wheel cylinder pressures of both wheels are unified by the pressure increasing mode. The pressure is reduced. Therefore, according to the braking control process, it is possible to suppress the occurrence of vibration and noise in the decompression mode while ensuring the stability of the vehicle 10 when descending the slope while maintaining the vehicle speed. In other words, it is possible to achieve both vehicle stability and comfort when maintaining the vehicle speed.

In this embodiment, the average value Mean of the wheel speed is used as an index representing the vehicle speed of the vehicle 10, but such an index is not limited to the average value Mean. For example, a relatively large wheel speed or a relatively small wheel speed of the front and rear wheel speeds may be used as an index. In the former case, since the target differential pressure Pt in the pressure increasing mode is relatively high, the braking performance can be improved. In the latter case, since the target differential pressure Pt is relatively small, stability such as avoidance of lock can be improved. Further, the ECU 100 may be configured so that one index can be selected as appropriate from the plurality of indexes. In this case, the calculation information regarding a plurality of indexes may be stored in advance in a ROM or the like.
Second Embodiment
In the first embodiment, the lock determination value Vdiff that defines whether or not to execute the decompression mode is a fixed value. However, by setting the lock determination value Vdiff more precisely, the vehicle 10 is further stabilized. It is also possible. Here, such a second embodiment of the present invention will be described with reference to FIG. FIG. 6 is a flowchart of the braking control process according to the second embodiment of the present invention. In the figure, the same reference numerals are given to the same portions as those in FIG. 3, and the description thereof will be omitted as appropriate.

  In FIG. 6, when the speed maintaining routine (the process from step A11 to step A15) is completed, the ECU 100 determines whether or not the slope is steep and the traveling direction of the vehicle is the backward direction (step B10). .

  The ECU 100 determines that the slope is steep when the gradient calculated based on the longitudinal acceleration of the vehicle 10 detected by the longitudinal G sensor 23 is equal to or greater than a predetermined determination value. Moreover, ECU100 specifies the advancing direction of the vehicle 10 based on the output value of each wheel speed sensor.

  If the slope is not steep or the vehicle 10 is moving forward and descending (step B10: NO), the ECU 100 proceeds to step A16, and the slope is steep and the vehicle 10 moves backward. When the vehicle is descending (step B10: YES), the lock determination value Vdiff is updated by subtracting the predetermined value A from the lock determination value Vdiff (step B11). In this embodiment, the reference lock determination value Vdiff (that is, 3 km / h) is newly updated to 1 km / h. The update mode of the lock determination value Vdiff is not limited to this. For example, a lock determination value for a steep slope and reverse descent may be stored in advance in the ROM.

  When going backward and down a steep slope, the ground contact load of the front wheel in the traveling direction, i.e. the rear wheel, increases, so that the balance between the ground load and braking force of the front and rear wheels is lost, and the rear wheel in the traveling direction, i.e. the front wheel However, according to the present embodiment, the lock determination value Vdiff is set to be smaller in such a case, so that the opportunity for executing the decompression mode increases. Therefore, it is possible to reliably ensure the stability of the vehicle 10 even in a scene where the stability of the vehicle 10 is likely to decrease.

  The present invention is not limited to the above-described embodiment, and can be appropriately changed without departing from the gist or concept of the invention that can be read from the claims and the entire specification. Moreover, it is included in the technical scope of the present invention.

1 is a schematic diagram of a vehicle according to a first embodiment of the present invention. It is a schematic diagram of the brake actuator in the vehicle of FIG. 3 is a flowchart of a braking control process executed by an ECU in the vehicle of FIG. It is a schematic diagram of the initial value setting map referred in the braking control process. It is a schematic diagram of the target vehicle speed setting map referred in the braking control process. It is a flowchart of the brake control process which concerns on 2nd Embodiment of this invention.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 10 ... Vehicle, 100 ... ECU, 200 ... Brake actuator, 205 ... Differential pressure valve, 207 ... Pressure increasing valve, 208 ... Pressure reducing valve, 209 ... Pressure increasing valve, 210 ... Pressure reducing valve

Claims (6)

A plurality of hydraulic pressure transmission systems for transmitting the hydraulic pressure of the braking fluid that defines the braking force to each of the plurality of braking target wheels are provided independently of each other, and each of the plurality of hydraulic pressure transmission systems is (I) arranged in the main path connected to the master cylinder upstream and when the hydraulic pressure at the downstream end is greater than the target differential pressure relative to the hydraulic pressure at the upstream end, the downstream end and the upstream A differential pressure valve that opens to maintain the differential pressure with the end at the target differential pressure; (ii) each of a plurality of pressure increasing paths that branch from the main path to each of the plurality of wheels on the downstream side of the differential pressure valve; And (iii) a pressure-increasing valve that opens and closes depending on whether or not energized, and (iii) a plurality of pressure-reducing paths that branch from each of the plurality of pressure-increasing paths on the downstream side of the pressure-increasing valve. In a vehicle with a braking system having a pressure reducing valve that opens and closes A brake control apparatus for controlling the braking system,
Wheel speed specifying means for specifying a wheel speed corresponding to each of the braking target wheels;
When an input indicating that the speed of the vehicle when descending a hill should be kept below the target speed is made, the speed of the vehicle is made below the target speed based on the wheel speed corresponding to each of the braking target wheels. Setting means for setting the target differential pressure to maintain
First control means for controlling the braking system so that the hydraulic pressure corresponding to each of the braking target wheels becomes a hydraulic pressure corresponding to the set target differential pressure via the pressure increasing valve;
When the difference in wheel speed corresponding to each of the braking target wheels exceeds the first reference value, the hydraulic pressure corresponding to the wheel having the relatively low wheel speed is decreased via the pressure reducing valve. And a second control means for controlling the braking system. The braking control device according to claim 1, wherein the setting unit sets the target differential pressure based on an average value of wheel speeds corresponding to each of the braking target wheels. The setting means (i) relatively increases the target differential pressure when the average value is equal to or higher than an upper limit value defined as a value equal to or higher than the target speed, and (ii) the average value is equal to the target speed. The braking control device according to claim 2, wherein the target differential pressure is set to be relatively small when the value is equal to or less than a lower limit value defined as the following value. The said setting means sets the said target differential pressure based on the wheel speed of the smaller one among the wheel speeds corresponding to each said brake object wheel, The Claim 1 characterized by the above-mentioned. Braking control device. The said setting means sets the said target differential pressure based on the wheel speed of the larger one among the wheel speeds corresponding to each said brake object wheel, The Claim 1 characterized by the above-mentioned. Braking control device. The braking target wheel includes one side front wheel and the other side rear wheel in the vehicle,
The braking control device includes:
Slope specifying means for specifying the slope of the road surface on which the vehicle travels;
A traveling direction identifying means for identifying the traveling direction of the vehicle,
The second control means includes (i) a second reference value in which the difference is smaller than the first reference value in a traveling condition in which the gradient is equal to or greater than a predetermined value and (ii) the traveling direction is a backward direction. 6. The brake system according to claim 1, wherein the braking system is controlled so that a hydraulic pressure corresponding to a wheel having a relatively low wheel speed is reduced via the pressure reducing valve when exceeding. A braking control device according to claim 1.

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