JP5115276B2 - Vehicle steering control device - Google Patents

Description

  The present invention relates to a vehicle steering control device.

  When oversteer occurs in the turning state of the vehicle, in order to stabilize the vehicle by suppressing the degree of oversteering, the steering wheel (steering wheel) is operated in the direction opposite to the turning direction of the vehicle and the steering wheel is turned in the turning direction of the vehicle. It is effective to steer in the opposite direction. Such an operation of the steering operation member in the direction opposite to the turning direction of the vehicle is also referred to as “counter steer (operation)”. Hereinafter, the steering direction opposite to the vehicle turning direction is also referred to as “countersteer direction”. Specifically, the “countersteer direction” is a direction in which the steering wheel is steered clockwise when viewed from the driver when the vehicle turning direction is left, and viewed from the driver when the vehicle turning direction is right. This is the direction in which the steering wheel is steered counterclockwise.

For this reason, when oversteer occurs, a device is known that applies a stabilizing force (stabilizing torque) for guiding or assisting a driver's countersteer operation to the steering operation member in the countersteer direction. (For example, refer to Patent Document 1).
Japanese Patent No. 3034430

  By the way, a driver who is skilled in counter steer operation (hereinafter referred to as “skilled driver”) can actively perform appropriate counter steer operation while predicting the behavior of the vehicle when oversteer occurs. it can. Therefore, when the skilled driver drives a vehicle equipped with the device described in the above document, if the oversteer occurs, the skilled driver can The counter steer operation is performed while feeling a steering force smaller than (expected) steering force (operation torque, road reaction force). As a result, a problem may arise that the skilled driver feels uncomfortable that the steering force is reduced unexpectedly.

  The present invention has been made in order to cope with the above-described problem. When oversteer occurs, the steering operation member is provided with a stabilizing force (stabilizing torque) for guiding or assisting a driver's countersteer operation. Accordingly, it is an object of the present invention to provide a vehicle steering control device that applies in the counter-steer direction, and that can suppress the “uncomfortable feeling that the steering force is reduced unexpectedly” that a skilled driver learns.

  The vehicle steering control apparatus according to the present invention includes state quantity calculation means, target steering angle calculation means, actual steering angle acquisition means, stabilization force calculation means, and force application means. Hereinafter, these means will be described in order.

  The state quantity calculation means obtains a value corresponding to the yawing motion of the vehicle, and calculates an oversteer state quantity representing the degree of oversteer of the vehicle based on the value corresponding to the yawing motion. The “value corresponding to the yawing motion” is, for example, yaw rate, vehicle body slip angle, vehicle body slip angular velocity, and the like.

  The target rudder angle calculating means calculates a value corresponding to the target rudder angle in the counter steer direction (rather than the neutral position) of the steering wheel of the vehicle for stabilizing the vehicle based on the oversteer state quantity. . The “value corresponding to the target rudder angle” is, for example, the target rudder angle itself, the target operation amount of the steering operation member corresponding to the target rudder angle, or the like. The target rudder angle calculating means calculates, for example, a yawing moment (stabilized yawing moment) in a direction opposite to the vehicle turning direction to be applied to stabilize the vehicle based on the oversteer state quantity. Based on the moment and the (reverse) model related to the yawing motion of the vehicle, the steering angle of the steered wheel necessary for generating the stabilized yawing moment may be calculated, and this steering angle may be set as the target steering angle.

  The actual rudder angle acquisition means acquires a value corresponding to the actual rudder angle of the steered wheel. The “value corresponding to the actual steering angle” is, for example, the actual steering angle itself, the actual operation amount of the steering operation member corresponding to the actual steering angle, or the like.

  The stabilizing force calculating means is a steering operation member that is operated by the driver of the vehicle to steer the steered wheel based on a comparison result between the target rudder angle equivalent value and the actual rudder angle equivalent value. The stabilizing force (stabilizing torque) for guiding or assisting the counter steer operation is calculated. For example, the stabilizing force calculating means zeroes the stabilizing force when a difference between the target rudder angle equivalent value and the actual rudder angle equivalent value (hereinafter referred to as “steer angle deviation”) is less than a threshold value. And when the steering angle deviation is equal to or greater than the threshold, the stabilization force is calculated so that the stabilization force increases (from zero) as the difference increases from the threshold. The

  The force applying means applies the stabilizing force to the steering operation member in a counter steer direction (a direction in which the steered wheels are steered in the counter steer direction).

