JP2007001449A - Steering device for vehicle and steering control method for vehicle - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide assist control instructing a suitable counter steering angle to a driver without judgement of the driver for variation of vehicle motion by visual information. <P>SOLUTION: When strong over-steer of the vehicle is detected and it is determined that a steering direction is a counter-steer direction, static/dynamic friction in a transmission element for transmitting steering torque to a steering wheel side is reduced or corrected to zero. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a steering force control for preventing strong oversteer of an automobile and improving maneuverability in a region close to strong oversteer.

As this type of technology, an electric power steering device is disclosed that performs control so that the vehicle behavior can be prevented from becoming unstable on a slippery road surface or the like. As the lateral grip force generated at the rear wheel approaches the limit, the force (hereinafter referred to as assist force) for assisting the driver's steering by the electric motor is reduced. That is, when the rear wheel loses gripping force and is in a so-called spin (strong oversteer) situation, the steering wheel becomes heavier and the steering to the opposite side of the vehicle turning direction (countersteer) is promoted. As a result, the front wheel lateral direction By reducing the gripping force, the vehicle can be prevented from spinning (see, for example, Patent Document 1).
Japanese Patent Laid-Open No. 11-048997

  However, in the above prior art, although the steering force is urged in the steering direction (counter steer direction) opposite to the vehicle turning direction by reducing the assist force, this control is used to determine the steering angle at which the steering wheel should be stopped. I don't tell you. If the steering angle in the counter steer direction is too large, the trajectory may unnecessarily bulge out of the turn or the turn may start in the reverse direction. That is, the steering angle in the counter steer direction must be changed according to the behavior of the vehicle. The driver does this based on visual information such as yaw movement of the vehicle, but there is a delay in determining changes in vehicle movement with visual information. Therefore, the counter steer operation becomes difficult.

  The present invention has been made paying attention to the above-mentioned problem, and the object of the present invention is to perform assist control in which the driver teaches the appropriate counter steering angle to the driver without determining the change in the vehicle motion by visual information. Is to provide.

  In order to achieve the above object, in the present invention, a transmission element that transmits steering torque to the steered wheel side detects a resistance element that generates a force in a direction that hinders steering independently of the steering situation, and detects a steering state of the vehicle. Steer state detecting means, counter steer determining means for determining whether the steering direction is steered in the counter steer direction opposite to the turning direction of the vehicle, and the steer state detecting means are strong indicating an oversteer tendency due to a predetermined condition of the vehicle. Correction means for reducing or correcting to zero the force generated by the resistance element when oversteer is detected and the steering direction is determined to be the countersteer direction.

  In the vehicle steering apparatus of the present invention, the force generated by the resistance element is reduced or corrected to zero, and the driver can determine the change in the vehicle motion based on the reaction force information instead of the visual information. Therefore, an appropriate counter steering angle can be taught to the driver.

  Hereinafter, the best mode for realizing the vehicle steering system of the present invention will be described based on the first to third embodiments.

  First, the configuration will be described.

  FIG. 1 is an overall system diagram of a vehicle equipped with a vehicle steering device. A vehicle equipped with a vehicle steering device includes a steering torque sensor (steering torque detecting means) 2 for detecting a steering torque input to the column shaft 5 from the handle 1 side, and a column shaft on the steered wheel 10 side from the steering torque sensor 2. 5, a steering angle sensor (steering angle detecting means) 3 for detecting a rotation angle of 5 (hereinafter referred to as a steering angle), an assist motor (actuator) 6 for generating a force for assisting a driver's steering, a vehicle steering situation, and a vehicle An assist controller (steering angle control means) 8 that controls the assist motor 6 according to the behavior is configured.

  The steering torque sensor 2 detects the steering torque input from the handle 1 to the column shaft 5 from the torsion amount of the torsion bar provided between the handle 1 and the column shaft 5. Since the torsion bar is present, the handle 1 and the column shaft 5 can be rotated relative to each other within the torsion bar torsional range, so that the rotation angle of the handle 1 and the steering angle of the column shaft 5 are different from each other. Become. For this reason, the torque detected by the steering torque sensor 2 is different from the torque input to the handle 1 by the driver. Hereinafter, the torque detected by the steering torque sensor 2 is referred to as steering torque, and the torque that the driver inputs to the handle 1 is referred to as driver input torque.

