JP2005088771A - Anti-skid control device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an anti-skid control device which executes the anti-skid control for a low μ road surface if the running road surface is judged as having a low μ as specified, capable of accurately judging whether the road surface has the specified μ value. <P>SOLUTION: The anti-skid control device works on the facts that the value of the wheel speed Vw of each driving wheel (accordingly the wheel acceleration DVw of each driving wheel) has a tendency to vary in the specified period corresponding to the natural frequency of the drive system of a vehicle in case the driver of the vehicle running on an icy road performs the brake operation to cause generation of an excessive slip in the wheels and that the outside air temperature becomes often equal to or below the specified temperature generally, and judges that the road surface is icy when there is a continued condition where the variation of the varying component DVwfluc of the wheel acceleration of the driving wheels exhibits a vibration of the drive system and the outside air temperature lies at or below the specified level and executes the ABS control to be proprietarily devoted to icy road surfaces in which recovering the rotating speed of the wheels is given a priority to maintaining a greater deceleration. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention adjusts the brake fluid pressure by at least reducing and increasing the brake fluid pressure supplied to the wheel cylinder of each wheel based on at least the wheel speed of each wheel of the vehicle. The present invention relates to an anti-skid control device that executes anti-skid control for preventing occurrence of slip.

  Conventionally, this type of anti-skid control device is very widely known. This type of device generally sets an estimated vehicle body speed based on a maximum speed (hereinafter sometimes referred to as “maximum wheel speed”) of wheel speeds of each wheel of the vehicle, and at least the estimated vehicle body speed. The anti-skid control is started / executed when the deviation between the wheel speed and each wheel speed (that is, the slip amount) exceeds a predetermined amount. As a result, the deceleration of the vehicle can be maintained at a large value.

  On the other hand, when the vehicle performs a braking operation while the vehicle is traveling on a road surface having a low friction coefficient (hereinafter sometimes referred to as “low μ”) such as an icy road, excessive slip occurs on the wheels. In general, since all the wheels start to decelerate in the same manner, it is difficult for a wheel speed difference between the wheels to occur, and as a result, anti-skid control is difficult to start.

  Further, in this case, even if the anti-skid control is started, the wheel rotational speed once lowered due to the small rotational moment in the speed increasing direction that the tire receives from the road surface is used for the brake fluid pressure reduction control. Accordingly, it takes a relatively long time to recover to the vehicle speed. Therefore, in this case, in order to ensure the running stability of the vehicle, priority should be given to recovering the rotational speed of the wheel rather than maintaining a large deceleration.

  From the above, when the road surface on which the vehicle is traveling is a low μ road surface such as an icy road, the control mode of the anti-skid control (for example, control start conditions, brake fluid pressure reduction / increase pattern, etc.) It is necessary to set a control mode dedicated to the low μ road surface.

For this reason, the anti-skid control device described in Patent Document 1 below is a time differential value of the estimated vehicle body speed when anti-skid control is not executed and braking force is applied to each wheel by brake fluid pressure. The anti-skid control mode is set to the control mode for icy roads when the estimated vehicle body deceleration based on the above is gradually increasing with increase / decrease. This is because when the driver performs a brake operation on an icy road, the driver is likely to cause a slight fluctuation in each wheel speed due to a delicate adjustment of the brake operation force, and as a result, based on the maximum wheel speed. This is based on the fact that the estimated vehicle body speed calculated in this way (and hence the estimated vehicle body deceleration) tends to gradually increase with an increase or decrease.
JP 7-329760 A

  In addition, when the driver performs braking operation on a low μ road surface such as an icy road and the wheels excessively slip, the rotational moment received by the tire from the road surface is small, which causes It is known that the wheel speed of each drive wheel connected to each other (and therefore the wheel acceleration, which is the time differential value) tends to fluctuate in a predetermined period corresponding to the natural frequency of the drive system. ing.

  For this reason, when the anti-skid control is not executed and the braking force by the brake fluid pressure is applied to each wheel, the change of the wheel acceleration of the drive wheel represents the vibration of the drive system of the vehicle. A technique for setting the control mode of anti-skid control to a control mode for low μ road surfaces is also known.

  As described above, the change history of the wheel speed (or the value based on the wheel speed (for example, wheel acceleration, estimated vehicle deceleration, etc.)) is acquired, and the acquired change history conforms to a predetermined pattern. By determining whether or not to perform, it is possible to determine whether or not the road surface on which the vehicle is traveling is a predetermined low μ road surface including an icy road.

  However, even if the driver performs a braking operation while the vehicle is traveling on a road surface having a relatively high road surface friction coefficient (hereinafter sometimes referred to as “high μ”) such as an asphalt road surface. Depending on how the road surface is undulated (for example, when the vehicle is traveling on a so-called wavy road), the change in the value based on the wheel speed may conform to the predetermined pattern. In this case, although the road surface on which the vehicle is traveling is a high μ road surface, it is erroneously determined that the road surface is the predetermined low μ road surface. As a result, the anti-skid control in the control mode for the low μ road surface is executed. Thus, there is a problem that a situation where a large deceleration cannot be maintained may occur.

  Therefore, the present invention has been made in order to cope with the above-described problem, and the purpose of the present invention is the same as that when it is determined that the road surface on which the vehicle is traveling is a predetermined low μ road surface including an icy road. It is an object of the present invention to provide an anti-skid control device that executes anti-skid control for μ road surface, which can accurately determine whether or not the road surface on which the vehicle is traveling is the same predetermined low μ road surface.

  A feature of the present invention is that wheel speed acquisition means for acquiring the wheel speed of each wheel of the vehicle and at least a brake fluid pressure supplied to a wheel cylinder of each wheel based on at least the acquired wheel speed. An anti-skid control means for adjusting anti-skid control for adjusting the brake hydraulic pressure by applying pressure and preventing anti-skid control to prevent excessive slip on each wheel. The outside air temperature acquisition means for acquiring the outside air temperature at the position where the vehicle is running and the anti-skid control is not executed, and the braking force by the brake fluid pressure is applied to each wheel. A predetermined road surface on which the vehicle travels includes an icy road based on the change of the value based on the wheel speed and the acquired outside air temperature. Road surface determination means for determining whether or not the road surface has a low friction coefficient, and when the road surface on which the vehicle is traveling is determined to be a road surface having the predetermined low friction coefficient, the anti-skid control And a control mode setting means for setting the control mode to a control mode for a road surface having the predetermined low friction coefficient.

  Here, the anti-skid control means sets, for example, an estimated vehicle body speed based on at least a maximum speed (maximum wheel speed) of wheel speeds of each wheel of the vehicle, and at least the estimated vehicle body speed, each wheel speed, The anti-skid control is configured to be started when the deviation becomes greater than or equal to a predetermined amount.

  Even if the outside air temperature acquisition means is, for example, a means for physically detecting the outside air temperature by a temperature sensor or the like for detecting the temperature of the air outside the vehicle body, the outside air temperature acquisition means is sucked from the intake pipe of the internal combustion engine that is the drive source of the vehicle It may be a means for estimating the outside air temperature by calculation or the like based on the intake air temperature or the like acquired by the means for detecting / estimating the temperature of the intake air.

