JP2014213690A - Vehicle - Google Patents

Abstract

PROBLEM TO BE SOLVED: To perform adequately stabilization of vehicle behavior upon abnormal time of a control system which controls forward movement of a vehicle.SOLUTION: A vehicle comprises: a forward movement control part 54 which generates restitutive force for self-aligning to steering wheels, a vehicle speed detection part which detects vehicle speed, a tire lateral force detection part 22a which detects tire lateral force of the vehicle, a steering angle detection part 4 which detects a steering angle of a steering wheel, a brake force giving part 20 which gives brake force to left and right wheels respectively, an abnormality detection part 58 which detects abnormality of the forward movement control part, and an abnormal time behavior control part 59 which calculates a target tire lateral force based on the steering angle and the vehicle speed and controls the brake force giving part so that the tire lateral force coincides with the target tire lateral force, to suppress influence of disturbance input from a road surface, when steering control abnormality of a steer-by-wire system is detected by the abnormality detection part.

Description

  The present invention relates to a vehicle equipped with a suspension device with high steering response and a steer-by-wire system.

Conventionally, it has been proposed that a steering control device for a vehicle employs a steer-by-wire (SBW) system in which mechanical connection between a steering wheel and a steered wheel is disconnected.
A vehicle employing this steer-by-wire is provided with an actuator capable of adjusting a steering torque for turning a steered wheel based on a steering input to a steering wheel. This actuator is required to maintain a stable vehicle behavior according to the steering state of the steering wheel.

  For example, in the technique described in Patent Document 1, when braking control is being executed during turning, a failure occurs in which a steering wheel, a steering gear box, and a backup mechanism such as a clutch are directly connected in the steer-by-wire control system. When controlling the braking force of each wheel based on the yaw rate calculated based on the angle, when a change in the vehicle responsiveness with respect to the steering angle is detected, the yaw rate calculation model is switched to prevent erroneous vehicle behavior control intervention Like to do.

JP 2008-30591 A

  By the way, in the prior art described in the above-mentioned patent document 1, the braking force of each wheel is set as a control target when a failure occurs in the steer-by-wire control system in which the steering wheel and the steering gear box are directly connected by a backup mechanism such as a clutch. Control is performed based on the yaw rate calculated based on the steering angle.

However, in the steer-by-wire system, various steering controls are performed, and when an abnormality that does not lead to the operation of the backup mechanism occurs, the conventional technique described in Patent Document 1 cannot cope with it. In particular, in vehicles equipped with suspension devices that place greater emphasis on steering response than straight-running stability, the steer-by-wire system ensures the straight-running stability of the vehicle, and an abnormality occurs in the straight-running stability control system. In this case, the abnormality is not so great as to operate the pack-up mechanism, and therefore, it is not included in the abnormality control target described in Patent Document 1.
An object of the present invention is to properly stabilize the behavior of a vehicle when an abnormality occurs in a control system that controls straight running stability.

  In order to solve the above problems, the vehicle according to the present invention estimates the vehicle behavior based on the tire lateral force and detects the steering angle and the vehicle speed when an abnormality is detected in the straightness control unit that controls the straightness of the vehicle. Based on the above, the target tire lateral force is calculated, and the braking force applied to the left and right steered wheels is controlled so that the tire lateral force matches the target tire lateral force.

  According to the present invention, when an abnormality occurs in the straightness control unit that controls the straightness of the vehicle, the vehicle behavior is estimated based on the tire lateral force. Therefore, the left and right response is higher than the braking force control based on the yaw rate. By controlling the braking force of the steered wheels, the response delay can be suppressed and the behavior of the vehicle can be stabilized quickly and appropriately.

1 is a schematic configuration diagram showing an automobile according to a first embodiment of the present invention. It is a perspective view which shows the structure of a suspension apparatus typically. It is a top view which shows the structure of a suspension apparatus typically. It is the partial front view and partial side view which show typically the structure of a suspension apparatus. It is a characteristic diagram which shows the relationship between the rack stroke of a suspension apparatus, and a rack axial force. It is a characteristic diagram which shows the relationship between the road surface landing point of the kingpin axis | shaft of a suspension, and lateral force. It is a conceptual diagram explaining the self-aligning torque at the time of setting it as a positive scrub. It is a block diagram which shows the specific structure of a steering control part and a behavior control part at the time of abnormality. It is a flowchart which shows an example of the abnormal behavior control processing procedure performed in the abnormal behavior control part of FIG. FIG. 6 is a characteristic diagram showing a target tire lateral force calculation map representing a relationship between a vehicle speed and a target tire lateral force with a steering angle as a parameter. FIG. 11 is a characteristic diagram showing a change in tire lateral force when the steering angle is 0 in FIG. 10. It is a figure which shows the characteristic of a suspension apparatus, Comprising: (a) is a figure which shows the relationship between a caster angle, responsiveness, and stability, (b) is a figure which shows the relationship between a caster trail, lateral force reduction allowance, and straightness It is. It is a figure which shows a steering response characteristic, Comprising: (a) is a characteristic diagram which shows the change of the response characteristic of a vehicle, (b) is a figure which shows the switching timing of a control characteristic. It is explanatory drawing which shows the vehicle behavior with which it uses for description of operation | movement of the behavior control part at the time of abnormality. It is a flowchart which shows an example of a steering control process. It is a typical top view which shows the other example of the suspension apparatus which can be applied to this invention. FIG. 9 is a schematic plan view showing still another example of a suspension device that can be applied to the present invention.

Embodiments of an automobile to which the present invention is applied will be described below with reference to the drawings.
(First embodiment)
(overall structure)
FIG. 1 is a schematic diagram showing a configuration of a vehicle 1 according to the first embodiment of the present invention.
In FIG. 1, a vehicle 1 includes a vehicle body 1A, a steering wheel 2, an input side steering shaft 3, a steering angle sensor 4 as a steering angle detection unit, a steering torque sensor 5, a steering reaction force actuator 6, and a steering. And a reaction force actuator angle sensor 7.

Further, the vehicle 1 includes a steering actuator 8, a steering actuator angle sensor 9, an output side steering shaft 10, a steering torque sensor 11, a pinion gear 12, a pinion angle sensor 13, and a rack shaft that constitute a steering mechanism. 14, tie rod 15, tie rod axial force sensor 16, and wheels 17FR, 17FL, 17RR, 17RL.
Further, the vehicle 1 includes a brake disc 18, a wheel cylinder 19, a pressure control unit 20, a vehicle state parameter acquisition unit 21, wheel speed sensors 24FR, 24FL, 24RR, 24RL, a control / drive circuit unit 26, And a mechanical backup 27.

The steering wheel 2 is configured to rotate integrally with the input side steering shaft 3, and transmits a steering input by the driver to the input side steering shaft 3.
The input-side steering shaft 3 includes a steering reaction force actuator 6, and applies a steering reaction force by the steering reaction force actuator 6 to the steering input input from the steering wheel 2.

The steering angle sensor 4 is provided on the input side steering shaft 3 and detects the rotation angle of the input side steering shaft 3 (that is, the steering input angle to the steering wheel 2 by the driver). Then, the steering angle sensor 4 outputs the detected rotation angle of the input side steering shaft 3 to the control / drive circuit unit 26.
The steering torque sensor 5 is installed on the input side steering shaft 3 and detects the rotational torque of the input side steering shaft 3 (that is, the steering input torque to the steering wheel 2). Then, the steering torque sensor 5 outputs the detected rotational torque of the input side steering shaft 3 to the control / drive circuit unit 26.

In the steering reaction force actuator 6, a gear that rotates integrally with the motor shaft meshes with a gear formed in a part of the input-side steering shaft 3, and input by the steering wheel 2 in accordance with an instruction from the control / drive circuit unit 26. A reaction force is applied to the rotation of the side steering shaft 3.
The steering reaction force actuator angle sensor 7 detects the rotation angle of the steering reaction force actuator 6 (that is, the rotation angle by the steering input transmitted to the steering reaction force actuator 6), and sends the detected rotation angle to the control / drive circuit unit 26. Output.

The steered actuator 8 has a gear that rotates integrally with the motor shaft meshes with a gear formed on a part of the output side steering shaft 10, and the output side steering shaft 10 is moved according to an instruction from the control / drive circuit unit 26. Rotate.
The steering actuator angle sensor 9 detects the rotation angle of the steering actuator 8 (that is, the rotation angle output by the steering actuator 8) and outputs the detected rotation angle to the control / drive circuit unit 26. To do.

The output side steering shaft 10 includes a steering actuator 8, and transmits the rotation input by the steering actuator 8 to the pinion gear 12.
The steering torque sensor 11 is installed on the output side steering shaft 10 and detects the rotational torque of the output side steering shaft 10 (that is, the steering torque of the wheels 17FR and 17FL via the rack shaft 14). Then, the steering torque sensor 11 outputs the detected rotational torque of the output side steering shaft 10 to the control / drive circuit unit 26.

