JP4983136B2 - Anti-skid control device for vehicle - Google Patents

Description

  The present invention relates to an anti-skid control device for a vehicle that executes anti-skid control for controlling the braking force acting on the wheels of the vehicle to suppress the occurrence of wheel lock. Hereinafter, the anti-skid control may be referred to as “ABS control”.

Conventionally, this type of anti-skid control device is widely known. In general, in such an anti-skid control device, an estimated value of the vehicle body speed is estimated based on the wheel speed of the wheel. This vehicle body speed estimated value is set to the maximum value among the wheel speeds of all the wheels, for example. The ABS control is executed by reducing / increasing the braking force acting on the wheel while monitoring the slip ratio of the wheel calculated using the estimated vehicle speed (see, for example, Patent Document 1). Therefore, in order to perform the ABS control with high accuracy, it is necessary to accurately calculate the vehicle body speed estimated value.
JP 2003-19952 A

  By the way, for example, when a brake operation is performed when a vehicle travels on a low μ road surface having a relatively low road surface friction coefficient, a tendency to lock all wheels may occur. In such a case, the estimated vehicle speed can be calculated to be much smaller than the actual value of the vehicle speed. As a result, there is a problem that the ABS control cannot be started / executed properly. .

  The present invention has been made to address the above problems, and an object of the present invention is to provide an anti-skid control device capable of estimating a vehicle speed estimation value used for ABS control appropriately and accurately. .

  An anti-skid control device for a vehicle according to the present invention comprises a vehicle body speed estimation means for estimating an estimated value of a vehicle body speed of the vehicle based on at least the speeds of the left and right rear wheels (wheel speeds of all wheels) of the vehicle, Normal ABS that reduces / increases at least the braking force acting on the wheel based on the comparison result between the slip ratio of the wheel and the slip ratio target value with respect to the wheel that satisfies the ABS control start condition using the estimated speed value Normal anti-skid control means capable of executing the control independently for each wheel.

  The anti-skid control device according to the present invention is characterized in that, when the ABS control start condition is established for both the left and right rear wheels (in a state where the ABS control start condition is established), instead of the normal ABS control, a slip ratio (actual A special ABS control that adjusts the braking force so that the slip ratio) is less than or equal to a threshold value less than the slip ratio target value is alternately executed for each of the left and right rear wheels for each predetermined period. There are special anti-skid control means. Here, as the special ABS control, it is preferable to perform control to keep the braking force constant so that the slip ratio changes below the threshold value.

  According to this, for example, assuming a sufficiently small value as the threshold value, the slip ratio of the rear wheel on which the special ABS control is executed (hereinafter referred to as “specific rear wheel”) is a sufficiently small value. As a result, the wheel speed of the specific rear wheel can be maintained close to the actual value of the vehicle body speed. Therefore, when ABS control is executed at least for both the left and right rear wheels (for example, when ABS control is executed for all wheels), the vehicle body speed estimated value is accurate based on the wheel speed of the specific rear wheel. Can be calculated well. Therefore, it is possible to appropriately execute and continue the ABS control.

  Here, as the threshold value (the sufficiently small value), the slip ratio (generally in the range of 10% to 15%) corresponding to the case where the road surface frictional force (the frictional force between the tire and the road surface) is maximized. Hereinafter, a value (for example, 3%, 5%, etc.) sufficiently smaller than “the maximum frictional force generation slip ratio” is employed. As the magnitude of the braking force (for example, wheel cylinder pressure) required to shift the slip ratio below the threshold value, for example, the braking force required to shift the slip ratio below the threshold value when traveling on a low μ road surface. A value obtained through an experiment or the like for obtaining the magnitude of (for example, wheel cylinder pressure) can be used.

  In addition, when the slip ratio of a wheel is changing below the threshold value, the road surface frictional force of the wheel is small. That is, when special ABS control is executed for a certain wheel, the road surface frictional force of that wheel is smaller than when normal ABS control is executed for that wheel. However, in the above configuration, the special ABS control is executed for the rear wheels that cannot contribute much to the deceleration of the vehicle during braking. That is, even if the special ABS control is executed for one rear wheel instead of the normal ABS control, it is considered that the degree of reduction in the deceleration force of the entire vehicle is small.

  In the above configuration, when the ABS control is executed for both the left and right rear wheels, the special ABS control is executed for one of the rear wheels, and the normal ABS control is executed for the other. This means that a yawing moment is generated in the vehicle due to the difference in braking force between the left and right rear wheels. However, in the above configuration, the special ABS control is alternately executed for each of the left and right rear wheels one by one every elapse of a predetermined period. Therefore, the direction of the yawing moment is switched alternately every time a predetermined period elapses. Thereby, it is considered that the degree of the influence of the yawing moment on the running state of the vehicle is small as compared with the case where the special ABS control is continued only on one of the rear wheels.

  In the anti-skid control device according to the present invention, the special anti-skid control means is configured to start the special ABS control from the one of the left and right rear wheels that satisfies the ABS control start condition first. Is preferred. According to this, when the ABS control is executed on at least the left and right rear wheels, the wheel speed of the specific rear wheel can be brought closer to the actual value of the vehicle body speed from an earlier stage. Therefore, the vehicle body speed estimated value can be accurately calculated from an earlier stage.