  For example, when the road surface determination unit determines that the road surface on which the vehicle is traveling is a road surface having the predetermined low friction coefficient, the control mode setting unit changes the control mode of the anti-skid control to a wheel. The road surface control mode is set for the road surface having the same low coefficient of friction as the main purpose of recovering the speed, and the road surface on which the vehicle is traveling has the same low coefficient of friction by the road surface determination means. When it is not determined to be a road surface, the control mode of the anti-skid control is set to a normal road surface control mode whose main purpose is to maintain a desired deceleration.

  Generally, when the road surface on which the vehicle is traveling is a predetermined low μ road surface including an icy road, the outside air temperature outside the vehicle body is, for example, a temperature necessary for the road surface to become an icy road (for example, a predetermined temperature or less). ) Often. Therefore, as described above, the vehicle travels based not only on the change of the value based on the acquired wheel speed (for example, wheel acceleration) but also on the outside air temperature acquired by the outside air temperature acquiring means. If it is configured to determine whether or not the road surface is a predetermined low μ road surface including an icy road, the vehicle is running on a high μ road surface and the outside air temperature is, for example, the road surface is an icy road. If the temperature is not necessary to become (for example, if the temperature exceeds the predetermined temperature), the process of changing the value based on the wheel speed is caused by the road surface undulation state, etc. Even if the vehicle conforms to the predetermined pattern, erroneous determination that the road surface on which the vehicle is traveling is the predetermined low μ road surface can be prevented. As a result, it is possible to prevent the occurrence of a situation in which a large deceleration cannot be maintained because the anti-skid control of the control mode for the low μ road surface is executed even though the vehicle is traveling on the high μ road surface.

  In this case, the road surface determination means determines that the road surface on which the vehicle is traveling is the predetermined road when the change in the value based on the obtained wheel speed of the drive wheel represents the vibration of the drive system of the vehicle. It is preferable to be configured to determine that the road surface has a low friction coefficient. Further, the road surface determination means has a predetermined value in which the wheel acceleration value of the drive wheel, which is a time differential value of the wheel speed of the drive wheel obtained, has a predetermined amplitude and corresponds to a natural frequency of the drive system of the vehicle. It is preferable to determine that the history of the change in the value based on the obtained wheel speed of the driving wheel represents the vibration of the driving system of the vehicle.

  As described above, when a driver performs a braking operation on a low μ road surface such as an icy road and an excessive slip occurs on a wheel, a value based on the wheel speed of each driving wheel (for example, each driving wheel Wheel acceleration value) tends to fluctuate in a predetermined period corresponding to the natural frequency of the vehicle drive system. Therefore, if configured as described above, since the necessary condition for determining that the road surface on which the vehicle is traveling is the predetermined low μ road surface is appropriately set, the road surface on which the vehicle is traveling is high. An erroneous determination that the road surface is a low μ road surface despite the fact that it is a μ road surface can be prevented more reliably.

  Hereinafter, an antiskid control device according to an embodiment of the present invention will be described 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. This vehicle is a four-wheel drive (4WD) system having two front wheels (left front wheel FL and right front wheel FR) as drive wheels and two rear wheels (left rear wheel RL and right rear wheel RR) as drive wheels. This is a four-wheel vehicle.

  The anti-skid control device 10 includes a brake fluid pressure control unit 30, a sensor unit 40, and an electric control device 50 for causing each wheel to generate a braking force due to the brake fluid pressure.

  As shown in FIG. 2 showing the schematic configuration, the brake fluid pressure control unit 30 includes a brake fluid pressure generating unit 32 that generates a brake fluid pressure corresponding to the operating force of the brake pedal BP, and each wheel FR, FL, RR. FR brake hydraulic pressure adjusting unit 33, FL brake hydraulic pressure adjusting unit 34, and RR brake hydraulic pressure adjusting unit 35 that can adjust the brake hydraulic pressure supplied to the wheel cylinders Wfr, Wfl, Wrr, Wrl respectively arranged on the RL, RL , RL brake fluid pressure adjustment unit 36 and reflux brake fluid supply unit 37.

  The brake fluid pressure generating unit 32 includes a vacuum booster VB that responds when the brake pedal BP is operated, and a master cylinder MC that is connected to the vacuum booster VB. The vacuum booster VB uses air pressure (negative pressure) in the intake pipe 21a of the engine 21 to assist the operating force of the brake pedal BP at a predetermined rate and transmit the assisted operating force to the master cylinder MC. It has become.

  The master cylinder MC has two output ports including a first port and a second port. The master cylinder MC receives the supply of brake fluid from the reservoir RS and responds to the assisted operating force by the first master. A cylinder hydraulic pressure is generated from the first port, and a second master cylinder hydraulic pressure corresponding to the assisted operating force, which is substantially the same hydraulic pressure as the first master cylinder hydraulic pressure, is supplied to the second port. It comes from the port. 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. Thus, the master cylinder MC and the vacuum booster VB generate the first master cylinder hydraulic pressure and the second master cylinder hydraulic pressure in accordance with the operating force of the brake pedal BP, respectively.

  The first port of the master cylinder MC is connected to each of the upstream side of the FR brake fluid pressure adjusting unit 33 and the upstream side of the FL brake fluid pressure adjusting unit 34. Similarly, the second port of the master cylinder MC is connected to each of the upstream side of the RR brake hydraulic pressure adjusting unit 35 and the upstream side of the RL brake hydraulic pressure adjusting unit 36. As a result, the first master cylinder hydraulic pressure is supplied to each of the upstream portion of the FR brake hydraulic pressure adjusting unit 33 and the upstream portion of the FL brake hydraulic pressure adjusting unit 34, and the upstream of the RR brake hydraulic pressure adjusting unit 35. The second master cylinder hydraulic pressure is supplied to each of the upstream portion of the RL brake hydraulic pressure adjusting portion 36 and the RL brake hydraulic pressure adjusting portion 36.

  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. The pressure increasing valve PUfr communicates the upstream portion of the FR brake hydraulic pressure adjusting unit 33 and the wheel cylinder Wfr when in the first position (position in the non-excited state) shown in FIG. When in the excited state), the communication between the upstream portion of the FR brake fluid pressure adjusting unit 33 and the wheel cylinder Wfr is cut off. When the pressure reducing valve PDfr is in the first position shown in FIG. 2 (position in the non-excited state), the communication between the wheel cylinder Wfr and the reservoir RSf is cut off and in the second position (position in the excited state). The wheel cylinder Wfr communicates with the reservoir RSf.

  As a result, the brake fluid pressure in the wheel cylinder Wfr is supplied to the wheel cylinder Wfr upstream of the FR brake fluid pressure adjusting unit 33 when both the pressure increasing valve PUfr and the pressure reducing valve PDfr are in the first position. When the pressure-increasing valve PUfr is in the second position and the pressure-reducing valve PDfr is in the first position, the fluid pressure at that time is irrespective of the fluid pressure upstream of the FR brake fluid pressure adjusting unit 33. When the pressure increasing valve PUfr and the pressure reducing valve PDfr are both in the second position, the brake fluid in the wheel cylinder Wfr is reduced in pressure by being returned to the reservoir RSf.

  Further, a check valve CV1 that allows only one-way flow of brake fluid from the wheel cylinder Wfr side to the upstream portion of the FR brake fluid pressure adjusting unit 33 is disposed in parallel with the pressure increasing valve PUfr. When the operated brake pedal BP is released, the brake fluid pressure in the wheel cylinder Wfr is quickly reduced.