  According to the above configuration, for example, the smaller the steering angle deviation, the smaller the stabilizing force (stabilizing torque) applied to the steering operation member in the countersteer direction. Here, a small steering angle deviation means that the driver is performing an appropriate counter-steer operation.

  As described above, when the skilled driver is performing an appropriate counter steering operation while predicting the behavior of the vehicle (the higher the achievement level of the counter steering operation), the stabilizing force applied to the steering operation member is small. Become. In other words, the degree to which the steering force (steering torque) is reduced by the stabilizing force is reduced. Therefore, the “uncomfortable feeling that the steering force is reduced unexpectedly” that the skilled driver learns can be suppressed. Further, when the rudder angle deviation is large, that is, when the driver is not performing an appropriate counter steering operation, the stabilizing force is increased. As a result, for a driver who is not a skilled driver, the countersteer operation can be appropriately or sufficiently guided or assisted by a large stabilizing force.

  Next, in the steering control device according to the present invention, in order to suppress oversteer, a target of the braking force to be applied to the front wheels outside the turning of the vehicle in order to stabilize the vehicle based on the oversteer state quantity. Consider a case in which a braking force calculating means for calculating a value and a braking force control means for applying a braking force to the front wheel outside the turn based on the target value of the braking force are provided.

  In this case, the braking force control means does not apply the braking force to the turning outer front wheel when the stabilizing force is zero, and controls the braking outer front wheel when the stabilizing force is greater than zero. It is preferable to be configured to apply power.

  In a vehicle in which a negative kingpin offset is adopted for the steered wheel (front wheel), if braking force is applied to the front outer wheel to suppress oversteer, the turning direction (steering) based on the so-called “torque steer” is applied to the steering operation member. Force in the direction of turning the direction wheel in the turning direction). On the other hand, as described above, the stabilizing force is applied to the steering operation member in the counter steer direction (direction in which the steered wheels are steered in the counter steer direction). Accordingly, in the process of increasing the amount of the oversteer state in the oversteer state, one of “applying the braking force to the front outer turning wheel” and “applying the stabilizing force to the steering operation member” is started before the other. Then, the driver feels “torque steer” caused by “applying the braking force to the front wheels on the outside of the turn”, leading to an uncomfortable feeling to the driver.

  On the other hand, in the above configuration, “applying a braking force to the front outer wheel” can be started when the stabilizing force increases from zero. That is, in the process of increasing the amount of oversteer state in the oversteer state, “applying the braking force to the turning outer front wheel” and “applying the stabilizing force to the steering operation member” can be started simultaneously. As a result, it becomes difficult for the driver to feel “torque steer” due to “applying braking force to the front wheel outside the turn”, and the stabilizing force is applied to the steering operation member without giving the driver a sense of incongruity. can do.

  In this case, the stabilizing force calculating means is configured to calculate the stabilizing force so that the stabilizing force increases stepwise from zero to a predetermined value when the steering angle deviation becomes the threshold value. Is preferable. Here, the predetermined value can be calculated based on at least one of the target value of the braking force and the oversteer state quantity.

  According to this, when the steering angle deviation becomes the threshold value in the process of increasing the amount of oversteer in the oversteer state, as described above, “applying braking force to the front wheel outside the turn” and “applying to the steering operation member” In addition to simultaneously starting the “giving of the stabilizing force”, the stabilizing force is increased stepwise from zero to a predetermined value (> zero) at that time. As a result, the “torque steer” is compensated, and the stabilizing force can be reliably applied in the counter steer direction.

  In the steering control device according to the present invention, the stabilization force calculating means is configured to calculate the stabilization force so that the stabilization force is limited to a predetermined limit value or less. Is preferred.

  According to this, it is possible to suppress the occurrence of a situation where the vehicle fluctuates due to an excessively large value of the stabilizing force and the driver operating the steering operation member excessively in the countersteer direction.

  Embodiments of a vehicle steering control device according to the present invention will be described below with reference to the drawings.

(First embodiment)
FIG. 1 shows a schematic configuration of a vehicle equipped with a steering control device according to a first embodiment of the present invention.