  In the anti-skid control device according to the present invention, it is preferable that the special anti-skid control means is configured to change the predetermined period in accordance with the estimated vehicle speed. Every time the specific rear wheel is switched, a period (very short period) in which both the wheel speeds of the left and right rear wheels are relatively much smaller than the actual value of the vehicle body speed may inevitably occur. From this point of view, it is preferable that the predetermined period is longer in order to reduce the number of times the specific rear wheel is switched.

  On the other hand, when the yaw rate is constant, the discomfort felt by the vehicle occupant increases as the vehicle body speed increases. This discomfort tends to decrease as the yaw moment direction switching period is shorter. From this viewpoint, it is preferable to shorten the predetermined period as the vehicle body speed increases.

  The above configuration is based on such knowledge. According to this, for example, the predetermined period can be shortened as the estimated vehicle speed is larger. Therefore, when the estimated vehicle speed is small, the number of switching of the specific rear wheel can be reduced, and when the estimated vehicle speed is large, an increase in the passenger's discomfort can be suppressed.

  In the anti-skid control device according to the present invention, the normal anti-skid control means performs control for adjusting the braking force so that the slip ratio matches the slip ratio target value as the normal ABS control. It is suitable to be configured. Here, the slip ratio target value is preferably set to a value equal to the maximum frictional force generation slip ratio, for example.

  According to this, for example, when the ABS control is executed for all the wheels, the slip ratio is set to the slip ratio target value (for example, the maximum frictional force generation slip ratio) for the three wheels other than the specific rear wheel. The braking force is adjusted to match. Thereby, the deceleration of the vehicle can be generated stably and effectively.

  In this case, the normal anti-skid control means sets the slip ratio target value of each wheel to a corresponding reference value (for example, the maximum frictional force generation slip ratio), and when the vehicle is turning, It is preferable that the slip ratio target value of the outer front wheel is set to a value obtained by subtracting a first predetermined value from the corresponding reference value instead of the corresponding reference value.

  Generally, the smaller the slip ratio of a wheel, the larger the maximum value of the cornering force that can be generated by the wheel. When the maximum value of the cornering force that the outer front wheel can generate during turning is large, the response of the vehicle in the yaw direction to steering is improved.

  The above configuration is based on such knowledge. According to this, when ABS control is performed on at least the outer front wheel during turning, the slip ratio target value of the outer front wheel is maintained at the corresponding reference value (for example, the maximum frictional force generation slip ratio). Compared to the above, the response of the yaw direction of the vehicle to steering can be improved.

  Furthermore, when the vehicle is turning and is in an understeer state, the slip ratio target value of the outer front wheel is further reduced by a second predetermined value from “a value obtained by subtracting the first predetermined value from the corresponding reference value”. It is preferable to set to a different value. Thereby, the maximum value of the cornering force that can be generated by the outer front wheel can be further increased. Thereby, an understeer state can be suppressed.

  On the other hand, when the vehicle is turning and is in an oversteer state, the third predetermined value is added to the slip ratio target value of the outer front wheel to a value obtained by subtracting the first predetermined value from the corresponding reference value. It is preferable to set the value. According to this, the maximum value of the cornering force that the outer front wheel can generate can be reduced. Thereby, an oversteer state can be suppressed.

  Embodiments of an anti-skid control device for a vehicle according to the present invention will be described below with reference to the drawings.

  FIG. 1 shows a schematic configuration of a vehicle equipped with an anti-skid control device 10 according to an embodiment of the present invention. The anti-skid control device 10 includes a brake hydraulic pressure control unit 30 that generates a braking force based on the brake hydraulic pressure on each wheel. The brake hydraulic pressure control unit 30 is shown in FIG. The brake fluid pressure generating unit 32 that generates the brake fluid pressure according to the operating force of the brake pedal BP and the wheel cylinders Wfr, Wfl, Wrr, Wrl respectively disposed on the wheels FR, FL, RR, RL are supplied. An FR brake fluid pressure adjusting unit 33, an FL brake fluid pressure adjusting unit 34, an RR brake fluid pressure adjusting unit 35, an RL brake fluid pressure adjusting unit 36, and a reflux brake fluid supplying unit 37, each of which can adjust the brake fluid pressure. It is configured to include.

  The brake fluid pressure generating unit 32 includes a vacuum booster VB and a master cylinder MC connected to the vacuum booster VB. Since the configurations and operations of the master cylinder MC and the vacuum booster VB are well known, a detailed description thereof will be omitted here.

  The FR brake fluid pressure adjusting unit 33 includes a pressure-increasing valve PUfr that is a 2-port 2-position switching type normally-open electromagnetic switching valve and a pressure-reducing valve PDfr that is a 2-port 2-position switching-type normally-closed electromagnetic switching valve. Yes.

  Similarly, the FL brake hydraulic pressure adjusting unit 34, the RR brake hydraulic pressure adjusting unit 35, and the RL brake hydraulic pressure adjusting unit 36 are respectively a pressure increasing valve PUfl and a pressure reducing valve PDfl, a pressure increasing valve PUrr and a pressure reducing valve PDrr, and a pressure increasing valve PUrl and It consists of a pressure reducing valve PDrl.

