JP2018095031A - Vehicle brake control device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a vehicle brake control device capable of sufficiently securing deceleration of a vehicle when a vehicle travels on a road surface where there are large road surface irregularities which are continuous by travel speed control.SOLUTION: A brake control device comprises: a wheel speed sensor for detecting wheel speed of wheels; and a controller comprising a travel speed control part for executing travel speed control for controlling a brake torque to wheels so that travel speed of the vehicle does not exceed set speed, when the vehicle travels on a downhill road and an anti-skid control part for executing anti-skid control for adjusting the brake torque so as to suppress excessive brake slip of the wheels. The anti-skid control part selects a selected wheel out of the wheels, when the travel speed control part executes travel speed control, and on the selected wheel, reduction of the brake torque by the anti-skid control is inhibited.SELECTED DRAWING: Figure 3

Description

  The present invention relates to a braking control device for a vehicle.

  Patent Document 1 discloses that during downhill road speed control at off-road, the braking force due to the wedge effect that the tire bites into the road surface can be effectively used to reliably reduce the vehicle speed to the target vehicle speed. The device is described. Specifically, the downhill traveling speed control device disclosed in Patent Document 1 has a set slip state of the anti-skid control device during the operation of the downhill traveling speed control device, and a predetermined value that makes it difficult to perform anti-skid control. The set slip state changing means for making the value larger than that is provided.

  By the way, in the off-road where the unevenness of the road surface is very large, the wheel may be separated from the road surface during traveling. When the braking torque is applied to the wheel, if the wheel leaves the road surface, a reaction force (frictional force) from the road surface cannot be obtained, so that the wheel tends to be locked. Anti-skid control is executed so as to suppress the locking tendency. At this time, since the ground contact load of the wheel is “0” (that is, not grounded on the road surface), braking torque (for example, braking fluid pressure) ) Is reduced to “0”. Then, when the wheel is brought into contact with the road surface again, the anti-skid control increases the braking torque from “0”.

  The time when the ground contact of the wheel is impaired due to road surface unevenness is instantaneous and extremely short. Further, in the braking control device (brake actuator), there is a limit to the increasing gradient of braking torque (the amount of increase in braking torque per unit time). For this reason, when driving on a road surface on which large road surface irregularities are continuous, the braking force of the entire vehicle may be insufficient. For this reason, what can respond to the said subject is anxious for the anti-skid control performed during driving speed control.

JP 2006-224946 A

  An object of the present invention is to provide a vehicle that can sufficiently ensure the deceleration of the vehicle when traveling on a road surface on which large road surface irregularities are continuous.

  A vehicle braking control apparatus according to the present invention is based on a wheel speed sensor (VWA **) for detecting a wheel speed (Vwa **) of a vehicle wheel (WH **) and the wheel speed (Vwa **). Thus, when the vehicle travels on a downhill road, the travel speed (Vxa) of the vehicle is controlled so as to control the braking torque (Pwa **) to the wheels (WH **) so as not to exceed the set speed (vxs). Travel speed control unit (DAC) that executes speed control, and anti-skid control that adjusts the braking torque (Pwa **) so as to suppress excessive braking slip of the wheel (WH **) A controller (ECU) including a control unit (ABS).

  In the vehicle braking control device according to the present invention, the anti-skid control unit (ABS) is configured to control the wheel (WH **) when the travel speed control unit (DAC) is executing the travel speed control. A selected wheel (WHs) is selected from among them, and the selected wheel (WHs) is configured to prohibit a decrease in the braking torque (Pwa) due to the anti-skid control.

  Since the vehicle is constantly moving, even if the ground contact state of the wheels is impaired and the slip state amount Slp of the selected wheel WHs becomes excessive, the ground contact state is recovered immediately. According to the above configuration, the braking torque Pwa is not reduced at the selected wheel WHs (for example, maintained as it is when the selected wheel WHs is selected). Once the braking torque Pwa is reduced, a delay occurs in the braking force immediately after the ground contact state is recovered. However, since the decrease of the braking torque Pwa is prohibited in the selected wheel WHs, the braking force is instantaneously recovered when the ground contact is recovered. Can be generated. Therefore, the deceleration of the vehicle is reliably maintained, and suitable travel speed control can be executed.

  In the vehicle braking control apparatus according to the present invention, the anti-skid control unit (ABS) selects a trough wheel (WHt) located on a trough side of the downhill road as the selected wheel (WHs), and the downhill road The mountain wheel (WHy) located on the mountain side is not selected as the selected wheel (WHs). Further, the anti-skid control unit (ABS) selects a mountain wheel (WHy) located on the mountain side of the downhill road as the selected wheel (WHs), and a valley located on the valley side of the downhill road. When the side wheel (WHt) is selected as the selected wheel (WHs), the selection of the mountain side wheel (WHy) as the selected wheel (WHs) is canceled.

  When traveling downhill, it is very important to secure the lateral force of the mountain wheel WHy in terms of vehicle stability. According to the above configuration, only the valley side wheel WHt is selected as the selected wheel WHs, or the valley side wheel WHt is preferentially selected as the selected wheel WHs. For this reason, in the mountain side wheel WHy, the braking torque Pwa is preferably reduced, and the lateral force can be secured. As a result, the stability of the vehicle is improved, and the swinging of the traveling can be suppressed.

  In the vehicle braking control apparatus according to the present invention, the anti-skid control unit (ABS) cancels the prohibition of the reduction of the braking torque (Pwa) when the state of the selected wheel has passed a predetermined time (tkx). It is configured as follows. Since the vehicle is moving, excessive wheel slip due to insufficient grounding should be short. According to the above configuration, the state of the selected wheel WHs is limited within the predetermined time tkx, and the control reliability can be improved.

1 is an overall configuration diagram for explaining an embodiment of a vehicle braking control device BCS according to the present invention. FIG. It is a flowchart for demonstrating the process of traveling speed control. It is a flowchart for demonstrating the process of anti-skid control. It is a functional block diagram for demonstrating the determination process of the selection wheel.

<Explanation of symbols>
In the following description, the component, the arithmetic processing, the signal, the characteristic, and the value to which the same symbol is attached exhibit the same function. Therefore, duplicate description may be omitted.

  The subscript “**” attached to the end of various symbols and the like is a comprehensive symbol indicating whether the vehicle is related to any of the four wheels on the front, rear, left and right. The subscript “**” may be omitted. Each subscript corresponds to “fl” for the left front wheel, “fr” for the right front wheel, “rl” for the left rear wheel, and “rr” for the right rear wheel, respectively. For example, the wheel speed sensor VWA ** includes a wheel speed sensor VWAfl for the left front wheel, a wheel speed sensor VWAfr for the right front wheel, a wheel speed sensor VWArl for the left rear wheel, and a wheel speed sensor VWArr for the right rear wheel. Shown in When the subscript “**” is omitted, it is simply written as “VWA”.

<First Embodiment of Brake Control Device for Vehicle according to the Present Invention>
An embodiment of a vehicle braking control apparatus BCS according to the present invention will be described with reference to the overall configuration diagram of FIG. A vehicle including the braking control device BCS includes a braking operation member BP, a braking operation amount sensor BPA, a braking switch BSW, an acceleration operation member AP, an acceleration operation amount sensor APA, a transmission operation member SF, a transmission position sensor SFA, and a wheel speed sensor VWA. , A traveling speed control switch SDA, a master cylinder MC, and a pressure regulating unit CAU are provided.

  Further, each wheel WH ** of the vehicle is provided with a brake caliper CP **, a wheel cylinder WC **, a rotating member KT **, a friction member MS **, and a wheel speed sensor VWA **. . And pressurization unit KAU and pressure regulation unit CAU are fluidly connected via the 1st and 2nd pressurization piping HK1 and HK2. Further, the pressure adjusting unit CAU and the wheel cylinder WC ** are fluidly connected via a pressure adjusting pipe HC ** corresponding to each wheel WH **.

