JP2010058570A - Steering device for vehicle - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a steering device for a vehicle capable of properly changing a turning range of a steered wheel according to a behavior state of the vehicle. <P>SOLUTION: An electronic control unit 36 compares a detected real yaw rate γ with a target yaw rate γ* for judging an oversteer condition to judge whether or not the vehicle is in an oversteer condition. If the vehicle is in an oversteer condition, the electronic control unit 36 calculates a turning range deficiency δa, that is, a difference between a mechanically maximum turning range of right and left front wheels FW1 and FW2 and a turning range thereof to be limited depending on a vehicle speed V, and calculates a vehicle body slip angle β generated in the vehicle body. Then, the electronic control unit 36 determines, by using the turning range deficiency δa and the vehicle body slip angle β, a turning range that allows the front wheels FW1 and FW2 to turn to the direction decreasing the vehicle body slip angle β. This enables effective counter-steering and stabilizes a turning behavior of the vehicle in an oversteer condition. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention includes a steering handle operated by a driver to steer a vehicle, a steering actuator for steering a steered wheel, vehicle speed detection means for detecting the vehicle speed of the vehicle, and driving the steering actuator. A steering control device that controls and steers the steered wheels by decreasing the steered range of the steered wheels in response to the operation of the steering wheel with an increase in the vehicle speed detected by the vehicle speed detecting means; The present invention relates to a steering device.

Conventionally, for example, a steering-by-wire vehicle steering apparatus disclosed in Patent Document 1 below is known. Conventionally, for example, a vehicle steering apparatus disclosed in Patent Document 2 below is also known. In these conventional vehicle steering devices, the steered wheels are steered with respect to the steering angle of the steering handle when the vehicle speed is low, and the steered wheels are steered with respect to the steering angle of the steering handle when the vehicle speed is high. It is designed to steer. In this way, by changing the steered amount of steered wheels according to the vehicle speed, the driver operates the vehicle without changing the steering handle to turn the vehicle in a desired manner.
JP 2007-320333 A JP 2007-137400 A

  By the way, generally, as a steering characteristic of a vehicle, an understeer characteristic in which an actual turning radius is larger than an intended turning radius even when the steered wheel is steered, and an intended turning radius by turning the steered wheel The oversteer characteristic that the actual turning radius becomes smaller than that can be mentioned. In particular, in a situation where an oversteer state where the vehicle turns too much when the steered wheels are steered by oversteer characteristics, the turning behavior of the vehicle is likely to be disturbed. For this reason, in a situation where an oversteer state has occurred, it is preferable to perform counter steering in which the steered wheels are steered in a direction in which the vehicle slip angle generated in the vehicle body becomes smaller along with turning to stabilize the turning behavior of the vehicle.

  However, the steering range of the steered wheels is limited, particularly when the steered wheels are steered small when the vehicle speed is high, as in the conventional vehicle steering apparatus. For this reason, in the unlikely event of an oversteer condition with a high vehicle speed, the countersteer can provide some improvement in the turning behavior of the vehicle, but the steered wheels cannot be sufficiently steered. It can be difficult to do more effective countersteering.

  The present invention has been made to solve the above-described problems, and an object thereof is to provide a vehicle steering apparatus capable of appropriately changing the steered range of steered wheels according to the behavior state of the vehicle. It is in.

  In order to achieve the above object, the present invention is characterized by a steering handle operated by a driver to steer a vehicle, a steering actuator for steering steered wheels, and a vehicle speed for detecting the vehicle speed of the vehicle. The steered wheel is steered by decreasing the steered range of the steered wheel with respect to the operation of the steering handle by increasing the vehicle speed detected by the vehicle speed sensing means by drivingly controlling the steerable actuator and the steerable actuator. A steering apparatus for a vehicle comprising a steering control device, wherein the steering control device detects a predetermined physical quantity that is generated in a vehicle in a turning state and represents a turning behavior of the vehicle, and the detected A turning behavior state determining means for comparing a predetermined physical quantity with a target physical amount representing a target turning behavior of the vehicle determined based on the detected vehicle speed and determining a turning behavior state of the vehicle When the turning behavior state determining means determines that the predetermined physical quantity detected is a turning behavior state of the vehicle that is larger than the target physical quantity, the maximum steerable wheel that can be steered is determined mechanically. The difference calculation means for calculating a difference between the steered wheel steered range reduced according to the detected vehicle speed with respect to the steered range and the difference computed by the difference computation means, the detection A turning range changing means for changing the turning range of the steered wheels, which is reduced according to the vehicle speed, to the steered range of the steered wheels in which the detected predetermined physical quantity is equal to or less than the target physical quantity. There is to be. In this case, the vehicle steering device may be, for example, a steering-by-wire system in which mechanical connection between the steering handle and the steered wheels is released.