The pinion gear 12 meshes with a rack gear formed on the rack shaft 14 and transmits the rotation input from the output side steering shaft 10 to the rack shaft 14.
The pinion angle sensor 13 detects the rotation angle of the pinion gear 12 (that is, the turning angle of the wheels 17FR and 17FL output via the rack shaft 14), and controls / detects the detected rotation angle of the pinion gear 12. Output to.

The rack shaft 14 has spur teeth that mesh with the pinion gear 12, and converts the rotation of the pinion gear 12 into a linear motion in the vehicle width direction.
The tie rod 15 connects both ends of the rack shaft 14 and the knuckle arms of the wheels 17FR and 17FL via ball joints.
The tie rod axial force sensor 16 is installed on each of the tie rods 15 installed at both ends of the rack shaft 14 and detects the axial force acting on the tie rod 15. The tie rod axial force sensor 16 outputs the detected axial force of the tie rod 15 to the control / drive circuit unit 26.

  The wheels 17FR, 17FL, 17RR, and 17RL are configured by attaching tires to tire wheels, and are installed on the vehicle body 1A via the front suspension device 1B. Among these, for the front wheels (steered wheels 17FR, 17FL), the direction of the steered wheels 17FR, 17FL with respect to the vehicle body 1A changes when the knuckle arm is swung by the tie rod 15.

  The pressure control unit 20 generates a braking force corresponding to the amount of depression of the brake pedal based on a braking control signal Sb output mainly from the control / drive circuit unit 26 in the wheel cylinders 19 provided on the wheels 17FR to 17RF. To control. Further, the pressure control unit 20 is a braking force applying unit that controls the braking force applied to one of the left and right steered wheels 17FR and 17FL based on the vehicle behavior control signal Sm output from the control / drive circuit unit 26. Also works.

  The vehicle state parameter acquisition unit 21 acquires the vehicle speed V based on a pulse signal indicating the rotation speed of the wheels output from the wheel speed sensors 24FR, 24FL, 24RR, 24RL. Moreover, the vehicle state parameter acquisition part 21 acquires the slip ratio of each wheel based on the vehicle speed V and the rotational speed of each wheel. Then, the vehicle state parameter acquisition unit 21 outputs the acquired parameters to the control / drive circuit unit 26.

  Further, the vehicle 1 is provided with a hub lateral force sensor 22a built in the hub unit of the front wheels 17FR and 17FL as a tire lateral force detection unit for detecting the tire lateral force of the vehicle 1, and is detected by the hub lateral force sensor 22a. The tire lateral force Ft is output to the control / drive circuit unit 26. Further, the vehicle 1 is provided with a yaw rate sensor 22 b that detects the yaw rate γ of the vehicle 1, and outputs the yaw rate γ detected by the yaw rate sensor 22 b to the control / drive circuit unit 26.

The wheel speed sensors 24FR, 24FL, 24RR, 24RL output a pulse signal indicating the rotational speed of each wheel to the vehicle state parameter acquisition unit 21 and the control / drive circuit unit 26.
The control / drive circuit unit 26 controls the vehicle 1 as a whole, and based on signals input from sensors installed in each part, the steering reaction force of the input side steering shaft 3, the turning angle of the front wheels, or the mechanical backup 27, various control signals are output to the steering reaction force actuator 6, the steering actuator 8, the mechanical backup 27, or the like.

  Further, the control / drive circuit unit 26 converts the detection value by each sensor into a value corresponding to the purpose of use. For example, the control / drive circuit unit 26 converts the rotation angle detected by the steering reaction force actuator angle sensor 7 into the steering angle θs, or converts the rotation angle detected by the steering actuator angle sensor 9 into the steered wheels 17FR and 17FL. The turning angle of the pinion gear 12 detected by the pinion angle sensor 13 is converted to the actual turning angle δr of the steered wheels 17FR and 17FL.

  Note that the control / drive circuit unit 26 includes the rotation angle of the input side steering shaft 3 detected by the steering angle sensor 4, the rotation angle of the steering reaction force actuator 6 detected by the steering reaction force actuator angle sensor 7, and the turning actuator. The rotation angle of the steering actuator 8 detected by the angle sensor 9 and the rotation angle of the pinion gear 12 detected by the pinion angle sensor 13 are monitored, and the occurrence of a failure in the steering system is detected based on these relationships. be able to. When a failure in the steering system is detected, the control / drive circuit unit 26 outputs an instruction signal for connecting the input side steering shaft 3 and the output side steering shaft 10 to the mechanical backup 27.

The mechanical backup 27 connects the input side steering shaft 3 and the output side steering shaft 10 in accordance with instructions from the control / drive circuit unit 26, and ensures transmission of force from the input side steering shaft 3 to the output side steering shaft 10. Mechanism. Here, the control / drive circuit unit 26 normally instructs the mechanical backup 27 not to connect the input side steering shaft 3 and the output side steering shaft 10. If the steering system needs to perform a steering operation without passing through the steering angle sensor 4, the steering torque sensor 5, the steering actuator 8, and the like due to the occurrence of a failure in the steering system, the input side steering shaft 3 and the output side steering shaft 10 is input.
The mechanical backup 27 can be configured by, for example, a cable type steering mechanism or an electromagnetic clutch mechanism.

(Suspension configuration)
FIG. 2 is a perspective view schematically showing the configuration of the front suspension apparatus 1B according to the first embodiment. FIG. 3 is a plan view schematically showing the configuration of the front suspension apparatus 1B of FIG. FIG. 4 is a (a) partial front view and (b) partial side view schematically showing the configuration of the front suspension apparatus 1B of FIG.
As shown in FIGS. 2 to 4, the front suspension apparatus 1B has wheels 17FR and 17FL attached to a wheel hub WH, and has an axle 32 that rotatably supports the wheels 17FR and 17FL. Axle carrier 33, a plurality of link members arranged in the vehicle body width direction from the support portion on the vehicle body side and connected to axle carrier 33, and a spring member 34 such as a coil spring are provided.

  The plurality of link members include a first link (first link member) 37 and a second link (second link member) 38, tie rods (tie rod members) 15, and struts (spring members 34 and shock absorbers) which are lower link members. 40). In the present embodiment, the front suspension device 1B is a strut suspension, and the upper end of the strut ST, in which the spring member 34 and the shock absorber 40 are integrated, is connected to a support portion on the vehicle body side located above the axle 32. (Hereinafter, the upper end of the strut is appropriately referred to as “upper pivot point P1”.) The first link 37 and the second link 38 constituting the lower arm connect the lower end of the axle carrier 33 and the support portion on the vehicle body side located below the axle 32. The lower arm is supported at two locations on the vehicle body side and has an A-arm shape that is coupled at one location with the axle 32 side (hereinafter, a connecting portion between the lower arm and the axle member 33 is appropriately referred to as “lower pivot point P2”. Called).

A stabilizer 41 is connected between the outer cylinders of the left and right shock absorbers 40. The stabilizer 41 is rotatably supported by a bracket 42 in which a linear portion 41a on the vehicle rear side is fixed to a vehicle body side member.
The tie rod 15 is positioned below the axle 32, and connects the rack shaft 14 and the axle member 33. The rack shaft 14 receives a rotational force (steering force) from the steering wheel 2 and is a steering shaft. Generate power. Accordingly, an axial force in the vehicle width direction is applied to the axle member 33 by the tie rod 15 in accordance with the rotation of the steering wheel 2, and the steered wheels 17FR and 17FL are steered through the axle member 33.

  In the present invention, the kingpin axis KS connecting the upper pivot point P1 and the lower pivot point P2 of the front suspension device 1B in the neutral position of the steering wheel 2, that is, in the state where the steered wheels 17FL and 17FR are traveling straight, The road surface contact point of the axis KS is positioned within the tire contact surface. In addition, the caster trail is set so as to be located within the tire ground contact surface.

  More specifically, in the front suspension apparatus 1B according to the present embodiment, the caster angle is set to a value close to zero, and the kingpin axis KS is set so that the caster trail approaches zero. Thereby, the tire twisting torque at the time of steering can be reduced, and the moment around the kingpin axis KS can be further reduced. The scrub radius is a positive scrub with zero or more. As a result, a caster trail corresponding to the scrub radius is generated with respect to the tire side slip angle at the time of turning, so that straight traveling performance can be ensured.

FIG. 5 is a diagram showing the analysis result of the rack axial force in the front suspension apparatus 1B according to the present embodiment.
The solid line shown in FIG. 5 indicates the rack axial force characteristics in the suspension structure shown in FIGS. 2 to 4 when the caster angle is 0 degree, the caster trail is 0 mm, and the scrub radius is +10 mm.
FIG. 5 also shows a comparative example (broken line) when the setting related to the kingpin axis KS is set in accordance with a structure that does not include the steer-by-wire type steering device, in the same suspension structure as the front suspension device 1B. It shows.
As shown in FIG. 5, when set according to the above examination results, the rack axial force can be reduced by about 30% compared to the comparative example.