  For example, a DC brushless motor is used as the assist motor 6, and the motor output shaft is connected to the column shaft 5 via the speed reducer 7, and outputs an assist force that assists the steering force of the driver to the column shaft 5.

  The rack 4 converts the rotation of the column shaft 5 into movement in the left-right direction of the vehicle by a rack and pinion, and turns the steered wheels 10. The rack axial force sensor 9 detects an axial force applied to the rack 4 and outputs a rack axial force detection value to the assist controller 8.

  The assist controller 8 is a motor command value for the assist motor 6 based on the steering torque information from the steering torque sensor 2, the steering angle information from the steering angle sensor 3, and the rack axial force information from the rack axial force sensor 9. To control.

  FIG. 2 is a control block diagram of the assist controller 8. The assist controller 8 detects steering in a direction opposite to the turning direction of the vehicle, that is, a so-called counter steer, outputs a friction flag, a steering angle servo unit 81 that generates a command signal to the assist motor 6, and a column shaft. The virtual steering model part 82 which calculates the virtual steering steering angle which is 5 target rotation angles, and the torque generation part (driver input torque estimation means) 83 which calculates a driver input torque are comprised.

  The counter control unit 80 inputs a side slip angular velocity, a driver input torque, a rack axial force, and the like of the vehicle, determines whether the vehicle is in a strong oversteer state or a countersteer state, and sends it to a virtual steering model 82 described later. Generate an input friction flag. Here, the strong oversteer means a state in which a so-called spin is generated because the grip force of the rear wheel is reduced when the vehicle is turning and the moment in the direction of turning in the turning direction is increased. Further, the side-slip acceleration of the vehicle can be obtained by calculation from, for example, front and rear G, side G, yaw rate, etc., and the calculation method may be a well-known one described in Japanese Patent No. 3303500, etc.

  The steering angle servo unit 81 calculates a motor command value of the assist motor 6 so that the detected value of the steering angle sensor follows the target steering angle that is the output of the virtual steering model unit 82 based on the general theory of control engineering. The calculated motor command value is output to a current driver (not shown), and current is supplied to the assist motor 6 via the current driver.

  The virtual steering model section 82 receives the driver input torque and the sum of the rack axial forces, and calculates the virtual steering steering angle output to the steering angle servo section 81. An example is shown in FIG. Here, since the dynamic characteristics of the model are represented by a continuous system, the integrators 82a and 82b are represented by 1 / s (s: Laplace operator). For ease of understanding, torque and steering angle are all converted around the column shaft. The multiplier 82c outputs a value obtained by multiplying the input by a reciprocal 1 / Ih of a desired steering inertia. The multiplier 82d multiplies the input by Ch to set a desired steering viscosity. The static / dynamic friction signal generation unit (friction generation means) 82e is a block that imitates and reproduces the actual static / dynamic friction generated in the column shaft 5 and the rack shaft 4. The static / dynamic friction correction unit 82f performs correction to reduce or eliminate static / dynamic friction when the friction flag generated by the counter control unit 80 is "1". The stack reproduction unit 82g is a block that reproduces that the steering wheel 1 has stopped due to static friction, and has a role of setting the steering angular velocity in the virtual model to zero.

  With the above configuration, the driver can enjoy the movement of the virtual steering model through the reaction force and the steering angle behavior during steering. By describing desired steering characteristics in the virtual steering model, a desired steering feeling can be experienced.

  The torque generator 83 calculates a driver input torque input to the virtual steering model. An example is shown in FIG.

  The multiplier 83a sets a value obtained by multiplying the steering torque trq by the inverse 1 / Kt of the torsional rigidity of the steering torque sensor 2 as a torsion angle trq / Kt, and outputs it to the adder 83b.