  In the first embodiment, when the steering wheel SW (corresponding to the “steering operation member”) is operated, the rotational motion is transmitted as rotational motion to the pinion gear PN via the steering shaft SH. The rotational movement of the pinion gear PN is converted into the reciprocating movement of the rack RK (movement in the left-right direction of the vehicle body) by the rack RK that is screwed with the pinion gear PN. In response to the movement of the rack RK, the tie rod TR integrated with the rack RK moves in the left-right direction of the vehicle body, whereby the steered wheels (front wheels in this example) WHfl and WHfr are steered. Thereby, the operation angle from the neutral position of the steering wheel SW and the steering angle from the neutral position (straight-running state) of the steered wheels WHfl and WHfr are determined on a one-to-one basis.

  An electric motor Me is connected to the tie rod TR via a speed reducer Ge. The driver's steering wheel operating force (steering torque) is reduced by the driving force of the electric motor Me, and a so-called power steering control (EPS control) function is achieved.

  The brake actuator BRK has a known configuration including a plurality of solenoid valves, a hydraulic pump, an electric motor, and the like. At the time of non-control, the brake fluid pressure corresponding to the operation of the brake pedal BP by the driver is supplied to the wheel cylinder WC ** of each wheel, and the braking torque corresponding to the brake pedal operation is given to each wheel. Wheel cylinder independent of brake pedal operation during braking control such as anti-skid control (ABS control), traction control (TCS control), or vehicle stability control (ESC control) that suppresses vehicle understeer / oversteer The brake fluid pressure in the WC ** is controlled for each wheel, and the braking torque can be adjusted for each wheel. The braking torque may be adjusted using an electric brake device without using the brake fluid pressure.

  In addition, “**” added to the end of various symbols etc. “fl”, “fr” etc. added to the end of various symbols etc. to indicate which wheel the various symbols etc. relate to Is a comprehensive notation. “Fl” indicates the left front wheel, “fr” indicates the right front wheel, “rl” indicates the left rear wheel, and “rr” indicates the right rear wheel. For example, the wheel cylinder WC ** comprehensively indicates a left front wheel wheel cylinder WCfl, a right front wheel wheel cylinder WCfr, a left rear wheel wheel cylinder WCrl, and a right rear wheel wheel cylinder WCrr.

  In the first embodiment, a wheel speed sensor WS ** that detects a wheel speed Vw ** and a steering wheel rotation angle sensor SA that detects a rotation angle (from a neutral position) (steering wheel operation angle θsw) of the steering wheel SW. A steering torque sensor ST that detects the steering torque Tsw of the steering wheel SW by the driver, a yaw rate sensor YR that detects the yaw rate Yr of the vehicle body, a longitudinal acceleration sensor GX that detects the longitudinal acceleration Gx in the vehicle body longitudinal direction, A lateral acceleration sensor GY that detects a lateral acceleration Gy in the lateral direction, a steering angle sensor FS that detects a turning angle δfa from a neutral position of a front wheel (steering wheel), and a wheel cylinder that detects a wheel cylinder pressure Pw ** A pressure sensor PS ** and an electronic control unit (ECU) are provided.

  The ECU is a microcomputer composed of ECUb, ECUe, and ECUs connected to each other via a communication bus CB. The ECU is electrically connected to various actuators such as a brake actuator BRK and the various sensors.

  The ECU b is adapted to execute braking control such as ABS control, TCS control, and ESC control based on signals from the wheel speed sensor WS **, the longitudinal acceleration sensor GX, the lateral acceleration sensor GY, and the like. The ECU e performs control of an engine (not shown). The ECUs execute EPS control based on signals from the steering torque sensor ST and the like.

(Oversteer suppression control)
Next, oversteer suppression control executed by the first embodiment will be described with reference to FIG. In the first embodiment, only steering torque control is executed as oversteer suppression control. Hereinafter, this steering torque control will be described.

  In the steering torque acquisition means A1, the steering torque Tsw (operation force of the steering operation member) of the steering wheel SW by the driver is acquired by the steering torque sensor ST. The EPS torque calculation means A2 calculates a target value Teps of power steering torque (EPS torque) for reducing the driver's steering torque based on the acquired steering torque Tsw. Teps is calculated to a larger value as Tsw is larger. Teps is a value in a direction to reduce the driver's steering torque Tsw.