  Thus, setting the caster angle to 0 degrees can improve the suspension rigidity, and setting the caster trail to 0 mm means that the landing point on the road surface of the kingpin axis KS as shown by reference numeral 3 in FIG. Means to coincide with the tire ground contact center point on the tire ground contact surface, whereby the lateral force reduction effect can be improved. In other words, steering is possible with a light steering force, and the steering response can be improved.

(Ensuring straightness by positive scrub)
FIG. 7 is a conceptual diagram for explaining the self-aligning torque in the case of a positive scrub.
As shown in FIG. 7, the restoring force (self-aligning torque) acting on the tire increases in proportion to the sum of the caster trail and the pneumatic trail.
Here, in the case of positive scrub, a distance εc (see FIG. 7) from the wheel center determined by the position of the leg of the perpendicular line that is lowered from the contact point of the kingpin shaft to the straight line in the direction of the side slip angle β of the tire passing through the tire contact center. It can be regarded as a caster trail.
Therefore, the greater the scrub radius of the positive scrub, the greater the restoring force acting on the tire during turning.

  In the present embodiment, in order to improve the steering response, the influence on the straight running performance by bringing the caster angle close to 0 is reduced by using a positive scrub. In addition, since the steer-by-wire system is adopted, it is possible to ensure the final straightness by the steered actuator 8. Therefore, as suspension geometry, steering response is more important than straightness.

(Suspension design example)
In the configuration of the front suspension apparatus 1B shown in FIGS. 2 to 4, according to the above examination results, the kingpin inclination angle 13.8 degrees, the caster trail 0 mm, the scrub radius 5.4 mm (positive scrub), the caster angle 5.2 degrees, the wheel center When the kingpin offset at the height is 86 mm, the rack axial force can be reduced by about 30%.

Regarding the design value, the suspension lower link moves to the rear of the vehicle at the time of braking, and the lower end of the kingpin moves to the rear of the vehicle at the same time. Therefore, the caster angle has a constant backward inclination. Incidentally, when the caster angle is 0 ° or less (when the kingpin shaft is tilted forward), the rack moment at the time of steering braking is increased, so that the rack axial force is increased. Therefore, the position of the kingpin is defined as described above.
That is, the kingpin lower pivot point (including the virtual pivot) is positioned behind the wheel center, and the kingpin upper pivot point (including the virtual pivot) is positioned behind the lower pivot point.

(Suspension action)
Next, the operation of the front suspension device 1B according to the present embodiment will be described.
In the front suspension apparatus 1B according to the present embodiment, the road contact point of the kingpin axis KS is set to be within the tire contact surface at least at the neutral position of the steering wheel 2. In addition, the caster trail is set to be located within the tire ground contact surface.
For example, the kingpin axis KS is set to a positive scrub having a caster angle of 0 degrees, a caster trail of 0 mm, and a scrub radius of 0 mm or more. The kingpin inclination angle is set within a range where the scrub radius can be a positive scrub and a smaller angle (for example, 15 degrees or less).

By setting it as such a suspension geometry, the locus | trajectory of the tire ground-contact surface center at the time of steering becomes smaller, and a tire torsion torque can be reduced.
Therefore, since the rack axial force can be made smaller, the moment around the kingpin axis KS can be made smaller, and the output of the steered actuator 8 can be reduced. Moreover, the direction of the wheel can be controlled with a smaller force, and the steering response can be improved.

  Also, in order to place importance on steering response, setting the caster angle to 0 degrees and the caster trail to 0 mm may affect the straightness on the suspension structure. The effect can be reduced. Further, in addition to the control by the steering actuator 8, the straightness is ensured. That is, maneuverability and stability can be improved.

  Further, when the tilt angle of the kingpin is limited to a certain range (15 degrees or less), it is possible to avoid the driver from feeling heavy in the steering operation by performing the steering with the steering actuator 8. Further, the kickback due to the external force from the road surface can be countered by the steering actuator 8, so that the influence on the driver can be avoided. That is, maneuverability and stability can be improved.

Next, steering response control in the control / drive circuit unit 26 for controlling the steering actuator 8 will be described with reference to FIG.
That is, as described above, the control / drive circuit unit 26 includes the steering torque Ts of the input side steering shaft 3 detected by the torque sensor 5, the vehicle speed V acquired by the vehicle state parameter acquisition unit 21, and the steering reaction force actuator. The rotation angle θmi of the actuator 6 detected by the angle sensor 7 is input.

The control / drive circuit unit 26 is provided with a steering control unit 50 shown in FIG. The steering control unit 50 includes a target turning angle calculation unit 51, a steering response setting unit 52, and an actuator control device 53.
The target turning angle calculation unit 51 receives the vehicle speed V and the rotation angle θmi, and calculates a target turning angle δ ^* for driving the turning actuator 8 based on these.
The steerable response setting unit 52 includes a straight travel performance securing unit 56 that secures the straight travel performance of the vehicle including the straight travel performance control unit 54 and the disturbance compensation unit 55, and a delay control unit 57.

The straightness control unit 54 compensates for the shortage of the self-aligning torque of the front suspension device 1B described above and gives the steered wheels 17FR, 17FL a restoring force for self-aligning. The straightness control unit 54 includes a self-aligning torque calculation unit 54a and a gain multiplication unit 54b that multiplies the self-aligning torque calculated by the self-aligning torque calculation unit 54a by a predetermined gain.
The self-aligning torque calculator 54a includes the vehicle speed V, the actual turning angle δr of the steered wheels 17FR and 17FL calculated based on the pinion angle detected by the pinion angle sensor 13, and the yaw rate γ detected by the yaw rate sensor 22b. Based on the above, the following equation (1) is calculated to calculate the self-aligning torque Tsa.

Where εc is the caster trail, Kf is the cornering power per front wheel, β is the slip angle at the center of gravity, Lf is the distance between the center of gravity of the front wheel, Kr is the cornering power per wheel of the rear wheel, and Lr is after the center of gravity. The distance between the wheel shafts, m is the mass of the vehicle, and L is the distance between the front and rear wheel shafts.
In this equation (1), the caster trail ε is set to a value obtained by subtracting the caster trail εc2 set in the present embodiment from the caster trail εc0 set in the normal suspension device, thereby applying the front suspension device applied to the present invention. It is possible to calculate the self-aligning torque Tsa to be complemented that is insufficient in 1B.

  The self-aligning torque Tsa is not limited to the case where it is calculated by the above equation (1), but a lateral acceleration sensor for detecting the lateral acceleration Gy of the vehicle is provided, and based on the lateral acceleration Gy of the vehicle and the yaw rate γ of the vehicle. The lateral force Fy is calculated based on the differential value of the yaw rate γ and the lateral acceleration Gy based on the equation of motion of the vehicle, and can be calculated by multiplying the lateral force Fy by the pneumatic trail εn. Furthermore, the steering angle detected by the steering angle sensor 4 by measuring the relationship between the steering angle θs of the steering wheel 2 and the self-aligning torque Tsa using the vehicle speed V as a parameter or referring to a control map calculated by simulation. Based on θs and the vehicle speed V, it is also possible to calculate the self-aligning torque Tsa to be supplemented that is insufficient in the front suspension device 1B. Further, when the steered wheels 17FR and 17FL are used as drive wheels, the generated torque Th generated at the time of steering by a torque steer phenomenon is estimated based on the left and right driving force difference, and the steering torque Ts detected by the steering torque sensor 5 is estimated. It is also possible to calculate the self-aligning torque Tsa to be complemented, which is insufficient in the front suspension device 1B, by reducing the generated torque Th from the above. Similarly, the self-aligning torque Tsa can be calculated based on the braking force difference between the left and right steered wheels 17FR and 17FL.

The gain multiplying unit 54b multiplies the self-aligning torque Tsa calculated by the self-aligning torque calculating unit 54a by a predetermined control gain Ksa to calculate a self-aligning torque control value Asa (= Ksa · Tsa) as a straight-line stability correction value. ) Is calculated.
The disturbance compensation unit 55 receives the steering torque Ts from the steering torque sensor 5, the rotation angle θmo from the steering actuator angle sensor 9, and the motor current imr from the motor current detection unit 64, and the disturbance input to the vehicle. A disturbance compensation value Adis for suppressing these disturbances is calculated by separating and estimating each frequency band.