  The reflux brake fluid supply unit 37 includes DC motors MTf and MTr and hydraulic pumps HPf and HPr that are independently driven by the DC motors MTf and MTr. The hydraulic pump HPf pumps up the brake fluid in the reservoir RSf that has been recirculated from the pressure reducing valves PDfr and PDfl, and supplies it to the upstream portion of the FR brake fluid pressure adjusting unit 33 and the FL brake fluid pressure adjusting unit 34. Yes.

  Similarly, the hydraulic pump HPr pumps up the brake fluid in the reservoir RSr returned from the pressure reducing valves PDrr and PDrl, and supplies it to the upstream portion of the RR brake fluid pressure adjusting unit 35 and the RL brake fluid pressure adjusting unit 36. It has become.

  The direct current motors MTf and MTr (and hence the hydraulic pumps HPf and HPr) are each driven at a predetermined rotational speed when the ABS control described later is being executed for at least one of the two wheels belonging to the corresponding system. It is supposed to be squeezed.

  Referring again to FIG. 1, the anti-skid control device 10 represents a wheel speed sensor 41fl, 41fr, 41rl, 41rr, a brake switch 42, and a steering angle θs that is a rotation angle from the neutral position of the steering wheel ST. A steering angle sensor 43 that outputs a signal, a yaw rate sensor 44 that outputs a signal representing the yaw rate Yr of the vehicle, and an electronic control unit 50 are provided.

  The electronic control unit 50 is a microcomputer that includes a CPU 51, a ROM 52, a RAM 53, a backup RAM 54, an interface 55, and the like that are connected to each other via a bus.

  The interface 55 is connected to the sensors 41 **, 43, and 44 and the brake switch 42, and supplies a signal to the CPU 51, and in response to an instruction from the CPU 51, an electromagnetic valve (a pressure increasing valve) of the brake hydraulic pressure control unit 30 is provided. Drive signals are sent to PU ** and pressure reducing valve PD **) and motors MTf and MTr.

  In addition, “**” appended to the end of various variables etc. “fl” added to the end of the various variables etc. to indicate which of the various wheels FR, etc. , “Fr”, etc., for example, the pressure increasing valve PU ** includes a left front wheel pressure increasing valve PUfl, a right front wheel pressure increasing valve PUfr, a left rear wheel pressure increasing valve PUrl, and a right rear wheel pressure increasing valve PUrr. Is shown.

  The anti-skid control device 10 according to the embodiment of the present invention configured as described above performs ABS control as follows in order to suppress the occurrence of wheel lock.

(Actual operation)
Next, with respect to the actual operation of the anti-skid control device 10 according to the embodiment of the present invention, FIG. 3 and FIG. 4 showing a routine (program) executed by the CPU 51 of the electronic control device 50 in a flowchart, and FIG. This will be described with reference to the time chart shown.

  FIG. 5 shows that on the low μ road surface, the driver started the operation of the brake pedal BP at time t0, so that all the wheels tend to be locked, and the ABS control is started almost simultaneously on all the wheels. In this case, an example of changes in the actual vehicle speed Vact, the wheel speed Vw **, and the wheel cylinder pressure P ** of the vehicle is shown. Strictly speaking, the ABS control is already started and executed for the wheels fl and fr before the time t1, the ABS control is started for the wheel rl at the time t1, and the wheel rr is started at the time tA. Even ABS control is started.

  The CPU 51 separately calculates the wheel speed of the wheel ** (the speed of the outer periphery of the wheel **) Vw ** based on the output signal of the wheel speed sensor 41 ** by a routine not shown, and the wheel speed Vw **. The vehicle body speed estimated value Vso, which is the maximum value of the vehicle wheel speed, is set as the wheel slip rate S ** = (Vso−Vw **) / Vso (0 ≦ S ** ≦ 1) of the wheel speed **. The wheel acceleration DVw ** of the wheel **, which is a time differential value, is calculated and updated.

  Further, the CPU 51 separately performs a yaw rate reference value Yrt based on a steering angle θs obtained from the steering angle sensor 43, the vehicle body speed estimated value Vso, vehicle specifications, and one of well-known calculation formulas by a routine (not shown). Is calculated and updated, and the deviation (yaw rate deviation ΔYr = | Yrt | − | Yr |) between the yaw rate reference value Yrt and the yaw rate Yr obtained from the yaw rate sensor 44 is calculated and updated.

  The CPU 51 repeatedly executes the routine for determining the start / end of the ABS control shown in FIG. 3 for each wheel every predetermined time. Accordingly, when the predetermined timing is reached, the CPU 51 starts processing from step 300, proceeds to step 305, and sets the vehicle body speed estimated value Vso to the maximum value of the wheel speed Vw ** at the present time.

  Subsequently, the CPU 51 proceeds to step 310 to determine whether or not the value of the flag ABS ** is “0”. Here, the flag ABS ** indicates that the ABS control is not executed when the value of the wheel ** is “0”, and the ABS control is executed when the value is “1”. Show.

  Now, it is assumed that the ABS control is not executed for the wheel ** and the ABS control start condition is not satisfied. In this case, since the value of the flag ABS ** is “0”, the CPU 51 determines “Yes” in step 310 and proceeds to step 315 to check whether the ABS control start condition is satisfied for the wheel **. Determine whether or not. In this example, the ABS control start condition is satisfied when “slip rate S **> Sref (constant) and wheel acceleration absolute value | DVw ** |> DVwref (constant)” is satisfied. To do.