The adder 83b is a value obtained by adding the torsional angle trq / Kt from the multiplier 83a and the steering angle theta _m and steering wheel angle theta _h, and outputs it to the multiplier 83c. The multiplier 83c is a transfer function s ² / approximating the second-order differentiation on the steering wheel angle ^{_{θ h (s 2 + 2ζω n}} s + ω n 2) The multiplication value wheel angular acceleration theta _h a "from the adder 83 b, a multiplier The multiplier 83d outputs to the adder 83e a value obtained by multiplying the steering wheel angular acceleration θ _h ″ from the multiplier 83c by the inverse 1 / Ih ₀ of the inertia of the steering wheel 1. The adder 83e sets a value obtained by adding the steering torque trq and the output θ _h "× 1 / Ih _{0 of} the multiplier 83d as the driver input torque trq _g and outputs the driver input torque trq _g to the virtual steering model unit 82.

  Next, the operation will be described.

  FIG. 5 is a diagram illustrating an example of vehicle behavior when the counter steer is performed and when the vehicle is in a strong oversteer state. As shown in FIG. 5 (a), when the grip force of the rear wheel of the vehicle 100 is reduced at the position indicated by the solid line and the counter steer is not performed when the vehicle is in a strong oversteer state, the turning direction is applied to the rear wheel. The lateral force generated on the outside increases. Therefore, the moment that rotates the vehicle 100 in the turning direction increases, and the vehicle 100 rotates in the turning direction as indicated by the dotted line and the alternate long and short dash line. On the other hand, as shown in FIG. 5B, when the countersteer is performed when the grip force of the rear wheel of the vehicle 100 decreases at the position indicated by the solid line and the vehicle is oversteered, the turning direction of the rear wheel A lateral force having substantially the same magnitude as the lateral force generated on the outside can be generated on the front wheels. At this time, as shown by the dotted line and the alternate long and short dash line in FIG. 5B, the turning locus bulges outward in the turning direction, but the rotation of the vehicle 100 in the turning direction can be prevented.

  When the vehicle is in a strong oversteer state, some conventional vehicle steering devices promote countersteering by reducing the assist force. However, in the conventional vehicle steering apparatus, the driver is not instructed at what steering angle the steering wheel should be stopped. If the steering angle during counter steering is too large, turning may start in the opposite direction. Even if this is not the case, the trajectory will unnecessarily bulge outward. On the other hand, if it is too small, the vehicle cannot be prevented from turning inward in the turning direction. That is, the steering angle when performing the counter steer must be changed according to the behavior of the vehicle. The driver does this based on visual information such as the yaw motion of the vehicle, but there is a delay in determining changes in the vehicle motion with the visual information. Therefore, the counter steer operation becomes difficult.

  In order to solve this problem, it is conceivable to perform assist control so that a change in vehicle motion can be determined by a reaction force. In other words, if the driver can judge from the reaction force that the vehicle has shifted to the stable state due to the counter-steer or is about to shift, the driver can safely set the steering speed generated by the counter-steer to substantially zero and enter the steady steering state. It is possible to migrate.

  The reaction force can be detected more accurately and quickly than the visual information by the driver, so that the driver can infer an appropriate steering angle (hereinafter referred to as counter-steer steering angle) more quickly and the vehicle maneuverability is improved. Can be expected.

  However, in order to realize this method, there are the following conditions that need to be solved.

Condition 1: The driver's steering hunting is not induced In the situation where the driver is steering as shown in FIG. 6, the driver 101 can be regarded as the control system including the assist controller 102 and the vehicle. . If the characteristics of the steering system including the vehicle change in such a way that the driver cannot understand, the driver cannot respond to the change and may induce steering hunting.

Condition 2: Permitting the driver's steering intervention The steering angle servo control for forcibly matching the steering angle with the countersteer steering angle may hinder steering for avoiding obstacles, for example. Therefore, the steering angle servo used in the lane keep control cannot be simply applied.

  The conventional vehicle steering system is improved, and the assist force is increased stepwise at the moment when the countersteer steering angle is reached. Certainly, if the assist force changes stepwise, it is possible to infer an appropriate counter steering angle from the reaction force change at this time. The steering angle cannot be inferred). Since this does not force the steering angle to coincide with the target steering angle (counter steering steering angle), Condition 2 is satisfied. However, an increase in assist force, that is, lighter steering, can cause excessive countersteering. Further, since the assist force is determined based on the driver's steering force, the reaction force change is not constant. For this reason, the driver cannot understand the reason for the reaction force change and may induce steering hunting. That is, condition 1 is not satisfied.