  In this disturbance compensator 55, as described in, for example, Japanese Patent Laid-Open No. 2007-237840, the steering torque Ts that is a steering input by the driver and the steering input by the steering actuator 8 are used as control inputs, and actual steering is performed. In a model using a state quantity as a control quantity, a disturbance is estimated based on a difference between a value obtained by passing the control input through a low-pass filter and a value obtained by passing the control quantity through an inverse characteristic of the model and the low-pass filter. A plurality of disturbance estimation units; Each disturbance estimation part isolate | separates a disturbance for every several frequency band by varying the cutoff frequency of a low-pass filter.

Then, the disturbance compensation value Adis calculated by the straightness control unit 54 and the disturbance compensation unit 55 and the self-aligning torque control value Asa are added by the adder 56a and become the output of the straightness guaranteeing unit 56. δa is calculated. The straight running stability control value δa is supplied to the delay control unit 57.
As shown in FIG. 8, the delay control unit 57 includes a steering start detection unit 57a, a monostable circuit 57b, a gain adjustment unit 57c, and a multiplier 57d.

The steering start detection unit 57a detects the timing of right steering or left steering from the state where the neutral position is maintained based on the steering angle θs detected by the steering angle sensor 4, and indicates the steering start signal SS indicating the steering start from the neutral state. Is output to the monostable circuit 57b.
Further, the monostable circuit 57b outputs a control start delay signal that is turned on for a predetermined delay time, for example, 0.1 seconds, to the gain adjustment unit 57c based on the steering start signal output from the steering start detection unit 57a.

The gain adjustment unit 57c sets the control gain Ga to “0” when the control start delay signal is on, and sets the control gain Ga to “1” when the control start delay signal is off. The set control gain Ga is output to the multiplier 57d.
The multiplier 57d receives the straight running stability control value δa output from the adder 56, multiplies the straight running stability control value δa by the control gain Ga, and outputs the multiplication result from the target turning angle calculation unit 51. The target turning angle δ ^* is supplied to the adder 57e.

Therefore, when the delay control unit 57 detects the steering start state in which the right steering or the left steering is performed from the state where the neutral state is maintained by the steering start detection unit 57a, the straight running stability calculated by the adder 56 is detected. The straight-line stability control value δa is controlled by the gain adjustment unit 57c so that the straight-line stability ensuring control for adding the control value δa to the target turning angle δ ^* is stopped for a predetermined time set by the monostable circuit 57b, for example, 0.1 second. Is set to “0”. When the output signal of the monostable circuit 57b is inverted to the OFF state after 0.1 seconds have elapsed, the gain adjusting unit 57c adds the straight-line stability control value δa to the target turning angle δ ^* . The control gain Ga is set to “1” so as to start the straight running stability ensuring control.

Further, when the steering wheel 2 is continuously steered, the delay control unit 57 does not detect the steering start from the neutral state by the steering start detection unit 57a, so that the output of the monostable circuit 57b maintains the off state. Thus, the control gain Ga is set to “1” by the gain adjusting unit 57c. For this reason, the straight running stability control value δa calculated by the adder 56 is supplied to the adder 56e as it is. For this reason, the straight-running stability control value δa is added to the target turning angle δ ^*, and straight-running stability ensuring control is performed.
Further, the turning control unit 50 includes an abnormality detection unit 58 that detects an abnormality of the straightness control unit 54 and an abnormal behavior control unit 59 that controls the vehicle behavior when the abnormality of the straightness control unit 54 is detected.

  The abnormality detection unit 58 includes the rotation angle θs of the input side steering shaft 3 detected by the steering angle sensor 4, the vehicle speed V calculated by the vehicle state parameter acquisition unit 21, and the self-aligning torque calculation unit 54a of the straightness control unit 54. The self-aligning torque Tsa output from is input. In this abnormality detection unit 58, for example, in a state where the vehicle has started running, that is, in a state where | V |> 0, and when the steering is started to the right or left from the neutral position of the steering angle θs, the change amount Δθs of the steering angle θs is changed. When the absolute value | Δθs | becomes equal to or larger than the predetermined threshold value Δθth, the change amount ΔTsa of the self-aligning torque Tsa calculated by the self-aligning torque calculation unit 54a according to the above equation (1) is set to a preset value ΔTss. It is determined whether it is above. Then, the abnormality detection unit 58 determines that the straightness control unit 54 is normal when the determination result is ΔTsa ≧ ΔTss, and determines that the straightness control unit 54 is abnormal when ΔTsa <ΔTss. To do. The abnormality detection unit 58 outputs a fail signal Sf having a logical value “0” when the straightness control unit 54 determines that the normality control unit 54 is normal, and outputs a logical value “1” when the straightness control unit 54 is abnormal. A fail signal Sf is output.

Note that the abnormality determination of the straightness control unit 54 in the abnormality detection unit 58 is not limited to the above, and is a situation where the self-aligning torque Tsa changes in the traveling state of the vehicle and in the steering state. Monitoring may be performed to determine that the straightness control unit 54 is abnormal when the change in the self-aligning torque Tsa is not longer than a predetermined time or when the amount of change within the predetermined time is small.
Further, the abnormality detection unit 58 may detect an abnormality of the straightness control unit 54 based on the self-aligning torque control value Asa output from the gain multiplication unit 54b.
Further, the control / drive circuit unit 26 includes an abnormal behavior control unit 59 that is operated when the abnormality detection unit 58 detects that the straightness control unit 54 is abnormal.

  The abnormal behavior control unit 59 receives the steering angle θs detected by the steering angle sensor 4, the tire lateral force Ft detected by the hub lateral force sensor 22 a, and the fail signal Sf from the abnormality detection unit 58. The vehicle speed V calculated by the state parameter acquisition unit 21 is input. The abnormal behavior control unit 59 enters an operating state when the failure signal Sf is input from the abnormality detection unit 58, calculates the target tire lateral force, and calculates the calculated target tire lateral force and tire lateral force Ft. The vehicle behavior control signal Sm is output to the pressure control unit 20 as a braking force applying unit that controls the braking force of the front wheels 17FR and 17FL so as to match.

The abnormal behavior control unit 59 executes an abnormal behavior control process for stabilizing the vehicle behavior when the fail signal Sf having the logical value “1” is input.
This abnormal behavior control process is started when the fail signal Sf is input, and is executed as a timer interrupt process executed every predetermined time (for example, 1 μsec).
In the abnormal behavior control process, as shown in FIG. 9, first, the vehicle speed V is read in step S1, then the process proceeds to step S2, and the steering angle θs is read in step S2, and then the process proceeds to step S3.

In this step S3, it is determined whether or not the steering angle θs read in step S2 is “0”, that is, whether the vehicle is traveling straight, and if θ ≠ 0, it is determined that the vehicle is turning, and the process proceeds to step S4. . In step S4, the tire lateral force Ft0 detected by the hub lateral force sensor 22a on the turning outer wheel side is read, and then the process proceeds to step S5.
In step S5, the target tire lateral force Ft ^* on the turning outer wheel side is calculated based on the vehicle speed V and the steering angle θs with reference to the target tire lateral force calculation map shown in FIG. 10, and then the process proceeds to step S6. Here, the target tire lateral force calculation map, as shown in FIG. 10, has a relationship between the vehicle speed V and the target tire lateral force Ft ^* on the turning outer wheel side with a positive steering angle θs (for example, when turning right) as a parameter. Represents. That is, characteristic lines L0, L1, L2, L3 representing the relationship between the vehicle speed V and the target tire lateral force Ft ^* on the turning outer wheel side for each of the steering angles θs0, θs1, θs2, θs3, and θs4 obtained through experiments or simulations. L4 is set.

  In this target tire lateral force calculation map, the points on the characteristic lines L1 to L4 represent the target tire lateral force having the vehicle steering characteristic as the neutral steering. Therefore, a region where the steering angle θs is small with the characteristic lines L1 to L4 as the boundary lines is set as an understeer region, and a region where the steering angle θs is large is set as an oversteer region. Similarly, although not shown, a target tire lateral force calculation map using a negative steering angle θs (for example, when turning left) as a parameter is also provided.

In a straight traveling state in which the steering angle θs is zero, the vehicle steer area cannot be set. Therefore, as shown in FIG. 11, the tire lateral force of the left and right wheels is read and a large value of the tire lateral force turns. Since it becomes an outer ring, a braking force is applied to the turning outer wheel to suppress turning.
In step S6, the calculated target tire lateral force Ft ^* and tire lateral force Ft are compared, and it is determined whether or not both are equal (Ft = Ft ^* ). If the tire lateral force Ft is equal to the target tire lateral force Ft ^* , that is, if Ft = Ft ^*, it is determined that the vehicle steer characteristic neutral steer is maintained, and the timer interrupt process is performed. To return to a predetermined main program.