  At this time, since the ABS control start condition for the wheel ** is not satisfied, the CPU 51 makes a “No” determination at step 315 and immediately proceeds to step 395 to end the present routine tentatively. Thereafter, the CPU 51 repeatedly executes the processes of steps 300, 305, 310, and 315 unless the ABS control start condition is satisfied.

  Next, in this state, it is assumed that the ABS control start condition is established for the wheel ** by the driver operating the brake pedal BP. In this case, when the CPU 51 proceeds to step 315, it determines “Yes”, proceeds to step 320, and changes the value of the flag ABS ** from “0” to “1”.

  Subsequently, the CPU 51 proceeds to Step 325 to determine whether or not the flag HOLD = 0 and the flag ABSrr = ABSrl = 1. If “No” is determined, the CPU 51 immediately proceeds to Step 395 to temporarily execute this routine. finish. Here, when the value of the flag HOLD is “1”, it indicates that the ABS control is being executed for both the left and right rear wheels (that is, ABSrr = ABSrl = 1), and when the value is “0”. This indicates that the ABS control is not executed for both the left and right rear wheels (that is, at least one of ABSrr and ABSrl is “0”).

  That is, in step 325, whether or not the ABS control start condition has been satisfied for the left and right rear wheels while the ABS control has already been executed for only one of the left and right rear wheels (that is, the ABS for both the left and right rear wheels). Whether the control start condition is satisfied) is monitored.

  Now, as shown at time tA in FIG. 5, ABS control is also started on the other (wheel rr) while ABS control has already been performed only on one (the wheel rl in FIG. 5) for the left and right rear wheels. If the condition is satisfied (that is, the wheel ** is the wheel rr at the current time), the CPU 51 determines “Yes” in step 325 and proceeds to step 330 to change the flag HOLD from “0” to “1”. change.

  Next, the CPU 51 proceeds to step 335 and identifies the rear wheel having the ABSr * = 1 first as the specific rear wheel rs. That is, in the case shown in FIG. 5, the rear wheel rl is identified as the specific rear wheel rs at time tA.

  Subsequently, the CPU 51 proceeds to step 340, and based on the vehicle body speed estimated value Vso at the present time (time tA in FIG. 5) updated in the previous step 305, and the holding period based on the table shown in FIG. Ts (corresponding to the “predetermined period”) is determined. Thereby, the holding period Ts is set to a shorter period as the vehicle body speed estimated value Vso is larger. The holding period Ts is a period for maintaining the special ABS control for the current specific rear wheel rs, as will be described later. In the case shown in FIG. 5, the holding period Ts set in step 340 corresponds to Ts1.

  Then, the CPU 51 proceeds to step 345 to initialize the elapsed time T to the elapsed time from the time when ABSrs = 1, and then proceeds to step 395. In the case shown in FIG. 5, the elapsed time T is initially set to a time between time t1 when ABSrs = 1 and time tA at the current time. The elapsed time T is measured by a timer (not shown) built in the electronic control unit 50 and increases.

  Thus, when the ABS control start condition is established for both the left and right rear wheels, the flag HOLD is changed from “0” to “1” at that time (time tA in FIG. 5). In addition, the elapsed time T is set to the elapsed time from the time when ABS control is started for the specific rear wheel rs (time t1 in FIG. 5).

  Thereafter, the CPU 51 makes a “No” determination when proceeding to step 310, and proceeds to step 350. In step 350, the CPU 51 monitors whether the ABS control end condition is satisfied for the wheel **. In this example, the ABS control end condition is increased when the brake switch 42 outputs a Low signal (OFF signal) (that is, when the driver ends the operation of the brake pedal BP) or for the wheel **. It is established when execution of pressure control continues for a predetermined time or more.

  Since the current time is immediately after the ABS control start condition is satisfied for the wheel ** (wheel rr in FIG. 5), the CPU 51 determines “No” in step 350. Thereafter, as long as the ABS control end condition in step 350 is not satisfied for the wheel **, the CPU 51 repeatedly executes the processing of steps 300, 305, 310, and 350 for the wheel **. While this process is repeated, the CPU 51 executes ABS control by executing a routine shown in FIG.

  The CPU 51 repeatedly executes the routine for performing the ABS control shown in FIG. 4 every elapse of a predetermined time. Therefore, when the predetermined timing is reached, the CPU 51 starts processing from step 400 and proceeds to step 405 to determine whether or not the flag ABS ** = 0 for all wheels (ie, ABS control is executed for all wheels). If the determination is “Yes”, the process proceeds to step 495 and the routine is temporarily terminated.

  Hereinafter, the description will be continued on the assumption that ABS control is being executed for at least one wheel **. For convenience of explanation, first, the case where the flag HOLD = 0 and the vehicle is not turning will be described. In this example, the turning is detected when the current steering angle θs (absolute value) obtained from the steering angle sensor 43 is larger than a predetermined minute value.