  Therefore, in this embodiment, the countersteer steering angle is taught by changing the static / dynamic friction generated in the column shaft 5 and the rack shaft 4 instead of teaching the countersteer steering angle by directly changing the assist force. . Further, in this embodiment, the static / dynamic friction generated in the column shaft 5 and the rack shaft 4 is not directly changed, but the column shaft 5 and the rack shaft output from the static / dynamic friction generating unit 82e in the virtual steering model unit 82. The static / dynamic friction correcting unit 82f corrects the value imitating the actual static / dynamic friction generated in No. 4. A virtual steering angle is calculated using the corrected static / dynamic friction, a motor command value is calculated, and the assist motor 6 is controlled to produce an effect that the static / dynamic friction has changed.

[Friction flag calculation process]
FIG. 7 is a flowchart showing a flow of processing executed in the counter control unit 80, and each step will be described below.

  In step S1, the side slip angular velocity of the vehicle is read.

  In step S2, it is determined whether the side slip angular velocity of the vehicle is equal to or greater than a predetermined value. This determines whether the vehicle is in a strong oversteer state. When the absolute value of the side slip angular velocity is equal to or greater than a predetermined value, it is estimated that the vehicle is in a strong oversteer state. Moreover, in order to prevent hunting of this judgment part, you may give the hysteresis characteristic generally used. If the skid angular velocity is greater than or equal to the predetermined value, the process proceeds to step S3. If the skid angular velocity is less than the predetermined value, the process proceeds to step S5. This step S2 corresponds to the steer state detecting means of the present invention.

  In step S3, it is determined which direction of steering is counter steer from the sign of the side slip angular velocity. Next, it is determined from the driver input torque, rack axial force, and the like whether or not the driver's steering is in the counter-steer direction. If the driver's steering is in the counter-steer direction, the process proceeds to step S4. If the driver's steering is not in the counter-steer direction, the process proceeds to step S5. This step S3 corresponds to the counter steer determination means of the present invention.

  In step S4, the friction flag is set to "1", and in step S5, the friction flag is set to "0".

[Driver input torque calculation processing]
A method for calculating the driver input torque by the torque generator 83 will be described.

First, an example of a method for calculating the handle angle is shown in the following formula (1). The torsion angle is calculated by dividing the steering torque by the torsional rigidity of the torsion bar, and the steering angle is added to that to obtain the handle angle.
θ _h = θ _m + trq / Kt (1)
Here, θ _h is a steering wheel angle, and θ _m is a steering angle. trq is the steering torque, and Kt is the torsional rigidity of the torsion bar (unit: [Nm / rad], for example).

Subsequently, the steering wheel angular acceleration is obtained by the second derivative of the steering wheel angle θ _h obtained by the equation (1). The double differentiation may be approximated by a transfer function as shown in the following formula (2), for example.
θ _h ”= θ _h × s ² / (s ² + 2ζω _n s + ω _n ² ) (2)

As an example, ζ is 0.9 and ω _n is 2 × π × 60 [rad / s]. These parameters are related to high-frequency noise removal, and signals with an angular frequency ω _n or higher are removed. If this is set to a small value, the steering feeling may be impaired.

From the above, the driver input torque is expressed by the following equation (3).
trq _g = trq + Ih ₀ × θ _h "(3)
Where trq _g is the driver input torque.

  With this action, only the torque that the driver inputs to the handle 1 can be calculated.

[Calculation of virtual steering model steering angle]
FIG. 8 is a flowchart showing a flow of processing executed by the assist controller 8, and each step will be described below. This control process is executed at predetermined intervals set in advance.

In step S11, reads the steering angle theta _m from the steering angle sensor 3, the process proceeds to step S12.

  In step S12, the steering torque is read from the steering torque sensor 2, and the process proceeds to step S13.

  In step S13, the counter control unit 80 calculates a friction flag and proceeds to step S14.

In step S14, the torque generating unit 83, estimates a steering wheel angle theta _h using equation (1), the process proceeds to step S15.

In step S15, the torque generation unit 83 estimates the steering wheel angular acceleration θ _h ″ using equation (2), and the process proceeds to step S16.