  In the actual steering angle acquisition means A3, the actual steering angle δfa of the front wheels (steering wheels) is acquired. The actual steering angle δfa is calculated based on the detection value of the steering angle sensor FS. The actual steering angle δfa can be calculated using the relationship of δfa = θsw / SG based on the steering wheel operation angle θsw detected by the steering wheel rotation angle sensor SA. Here, SG is a steering gear ratio.

  The actual yawing behavior acquisition means A4 acquires the actual yawing behavior YMa (for example, yaw rate Yr). The “yawing behavior” is a movement in the yaw direction of the vehicle, and is a movement in which the direction in which the vehicle travels changes (movement in which the vehicle deflects). Accordingly, the yaw rate Yr or a value calculated based on the yaw rate Yr is used as the yawing behavior YMa.

  The target yawing behavior calculation means A5 calculates a target yawing behavior (target yawing behavior) YMt. YMt is calculated based on, for example, the vehicle speed Vx obtained from the steering wheel operation angle θsw and the wheel speed Vw **.

  The oversteer state quantity calculation means A6 calculates an oversteer state quantity Jros representing the degree of oversteer based on the comparison result between YMa and YMt (for example, the deviation between YMa and YMt).

  Jros can be calculated based on YMa without using YMt. In this case, Jros is calculated based on, for example, the table shown in FIG. 3, the side slip angle (slip angle) β of the vehicle, and the side slip angular velocity dβ. In the table shown in FIG. 3, with the curve corresponding to Jros = 0 as the base line, the oversteer state quantity Jros is determined to be larger in the upper right region.

  The side slip angle β (actual yawing behavior YMa) of the vehicle is calculated based on the yaw rate Yr, the lateral acceleration Gy, the vehicle speed Vx, and the like by a known method. Similarly, the side slip angular velocity dβ (actual yawing behavior YMa) of the vehicle is calculated based on the yaw rate Yr, the lateral acceleration Gy, the vehicle speed Vx, and the like by a known method.

  In the table shown in FIG. 3, the side slip angle deviation hβ can be used for the horizontal axis instead of the side slip angle β. The side slip angle deviation hβ is a deviation between the side slip angle target value βt (target yawing behavior YMt) and the side slip angle actual value βa (actual yawing behavior YMa). Similarly, in the table shown in FIG. 3, the yaw rate deviation hYr can be used for the vertical axis instead of the side slip angular velocity dβ. The yaw rate deviation hYr is a deviation between the yaw rate target value Yrt (target yawing behavior YMt) and the actual yaw rate value Yra (actual yawing behavior YMa). Here, the side slip angle target value βt and the yaw rate target value Yrt are calculated based on the driver's driving operation (steering wheel operation angle θsw, vehicle speed Vx, etc.) by a known method.

  In the target rudder angle calculation means A7, the target rudder angle δft of the front wheels is calculated based on the oversteer state quantity Jros. Specifically, as shown in FIG. 4, first, a stabilizing yawing moment Mq necessary for stabilizing the vehicle is calculated based on the oversteer state quantity Jros. Thereby, Mq is calculated to a larger value as the oversteer state quantity Jros is larger.

  Next, Mq is input to the inverse model of the vehicle, and the target rudder angle δft is calculated. Here, the reverse model of the vehicle is a reverse model of a vehicle model that calculates vehicle behavior such as yaw rate by inputting a vehicle speed, a steering angle, and the like, and inputs a vehicle behavior such as yaw rate to target steering angle δft of the front wheels. Is a model (a known simultaneous equation of motion). That is, for example, with respect to the current vehicle speed Vx, lateral acceleration Gy, yaw rate Yr, and actual steering angle δfa (or steering wheel operation angle θsw), the target steering angle δft of the front wheels necessary to obtain a stable yawing moment Mq. Is calculated using an inverse model of the vehicle including a tire model representing tire characteristics.

  In the stabilization torque calculation means A8, a stabilization torque Tstb (corresponding to the “stabilization force”), which is a steering torque for guiding or assisting a counter-steer operation for stabilizing the vehicle based on the steering angle deviation hδf. Is calculated according to the characteristic indicated by the solid line in FIG. The steering angle deviation hδf is a deviation (= δft−δfa) between the target steering angle δft and the actual steering angle δfa. Tstb is a value in the counter steer direction (direction in which the steered wheels are steered in the counter steer direction).