  In this case, the CPU 51 makes a “No” determination at step 405 to proceed to step 410 to set the slip ratio target value Stf * for the left and right front wheels to the front wheel side reference value Stfref (constant) and to determine the slip ratio for the left and right rear wheels. The target value Str * is set to the rear wheel side reference value Strref (constant). In this example, both the front wheel side reference value Stfref and the rear wheel side reference value Strref are set to the slip ratio corresponding to the case where the braking force is maximized (that is, the “maximum frictional force generation slip ratio”).

  Subsequently, the CPU 51 proceeds to step 415, determines whether or not the vehicle is turning, determines “No” in step 415, immediately proceeds to step 420, and determines whether or not the flag HOLD = 0. In step 420, “Yes” is determined, and the process proceeds to step 425.

  When the CPU 51 proceeds to step 425, the pressure increasing valve is set so that the slip ratio S ** coincides with the slip ratio target value St ** for the wheel of ABS ** = 1 (that is, the wheel for which ABS control is being executed). The PU ** and the pressure reducing valve PD ** are controlled to control the pressure reduction / holding / pressure increase with respect to the wheel cylinder pressure P **. That is, the “normal ABS control” is executed for all the wheels that are executing the ABS control.

  As a result, the wheel cylinder pressure P ** (accordingly, the braking force) is adjusted so that the slip ratio S ** matches the “maximum frictional force generation slip ratio” for all the wheels that are executing the ABS control. The Thereby, the deceleration of the vehicle can be generated stably and effectively.

  Next, a case where the flag HOLD = 1 and the vehicle is not turning will be described. Now, it is assumed that it is immediately after the flag HOLD is changed from “0” to “1” by the processing of step 330 described above (see time tA in FIG. 5).

  In this case, the CPU 51 that repeatedly executes the routine of FIG. 4 determines “No” in Step 415 and proceeds to Step 420, determines “No” and proceeds to Step 430, and then proceeds to Step 345. It is determined whether the elapsed time T set in FIG. 5 (the elapsed time from time t1 in FIG. 5) has reached the holding period Ts (Ts1 in FIG. 5) set in the previous step 340.

  At the present time (time tA in FIG. 5), the elapsed time T has not reached the holding period Ts. Therefore, the CPU 51 makes a “No” determination at step 430 to immediately proceed to step 450, and is identified at the previous step 335 for the wheel of ABS ** = 1 (ie, the wheel for which ABS control is being executed). For the wheels other than the specific rear wheel rs (three wheels other than the wheel rl in FIG. 5), the slip ratio S ** is the slip ratio target value St ** (= “maximum frictional force generation”, as in the previous step 425. “Normal ABS control” is executed so as to coincide with the slip rate “).

  On the other hand, for the specific rear wheel rs (wheel rl in FIG. 5), the pressure increasing valve PUrs and the pressure reducing valve PDrs are controlled to a pressure corresponding to a minute slip ratio Stmin (<Strref, corresponding to the “threshold”) or less. After the wheel cylinder pressure Prs is reduced, the wheel cylinder pressure Prs is held (see time t1 (tA) to t2 in FIG. 5). That is, the “special ABS control” is executed for the specific rear wheel rs. As a result, the wheel cylinder pressure Prs (and hence the braking force) is adjusted so that the actual slip ratio value changes below the minute slip ratio Stmin with respect to the specific rear wheel rs that is executing the ABS control.

  Thereby, the wheel speed Vwrs (the wheel speed Vwrl in FIG. 5) of the specific rear wheel rs can be maintained at a value close to the actual vehicle speed Vact (see time t1 (tA) to t2 in FIG. 5). Therefore, the estimated vehicle speed Vso set to the maximum value among the wheel speeds Vw ** in step 305 can be set equal to the wheel speed Vwrs of the specific rear wheel rs, and the estimated vehicle speed Vso is accurate. Can be calculated well. Therefore, it is possible to appropriately execute and continue ABS control (that is, normal ABS control) for wheels other than the specific rear wheel rs (in FIG. 5, three wheels other than the wheel rl). Such a process is repeatedly executed until “Yes” is determined in Step 430 (until time t2 in FIG. 5).

  Next, the case where “Yes” is determined in step 430 in this state (see time t2 in FIG. 5) will be described. In this case, the CPU 51 determines “Yes” in step 430 and proceeds to step 435 to change (switch) the specific rear wheel rs to the other rear wheel. In FIG. 5, the specific rear wheel rs is switched from the wheel rl to the wheel rr at time t2.

  Subsequently, the CPU 51 proceeds to step 440, performs the same processing as the previous step 340, and determines the holding period Ts based on the estimated vehicle speed Vso at the present time (time t2 in FIG. 5). In the case shown in FIG. 5, the retention period Ts determined at this time corresponds to Ts2.

  Next, the CPU 51 proceeds to step 445 to reset the elapsed time T, and then performs the process of step 450 described above. As a result, wheels other than the specific rear wheel rs newly specified in step 435 (3 in addition to the wheel rr in FIG. 5) for the wheel of ABS ** = 1 (that is, the wheel for which ABS control is being executed). The “normal ABS control” is executed for each wheel, and the “special ABS control” is executed for the newly specified specific rear wheel rs (wheel rr in FIG. 5).