  The braking operation member (for example, a brake pedal) BP is a member that the driver operates to decelerate the vehicle. By operating the braking operation member BP, the braking torque for the wheel WH ** is adjusted, and a braking force is generated on the wheel WH. Specifically, a rotating member (for example, a brake disc) KT ** is fixed to the vehicle wheel WH. A brake caliper CP ** is arranged so as to sandwich the rotating member KT **. A brake caliper (also simply referred to as a caliper) CP ** is provided with a wheel cylinder WC **.

  By adjusting (increasing or decreasing) the hydraulic pressure (braking hydraulic pressure) in the wheel cylinder WC of the caliper CP, the piston in the wheel cylinder WC moves (forwards or reverses) with respect to the rotating member KT. Is done. By this movement of the piston, a friction member (for example, a brake pad) MS ** (not shown) is pressed against the rotating member KT **, and a pressing force is generated. The rotating member KT ** and the wheel WH ** are fixed so as to rotate together. For this reason, braking torque is applied to the wheel WH ** by the frictional force between the friction member MS ** and the rotation member KT ** generated by the pressing force. As a result, braking force is generated on the wheels WH **, and the vehicle decelerates.

  The braking operation member BP is provided with a braking operation amount sensor BPA. The brake operation amount sensor BPA detects the operation amount Bpa of the brake operation member (brake pedal) BP by the driver. Specifically, at least one of a brake operation displacement sensor that detects an operation displacement of the brake operation member BP and a brake operation force sensor that detects an operation force of the brake operation member BP is employed as the brake operation amount sensor BPA. Is done. A master cylinder hydraulic pressure sensor (also simply referred to as “hydraulic pressure sensor”) PMC that detects the hydraulic pressure Pmc of the master cylinder MC may be employed as the braking operation amount sensor BPA.

  In other words, the braking operation amount sensor BPA is a general term for the braking operation displacement sensor, the braking operation force sensor, and the master cylinder hydraulic pressure sensor PMC. Therefore, the brake operation amount Bpa is determined based on at least one of the operation displacement of the brake operation member BP, the operation force of the brake operation member BP, and the master cylinder hydraulic pressure Pmc. The detected value Bpa of the braking operation amount is input to the controller ECU.

  Further, the brake operation member BP is provided with a brake switch BSW. The brake switch BSW is an ON / OFF switch, and detects whether or not the brake operation member BP is operated. The signal Bsw detected by the brake switch BSW is input to the controller ECU. Specifically, as the brake switch signal Bsw, an ON signal is detected when the brake operation member BP is operated, and an OFF signal is detected when the brake operation member BP is not operated.

  The acceleration operation member (for example, accelerator pedal) AP is a member that the driver operates to accelerate the vehicle. By operating the acceleration operation member AP, the output of the power source (for example, an internal combustion engine) of the vehicle is increased, and the driving torque for the wheel WH ** is applied. As a result, driving force is generated on the wheels WH, and the vehicle is accelerated.

  The acceleration operation member AP is provided with an acceleration operation amount sensor APA. The acceleration operation amount sensor APA detects the operation amount Apa of the acceleration operation member (accelerator pedal) AP by the driver. Specifically, at least one of an acceleration operation displacement sensor that detects an operation displacement of the acceleration operation member AP and an acceleration operation force sensor that detects an operation force of the acceleration operation member AP is employed as the acceleration operation amount sensor APA. Is done. The acceleration operation amount detection value Apa is input to the controller ECU.

  The speed change operation member (for example, shift lever) SF is a member for the driver to instruct the gear position of the transmission. Further, the forward or backward movement of the vehicle is instructed by the speed change operation member SF. The speed change operation member SF is also referred to as a “select lever”. The shift operation member SF is provided with a shift position sensor (also referred to as a “shift position sensor”) SFA. The shift position signal Sfa selected by the shift operation member SF is detected by the shift position sensor SFA. Here, the shift position Sfa includes vehicle forward and backward instruction information.

  A wheel speed sensor VWA ** is provided for each wheel WH ** of the vehicle. A rotational speed (wheel speed) Vwa ** of each wheel WH ** is detected by the wheel speed sensor VWA **. The wheel speed Vwa ** is used for execution of travel speed control and anti-skid control described later. The detected value Vwa ** of the wheel speed is input to the controller ECU.

  A travel speed control switch (also simply referred to as “control switch”) SDA is provided on the operation panel of the vehicle. The control switch SDA is an on / off switch, and is instructed whether or not the driver is requested to execute the traveling speed control. For example, a rocker switch, a push button switch, or the like is employed as the control switch SDA. When traveling speed control is required, an ON signal is transmitted as a signal (instruction signal) Sda of the control switch SDA. On the other hand, when traveling speed control is not required, an off signal is output as the instruction signal Sda.

  The tandem master cylinder (simply referred to as “master cylinder”) MC converts the operation force of the brake operation member BP into a hydraulic pressure and pumps the brake fluid (brake fluid) to the wheel cylinder WC ** of each wheel WH **. To do. Specifically, the interior of the master cylinder MC is partitioned by an inner wall of the master cylinder MC and two first and second pistons PS1 and PS2, and two hydraulic chambers (first and second hydraulic chambers Rm1, Rm2) is formed. The first hydraulic chamber Rm1 has a first port, and the second hydraulic chamber Rm2 has a second port. The first and second hydraulic chambers Rm1 and Rm2 of the master cylinder MC receive the supply of the brake fluid from the master reservoir RVM and pump the brake fluid from the two ports.

  The first hydraulic chamber Rm1 of the master cylinder MC is fluidly connected to the wheel cylinder WCfl of the left front wheel WHfl and the wheel cylinder WCrr of the right rear wheel WHrr. When the braking operation member BP is operated, the piston PS1 moves forward (moves leftward in the figure), and the volume of the first hydraulic chamber Rm1 is reduced. Accordingly, the brake fluid in the first hydraulic chamber Rm1 is pumped from the first hydraulic chamber Rm1 toward the left front wheel cylinder WCfl and the right rear wheel cylinder WCrr.

  Similarly, the second hydraulic chamber Rm2 of the master cylinder MC is fluidly connected to the wheel cylinder WCfr of the right front wheel WHfr and the wheel cylinder WCrl of the left rear wheel WHrl. When the braking operation member BP is operated, the piston PS2 moves forward (moves leftward in the figure), and the volume of the second hydraulic chamber Rm2 is reduced. Accordingly, the brake fluid in the second hydraulic chamber Rm2 is pumped from the second hydraulic chamber Rm2 toward the right front wheel wheel cylinder WCfr and the left rear wheel wheel cylinder WCrl.

  As described above, the path (fluid path) through which the brake fluid is moved between the master cylinder MC and the four wheel cylinders WC ** is composed of two braking systems. A so-called diagonal piping (also referred to as X piping) is adopted as a braking system.

≪Pressure adjustment unit CAU≫
Next, the pressure adjusting unit CAU will be described. The pressure adjusting unit CAU is disposed between the master cylinder MC and the wheel cylinder WC **, and the master cylinder MC generates the brake fluid pressure Pwa ** (resulting in braking torque) in each wheel cylinder WC **. Independently from the hydraulic pressure, and individually controlled at each wheel WH **. The pressure adjustment unit CAU is composed of a modulator HMJ and a controller ECU.