  Accordingly, the stabilization torque Tstb is calculated to be “0” when the steering angle deviation hδf is less than the threshold value δf1, and increases from “0” as hδf increases from δf1 when hδf is equal to or greater than δf1. Is calculated. However, the stabilization torque Tstb is limited to a predetermined limit value Ts1 or less due to the characteristics shown in FIG. Note that the stabilization torque Tstb may be limited to a limit value Ts1 or less by limiting the steering angle deviation hδf.

  In the motor driving means A9, the electric motor Me is driven based on a target value Tmtr (= Teps + Tstb) for driving control of the electric motor Me obtained by adding Tstb to Teps.

  As a result, a driving force corresponding to Tmtr is applied to the tie rod TR, and the torque in the direction of reducing the steering torque Tsw of the driver (EPS torque Teps) and the torque in the counter steer direction (stabilization) with respect to the steering wheel SW. Torque Tstb). As a result, the driver is guided or assisted with the counter steer operation by this Tstb.

  As described above, the steering torque control is executed based on the steering torque Tsw and the steering angle deviation hδf. In the oversteer state, the stabilization torque Tstb is in the countersteer direction (the direction opposite to the vehicle turning direction) with respect to the steering wheel SW. (Steering direction). Here, as described above, the smaller the steering angle deviation hδf, the smaller the stabilization torque Tstb (see FIG. 5). On the other hand, a small steering angle deviation hδf means that the driver is performing an appropriate counter-steer operation.

  Therefore, when the skilled driver performs an appropriate counter steering operation while predicting the behavior of the vehicle, the stabilization torque Tstb is reduced. Therefore, the “uncomfortable feeling that the steering force is reduced unexpectedly” that the skilled driver learns can be suppressed.

  On the other hand, when the steering angle deviation hδf is large, that is, when the driver is not performing an appropriate counter steering operation, the stabilization torque Tstb is large. As a result, for the driver who is not an expert driver, the countersteer operation can be appropriately or sufficiently guided or assisted by the large stabilization torque Tstb.

  Hereinafter, the operation of the first embodiment will be described with reference to FIG. FIG. 6 shows general tire characteristics (relationship between the steering wheel slip angle α and the lateral force Fy). Here, the slip angle α of the steered wheel has a predetermined relationship with the actual rudder angle δfa (or the target rudder angle δft), and the lateral force Fy of the steered wheel is equal to the predetermined yawing moment Mq. There is a relationship. Therefore, in the tire characteristics shown in FIG. 6, the horizontal axis also represents the actual steering angle δfa (δft), and the vertical axis also represents the stabilization yawing moment Mq, so that the characteristics shown in FIG. 6 are used. The operation of the first embodiment can be described as follows. In the characteristics shown in FIG. 6, the first quadrant (upper right area) corresponds to the left turning state, and the third quadrant (lower left area) corresponds to the right turning state.

  When the vehicle is in an excessive oversteer state, it is necessary to perform a countersteer operation in order to ensure the stability of the vehicle and generate a stabilizing yawing moment Mq that stabilizes the vehicle. For example, as shown in FIG. 7, when oversteer occurs while the vehicle is turning right (turning clockwise as viewed from above the vehicle), the countersteer operation is performed in the left turn direction (steering as viewed from the driver). Go in the counterclockwise direction of the wheel and reduce the yawing moment in the right turn direction (clockwise as seen from the top of the vehicle) and reduce the yawing moment in the left turn direction (counterclockwise as seen from the top of the vehicle) To increase the stabilization moment Mq (see FIG. 7). In this case, in order to generate the stabilization moment Mq in the left turn direction, it is necessary to perform a counter steer operation to set the front wheel steering angle to δft (corresponding to point B). However, when the front wheel steering angle is δfa (corresponding to point A) because the driver does not perform the counter steering operation or is insufficient, the steering angle deviation hδf (= δft−δfa) Accordingly, the stabilization torque Tstb is applied to the steering wheel SW in the left turning direction (the counterclockwise direction of the steering wheel as viewed from the driver and the steering wheel is steered to the left). (See FIG. 5).

