JP5780381B2 - Vehicle motion control device - Google Patents

Description

  The present invention relates to a vehicle motion control device that increases the braking torque of a wheel to improve the stability of the vehicle.

  In Patent Document 1, “Providing a method for controlling running stability that can respond as quickly as possible to an expected unstable running situation by an intervention that alleviates or avoids a critical running situation. For the purpose of this, pre-braking intervention is performed on the front wheels outside the curve in anticipation of sudden steering based on the average steering wheel acceleration (| maximum SWAP | / (T2-T1)) etc. until the maximum steering wheel angular velocity is reached. Then, as long as the condition of | SWAPt−maximum SWAP | / (t−T2)> reference amount 4 is satisfied, the pre-braking intervention is continued (where SWAPt is the steering wheel angular velocity at an arbitrary time point t). The braking torque applied by prior braking intervention depends on the vehicle speed and / or the maximum steering wheel angular velocity (maximum SWAP) That. Vehicle speed, and / or the larger the maximum SWAP, braking torque is great. "It has been described.

  Patent Document 2 states that “when skidding is identified during braking and / or deceleration, in order to prevent skidding when exceeding the limits of travel dynamics, such as vehicle skidding at an excessively high curve speed, The front-wheel anti-lock braking system is stopped and the front wheel is automatically braked strongly, causing a sufficient slip on the front wheel. "

US Pat. No. 6,957,873 US Pat. No. 5,255,194

  By the way, the yawing motion related to the vehicle stability is affected not only by the steering speed but also by the traveling road surface condition of the vehicle. For example, when the road friction coefficient such as a dry asphalt road surface is high, a fast and large yawing motion occurs with respect to sudden steering, but when the friction coefficient such as a snowy road surface is low, it is not so much. No yawing movement occurs. For this reason, merely determining the magnitude of the braking torque in accordance with the vehicle speed and the steering speed results in excessive or insufficient braking torque. Further, if the braking torque is excessive, the wheel lateral force is significantly reduced, and the vehicle behavior following the steering may not be obtained. Therefore, it is desirable to apply the braking torque so that the minimum necessary wheel lateral force is ensured. An object of the present invention is to provide a vehicle motion control device that can appropriately ensure vehicle stability by braking control according to a road surface state where a vehicle travels and a steering state.

  The vehicle motion control apparatus according to the present invention includes braking means (MBR), control means (CTL), wheel speed acquisition means (VWA), and suppression means (ASL). The braking means (MBR) applies a braking torque to the vehicle wheel (WH [**]). The control means (CTL) includes a steering state (Saa, dSa) of a steering operation member (SW) operated by a driver of the vehicle, and a turning amount (Tca) representing a degree of turning motion of the vehicle. Based on at least one, the braking torque (Pwt [**], Pwa [**]) is increased via the braking means (MBR). Hereinafter, the braking control for increasing the braking torque is simply referred to as “braking control”. The wheel speed acquisition means (VWA) acquires a wheel speed (Vwa [**]) that is a rotation speed of the vehicle wheel (WH [**]). The restraining means (ASL) calculates the front / rear slip amount (Slp [**]) of the wheel based on the wheel speed (Vwa [**]), and the front / rear slip amount (Slp [**]) is calculated. When the threshold slip amount (Tsp) is exceeded, the braking torque (Pwt [**], Pwa [**]) is adjusted to suppress the front / rear slip amount (Slp [**]). To do. Further, the suppression means (ASL) increases the threshold slip amount (Tsp) when the control means (CTL) increases the braking torque (Pwt [**], Pwa [**]). Configured.

  Since this invention is comprised as mentioned above, there exist the following effects.

  The braking load of the wheel (braking force with respect to the ground load) is reflected in the front-rear slip amount of the wheel. If a slip angle (lateral slip amount) occurs in the wheel, the wheel becomes difficult to rotate, so the front / rear slip amount increases even with an equivalent braking load. In a sudden steering state in which the wheel slip angle suddenly increases, the steering state (eg, steering amount, steering speed) of the steering operation member (eg, steering wheel) and the turning amount of the vehicle (eg, lateral acceleration, yaw rate) When braking control in which braking torque is increased based on at least one of them (hereinafter simply referred to as braking control) is executed, the threshold slip amount (threshold) is increased and slip suppression control is executed. Therefore, an appropriate braking torque is applied by the braking control, an excessive wheel lateral force is suppressed, and vehicle stability is maintained. In addition, the wheel lateral force necessary for emergency avoidance can be ensured.

1 is a diagram illustrating an overall configuration of a vehicle including a vehicle motion control device according to an embodiment of the present invention. It is a figure which shows the whole structure of the brake actuator BRK. It is a figure explaining steering operation in the case of avoiding an obstacle urgently. It is a functional block diagram which shows the example of arithmetic processing of the vehicle motion control apparatus in this embodiment. It is a functional block diagram which shows the other example of a calculation process about the slip suppression control calculation block ASL. It is a functional block diagram which shows the example of a calculation process in the braking control calculation block CTL. It is a functional block diagram which shows the other example of a calculation process in the braking control calculation block CTL. It is a control flowchart which shows the example of a calculation process in the control execution determination part of the target braking torque calculation block PWT. It is a time series diagram for demonstrating the effect | action and effect of the vehicle motion control apparatus which concerns on embodiment of this invention.

  FIG. 1 is a diagram illustrating an overall configuration of a vehicle including a vehicle motion control apparatus according to an embodiment of the present invention. The subscript [**] attached to the end of various symbols indicates whether the various symbols are related to any of the four wheels. “F” is the front wheel, “r” is the rear wheel, “m” is the right wheel with respect to the vehicle traveling direction, “h” is the left wheel, “o” is the outer wheel (outer wheel) with respect to the turning direction, “i” "Indicates an inner wheel (inner ring). Therefore, “fh” indicates the left front wheel, “fm” indicates the right front wheel, “rh” indicates the left rear wheel, and “rm” indicates the right rear wheel. “Fo” is the outer front wheel (outer front wheel), “fi” is the inner front wheel (inner front wheel), “ro” is the outer rear wheel (outer rear wheel), and “ri” is the inner rear wheel (inner). Rear wheel).

  Further, the turning direction of the vehicle may be rightward or leftward. They are generally given positive and negative signs, for example, the left direction is represented as a positive sign and the right direction is represented as a negative sign. Further, the acceleration / deceleration of the vehicle is generally given a positive / negative sign, for example, acceleration is expressed as a positive sign and deceleration is expressed as a negative sign. However, when describing the magnitude relationship of the values or the increase / decrease in the values, it becomes very complicated when the sign is taken into account. Therefore, unless there is a particular limitation, the absolute value magnitude relationship and the absolute value increase / decrease are represented. The predetermined value is a positive value set in advance.

  The vehicle includes a wheel speed sensor WS [**] that detects the wheel speed Vwa [**], and a rotation angle θsw of the steering wheel SW (from a neutral position “0” of the steering device that corresponds to the vehicle traveling straight). Steering wheel angle sensor SA for detecting steering angle, front wheel steering angle sensor FS for detecting steering angle δfa of the steered wheel (front wheel), and steering torque sensor ST for detecting torque Tsw when the driver operates the steering wheel SW A yaw rate sensor YR that detects an actual yaw rate Yra acting on the vehicle, a longitudinal acceleration sensor GX that detects a longitudinal acceleration Gxa in the longitudinal direction of the vehicle body, a lateral acceleration sensor GY that detects a lateral acceleration Gya in the lateral direction of the vehicle body, A wheel cylinder pressure sensor PW [**] that detects the brake fluid pressure Pwa [**] of the wheel cylinder WC [**], and a rotation of the engine EG An engine rotational speed sensor NE for detecting the speed Nea, throttle position sensor TS is provided for detecting the opening Tsa of the throttle valve of the engine.

  As means for detecting the driver's driving operation, an acceleration operation amount sensor AS for detecting the operation amount Asa of the driver's acceleration operation member (for example, accelerator pedal) AP, and the driver's braking operation member (for example, brake) Pedal) A braking operation amount sensor BS for detecting the operation amount Bsa of the BP and a shift position sensor HS for detecting the shift position Hsa of the speed change operation member SF are provided.

  The vehicle also includes a brake actuator BRK that controls the brake fluid pressure, a throttle actuator TH that controls the throttle valve, a fuel injection actuator FI that controls fuel injection, and an automatic transmission AT that controls the shift. It has been.

  In addition, the vehicle includes an electronic control unit ECU that is electrically connected to the above-described various actuators (such as BRK) and the above-described various sensors (such as WS [**]). The electronic control unit ECU is a microcomputer composed of a plurality of independent electronic control units ECU (ECUb, ECUs, ECUe, ECUa) connected to each other via a communication bus CB. Each system electronic control unit (ECUb, etc.) in the electronic control unit ECU executes a dedicated control program. Signals (sensor values) of various sensors and signals (internally calculated values) calculated in each electronic control unit (ECUb or the like) are shared via the communication bus CB.

  The arithmetic processing of this apparatus is provided in the electronic control unit ECU. For example, the arithmetic processing of this device is programmed in the brake system electronic control unit ECUb that controls the brake actuator BRK. In the brake system electronic control unit ECUb, anti-skid control (ABS control) and the like are executed based on signals from the wheel speed sensor WS [**], the yaw rate sensor YR, the lateral acceleration sensor GY, and the like. Further, based on the wheel speed Vwa [**] of each wheel detected by the wheel speed sensor WS [**], the traveling speed (vehicle speed) Vxa of the vehicle is calculated by a known method.