On the other hand, when the determination result in step S6 is Ft ≠ Ft ^* , the process proceeds to step S7, and the deviation obtained by subtracting the tire lateral force Ft on the outer turning wheel side from the target tire lateral force Ft ^* on the outer turning wheel side is positive. It is determined whether or not there is. When the determination result is Ft ^* −Ft> 0, it is determined that the tire lateral force Ft is smaller than the target tire lateral force Ft ^* and the vehicle characteristic is understeer, and the process proceeds to step S8. In this step S8, a vehicle behavior control signal Sm for applying a braking force to the wheel cylinder 19 of the turning inner wheel is output to the pressure control unit 20, and then the timer interruption process is terminated and a predetermined main Return to the program.

On the other hand, when the determination result of step S7 is Ft ^* −Ft <0, it is determined that the vehicle steer characteristic is oversteer, and the process proceeds to step S9. In this step S9, after outputting a vehicle behavior control signal Sm for applying a braking force to the wheel cylinder 19 of the wheel on the turning outer wheel side, the timer interruption process is terminated.
Further, when the determination result of step S3 described above is θs ≠ 0, the process proceeds to step S10, and the tire lateral forces FtL and FtR of the left and right wheels are read, and then the process proceeds to step S11.

  In this step S11, it is determined whether or not a deviation obtained by subtracting the tire lateral force FtL of the left wheel from the tire lateral force FtR of the right wheel is positive. When the determination result is FtR−FtL> 0, it is determined that the vehicle is going to shift from the straight traveling state to the right turning state, and the process proceeds to step S12. In step S12, a vehicle behavior control signal Sm for applying a braking force to the wheel cylinder 19 for the right wheel is output to the pressure control unit 20, and then the timer interruption process is terminated and the process returns to a predetermined main program.

  Further, when the determination result in step S11 is FtR−FtL ≦ 0, the process proceeds to step S13 to determine whether or not FtR−FtL <0. When this determination result is FtR−FtL <0, it is determined that the vehicle is about to shift to the left turn state, the process proceeds to step S14, and the vehicle behavior control for applying the braking force to the wheel cylinder 19 of the left wheel is performed. After outputting the signal Sm to the pressure control unit 20, the timer interruption process is terminated and the process returns to a predetermined main program.

Furthermore, when the determination result in step S13 is FtR = FtL, it is determined that the straight traveling state is maintained, the timer interruption process is terminated, and the process returns to the predetermined main program.
The actuator control device 53 includes a turning angle deviation calculation unit 61 that calculates a turning angle deviation Δδ, a turning motor control unit 62, a current deviation calculation unit 63, and a motor current control unit 65.

The turning angle deviation calculating unit 61 subtracts the actual turning angle δr based on the turning actuator angle output from the turning actuator angle sensor 9 from the target steering angle correction value δ ^* a output from the adder 57e. The steering angle deviation Δδ is calculated, and the calculated steering angle deviation Δδ is output to the steered motor control unit 62.
The steered motor control unit 62 calculates the drive command current im ^* of the steered motor 8a constituting the actuator 8 so that the input steered angle deviation Δδ becomes zero, and the calculated drive command current im ^* Output to the deviation calculator 63.

The current deviation calculation unit 63 subtracts the motor current imr output from the motor current detection unit 64 that detects the motor current supplied to the steered motor 8a constituting the steered actuator 8 from the input drive command current im ^*. The current deviation Δi is calculated, and the calculated current deviation Δi is output to the motor current control unit 65.
The motor current control unit 65 performs feedback control so that the input current deviation Δi becomes zero, that is, the actual motor current imr follows the drive command current im ^* , and this motor current imt is the turning motor. Is output to 8a.

(Operation of the first embodiment)
Next, the operation of the first embodiment will be described with reference to FIGS.
It is assumed that the straightness control unit 54 is normal and the vehicle is traveling straight with the steering wheel 2 held at the neutral position.
In this straight traveling state, the target turning angle δ ^* calculated by the target turning angle calculation unit 51 is zero. For this reason, the rack shaft 14 is controlled to the neutral position by the steering motor 8a controlled by the actuator control device 53, and the steering angle δr of the steered wheels 17FR and 17FL is controlled to zero through the tie rod 15. At this time, since the steering wheel 2 holds the neutral position, the yaw rate γ of the vehicle detected by the yaw rate sensor 22b is zero, and the self-aligning torque calculation unit 54a of the straightness control unit 54 performs the above (1). The self-aligning torque Tsa calculated according to the equation is zero because the center-of-gravity point side slip angle β is zero and the yaw rate γ is zero because the steering angle δr is zero.

The disturbance compensation unit 55 calculates a disturbance compensation value Adis that suppresses the disturbance. Therefore, when the disturbance is not generated, the disturbance compensation value Adis is also zero.
Further, the abnormality behavior control unit 59 stops operating because the straightness control unit 54 is normal and the failure signal Sf having the logical value “1” is not input from the abnormality detection unit 58.
In this state, the turning angle deviation Δδ output from the turning angle deviation calculating unit 61 of the actuator control device 53 is also zero, and the motor current command value im ^* output from the turning motor control unit 62 is also zero. Therefore, the motor current imt is not output from the motor current control unit 65, the steered motor 8a maintains the stopped state, the rack shaft 14 maintains the neutral position, and the steered angles δt of the steered wheels 17FR and 17FL are “0”. Is controlled.

  In this straight traveling state, when at least one of the steered wheels 17FR and 17FL is trapped, passes through the manhole cover, and one of the steered wheels 17FR and 17FL is steered, or yaw rate γ is generated, The self-aligning torque Tsa calculated by the self-aligning torque calculating unit 54a of the straightness control unit 54 increases. At this time, when the steering wheel 2 is set to pass through the tire contact surface with the steering wheel 2 in the neutral position as in the above-described front suspension device 1B, the steering response is more important than the straight running stability. The self-aligning torque Tsa generated in the front suspension device 1B itself is insufficient.

  However, in the present embodiment, since the self-aligning torque Tsa is calculated based on the above-described equation (1), the present embodiment is implemented from the caster trail εc0 that is set by the normal front suspension device in the equation (1). The self-aligning torque Tsa calculated by setting the value obtained by subtracting the caster trail εc2 of the front suspension device that places importance on the responsiveness set in the form places importance on the turning responsiveness applied to the present embodiment The value to be complemented corresponding to the self-aligning torque that is insufficient in the front suspension apparatus 1B can be calculated. Then, the calculated self-aligning torque Tsa is multiplied by the gain Ksa to calculate the self-aligning torque control value Asa, and this self-aligning torque control value Asa is supplied to the delay control unit 57.

At this time, since the delay control unit 57 is in the straight traveling state, the steering start detection unit 57a does not detect the start of steering, and the gain adjustment unit 57c sets the gain Ga to “1”. For this reason, the self-aligning torque control value Asa is supplied to the adder 57e as it is.
For this reason, when the target turning angle δ ^* is corrected by the self-aligning torque control value Asa, the steering motor 8a constituting the turning actuator 8 is driven and controlled by the actuator control device 53, and the turning motor 8a is controlled. Thus, a restoring force for self-aligning corresponding to the self-aligning torque Tsa is generated and transmitted to the steered wheels 17FR and 17FL via the rack shaft 14 and the tie rod 15.

For this reason, the self-aligning torque Tsa serving as a restoring force for self-aligning is applied to the steered wheels 17FR and 17FL, so that the shortage of the self-aligning torque in the front suspension device 1B is complemented and the vehicle is traveling straight. Can be secured.
However, when the steering wheel 2 is steered to the right (or left) from the state of maintaining the straight traveling state in which the steering wheel 2 is held at the neutral position, the steered state by steering from the straight traveling state The shift to is detected by the steering start detector 57a.

  For this reason, a control delay signal that is turned on for a predetermined time, for example, 0.1 seconds, is output from the monostable circuit 57b to the gain adjusting unit 57c. Accordingly, the gain adjustment unit 57c sets the control gain Ga to “0” while the control delay signal is kept on. For this reason, the multiplication output outputted from the multiplier 57d is “0”, and the output of the straightness ensuring control value δa to the adder 57e is stopped.

Therefore, since the control gain Ga is set to “0” during the initial response period T1 of 0.1 seconds from the time when the steering is started from the neutral position of the steering wheel 2, the multiplication output output from the multiplier 57d is It becomes “0”, and the straight traveling guarantee control with respect to the target turning angle δ ^* is stopped as shown by the solid line in FIG.
Therefore, the steering angle θs detected by the steering angle sensor 4 is supplied to the target turning angle calculation unit 51, and the target turning angle δ ^* calculated by the target turning angle calculation unit 51 is directly calculated as the turning angle deviation. Supplied to the unit 61. For this reason, the turning motor 8a is rotationally driven so as to coincide with the target turning angle δ ^* . During this time, the straightness ensuring control in the straightness control unit 54 is stopped.

Therefore, in the initial response period T1, the turning by the front suspension device 1B in which the road surface contact point of the kingpin axis KS is set at the contact center position in the tire contact surface and the caster angle is set to zero is started.
At this time, the caster angle of the front suspension device 1B is set to zero. As shown in FIG. 12A, when the caster angle is zero, the relationship between the caster angle, the steering response, and the steering stability is high, but the steering stability is high. It cannot be ensured, that is, there is a trade-off relationship between the steering response to the caster angle and the steering stability.