  More specifically, the turning behavior state of the vehicle determined by the turning behavior state determination means using the detected predetermined physical quantity is an overshoot of the vehicle when turning the steered wheels. The steered range changing means is configured to change a steered range of the steered wheels, which is decreased according to the detected vehicle speed, to a vehicle slip angle generated in the vehicle body when the oversteer state occurs. It is good to change to the steered range which permits the steered wheels to be steered in the decreasing direction.

  In this case, more specifically, the predetermined physical quantity detected by the physical quantity detection means is a yaw rate generated in a vehicle in a turning state, and the turning behavior state determination means includes at least the detected yaw rate, A target yaw rate determined according to the detected vehicle speed is compared, and when the detected yaw rate is larger than the target yaw rate, it is preferable to determine that the turning behavior state of the vehicle is the oversteer state.

  The steered range changing means detects the steered range of the steered wheels that is decreased according to the detected vehicle speed when the detected vehicle speed is higher than a predetermined vehicle speed set in advance. It is good to change into the steered range of the steered wheels in which the predetermined physical quantity made becomes below the target physical quantity.

  Further, the turning range changing means is configured to reduce the neutral position in the turning range of the steered wheels that has been decreased according to the detected vehicle speed, so that the detected predetermined physical quantity is equal to or less than the target physical quantity. It is good to change to the neutral position in the turning range.

  Further, when the steered range of the steered wheels changed by the steered range changing unit according to the detected vehicle speed is changed by the steered range changing unit, the steered actuator is driven to control the steered actuator. It is good to provide the steering actuator drive control means which steers the steered wheel to within the steered range of the changed steered wheel.

  According to these, even when the steered range of the steered wheels is reduced according to the vehicle speed, the turning behavior state of the vehicle in the turning state, more specifically, when the vehicle is in the oversteer state, It is possible to change to a steered range that allows the steered wheels to be steered in a direction that eliminates the oversteer state and stabilizes the turning behavior state of the vehicle. More specifically, the steering range can be changed to allow the steered wheels to be steered in a direction that reduces the vehicle slip angle generated in the vehicle body in the oversteer state.

  As a result, when the vehicle is traveling in a vehicle speed range where the vehicle speed is high to some extent, even if an oversteer condition occurs in the event of a turn, the direction in which the vehicle slip angle is sufficiently reduced by the appropriate countersteer Can be steered to. Therefore, the turning behavior of the vehicle can be stabilized satisfactorily.

  Further, when the steered range of the steered wheels is changed, the steered wheels can be steered to the changed steered range by automatically driving and controlling the steered actuator. Thus, for example, even when the driver does not perform counter-steer by actively operating the steering handle, the steered wheels can be automatically steered in a direction in which the vehicle slip angle decreases. Therefore, the turning behavior of the vehicle can be stabilized satisfactorily and reliably.

  Hereinafter, a vehicle steering apparatus according to an embodiment of the present invention will be described in detail with reference to the drawings. FIG. 1 schematically illustrates a steering-by-wire vehicle steering apparatus according to an embodiment of the present invention.

  The vehicle steering apparatus includes a steering handle 11 that is turned by a driver to steer left and right front wheels FW1 and FW2 as steered wheels. The steering handle 11 is fixed to the upper end of the steering input shaft 12, and the lower end of the steering input shaft 12 is connected to a reaction force actuator 13 including an electric motor and a speed reduction mechanism. The reaction force actuator 13 applies a reaction force to the turning operation of the steering handle 11 by the driver.

  Further, the vehicle steering apparatus includes a steering actuator 21 including an electric motor and a speed reduction mechanism. The turning force by the turning actuator 21 is transmitted to the left and right front wheels FW1 and FW2 via the turning output shaft 22, the pinion gear 23, and the rack bar 24. With this configuration, the rotational force from the steering actuator 21 is transmitted to the pinion gear 23 via the steering output shaft 22, and the rack bar 24 is displaced in the axial direction by the rotation of the pinion gear 23. Due to the displacement in the axial direction, the left and right front wheels FW1, FW2 are steered left and right.

  Next, an electric control device that controls the operation of the reaction force actuator 13 and the steering actuator 21 will be described. The electric control device includes a steering angle sensor 31, a turning angle sensor 32, a vehicle speed sensor 33, a ground speed sensor 34, and a yaw rate sensor 35.