  In step S16, the torque generation unit 83 generates driver input torque using equation (3), and the process proceeds to step S17.

  In step S17, the virtual steering model unit 82 calculates the virtual steering steering angle based on the virtual steering model based on the driver input torque generated in step S16, the rack axial force read from the rack axial force sensor 9, and the like. . At this time, the static / dynamic friction correction unit 82f does not perform correction when the friction flag is "0", and when the friction flag is "1", the static / dynamic friction is reduced or reduced to zero. The corner is calculated and the process proceeds to step S18.

  In step S18, the steering angle servo unit 81 performs the steering angle servo control for causing the actual steering angle to follow the virtual steering angle, and the process proceeds to return.

[Generation of reaction force]
The outputs of the counter control unit 80, the steering angle servo unit 81, the virtual steering model unit 82, and the torque generation unit 83 in this embodiment are represented by the equivalent model 11 in FIG. The driver feels a reaction force according to the output of the steering angle by inputting the skid angular velocity, the driver input torque, the rack axial force, and the like. In order to facilitate understanding, the reaction force felt by the driver is defined as follows. Equation (4) is obtained by the equation of motion around the handle axis.
Ih * d ² θ / dt ² = (Rack axial force) + (Driver steering force) + (Static / dynamic friction)… (4)
Here, Ih is the steering inertia, θ is the steering angle, rack axial force, driver steering force, and static / dynamic friction is the torque converted around the steering axis. Other torques are omitted here. Here, since the reaction force felt by the driver is equal to the driver steering force and in the opposite direction, (reaction force) = − (driver steering force). Therefore, the following equation (5) is obtained.
(Reaction force) = -Ih * d ² θ / dt ² + (Rack axial force) + (Static / dynamic friction) (5)
In the following description, it is assumed that the steering inertia Ih is sufficiently small, and the steering inertia Ih is approximated to zero.

(Reaction force at the start of counter steer cutting)
First, the reaction force felt by the driver when the driver has started to turn the handle 1 in the counter steer direction, that is, while the driver has started to apply the steering force in the counter steer direction but the handle 1 has not yet moved will be described. Here, the vehicle is currently turning right and the counter-steer direction is left. The leftward force is positive.

In a state where the driver holds the handle 1, the driver feels a reaction force expressed by the following equation (6).
(Reaction force) = (Rack axial force) + (Static friction) (6)

At the moment of starting to steer in the counter-steer direction (left), static friction is generated in the direction that prevents steering (right). For example, when the rack axial force is 10 and the static friction is “−5”, the driver feels the reaction force “5” expressed by the following equation (7).
(Reaction force) = 10 + (−5) = 5 (7)

When the skid angular velocity is equal to or greater than the predetermined value and the driver steers in the counter steer direction, the counter control unit 80 sets the friction flag to “1”, and the static / dynamic friction correction unit 82f of the virtual steering model unit 82 , Reduce or reduce static friction. Here, if the static / dynamic friction correction unit 82f reduces the size of the static friction by “2” and sets the static friction to “−3”, the driver will react as shown in the equation (8). I feel 7 ".
(Reaction force) = 10 + (−3) = 7 (8)

  As is clear from the comparison between Expression (7) and Expression (8), the reaction force felt by the driver is increased in the counter-steer direction by the operation of the present embodiment, and the driver is guided by steering in the counter-steer direction. On the other hand, when attempting to steer in the direction opposite to the counter steer direction, the static friction does not change, so the driver is not guided to steer in the direction opposite to the counter steer direction. Therefore, it is possible to assist the driver to start steering in the counter steer direction and to avoid strong oversteer.

(Reaction force during counter-steer)
Next, the reaction force felt by the driver when the driver is moving the handle 1 in the counter-steer direction will be described. Here, the vehicle is currently turning right and the counter-steer direction is left. The leftward force is positive.