  In the steering system electronic control unit ECUs, electric power steering control (EPS control) is executed based on a signal from the steering torque sensor ST or the like. In the engine system electronic control unit ECUe, the throttle actuator TH and the fuel injection actuator FI are controlled based on the signal Asa from the acceleration operation amount sensor AS and the like. In the transmission system electronic control unit ECUa, control of the gear ratio of the automatic transmission AT is executed.

  The brake actuator BRK (corresponding to a part of the braking means MBR) has a known configuration including a plurality of electromagnetic valves (hydraulic pressure adjusting valves), a hydraulic pump, an electric motor, and the like. When executing the brake control, the brake actuator BRK can control the brake fluid pressure for each wheel cylinder WC [**] independently of the operation of the brake pedal BP, and adjust the brake torque for each wheel.

  Each wheel is provided with a known wheel cylinder WC [**], brake caliper BC [**], brake pad PD [**], and brake rotor RT [**] as braking means MBR. When brake fluid pressure is applied to the wheel cylinder WC [**] provided in the brake caliper BC [**], the brake pad PD [**] is pressed against the brake rotor RT [**], and the friction force Thus, a braking torque is applied to each wheel. Note that the control of the braking torque is not limited to that based on the braking hydraulic pressure, and can be performed using an electric brake device.

  FIG. 2 is a diagram showing an overall configuration of the brake actuator BRK. When the driver depresses a braking operation member (for example, a brake pedal) BP, the pedaling force is boosted by the booster VB, and the master piston provided in the master cylinder MC is pushed. As a result, the same master cylinder pressure Pmc is generated in the first chamber and the second chamber defined by the master piston. Master cylinder pressure Pmc is applied to wheel cylinder WC [**] of each wheel WH [**] through brake actuator BRK.

  The brake actuator BRK has a first piping system HP1 connected to the first chamber of the master cylinder MC and a second piping system HP2 connected to the second chamber of the master cylinder MC. The first piping system HP1 controls the brake fluid pressure applied to the left front wheel WH [fh] and the right rear wheel WH [rm]. The second piping system HP2 controls the brake fluid pressure applied to the right front wheel WH [fm] and the left rear wheel WH [rh]. Since the first piping system HP1 and the second piping system HP2 have the same configuration, only the first piping system HP1 will be described below, and the description of the second piping system HP2 will be omitted. The configuration shown in FIG. 2 is a diagonal piping configuration, but the brake piping configuration may be front and rear piping.

  The first piping system HP1 includes a pipe line LA that generates braking hydraulic pressures (hydraulic pressures in the wheel cylinders) Pw [fh] and Pw [rm]. The pipe line LA is provided with a first differential pressure control valve SS1 that can be controlled between a communication state and a differential pressure state. Then, the master cylinder pressure Pmc is transmitted to the wheel cylinder WC [fh] provided in the left front wheel WH [fh] and the wheel cylinder WC [rm] provided in the right rear wheel WH [rm]. During normal braking in which the driver operates the brake pedal BP (when brake control is not being executed), the valve position of the first differential pressure control valve SS1 is adjusted to an open state so as to be in a communicating state. . When the first differential pressure control valve SS1 is energized, the valve position is adjusted to the closed state, and the first differential pressure control valve SS1 is set to the differential pressure state.

  The pipe line LA branches into two pipe lines LA [fh] and LA [rm] on the side of the wheel cylinders WC [fh] and WC [rm] from the first differential pressure control valve SS1. The line LA [fh] is provided with a first pressure increase control valve SZ [fh] that controls the increase of the brake fluid pressure to the wheel cylinder WC [fh]. The pipe line LA [rm] is provided with a second pressure increase control valve SZ [rm] for controlling the increase of the brake fluid pressure to the wheel cylinder WC [rm]. The first and second pressure-increasing control valves SZ [fh] and SZ [rm] are constituted by two-position electromagnetic valves that can control the communication / blocking state. The first and second pressure increase control valves SZ [fh] and SZ [rm] are in a communication state (open state) when the supplied current is “0” (when not energized), and the current flows. Is controlled to be in a shut-off state (closed state). The first and second pressure increase control valves SZ [fh], SZ [rm] are so-called normally open types.

  The pipe line LB is a pressure reducing unit that connects the first and second pressure increase control valves SZ [fh], SZ [rm] and the wheel cylinders WC [fh], WC [rm] and the pressure regulating reservoir R1. It is a pipe line for. The pipe LB is provided with a first pressure reduction control valve SG [fh] and a second pressure reduction control valve SG [rm] configured by two-position electromagnetic valves capable of controlling the communication / blocking state. The first and second pressure reduction control valves SG [fh] and SG [rm] are closed when not energized and opened when energized. These are so-called normally closed types.

  A pipeline LC is disposed between the pressure regulating reservoir R1 and the pipeline LA. A hydraulic pump OP1 is provided in the pipeline LC. The brake fluid is sucked from the pressure adjusting reservoir R1 by the hydraulic pump OP1, and is discharged toward the master cylinder MC or the wheel cylinders WC [fh] and WC [rm]. The hydraulic pump OP1 is driven by an electric motor MT. A pipe line LD is provided between the pressure regulating reservoir R1 and the master cylinder MC. When automatic pressurization such as vehicle stability control or traction control is performed, brake fluid is sucked from the master cylinder MC through the line LD by the hydraulic pump OP1 and discharged to the lines LA [fh] and LA [rm]. The As a result, the brake fluid is supplied to the wheel cylinders WC [fh] and WC [rm], the brake fluid pressure of the wheel cylinder WC [**] of the target wheel is increased, and braking torque is applied.

  First, with reference to FIG. 3, a steering operation when an obstacle is urgently avoided will be described.

  FIG. 3A is referred to as J-turn steering, and is a case where an abrupt steering wheel operation is performed in one direction (that is, one of the left direction and the right direction). The steering operation by the driver is started at time p0, and the steering amount Saa (steering angle, steering wheel angle θsw or steering wheel rudder angle δfa) is “0 (steering neutral position until time p2; Corresponding to the vehicle's straight travel) ", and then reaches a steady value. At this time, the steering speed dSa (the steering angular speed, the time differential value of the steering amount) rises from “0” at time p0, reaches the maximum value (peak value) dSap at time p1, and becomes “0” at time p2. Return to.

  In J-turn steering, there is a low possibility that the stability of the vehicle in yawing motion (called yawing stability) will be impaired. However, when the road surface friction coefficient is high, the stability of the vehicle (referred to as rolling stability) in rolling motion may decrease.

  FIG. 3B is called lane change steering, and is continuously performed after a steering wheel operation is suddenly performed in one direction (that is, one of the left direction and the right direction, for example, the left steering direction). In this case, the steering wheel operation is performed in the other direction opposite to the one direction (that is, the other of the left direction and the right direction, for example, the right steering direction). At time q0, the steering operation by the driver is started in one direction (one steering direction). The steering amount (steering angle) Saa is increased from “0 (neutral position of steering, corresponding to straight traveling of the vehicle)” to one steering direction until time q1, and toward “0” after time q1. Returned. Further, the steering operation is started in the other direction (other steering direction) continuously at time q2. The steering amount Saa is increased from “0” to the other steering direction from time q2 to time q3, is returned toward “0” after time q3, and becomes “0” again at time q4. Here, an operation that is steered in one direction first is referred to as “first steering”, and an operation that is steered in the other direction continuously after this “first steering” is referred to as “second steering”. A continuous steering operation when the first steering and the second steering are performed is referred to as “transient steering”. Further, when the steering amount Saa moves away from “0 (steering neutral position)” (when the magnitude (absolute value) of the steering amount Saa increases), the steering amount Saa is “0 (steering). The case of approaching the “neutral position” (when the magnitude (absolute value) of the steering amount Saa decreases) is referred to as “returning” steering.

  In transient steering (for example, lane change steering) in which the steering amount continuously increases / decreases, when the first steering is switched back (from time q1 to time q2), or when the second steering is switched back (from time q2 to time) When the steering speed dSa in q3) is large, the yawing stability is likely to be impaired. This tendency is particularly noticeable when the road surface friction coefficient is low. That is, in low road surface friction, yawing stability may be impaired even when the steering speed dSa is relatively small. On the other hand, when the first steering is performed relatively slowly after the first steering is performed as indicated by the broken line in FIG. 3B, the second steering is not performed (that is, the transient steering is not performed). If it is not performed), even if the sudden steering is performed when the first steering is increased, the possibility that the yawing stability is lowered is low.

  FIG. 4 is a functional block diagram showing an example of arithmetic processing of the vehicle motion control apparatus in the present embodiment. The subscript [**] attached to the end of various symbols indicates whether the various symbols are related to any of the four wheels. “F” is the front wheel, “r” is the rear wheel, “m” is the right wheel with respect to the vehicle traveling direction, “h” is the left wheel, “o” is the outer wheel (outer wheel) with respect to the turning direction, “i” "Indicates an inner wheel (inner ring). Therefore, “fh” indicates the left front wheel, “fm” indicates the right front wheel, “rh” indicates the left rear wheel, and “rm” indicates the right rear wheel. “Fo” is the outer front wheel (outer front wheel), “fi” is the inner front wheel (inner front wheel), “ro” is the outer rear wheel (outer rear wheel), and “ri” is the inner rear wheel (inner). Rear wheel). Further, the turning direction of the vehicle may be rightward or leftward. They are generally given positive and negative signs, for example, the left direction is represented as a positive sign and the right direction is represented as a negative sign. Further, the acceleration / deceleration of the vehicle is generally given a positive / negative sign, for example, acceleration is expressed as a positive sign and deceleration is expressed as a negative sign. However, when describing the magnitude relationship of the values or the increase / decrease in the values, it becomes very complicated when the sign is taken into account. Therefore, unless there is a particular limitation, it represents the magnitude relationship between the absolute values and increases / decreases in the absolute values, and the predetermined value is a positive value.