  The steering angle sensor 31 is assembled to the steering input shaft 12, detects the rotation angle from the neutral position of the steering input shaft 12, that is, the steering handle 11, and outputs it as the steering angle θ. The steered angle sensor 32 is assembled to the steered output shaft 22, detects the rotational angle from the neutral position of the steered output shaft 22, and corresponds to the actual steered angle δ (the steered angle of the left and right front wheels FW1, FW2). ) Is output. Note that the steering angle θ and the actual turning angle δ are represented by setting the neutral position to “0”, the left rotation angle as a positive value, and the right rotation angle as a negative value. The vehicle speed sensor 33 detects and outputs the vehicle speed V. The ground speed sensor 34 detects and outputs the speeds Vx, Vy of the front, rear, left and right of the vehicle with respect to the road surface using, for example, light or sound. The yaw rate sensor 35 detects and outputs the actual yaw rate γ of the vehicle. Note that the front and rear, left and right speeds Vx and Vy of the vehicle represent the front and left speeds of the vehicle as positive values, and the rear and right speeds of the vehicle as negative values. The actual yaw rate γ represents the left yaw rate as a positive value and the right yaw rate as a negative value.

  Each of these sensors 31 to 35 is connected to the electronic control unit 36. The electronic control unit 36 includes a microcomputer including a CPU, a ROM, a RAM, and the like as main components, and operates the reaction force actuator 13 and the turning actuator 21 by executing various programs including a turning range changing program described later. To control each. Drive circuits 37 and 38 for driving and controlling the reaction force actuator 13 and the steering actuator 21 are connected to the output side of the electronic control unit 36, respectively. In the drive circuits 37 and 38, current detectors 37a and 38a for detecting a drive current flowing in the electric motors in the reaction force actuator 13 and the steering actuator 21 are provided. The drive current detected by the current detectors 37a and 38a is fed back to the electronic control unit 36 in order to control the drive of both electric motors.

  Next, the operation when the vehicle steering apparatus configured as described above is operated by the driver will be described. When an ignition switch (not shown) is turned on by the driver, the electronic control unit 36 executes a program (not shown) to control the operation of the reaction force actuator 13 and the steering actuator 21.

  That is, the electronic control unit 36 inputs the steering angle θ of the steering handle 11 detected by the steering angle sensor 31 and also inputs the vehicle speed V detected by the vehicle speed sensor 33. The electronic control unit 36 controls the operation of the reaction force actuator 13 according to the input steering angle θ, thereby giving an appropriate reaction force to the turning operation of the steering handle 11 by the driver, and the input steering angle. By controlling the operation of the steering actuator 21 according to θ and the vehicle speed V, the left and right front wheels FW1, FW2 are steered to turn the vehicle in a manner intended by the driver.

  More specifically, the electronic control unit 36 determines a reaction force torque Tz that changes linearly (proportional function) with respect to the absolute value of the detected steering angle θ input from the steering angle sensor 31. The reaction torque Tz may be a change characteristic that increases as the absolute value of the detected steering angle θ increases. For example, instead of a linear change characteristic, the reaction force torque Tz may increase the absolute value of the detected steering angle θ. On the other hand, it is also possible to employ a change characteristic that increases nonlinearly (power function or exponential function).

  Then, the electronic control unit 36 controls the drive circuit 37 so that the determined reaction force torque Tz is input to the steering handle 11. That is, the electronic control unit 36 inputs a drive current flowing from the current detector 37 a of the drive circuit 37 to the electric motor in the reaction force actuator 13. The electronic control unit 36 then feedback-controls the drive circuit 37 so that a drive current corresponding to the reaction force torque Tz input to the steering handle 11 (more specifically, the steering input shaft 12) flows appropriately. As a result, a reaction force torque Tz is applied to the steering handle 11, and the driver can turn the steering handle 11 while perceiving an appropriate reaction force torque Tz, that is, a reaction force.

On the other hand, the electronic control unit 36 calculates the target turning angle δd of the left and right front wheels FW1, FW2 in accordance with the detected steering angle θ input from the steering angle sensor 31. Specifically, when the detected steering angle θ is input, the electronic control unit 36 calculates the target turning angle δd of the left and right front wheels FW1, FW2 according to the input steering angle θ, for example, according to the following equation 1.
δd = (1 + Kh · V ² ) / V · L · γg · θ Equation 1
In Equation 1, Kh represents a predetermined stability factor (constant), V represents a vehicle speed detected by the vehicle speed sensor 33, and L represents a vehicle wheel base (constant). Γg represents the yaw gain at the vehicle speed V detected by the vehicle speed sensor 33, and θ represents the steering angle detected by the steering angle sensor 31.