While the driver is moving the handle 1, the driver feels the reaction force shown in the following equation (9).
(Reaction force) = (Rack axial force) + (Dynamic friction) (9)

In the static / dynamic friction correction unit 82f of the virtual steering model unit 82, when the dynamic friction is not corrected, for example, when the rack axial force is 10 and the dynamic friction is “−4”, the driver Feel the reaction force "6" shown in 10).
(Reaction force) = 10 + (−4) = 6 (10)

When the skid angular velocity is equal to or greater than the predetermined value and the driver steers in the counter steer direction, the counter control unit 80 sets the friction flag to “1”, and the static / dynamic friction correction unit 82f of the virtual steering model unit 82 , Reduce or eliminate dynamic friction. Here, if the static / dynamic friction correction unit 82f reduces the magnitude of the dynamic friction by “2” and sets the dynamic friction to “−2”, the driver will react as shown in the equation (11). I feel 8 ".
(Reaction force) = 10 + (−2) = 8 (11)

  As is clear from the comparison between Expression (10) and Expression (11), the reaction force felt by the driver is increased in the counter-steer direction by the operation of the present embodiment, and the driver is guided by steering in the counter-steer direction. On the other hand, when attempting to steer in the direction opposite to the counter steer direction, the dynamic friction does not change, so the driver is not guided to steer in the direction opposite to the counter steer direction. Therefore, it is possible to assist the driver to start steering in the countersteer direction and to avoid strong oversteer.

(Reaction force at counter-steer steering angle)
When the steering angle matches or substantially matches the appropriate counter steering angle, the skid angular velocity becomes equal to or less than a predetermined value, so the counter control unit 80 sets the friction flag to “0”. Since the static / dynamic friction correction unit 82f of the virtual steering model unit 82 ends the correction of the static / dynamic friction, the static / dynamic friction returns to a normal value.

  Hereinafter, the reaction force felt by the driver when the steering angle matches or substantially matches the appropriate counter steering angle will be described. Here, the vehicle is currently turning right and the counter-steer direction is left. The leftward force is positive.

Immediately before the driver matches the steering wheel 1 to an appropriate counter steering angle, the static / dynamic friction correction unit 82f of the virtual steering model unit 82 corrects the dynamic friction. For example, if the rack axial force is 10, the size of the dynamic friction is reduced by "2", and the dynamic friction is set to "-2", the driver applies the reaction force "8" as shown in equation (12). feel.
(Reaction force) = 10 + (−2) = 8 (12)

When the driver matches the steering wheel 1 to an appropriate counter steering angle, the static / dynamic friction correcting unit 82f of the virtual steering model unit 82 does not correct the dynamic friction. For example, when the rack axial force is 10 and the dynamic friction is “−4”, the driver feels the reaction force “6” expressed by the following equation (13).
(Reaction force) = 10 + (−4) = 6 (13)

  That is, the reaction force that leads to the counter steer is weakened. By this reaction force change, the driver can surely feel an appropriate counter-steer steering angle, and the steering wheel 1 can be shifted to the steered state. Since the static friction after the steering wheel 1 is shifted to the steering holding state is not corrected in the static / dynamic friction correcting unit 82f of the virtual steering model unit 82, the reaction force felt by the driver during steering of the steering wheel 1 changes. The driver can infer an appropriate countersteer steering angle.

  Condition 1 and condition 2 described above can be satisfied by the action of the vehicle steering system in the present embodiment.

Condition 1: The driver's steering hunting should not be induced. Static / dynamic friction is a characteristic that drivers usually experience, and the difference is easy to understand, so the driver's hunting steering is not induced. Also, the left-right difference in friction is unique to the action of the present embodiment that does not appear for other reasons, and the driver can clearly understand this reaction force change through the steering reaction force. Therefore, condition 1 is satisfied.

Condition 2: Allowing driver's steering intervention Static / dynamic friction is only reduced or corrected to zero, and does not interfere with driver's steering intervention. Therefore, it shows that Condition 2 is satisfied.

  With the above-described operation, the vehicle steering apparatus in the present embodiment can teach the driver the appropriate counter steering angle.

  As described above, the static / dynamic friction reproduced by the static / dynamic friction generating unit 82e is corrected by the static / dynamic friction correcting unit 82f, and the virtual model steering angle is output from the virtual steering model unit 82. The steering angle servo unit 81 outputs a motor command value corresponding to the virtual model steering angle and controls the assist motor 6 to give the driver a reaction force in which static / dynamic friction has changed. Rather than correcting the static / dynamic friction reproduced in this way, a resistor that actually generates the static / dynamic friction is provided around the rack shaft 4 to correct the static / dynamic friction generated by the resistor. You may do it.