  The modulator HMJ is formed including a plurality of solenoid valves (SL1 and the like), a fluid pump (HP1 and the like), and an electric motor MT. First, components of the modulator HMJ related to the first braking system SK1 will be described. The normally-open first linear solenoid valve SL1 includes a first port of the first hydraulic chamber Rm1 of the master cylinder MC, a pressure adjusting unit CAfl for the left front wheel WHfl, and a pressure adjusting unit CArr for the right rear wheel WHrr. Between the first and second upstream pipes HK1. Here, the “upstream part” is a part near the master cylinder MC in the fluid path. For example, the upstream portion of the left front wheel pressure regulator CAfl is located on the side of the fluid path closer to the first hydraulic pressure chamber Rm1 (that is, between the first linear electromagnetic valve SL1 and the pressure increasing valve SZfl with respect to the pressure increasing valve SZfl). Between).

  The valve body of the first linear solenoid valve SL1 has a force in the opening direction (the first pressure chamber CAfl, the upstream portion of the CArr (side closer to the master cylinder MC)) and the first hydraulic chamber Rm1 due to the hydraulic pressure difference (first 1 force that attempts to bring the linear solenoid valve SL1 into a communication state). On the other hand, a force in the closing direction (a force to make the first linear electromagnetic valve SL1 non-communication) acts on the valve body by an attractive force corresponding to a current value supplied to the first linear electromagnetic valve SL1. . The first linear solenoid valve SL1 is closed when the suction force is larger than the force due to the hydraulic pressure difference, and the communication between the first hydraulic pressure chamber Rm1 and the upstream portion of the pressure adjusting units CAfl and CArr is blocked. On the other hand, when the suction force is smaller than the force due to the hydraulic pressure difference, the first linear electromagnetic valve SL1 is opened, and the first hydraulic pressure chamber Rm1 communicates with the upstream portions of the pressure adjusting sections CAfl and CArr.

  When the electric motor MT is driven and the first fluid pump HP1 discharges the brake fluid, the first hydraulic pressure chamber Rm1 and the pressure adjusting unit CAfl are generated by the suction force corresponding to the current value to the first linear electromagnetic valve SL1. , The hydraulic pressure difference with CArr can be controlled. In other words, the hydraulic pressure upstream of the pressure adjusting units CAfl and CArr is adjusted to a value obtained by adding the hydraulic pressure difference generated by the current value to the hydraulic pressure Pm1 in the first hydraulic pressure chamber Rm1. Therefore, even if the hydraulic pressure of the MC is “0”, the hydraulic pressure is generated in the upstream portion of the pressure adjusting sections CAfl and CArr.

  Note that when the current value to the first linear solenoid valve SL1 is set to “0” and is in a non-excited state, the hydraulic pressure upstream of the pressure regulating sections CAfl and CArr is the hydraulic pressure in the first hydraulic pressure chamber Rm1. It becomes equal to Pm1. Since the suction force of the first linear solenoid valve SL1 is not generated, the hydraulic pressure difference is set to “0”. The linear solenoid valve is also referred to as a “differential pressure valve”.

  A pressure adjusting part CAfl for the left front wheel WHfl is formed by a pressure increasing valve SZfl and a pressure reducing valve SGfl. As the pressure increasing valve SZfl, a normally open two-position electromagnetic valve (so-called NO valve) is employed. That is, the pressure increasing valve SZfl is in an open position (communication state) when not energized, and is in a closed position (non-communication state) when energized. Further, a normally closed two-position electromagnetic valve (so-called NC valve) is employed as the pressure reducing valve SGfl. That is, the pressure reducing valve SGfl is in a closed position (non-communication state) when not energized, and is in an open position (communication state) when energized.

  The communication state (communication or blocking) between the upstream portion of the pressure adjustment section CAfl for the left front wheel WHfl and the wheel cylinder WCfl is selectively switched by the pressure increasing valve SZfl. Since the pressure increasing valve SZfl is a normally open type, the upstream portion of the pressure adjusting section CAfl and the wheel cylinder WCfl are in communication with each other when not energized (non-excited state). On the other hand, when the pressure increasing valve SZfl is energized and the excited state is achieved, the communication state between the upstream portion of the pressure regulating unit CAfl and the wheel cylinder WCfl is cut off and changed to the non-communication state.

  Similarly, the communication state (communication or blocking) between the wheel cylinder WCfl and the first reservoir RV1 is selectively switched by the pressure reducing valve SGfl. Since SGfl is a normally closed type, the communication state between the wheel cylinder WCfl and the first reservoir RV1 is cut off (non-communication state) in a non-energized state (non-excitation state). When energization is performed on SGfl (that is, when excitation is performed), the wheel cylinder WCfl and the first reservoir RV1 are changed to a communication state.

  The left front wheel cylinder WCfl is connected to a fluid path between the pressure increasing valve SZfl and the pressure reducing valve SGfl via a pressure adjusting pipe HCfl. Therefore, by controlling the pressure increasing valve SZfl and the pressure reducing valve SGfl, the brake fluid pressure (resulting in braking torque) Pwafl in the wheel cylinder WCfl is adjusted separately from the brake fluid pressures of the other wheel cylinders ( (Pressure increase, hold, or pressure reduction).

  Similarly, a pressure adjusting part CArr for the right rear wheel WHrr is formed by the pressure increasing valve SZrr and the pressure reducing valve SGrr. The communication state between the first hydraulic pressure chamber Rm1 (specifically, the upstream portion of the pressure adjusting unit CArr) and the wheel cylinder WCrr is switched by the pressure increasing valve SZrr, and the right rear wheel wheel cylinder WCrr is switched by the pressure reducing valve SGrr. The communication state with the first reservoir RV1 is switched. The wheel cylinder WCrr is connected to a fluid path between the pressure increasing valve SZrr and the pressure reducing valve SGrr via a pressure regulating pipe HCrr. Therefore, by controlling the pressure increasing valve SZrr and the pressure reducing valve SGrr, the brake hydraulic pressure Pwarr in the wheel cylinder WCrr is adjusted separately from the brake hydraulic pressures of the other wheel cylinders.

  The brake fluid supply part RT is formed including the electric motor MT and the first fluid pump HP1. The first fluid pump HP1 is driven by an electric motor MT. The first fluid pump HP1 pumps up the brake fluid in the first reservoir RV1 that has been refluxed from the pressure reducing valves SGfl and SGrr. Then, the pumped brake fluid is supplied to the upstream portions of the pressure adjusting sections CAfl and CArr of the first braking system SK1 (the fluid path between the first linear electromagnetic valve SL1 and the pressure increasing valves SZfl and SZrr) ( Returned).

  A master cylinder hydraulic pressure sensor (also simply referred to as “hydraulic pressure sensor”) PMC is provided at the upstream portion of the pressure adjusting portion CAfl for the left front wheel WHfl (same as the upstream portion of the pressure adjusting portion CArr for the right rear wheel WHrr). Provided. That is, the hydraulic pressure of the first pressurizing pipe HK1 in the modulator HMJ is detected as the master cylinder hydraulic pressure Pmc by the hydraulic pressure sensor PMC. The detection value Pmc of the hydraulic pressure sensor PMC is input to the controller ECU.

  Since the components of the modulator HMJ related to the second braking system SK2 are the same as those related to the first braking system SK1, detailed description thereof will be omitted. Regarding the respective components related to the second braking system SK2, in the description relating to the first braking system SK1, “first” is “second”, “SK1” is “SK2”, and “SL1” is “ “SL2”, “Rm1” to “Rm2”, “HK1” to “HK2”, “HP1” to “HP2”, “RV1” to “RV2”, “CAfl” to “CAfr”, “ "SZfl" is "SZfr", "SGfl" is "SGfr", "HCfl" is "HCfr", "CArr" is "CArl", "SZrr" is "SZrl", and "SGrr" is "SGrl" "HCrr" can be explained as "HCrl", respectively.