  In the steering amount acquisition calculation block (corresponding to the steering amount acquisition means) SAA, the steering amount (for example, steering angle) Saa of the steering operation member SW operated by the vehicle driver is acquired. Specifically, the steering amount Saa is calculated based on a signal (steering wheel angle θsw which is the rotation angle of the steering wheel SW) detected by the steering wheel angle sensor SA. Further, it can be calculated based on the front wheel steering angle δfa detected by the front wheel steering angle sensor FS. That is, the steering amount (steering angle) Saa can be calculated based on at least one of the steering wheel angle θsw and the front wheel steering angle δfa.

  In a steering speed acquisition calculation block (corresponding to a steering speed acquisition means) DSA, a steering speed (for example, steering angular speed) dSa that is an operation speed of the steering operation member SW operated by the driver of the vehicle is acquired. The steering speed dSa can be calculated based on the steering amount Saa by time differentiation.

  In a wheel speed acquisition calculation block (corresponding to a wheel speed acquisition means) VWA, a wheel speed Vwa [**] that is a rotation speed of each wheel WH [**] is acquired. Specifically, the wheel speed Vwa [**] is calculated based on the detection result of the wheel speed sensor WS [**].

  In a turning amount acquisition calculation block (corresponding to a turning amount acquisition means) TCA, a turning amount Tca that is a state amount indicating the degree (size) of the turning state of the vehicle is acquired. As the turning amount Tca, a value corresponding to the lateral acceleration of the vehicle (a value corresponding to the lateral acceleration) can be calculated. The lateral acceleration equivalent value reflects the influence of the road surface friction coefficient. By using the lateral acceleration equivalent value, braking control according to the road surface condition can be performed. Specifically, the lateral acceleration (actual lateral acceleration) Gya detected by the lateral acceleration sensor GY is acquired as the turning amount Tca. Further, based on the yaw rate Yra detected by the yaw rate sensor YR (by multiplying the yaw rate Yra by the vehicle speed Vxa), the calculated lateral acceleration Gye can be calculated as the turning amount Tca. Here, the vehicle speed Vxa can be calculated based on the detection result (wheel speed Vwa [**]) of the wheel speed acquisition means VWA (for example, the wheel speed sensor WS [**]).

  In a braking operation amount acquisition calculation block (corresponding to a braking operation amount acquisition means) BSA, an operation amount Bsa of a braking operation member (for example, a brake pedal) BP of the vehicle operated by the driver is acquired.

  Steering amount Saa, steering speed dSa, turning amount Tca (for example, lateral acceleration Gya, yaw rate Yra), vehicle speed Vxa (= vehicle speed Vso), wheel speed Vwa [**], and braking operation amount Bsa are communication buses. It can be calculated based on sensor values obtained via CB and / or internal calculated values in other systems.

  In the braking control calculation block (corresponding to the control means) CTL, the steering state (for example, the steering amount Saa, the steering speed dSa) of the steering operation member SW operated by the vehicle driver, and the degree of the turning motion of the vehicle are determined. A target value Pwt [**] of braking control (simply referred to as braking control) in which the braking torque of each wheel is increased based on at least one of the represented turning amount Tca (for example, lateral acceleration Gya, yaw rate Yra). Calculated. That is, the target braking torque Pwt [**] of each wheel is calculated based on at least one of the turning amount Tca, the steering speed dSa, and the steering amount Saa. The target braking torque Pwt [**] is calculated as “0” when the turning amount Tca (or the steering speed dSa, the steering amount Saa) is less than the predetermined value pr1, and the turning amount Tca (or the steering speed dSa, When the steering amount Saa) is greater than or equal to the predetermined value pr1, the calculation is performed so as to increase as the turning amount Tca (or the steering speed dSa, the steering amount Saa) increases. Further, the target braking torque Pwt [**] can be calculated by combining a plurality of state quantities among the turning amount Tca, the steering speed dSa, and the steering amount Saa. For example, when the state quantity combining the turning amount Tca and the steering speed dSa is less than a predetermined value pr1, Pwt [**] = 0 is calculated, and when the state quantity is the predetermined value pr1 or more, the state quantity is calculated. The target braking torque Pwt [**] is calculated so as to increase with increasing. Further, the target braking torque Pwt [**] increases stepwise to the predetermined value plm when the turning amount Tca or the like is equal to or larger than the predetermined value pr1 instead of the characteristic of gradually increasing as the turning amount Tca or the like increases. Thus, the target braking torque Pwt [**] can be calculated (see the characteristics of the one-dot chain line in the figure).

  Slip suppression control calculation block (corresponding to suppression means) ASL, Slip suppression control (anti-slip in the rotational direction, also referred to as the front and rear slip) based on the wheel speed Vwa [**] Skid control) is executed. The slip suppression control calculation block ASL includes a front / rear slip amount calculation block SLP, a threshold slip amount setting calculation block TSP, and each wheel control mode calculation block MOC.

  In the front / rear slip amount calculation block SLP, the vehicle body speed Vso is calculated using a known method based on the rotational speed Vwa [**] of each wheel. Then, the front / rear slip amount (slip speed) Slp [**] of each wheel is calculated as a deviation (= Vso−Vwa [**]) between the vehicle body speed Vso and the wheel speed Vwa [**]. Further, a slip ratio (= {Vso−Vwa [**]} / Vso) is calculated by dividing the slip speed by the vehicle body speed Vso, and this slip ratio can be used as the front / rear slip amount Slp [**].

  In the threshold slip amount setting calculation block TSP, the threshold slip amount Tsp of each wheel can be calculated. The threshold slip amount Tsp is a control threshold value for front-rear slip for executing slip suppression control (anti-skid control), and can be set independently for each wheel. The threshold slip amount Tsp is increased from the predetermined value ts1 to the predetermined value ts2 when an increase in braking torque based on the turning amount Tca or the like is started. Here, the predetermined value ts1 is a threshold slip amount of the slip suppression control when braking control (braking torque increase) is not performed, and the predetermined value ts2 is a value larger than the predetermined value ts1.

  The threshold slip amount Tsp can be set based on the steering amount Saa. When the steering amount Saa is less than the predetermined value sa1, the threshold slip amount Tsp is set to the predetermined value ts1, and when the steering amount Saa is equal to or greater than the predetermined value sa1, the threshold value gradually increases from the predetermined value ts1 to the predetermined value ts2 as the steering amount Saa increases. The threshold slip amount Tsp is calculated so as to increase. Further, when the steering amount Saa is less than the predetermined value sa1, the threshold slip amount Tsp is set to the predetermined value ts1, and when the steering amount Saa is equal to or larger than the predetermined value sa1, the predetermined value ts1 is stepped from the predetermined value ts2. The threshold slip amount Tsp can be calculated so as to increase (see the characteristics of the alternate long and short dash line in the figure). The threshold slip amount Tsp can be set based on the turning amount Tca instead of the steering amount Saa. In this case, the threshold slip amount Tsp is set in accordance with the same characteristics as those based on the steering amount Saa.

  In each wheel control mode calculation block MOC, the front / rear slip amount Slp [**] calculated by the front / rear slip amount calculation block SLP and the threshold slip amount Tsp set by the threshold slip amount setting calculation block TSP are The target braking torque Pwt [**] is adjusted by the comparison. If the slip suppression control has not yet started and the front / rear slip amount Slp [**] is equal to or less than the threshold slip amount Tsp, the target braking torque Pwt [**] is not adjusted and the target value Pws [* *], The target braking torque Pwt [**] is output as it is. When the front / rear slip amount Slp [**] exceeds the threshold slip amount Tsp, slip suppression control is started and the target braking torque Pwt [**] is adjusted to decrease. That is, the “reduction mode” of the braking torque is selected, the target braking torque Pwt [**] is reduced, and the target braking torque Pws [**] adjusted by the slip suppression control is calculated. When the braking torque decreases, the front / rear slip amount Slp [**] decreases, and when the front / rear slip amount Slp [**] falls below the threshold slip amount Tsp, the target braking torque Pwt [**] is adjusted to increase. The That is, the “increase mode” of the braking torque is selected, the target braking torque Pwt [**] is increased, and the target braking torque Pws [**] adjusted by the slip suppression control is calculated. The “decrease mode” and the “increase mode” are repeatedly selected until the slip suppression control satisfies the end condition.

  In the slip suppression control calculation block ASL, when the braking torque is increased according to at least one of the steering state of the steering operation member SW (for example, the steering speed dSa) and the turning amount Tca of the vehicle, The threshold slip amount of the suppression control is increased. For this reason, larger front / rear slips are allowed than when normal slip suppression control is executed, excessive wheel lateral force is suppressed, vehicle stability (especially yawing stability) is maintained, and at least necessary for emergency avoidance. The wheel lateral force can be secured.

  Based on the target braking torque Pws [**], the braking means MBR controls the driving means of the brake actuator BRK (for example, the electric motor for driving the hydraulic pump, the driving means for the solenoid valve), and the braking torque of the wheels. Is increased. When the driver is operating the braking operation member BP, the braking torque by the braking control is increased with respect to the braking torque corresponding to the operation amount. When the driver is not performing a braking operation, the braking torque is increased from “0” by the braking control.