  When the input detected vehicle speed V is small, the electronic control unit 36 calculates a target turning angle δd that is large with respect to the steering angle θ according to the equation 1. On the other hand, when the input detected vehicle speed V is large, the electronic control unit 36 calculates a target turning angle δd that is small with respect to the steering angle θ according to the equation (1).

  When the target turning angle δd is calculated in this way, the electronic control unit 36 controls the drive circuit 38 so that the left and right front wheels FW1, FW2 become the target turning angle δd. That is, the electronic control unit 36 inputs the actual turning angle δ detected by the turning angle sensor 33 and also inputs the drive current flowing from the current detector 38a of the drive circuit 38 to the electric motor in the turning actuator 21. . The electronic control unit 36 performs feedback control of the drive circuit 38 in order to drive the electric motor until the actual turning angle δ of the left and right front wheels FW1 and FW2 matches the target turning angle δd. Thus, the left and right front wheels FW1, FW2 are steered to the target turning angle δd, and the driver can turn the vehicle in a manner corresponding to the vehicle speed V.

  That is, in a situation where the vehicle is traveling at a low speed with a low vehicle speed V, the left and right front wheels FW1, FW2 are steered large (quickly) with respect to the turning operation of the steering handle 11 by the driver. As a result, in the low speed range, the driver can turn the left and right front wheels FW1, FW2 greatly by rotating the steering handle 11 less than 180 ° without changing the steering handle 11 specifically. Thus, the handling of the vehicle can be greatly improved while reducing the operation burden.

  On the other hand, in a situation where the vehicle is traveling at a medium / high speed with a relatively large vehicle speed V, the left and right front wheels FW1, FW2 are steered small (slowly) with respect to the turning operation of the steering handle 11 by the driver. As a result, in the middle and high speed range, it is possible to prevent the left and right front wheels FW1 and FW2 from being steered sharply in response to the turning operation of the steering handle 11 by the driver. It can be stabilized.

  More specifically, in a vehicle steering apparatus employing a steering-by-wire system, as shown in FIG. 2, the turning range of the left and right front wheels FW1, FW2 changes according to the magnitude of the detected vehicle speed V. To do. That is, when the vehicle is traveling in a low speed range, the steering range of the left and right front wheels FW1 and FW2 becomes the steering range set by the left end position and the right end position determined mechanically, and the steering handle 11 The left and right front wheels FW1, FW2 are steered large (quickly) with respect to the turning operation. As the detected vehicle speed V increases, the steered range of the left and right front wheels FW1, FW2 is uniformly narrowed and becomes the smallest steered range as shown in FIG. The left and right front wheels FW1, FW2 are steered small (slowly) with respect to the turning operation.

  In other words, in a vehicle steering apparatus that employs a steering-by-wire system, the turning range of the steering handle 11 from the low speed range to the high speed range (specifically, by changing the turning range according to the magnitude of the detected vehicle speed V (specifically). Specifically, the left and right front wheels FW1, FW2 can be steered without changing the rotation operation range of the steering handle 11 less than 180 °. As a result, the driver always enjoys good vehicle handling at low speeds and good behavioral stability at medium and high speeds by turning the steering wheel 11 within the same operating range. Can do.

  By the way, as the steering characteristics of the vehicle, in general, even if the left and right front wheels FW1, FW2 are steered, the vehicle is difficult to turn (the actual turning radius is larger than the intended turning radius), that is, the understeer characteristic, By turning the front wheels FW1 and FW2, there is a characteristic that the vehicle easily turns (the actual turning radius is smaller than the intended turning radius), that is, an oversteer characteristic. In particular, a counter that steers the left and right front wheels FW1 and FW2 in a direction in which the vehicle slip angle generated in the vehicle body with the turning decreases when the vehicle turns too much (oversteer state) due to oversteer characteristics. By performing the steering, the behavior of the vehicle can be stabilized.

  However, as described above, in the situation where the turning range of the left and right front wheels FW1, FW2 is narrowed according to the increase in the detected vehicle speed V, particularly in the situation where the vehicle is traveling in the high speed range and the turning range is the narrowest, In the unlikely event that an oversteer condition occurs, the steered range is limited, so the amount of steered (steered angle) of the left and right front wheels FW1, FW2 may be insufficient, and effective countersteer may not be performed. There is. Therefore, the electronic control unit 36 executes the steered range changing program shown in FIG. 3 so that it can appropriately cope with the occurrence of the oversteer state. Hereinafter, this steering range change program will be described in detail.