  A controller (electronic control unit) ECU in the CAU is formed by an electric circuit board on which a microprocessor and the like are mounted, and a control algorithm programmed in the microprocessor. The controller ECU controls the modulator HMJ based on the wheel speed Vwa ** and the like, and the hydraulic pressure Pwa ** in each wheel cylinder WC ** is adjusted individually. Specifically, based on the control algorithm, signals for controlling the electromagnetic valves (SL1 and the like) constituting the modulator HMJ and the electric motor MT are calculated and output from the controller ECU.

  The control algorithm of the controller ECU includes a travel speed control unit DAC and an anti-skid control unit ABS. The traveling speed control unit DAC executes traveling speed control that travels on a steeply descending downhill road by an automatic brake at a substantially constant low vehicle speed. The anti-skid control unit ABS executes anti-skid control that reduces excessive wheel slip and suppresses the tendency of the wheels to lock. Details of both controls will be described later. The pressure regulating unit CAU has been described above.

<Travel speed control process>
With reference to the flowchart of FIG. 2, the process in the travel speed control part DAC performed by controller ECU of the pressure regulation unit CAU is demonstrated. The traveling speed control is a control that automatically controls the braking device and maintains a substantially constant low vehicle speed when traveling on a steep downhill road. While the traveling speed control is being executed, the driver does not need to perform acceleration / deceleration operations and can concentrate on the steering operation. The traveling speed control is also referred to as Hill Descent Control or Downhill Assist Control.

  The traveling speed control process is a control algorithm and is programmed in the controller ECU. Note that, as described above, components having the same symbol, arithmetic processing, signals, characteristics, and values exhibit the same function. Each subscript “**” represents “fl” for the left front wheel, “fr” for the right front wheel, “rl” for the left rear wheel, and “rr” for the right rear wheel.

  In step S110, signals necessary for traveling speed control are read. Specifically, the braking switch signal Bsw, the braking operation amount Bpa, the acceleration operation amount Apa, the shift position signal Sfa, the control switch signal Sda, and the wheel speed Vwa ** are read.

  The brake switch signal Bsw is an on / off signal of the brake switch BSW. The braking operation amount Bpa is detected by a braking operation amount sensor BPA (for example, a braking operation displacement sensor, a hydraulic pressure sensor PMC). The acceleration operation amount Apa and the shift position Sfa are detected by the acceleration operation amount sensor APA and the shift position sensor SFA. The control switch signal Sda is a signal for turning on or off the control switch SDA. The wheel speed Vwa ** is detected by a wheel speed sensor VWA ** provided in each wheel WH **.

  In step S120, “whether or not the control switch signal Sda is in an on state” is determined. That is, it is determined whether or not the driver is requested to execute the traveling speed control. If there is no request for traveling speed control, the control switch signal (instruction signal) Sda is off, and step S120 is negative (in the case of “NO”), the process proceeds to step S160. If traveling speed control is requested, the control switch signal Sda is on, and step S120 is affirmative (if “YES”), the process proceeds to step S130.

  In step S130, “whether or not the shift position Sfa is the forward position or the reverse position” is determined. Here, the shift position Sfa includes a neutral position and a parking position in addition to the forward position and the reverse position. In a general automatic transmission, the forward position, the reverse position, the neutral position, and the parking position are respectively displayed as “D”, “R”, “N”, and “P”.

  If the shift position signal Sfa is one of the forward position and the reverse position, and step S130 is positive (if “YES”), the process proceeds to step S140. On the other hand, if the shift position Sfa is one of the neutral position and the parking position and Step S130 is negative ("NO"), the process proceeds to Step S160.

  In step S140, it is determined whether or not there is an acceleration operation or a deceleration operation. The presence or absence of the acceleration operation is determined based on the acceleration operation amount Apa. Specifically, when the acceleration operation amount Apa is equal to or greater than the predetermined amount ap0, it is determined that “there is an acceleration operation”, and when the acceleration operation amount Apa is less than the predetermined amount ap0, “acceleration operation is performed”. It is determined that no. Here, the predetermined amount ap0 is a threshold value for determination, and is a predetermined value set in advance. The predetermined amount ap0 is a value corresponding to “play” of the acceleration operation member (accelerator pedal) AP.

  The presence or absence of a braking operation is determined based on the braking operation amount Bpa. Specifically, when the braking operation amount Bpa is greater than or equal to the predetermined amount bp0, it is determined that “there is a braking operation”, and when the braking operation amount Bpa is less than the predetermined amount bp0, It is determined that no. Here, the predetermined amount bp0 is a threshold value for determination, and is a predetermined value set in advance. The predetermined amount bp0 is a value corresponding to “play” of the braking operation member (brake pedal) BP.

  The presence or absence of a braking operation is determined based on the brake switch Bsw. Specifically, when the switch signal Bsw represents an on state (ON signal), it is determined that “there is a braking operation”, and when the switch signal Bsw represents an off state (OFF signal), “braking” It is determined that there is no operation.

  If neither the acceleration operation nor the braking operation is performed, and step S140 is affirmed (in the case of “YES”), the process proceeds to step S150. On the other hand, when either the acceleration operation or the braking operation is performed and step S140 is negative (in the case of “NO”), the process proceeds to step S160.

  In step S150 and step S160, a control flag FLda indicating the execution status of the traveling speed control is set. During the execution of the traveling speed control, the control flag FLda is set to “1”. On the other hand, when the traveling speed control is not executed, the control flag FLda is set to “0”. Note that the control flag FLda indicating the execution state of the traveling speed control is set to “0” as an initial state (default).

  After “FLda = 1” is set in step S150, the process proceeds to step S170. On the other hand, if “FLda = 0” is set in step S160, the current calculation process is terminated.

  In step S170, the set speed vxs is set (instructed). For example, the set speed vxs is set by the driver. Further, based on the driver's operation, the set speed vxs is determined by selecting from a plurality of options. For example, the set speed vxs is determined based on the transfer gear position (high-speed drive position or low-speed drive position). Here, the set speed vxs is set to a smaller value in the low-speed drive position than in the high-speed drive position.

  In step S180, the vehicle body speed Vxa is calculated based on the wheel speed Vwa **. The vehicle body speed Vxa is the traveling speed of the vehicle. For example, the largest one (the fastest value) among the plurality of wheel speeds Vwa ** is determined as the vehicle body speed Vxa.

  In the processing from step S190 to step S230, based on the comparison between the vehicle speed Vxa and the set speed vxs, the braking torque (in order that the vehicle speed Vxa does not exceed the set speed vxs and substantially matches the set speed vxs). For example, the braking fluid pressure) is adjusted (increased, decreased or maintained).

  In step S190, it is determined whether or not “vehicle speed Vxa is equal to or higher than first predetermined vehicle speed vxz”. Here, the first predetermined vehicle speed vxz is a threshold value in which a minute speed α (hysteresis) is considered with respect to the set speed vxs so that the control is not switched complicatedly. The first predetermined vehicle speed vxz is also referred to as a “pressure increase threshold value”. If “Vxa ≧ vxz” and step S190 is positive (if “YES”), the process proceeds to step S210. If “Vxa <vxz” and step S190 is negative (“NO”), the process proceeds to step S200.

  In step S200, it is determined whether or not “vehicle speed Vxa is equal to or lower than second predetermined vehicle speed vxg”. Similar to the first predetermined vehicle speed vxz, the second predetermined vehicle speed vxg is a threshold value in which a hysteresis value α (predetermined minute speed) is added to the set speed vxs. The second predetermined vehicle speed vxg is also referred to as a “decompression threshold value”. If “Vxa ≦ vxg” and step S200 is positive (“YES”), the process proceeds to step S220. If “Vxa> vxg” and step S200 is negative (“NO”), the process proceeds to step S230.