  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, a pressure increasing valve PUrl, and The pressure reducing valve PDrl is configured, and by controlling the position of each pressure increasing valve and each pressure reducing valve, the brake fluid pressure in the wheel cylinder Wfl, the wheel cylinder Wrr, and the wheel cylinder Wrl is increased and held, respectively. The pressure can be reduced. In addition, check valves CV2, CV3, and CV4 that can achieve the same function as the check valve CV1 are arranged in parallel on the pressure increasing valves PUfl, PUrr, and PUrl, respectively.

  The reflux brake fluid supply unit 37 includes a DC motor MT and two hydraulic pumps HPf and HPr that are simultaneously driven by the motor MT. 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 the pumped brake fluid passes through the check valves CV5 and CV6 to the FR brake fluid pressure adjusting unit 33 and the FL brake fluid. The pressure adjusting unit 34 is supplied to the upstream portion.

  Similarly, the hydraulic pump HPr pumps up the brake fluid in the reservoir RSr that has been refluxed from the pressure reducing valves PDrr and PDrl, and the pumped brake fluid through the check valves CV7 and CV8, and the RR brake fluid pressure adjusting unit 35 and The RL brake fluid pressure adjusting unit 36 is supplied upstream. In order to reduce the pulsation of the discharge pressures of the hydraulic pumps HPf and HPr, a hydraulic circuit between the check valves CV5 and CV6 and a hydraulic circuit between the check valves CV7 and CV8 are provided with dampers DMf, DMr is disposed.

  As described above, the brake hydraulic pressure control unit 30 can supply the brake hydraulic pressure corresponding to the operating force of the brake pedal BP to each wheel cylinder when all the solenoid valves are in the first position. Yes. In this state, for example, by controlling the pressure increasing valve PUrr and the pressure reducing valve PDrr, for example, only the brake fluid pressure in the wheel cylinder Wrr can be reduced by a predetermined amount. That is, the brake fluid pressure control unit 30 can reduce the brake fluid pressure in the wheel cylinder of each wheel independently from the brake fluid pressure corresponding to the operating force of the brake pedal BP.

  Referring to FIG. 1 again, the sensor unit 40 determines whether or not the wheel speed sensors 41FL, 41FR, 41RL, and 41RR that output a pulse signal each time the corresponding wheel rotates by a predetermined angle and the brake pedal BP are operated. A brake switch 42 that outputs an STP signal that is turned on or off in response thereto, and an outside air temperature sensor 43 that detects an outside air temperature that is the temperature of the air outside the vehicle body and outputs a signal indicating the outside air temperature Tout are provided. .

  The electric control device 50 is connected to each other via a bus. The CPU 51, a routine (program) executed by the CPU 51, a table (lookup table, map), a ROM 52 in which constants are stored in advance, and the CPU 51 store data as necessary. A microcomputer comprising a RAM 53 for temporary storage, a backup RAM 54 for storing data while the power is turned on, and retaining the stored data even while the power is shut off, and an interface 55 including an AD converter. is there.

  The interface 55 is connected to the sensors 41 to 43, supplies signals from the sensors 41 to 43 to the CPU 51, and according to instructions from the CPU 51, the electromagnetic valves of the brake fluid pressure control unit 30 and the motor MT. A drive signal is sent to the.

(Outline of anti-skid control for normal road surface)
Next, for an ordinary road surface (that is, a low μ road surface to be described later) executed by the anti-skid control device 10 (hereinafter also referred to as “the present device”) according to the embodiment of the present invention configured as described above. Anti-skid control (hereinafter, also referred to as “abs control for normal road surface”) control mode (that is, control start conditions, brake fluid pressure reduction, The holding / pressure increasing pattern) will be described. The ABS control for the normal road surface is a control whose main purpose is to maintain a desired deceleration.

This apparatus sequentially calculates the wheel speed Vw ** of each wheel based on the output of the wheel speed sensors 41FL, 41FR, 41RL, and 41RR when executing the ABS control for the normal road surface. The wheel acceleration DVw ** of each wheel is sequentially calculated from the temporal change rate of the speed Vw **. In the following, “**” appended to the end of various variables, etc., “fl” appended to the end of the various variables, etc., to indicate which of the various wheels FR, etc. , “Fr”, etc., for example, the wheel speed Vw ** is the left front wheel speed Vwfl,
The right front wheel speed Vwfr, the left rear wheel speed Vwrl, and the right rear wheel speed Vwrr are comprehensively shown.

  On the other hand, this apparatus sequentially obtains the estimated vehicle body speed Vso of the vehicle according to the following equation (1). In the following equation (1), the function max is a function that takes the maximum value of each argument. Further, the value gradlimit is the maximum reduction amount of vehicle body speed per unit time that can actually be achieved when the vehicle decelerates (maximum reduction gradient of vehicle body speed), and is a constant in this example. In addition, when this apparatus is provided with the means which acquires the road surface friction coefficient of the road surface where the vehicle is drive | working sequentially, you may comprise so that value gradlimit may be changed according to the acquired road surface friction coefficient. Δt is a calculation cycle of the CPU 51.

Vso = max (max (Vw **), Vso-gradlimit · Δt) (1)

  As can be understood from the above equation (1), the current estimated vehicle speed Vso is the current maximum wheel speed max (Vw **) and the value obtained by multiplying the previous estimated vehicle speed Vso by the value gradlimit by Δt. It is determined as the larger of the values.

  And when the following formula (2) and the following formula (3) are established, the present apparatus starts the ABS control for the normal road surface for the wheel **. That is, the following formula (2) and the following formula (3) represent the start conditions of the ABS control for the normal road surface.

Vso-Vw **> ΔVwrefnorm (2)
DVw ** <DVwrefnorm (3)

  In the above equation (2), “Vso−Vw **” represents the slip amount of the wheel **. ΔVwrefnorm is a slip amount reference value (positive constant value) for ABS control start determination for a normal road surface. In the above equation (3), DVwrefnorm is a wheel acceleration reference value (negative constant value) for ABS control start determination for a normal road surface.

  When the start condition for the normal road surface ABS control is satisfied, the present apparatus immediately starts and executes the normal road surface ABS control as shown in FIG. FIG. 3 (a) shows a wheel (i.e., at time t0) from which ABS control for normal road surface is started at time t0 until it is completed at time t8. The basic brake fluid pressure control mode (the pressure increasing mode, the holding mode, and the pressure reducing mode) for the wheel for which the ABS control start condition for the normal road surface is satisfied. It is a time chart showing changes in the mode. FIG. 3B is a time chart showing a change in the brake fluid pressure for the wheel to be controlled in accordance with the change in the brake fluid pressure control mode.

  As can be understood from FIGS. 3 (a) and 3 (b), this apparatus reduces the brake fluid pressure control mode for the wheel to be controlled from the pressure increasing mode (the state in which ABS control is not executed) at time t0. In addition to switching to the mode, after maintaining at the time t1 when a predetermined normal road surface pressure reduction time T1 elapses after the same point, the pressure reduction mode is switched to the holding mode at the same time t1. As a result, the brake fluid pressure for the wheel to be controlled continues to decrease from time t0 to time t1, and is maintained at a value at the same point after time t1. As a result, it is assumed that the wheel acceleration DVw ** of the wheel to be controlled increases, so that the value of the wheel acceleration DVw ** changes from a negative value to a positive value at time t2.