  As described above, according to the steering control device according to the first embodiment of the present invention, the steering torque control (“giving the stabilization torque Tstb”) is executed as the oversteer suppression control. In the steering torque control, an EPS torque Teps for reducing the steering torque is calculated based on the steering torque Tsw by the driver. Based on the oversteer state quantity Jros representing the degree of oversteer, the target steering angle δft in the countersteer direction is calculated. Based on the deviation (steering angle deviation hδf = δft−δfa) between the target steering angle δft and the actual steering angle δfa, a stabilizing torque Tstb for guiding or assisting the countersteer operation is calculated. Torque Teps in a direction that reduces the steering torque Tsw of the driver and torque Tstb in the counter steer direction are applied to the steering wheel SW. As a result, the driver is guided or assisted with the counter steer operation by this Tstb.

  Here, when the steering angle deviation hδf is large, that is, when the driver is not performing an appropriate counter-steer operation, the stabilization torque Tstb is set to a large value. As a result, for the driver who is not an expert driver, the countersteer operation can be appropriately or sufficiently guided or assisted by the large stabilization torque Tstb. On the other hand, when the steering angle deviation hδf is small, that is, when the driver is performing an appropriate counter steering operation while predicting the behavior of the vehicle, the stabilization torque Tstb is set to a small value. As a result, it is possible to suppress the “uncomfortable feeling that the steering force during the counter-steer operation is reduced unexpectedly” that the skilled driver learns.

(Second Embodiment)
Next, a steering control device according to a second embodiment of the present invention will be described. In the second embodiment, as the oversteer suppression control, in addition to the steering torque control (“applying the stabilization torque Tstb”) in the first embodiment, the braking force control (“applying the braking force to the turning outer front wheel”). ) Is different from the first embodiment. Only such differences will be described below.

  FIG. 8 is a functional block diagram when oversteer suppression control is performed by the steering control device according to the second embodiment. As shown in FIG. 8, in the second embodiment, compared to the first embodiment (see FIG. 2), the target braking force calculation means A10, the control start determination means A11, the switching means A12, and the braking force control. Means A13 is added. Thereby, braking force control (ESC control) for suppressing oversteer of the vehicle is performed based on Jros.

  Specifically, the target braking force calculation means A10 calculates the target value (target braking force Fxt **) of the braking force of each wheel according to the characteristics shown in FIG. 9 based on the oversteer state quantity Jros. Thus, Fxt ** is calculated to be “0” when Jros is less than the threshold value Jr1, and increases from “0” as Jros increases from Jr1 when Jros is equal to or greater than Jr1 (however, (Restricted to a value Fx1 or less).

  In the control start determination means A11, the start determination of the braking force control is performed based on the stabilization torque Tstb. Specifically, when the stabilization torque Tstb is “0”, a determination is made to deny the start of the braking force control. When Tstb becomes a value larger than “0”, the start of the braking force control is determined. An affirmative determination is made.

  The switching means A12 outputs the target braking force Fxt ** to the braking force control means A13 when it is determined to deny the start of the braking force control based on the determination result Hns of the control start determination means A11. When the determination to affirm the start of the braking force control is made, the target braking force Fxt ** is output to the braking force control means A13.

  In the braking force control means A13, when the target braking force Fxt ** is being output to the braking force control means A13, the brake actuator BRK is driven based on Fxt **. As a result, the braking force of each wheel is adjusted to coincide with Fxt **. As a result, the braking force of the front wheels outside the turn is increased independently of the operation of the brake pedal BP by the driver.

  As a result, when the stabilization torque Tstb is “0”, the braking force control (“applying braking force to the turning outer front wheel”) is not executed. On the other hand, braking force control is executed based on Jros using “Tstb> 0” as a start condition. That is, “applying the braking force to the front outer wheel” and “applying the stabilizing torque Tstb” are started simultaneously. In the second embodiment, in addition to the application of Tstb in the steering torque control described above in the first embodiment, this braking force control also suppresses oversteer.

  Now, as shown in FIG. 10, consider a vehicle in which a negative kingpin offset is adopted for the steered wheels (front wheels). The negative kingpin offset refers to a case where the grounding point Pkp of the kingpin center axis is outside the front-and-rear force (Fxfr) force point Pbf in the vehicle width direction.

  In a vehicle in which a negative kingpin offset is adopted for the steering wheel, when a braking force is applied to the steering wheel, the distance (kingpin offset) Ofs between the braking force application point Pbf and the kingpin center axis grounding point Pkp Due to the presence, a torque for turning the steered wheels according to the braking force is generated. This phenomenon is also called “torque steer”.