  In step S210, the braking torque (braking fluid pressure) is increased so that the vehicle body speed Vxa decreases. In step S220, the braking torque (braking fluid pressure) is decreased so that the vehicle body speed Vxa increases. In step S230, the braking torque (braking fluid pressure) is maintained so that the vehicle body speed Vxa is maintained. By adjusting the braking torque in steps S210 to S230, the vehicle body speed Vxa is controlled to substantially match the set speed vxs.

  As described above, the processing from step S110 to step S230 corresponds to the traveling speed control unit DAC. In the traveling speed control, the control switch SDA is in the ON state, the shift position Sfa is “forward D” or “reverse R”, and the acceleration operation member AP and the braking operation member BP are operated by the driver. If not, it will be executed. Therefore, the adjustment of the braking torque is achieved by automatic braking.

<Anti-skid control process>
With reference to the flowchart of FIG. 3, the process in the anti-skid control unit ABS will be described. Here, the anti-skid control is to suppress an excessive front / rear slip of the wheel (that is, the tendency of the wheel to lock) based on the degree of slip in the rotational direction of the wheel (for example, slip speed Vsl, wheel acceleration dVw). is there. The anti-skid control includes “normal anti-skid control” executed when the running speed control is not executed (that is, when “FLda = 0”) and running speed control is executed ( That is, “anti-skid control during travel speed control” executed when “FLda = 1” is included. Similar to the travel speed control process, the anti-skid control process is a control algorithm and is programmed in the controller ECU.

  In step S310, a signal necessary for executing anti-skid control is read. Specifically, the braking operation amount Bpa, the braking switch signal Bsw, the shift position Sfa, the traveling speed control control flag FLda, and the wheel speed Vwa ** are read.

  In step S320, based on the control flag FLda, “whether or not traveling speed control is being executed” is determined. If the traveling speed control is not executed, “FLda = 0” is displayed, and step S320 is negative (“NO”), the process proceeds to step S330. If the traveling speed control is being executed, “FLda = 1” is displayed, and step S320 is affirmed (in the case of “YES”), the process proceeds to step S410.

≪Normal anti-skid control≫
Step S330 and subsequent steps are processing at the time of normal braking when the traveling speed control is not operating. In step S330, based on at least one of the braking operation amount Bpa and the switch signal Bsw, it is determined whether or not the vehicle is braking. For example, when the braking operation amount Bpa is equal to or greater than a predetermined value bp0, it is determined that braking is being performed, and when the braking operation amount Bpa is less than the predetermined value bp0, it is determined that braking is not being performed. . Here, the predetermined value bp0 is a predetermined threshold for determination. Further, when the switch signal Bsw indicates an on state, it is determined that braking is being performed, and when the switch signal Bsw indicates an off state, it is determined that braking is not being performed.

  If the braking operation is not being performed and step S330 is negative (in the case of “NO”), the current calculation process is terminated and the anti-skid control is not executed. If the braking operation is being performed and step S330 is affirmative (if “YES”), the process proceeds to step S340.

  In step S340, the vehicle body speed Vxa is calculated based on the wheel speed Vwa ** of each wheel WH **. For example, the largest one (ie, the fastest value) among the plurality of wheel speeds Vwa ** is determined as the vehicle body speed Vxa. Further, the vehicle body speed Vxa calculated in step S180 may be read.

  In addition, when the vehicle body speed Vxa is calculated, a restriction can be provided in the amount of time change of the vehicle body speed Vxa. That is, the upper limit value αup of the increase gradient of the vehicle body speed Vxa and the lower limit value αdn of the decrease gradient are set, and the change of the vehicle body speed Vxa is restricted by the upper and lower limit values αup, αdn. This is due to the fact that the inertia of the entire vehicle is very large and difficult to change compared to the inertia of the wheel WH.

  For example, when the upper and lower limits αup and αdn of the change gradient are not limited, the maximum value of the wheel speeds Vwa ** is determined as it is as the vehicle body speed Vxa. On the other hand, when the upper and lower limit values αup and αdn are limited, the maximum value is limited by the upper and lower limit values αup and αdn, and the vehicle body speed Vxa is calculated.

  In step S350, wheel acceleration (time change amount of wheel speed) dVw ** is calculated based on the wheel speed Vwa **. Specifically, the wheel acceleration dVw ** (also simply referred to as “dVw”) is calculated by differentiating the wheel speed Vwa ** with respect to time. The wheel acceleration dVw is calculated as a positive (plus) sign when the rotational motion of the wheel WH is accelerating, and a negative (minus) sign when the rotational motion of the wheel WH is decelerating. The wheel acceleration dVw is one of the slip state quantities Slp and is a variable.

  In step S360, the slip speed Vsl ** of the wheel WH ** is calculated based on the comparison between the vehicle body speed Vxa and the wheel speed Vwa **. Here, the slip speed Vsl ** (also simply referred to as “Vsl”) is a state quantity Slp ** that represents the degree of the slip state of the wheel WH. That is, the slip speed Vsl is one of the slip state quantities Slp and is a variable, like the wheel acceleration dVw. For example, the deviation of the vehicle speed Vxa and the wheel speed Vwa is adopted as the slip speed Vsl. That is, the slip speed Vsl is calculated by “Vsl ** = Vxa−Vwa **”. Further, “Vsl ** / Vxa” obtained by making the deviation non-dimensional by the vehicle body speed Vxa (that is, the slip ratio) can be adopted as the slip speed Vsl **.

  In step S370, normal anti-skid control is executed based on the wheel acceleration dVw ** and the slip speed Vsl **. That is, the anti-skid control is executed based on the slip state amount Slp indicating the degree of slip in the wheel rotation direction. Here, “normal time” refers to a case where traveling speed control is not being executed.

  Adjustment of the brake fluid pressure by the anti-skid control is achieved by selecting one of the decrease mode Mgn and the increase mode Mzo. Here, the decrease mode Mgn decreases the braking torque, and is also referred to as a “decompression mode”. Further, the increase mode Mzo increases the braking torque, and is also referred to as “pressure increase mode”. The decrease mode Mgn and the increase mode Mzo are collectively referred to as “control mode”.

  A threshold value is set in advance for each control mode of the anti-skid control. Then, based on the correlation between the slip state quantity Slp (wheel acceleration dVw **, slip speed Vsl **) and the threshold value, one of the decrease mode and the increase mode is selected. The In addition, the duty ratio of the pressure reducing valve SG ** and the duty ratio of the pressure increasing valve SZ ** are determined. Then, based on the selected control mode and the determined duty ratio, the electromagnetic valve of the pressure adjusting unit CAU is driven, and the brake hydraulic pressure Pwa of the wheel cylinder WC is adjusted.

  When the braking hydraulic pressure is reduced by the anti-skid control reduction mode Mgn, the normally open pressure increasing valve SZ ** is closed and the normally closed pressure reducing valve SG ** is opened. . Since the brake fluid in the wheel cylinder WC ** is moved to the low pressure reservoirs RV1, RV2, the brake fluid pressure of the wheel cylinder is reduced. Here, the pressure reduction speed (pressure reduction amount per unit time) is determined by the duty ratio (time ratio of the energized state in a constant cycle) Dg ** of the pressure reducing valve SG **. Specifically, “100%” of the duty ratio Dg ** always corresponds to the open state, and the braking hydraulic pressure is rapidly reduced. Note that “0%” of the duty ratio Dg ** always corresponds to the closed state.

  When the brake fluid pressure is increased by the increase mode Mzo of the anti-skid control, the pressure increasing valve SZ ** is opened and the pressure reducing valve SG ** is closed. Then, the brake fluid is moved from the master cylinder MC to the wheel cylinder WC, and the brake fluid pressure of the wheel cylinder WC is increased. Here, the pressure increasing speed (pressure increasing amount per unit time) is determined by the duty ratio (time ratio of the energized state in a constant cycle) Dz ** of the pressure increasing valve SZ **. Specifically, “0%” of the duty ratio Dz ** always corresponds to the open state, and the braking hydraulic pressure is rapidly increased. Note that “100%” of the duty ratio Dz ** always corresponds to the closed state.