  At time t2, this apparatus switches the brake fluid pressure control mode for the wheel to be controlled from the holding mode to the pressure increasing mode at the same time, and after that time, a predetermined normal road surface pressure increasing time T2 is set. The pressure-increasing mode is maintained until time t3 that elapses, and the pressure-increasing mode is switched from the pressure-increasing mode to time t3 at time t3, and after time t4 until time t4 when a predetermined normal road surface holding time T3 elapses. , Keep in hold mode. As a result, the brake fluid pressure for the wheel to be controlled continues to increase from time t2 to time t3, and is maintained at the value at time t3 from time t3 to time t4.

  After time t4, this device also sets the brake fluid pressure control mode for the wheel to be controlled to the normal road surface pressure increase at time t4 to time t6 and time t6 to time t8, similarly to the time t2 to time t4 described above. A process of maintaining the pressure increasing mode for the time T2 and maintaining the holding mode for the normal road surface holding time T3 is performed (that is, the processes from the time t2 to the time t4 are repeated three times in total). At t8, the brake fluid pressure control mode for the wheel to be controlled is switched from the holding mode to the pressure increasing mode (a state where the ABS control is not executed), thereby terminating the ABS control for the normal road surface.

  The normal road surface pressure reducing time T1, the normal road surface pressure increasing time T2, and the normal road surface holding time T3 are determined based on the start conditions of the normal road surface ABS control shown in the above formula (2) and the above formula (3). It is set according to the change speed (time differential value) DDVw ** of the wheel acceleration DVw ** of the wheel ** at the time of establishment.

  Note that the increase speed of the wheel acceleration DVw ** of the control target wheel after time t0 is large, and the value of the time t2 (that is, the wheel acceleration DVw ** of the control target wheel changes from a negative value to a positive value). Time) is the time before the time t1 (that is, the time when the normal road pressure reduction time T1 elapses from the time t0), the device sets the brake fluid pressure control mode for the wheel to be controlled at the same time. At t2, the pressure reduction mode is immediately switched to the pressure increase mode, and processing from time t2 to time t8 shown in FIG.

  On the other hand, the increase speed of the wheel acceleration DVw ** of the wheel to be controlled after time t0 is small (or the wheel acceleration DVw ** does not increase), and the above equation (2) and (3) also at time t1. When the start condition of the ABS control for the normal road surface shown in the equation is still satisfied, the simultaneous point is reset as a new time t0, and after the new time t0, the time t0 shown in FIG. Processing up to time t8 is executed. As a result, the decompression mode is continuously executed over a period twice as long as the normal road surface decompression time T1 after the initial condition for starting the normal road surface ABS control is satisfied. The above is the outline of the control mode of the ABS control for the normal road surface.

(Outline of low μ road surface judgment)
As described above, when the driver performs a braking operation on a low μ road surface such as an icy road and an excessive slip occurs on the wheel, the wheel speed Vw ** of each driving wheel (therefore, the wheel acceleration of each driving wheel). DVw **) tends to fluctuate in a predetermined period corresponding to the natural frequency of the vehicle drive system. This tendency will be described with reference to FIG.

  FIG. 4 shows a case where the driver starts operating the brake pedal BP at time ta while the vehicle shown in FIG. 1 is traveling on a low μ road surface at a constant speed (that is, when ABS control is not executed). 4 is a time chart showing changes in the STP signal output from the brake switch 42, the wheel speed Vw of the drive wheel, the wheel acceleration DVw of the drive wheel, and the like. As shown in FIG. 4A, the STP signal is in an OFF state until the time ta arrives, and is maintained in the ON state after the simultaneous operation of the brake pedal BP is started at the time ta.

  After the time ta, the wheel speed Vw of the drive wheel decreases while fluctuating at a predetermined period (for example, 100 msec) corresponding to the natural frequency of the drive system of the vehicle, as shown in FIG. Along with this, as shown in FIG. 4C, the wheel acceleration DVw of the driving wheel also fluctuates at the predetermined cycle with a predetermined amplitude whose center value is a predetermined negative constant value.

  In order to easily extract only the fluctuation component of the wheel acceleration DVw of the drive wheel shown in FIG. 4C, the value of the wheel acceleration DVw has a predetermined cut-off frequency as shown in FIG. As shown in FIG. 4 (e), a filtered wheel acceleration DVwsm obtained by removing the fluctuation component by processing with a low-pass filter is obtained, and a value obtained by subtracting the filtered wheel acceleration DVwsm from the wheel acceleration DVw is shown in FIG. What is necessary is just to obtain | require as the fluctuation component DVwfluc centering on "0".

  The fluctuation amplitude (peak-to-peak value) A of the fluctuation component DVwfluc is within a predetermined range, and the fluctuation period P corresponds to the natural frequency of the drive system of the vehicle. It can be said that the change of the variation component DVwfluc (and thus the wheel acceleration DVw of the drive wheel) represents the vibration of the drive system of the vehicle. In general, when the road surface on which the vehicle is traveling is an icy road, the outside air temperature Tout outside the vehicle body is often, for example, a predetermined temperature Tref or lower (for example, 0 ° C. or lower).

  In view of the above, the present apparatus is configured such that the STP signal is maintained in the ON state, the fluctuation of the fluctuation component DVwfluc of the wheel acceleration of the driving wheel has an amplitude A within the predetermined range, and the cycle thereof. In a state where P is continuously in a predetermined range including a predetermined period corresponding to the natural frequency of the drive system of the vehicle, and continues for a predetermined number of times Nref (for example, three times), the filtered wheel The acceleration DVwsm is below the reference value DVw1 (negative constant value) over a predetermined time Time0 (for example, 18 msec), and the outside air temperature Tout detected by the outside air temperature sensor 43 is equal to or less than the predetermined temperature Tref. It is sequentially determined whether or not all the conditions are satisfied. The device determines that the road surface on which the vehicle is traveling is a predetermined low μ road surface only when all the above conditions are satisfied. The above is the outline of the determination of the low μ road surface.

(Outline of anti-skid control for low μ road surfaces)
Since the vehicle shown in FIG. 1 is a 4WD type vehicle, all the wheels are connected to each other via a drive system. Therefore, when the braking operation is executed on the low μ road surface, the wheel speeds Vw ** of all the wheels (drive wheels) are decreased while fluctuating similarly as shown in FIG. 4B described above. .

  Therefore, in this case, the wheel speed difference hardly occurs, and the slip amount “Vso-Vw **” of each wheel does not exceed the normal road surface ABS control start determination slip amount reference value ΔVwrefnorm (ie, As a result, it is difficult to start the ABS control at an appropriate timing. Therefore, in this case, it is necessary to correct the ABS control start condition so that the control is easily started. Note that when a very strong sudden braking operation is performed on a low μ road surface, the wheel speeds Vw ** of each wheel are all abruptly decreased, and as shown in the above equation (1), The vehicle body speed Vso is not the current maximum wheel speed max (Vw **), but the value obtained by subtracting the value gradlimit multiplied by Δt from the previous estimated vehicle body speed Vso. -Vw ** "can be larger than the normal road surface ABS control start determination slip amount reference value ΔVwrefnorm. As a result, the ABS control can be started at an appropriate timing.

  On the low μ road surface, even if ABS control is started, the wheel speed of the wheel once lowered due to the small rotational moment in the speed increasing direction that the tire receives from the road surface is controlled to reduce the brake fluid pressure. Accordingly, it takes a relatively long time to recover to the vehicle speed. Therefore, in this case, in order to ensure the running stability of the vehicle, priority should be given to restoring the wheel speed of the wheels rather than maintaining a large deceleration.