  A sensor (for example, a pressure sensor PW [**]) that detects an actual value Pwa [**] of the braking torque corresponding to the target value Pws [**] of the braking torque may be provided on the wheel. Based on the target value Pws [**] and the actual value Pwa [**], the driving means can be controlled so that the actual value Pwa [**] matches the target value Pws [**].

  In the slip suppression control calculation block ASL, the threshold slip amount of the front outer wheel that is the front wheel outside the turning of the vehicle is increased from the initial value, and the threshold slip amount of the front inner wheel that is the front wheel inside the turning of the vehicle is the initial value. Is retained. Further, the threshold slip amount of the rear wheel is also maintained at the initial value. In the turning motion, the generated force of the front wheels is dominant. Therefore, the threshold slip amount of the front outer wheel where the ground contact load increases due to load movement caused by turning can be increased, and the generation of excessive wheel lateral force can be suppressed. Furthermore, a yawing moment that stabilizes the vehicle may be generated due to a difference in braking force between the front outer wheel and the front inner wheel.

  In the braking control calculation block CTL, the target braking torque Pwt [f *] for the front wheels is increased, but the target braking torque Pwt [r *] for the rear wheels can be invalidated (Pwt [r *] = 0). . That is, the braking torque of the front wheels is increased, and the braking torque of the rear wheels is not increased (the braking torque before the braking control is executed is held). The front wheel lateral force is reduced by the increase of the braking torque of the front wheels, and the rear wheel braking torque is not increased (maintained) and the rear wheel lateral force is secured, so that the stability of the vehicle can be secured.

  FIG. 5 is a functional block diagram showing another example of calculation processing for the slip suppression control calculation block ASL. This calculation processing example is different from the calculation processing example of the slip suppression control calculation block ASL shown in FIG. 4 in the following points. The first difference is that the threshold value of the slip suppression control is set in two stages, and the second difference is that the front-rear slip amount Slp [**] is not directly calculated and is calculated from the vehicle body speed Vso. The threshold speed is subtracted to set the reference speed. Based on the comparison result between this reference speed and the actual wheel speed Vwa [**], the braking torque increase / decrease mode of each wheel (control mode) Is to be determined.

  In the vehicle body speed calculation block VSO, a vehicle body speed (vehicle speed) Vso is calculated by a known method based on the wheel speed Vwa [**] of each wheel. In the wheel acceleration calculation block DVW, the wheel acceleration dVw [**] is calculated by a known method based on the wheel speed Vwa [**] of each wheel.

  In the threshold slip amount setting calculation block TSQ, as in the threshold slip amount setting calculation block TSP, the threshold slip amount when the braking torque increase corresponding to the turning amount Tca is executed is calculated. In the threshold slip amount setting calculation block TSQ, the threshold value for the slip suppression control is set at two levels of the first and second threshold slip amounts Sp1 and Sp2. The first threshold slip amount Sp1 and the second threshold slip amount Sp2 have a relationship of Sp1 <Sp2, and increase from the predetermined values sp11 and sp21 to the predetermined values sp12 and sp22, respectively, when the braking torque increase is started. Is done. Here, the predetermined values sp11 and sp21 are the threshold slip amounts of the slip suppression control when braking control (braking torque increase) is not performed, and the relationship is sp11 <sp21. The predetermined value sp12 is a value larger than the predetermined value sp11, and the predetermined value sp22 is a value larger than the predetermined value sp21.

  Further, the first and second threshold slip amounts Sp1, Sp2 can be set based on the steering amount Saa (or the turning amount Tca). When the steering amount Saa (or the turning amount Tca) is less than the predetermined value sa1, the threshold slip amounts Sp1 and Sp2 are set to the predetermined values sp11 and sp21, and the steering amount Saa (or the turning amount Tca) is set to the predetermined value sa1. As described above, the threshold slip amounts Sp1 and Sp2 are calculated so as to increase from the predetermined values sp11 and sp21 as the steering amount Saa (or the turning amount Tca) increases. When the steering amount Saa (or the turning amount Tca) is less than the predetermined value sa1, the threshold slip amounts Sp1 and Sp2 are set to the predetermined values sp11 and sp21, and the steering amount Saa (or the turning amount Tca) is predetermined. When the value is greater than or equal to sa1, the threshold slip amounts Sp1 and Sp2 can be calculated so as to increase stepwise from the predetermined values sp11 and sp21 to the predetermined values sp12 and sp22 (see the characteristics of the one-dot chain line in the figure). In addition, the magnitude relationship of each value exists in Sp1 <Sp2, sp11 <sp21, and sp12 <sp22.

  The first and second threshold slip amounts Sp1 and Sp2 are subtracted from the vehicle body speed Vso to calculate slip suppression control reference speeds (threshold values) van (= Vso-Sp1) and vah (= Vso-Sp2), respectively. Is done. The threshold slip amounts Sp1, Sp2 are front and rear slip amounts (slip speeds) for determining the reference speeds van, vah at the wheel speed. The wheel speed Vwa [**] is compared with the reference speeds van and vah. Further, the wheel acceleration dVw [**] is compared with the reference accelerations (threshold values) ga1 and ga2. The reference accelerations ga1 and ga2 are predetermined values set in advance and have a relationship of ga1 <ga2. A control map shown in each wheel control mode calculation block MOD is referred to, and a control mode (increase mode or decrease mode) is selected based on the magnitude relationship between them. For example, when the wheel speed Vwa [**] is less than the reference speed van and greater than or equal to the reference speed vah, and the wheel acceleration dVw [**] is less than the reference acceleration ga1, the braking torque is reduced. Mode "is selected.

  In each wheel control mode calculation block MOD, a control mode of slip suppression control (anti-skid control) of each wheel is determined, and a final target braking torque Pws [**] is calculated. The control mode is determined in order to adjust the target braking torque Pwt [**]. The control mode includes an “increase mode (indicated by“ increase ”” in the control map) in which the braking torque is increased and a “decrease mode (indicated by“ decrease ”in the control map)” in which the braking torque is decreased. . It should be noted that the amount of braking torque decrease differs in the control modes indicated by “decrease (A)” and “decrease (B)” on the control map. The braking torque reduction amount of “decrease (B)” is larger than the reduction amount of “decrease (A)”.

  When the “decrease mode” is selected, the target braking torque Pws [**] is calculated by adjusting the previous value Pws [**] in the calculation process so as to decrease. When the “increase mode” is selected, the target braking torque Pws [**] is calculated by adjusting so as to increase from the previous value of the target braking torque Pws [**].

  In the threshold slip amount setting calculation block TSQ, slip suppression is performed when braking control is performed in which the braking torque is increased according to at least one of the steering state of the steering operation member SW and the turning amount Tca of the vehicle. The control threshold slip amounts Sp1, Sp2 are increased. During sudden steering where the slip angle of the wheel suddenly increases, the wheel becomes difficult to roll. Therefore, when normal slip suppression control (control in which the threshold slip amount is not increased) is executed, braking by braking control is performed. The torque increase may be insufficient. When the braking control is performed, the threshold slip amount (threshold value) of the slip suppression control is increased. Therefore, even if the slip suppression control is executed due to the increase of the braking torque by the braking control, an appropriate braking torque is ensured. obtain.

  With reference to FIG. 6, an example of calculation processing in the braking control calculation block CTL will be described.

  In the transient steering determination calculation block KAT, it is determined whether or not the steering operation state is a transient steering state (a steering operation state in which the steering amount of the steering operation member is continuously increased or decreased). Here, the transient steering state is a state of a steering operation that fluctuates when transitioning from a steady steering state where the steering amount is constant to another steady steering state. For example, in the transient steering state, the steering direction continuously changes from side to side. In the transient steering discrimination calculation block KAT, a first state (transient steering non-discrimination state) in which the transient steering state is not discriminated is set as an initial state. Then, a second state (transitional steering determination state) in which the transient steering state is determined based on the steering amount Saa is determined.

  The transient steering discrimination calculation block KAT includes a steering direction calculation block DSTR and a steering state determination block KTI. In the steering direction calculation block DSTR, based on the steering amount Saa, the steering direction Dstr is one direction (that is, one of the left direction and the right direction) or the other direction (that is, the left direction and the right direction). Is the other of the two directions different from the one direction). Specifically, any one of the straight traveling direction, the left steering direction, and the right steering direction is calculated as the steering direction Dstr. For example, the steering direction Dstr is determined based on the absolute value and sign of the steering amount Saa. When the absolute value of the steering amount Saa is less than the predetermined value saa0 (a value near zero), the straight traveling direction is determined as the steering direction Dstr. When the absolute value of the steering amount Saa is equal to or greater than the predetermined value saa0 and the sign of the steering amount Saa is a positive sign (+), the left steering direction (corresponding to the left turn of the vehicle) is determined as the steering direction Dstr. . When the absolute value of the steering amount Saa is equal to or greater than the predetermined value saa0 and the sign of the steering amount Saa is negative (−), the right steering direction (corresponding to the right turn of the vehicle) is determined as the steering direction Dstr. The

  In the steering state determination block KTI, a transient steering state (a steering operation state in which increase or decrease of the steering amount is continuously performed) is determined based on the steering direction Dstr. That is, one of the first state and the second state is selected. The determination result is output as a control flag Kat. When it is determined that the steering direction Dstr is one direction (for example, the left direction), the transient steering state is not determined and Kat = 0 is output. When the steering direction Dstr is determined to be one direction (for example, the left direction) and then continuously determined to be the other direction (for example, the right direction), the transient steering state is determined and Kat = 1 is output. Specifically, after the steering direction Dstr is calculated as one direction, it is calculated as the other direction, and the time (transition time) required for transition from one direction of the steering direction Dstr to the other direction is a predetermined time (predetermined value). When it is less than tka0, the transient steering state is determined. In the steering state determination block KTI, the first state (Kat = 0) is set as the initial state of the determination result. Further, when the steering direction Dstr is a straight traveling direction, the first state (Kat = 0) is determined unless the steering direction Dstr is a transition from one direction to the other direction and the transition time is less than tka0. Is done.