For this reason, in the initial state where the steering is started from the neutral position, the straight suspension ensuring control by the steer-by-wire control is not executed, and the front suspension device 1B covers this initial turning.
In the initial response period T1, the front suspension apparatus 1B has a caster angle of zero and high steering response as described above, and therefore, as indicated by the characteristic line L1 shown by the solid line in FIG. A steered response characteristic (yaw rate) higher than a steered response characteristic (yaw rate) in a vehicle having a general steer-by-wire steering system indicated by a characteristic line L2 shown in the drawing can be obtained. At this time, since the turning angle changes corresponding to the steering angle change caused by the steering of the steering wheel 2 by the driver, the driver does not feel uncomfortable.

  However, if the steering is continued beyond the initial response period T1 only by the steering response by the front suspension device 1B, the middle response period T2 and the late response period T3 as shown by the characteristic line L3 in FIG. The steering response of the vehicle by steering becomes sensitive. In addition, the phenomenon of getting inside the vehicle from the middle period response period T2 to the latter period response period T3 becomes large.

Therefore, in the first embodiment, as shown in FIG. 13B, the target turning angle by the straightness control unit 54 and the disturbance compensation unit 55 is, for example, 0.1 seconds after the initial response period T1 has elapsed. Straightness guarantee control for δ ^* is started in steps. For this reason, the steering response of the vehicle by the front suspension device 1B is suppressed to suppress the vehicle wobble, and the straightness of the front suspension device 1B is controlled by the steer-by-wire control as shown by the dotted line in FIG. It can be supplemented to ensure steering stability.

  Thereafter, after 0.3 second has elapsed, for example, when the medium-term response period T2 ends, the turning response characteristic is further suppressed by the straightness ensuring control by the straightness control unit 54 even when compared with a general vehicle turning response characteristic. And understeer tendency. Thereby, as shown by the characteristic line L1 shown by the solid line in FIG. 13A, the steering stability can be improved, and an ideal vehicle turning response characteristic indicated by the characteristic line L1 can be realized. .

  When the straightness control unit 54 is in a normal state, an abnormality occurs in the straightness control unit 54, or a disconnection or a ground fault occurs in the input system of the straightness control unit 54, thereby forming the straightness control unit 54. When the self-aligning torque Tsa calculated by the self-aligning torque calculating unit cannot be calculated, the abnormality detecting unit 58 detects this. Therefore, a failure signal Sf having a logical value “1” is output from the abnormality detection unit 58 to the behavior control unit 59 at the time of abnormality.

However, in this embodiment, when the failure signal Sf having the logical value “1” is input from the abnormality detection unit 58 to the abnormal behavior control unit 59, the abnormal behavior control unit 59 is activated at the same time. , The abnormal behavior control process shown in FIG. 9 is executed.
Therefore, when the vehicle is in a turning state, the steering angle θs read in step S2 is θs ≠ 0. Therefore, in the process of FIG. 9, the process proceeds from step S3 to step S4, and the turning outer wheel side The tire lateral force Ft detected by the hub lateral force sensor 22a is read. Next, the process proceeds to step S5, where the characteristic line Li (Li = L1 to L4) of the target tire lateral force calculation map shown in FIG. 10 is selected based on the steering angle θs, and the selected characteristic line Li and the vehicle speed V Based on the above, a target tire lateral force Ft ^* on the outer wheel side having neutral characteristics is calculated.

Thereafter, a deviation Ft ^* −Ft obtained by subtracting the tire lateral force Ft of the outer wheel from the target tire lateral force Ft ^* on the outer wheel side is calculated, and when the deviation Ft ^* −Ft is “0”, the neutral steer characteristic is The timer interrupt process is terminated as it is maintained, and it waits until the next timer interrupt process is started.
However, when the road surface external force acts on the turning outer wheel side and the tire lateral force Ft on the turning outer wheel side is smaller than the target tire lateral force Ft ^* , the outer wheel side of the steered wheels 17FR and 17FL returns to the understeer side, that is, the straight traveling state. It is determined that the tire lateral force is acting in the direction. Accordingly, the process proceeds from step S7 to step S8, and the vehicle behavior control signal Sm for generating a braking force corresponding to the tire lateral force deviation is output to the pressure control unit 20 on the turning inner wheel side wheel. For this reason, the pressure control unit 20 supplies a braking pressure to the wheel cylinder 19 of the turning inner wheel side wheel to apply a braking force to the turning inner wheel side wheel. For this reason, a yaw moment for returning the vehicle to the neutral steering direction is generated, and the steering characteristic of the vehicle is corrected to the neutral steering side.

Conversely, when the road lateral force acts on the turning outer wheel side and the tire lateral force Ft on the turning outer wheel side is larger than the target tire lateral force Ft ^* , the outer wheel side of the steered wheels 17FR and 17FL is on the oversteer side, that is, the turning radius. It is determined that the tire lateral force is acting in the direction of decreasing. Accordingly, the process proceeds from step S7 to step S9, and the vehicle behavior control signal Sm for generating the braking force corresponding to the tire lateral force deviation is output to the pressure control unit 20 on the wheels on the turning outer wheel side. For this reason, the pressure control unit 20 supplies a braking pressure to the wheel cylinder 19 of the turning outer wheel side wheel to apply a braking force to the turning outer wheel side wheel. For this reason, a yaw moment for returning the vehicle to the neutral steering direction is generated, and the steering characteristic of the vehicle is corrected to the neutral steering side.

Therefore, as shown in FIG. 14, when an abnormality occurs in the steer-by-wire system SBW and it becomes impossible to perform the steering control of the steered wheels 17FR and 17FL, the vehicle characteristics vary depending on the steering angle θs at that time. A target tire lateral force Ft ^* that is neutral steer is calculated, and a braking force is applied to either of the left and right wheels so that the tire lateral force Ft coincides with the target tire lateral force Ft ^* and is shown by a curve L11 in FIG. As described above, the vehicle can turn while maintaining the neutral steer.

  Incidentally, when the abnormal behavior control unit 59 is not applied, since the steering response to the front suspension device 1 is high and the self-aligning torque is insufficient, the steered wheels 17FR and 17FL are steered by disturbance input from the road surface. It becomes easy to be done. For this reason, the behavior of the vehicle becomes unstable, and the turning travel route of the vehicle becomes a zigzag travel route as shown exaggeratedly by the curved line L12 shown in FIG. 14, which gives the driver an uncomfortable feeling.

  According to the present embodiment, as described above, since the braking force of the left and right wheels is controlled by the abnormal behavior control unit 59 so as to maintain the neutral steer, the vehicle behavior is stable without being affected by disturbance input from the road surface. It is possible to turn and travel through a smooth travel route. Therefore, the driver does not feel uncomfortable.

  In addition, when the vehicle is traveling straight and the steering angle θs is “0”, the steering characteristic of the vehicle cannot be determined as in the turning state, so that the left and right steered wheels 17FR and 17FL are located next to the hub. The tire lateral forces FtR and FtL detected by the force sensor 22a are read (step S10). As shown in FIG. 11, when the tire lateral force FtR of the right wheel 17FR is greater than the tire lateral force FtL of the left wheel 17FL among the left and right tire lateral forces FtR and FtL (FtR−FtL> 0), the vehicle turns counterclockwise. It is determined that the tire lateral force is acting in the direction of rotation. For this reason, a braking pressure is applied to the wheel cylinder 19 of the right steered wheel 17FL so as to generate a braking force corresponding to the tire lateral force deviation. For this reason, the left turn of a vehicle is suppressed, neutral steer can be maintained, and straightness can be secured.

  Conversely, when the tire lateral force FtL of the left wheel 17FL is greater than the tire lateral force FtR of the right wheel 17FR among the left and right tire lateral forces FtR and FtL (FtR-FtL <0), the tire is turned in the direction of turning right. Judge that the lateral force is acting. For this reason, a braking pressure is applied to the wheel cylinder 19 of the left steered wheel 17FL so as to generate a braking force corresponding to the tire lateral force deviation. For this reason, the right turn of the vehicle is suppressed, neutral steering can be maintained, and straight travel performance can be ensured.

Further, when the left and right tire lateral forces FtR and FtTL are equal (FtR = FtL), it is determined that the vehicle has the neutral steer characteristic and the vehicle behavior control signal Sm is output to the pressure control unit 20. It ends the timer interrupt process and waits for the next timer interrupt process.
As described above, when an abnormality occurs in the straightness control unit 54 and an abnormal state occurs in which the self-aligning torque generated in the front suspension device 1B is insufficient, the abnormal behavior control unit 59 is activated and is caused by the road surface external force. Steering of the front suspension can be suppressed. Therefore, it is possible to stabilize the vehicle behavior by suppressing the yaw rate change due to the road surface disturbance when the straightness control unit 54 is abnormal.