  When an ignition switch (not shown) is turned on by the driver, the electronic control unit 36 (more specifically, the CPU) repeatedly executes the steered range changing program shown in FIG. 3 every predetermined short time.

  That is, the electronic control unit 36 starts execution of the steered range changing program in step S10. In step S11, the electronic control unit 36 detects each of the steering angle sensor 31, the vehicle speed sensor 33, the ground speed sensor 34, and the yaw rate sensor 35 detected by the steering angle sensor 31. The detected values, that is, the steering angle θ, the vehicle speed V, the front and rear speeds Vx and Vy, and the yaw rate γ are input. And the electronic control unit 36 will progress to step S12, if each detection value is input.

In step S12, the electronic control unit 36 determines whether or not the vehicle is in an oversteer state. More specifically, the electronic control unit 36 calculates the absolute value of the actual yaw rate γ input from the yaw rate sensor 35 in step S11 and the absolute value of the target yaw rate γ * for determining the oversteer state by the following equation. Compare according to 2.
| Γ | − | γ * |> γo Equation 2
However, γo in the expression 2 is a predetermined positive constant experimentally set in advance. Further, the target yaw rate γ * is experimentally determined in advance based on a well-known relationship using, for example, the cornering power of the front and rear wheels of the vehicle, the yawing inertia moment, the vehicle speed, the turning angle, and the like as parameters. For this reason, for example, the target turning angle δd calculated according to the detected vehicle speed V according to the equation 1 and the actual turning angle δ detected by the turning angle sensor 32 are used, and the electronic control unit 36 makes this target turning. A target yaw rate γ * corresponding to the angle δd and the actual turning angle δ may be set.

  And when the said Formula 2 is materialized, since the vehicle is an oversteer state, the electronic control unit 36 will determine "Yes", and will progress to step S13. On the other hand, if Formula 2 is not satisfied, the vehicle is not in an oversteer state, so it is determined as “No”, the process proceeds to Step S15, and the execution of the steered range changing program is temporarily terminated. In this case, since the oversteer state has not occurred, the vehicle can be appropriately turned by turning the left and right front wheels FW1, FW2 within the turning range shown in FIG. Then, after a predetermined short time has elapsed, the electronic control unit 36 again starts executing the steered range changing program in step S10.

  In step S13, the electronic control unit 36 turns the left and right front wheels FW1, FW2 within the turning range that is changed (restricted) according to the detected vehicle speed V as shown in FIG. The maximum turning angle δmax from the neutral position (that is, neutral position) and the maximum left and right front wheels FW1, FW2 from the neutral position to the left end position (or right end position) can be mechanically steered. A difference from the tire angle ΔMAX (hereinafter, this difference is referred to as an insufficient steering amount δa) is calculated. Hereinafter, the calculation of the steering insufficient amount Δa will be described in detail.

  As described above, the steering range of the left and right front wheels FW1 and FW2 when the vehicle is traveling in a low speed range is the steering range from the neutral position to the left end position (or right end position), and the left and right front wheels FW1 and FW2 Can be steered to the maximum tire angle ΔMAX with respect to the turning operation of the steering handle 11. When the vehicle is traveling in the middle / high speed range where the detected vehicle speed V is greater than a predetermined vehicle speed Vo set in advance, the maximum turning angle δmax of the left and right front wheels FW1, FW2 is greater than the maximum tire angle ΔMAX. Becomes smaller. That is, as shown in FIG. 4, the maximum turning angle δmax of the left and right front wheels FW1 and FW2 becomes smaller than the maximum tire angle ΔMAX when the detected vehicle speed V becomes larger than a predetermined vehicle speed Vo, and the steering shortage amount δa becomes smaller. It comes to occur.

Here, the maximum turning angle δmax of the left and right front wheels FW1 and FW2 when the detected vehicle speed V is higher than the predetermined vehicle speed Vo is the maximum steering angle of the steering handle 11 that is predetermined with respect to the steering angle θ in the equation (1). It can be expressed by the following formula 3 in which θmax is substituted.
δmax = (1 + Kh · V ² ) / V · L · γg · θmax Equation 3
Therefore, the steering deficit amount δa that occurs when the detected vehicle speed V is greater than the predetermined vehicle speed Vo is calculated by using the detected vehicle speed V and the maximum turning angle δmax calculated according to the above-described equation 3 and the predetermined maximum tire angle. It is calculated according to the following equation 4 consisting of ΔMAX.
δa = ΔMAX−δmax Equation 4
Then, when the electronic control unit 36 calculates the steering shortage amount δa according to the equation 4, the electronic control unit 36 proceeds to step S14.