  For example, as shown in FIG. 10, when oversteer occurs during a left turn, when the braking force Fxfr is applied to the turning outer front wheel WHfr by the above-described braking force control (ESC control), “torque steer” Torque Tkp (= Ofs · Fxfr) for turning the front wheel in the left turn direction acts on the front wheel. This torque Tkp acts as a torque Tsk that rotates the steering wheel SW in the left turn direction (counterclockwise direction as viewed from the driver).

  On the other hand, in this case, since the countersteer direction is the right turning direction, the stabilization torque Tstb is applied to the steering wheel SW in the right turning direction (clockwise as viewed from the driver).

  Therefore, in the process of increasing the amount of oversteering in the oversteering state, when either “applying braking force to the front outer turning wheel” or “applying stabilizing torque Tstb” is started before the other (both are simultaneously If it is not started), the driver will feel “torque steer” caused by “applying braking force to the front wheel outside the turn”, leading to an uncomfortable feeling to the driver.

  On the other hand, in the second embodiment, as described above, the start conditions (“Tstb> 0”) of “applying braking force to the outer front wheel” and “applying stabilizing torque Tstb” are the same. Accordingly, in the process of increasing Jros in the oversteer state, “applying a braking force to the turning outer front wheel” and “applying the stabilizing torque Tstb” are started simultaneously. As a result, it becomes difficult for the driver to feel “torque steer” due to “applying the braking force to the front outer wheel”, and the application of the stabilization torque Tstb can be executed without causing the driver to feel uncomfortable.

  The present invention is not limited to the above embodiments, and various modifications can be adopted within the scope of the present invention. For example, in each of the above embodiments, the steering wheel SW and the steered wheels WHfl and WHfr are mechanically connected, but the steering wheel SW and the steered wheels WHfl and WHfr are not mechanically connected. A steer-by-wire system (that is, a mechanism for controlling the front wheel steering angle based on an electrical signal indicating the operation angle θsw of the steering wheel SW) may be employed. In this case, a rod-shaped member (so-called joystick) may be used as the “steering operation member” instead of the steering wheel SW.

  In the second embodiment, the torque Tsk acting on the steering wheel SW based on the “torque steer” depends on the braking force (accordingly, the oversteer state amount Jros) applied to the front wheel outside the turn (see FIG. 9). On the other hand, the stabilization torque Tstb depends on the steering angle deviation hδf (not on Jros) (see FIG. 5). Therefore, when both “applying braking force to the outer front wheel on turning” and “applying stabilizing torque Tstb” are executed (hδf> δf1 and Jros> Jr1), when hδf is small and Jros is large , Tsk> Tstb may occur.

  On the other hand, while Tsk and Tstb are generated, the braking force applied to the front wheels outside the turn (calculated with the characteristics shown in FIG. 9) is limited so that Tsk <Tstb is always satisfied. May be. The torque Tsk with respect to the braking force (accordingly, Jros) applied to the front wheel outside the turn can be acquired in advance through experiments or the like. With this configuration, the torque Tsk based on the “torque steer” can be completely absorbed by applying the stabilization torque Tstb. As a result, it becomes more difficult for the driver to feel the “torque steer”.

  Further, since the torque Tsk with respect to the braking force (accordingly, Jros) applied to the front wheel outside the turn can be acquired in advance through experiments or the like, the torque Tsk can be taken into account in setting the stabilization torque Tstb. Specifically, a characteristic in which Tstb is increased stepwise from “0” to value Ts2 when the steering angle deviation hδf reaches the value δf1, as shown by the broken line in FIG. Here, the value Ts2 may be a predetermined value set in advance. Further, Ts2 can be calculated based on at least one of braking force (for example, target value Fxt **) applied to the front outside wheel and Jros. As a result, when hδf becomes larger than δf1, “applying stabilization torque Tstb” and “applying braking force to the front front wheel” are simultaneously started, and at that time, stabilization torque Tstb is “ It is increased stepwise from “0” to Ts2. As a result, the torque Tsk is compensated, and the stabilizing torque can be reliably applied in the counter steer direction.

  In addition, in each of the above embodiments, the electric motor Me is driven based on the target value Tmtr (= Teps + Tstb) for driving control of the electric motor Me, but for driving control of the electric motor Me. The electric motor Me may be driven based on the target value Tmtr (= Tstb). In this case, only Tstb is applied to the steering wheel SW in the counter steer direction. Also by this, the driver can guide or assist the counter steer operation by this Tstb.