  In the decrease mode Mgn, the brake fluid accumulated in the low pressure reservoirs RV1 and RV2 is returned to the fluid path between the pressure increasing valve SZ ** and the master cylinder MC by the hydraulic pumps HP1 and HP2 driven by the electric motor MT. (Refluxed). Each solenoid valve (SG **, etc.) and the electric motor MT are driven (controlled) by the ECU.

  When it is necessary to maintain the brake fluid pressure by the anti-skid control, the pressure reducing valve SG ** or the pressure increasing valve SZ ** is always closed in the decrease mode Mgn or the increase mode Mzo. Is done. Specifically, when the braking hydraulic pressure needs to be maintained in the decrease mode Mgn, the duty ratio Dg ** of the pressure reducing valve SG ** is determined to be “0% (normally closed state)”. In the increase mode Mzo, when it is necessary to maintain the brake fluid pressure, the duty ratio Dz ** of the pressure increasing valve SZ ** is determined to be “100% (normally closed state)”. The anti-skid control during normal time has been described above.

≪Anti-skid control during running speed control≫
Next, the anti-skid control at the time of traveling speed control will be described. Anti-skid control at the time of traveling speed control basically conforms to normal anti-skid control. The difference is that a threshold for determining each control mode and that excessive wheel slip (eg, wheel lock) for one or two wheels is allowed (ie, determination of the selected wheel). Hereinafter, differences will be mainly described.

  In step S410, the vehicle body speed Vxa is calculated based on each wheel speed Vwa in the same manner as in step S340. In step S420, the wheel acceleration dVw is calculated based on the wheel speed Vwa in the same manner as in step S350. In step S430, the slip speed Vsl is calculated based on the comparison between the vehicle body speed Vxa and the wheel speed Vwa in the same manner as in step S360.

  In step S440, the mountain side wheel WHy and the valley side wheel WHt are determined based on the shift position signal Sfa. Here, the mountain side wheel WHy is two wheels located on the valley side (the side with the lower altitude) among the four wheels WH ** on the downhill road where the vehicle is traveling. Moreover, the valley side wheel WHt is two wheels located on the mountain side (high altitude side) among the four wheels WH ** on the downhill road where the vehicle is traveling.

  In step S440, whether the traveling direction of the vehicle is forward or reverse is identified based on the shift position Sfa. When the shift position Sfa is “D” and the vehicle is moving forward, the mountain-side wheels WHy are the rear wheels WHrl and WHrr, and the valley-side wheels WHt are the front wheels WHfl and WHfr. Conversely, when the shift position Sfa is “R” and the vehicle is moving backward, the mountain-side wheels WHy are the front wheels WHfl and WHfr, and the valley-side wheels WHt are the rear wheels WHrl and WHrr.

  In step S450, the selected wheel WHs is determined. “Selected wheel WHs” is a wheel in which, although anti-skid control is being executed, reduction of braking torque by reduction mode Mgn is prohibited, and excessive slip (for example, wheel lock) of the wheel is allowed. . Among the four wheels WH **, one or two wheels are selected as the selected wheels WHs. A wheel that is not selected as the selected wheel WHs is referred to as “non-selected wheel WHn”. In other words, in step S450, the four wheels WH ** are separated into selected wheels WHs and non-selected wheels WHn. A detailed method for determining the selected wheel WHs will be described later.

  In step S460, anti-skid control during travel speed control is executed. Anti-skid control at the time of traveling speed control is basically the same as that at normal time. That is, any one of the decrease mode Mgn and the increase mode Mzo is selected based on the comparison between the preset threshold value of each control mode and the slip state amount Slp **. The braking torque of the wheel WH ** is adjusted (decrease, increase, hold).

  Next, the difference between the anti-skid control during the traveling speed control and the normal anti-skid control will be described.

  First, in the selected wheel WHs determined in step S450, the reduction of the braking torque Pwa by the anti-skid control is prohibited. That is, in the selected wheel WHs, even if the condition of the reduction mode Mgn is satisfied, the reduction of the braking torque Pwa is not started. Note that, in the non-selected wheel WHn that is not the selected wheel WHs, when the condition of the reduction mode Mgn is satisfied, the reduction of the braking torque Pwa is started as in the normal time.

  In the selected wheel WHs, when the braking torque Pwa is increased, the increase in the braking torque Pwa is continued even if the condition of the decrease mode Mgn is satisfied. Alternatively, in the selected wheel WHs, the value of the braking torque (braking hydraulic pressure) Pwa at the time is held at the time when the condition of the decrease mode Mgn is satisfied for the first time (calculation cycle) while the mode is the increase mode Mzo. . In any case, the braking torque Pwa is not reduced at the selected wheel WHs. As a result, the slip state amount Slp is not decreased but is maintained or increased.

  When the condition of the increase mode Mzo is satisfied in the selected wheel WHs that is in the state of the decrease mode Mgn, the setting of the selected wheel WHs is canceled and the selected wheel WHn is set. The situation occurs when the wheel whose ground contact state has been damaged contacts the road surface again. When the condition of the increase mode Mzo is satisfied (calculation cycle), the braking torque Pwa is not decreased, so the braking torque Pwa is immediately applied to the wheel. In the normal anti-skid control, the braking torque Pwa is substantially “0” when the wheel is locked, and when the increase mode Mzo is determined, the braking torque Pwa is increased from “0”. However, since the decrease of the braking torque Pwa is prohibited in the reduction mode Mgn at the selected wheel WHs, when the state of the selected wheel WHs is canceled, there is no time delay in the increase of the braking torque Pwa, and the control is immediately controlled. Power is generated. As a result, the braking force of the entire vehicle can be sufficiently ensured.

  During traveling speed control on a downhill road, the vehicle is constantly moving. For this reason, the non-grounding state of the wheel resulting from the undulation of the road surface is not continued for a long time. Accordingly, when the state of the selected wheel WHs is continued for a predetermined time tkx (calculation cycle), the designation of the selected wheel WHs on the wheel is canceled. That is, the reduction of the braking torque Pwa is started at the wheel where the reduction of the braking torque Pwa by the reduction mode Mgn is prohibited. Here, the predetermined time tkx is a threshold value for selection cancellation determination, and is a predetermined value set in advance.

  The duration T of the state of the selected wheel WHs is counted from the time point (calculation cycle) when the condition of the decrease mode Mgn is satisfied for the first time. Further, the duration T is accumulated from the time when the slip state amount Slp of the selected wheel WHs becomes excessive (for example, when the selected wheel WHs is locked and becomes “Vwa = 0”). That is, the time T set based on the slip state amount Slp (referred to as “the time of occurrence of excessive slip”) is used as a starting point, and the duration T is measured. When the decrease mode Mgn is continued, the setting of the selected wheel WHs is canceled and the braking torque Pwa starts to decrease when the duration T becomes equal to or longer than the predetermined time tkx.

  The number of selected wheels WHs is limited to one. Further, the number of selected wheels WHs may be limited to two. That is, the number of selected wheels WHs can be limited to 1 or 2. As described above, when the selected wheel WHs is released based on the restoration of the ground contact state of the selected wheel WHs or the elapsed time T of the selected wheel WHs, the number of the selected wheels WHs decreases. For this reason, next, a wheel that satisfies the condition of the reduction mode Mgn is designated as the selected wheel WHs.