  In step S14, the electronic control unit 36 changes the steered range of the left and right front wheels FW1 and FW2 so that counter-steering for coping with the oversteer state currently occurring in the vehicle can be appropriately performed. This will be specifically described below.

As described above, when an oversteer condition occurs in the vehicle, the left and right front wheels FW1 and FW2 are steered by the countersteer so that the slip angle of the vehicle body generated along with the turning is reduced, thereby stabilizing the behavior of the vehicle. It is effective to make it. For this reason, the electronic control unit 36 calculates the vehicle slip angle β currently occurring in the vehicle body. Specifically, the electronic control unit 36 calculates the vehicle slip angle β according to the following equation 5 using the vehicle longitudinal velocity Vx and the vehicle lateral velocity Vy input from the ground speed sensor 34 in step S11. To do.
β = tan ^-1 (Vy / Vx) ... Formula 5
Note that various methods can be employed for calculating the vehicle slip angle β. Instead of using the vehicle longitudinal speed Vx and the vehicle lateral speed Vy, for example, by using an acceleration sensor mounted on the vehicle. It is also possible to calculate by transforming Equation 5 with the detected longitudinal acceleration of the vehicle as acceleration Gx and the lateral acceleration of the vehicle as acceleration Gy.

  The electronic control unit 36 corrects and changes the neutral position in accordance with the calculated vehicle slip angle β while maintaining the size of the limited turning range in the normal control shown in FIG. Specifically, as shown in FIG. 5, the electronic control unit 36 refers to a table representing the change characteristic of the neutral position correction amount δo with respect to the change in the absolute value of the vehicle slip angle β, and calculates the calculated vehicle slip angle. A correction amount δo corresponding to the absolute value of β is calculated. As shown in FIG. 5, the correction amount δo has a characteristic that changes to the steering shortage amount δa calculated in step S13 with respect to an increase in the absolute value of the vehicle slip angle β.

Thus, when the neutral position correction amount δo is calculated, the electronic control unit 36 changes according to the vehicle body slip angle β that changes from moment to moment according to the following equation 6 using the neutral position correction amount δo. A neutral position δc_new is determined.
δc_new = δc_old−sign (γ) · δo Equation 6
However, δc_old in the equation 6 represents a neutral position determined by executing the program up to the previous time. Further, sign (γ) in the above equation 6 represents the sign function of the actual yaw rate γ, and when the vehicle turns left, that is, when the actual yaw rate γ is positive, sign (γ) becomes “+”, and the right side of the vehicle When the turning, that is, the actual yaw rate γ is negative, the sign (γ) is “−”.

  Thus, by determining the neutral position Δc_new, for example, even if an oversteer condition occurs in the vehicle in the high speed range, appropriate countersteering can be performed. This will be described with a specific example.

  Assume a situation in which a vehicle running in a high speed region starts turning rightward, and as a result, an oversteer state has occurred in the vehicle. In this situation, since the vehicle is turning rightward, the actual yaw rate γ generated in the vehicle is generated in the right direction, and the direction of the vehicle slip angle β generated in the vehicle body is the left direction of the vehicle. Therefore, in this situation, in order to cope with the oversteer state that has occurred in the vehicle, it is necessary to counter-steer the left and right front wheels FW1, FW2 in the left direction.

  Here, since the vehicle is turning rightward, the actual yaw rate γ input from the yaw rate sensor 35 by the electronic control unit 36 is a negative value. Therefore, according to Equation 6, the neutral position δc_new is “+ δo” if the neutral position δc_old is “0”. That is, in this case, as shown in FIG. 6, the neutral position δc_new is changed by “+ δo” in the left direction of the vehicle, and the turning range of the left and right front wheels FW1 and FW2 around the changed neutral position is It is maintained to be the same as the size of the steering range in the normal control. In this way, by changing the neutral position, the steered range of the left and right front wheels FW1, FW2 in the left direction of the vehicle can be increased compared to the case of normal control. Counter-steering in the left direction to deal with the oversteer state that has occurred can be appropriately performed.