  In the present embodiment, the input side steering shaft 3, the steering reaction force actuator 6, the steering reaction force actuator angle sensor 7, the turning actuator 8, the turning actuator angle sensor 9, the output side steering shaft 10, and the turning control unit. A control / drive circuit unit 26 including 50 constitutes a steer-by-wire system SBW. The wheels 17FR, 17FL, 17RR, and 17RL correspond to a tire wheel, a tire, and a wheel hub mechanism, and the first link 37, the second link 38, and the shock absorber 40 correspond to a plurality of link members. The first link 37 and the second link 38 constitute a lower arm, and the spring member 34 and the shock absorber 40 constitute a strut member ST.

In the first embodiment, the case where the turning control unit 50 is configured by hardware has been described. However, the present invention is not limited to this, and for example, the target turning angle calculation unit 51, the turning responsiveness, and the like. The setting unit 52 may be configured by an arithmetic processing device such as a microcomputer, and the steering control processing shown in FIG. 15 may be executed by this arithmetic processing device.
As shown in FIG. 15, in this steering control process, first, in step S21, the vehicle speed V, the steering angle θs detected by the steering angle sensor 4, the rotation angle θmo detected by the steering actuator angle sensor 9, the steering torque sensor Data necessary for the calculation processing such as the steering torque Ts detected in 5 is read. Subsequently, the process proceeds to step S22, and whether or not the steering wheel 2 is steered to the right or left from the state in which the steering wheel 2 holds the neutral position based on the steering angle θs detected by the steering angle sensor 4 is determined. When the steering is not started, the process proceeds to step S23.

In this step S23, it is determined whether or not the control flag F indicating the steering start control state is set to “1”. When the control flag F is reset to “0”, the process proceeds to step S24. Then, after the control gain Ga is set to “1”, the process proceeds to step S25.
In this step S25, the target turning angle δ ^* is calculated based on the vehicle speed V and the steering angle θs as in the target turning angle calculation unit 51 described above.
Subsequently, the process proceeds to step S26, and the self-aligning torque Tsa which is insufficient in the front suspension device 1B by performing the calculation of the above-described equation (1), similarly to the self-aligning torque calculating unit 54a of the straightness control unit 54 described above. Is calculated by multiplying the self-aligning torque Tsa by a predetermined gain Ksa to calculate the self-aligning torque control value Asa.

Next, the process proceeds to step S27, and the disturbance input to the vehicle is determined for each frequency band based on the motor rotation angle θmo from the steering actuator angle sensor 9, the steering torque Ts, and the motor current imr detected by the motor current detection unit 64. The disturbance compensation value Adis for suppressing these disturbances is calculated.
Next, the process proceeds to step S28, where the target turning angle after addition is performed by calculating the following formula (2) based on the target turning angle δ ^* , the self-aligning torque control value Asa, and the disturbance compensation value Adis. δ ^* a is calculated.
δ ^* a = δ ^* + Ga (Asa + Adis) (2)

Next, the process proceeds to step S29, where the post-addition target turning angle δ ^* a calculated in step S28 is output to the turning angle deviation calculating unit 61 in FIG. 8, and then the process returns to step S21.
When the determination result in step S22 is the steering start state, the process proceeds to step S30, and the control flag F is set to “1”, and then the process proceeds to step S31. Further, when the determination result of step S23 indicates that the control flag F is set to “1”, the process directly proceeds to step S31.

In step S31, it is determined whether a preset delay time (for example, 0.1 second) has elapsed. At this time, when the delay time has not elapsed, the process proceeds to step S32, the control gain Ga is set to “0”, then the process proceeds to step S25, and the target turning angle δ ^* is calculated.
If the determination result in step S31 indicates that a predetermined delay time (for example, 0.1 second) has elapsed, the process proceeds to step S33, the control flag F is reset to “0”, and then the process proceeds to step S24. Thus, the control gain Ga is set to “1”.

Also in the steering control calculation process shown in FIG. 15, when the steering wheel 2 is not in the steering start state in which the steering is started to the right or left from the state where the steering wheel 2 is held at the neutral position, the target steering angle δ ^{* is set} to the self-adjusting angle. Straightness ensuring control is performed in which the straightness ensuring control value δa obtained by adding the lining torque control value Asa and the disturbance compensation value Adis is added to the target turning angle δ ^* .
On the other hand, when the steering wheel 2 is in the steering start state in which the steering is started to the right or left from the state where the steering wheel 2 is held in the neutral position, the control gain Ga is set until the preset delay time elapses. Since it is set to “0”, the straight travel guarantee control is stopped. For this reason, only the target turning angle δ ^* is output to the turning angle deviation calculating unit 61, and thereby the turning motor 8a constituting the turning actuator 8 is rotationally driven. For this reason, the high turning response of the suspension device itself is set as the initial turning response, and the high turning response can be obtained.

Thereafter, when the delay time elapses, the control gain Ga is set to “1”. Therefore, the straight travel guarantee control value δa obtained by adding the self-aligning torque control value Asa and the disturbance compensation value Adis to the target turning angle δ ^*. Is rotated by a value obtained by adding to the target turning angle δ ^* . For this reason, while the high steering response of the front suspension apparatus 1B is suppressed, the straight advanceability of the front suspension apparatus 1B is ensured, and an ideal steering response characteristic can be obtained.

Even in this steering control process, when the vehicle is traveling straight, the target turning angle δ ^* is zero, and when no disturbance occurs, the target turning angle δ ^* is directly converted into the turning angle deviation calculation unit of FIG. Since it is supplied to 61, the straightness is secured by the actuator control device 53 as described above.
In the process of FIG. 15, the process of step S25 corresponds to the target turning angle calculation unit 51, the process of step S26 corresponds to the straightness control unit 54, the process of step S27 corresponds to the disturbance compensation unit 55, The processes of steps S22 to S24 and S30 to S33 correspond to the delay control unit 57, and the processes of steps S22 to 33 correspond to the steering response setting unit 52.

(Effect of 1st Embodiment)
(1) A front suspension device in which the kingpin shaft passing through the upper pivot point and the lower pivot point is set to pass through the tire ground contact surface at the neutral position of the steering wheel, and the actuator is operated according to the steering state of the steering wheel, A steer-by-wire system that steers left and right steered wheels separated from a steering wheel, and operates the actuator provided in the steer-by-wire system to restore the steered wheels for self-alignment A straightness control unit that generates force, a vehicle speed detection unit that detects the vehicle speed of the vehicle, a tire lateral force detection unit that detects tire lateral force of the vehicle, and a steering angle detection unit that detects the steering angle of the steering wheel , Braking that individually applies braking force to the left and right wheels An abnormality detection unit that detects an abnormality in the imparting unit, an abnormality detection unit that detects an abnormality in the straightness control unit, and a target tire lateral force based on the steering angle and the vehicle speed when the abnormality detection unit detects an abnormality in the straightness control unit. And an abnormal behavior control unit that controls the braking force application unit so that the tire lateral force coincides with the target tire lateral force.

According to this configuration, since the moment around the kingpin axis of the suspension device can be further reduced, the steering can be performed with a smaller rack axial force, and the direction of the wheel can be controlled with a smaller force.
Therefore, the steering response can be improved. At this time, by setting the caster angle to a value close to zero, it is possible to configure a suspension device with improved steering response.
Furthermore, the straightness control unit can ensure the decrease in straightness of the vehicle due to ensuring the steering response of the suspension device.

  Then, when an abnormality occurs in the straightness control unit and the restoring force for self-aligning generated in the front suspension device becomes insufficient, the abnormal behavior control unit is activated and the tire sideways The braking force application unit is controlled so that the force matches the target tire lateral force. For this reason, it is possible to stabilize the vehicle behavior by suppressing the fluctuation of the vehicle steer characteristic due to the influence of the external input from the road surface. At this time, stabilization control of the vehicle behavior is performed by detecting the tire lateral force and controlling the braking force of the braking force applying unit so that the tire lateral force coincides with the target tire lateral force. Therefore, the yaw rate is calculated as in the conventional example, and the response delay caused when the vehicle behavior control is performed based on the calculated yaw rate can be suppressed, and the quick behavior control can be appropriately performed.

(2) The front suspension device that supports the steered wheels is set to a suspension geometry that places greater emphasis on steered response than straight-line stability.
According to this configuration, the front suspension device can be turned with a light turning force, and the turning mechanism can be reduced in weight.
(3) The straightness control unit calculates a self-aligning torque that complements the shortage of the self-aligning torque of the front suspension device.
According to this configuration, the shortage of the self-aligning torque of the front suspension device can be supplemented to ensure the straight running stability of the vehicle.