  In the selected wheel WHs, reduction of the braking torque by the anti-skid control is prohibited (for example, the braking torque is maintained as it is), and an excessive wheel slip may occur. However, reduction of braking torque is not prohibited on all four wheels or on all three wheels. In addition, in the selected wheel WHs, the wheel slip becomes excessive for a very short time. For this reason, the stability of the vehicle is maintained. Since the braking torque Pwa is maintained as it is for the selected wheel WHs, the wheel generates a braking force without a time delay when the grounding state of the wheel is ensured. Accordingly, the braking force of the entire vehicle can be sufficiently ensured. The anti-skid control at the time of traveling speed control has been described above.

<Determination processing of selected wheel WHs>
With reference to the functional block diagram of FIG. 4, the process of determining the selected wheel WHs will be described (see step S450). The anti-skid control unit ABS includes a vehicle body speed calculation block VXA (corresponding to steps S340 and S410), a wheel acceleration calculation block DVW (corresponding to steps S350 and S420), and a slip speed calculation block VSL (corresponding to steps S360 and S430). It is comprised including.

  In the vehicle body speed calculation block VXA, the vehicle body speed Vxa is calculated based on the wheel speed Vwa. In the wheel acceleration calculation block DVW, the wheel speed Vwa is time-differentiated to calculate the wheel acceleration dVw. In the slip speed calculation block VSL, the slip speed Vsl is calculated based on the wheel speed Vwa and the vehicle body speed Vxa. Here, the wheel acceleration dVw and the slip speed Vsl are slip state quantities Slp (generic name) that express the degree of slip in the rotation direction of the wheel (lock tendency of the wheel). As the absolute value of the slip state amount Slp is larger, the degree of slip is larger.

  In the normal anti-skid control (step S370), the control mode is determined based on the wheel acceleration dVw and the slip speed Vsl. Specifically, the reduction mode Mgn is determined when the slip speed Vsl is equal to or higher than the first predetermined speed vsx and the wheel acceleration dVw is lower than the first predetermined acceleration dvx. Further, when at least one of the conditions that the slip speed Vsl is less than the first predetermined speed vsx and the wheel acceleration dVw is equal to or higher than the first predetermined acceleration dvx is satisfied, the increase mode Mzo is determined. Here, the first predetermined speed vsx and the first predetermined acceleration dvx are preset threshold values for determining the control mode. The first predetermined speed vsx is a positive predetermined value, and the first predetermined acceleration dvx is a negative predetermined value.

  In the anti-skid control (step S460) during the traveling speed control, the control mode is determined based on the wheel acceleration dVw and the slip speed Vsl as in the normal state. Specifically, the reduction mode Mgn is determined when the slip speed Vsl is equal to or higher than the second predetermined speed vsy and the wheel acceleration dVw is lower than the second predetermined acceleration dvy. Further, when at least one of the conditions that the slip speed Vsl is less than the second predetermined speed vsy and the wheel acceleration dVw is equal to or higher than the second predetermined acceleration dvy is satisfied, the increase mode Mzo is determined. Here, the second predetermined speed vsy and the second predetermined acceleration dvy are preset threshold values for determining the control mode, and the second predetermined speed vsy is a positive predetermined value and the second predetermined acceleration dvy. Is a negative predetermined value.

  The threshold value relationship between the normal time and the traveling speed control is “vsy ≧ vsx” and “dvy ≦ dvx”. That is, in the case of “vsy = vsx” and “dvy = dvx”, the same anti-skid control is executed in the normal time and the traveling speed control time. On the other hand, when at least one of “vsy> vsx” and “dvy <dvx” is set, the anti-skid control is less likely to be executed in the running speed control than in the normal time (in particular, The decrease mode Mgn is difficult to start). This is because the traveling speed control is generally executed on rough terrain, and the “wedge effect” can be expected.

  First, the relationship between the threshold for anti-skid control and the threshold for determining the selected wheel WHs will be described. The selected wheel WHs is determined based on the wheel acceleration dVw and the slip speed Vsl as in the anti-skid control. Specifically, in the wheel WH **, when the condition that the slip speed Vsl is equal to or higher than the third predetermined speed vsz and the wheel acceleration dVw is less than the third predetermined acceleration dvz is satisfied, the selected wheel WHs is determined. . Here, the condition “Vsl ≧ vsz” and “dVw <dvz” is referred to as “selection condition”. The third predetermined speed vsz and the third predetermined acceleration dvz are preset threshold values for determining the selected wheel WHs, the third predetermined speed vsz is a positive predetermined value, and the third predetermined acceleration dvz is Negative predetermined value. The magnitude relationship between the threshold value of the anti-skid control during the traveling speed control and the threshold value for determining the selected wheel WHs is “vsz <vsy” and “dvz> dvy”. Accordingly, the selected wheel WHs is determined before the decrease mode Mgn is started by the anti-skid control.

  The number of selected wheels WHs is limited to 1 or 2. For example, when the number of selected wheels WHs is one, a wheel that satisfies the above selection conditions (“Vsl ≧ vsz” and “dVw <dvz”) first is adopted as the selected wheel WHs. Therefore, next, the wheel that satisfies the selection condition is not adopted as the selected wheel WHs and remains the non-selected wheel WHn. When the number of the selected wheels WHs is two, the first wheel that satisfies the selection condition and the second wheel that satisfies the selection condition are adopted as the selected wheel WHs. Accordingly, at least two wheels remain unselected wheels WHn.

  For example, when the threshold value is changed so that the anti-skid control is difficult to be executed during the traveling speed control, a case where the wheel slip becomes large in all four wheels may occur. In this situation, the lateral force of the wheels is difficult to be secured, so that the vehicle may wobble. On the other hand, since the number of the selected wheels WHs for which the reduction of the braking torque Pwa is prohibited is limited, the lateral force is secured by anti-skid control on the 2 or 3 wheels. For this reason, stability is ensured without a vehicle wobbling.

  Next, the priority order of the selected wheels WHs will be described. When traveling downhill, it is very important to secure the lateral force of the mountain wheel WHy in terms of vehicle stability. Here, the mountain-side wheel WHy (the wheel located on the mountain side in the downhill road) is the rear wheels WHrl and WHrr when traveling forward and down the slope, and the front wheel WHfl when traveling backward and down the slope. , WHfr. Accordingly, the valley-side wheel WHt (wheel located on the valley side in the downhill road) corresponds to the front wheels WHfl and WHfr in the case of forward downhill, and the rear wheels WHrl and WHrr in the case of reverse downhill.

  In the determination of the selected wheel WHs, the valley wheel WHt is given priority over the mountain wheel WHy so as to improve the vehicle stability during the traveling speed control. Here, the peak wheel WHy and the valley wheel WHt are determined based on the shift position Sfa (see step S440). Specifically, when the number of selected wheels WHs is limited to one and one of the mountain-side wheels WHy is adopted as the selected wheel WHs, the selection condition is satisfied by one of the valley-side wheels WHt. Then, the mountain wheel WHy that was the selected wheel WHs is changed to a non-selected wheel WHn, and the valley wheel WHt is newly determined as the selected wheel WHs. Similarly, even when the number of selected wheels WHs is limited to two, the valley-side wheel WHt has priority over the mountain-side wheel WHy in determining the selected wheel WHs.

  Further, only the valley side wheel WHt can be adopted as the selected wheel WHs. In this case, at least one of the two valley-side wheels WHt is adopted as the selected wheel WHs, and the reduction of the braking torque Pwa can be limited. Accordingly, even if the selection condition is satisfied, the mountain-side wheel WHy is not adopted as the selection wheel WHs, and the reduction mode Mgn is applied to reduce the braking torque Pwa. In the mountain-side wheel WHy, since the lateral force is reliably ensured, the vehicle wobble on the downhill road can be suppressed.