  Even in the situation where the oversteer state occurs, the size of the steered range of the left and right front wheels FW1 and FW2 with the neutral position as the center is maintained to be the same as in the case of normal control. FW1 and FW2 are gently steered in the same manner as in the normal control with respect to the turning operation of the steering handle 11 by the driver. Therefore, even when the driver actively rotates the steering handle 11 to perform counter-steering, the left and right front wheels FW1 and FW2 are not steered sharply, and the steering handle 11 is rotated. Accordingly, it is possible to prevent the behavior of the vehicle from being disturbed.

  On the other hand, the electronic control unit 36 operates the steering actuator 21 to turn the vehicle body slip angle β even when, for example, a delay occurs in the turning operation of the steering handle 11 for the driver to perform counter-steering. The left and right front wheels FW1, FW2 can be steered (so-called active counter-steering) in the direction of decreasing. Therefore, it is possible to favorably assist the driver to rotate the steering handle 11, and the behavior of the vehicle can be stabilized. Further, for example, even when the driver does not actively perform counter-steering, the electronic control unit 36 appropriately handles the left and right front wheels FW1 and FW2 by active counter-steering in response to an oversteer state occurring in the vehicle. The vehicle can be steered in the direction, and the behavior of the vehicle can be stabilized.

  As can be understood from the above description, according to the present embodiment, even when the steered range of the left and right front wheels FW1, FW2 is reduced according to the detected vehicle speed V by the normal control, the vehicle is in the oversteer state. In this case, the steering range can be changed to allow the left and right front wheels FW1 and FW2 to be steered in a direction in which the oversteer state is canceled and the turning behavior state of the vehicle is stabilized. More specifically, the steering range can be changed to allow the left and right front wheels FW1 and FW2 to be steered in the direction of decreasing the vehicle slip angle β generated in the vehicle body in the oversteer state.

  As a result, when the vehicle is traveling in a medium / high speed range where the vehicle speed is somewhat high, even if an oversteer condition occurs due to turning, the left and right front wheels FW1 and FW2 are sufficiently slipped by appropriate countersteering. It can be steered in the direction in which the angle β decreases. Therefore, the turning behavior of the vehicle can be stabilized satisfactorily.

  Further, when the turning range of the left and right front wheels FW1, FW2 is changed, the steering actuator 21 is automatically driven and controlled, and the left and right front wheels FW1, FW2 can be turned to the changed turning range. Thereby, for example, even when the driver does not actively operate the steering handle 11 to perform counter-steering, the left and right front wheels FW1, FW2 are automatically steered in the direction in which the vehicle body slip angle β decreases. be able to. Therefore, the turning behavior of the vehicle can be stabilized satisfactorily and reliably.

  In carrying out the present invention, the present invention is not limited to the above embodiment, and various modifications can be made without departing from the object of the present invention.

  For example, in the above-described embodiment, a steering-by-wire type steering device is adopted as a steering device in which the steering input shaft 12 and the steering output shaft 22 can rotate relative to each other, and the counter steer is generated when an oversteer state occurs in the vehicle. The steering range of the left and right front wheels FW1, FW2 was changed so as to be surely performed. However, as a steering device in which the steering input shaft and the steering output shaft can rotate relative to each other, for example, a transmission device having a variable transmission ratio system including an electric motor (corresponding to a steering actuator) that changes the transmission ratio according to the vehicle speed. It is also possible to change the steered range of the left and right front wheels FW1, FW2 so that countersteering can be reliably performed when an oversteer condition occurs in the vehicle.

  Even in such a transmission ratio variable type steering device, the driver can increase the steered wheel with respect to the turning operation of the steering handle by the driver in the low speed range by driving the electric motor without changing the steering handle ( The steering wheel can be steered quickly, and the steered wheel can be steered small (slowly) in response to the turning operation of the steering handle by the driver in the middle / high speed range. Therefore, also in this transmission ratio variable type steering device, as in the case of the steering-by-wire type steering device of the above-described embodiment, in the unlikely event that an oversteer state occurs in the vehicle, the turning amount of the steered wheels (the turning angle) ) May not be effective and effective counter-steering may not be possible.

  On the other hand, in the transmission ratio variable type steering device, by executing the steering range change program of the above-described embodiment, it is possible to appropriately change the steered range of the steered wheels when the oversteer state occurs. it can. Therefore, the same effect as that of the above-described embodiment can also be expected in the transmission ratio variable type steering device.

  In the above embodiment, the steering handle 11 that is turned to steer the vehicle is used. However, instead of this, for example, a joystick-type steering handle that is linearly displaced may be used, or any other one that can be operated by the driver and instructed to steer the vehicle is used. May be.