  As a result, the wheel speed Vwrs (the wheel speed Vwrr in FIG. 5) of the newly specified specific rear wheel rs can be maintained at a value close to the actual vehicle speed Vact (in FIG. 5, refer to times t2 to t3). ). Therefore, the vehicle body speed estimated value Vso can be set to a value equal to the wheel speed Vwrs of the newly specified specific rear wheel rs, and the vehicle body speed estimated value Vso can be calculated with high accuracy. Such a process is repeatedly executed until “Yes” is again determined in step 430 (until time t3 in FIG. 5).

  Similarly thereafter, every time the holding period Ts determined in step 440 elapses, the specific rear wheel rs is alternately switched (see times t3 and t4 in FIG. 5). That is, the “special ABS control” is alternately executed on the left and right rear wheels one by one every time the holding period Ts elapses.

  Accordingly, as can be understood from FIG. 5, every time the specific rear wheel rs is switched, immediately after that, any wheel speed Vwr * of the left and right rear wheels is relatively smaller than the vehicle speed actual value Vact (very short-term). May occur inevitably, but each wheel speed Vwrs of the specific rear wheel rs can be maintained at a value close to the actual vehicle speed Vact for most of each holding period Ts. Therefore, the vehicle body speed estimated value Vso (= max (Vw **) = Vwrs) can be stably and accurately calculated based on the respective wheel speeds Vwrs in each holding period Ts.

  In this example, the “special ABS control” in which the road surface friction force is smaller than the “normal ABS control” in which the braking force is controlled so that the slip rate matches the “maximum frictional force generation slip rate”. It is executed for rear wheels that cannot contribute much to the deceleration of the vehicle during braking. Therefore, it is considered that the degree of reduction in the deceleration force of the entire vehicle by executing “special ABS control” instead of “normal ABS control” for one rear wheel is small.

  Further, in this example, the “special ABS control” is alternately performed on the left and right rear wheels one by one every time the holding period Ts elapses. The direction of the generated yawing moment is switched alternately every time the holding period Ts elapses. As a result, the degree of influence of the yawing moment on the running state of the vehicle is considered to be smaller than when the “special ABS control” is continued only on one of the rear wheels.

  Further, in this example, the “special ABS control” is started from the left and right rear wheels that satisfy the ABS control start condition first (wheel rl in FIG. 5). Therefore, the wheel speed Vwrs of the specific rear wheel rs can be brought closer to the vehicle body speed actual value Vact from an earlier stage. Therefore, the vehicle body speed estimated value Vso can be accurately calculated from an earlier stage.

  In addition, in this example, the holding period Ts is set to a shorter time as the vehicle body speed estimated value Vso is larger. As a result, when the estimated vehicle speed Vso is small, the number of switching of the specific rear wheel rs can be reduced, and as a result, the frequency at which the wheel speed Vwrs of the specific rear wheel rs deviates from the actual vehicle speed Vact is reduced. can do. On the other hand, when the estimated vehicle speed Vso is large, the switching cycle of the yawing moment direction can be shortened, and an increase in passenger discomfort caused by the yawing moment can be suppressed.

  Next, a case where the vehicle is turning will be described. In this case, the CPU 51 that repeatedly executes the routine of FIG. 4 determines “Yes” in step 415 and proceeds to step 455 to identify the outer front wheel fo, and in the subsequent step 460, the understeer (US) state. Or whether it is in an oversteer (OS) state. In this example, being in the US state is detected when the above-described yaw rate deviation ΔYr (= | Yrt | − | Yr |) is greater than a predetermined value (positive value), and being in the OS state indicates that the yaw rate is It is detected when the deviation ΔYr is smaller than − (predetermined value).

  If neither the US state nor the OS state, the CPU 51 makes a “No” determination at step 460 to proceed to step 465 to set the slip ratio target value Stfo of the outer front wheel fo from the front wheel side reference value Stfref to a predetermined value α (positive ) Is subtracted. Thereby, when the “normal ABS control” is executed for the outer front wheel by the processing of step 425 or step 450, the slip ratio Stfo of the outer front wheel fo is controlled to match the value (Stfref−α). . As a result, the maximum value of the cornering force that can be generated by the outer front wheel fo is larger than when the slip ratio target value Stfo of the outer front wheel fo is controlled to the value Stfref (= “maximum frictional force generation slip ratio”). The response of the yaw direction of the vehicle to steering can be improved.

  In the case of the US state, the CPU 51 determines “Yes” in step 460 and proceeds to step 470 to determine whether or not it is in the US state, determines “Yes” in step 470 and proceeds to step 475. The slip ratio target value Stfo of the outer front wheel fo is set to a value (Stfref−α−β). Here, β is a predetermined value (positive). As a result, when “normal ABS control” is executed for the outer front wheel by the processing of step 425 or step 450, the slip rate Stfo of the outer front wheel fo is controlled to match the value (Stfref−α−β). Is done. As a result, the maximum value of the cornering force that can be generated by the outer front wheel fo can be further increased as compared with the case where the slip ratio target value Stfo of the outer front wheel fo is controlled to the value (Stfref−α). Thereby, an understeer state can be suppressed.