<Action and effect>
The actions and effects of the vehicle braking control apparatus BCS according to the present invention will be summarized. The ECU of the vehicle includes a travel speed control unit DAC (calculation processing in steps S110 to S230) and an anti-skid control unit ABS (calculation processing in steps S310 to S460). The traveling speed control is based on the wheel speed Vwa ** and controls the braking torque Pwa ** of the wheel WH ** so that the traveling speed Vxa does not exceed the set speed vxs when the vehicle travels on a downhill road. is there. The anti-skid control adjusts the braking torque Pwa ** of the wheel WH ** so as to suppress excessive braking slip of the wheel WH ** based on the wheel speed Vwa **.

  When the traveling speed control is executed by the anti-skid control unit ABS, the selected wheel WHs is selected from the wheels WH **, and the reduction of the braking torque Pwa by the anti-skid control is prohibited in the selected wheel WHs. . On the other hand, in the non-selected wheel WHn that is not selected as the selected wheel WHs, the braking torque Pwa is decreased and adjusted by the anti-skid control.

  Since the vehicle is constantly moving, even if the ground contact state of the wheels is impaired and the slip state amount Slp of the selected wheel WHs becomes excessive, the ground contact state is recovered immediately. For this reason, the braking torque Pwa is not reduced at the selected wheel WHs. For example, the braking torque Pwa when the selected wheel WHs is selected is maintained as it is. Once the braking torque Pwa is reduced, a delay occurs in the braking force immediately after the ground contact state is recovered. However, since the decrease of the braking torque Pwa is prohibited in the selected wheel WHs, the braking force is instantaneously recovered when the ground contact is recovered. Can be generated. Therefore, the deceleration of the vehicle is reliably maintained, and suitable travel speed control can be executed.

  One or two wheels are selected as the selected wheel WHs. That is, not all wheels are selected as the selected wheel WHs, but the number of wheels adopted as the selected wheel WHs is limited. For this reason, there are three or two non-selected wheels WHn that are not selected as the selected wheels WHs. In the wheel, the braking torque Pwa is reduced by the anti-skid control, and the lateral force is secured. For this reason, stability can be ensured for the entire vehicle.

  As the selected wheel WHs, a valley wheel WHt located on the valley side of the downhill road is selected. The mountain-side wheel WHy located on the mountain side of the downhill road (the wheel located on the side opposite to the valley-side wheel WHt) is not selected as the selected wheel WHs. When traveling downhill, securing the lateral force of the mountain-side wheel WHy is dominant in the stability of the vehicle. For this reason, in the mountain side wheel WHy, the reduction of the braking torque Pwa by the reduction mode Mgn is not prohibited so as to ensure the lateral force. When the vehicle moves forward on the downhill road, the valley-side wheel WHt is the front wheels WHfl and WHfr. On the other hand, when the vehicle moves backward on the downhill road, the valley-side wheel WHt is the rear wheels WHrl and WHrr.

  In the selection of the selected wheel WHs, the valley wheel WHt has priority over the mountain wheel WHy. That is, when the mountain-side wheel WHy is selected as the selected wheel WHs and the selection condition is satisfied by the valley-side wheel WHt, the selected wheel WHs is the mountain-side wheel when the condition is satisfied. It is switched from WHy to valley side wheel WHt. For this reason, in the mountain side wheel WHy, lateral force is ensured and vehicle stability can be improved.

  When the state of the selected wheel WHs has passed the predetermined time tkx, the selected wheel WHs is changed to the non-selected wheel WHn, and the inhibition of the reduction of the braking torque Pwa is released. That is, when the predetermined time tkx has elapsed, the braking torque Pwa is reduced by the reduction mode Mgn. For example, in the state of the selected wheel WHs, time measurement is started from the time (calculation cycle) when the selected wheel WHs is adopted. In addition, when the braking torque Pwa is not reduced, the selected wheel WHs immediately reaches the lock state, so that the state of the selected wheel WHs can be timed from the time when the selected wheel WHs is locked.

  Since the vehicle is moving during the traveling speed control, the duration in which the wheel slip becomes excessive due to poor grounding is limited. For this reason, the reliability of control can be improved by restricting the state of the selected wheel WHs within the predetermined time tkx.

<Other embodiments>
Hereinafter, other embodiments will be described. In other embodiments, the same effects as described above are obtained.

  In the above embodiment, the control mode of the anti-skid control is determined based on the slip speed Vsl and the wheel acceleration dVw. Instead, the control mode is determined based on at least one of the slip speed Vsl and the wheel acceleration dVw. The slip speed Vsl and the wheel acceleration dVw are collectively referred to as a slip state quantity Slp, and the control mode of the anti-skid control is determined by a correlation between the slip state quantity Slp and a threshold value.

  In the above embodiment, the selected wheel WHs is determined based on the slip speed Vsl and the wheel acceleration dVw. Instead, the selected wheel WHs is determined based on at least one of the slip speed Vsl and the wheel acceleration dVw. The slip speed Vsl and the wheel acceleration dVw are collectively referred to as a slip state amount Slp, and the selection condition is set by a mutual relationship between the slip state amount Slp and a selection threshold value. Even in this case, the selection threshold value is set to a value smaller than the anti-skid control threshold value in the degree of wheel slip. Accordingly, the selected wheel WHs can be determined in advance before the decrease mode Mgn is determined.

  In the above embodiment, so-called diagonal piping is employed as the braking system. Instead of this, a configuration of front and rear pipes (also referred to as H-type pipes) can be adopted. Moreover, the structure of the electric brake which does not employ | adopt braking fluid may be employ | adopted.

WH ** ... Wheel, MS ** ... Friction member, KT ** ... Rotating member, WC ** ... Wheel cylinder, MC ... Master cylinder, CAU ... Pressure adjustment unit, HMJ ... Modulator, ECU ... Controller, AP ... Acceleration operation Member (for example, accelerator pedal), BP ... Brake operation member (for example, brake pedal), SF ... Shift operation member (for example, shift lever), SDA ... Control switch, APA ... Acceleration operation amount sensor, BPA ... Brake operation amount sensor , SFA ... shift position sensor, VWA ... wheel speed sensor, Apa ... acceleration operation amount, Bpa ... deceleration operation amount, Sfa ... shift position, Vwa ** ... wheel speed, Vxa ... body speed, WHn ... non-selected wheel, WHs ... Selected wheel, Pwa ... braking torque, Slp ** ... slip state quantity, DAC ... running speed control unit, ABS ... anti-skid control unit.

Claims (4)

A wheel speed sensor for detecting a wheel speed of a vehicle wheel;
Based on the wheel speed, when the vehicle travels on a downhill road, a traveling speed control unit that executes a traveling speed control that controls braking torque to the wheels so that the traveling speed of the vehicle does not exceed a set speed; and A controller including an anti-skid control unit that executes anti-skid control for adjusting the braking torque so as to suppress an excessive braking slip of the wheel;
In a vehicle braking control apparatus comprising:
The anti-skid control unit
When the traveling speed control unit is executing the traveling speed control,
Select a selected wheel from the wheels,
A braking control device for a vehicle configured to prohibit the reduction of the braking torque by the anti-skid control at the selected wheel. The vehicle braking control device according to claim 1,
The anti-skid control unit
Select the trough wheel located on the trough side of the downhill road as the selected wheel,
A braking control device for a vehicle, configured such that a mountain wheel located on a mountain side of the downhill road is not selected as the selected wheel. The vehicle braking control device according to claim 1,
The anti-skid control unit
When the mountain side wheel located on the mountain side of the downhill road is selected as the selected wheel,
At the time of selecting the valley side wheel located on the valley side of the downhill road as the selected wheel,
A braking control device for a vehicle configured to cancel the selection of the mountain side wheel as the selected wheel. The vehicle braking control device according to any one of claims 1 to 3,
The anti-skid control unit
A braking control device for a vehicle configured to cancel prohibition of a decrease in the braking torque when a state of the selected wheel has passed a predetermined time.