  Further, in each of the above embodiments, the left and right front wheels FW1 and FW2 are steered by rotating the steered output shaft 22 using the steered actuator 21. However, instead of this, the left and right front wheels FW1, FW2 may be steered by linearly displacing the rack bar 24 using the steered actuator 21.

1 is a schematic view of a vehicle steering apparatus according to an embodiment of the present invention. It is a figure for demonstrating the steered range of the steered wheel in normal control. It is a flowchart which shows the steering range change program performed by the electronic control unit of FIG. It is a figure for demonstrating the steering shortage amount. It is a graph which shows the relationship between the corrected amount for changing a neutral position, and a vehicle body slip angle. It is a figure for demonstrating the change of the steered range of a steered wheel when an oversteer state generate | occur | produces.

Explanation of symbols

FW1, FW2 ... front wheels, 11 ... steering handle, 12 ... steering input shaft, 13 ... reaction actuator, 21 ... steering actuator, 22 ... steering output shaft, 31 ... steering angle sensor, 32 ... steering angle sensor, 33 ... Vehicle speed sensor 34 ... Ground speed sensor 35 ... Yaw rate sensor 36 ... Electronic control unit

Claims (7)

A steering handle operated by a driver to steer the vehicle, a steering actuator for steering the steered wheels, vehicle speed detection means for detecting the vehicle speed of the vehicle, and driving control of the steering actuator to In a steering apparatus for a vehicle, comprising: a steering control device that reduces the steered range of the steered wheels in response to an operation of a steering wheel as the vehicle speed detected by the vehicle speed detecting means decreases and steers the steered wheels; The steering control device,
Physical quantity detection means for detecting a predetermined physical quantity generated in a vehicle in a turning state and representing the turning behavior of the vehicle;
A turning behavior state determining means for comparing the detected predetermined physical quantity and a target physical quantity representing a target turning behavior of the vehicle determined based on the detected vehicle speed to determine a turning behavior state of the vehicle;
When it is determined that the predetermined physical quantity detected by the turning behavior state determining means is a turning behavior state of the vehicle that is larger than the target physical quantity, the maximum steerable wheel that can be steered mechanically is determined. Difference calculating means for calculating a difference with the steered range of the steered wheels that has been reduced according to the detected vehicle speed with respect to the steered range;
A steered wheel in which the detected predetermined physical quantity is equal to or less than the target physical quantity in the steered range of the steered wheel that has been reduced according to the detected vehicle speed using the difference calculated by the difference calculating means. A vehicle steering apparatus comprising: a turning range changing means for changing to a turning range. In the vehicle steering apparatus according to claim 1,
The turning behavior state of the vehicle determined by the turning behavior state determining means using the detected predetermined physical quantity is an oversteer state in which the vehicle turns too much when turning the steered wheels,
The steered range changing means is
The turning range of the steered wheels reduced according to the detected vehicle speed is allowed to steer the steered wheels in a direction to reduce the vehicle slip angle generated in the car body due to the occurrence of the oversteer state. A steering apparatus for a vehicle, wherein the steering range is changed to a steering range. In the vehicle steering apparatus according to claim 2,
The predetermined physical quantity detected by the physical quantity detection means is a yaw rate generated in a vehicle in a turning state,
The turning behavior state determination means compares the detected yaw rate with a target yaw rate determined according to at least the detected vehicle speed, and when the detected yaw rate is greater than the target yaw rate, the vehicle It is determined that the turning behavior state of the vehicle is the oversteer state. In the vehicle steering apparatus according to claim 1,
The steered range changing means is
When the detected vehicle speed is larger than a predetermined vehicle speed set in advance, the detected predetermined physical quantity is less than the target physical quantity in the steered range of the steered wheels that is decreased according to the detected vehicle speed. The vehicle steering apparatus is changed to a steered range of the steered wheels. In the vehicle steering apparatus according to claim 1,
The steered range changing means is
Changing the neutral position in the steered range of the steered wheels, which is decreased according to the detected vehicle speed, to the neutral position in the steered range of the steered wheels in which the detected predetermined physical quantity is equal to or less than the target physical quantity. A vehicle steering apparatus characterized by the above. In the vehicle steering apparatus according to claim 1,
The steering control device,
When the steered range of the steered wheels decreased according to the detected vehicle speed by the steered range changing means is changed, the steered actuator is driven and controlled to change the steered wheels. A steering apparatus for a vehicle, comprising a steering actuator drive control means for steering the steered wheels to within a range.   The vehicle steering apparatus according to claim 1, wherein the mechanical connection between the steering wheel and the steered wheel is released.

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