  From the above, as described above, when it is determined that the road surface on which the vehicle is traveling is a predetermined low μ road surface, this device satisfies the following formulas (4) and (5): When the wheel ** starts ABS control for the low μ road surface. That is, the following formula (4) and the following formula (5) represent the start conditions of the ABS control for the low μ road surface.

Vso-Vw **> ΔVwreflow (4)
DVw ** <DVwreflow (5)

  In the above equation (4), ΔVwrefflow is an ABS control start determination slip amount reference value (positive constant value) for a low μ road surface, which is larger than the ABS control start determination slip amount reference value ΔVwrefnorm for the normal road surface. Small value. In the above equation (5), DVwreflow is a wheel acceleration reference value for ABS control start determination for a low μ road surface (a negative constant value), which is larger than the ABS control start determination wheel acceleration reference value Dvwrefnowm for the normal road surface. Value (value with a small absolute value).

  And this apparatus is a case where it determines with the road surface where the vehicle is driving | running | working being a predetermined | prescribed low micro road surface, Comprising: When the starting condition of the ABS control for the said low micro road surface is satisfied, the above figure 3 (b) (same as the solid line in FIG. 5), the normal road surface pressure reduction time T1, the normal road surface pressure increase time T2, as indicated by the broken line in FIG. The low μ road surface ABS control is executed by replacing the normal road surface holding time T3 with the low μ road surface pressure reducing time T1 ′, the low μ road surface pressure increasing time T2 ′, and the low μ road surface holding time T3 ′. To do.

  Here, the low μ road surface pressure reducing time T1 ′, the low μ road surface pressure increasing time T2 ′, and the low μ road surface holding time T3 ′ are the low μ values shown in the above equations (4) and (5). It is set according to the change speed (time differential value) DDVw ** of the wheel acceleration DVw ** of the wheel ** at the time when the road surface ABS control start condition is satisfied, and “low μ road surface decompression time T1 ′> normal Road surface pressure reduction time T1 ”,“ low μ road pressure increase time T2 ′ <normal road surface pressure increase time T2 ”,“ low μ road surface retention time T3 ′> normal road surface retention time T3 ”.

  That is, as can be understood from FIG. 5, in the ABS control for the low μ road surface, the degree of pressure reduction (pressure reduction amount, pressure reduction period) of the brake fluid pressure of the wheel to be controlled is larger than the ABS control for the normal road surface. Thus, restoring the wheel speed of the wheel is prioritized over maintaining a large deceleration. In other words, the ABS control for the low μ road surface is a control whose main purpose is to recover the wheel speed. The above is the outline of the anti-skid control for the low μ road surface.

(Actual operation)
Next, the actual operation of the anti-skid control device 10 according to the present invention configured as described above will be described with reference to FIGS. 6 to 9 showing the routines executed by the CPU 51 of the electric control device 50 in the form of flowcharts. To do.

  The CPU 51 repeatedly executes the routine for calculating the wheel speed and the like shown in FIG. 6 every elapse of a predetermined time. Accordingly, when the predetermined timing is reached, the CPU 51 starts processing from step 600 and proceeds to step 605 to calculate the wheel speed of the wheel ** (the speed of the outer periphery of the tire of the wheel **) Vw **. Specifically, the CPU 51 calculates the wheel speed Vw ** based on the time interval of pulses included in the signal output from the wheel speed sensor 41 **.

  Next, the CPU 51 proceeds to step 610, where the wheel speed Vw **, the previous estimated vehicle body speed Vso calculated in step 610 at the time of the previous execution of this routine, and the step 610 based on the above equation (1) are described. The estimated vehicle body speed Vso of this time is calculated based on the above formula. Next, the CPU 51 proceeds to step 615 to calculate the wheel acceleration DVw ** which is a time differential value of the wheel speed ** according to the following equation (6). In the following formula (6), Vwb ** is the wheel speed Vw ** calculated in step 605 at the previous execution of this routine, and Δt is the predetermined time (the calculation cycle of the CPU 51).

DVw ** = (Vw **-Vwb **) / Δt (6)

  Next, the CPU 51 proceeds to step 620 and obtains the filtered wheel acceleration DVwsm ** after processing the wheel acceleration DVw ** sequentially obtained in step 615 with the low-pass filter, and then continues to step 625. Then, the fluctuation component DVwfluc ** is obtained based on the wheel acceleration DVw ** obtained in step 615, the filtered wheel acceleration DVwsm ** obtained in step 620, and the formula described in step 625, respectively. .

  Then, the CPU 51 proceeds to step 630 to calculate the change speed DDVw ** of the wheel acceleration DVw ** according to the following equation (7), and then proceeds to step 695 to end the present routine tentatively. Thereafter, the CPU 51 repeatedly executes this routine. In the following equation (7), DVwb ** is the wheel acceleration DVw ** calculated in step 615 at the previous execution of this routine, and Δt is the predetermined time (the calculation cycle of the CPU 51).

DDVw ** = (DVw **-DVwb **) / Δt (7)

  Next, the operation when selecting a control pattern (selecting which anti-skid control for normal road surface or low μ road surface is executed) will be described. Hereinafter, first, a case where the vehicle is traveling on a flat asphalt road surface (accordingly, a high μ road surface) will be described.

<When the vehicle is traveling on a flat high-μ road surface>
The CPU 51 repeatedly executes the routine shown in FIG. 7 every elapse of a predetermined time. Therefore, when the predetermined timing comes, the CPU 51 starts processing from step 700, proceeds to step 705, the STP signal is maintained in the ON state, and the ABS control execution flag ABS ** for the wheel **. It is determined whether the value of “0” is “0”. Here, the ABS control execution flag ABS indicates that anti-skid control is being executed when its value is “1” (regardless of whether it is for a normal road surface or a low μ road surface), and its value is “0”. "Indicates that the anti-skid control is not being executed.

  Assuming that the driver has not operated the brake pedal BP and therefore ABS control is not being executed for the wheel **, the CPU 51 makes a “No” determination at step 705 to proceed to step 710, Both the value of the counter N ** and the value of the counter M ** for the wheel ** are cleared to “0”. The counter N ** and the counter M ** will be described later.

  Next, the CPU 51 proceeds to step 715, sets the value of the low μ determination flag LOW ** for the wheel ** to “0”, and then proceeds to step 795 to end the present routine tentatively. Here, the low μ determination flag LOW indicates that when the value is “1”, it is determined that the road surface on which the vehicle is traveling is a predetermined low μ road surface, and when the value is “0”. This indicates that the road surface on which the vehicle is traveling is not determined to be a predetermined low μ road surface (thus, it is determined to be a high μ road surface). Thereafter, as long as the driver does not operate the brake pedal BP, the CPU 51 repeatedly executes the processes of steps 700, 705, 710, and 715.

  Next, the case where the driver operates the brake pedal BP from this state and the wheel ** slips will be described. In this case, the STP signal is changed from the OFF state to the ON state, and the ABS control is executed. Since the value of the middle flag ABS ** remains “0”, the CPU 51 determines “Yes” when the process proceeds to step 705, and proceeds to step 720. In step 720, the process proceeds to step 625 in FIG. 6. Whether the fluctuation component DVwfluc ** that has been sequentially calculated is in a state where the change history of the drive system represents vibration, that is, the fluctuation amplitude of the fluctuation component DVwfluc ** is within a predetermined range. In addition, it is determined for each wheel whether or not a state in which the period of the variation is within a predetermined range including a predetermined period corresponding to the natural frequency of the drive system continues.