  The transient steering determination calculation block KAT is configured by a switch-over / switchback steering identification calculation block (identification calculation block) SJH and a steering state determination block KTI instead of the steering direction calculation block DSTR. In the identification calculation block SJH, based on the steering amount Saa, it is identified whether the steering state is holding steering, additional steering, or switching back steering. Here, “holding steering” is a state in which the steering amount Saa is substantially constant. Further, the “increase state” is a state in which the steering amount Saa is increased (a state in which the steering amount Saa is moved away from the steering neutral position), and the “return state” is a state in which the steering amount Saa is decreased (the steering amount). Saa is approaching the steering neutral position). The steering state identification result Sjh is output to the steering state determination block KTI.

  In the steering state determination block KTI, the transient steering state is determined based on the discrimination result Sjh of the additional steering and the return steering. That is, one of the first state and the second state is selected. The determination result is output as a control flag Kat. As a determination result, the first state (Kat = 0) is set as an initial state. When the identification result Sjh is shifted from holding steering or holding steering to transition to steering, the transient steering state is not discriminated and Kat = 0 is output. Then, when the identification result Sjh increases and transitions continuously from steering to return steering, the transient steering state is determined and Kat = 1 is output. Here, “continuously” refers to a case where the time for transition from the additional steering to the switchback steering (referred to as the transition time as in the case of determination based on the steering direction Dstr) is less than the predetermined time (predetermined value) tka1. Say. For example, after the steering amount Saa continues to be substantially constant (a value in a predetermined range that is ± saa1 (predetermined value)) for a predetermined time (predetermined value) tsa1 or more (after holding steering), the steering amount Saa is If it increases, the first state (Kat = 0) is determined. The second state (Kat = 1) is determined when the steering amount Saa continuously decreases after the steering amount Saa has increased. The transient steering state can be determined not only in the case of additional steering / return steering from the straight traveling state but also in the case of additional steering / return steering from the steady turning state.

  Holding steering, additional turning steering, and switching back steering can be identified based on the sign of the steering speed dSa. After the steering speed dSa continues below the predetermined speed (predetermined value) dsa0 for a predetermined time (predetermined value) tsa2 (after holding steering), the steering speed dSa is equal to or higher than the predetermined speed dsa0 (positive increase) In the case of steering), the first state (Kat = 0) is determined. When the steering speed dSa is equal to or higher than the predetermined speed dsa0 (positive steering), the second state (when the steering speed dSa is continuously equal to or lower than the predetermined speed -dsa0 and is negative (switchback steering)). Kat = 1) is determined. Here, “continuously” means that, as described above, the transition from the additional steering to the switching back steering is made within the transition time less than the predetermined time (predetermined value) tka2.

  In the steering state determination block KTI, the transient steering state can be determined based on the steering direction Dstr and / or the increase / return identification result Sjh. The determination reliability can be improved by a plurality of transient steering determinations. In the transient steering discrimination calculation block KAT, transient steering discrimination is performed based on at least one of the steering amount Saa and the steering speed dSa.

  In the reference amount calculation block TRF, the reference amount Trf (Trf1, Trf2) is calculated based on the control flag Kat and the steering speed dSa using the calculation map. In the case of Kat = 0 (first state), as indicated by the characteristic Chc1, when the steering speed dSa is less than the predetermined speed ds1, the first reference amount Trf1 is calculated as the predetermined amount tr1, and the steering speed dSa is set to the predetermined speed ( When the steering speed dSa is greater than or equal to the predetermined value) ds1 and less than the predetermined speed (predetermined value) ds2, the first reference amount Trf1 is calculated to decrease as the steering speed dSa increases. The amount Trf1 is calculated to be a predetermined amount tr2. In the case of Kat = 1 (second state), instead of the first reference amount Trf1, the second reference amount Trf2 is set when the steering speed dSa is less than the predetermined speed ds1, as indicated by a characteristic Chc2 smaller than the characteristic Chc1. A predetermined amount tr3 (<tr1) is calculated. When the steering speed dSa is equal to or higher than the predetermined speed ds1 and lower than the predetermined speed ds2, the second reference amount Trf2 is calculated to decrease as the steering speed dSa increases, and the steering speed dSa is calculated. Is equal to or greater than the predetermined speed ds2, the second reference amount Trf2 is calculated as the predetermined amount tr4 (<tr2). The second reference amount Trf2 (reference amount Trf in the second state) is always calculated to be smaller than the first reference amount Trf1 (reference amount Trf in the first state) regardless of the value of the steering speed dSa. From the reference amount calculation block TRF, when Kat = 0, the first reference amount Trf1 is output to the target control torque calculation block PWT, and when Kat = 1, the second reference amount Trf2 is output to the target control torque calculation block PWT. Is output.

  Further, instead of determining the second reference amount Trf2 based on the calculation map for the steering speed dSa, the second reference amount Trf2 can be calculated as a value smaller than the first reference amount Trf1 by a predetermined value trf0. That is, the second reference amount Trf2 is determined by Trf2 = Trf1-trf0. At this time, since the first reference amount Trf1 is calculated based on the steering speed dSa, the second reference amount Trf2 is indirectly calculated based on the steering speed dSa.

  In the target control torque calculation block PWT, the target braking torque Pwt [**] is calculated based on the turning amount Tca and the reference amount Trf (Trf1, Trf2). When Kat = 0 (when transient steering is not determined), the turning amount Tca is compared with the first reference amount Trf1. When the turning amount Tca is equal to or less than the first reference amount Trf1, the target braking torque Pwt [**] is calculated as “0”, and the target braking torque Pwt [**] is not increased. When the turning amount Tca exceeds the first reference amount Trf1, the target braking torque Pwt [**] increases as the deviation ΔTc (= Tca−Trf1) between the turning amount Tca and the first reference amount Trf1 increases. To increase the target braking torque Pwt [**]. When Kat = 1 (when determining the transient steering), the turning amount Tca is compared with the second reference amount Trf2. When the turning amount Tca is equal to or smaller than the second reference amount Trf2, the target braking torque Pwt [**] is calculated as “0”, and the target braking torque Pwt [**] is not increased. When the turning amount Tca exceeds the second reference amount Trf2, the target braking torque Pwt [**] increases as the deviation ΔTc (= Tca−Trf2) between the turning amount Tca and the second reference amount Trf2 increases. To increase the target braking torque Pwt [**]. An upper limit value pw1 can be set for the target braking torque Pwt [**].

  In the reference amount calculation block TRF, the reference amount Trf (Trf1, Trf2) can be calculated based on the peak value (peak steering speed) dSap of the steering speed instead of the steering speed dSa. In this case, the steering speed peak value storage calculation block steering speed peak value storage calculation block DSAP calculates the peak steering speed dSap based on the steering speed dSa. Specifically, the peak steering speed dSap [n-1] until the previous calculation cycle is stored, and the peak value dSap [n-1] is compared with the steering speed dSa [n] of the current calculation cycle. . The larger value of the peak steering speed dSap [n-1] up to the previous calculation cycle and the steering speed dSa [n] of the current calculation cycle is the peak steering speed dSap [ n] and is stored as a new peak steering speed dSap [n]. The subscript [n-1] represents the previous operation cycle, and the subscript [n] represents the current operation cycle. For example, referring to FIG. 3A, the steering speed dSa for each control cycle is updated as the peak steering speed dSap until time p1, and the value of the steering speed dSa at time p1 (point P) is peak steering after time p1. Maintained as speed dSap.

  With reference to FIG. 7, another calculation processing example in the braking control calculation block CTL will be described. The transient steering determination calculation block KAT is the same as that shown in FIG.

  In the threshold value calculation block SKE, threshold values Stc, Sds, and Sdt are calculated based on the control flag Kat using predetermined values that are preset and stored. In the case of the threshold value (threshold amount) Stc for the turning amount Tca, the first threshold amount (predetermined value) stc1 is set when Kat = 0 (in the first state and when transient steering is not determined). When the threshold value Stc is set and Kat = 1 (when the transient steering is determined in the second state), the second threshold value (predetermined value) stc2 (<stc1) smaller than the first threshold value stc1 Is set as the threshold amount Stc. In the case of the threshold value (threshold speed) Sds for the steering speed dSa, the first threshold speed (predetermined value) sds1 is Sds when Kat = 0 (in the first state when transient steering is not determined). When Kat = 1 (when determining the transient steering in the second state), the second threshold speed (predetermined value) sds2 (<sds1) smaller than the first threshold speed sds1 is set. Set as speed Sds. In the case of the threshold value (threshold change amount) Sdt for the turning change amount dTc, the first threshold change amount (predetermined value) is obtained when Kat = 0 (when the transient state is not determined in the first state). When sdt1 is set as the threshold change amount Sdt and Kat = 1 (when the transient steering is determined in the second state), the second threshold change amount (predetermined value) smaller than the first threshold change amount stc1. ) Sdt2 (<sdt1) is set as the threshold change amount Sdt.