  In the OS state, the CPU 51 makes a “No” determination at step 470 to proceed to step 480, and sets the slip ratio target value Stfo of the outer front wheel fo to a value (Stfref−α + γ). Here, γ is a predetermined value (positive). As a result, when the “normal ABS control” is performed on the outer front wheel by the processing of step 425 or step 450, the slip ratio Stfo of the outer front wheel fo is controlled to match the value (Stfref−α + γ). . As a result, the maximum value of the cornering force that can be generated by the outer front wheel fo can be made smaller than when the slip ratio target value Stfo of the outer front wheel fo is controlled to a value (Stfref−α). Thereby, an oversteer state can be suppressed.

  The operation described above by the CPU 51 can be executed as long as the ABS control end condition of step 350 in the routine of FIG. 3 in which the processing of steps 305, 310, and 350 is repeatedly executed is not satisfied for the wheel **. is there.

  Accordingly, when the condition of step 350 is satisfied for the wheel **, such as when the driver ends the operation of the brake pedal BP during the operation described above, the CPU 51 determines “Yes” in step 350 and proceeds to step 355. Then, the value of the flag ABS ** is changed from “1” to “0”, and in step 360, a predetermined ABS control end process is performed for the wheel **. Thereby, the ABS control that has been executed for the wheel ** is completed.

  Subsequently, the CPU 51 proceeds to step 365 to determine whether or not the flag ABSrr = ABSrl = 1. If “No” is determined, the CPU 51 sets the value of the flag HOLD to “0” in step 370. That is, when the ABS control is performed on the left and right rear wheels, the value of the flag HOLD is changed from “1” to “0”. Accordingly, “Yes” is determined at step 420 in FIG. 4 and “special ABS control” is not executed.

  As described above, according to the anti-skid control device for a vehicle according to the embodiment of the present invention, in principle, the slip ratio S ** is “maximum frictional force generation slip ratio” for each wheel. “Normal ABS control” in which the braking force (wheel cylinder pressure P **) is controlled so as to coincide with each other is executed. On the other hand, when the ABS control is executed for both the left and right rear wheels (when the ABS control start condition is satisfied for both), the actual slip ratio is replaced with the minute slip ratio Stmin (< “Special ABS control”, in which braking force (wheel cylinder pressure) is adjusted so that it is less than or equal to “maximum frictional force generation slip ratio”, alternates for each left and right rear wheel for each holding period Ts. Will be executed.

  As a result, the vehicle body speed estimated value Vso is calculated stably and accurately based on the wheel speed Vwrs of the wheel (specific rear wheel rs) for which “special anti-skid control” is newly executed every time the holding period Ts elapses. It will be done. As a result, ABS control (that is, “normal ABS control”) for the wheels other than the specific rear wheel rs can be appropriately executed and continued.

  The present invention is not limited to the above embodiment, and various modifications can be employed within the scope of the present invention. For example, in the above embodiment, as “normal ABS control”, control is performed in which the braking force is adjusted so that the slip rate S ** matches the “maximum frictional force generation slip rate”. -Well-known ABS control which makes holding control and pressure increase control a set may be performed.

  Similarly, in the above-described embodiment, as the “special ABS control”, a control in which the braking force is adjusted so that the actual value of the slip ratio changes below the minute slip ratio Stmin (<“maximum frictional force generation slip ratio”). In principle, the well-known ABS control, which is a set of pressure reduction control, holding control, and pressure increase control, is executed, and the pressure increase control is executed over the period of the specific rear wheel rs. Control that prohibits the above may be executed.

  Further, in the above embodiment, the holding period Ts is configured to be changed according to the vehicle body speed estimation value Vso, but the holding period Ts may be constant.

  In the above embodiment, the value α (the first predetermined value), the value β (the second predetermined value), and the value γ (the third predetermined value) are constant. Alternatively, the values α, β, and γ may be changed according to the degree of the OS state (for example, the yaw rate deviation ΔYr). In this case, it is preferable to set the values α, β, and γ to larger values as the degree of the US state or the OS state is larger.

  In the above embodiment, only the slip ratio target value Stfo of the outer front wheel is changed depending on whether the vehicle is turning or is in the US / OS state. In addition to the rate target value Stfo, the slip rate target value Stfi of the inner front wheel may be changed. In this case, it is preferable that the slip ratio target value Stfi of the inner front wheel is set to a value shifted in the opposite direction to the slip ratio target value Stfo of the outer front wheel with respect to the front wheel side reference value Stfref.

  In the above embodiment, the specific rear wheel on which the “special ABS control” is executed is alternately switched every time the holding period Ts elapses. However, the absolute yaw rate of the vehicle is not increased until the holding period Ts elapses. If the value exceeds a predetermined value, the specific rear wheel may be switched at that time without waiting for the retention period Ts to elapse.

  In addition, in the above embodiment, the hydraulic pumps HPf and HPr are driven independently by the motors MTf and MTr, respectively, but both the hydraulic pumps HPf and HPr are driven by a single motor. You may comprise.