  At the present stage, the vehicle is traveling on a high μ road surface, and the process of change of the fluctuation component DVwfluc ** is not in a state representing the vibration of the drive system, so the CPU 51 determines “No” in step 720. After executing the processing of the previous steps 710 and 715, the routine proceeds to step 795 and this routine is temporarily terminated.

  Thereafter, as long as this state continues, the CPU 51 repeatedly executes the processes of steps 700, 705, 720, 710, and 715. In this way, when the vehicle is traveling on a flat high μ road surface and slip occurs due to the operation of the brake pedal BP, the value of the low μ determination flag LOW ** is maintained at “0”.

  Further, the CPU 51 repeatedly executes a routine for performing the ABS control start determination shown in FIG. 8 every elapse of a predetermined time. Therefore, when the predetermined timing is reached, the CPU 51 starts processing from step 800 and proceeds to step 805. As in the previous step 705, the STP signal is maintained in the ON state and the ABS control execution flag ABS is reached. It is determined whether or not the value of ** is “0”. If it is determined “No”, the process immediately proceeds to step 895 to end the present routine tentatively.

  Now, assuming that the above-described state (the state in which the driver operates the brake pedal BP and slips on the wheel ** while traveling on a high μ road surface) continues, the CPU 51 proceeds to Step 805. If “Yes” is determined, the process proceeds to step 810 to determine whether or not the value of the low μ determination flag LOW ** is “0”.

  As described above, since the value of the low μ determination flag LOW ** is currently maintained at “0” as described above, the CPU 51 determines “Yes” at step 810 and proceeds to step 815 to perform the above-described normal road surface use. The ABS control start determination slip amount reference value ΔVwrefnorm for the wheel ** is set as the ABS control start determination slip amount reference value ΔVwref ** for the wheel **, and the above-described ABS acceleration start determination wheel acceleration reference for the normal road surface is used. The value DVwrefnorm is set as an ABS control start determination wheel acceleration reference value DVwref ** for the wheel **.

  Next, the CPU 51 proceeds to step 820, and based on the above formula (2) and the formula described in step 820 corresponding to the above formula (3), the ABS control start condition for the wheel ** (currently normal) Whether or not the road surface ABS control start condition) is satisfied is determined for each wheel, and if “No” is determined, the process immediately proceeds to step 895 to end the present routine tentatively.

  On the other hand, if the ABS control start condition (for the normal road surface) is satisfied for the wheel **, the CPU 51 determines “Yes” in step 820 and proceeds to step 825 to set the low μ determination flag LOW **. It is determined whether or not the value is “0”, “Yes” is determined in step 825, and the process proceeds to step 830.

  In step 830, the CPU 51 determines the normal road surface decompression time T1, which is set according to the wheel acceleration change speed DDVw ** for the latest wheel ** calculated in step 630 of FIG. The values of the road surface pressure increasing time T2 and the normal road surface holding time T3 are respectively the pressure reducing time T1 ** for the wheel **, the pressure increasing time T2 ** for the wheel **, and the holding time T3 for the wheel **. Set as **.

  Then, the CPU 51 proceeds to step 835 to reset the elapsed time T ** from the time when the ABS control start condition for the wheel ** is satisfied, and in the subsequent step 840, the ABS control execution flag ABS for the wheel **. After changing the value of ** from “0” to “1”, the routine proceeds to step 895 to end the present routine tentatively. The elapsed time T ** is acquired for each wheel based on the output of a timer (not shown) built in the electric control device 50.

  As a result, since the value of the ABS control execution flag ABS ** is changed / maintained to “1”, when the CPU 51 proceeds to step 805, the wheel ** (the ABS control execution flag ABS ** The wheel whose value is “1” is determined as “No”, and the process immediately proceeds to step 895 so as to end this routine once. As described above, the start condition of the ABS control, the pressure reduction time T1 **, the pressure increase time T2 **, and the holding time T3 ** are for the normal road surface according to the value of the low μ determination flag LOW **. And any value for low μ road surfaces. As described above, the ABS control start determination (current road start determination) is executed.

  Further, the CPU 51 repeatedly executes a routine for executing the ABS control shown in FIG. 9 every elapse of a predetermined time. Accordingly, when the predetermined timing is reached, the CPU 51 starts processing from step 900 and proceeds to step 905 to determine whether or not the value of the ABS control execution flag ABS ** is “1”. For the wheels that are judged as “”, the process immediately proceeds to step 995 to end the present routine tentatively.

  Now, it is assumed that the ABS control start condition (for the normal road surface) for the wheel ** shown in the previous step 820 is satisfied and immediately after the processing of the previous step 840 is executed for the wheel **. The CPU 51 determines “Yes” for the wheel ** in step 905 and proceeds to step 910. In addition to the ABS control start condition, the condition “the elapsed time T ** is set in the previous step 830. It is determined whether or not both the above-described decompression time T1 ** (that is, the normal road surface decompression time T1) has been satisfied.

  Since the present time is immediately after the ABS control start condition for the wheel ** is established, the elapsed time T ** does not exceed the pressure reduction time T1 **. Therefore, the CPU 51 makes a “No” determination at step 910 to immediately proceed to step 920.

  If the CPU 51 determines “Yes” in step 910, it proceeds to step 915 to reset the elapsed time T ** and then proceeds to step 920. This process is performed when “the start condition of the ABS control for the normal road surface expressed by the equations (2) and (3) is still satisfied even at the time t1 shown in FIG. 3” described above. This corresponds to processing.

  When the CPU 51 proceeds to step 920, the current elapsed time T **, the pressure reduction time T1 **, the pressure increase time T2 **, and the holding time T3 ** set in step 830, and FIG. ) By controlling the pressure increasing valve PU ** and the pressure reducing valve PD ** for the wheel ** in accordance with the time chart described in step 920 corresponding to the time chart of the brake fluid pressure control mode shown in FIG. * Set the brake fluid pressure control mode for (control target wheel) according to the elapsed time T **.

  Subsequently, the CPU 51 proceeds to step 925 to check whether or not the elapsed time T ** for the wheel ** (control target wheel) matches the time corresponding to the time t8 in step 920 (that is, the wheel ** It is determined whether or not the ABS control is completed for the current time, and since the same elapsed time T ** has not reached the time corresponding to the same time t8 at this time, it is determined as “No” and the process immediately proceeds to step 995. This routine is temporarily terminated.

  Thereafter, the CPU 51 repeatedly executes the processes of steps 900, 905, 910, (915), 920, 925, and 995 until the elapsed time T ** reaches the time corresponding to the time t8. As a result, the brake fluid pressure control mode for the wheel ** is changed as the elapsed time T ** increases.

  When the predetermined time has elapsed and the elapsed time T ** reaches the time corresponding to the time t8, the CPU 51 proceeds to step 925 to determine “Yes” and proceeds to step 930 to execute ABS control. The value of the flag ABS ** is changed from “1” to “0”, and the process proceeds to step 995 to end the present routine tentatively.

  As a result, the value of the ABS control execution flag ABS ** becomes “0”, so when the CPU 51 proceeds to step 905, it determines “No” for the wheel ** and immediately proceeds to step 995. The routine is temporarily terminated. In this way, the ABS control (at this stage, the normal road surface ABS control indicated by the solid line in FIG. 5) is executed.