  From the threshold calculation block SKE, the first threshold values stc1, sds1, and sdt1 are output to the target control torque calculation block PWT when Kat = 0, and the second threshold value stc2 when Kat = 1. , Sds2, sdt2 are output to the target control torque calculation block PWT.

  In the target control torque calculation block PWT, based on the turning amount Tca, the steering speed dSa, the turning change amount dTc, and the respective threshold values (threshold amount Stc, etc.) for each state quantity (turning amount Tca, etc.). A target braking torque Pwt [**] is calculated. The target braking torque calculation block PWT includes a control execution determination unit and a braking torque increase amount setting unit. In the braking torque increase amount setting unit, the braking torque amount Pwt [**] to be increased is calculated and set. The control execution determination unit determines whether or not the braking torque increase amount Pwt [**] is output. That is, the control execution determination unit determines whether braking control is possible. The target braking torque Pwt [**] is output as “0” when the control execution determination unit determines that it is valid (control permission) and determines that it is invalid (control prohibition). The braking torque is not increased.

  In the braking torque increase amount setting unit, a braking torque increase amount Pwt [**] is calculated based on the turning amount Tca. Specifically, the target braking torque Pwt [**] is calculated so as to increase as the turning amount Tca increases. An upper limit value pw1 can be set for the target braking torque Pwt [**].

  Further, the target braking torque Pwt [**] can be calculated based on a deviation ΔTc between the turning amount Tca and the threshold amount Stc (stc1, stc2). When Kat = 0 (when transient steering is not determined), the turning amount Tca and the first threshold amount stc1 are compared. When the turning amount Tca is equal to or less than the first threshold amount stc1, the target braking torque Pwt [**] is calculated as “0”, and the target braking torque Pwt [**] is not increased. When the turning amount Tca exceeds the first threshold amount stc1, the target braking torque Pwt [**] increases as the deviation ΔTc (= Tca−stc1) between the turning amount Tca and the first threshold amount stc1 increases. The target braking torque Pwt [**] is increased. When Kat = 1 (when determining the transient steering), the turning amount Tca and the second threshold amount stc2 are compared. When the turning amount Tca is less than or equal to the second threshold amount stc2, the target braking torque Pwt [**] is calculated as “0”, and the target braking torque Pwt [**] is not increased. When the turning amount Tca exceeds the second threshold amount stc2, the target braking torque Pwt [**] increases as the deviation ΔTc (= Tca−stc2) between the turning amount Tca and the second threshold amount stc2 increases. The target braking torque Pwt [**] is increased. Similarly, an upper limit value pw1 can be set for the target braking torque Pwt [**].

  The control execution determination unit performs braking based on the comparison result between the turning amount Tca and the threshold amount Stc, the comparison result between the steering speed dSa and the threshold speed Sds, and the comparison result between the turning change amount dTc and the threshold change amount Sdt. It is determined whether control can be executed. When Kat = 0 (when transient steering is not determined), the turning amount Tca and the first threshold amount stc1, the steering speed dSa and the first threshold velocity sds1, and the turning change amount dTc and the first threshold change The quantity sdt1 is compared. When all of Tca> stc1, dSa> sds1, and dTc> sdt1 are satisfied, control execution is permitted (valid state), and the target calculated by the braking torque increase amount setting unit from the target braking torque calculation block PWT. The braking torque Pwt [**] is output. However, if at least one of these three conditions is not satisfied, control execution is prohibited (invalid state), and the target braking torque Pwt [**] is not output from the target braking torque calculation block PWT (Pwt [ **] = 0). When Kat = 1 (when determining the transient steering), the turning amount Tca and the second threshold amount stc2, the steering speed dSa and the second threshold speed sds2, and the turning change amount dTc and the second threshold change amount. sdt2 is compared. When all of Tca> stc2, dSa> sds2, and dTc> sdt2 are satisfied, control execution is permitted (valid state), and the target calculated by the braking torque increase amount setting unit from the target braking torque calculation block PWT. The braking torque Pwt [**] is output. However, when at least one of the above three conditions is not satisfied, control execution is prohibited (invalid state), and the target braking torque Pwt [**] is not output from the target braking torque calculation block PWT (Pwt [ **] = 0). Each threshold has a relationship of stc1> stc2, sds1> sds2, and sdt1> sdt2.

  In the target braking torque calculation block PWT, whether or not control can be executed can be determined based on the peak value (peak steering speed) dSap of the steering speed instead of the steering speed dSa. That is, whether control is possible or not can be determined based on a comparison between the steering speed peak value dSap and the threshold speed Sds. In this case, the steering speed peak value storage calculation block steering speed peak value storage calculation block DSAP calculates the peak steering speed dSap based on the steering speed dSa. Specifically, the peak steering speed dSap [n-1] until the previous calculation cycle is stored, and the peak value dSap [n-1] is compared with the steering speed dSa [n] of the current calculation cycle. . The larger value of the peak steering speed dSap [n-1] up to the previous calculation cycle and the steering speed dSa [n] of the current calculation cycle is the peak steering speed dSap [ n] and is stored as a new peak steering speed dSap [n]. The subscript [n-1] represents the previous operation cycle, and the subscript [n] represents the current operation cycle. For example, referring to FIG. 3A, the steering speed dSa for each control cycle is updated as the peak steering speed dSap until time p1, and the value of the steering speed dSa at time p1 (point P) is peak steering after time p1. Maintained as speed dSap.

  At least one of the adjustment of the threshold speed Sds and the threshold change amount Sdt performed in the threshold value calculation block SKE may be omitted. If this adjustment is omitted, the same threshold value is set when transient steering is not discriminated (Kat = 0) and when discriminating (Kat = 1). Further, the control availability determination based on the comparison between the turning change amount dTc and the threshold change amount Sdt can be omitted.

  FIG. 8 is a control flow diagram for explaining an example of calculation processing in the control execution determination unit of the target braking torque calculation block PWT.

  First, initialization is performed in step S110. Here, the threshold values Stc, Sds, and Sdt are set to the first threshold values stc1, sds1, and sdt1, which are initial values (values when the transient steering state is not determined). In step S120, a sensor value and / or an internal calculation value of another system is read. In step S130, the above-described respective state quantities (such as the turning amount Tca) are calculated.

  In the determination step S140, the state of the steering operation by the driver is a transient steering state (a steering operation state in which the steering amount of the steering operation member is continuously increased or decreased. For example, in the transient steering state, the steering direction Is continuously changing) or not. The transient steering state is determined based on the steering amount Saa. If the transient steering state is not determined in step S140, the calculation process proceeds to step S150. In step S150, threshold amount Stc (threshold value corresponding to turning amount Tca), threshold speed Sds (threshold value corresponding to steering speed dSa), and threshold change amount Sdt (corresponding to turning change amount dTc). Threshold value) is set to the first threshold values stc1, sds1, and sdt1, respectively.

  Next, in steps S160, S170, and S180, it is determined whether or not to execute braking control (increase braking torque) (whether or not to prohibit). In step S160, it is determined whether the turning amount (for example, lateral acceleration) Tca is larger than the first threshold amount dtc1. If Tca> dtc1 and an affirmative determination (Yes) is made in step S160, the arithmetic processing proceeds to step S170. In step S170, it is determined whether the steering speed (for example, the steering angular speed) dSa is greater than the first threshold speed sds1. If dSa> sds1, and an affirmative determination (Yes) is made in step S170, the arithmetic processing proceeds to step S180. In step S180, it is determined whether the turning change amount (for example, yaw angular acceleration) dTc is larger than the first threshold change amount sdt1. If dTc> sdt1, and an affirmative determination (Yes) is made in step S180, the arithmetic processing proceeds to step S190. In step S190, the braking control is enabled, and the target braking torque Pwt [**] calculated by the braking torque increase amount setting unit is transmitted to the braking means MBR.

  If a negative determination (No) is made in at least one of steps S160, S170, and S180, the calculation process proceeds to step S200, the braking control is disabled, and Pwt [**] = 0.

  When the transient steering state is determined in step S140, the calculation process proceeds to step S210. In step S210, threshold values Stc, Sds, and Sdt are set to second threshold values stc2, sds2, and sdt2, respectively. The second threshold value is smaller than the first threshold value and has a relationship of stc2 <stc1, sds2 <sds1, sdt2 <sdt1.

  As in the case of non-discrimination of transient steering, in steps S220, S230, and S240, it is determined whether or not the brake control (braking torque increase) at the time of discrimination of transient steering is executable. In step S220, it is determined whether the turning amount (for example, lateral acceleration) Tca is larger than the second threshold amount stc2. If Tca> stc2 and the determination is affirmative (Yes) in step S220, the arithmetic processing proceeds to step S230. In step S230, it is determined whether the steering speed (for example, the steering angular speed) dSa is greater than the second threshold speed sds2. If dSa> sds2, and an affirmative determination (Yes) is made in step S230, the arithmetic processing proceeds to step S240. In step S240, it is determined whether the turning change amount (for example, yaw angular acceleration) dTc is larger than the second threshold change amount sdt2. If dTc> sdt2, and an affirmative determination (Yes) is made in step S180, the arithmetic processing proceeds to step S190. In step S190, the braking control is enabled, and the target braking torque Pwt [**] calculated by the braking torque increase amount setting unit is transmitted to the braking means MBR.

  When a negative determination (No) is made in at least one of steps S220, S230, and S240, the calculation process proceeds to step S200, the braking control is disabled, and Pwt [**] = 0.