(4) The abnormal behavior control unit applies a braking force to one of the left and right wheels so that the tire lateral force and the target tire lateral force coincide with each other, thereby setting the vehicle steering characteristic to neutral steering.
According to this configuration, it is possible to obtain a vehicle steering characteristic in accordance with the steering feeling when the driver steers the steering wheel, and to reliably prevent the driver from feeling uncomfortable.

(5) The abnormal behavior control unit calculates the target tire lateral force with reference to a target tire lateral force calculation map in which a characteristic line representing a relationship between the vehicle speed and the tire lateral force is set with the steering angle as a parameter.
According to this configuration, the target tire lateral force can be calculated immediately by referring to the target tire lateral force calculation map based on the steering angle and the vehicle speed, and the target tire lateral force can be calculated quickly and accurately. Can be done.

(6) In the target tire lateral force calculation map, a tire lateral force necessary to obtain a neutral steering characteristic corresponding to the steering angle is defined.
According to this configuration, the vehicle steering characteristic is set to neutral steer only by controlling the braking force on the left and right wheels so that the tire lateral force matches the target tire lateral force calculated with reference to the target tire lateral force calculation map. Can be controlled.

(7) The tire lateral force detection unit includes a hub lateral force sensor built in the hub unit.
According to this configuration, the lateral force acting on the tire can be directly and accurately detected by the hub lateral force sensor without causing a detection delay.
(8) The front suspension device is set so that the kingpin shaft passes through the tire contact surface when the steering wheel is in the neutral position. In addition, the straightness of the suspension device is secured by the straightness securing portion.

(Application example of the first embodiment)
In the first embodiment, the case where the steering rack member 14 is driven by one steering actuator 8 has been described. However, the present invention is not limited to this, and the steering rack member 14 is applied by applying two steering actuators. May be driven. In this case, the steering rack member 14 can be driven even if one of the steering actuators fails.

(Modification of steering mechanism)
Note that a ball screw mechanism can be applied as a turning mechanism for turning the steered wheels instead of the rack and pinion mechanism. In this case, the ball nut is rotated by the turning actuator 8. Good. Thus, the turning angle can be controlled with high accuracy by applying the ball screw mechanism.
Further, instead of the pinion and rack mechanism and the ball screw mechanism, other types of steering mechanisms can be applied as the steering mechanism.

(Application example of abnormal behavior control unit of the present invention)
In the above embodiment, the case where the target tire lateral force is calculated with reference to the target tire lateral force calculation map has been described. However, the present invention is not limited to the above. Instead of referring to the target tire lateral force calculation map, a plurality of steering angle characteristic lines having the steering angle as a parameter are used as functions of the vehicle speed and the target tire lateral force. The target tire lateral force may be calculated by selecting a steering angle characteristic line based on the steering angle θs and substituting the vehicle speed V into the selected steering angle characteristic line.

By expressing the steering characteristic line as a function of the vehicle speed and the target tire lateral force in this way, the target tire lateral force is calculated by selecting and calculating the steering angle characteristic line without using the target tire lateral force calculation map. can do.
In the embodiment described above, the case where the number of steering angle characteristic lines in the target tire lateral force calculation map is set to four has been described. However, the number of steering angle characteristic lines is not limited to four, and may be set to an arbitrary number. Can do.
In the above embodiment, the case where the braking force is applied to one of the steered wheels 17FR and 17FL by outputting the vehicle behavior control signal Sm to the pressure control unit 20 by the abnormal behavior control unit 59 has been described. However, the present invention is not limited to this, and the vehicle may be turned by applying a braking force to one of the left and right left and right wheels at the same time.

(Application example of front suspension applied to the present invention)
In the above-described embodiment, the case where the lower link of the front suspension device is configured by the first link 37 and the second link 38 that do not cross each other has been described. However, the configuration of the suspension device is not limited to the above-described configuration, and it is only necessary to set the kingpin shaft so as to pass through the tire contact surface to reduce the turning force. For this reason, the lower link structure can be constituted by a transverse link 81 and a compression link 82 that intersect each other, as schematically shown in FIG. 16, for example. Further, as schematically shown in FIG. 17, the lower link structure can be configured by a transverse link 81 and a tension link 83 that intersect each other.

(Effects of application examples)
In this way, by configuring the lower link structure with the first link and the second link that intersect each other in plan view, the lower pivot point constituting the kingpin axis can be set as the intersection position of both links. For this reason, the position of the lower pivot point can be made closer to the inside of the steered wheel body. Therefore, it becomes easy to set the kingpin shaft so that it passes through the tire ground contact surface.
Further, the front suspension device 1B is not limited to the above-described configuration, and suspension devices having other various configurations can be applied.

DESCRIPTION OF SYMBOLS 1 ... Vehicle, 1A ... Vehicle body, 1B ... Suspension device, 2 ... Steering wheel, 3 ... Input side steering shaft, 4 ... Steering angle sensor, 5 ... Steering torque sensor, 6 ... Steering reaction force actuator, 7 ... Steering reaction force actuator Angle sensor, 8 ... steering actuator, 8a ... steering motor, 9 ... steering actuator angle sensor, 10 ... output-side steering shaft, 11 ... steering torque sensor, 12 ... pinion gear, 13 ... pinion angle sensor, 14 ... rack Axis, 15 ... tie rod, 16 ... tie rod axial force sensor, 17FR, 17FL, 17RR, 17RL ... wheel, 18 ... brake disc, 19 ... wheel cylinder, 20 ... pressure control unit, 21 ... vehicle condition parameter acquisition unit, 22a ... hub Lateral force sensor, 22b ... Yaw rate sensor, 24FR, 24FL, 24 R, 24RL ... wheel speed sensor, 26 ... drive circuit unit, 27 ... mechanical backup, 32 ... axle, 33 ... axle carrier, 34 ... spring member, 37 ... first link, 38 ... second link, 40 ... shock absorber, DESCRIPTION OF SYMBOLS 41 ... Stabilizer, SBW ... Steer-by-wire system, 50 ... Steering control part, 51 ... Target turning angle calculating part, 52 ... Steering response setting part, 53 ... Actuator control apparatus, 54 ... Straightness control part, 54a ... Self aligning torque calculation unit, 54b ... gain multiplication unit, 55 ... disturbance compensation unit, 56 ... straight advance guarantee unit, 56a ... adder, 57 ... delay control unit, 57a ... steering start detection unit, 57b ... monostable circuit, 57c ... gain adjustment unit, 57d ... multiplier, 57e ... adder, 58 ... abnormality detection unit, 59 ... abnormality behavior control unit, 60 ... current deviation calculation unit, 6 ... turning angle deviation calculating part, 62 turning motor control part, 63 ... current deviation calculating part, 64 ... motor current detecting part, 65 ... motor current controlling part, 81 ... transverse link, 82 ... compression link, 83 ... tension Link

Claims (7)

A front suspension device in which the kingpin shaft passing through the upper pivot point and the lower pivot point is set so as to pass through the tire ground contact surface at the neutral position of the steering wheel, and an actuator is operated according to the steering state of the steering wheel. A vehicle with a steer-by-wire system that steers left and right steered wheels,
A straightness control unit that operates the actuator provided in the steer-by-wire system to generate a restoring force for self-aligning the steered wheels;
A vehicle speed detector for detecting the vehicle speed;
A tire lateral force detector that detects the tire lateral force of the vehicle;
A steering angle detector for detecting a steering angle of the steering wheel;
A braking force applying unit that individually applies a braking force to the left and right wheels;
An abnormality detection unit for detecting an abnormality in the straightness control unit;
When the abnormality detection unit detects an abnormality in the straightness control unit, a target tire lateral force is calculated based on the steering angle and the vehicle speed so that the tire lateral force matches the target tire lateral force. An abnormality behavior control unit that controls the braking force application unit.   The vehicle according to claim 1, wherein the front suspension device is set such that a suspension geometry places more importance on steering response than straight-line stability.   The vehicle according to claim 2, wherein the straightness control unit calculates a self-aligning torque that complements a shortage of the self-aligning torque of the front suspension device.   The abnormal behavior control unit applies a braking force to one of the left and right wheels so that the tire lateral force and the target tire lateral force coincide with each other, and sets the vehicle steering characteristic to neutral steering. The vehicle according to any one of 1 to 3.   The abnormal behavior control unit calculates a target tire lateral force with reference to a target tire lateral force calculation map in which a characteristic line representing a relationship between a vehicle speed and a tire lateral force is set with a steering angle as a parameter. The vehicle according to any one of claims 1 to 4.   The vehicle according to claim 5, wherein the target tire lateral force calculation map defines a tire lateral force necessary for obtaining a neutral steer characteristic according to a steering angle.   The vehicle according to any one of claims 1 to 6, wherein the tire lateral force detection unit includes a hub lateral force sensor built in a hub unit.

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