  As described above, the case where the driver operates the brake pedal BP when the vehicle is traveling on a flat high μ road surface has been described. Next, the case where the driver operates the brake pedal BP and the wheel ** slips when the vehicle is traveling on an icy road will be described.

<When the vehicle is traveling on a low μ road>
In this case, as described above, after the brake pedal BP is operated, the wheel speed Vw ** of each drive wheel (therefore, the fluctuation component DVwfluc ** of each drive wheel) is continuously increased with the vibration of the drive system. Fluctuates.

  Now, assuming that the driver has just operated the brake pedal BP when ABS control is not being executed, the STP signal has been changed from the OFF state to the ON state. The CPU 51 that has repeatedly executed the processing of steps 700, 705, 710, and 715 every time a predetermined time elapses makes a determination of “Yes” when proceeding to step 705, and performs the above-described determination of step 720. At this time, the value of the counter N ** (and the counter M **) is “0” by the processing in step 710.

  At this time, as described above, since the state in which the fluctuation of the value of the fluctuation component DVwfluc ** represents the vibration of the drive system continues, the CPU 51 determines “Yes” in Step 720 and proceeds to Step 725. Every time the maximum value of the fluctuation component DVwfluc ** appears, the value of the counter N ** (currently “0”) is incremented. That is, the counter N ** represents the number of times that the fluctuation of the fluctuation component DVwfluc ** about the wheel ** representing the vibration of the drive system continues continuously.

  Next, the CPU 51 proceeds to step 730 and determines whether or not the value of the counter N ** is equal to or greater than the predetermined number Nref (therefore, the variation of the fluctuation component DVwfluc ** representing the vibration of the drive system is continuously repeated the same predetermined number of times. Whether or not it continues for Nref or more). At this time, the value of the counter N ** is “0”. Therefore, the CPU 51 determines “No” in step 730, proceeds to step 795 via the previous step 715, and ends this routine once. Therefore, at this stage, the value of the low μ determination flag LOW ** is maintained at “0”.

  Thereafter, as long as the fluctuation of the value of the fluctuation component DVwfluc ** continues to indicate the vibration of the drive system, the CPU 51 determines that the value of the counter N ** that increases through the repeated processing of step 725 is a predetermined number of times. Until Nref is reached, the processes of steps 700, 705, 720, 725, 730, and 715 are repeatedly executed.

  Then, when the predetermined time has elapsed and the value of the counter N ** reaches the predetermined number Nref, the CPU 51 determines “Yes” when it proceeds to step 730, proceeds to step 735, and repeats at step 620 in FIG. 6. It is determined whether or not the calculated post-filter wheel acceleration DVwsm ** value is below the reference value DVw1, and if “No” is determined, the process proceeds to step 745 and the value of the counter M ** is determined. Is set to “0”, the process proceeds to step 795 via step 715 to end the present routine tentatively.

  On the other hand, when determining “Yes” in the determination in step 735, the CPU 51 proceeds to step 740 and increments the value of the counter M **. That is, the value of the counter M ** is the value of the wheel acceleration DVwsm ** after passing through the filter in a state where the fluctuation of the fluctuation component DVwfluc ** representing the vibration of the drive system continues continuously for a predetermined number Nref or more. Represents the duration of the state below the value DVw1.

  Next, the CPU 51 proceeds to step 750 to determine whether or not the value of the counter M ** is equal to or greater than a reference value Mref corresponding to the predetermined time Time0. Then, it is determined whether or not the outside air temperature Tout detected by the outside air temperature sensor 43 is equal to or lower than the predetermined temperature Tref. If the CPU 51 determines “No” in either step 750 or step 755, the CPU 51 immediately proceeds to step 795 via step 715, and once ends this routine.

  On the other hand, if the determination is “Yes” in step 755, the CPU 51 proceeds to step 760 to set the value of the low μ determination flag LOW ** to “1”, and then proceeds to step 795 to end the present routine temporarily. . As described above, it is low only when the value of the counter N ** is equal to or greater than the predetermined number Nref, the value of the counter M ** is equal to or greater than the reference value Mref, and the outside air temperature Tout is equal to or less than the predetermined temperature Tref. The value of the μ determination flag LOW ** is set to “1”.

  Thus, when the value of the low μ determination flag LOW ** is set to “1”, the CPU 51 that repeatedly executes the routine of FIG. Proceeding to 845, the above-mentioned slip amount reference value ΔVwreflow for ABS control start determination for low μ road is set as the ABS control start determination slip amount reference value ΔVwref ** for the wheel **, and the low μ described above The wheel acceleration reference value Dvwreflow for ABS control start determination for the road surface is set as the wheel acceleration reference value DVwref ** for ABS control start determination for the wheel **.

  That is, in the following step 820, the CPU 51 starts the ABS control start condition for the wheel ** based on the above formula (4) and the formula in step 820 corresponding to the above formula (5) (currently low). Whether or not the μ road surface ABS control start condition) is satisfied is determined for each wheel. If the start condition of the ABS control for the low μ road surface is established for the wheel **, the CPU 51 makes a “No” determination at step 825 to proceed to step 850, and is calculated at step 630 in FIG. The low μ road surface decompression time T1 ′, the low μ road surface pressure increase time T2 ′, and the low μ road surface retention time set according to the wheel acceleration change speed DDVw ** for the latest wheel ** After setting the values of T3 ′ as the pressure reduction time T1 ** for the wheel **, the pressure increase time T2 ** for the wheel **, and the holding time T3 ** for the wheel **, steps 835 and 840 are performed. Then, the process proceeds to step 895 to end the present routine tentatively.

  As a result, the value of the ABS control execution flag ABS ** becomes “1” by the process of step 840, so that the CPU 51 that repeatedly executes the routine of FIG. 9 determines “Yes” when the routine proceeds to step 905. Then, the ABS control execution process after step 910 is performed. In this case, since the decompression time T1 **, the pressure increase time T2 **, and the holding time T3 ** are set as values for the low μ road surface by executing the previous step 850, the CPU 51 determines in step 920. The ABS control for the low μ road surface indicated by the broken line in FIG. 5 is executed.

  As described above, the case where the driver operates the brake pedal BP when the vehicle is traveling on the low μ road surface has been described. Next, in the case where the vehicle is traveling on a high μ μ wave road (a road surface having convex portions at regular intervals) under an outside air temperature Tout that is high enough to prevent the road surface from becoming an icy road, A case where the brake pedal BP is operated will be described.

<When the vehicle is traveling on a high μ wavy road>
When the vehicle is traveling on a wavy road, depending on the vehicle speed of the vehicle, the cycle in which the vehicle passes the convex portion of the wavy road substantially coincides with the cycle corresponding to the natural frequency of the drive system. There may be a case where the state of the vibration of the drive system continues due to the apparent change in the wheel speed Vw ** of the wheel (therefore, the fluctuation component DVwfluc ** of each drive wheel).

  In such a case, the fluctuation of the fluctuation component DVwfluc ** representing the vibration of the drive system continues continuously for a predetermined number of times Nref and the state where the wheel acceleration DVwsm ** after passing through the filter falls below the reference value DVw1 is predetermined. It may occur that the time continues for more than Time0. In other words, the CPU 51 that repeatedly executes the routine of FIG. 7 returns “Yes” in steps 730 and 750, even though the wheel speed Vw ** does not vary due to the vibration of the drive system. It may occur that the determination and proceed to step 755.