  At least one of the determination step (S170, S230) for the steering speed dSa and the determination step (S180, S240) for the turning change amount dTc may be omitted. Further, the threshold speed Sds is changed (change from the first threshold speed sds1 to the second threshold speed sds2), and the threshold change amount Sdt is changed (from the first threshold change amount sdt1 to the second threshold change). At least one of the changes to the quantity sdt2) may be omitted. That is, even when determining transient steering, the first threshold speed sds1 is set as the threshold speed Sds and / or the first threshold change amount sdt1 is set as the threshold change amount Sdt. Furthermore, in the determination step (S170, S230) for the steering speed dSa, the steering speed peak value dSap can be used instead of the steering speed dSa.

  FIG. 9 is a time-series diagram for explaining the operation and effect of the vehicle motion control apparatus according to the embodiment of the present invention. Although the description will be given using the calculation processing example of FIG. 6 as the start condition of the braking control (braking torque increase), the same operation and effect are obtained even if other calculation processing examples of FIGS. 7 and 8 are used.

  Until the time (time point) v0 is reached, the steering operation is not performed and the turning amount (state amount indicating the degree of turning motion of the vehicle) Tca is “0 (straight running)”, and the control flag Kat is “0” as an initial value. The first reference amount Trf1, which is a threshold value (reference amount Trf) of the execution condition (for example, start condition) of the braking control (increase of braking torque), is calculated to the maximum value tr1. ing. Further, the threshold slip amount (control threshold value for determining execution of anti-skid control) Tsp of slip suppression control (anti-skid control) is set to a predetermined value ts1 as an initial value (set value before starting braking control). Is set.

  At time v0, the steering operation is started by the driver, and based on the steering speed dSa (or peak steering speed dSap), the first reference amount Trf1 is calculated by being reduced from the predetermined amount tr1 (see the broken line). . At this time, the transient steering determination calculation block KAT continues the state in which the transient steering state is not determined (Kat = 0), and the reference amount calculation block TRF outputs the first reference amount Trf1 as the reference amount Trf. At time v1, transient steering is determined by the transient steering determination calculation block KAT (Kat = 1), and the reference amount Trf output from the reference amount calculation block TRF is changed from the first reference amount Trf1 to the second reference amount Trf2 (< Trf1) is changed (switched). For example, the second reference amount Trf2 can be calculated to a value smaller than the first reference amount Trf1 by a predetermined amount trf0.

  The transient steering state is determined at time v1, and the reference amount Trf is changed to a relatively small value as compared to when the transient steering is not determined. That is, the reference amount Trf is changed from the first reference amount Trf1 to the second reference amount Trf2 (<Trf2). When the turning amount Tca is equal to or less than the reference amount Trf, the braking control is not performed. At the time point v2 when the turning amount Tca exceeds the reference amount Trf (second reference amount Trf2 because it is in a transient steering state), execution of the braking control is started and the braking torque is increased.

  When transient steering is performed, the possibility that the vehicle stability is reduced is higher than when transient steering is not performed. When the transient steering state is determined, the reference amount Trf is changed (adjusted) to a smaller value than when the transient steering state is not determined, so that the stability of the vehicle (particularly yawing stability) is reliably maintained. obtain. Furthermore, since the transient steering state is not discriminated at the time of the additional steering of the first steering, early braking torque increase can be suppressed, and the turning ability of the vehicle (followability of the turning behavior with respect to the steering operation) can be ensured.

  Further, at time v2, the threshold slip amount Tsp of the slip suppression control is changed so as to increase from the initial value ts1 to a predetermined value ts2 (> ts1). When the front / rear slip amount Slp [**] increases as the braking torque increases and exceeds the threshold slip amount Tsp (predetermined value ts2), the increase in the braking torque is suppressed by the slip suppression control.

  The front-rear slip amount of the wheel represents the braking load of the wheel (braking force with respect to the ground load). If a large slip angle (lateral slip amount) occurs in the wheel as in the case of sudden steering in which the wheel slip angle increases rapidly, the wheel becomes difficult to rotate and the front / rear slip amount increases. When braking torque is increased to maintain vehicle stability during sudden steering, the threshold slip amount (threshold) is increased and slip suppression control is executed. Even when the slip suppression control is executed, a sufficiently large front / rear slip is allowed and an appropriate braking torque is applied, so that excessive wheel lateral force is suppressed and vehicle stability is maintained, and at the same time, emergency avoidance is minimized. The necessary wheel lateral force can be ensured.

  In FIG. 9, transient steering is determined and the reference amount Trf is changed from the first reference amount Trf1 to the second reference amount Trf2, and then the braking torque is increased, but the turning amount Tca exceeds the first reference amount Trf1. In some cases, the braking torque can be increased. Also in this case, the threshold slip amount Tsp of the slip suppression control can be changed so as to increase from the initial value ts1 (threshold value when the braking torque increase is not executed) to a predetermined value ts2 (> ts1). As the braking torque increases, the front / rear slip amount Slp [**] increases, and when the threshold slip amount Tsp (predetermined value ts2) is exceeded, the increase in the braking torque is suppressed (limited) by the slip suppression control.

  When the braking torque increase is executed, the threshold slip amounts Tsp, Sp1, Sp2 of the slip suppression control can be increased based on the steering amount Saa. Specifically, the increase amounts of the threshold slip amounts Tsp, Sp1, Sp2 can be determined so as to increase as the steering amount Saa increases. Further, when the braking torque increase is executed, the threshold slip amounts Tsp, Sp1, Sp2 of the slip suppression control can be increased based on the turning amount Tca. Specifically, the increase amounts of the threshold slip amounts Tsp, Sp1, Sp2 can be determined so as to increase as the turning amount Tca increases.

  In the target control torque calculation block PWT, only the braking torque of the front wheels is increased, and the braking torque of the rear wheels is not increased (the braking torque before the braking control is executed is held). That is, in the target braking torque calculation block PWT, the increase amount of the target braking torque Pwt [f *] for the front wheels is calculated, and the target braking torque Pwt [r *] for the rear wheels is set to “0 (hold)”. The front wheel lateral force is reduced by the increase in the braking torque of the front wheels, and the rear wheel braking torque is not increased (retained in the state before the start of the braking control), so that the rear wheel lateral force is secured. Can be secured.

  The threshold slip amount increased in the slip suppression control calculation block ASL can be adjusted separately for each wheel. In the front outer wheel WH [fo], which is a front wheel on the outer side of the turning of the vehicle, the threshold slip amounts Tsp [fo], Sp1 [fo], Sp2 [fo] are increased when the braking torque is increased. On the other hand, the threshold slip amounts Tsp [fi], Sp1 [fi], Sp2 [fi] are set to initial values (in the case where no increase in braking torque is performed) in the front inner wheel WH [fi], which is the front wheel inside the vehicle turning. Threshold).