1 is a schematic configuration diagram of a vehicle equipped with an anti-skid control device for a vehicle according to an embodiment of the present invention. It is a schematic block diagram of the brake fluid pressure control part shown in FIG. 3 is a flowchart showing a routine for performing start / end determination of ABS control executed by a CPU shown in FIG. 1. 2 is a flowchart showing a routine for performing ABS control executed by a CPU shown in FIG. 1. 2 is a time chart showing an example of changes in actual vehicle speed, wheel speed, and wheel cylinder pressure when ABS control is started and executed for all wheels by the anti-skid control device shown in FIG. . 3 is a graph showing a table that defines a relationship between a vehicle body speed estimated value and a holding period, which is referred to by a CPU shown in FIG. 1.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 ... Anti skid control apparatus of a vehicle, 30 ... Brake hydraulic pressure control part, 41 ** ... Wheel speed sensor, 42 ... Brake switch, 43 ... Steering angle sensor, 44 ... Yaw rate sensor, 50 ... Electronic control unit, 51 ... CPU , PU ** ... Booster valve, PD ** ... Pressure reducing valve, MTf, MTr ... Motor

Claims (9)

Vehicle body speed estimation means (51, 305) for estimating an estimated value (Vso) of the vehicle body speed of the vehicle based on the speeds of the left and right front and rear wheels (Vw *) of the vehicle;
Based on the comparison result of the slip ratio of the wheel and the slip ratio target value (St **) for the wheel for which the anti-skid control start condition is satisfied, using the estimated vehicle speed (Vso) Normal anti-skid control means (51, routine of FIG. 4) capable of executing normal anti-skid control for reducing / increasing braking force acting on each wheel independently of each other;
When the anti-skid control start condition is satisfied for both the left and right rear wheels, instead of the normal anti-skid control, the slip rate changes below a threshold value (Stmin) smaller than the slip rate target value (St **). Special anti-skid control means for adjusting the braking force in such a manner that one wheel (specific rear wheel rs) is alternately executed every predetermined period (Ts) with respect to the left and right rear wheels. (51, 325-345, 420, 430-450),
Anti-skid control device for vehicles equipped with The anti-skid control device for a vehicle according to claim 1,
The special anti-skid control means includes
As the special anti-skid control, an anti-skid control device for a vehicle configured to perform a control (450) for keeping the braking force constant so that the slip ratio changes below the threshold (Stmin). In the anti-skid control device for a vehicle according to claim 1 or 2,
The special anti-skid control means includes
A vehicle anti-skid control device configured to start (335) the special anti-skid control from the left and right rear wheels, which satisfies the anti-skid control start condition first. The anti-skid control device for a vehicle according to any one of claims 1 to 3,
The special anti-skid control means includes
The vehicle anti-skid control apparatus configured to set the predetermined period (Ts) to a shorter time as the vehicle body speed estimation value (Vso) is larger (340, 440). The anti-skid control device for a vehicle according to any one of claims 1 to 4,
The normal anti-skid control means includes
As the normal anti-skid control, anti-skid control of a vehicle configured to perform control (425, 450) to adjust the braking force so that the slip ratio matches the slip ratio target value (St **). apparatus. The vehicle anti-skid control device according to claim 5,
The normal anti-skid control means includes
While setting the slip ratio target value (St **) of each wheel to the corresponding reference value (Stfref, Strref),
When the vehicle is turning, the first predetermined value from the corresponding reference value (Stfref) is substituted for the slip ratio target value (Stfo) of the outer front wheel (fo) instead of the corresponding reference value (Stfref). A vehicle anti-skid control device configured to set (α) to a value obtained by subtracting (460, 465). The vehicle anti-skid control device according to claim 6,
The normal anti-skid control means includes
When the vehicle is turning and is in an understeer state, the slip ratio target value (Stfo) of the outer front wheel (fo) is changed from the corresponding reference value (Stfref) to the first predetermined value (α). Instead of the subtracted value, a value obtained by subtracting the second predetermined value (β) from the value obtained by subtracting the first predetermined value (α) from the corresponding reference value (Stfref) is set (470, 475). An anti-skid control device for a vehicle constructed in The vehicle anti-skid control device according to claim 6,
The normal anti-skid control means includes
When the vehicle is turning and is in an oversteer state, the slip ratio target value (Stfo) of the outer front wheel (fo) is set to the first predetermined value (α) from the corresponding reference value (Stfref). Instead of the value obtained by subtracting the first predetermined value (α) from the corresponding reference value (Stfref), a value obtained by adding a third predetermined value (γ) is set (470, 480). An anti-skid control device for a vehicle constructed in A vehicle anti-skid control program for causing a computer to execute anti-skid control of a vehicle,
Estimating an estimated value (Vso) of the vehicle body speed of the vehicle based on the speed of the left and right front and rear wheels (Vw **) of the vehicle;
Based on the comparison result of the slip ratio of the wheel and the slip ratio target value (St **) for the wheel for which the anti-skid control start condition is satisfied, using the estimated vehicle speed (Vso) A step (routine of FIG. 4) in which normal anti-skid control for reducing / increasing the braking force acting on the vehicle can be executed independently for each wheel;
When the anti-skid control start condition is satisfied for both the left and right rear wheels, instead of the normal anti-skid control, the slip rate changes below a threshold value (Stmin) smaller than the slip rate target value (St **). Special anti-skid control for adjusting the braking force is executed alternately for each of the left and right rear wheels by one wheel (specific rear wheel rs) every predetermined period (Ts) (325 to 345). 420, 430-450),
Anti-skid control program for vehicles with

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