  However, in this case, since the outside air temperature Tout is higher than the predetermined temperature Tref, the CPU 51 makes a “No” determination at step 755 to proceed to step 715. As a result, the low μ determination flag LOW ** Is set to “0”. Accordingly, it is possible to prevent the ABS control for the low μ road surface from being executed even though the road surface on which the vehicle is traveling is high μ.

  As described above, according to the embodiment of the anti-skid control device according to the present invention, when the driver performs a braking operation on a low μ road surface such as an icy road and an excessive slip occurs on the wheel, each drive The wheel speed Vw of the wheel (and hence the wheel acceleration DVw of each driving wheel) tends to fluctuate in a predetermined period corresponding to the natural frequency of the vehicle drive system, and the outside air temperature Tout is generally a predetermined temperature. Focusing on the fact that the STP signal is maintained in the ON state in many cases, the amplitude A of the fluctuation component DVwfluc of the driving wheel of the driving wheel is within the predetermined range. In addition, in a state in which the period P is within a predetermined range including a predetermined period corresponding to the natural frequency of the drive system of the vehicle and continues for a predetermined number of times Nref or more, the filtered wheel acceleration DVwsm is Pass over Time0 Only when all the conditions that the reference temperature DVw1 is below and the outside temperature Tout detected by the outside temperature sensor 43 is equal to or lower than the predetermined temperature Tref are simultaneously satisfied. It is determined that the road surface on which the vehicle is traveling is a predetermined low-μ road surface, and the ABS control dedicated to the low-μ road surface, which gives priority to recovering the rotational speed of the wheel rather than maintaining a large deceleration, is executed.

  Therefore, for example, when the vehicle is traveling on a high μ wave-like road, there is a state in which the fluctuation of the fluctuation component DVwfluc of the driving wheel due to the undulating state of the road surface is apparently expressed as the vibration of the driving system. Even if it occurs, if the outside air temperature Tout is not lower than the predetermined temperature Tref, it is not determined that the road surface on which the vehicle is traveling is the predetermined low μ road surface. Accordingly, it is possible to prevent a situation in which a large deceleration cannot be maintained due to execution of the ABS control for the low μ road surface even though the vehicle is traveling on the high μ road surface.

  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-described embodiment, when the outside air temperature Tout detected by the outside air temperature sensor 43 is currently equal to or lower than the predetermined temperature Tref, the road surface on which the vehicle is traveling is a predetermined low μ road surface. Although it is a necessary condition for determination, the process of the change of the outside air temperature Tout is in a predetermined state (for example, the outside air temperature Tout is not more than a predetermined temperature Tref for a predetermined time) Etc.) may be necessary conditions for determining that the road surface on which the vehicle is traveling is a predetermined low μ road surface.

  Further, in the above-described embodiment, the value of the wheel acceleration DVwsm ** after passing through the filter is the reference value DVw1 in a state where the fluctuation of the fluctuation component DVwfluc ** representing the vibration of the drive system continues continuously for a predetermined number of times Nref or more. It is determined whether or not the outside air temperature Tout is equal to or lower than the predetermined temperature Tref after detecting that the state below the predetermined time Time0 is continued (see step 755 in FIG. 7). Whether or not the temperature is equal to or lower than the predetermined temperature Tref is determined between Step 705 and Step 720. If the outside air temperature Tout is equal to or lower than the predetermined temperature Tref, the process proceeds to Step 720, where the outside air temperature Tout is equal to or lower than the predetermined temperature Tref. If it is not, the same effect can be obtained even if it is configured to proceed to steps 710 and 715 immediately.

It is a schematic block diagram of the vehicle carrying the anti-skid control apparatus which concerns on embodiment of this invention. It is a schematic block diagram of the brake fluid pressure control apparatus shown in FIG. FIG. 3A is a time chart showing changes in the basic brake fluid pressure control mode for the wheel to be controlled on which the normal road surface ABS control is executed. FIG. 3B is a time chart showing a change in the brake fluid pressure for the wheel to be controlled in accordance with the change in the brake fluid pressure control mode. When a braking operation is performed at time Ta while traveling on a low μ road surface, the output signal of the brake switch, the wheel speed of the driving wheel, the wheel acceleration of the driving wheel, the wheel acceleration after passing through the low pass filter of the driving wheel, and It is the time chart which showed the change of the fluctuation component of the wheel acceleration of the drive wheel, respectively. The time shown by comparing the change in the brake fluid pressure for the wheel to be controlled on which the ABS control is executed between the case where the ABS control for the normal road surface is executed and the case where the ABS control for the low μ road surface is executed It is a chart. It is the flowchart which showed the routine for calculating the wheel speed etc. which CPU shown in FIG. 1 performs. 3 is a flowchart showing a routine for selecting a control pattern to be executed by a CPU shown in FIG. 1. FIG. 3 is a flowchart showing a routine for performing a start determination of ABS control executed by a CPU shown in FIG. 1. FIG. It is the flowchart which showed the routine for performing ABS control which CPU shown in FIG. 1 performs.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 ... Anti skid control apparatus, 30 ... Brake hydraulic pressure control part, 41 ** ... Wheel speed sensor, 42 ... Brake switch, 43 ... Outside temperature sensor, 50 ... Electric control apparatus, 51 ... CPU

Claims (4)

Wheel speed acquisition means for acquiring the wheel speed of each wheel of the vehicle;
The brake fluid pressure is adjusted by at least reducing and increasing the brake fluid pressure supplied to the wheel cylinder of each wheel based on at least the acquired wheel speed, and excessive slip occurs in each wheel. An anti-skid control means for performing anti-skid control for preventing
Outside air temperature acquisition means for acquiring outside air temperature at a position where the vehicle is traveling;
When the anti-skid control is not executed and a braking force is applied to each wheel by a brake fluid pressure, the process of changing the value based on the acquired wheel speed and the acquired outside air Road surface determination means for determining whether the road surface on which the vehicle is traveling is a road surface having a predetermined low friction coefficient including an icy road, based on the temperature;
When it is determined that the road surface on which the vehicle is traveling is the road surface having the predetermined low friction coefficient, the control mode of the anti-skid control is set to the control mode for the road surface having the predetermined low friction coefficient. Control mode setting means for
Anti-skid control device with The anti-skid control device according to claim 1, wherein
The road surface judging means
The road surface on which the vehicle is traveling is the road surface having the predetermined low friction coefficient when the history of the change in the value based on the wheel speed of the acquired drive wheel represents the vibration of the drive system of the vehicle. An anti-skid control device configured to determine The anti-skid control device according to claim 2,
The road surface judging means
When the wheel acceleration value of the drive wheel, which is the time differential value of the wheel speed of the acquired drive wheel, fluctuates with a predetermined amplitude and with a predetermined period corresponding to the natural frequency of the drive system of the vehicle, An anti-skid control device configured to determine that a history of a change in value based on the wheel speed of the acquired drive wheel represents vibration of a drive system of the vehicle. In the anti-skid control device according to any one of claims 1 to 3,
The road surface judging means
An anti-skid control device configured to determine that a road surface on which the vehicle is traveling is a road surface having the predetermined low friction coefficient when the acquired outside air temperature is equal to or lower than a predetermined temperature.

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