In the above configuration, the target value Pwt [**] of the braking torque is adjusted by the slip suppression control (anti-skid control), and the new target value Pws [**] is calculated, but the target value Pwt [** ], The actual value Pwa [**] of the braking torque may be controlled by the braking means MBR, and the actual value Pwa [**] may be directly adjusted by the slip suppression control. Also in this case, when the braking control is executed, the threshold slip amounts Tsp, Sp1, Sp2 are increased from the initial values (threshold slip amounts at the time of non-braking control), so the slip suppression control is executed. In some cases, a proper front-rear slip is ensured.
The technical idea that can be grasped from the above embodiment will be added below.
(1)
Based on at least one of braking means for applying a braking torque to the wheels of the vehicle, a steering state of a steering operation member operated by a driver of the vehicle, and a turning amount representing the degree of turning motion of the vehicle, A vehicle motion control device comprising a control means for increasing the braking torque via the braking means, a wheel speed obtaining means for obtaining a wheel speed that is a rotational speed of a wheel of the vehicle, and the wheel speed. And a suppression means for adjusting the braking torque to suppress the front-rear slip amount when the front-rear slip amount of the wheel exceeds the threshold slip amount, and the suppression means includes the The vehicle motion control apparatus according to claim 1, wherein the threshold slip amount is increased when the control means increases the braking torque.
The vehicle motion control apparatus according to the present invention includes braking means (MBR), control means (CTL), wheel speed acquisition means (VWA), and suppression means (ASL). The braking means (MBR) applies a braking torque to the vehicle wheel (WH [**]). The control means (CTL) includes a steering state (Saa, dSa) of a steering operation member (SW) operated by a driver of the vehicle, and a turning amount (Tca) representing a degree of turning motion of the vehicle. Based on at least one, the braking torque (Pwt [**], Pwa [**]) is increased via the braking means (MBR). Hereinafter, the braking control for increasing the braking torque is simply referred to as “braking control”. The wheel speed acquisition means (VWA) acquires a wheel speed (Vwa [**]) that is a rotation speed of the vehicle wheel (WH [**]). The restraining means (ASL) calculates the front / rear slip amount (Slp [**]) of the wheel based on the wheel speed (Vwa [**]), and the front / rear slip amount (Slp [**]) is calculated. When the threshold slip amount (Tsp) is exceeded, the braking torque (Pwt [**], Pwa [**]) is adjusted to suppress the front / rear slip amount (Slp [**]). To do. Further, the suppression means (ASL) increases the threshold slip amount (Tsp) when the control means (CTL) increases the braking torque (Pwt [**], Pwa [**]). Configured.
The braking load of the wheel (braking force with respect to the ground load) is reflected in the front-rear slip amount of the wheel. If a slip angle (lateral slip amount) occurs in the wheel, the wheel becomes difficult to rotate, so the front / rear slip amount increases even with an equivalent braking load. In a sudden steering state in which the wheel slip angle suddenly increases, the steering state (eg, steering amount, steering speed) of the steering operation member (eg, steering wheel) and the turning amount of the vehicle (eg, lateral acceleration, yaw rate) When braking control in which braking torque is increased based on at least one of them (hereinafter simply referred to as braking control) is executed, the threshold slip amount (threshold) is increased and slip suppression control is executed. Therefore, an appropriate braking torque is applied by the braking control, an excessive wheel lateral force is suppressed, and vehicle stability is maintained. In addition, the wheel lateral force necessary for emergency avoidance can be ensured.
(2)
In the vehicle motion control device described in (1), the suppression means increases the threshold slip amount of the front outer wheel that is a wheel on the front side of the turning outer side of the vehicle, and the wheel on the front side of the turning inner side of the vehicle. A motion control apparatus for a vehicle, wherein the threshold slip amount of a certain front inner ring is maintained.
The suppression means (ASL) increases the threshold slip amount (Tsp [fo]) of a front outer wheel which is a front wheel on the outer side of the turning of the vehicle, and the front inner wheel which is a front wheel on the inner side of the turning of the vehicle. The threshold slip amount (Tsp [fi]) may be maintained (maintained).
Since the turning motion of the vehicle is started when a lateral force is generated on the front wheels, the generated force of the front wheels is dominant in the turning motion. The threshold slip amount of the front outer wheel where the ground contact load increases due to the load movement caused by the turning motion of the vehicle is increased, and the generation of excessive wheel lateral force can be suppressed. Further, the threshold slip amount of the front inner wheel where the ground load decreases is maintained (maintained), and a yawing moment that stabilizes the vehicle can be generated due to the braking force difference between the front outer wheel and the front inner wheel.
(3)
The vehicle motion control apparatus according to (1) or (2), further comprising a steering amount acquisition unit that acquires a steering amount of the steering operation member, wherein the suppression unit is configured to perform the threshold based on the steering amount. A vehicle motion control apparatus characterized by increasing a slip amount.
The vehicle motion control apparatus according to the present invention includes a steering amount acquisition means (SAA), and acquires the steering amount (Saa) of the steering operation member (SW). The suppression means (ASL) may be configured to increase the threshold slip amount (Tsp) based on the steering amount (Saa). Specifically, the increase amount of the threshold slip amount (Tsp) is determined to be larger as the steering amount (Saa) is larger, or is determined to be smaller as the steering amount (Saa) is smaller.
The wheel slip angle depends on the magnitude of the steering amount (for example, the steering angle). Therefore, since the threshold slip amount (the increase amount of the threshold slip amount) is determined based on the steering amount, the braking control according to the magnitude of the wheel slip angle can be executed.
(4)
The vehicle motion control device according to any one of (1) to (3), further comprising a turning amount acquisition unit that acquires a turning amount that represents a degree of turning of the vehicle, and the suppression unit is based on the turning amount. A vehicle motion control apparatus characterized by increasing the threshold slip amount.
The motion control apparatus for a vehicle according to the present invention includes a turning amount acquisition means (TCA), and acquires the turning amount (Tca) of the vehicle. The suppression means (ASL) may be configured to increase the threshold slip amount (Tsp) based on the turning amount (Tca). Specifically, the increase amount of the threshold slip amount (Tsp) is determined to be larger as the turning amount (Tca) is larger, or is determined to be smaller as the turning amount (Tca) is smaller.
A road surface condition (for example, a road surface friction coefficient) is reflected in the turning amount of the vehicle. Since the threshold slip amount (an increase amount of the threshold slip amount) is determined based on the turning amount, the braking control according to the road surface state can be executed.
(5)
The vehicle motion control apparatus according to any one of (1) to (4), further comprising a steering amount acquisition unit that acquires a steering amount of the steering operation member, wherein the control unit sets a reference value for the turning amount. When the turning amount exceeds the reference value, the braking torque is increased, and a transient steering state in which the steering amount continuously increases or decreases is determined based on the steering amount, and the transient steering state is determined. A vehicle motion control device, wherein the reference value is changed to a small value in the determination.
The vehicle motion control apparatus according to the present invention includes a steering amount acquisition means (SAA), and acquires the steering amount (Saa) of the steering operation member (SW). The control means (CTL) sets a reference value (Stc, Trf) for the turning amount (Tca), and the turning amount (Tca) exceeds the reference value (Stc, Trf). The braking torque (Pwt [**], Pwa [**]) is increased. Further, the control means (CTL) determines a transient steering state in which the steering amount (Saa) continuously increases or decreases based on the steering amount (Saa). The control means (CTL) is configured to change the reference values (Stc, Trf) to small values (stc2, Trf2) when determining the transient steering state.
Specifically, the control means (CTL) determines the transient steering when it is determined that the direction is the other direction continuously after the direction is determined based on the steering amount (Saa). Determine the state. The control means (CTL) may determine the transient steering state when the steering amount (Saa) continuously decreases after increasing.
The degree to which vehicle stability can be ensured differs depending on the steering state (whether or not it is a transient steering state). Since the turning amount threshold values (first reference value and second reference value) are set according to the steering state, braking control according to the steering state can be performed. Furthermore, since the road surface state (for example, the road surface friction coefficient) is reflected in the turning amount, it is possible to determine whether or not the braking control can be appropriately executed according to the road surface state by setting the reference value of the turning amount.
(6)
The vehicle motion control device according to (5), further comprising a steering speed acquisition unit that acquires a steering speed of the steering operation member, wherein the control unit sets the reference value based on the steering speed. A vehicle motion control device.
The vehicle motion control apparatus according to the present invention includes a steering speed acquisition means (DSA), and acquires the steering speed (dSa) of the steering operation member (SW). The control means (CTL) may be configured to set the reference value (Trf) based on the steering speed (dSa). Specifically, the reference value (Trf) is determined to be smaller as the steering speed (dSa) is larger, or is determined to be larger as the steering speed (dSa) is smaller.
When the road surface friction coefficient is low, a sudden turning motion may not occur even if a sudden steering is performed. Since the reference value of the turning amount is set according to the steering speed, the braking control according to the road surface condition can be performed.
(7)
The vehicle motion control apparatus according to any one of (1) to (6), further comprising: a braking operation amount acquisition unit that acquires a braking operation amount of a braking operation member operated by a driver of the vehicle; The vehicle motion control device increases the braking torque when the braking operation amount is less than or equal to a predetermined operation amount, and holds the braking torque when the braking operation amount is larger than the predetermined operation amount. .
The vehicle motion control apparatus according to the present invention includes a braking operation amount acquisition means (BSA), and acquires a braking operation amount (Bsa) of a braking operation member (BP) operated by a driver of the vehicle. The control means (CTL) increases the braking torque (Pwt [**], Pwa [**]) when the braking operation amount (Bsa) is equal to or less than a predetermined operation amount (predetermined value bsa1), The brake torque (Pwt [**], Pwa [**]) may be held when the brake operation amount (Bsa) is larger than the predetermined operation amount (bsa1).
When the driver is performing a braking operation, braking torque is already applied to the wheels, so braking control is not necessary. Since the braking torque is increased only when the braking operation amount is equal to or less than the predetermined operation amount bsa1 (for example, when bsa1 = 0 and no braking operation is performed), an unnecessary increase in braking torque can be suppressed. .

  VWA: Wheel speed acquisition means, Vwa [**] ... Wheel speed of each wheel, TCA ... Turning amount acquisition means, Tca ... Turning amount, SAA ... Steering amount acquisition means, Saa ... Steering amount, DSA ... Steering speed acquisition means, dSa ... Steering speed, CTL ... Control means (brake control means), MBR ... Braking means, BRK ... Brake actuator, ASL ... Suppression means (slip suppression control), TSP, TSQ ... Threshold slip amount setting calculation, Tsp, Sp1, Sp2 ... Threshold slip amount

Claims (3)

Braking means for applying braking torque to the wheels of the vehicle;
When the driver of the vehicle is not performing a braking operation based on at least one of the steering state of the steering operation member operated by the driver of the vehicle and the turning amount representing the degree of the turning motion of the vehicle And a control means for increasing the braking torque via the braking means.
Wheel speed acquisition means for acquiring a wheel speed that is a rotation speed of a wheel of the vehicle;
On the basis of the wheel speeds, without adjusting the braking torque when the front and rear slip amount of the wheel is below a threshold slip amount, wherein when the front and rear slip amount of the wheel exceeds the threshold slip amount And a suppression means for performing slip suppression control that suppresses the front-rear slip amount by adjusting the braking torque to decrease , and
The suppression means is
When the control means does not increase the braking torque, the threshold slip amount is set to an initial value, and when the control means increases the braking torque, the front outer wheel that is the front wheel outside the turning of the vehicle. It said threshold slip amount increased from the initial value, the motion control apparatus for a vehicle, characterized in that for holding the threshold slip amount of the inner ring before the a turning inner front wheel of the vehicle to the initial value. A vehicle motion control device according to claim 1,
A steering amount acquisition means for acquiring a steering amount of the steering operation member;
The vehicle motion control device according to claim 1, wherein the suppression means increases the threshold slip amount based on the steering amount. A vehicle motion control device according to claim 1 or 2, wherein
A turning amount acquisition means for acquiring a turning amount representing a degree of turning of the vehicle;
The vehicle motion control device according to claim 1, wherein the suppression means increases the threshold slip amount based on the turning amount.

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