1 is a schematic configuration diagram of a vehicle equipped with a steering control device according to a first embodiment of the present invention. FIG. 2 is a functional block diagram when oversteer suppression control is performed by the steering control device shown in FIG. 1. It is the graph which showed the characteristic of the amount of oversteer states to the side slip angle and side slip angular velocity of vehicles. FIG. 2 is a functional block diagram when a target steering angle is calculated from an oversteer state quantity by the steering control device shown in FIG. 1. It is the graph which showed the characteristic of stabilization torque with respect to steering angle deviation. It is the graph which showed the tire characteristic (relationship between the slip angle of a steering wheel and lateral force). It is the graph which showed an example of the relationship between counter steer and stabilization yawing moment. It is a functional block diagram at the time of performing oversteer control by the steering control device concerning a 2nd embodiment of the present invention. It is the graph which showed the characteristic of braking force to oversteer state quantity. It is a figure for demonstrating the "torque steer" which generate | occur | produces in the vehicle by which the negative kingpin offset is employ | adopted about the steering wheel.

Explanation of symbols

  BRK ... Brake actuator, ECU ... Electronic control device, Me ... Electric motor, Mv ... Electric motor, SW ... Steering wheel, FS ... Steering angle sensor, SA ... Steering wheel rotation angle sensor, ST ... Steering torque sensor, YR ... Yaw rate sensor , WS ** ... Wheel speed sensor

Claims (5)

A state quantity calculating means (A4, which obtains a value (YMa) corresponding to the yawing motion of the vehicle, and calculates an oversteer state quantity (Jros) representing the degree of oversteer of the vehicle based on the value corresponding to the yawing motion. A5, A6) and
A target for calculating a value (δft) corresponding to a target steering angle in a direction opposite to the turning direction of the vehicle of the steering wheel (WHf *) of the vehicle for stabilizing the vehicle based on the oversteer state quantity. Rudder angle calculation means (A7),
Actual steering angle acquisition means (A3) for acquiring a value (δfa, θsw) corresponding to the actual steering angle of the steering wheel;
Based on the comparison result between the target rudder angle equivalent value and the actual rudder angle equivalent value, the turning direction of the steering operation member (SW) operated by the vehicle driver to steer the steered wheel Stabilizing force calculating means (A8) for calculating a stabilizing force (Tstb) for guiding or assisting the operation in the opposite direction, and
Force applying means (A9) for applying the stabilizing force to the steering operation member in a direction opposite to the turning direction;
In a vehicle steering control device comprising :
The stabilizing force calculation means includes:
When the difference (hδf) between the target rudder angle equivalent value and the actual rudder angle equivalent value is less than a threshold value (δf1), the stabilizing force is calculated to be zero, and when the difference is equal to or greater than the threshold value, A vehicle steering control device configured to calculate the stabilizing force such that the stabilizing force increases with an increase from the threshold. The vehicle steering control device according to claim 1 ,
Braking force calculation means (A10) for calculating a target value (Fxt **) of the braking force to be applied to the front wheel outside the turning of the vehicle in order to stabilize the vehicle based on the oversteer state quantity;
Based on the target value of the braking force, braking force control means (A11, A12, A13) for applying a braking force to the front wheel outside the turn,
With
The braking force control means includes
When the stabilizing force is zero, no braking force is applied to the outer front wheel, and when the stabilizing force is greater than zero, the braking force is applied to the outer front wheel (A11, A12). A vehicle steering control apparatus configured as described above. The vehicle steering control device according to claim 2 ,
The stabilizing force calculation means includes:
A vehicle steering control device configured to calculate the stabilizing force so that the stabilizing force increases stepwise from zero to a predetermined value (Ts2) when the difference becomes the threshold value. In the vehicle steering control device according to claim 3 ,
The vehicle steering control device, wherein the predetermined value is calculated based on at least one of the target value of the braking force and the oversteer state quantity. The vehicle steering control device according to any one of claims 1 to 4 ,
The stabilizing force calculation means includes:
A vehicle steering control device configured to calculate the stabilization force such that the stabilization force is limited to a predetermined limit value (Ts1) or less.

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