  Next, the effect will be described.

(1) When strong oversteer of the vehicle is detected and the driver's steering is in the countersteer direction, the static / dynamic friction that is a resistance element that hinders the steering in the countersteer direction is reduced or corrected to zero. Therefore, the reaction force in the counter steer direction increases, and the driver can easily steer in the counter steer direction.
In addition, when strong oversteer of the vehicle is not detected by steering in the counter steer direction, the static / dynamic friction is not corrected, and the reaction force in the counter steer direction is reduced. Therefore, the reaction force felt by the driver during steering of the steering wheel 1 changes, and the driver can infer an appropriate countersteer steering angle.

  (2) When a strong oversteer of the vehicle is detected and the driver's steering is in the countersteer direction, the static / dynamic friction is reduced or made zero. Therefore, the static / dynamic friction is a characteristic that the driver usually experiences, and the difference is easy to understand, so the driver's hunting steering is not induced. Further, the left-right difference in friction is unique to the action of this embodiment that does not appear for other causes, and the driver can clearly understand the reaction force change due to friction through the steering reaction force. In addition, the static / dynamic friction is only reduced or corrected to zero, and does not hinder the driver's steering intervention.

(3) An assist motor 6 that outputs an assist force that assists the steering force of the driver to the column shaft 5, a steering torque sensor 2 that detects an input torque input to the column shaft 5 from the handle 1, and a steering angle In the vehicle steering apparatus, which includes a steering angle sensor 3 for detecting the torque and a torque generation unit that calculates a driver input torque trq _g that is a torque input by the driver to the steering wheel from the steering torque and the steering angle, The static / dynamic friction generating unit 82e that simulates and reproduces the actual static / dynamic friction generated in the rack shaft 4, the virtual steering model unit 82 that calculates the target rotation angle of the column shaft 5, and the assist motor 6 are controlled. An assist controller 8; a counter control unit 80 for determining strong oversteering based on the side slip angular velocity of the vehicle; And a static / dynamic friction correction unit 82f for correcting the static / dynamic friction to be reduced or zero when the friction flag generated by the data controller 80 is 1. Therefore, it is possible to give the driver a sense that the static / dynamic friction has changed without providing a new resistor that directly generates static / dynamic friction, and to generate a reaction force without a sense of incongruity. Can do.

  (4) The static / dynamic friction generating unit 82e simulates the static friction when the handle 1 is held and not rotating, and simulates the dynamic friction when the handle 1 is rotating. And reproduced it. Therefore, the driver can experience a change in friction that is closer to reality without a sense of incongruity.

  First, the configuration will be described.

  The configuration of this embodiment is different from that of the first embodiment only in the configuration of the counter control unit 84 of the assist controller 8, and the same components are denoted by the same reference numerals and description thereof is omitted.

  FIG. 10 is a control block diagram of the assist controller 8.

  The counter control unit 84 inputs a side slip angular velocity of the vehicle, a driver input torque, a rack axial force, and the like to generate a friction flag and outputs a counter control torque.

  The virtual steering model section 82 receives the sum of the driver input torque, rack axial force, and counter control torque, and calculates the virtual steering steering angle output to the steering angle servo section 81.

  Next, the operation will be described.

[Calculation of friction flag and generation of counter control torque]
FIG. 11 is a flowchart showing the flow of processing executed in the counter control unit 84. Each step will be described below.

  In step S21, the side slip angular velocity of the vehicle is read.

  In step S22, it is determined whether or not the side slip angular velocity of the vehicle is greater than or equal to a predetermined value. This determines whether the vehicle is about to enter strong oversteer. When the absolute value of the side slip angular velocity is equal to or greater than a predetermined value, it is estimated that the vehicle is about to enter strong oversteer. Moreover, in order to prevent hunting of this judgment part, you may give the hysteresis characteristic generally used. If the skid angular velocity is greater than or equal to the predetermined value, the process proceeds to step S23, and if the skid angular velocity is less than the predetermined value, the process proceeds to step S26 to turn off the counter control torque so that the counter control torque is not generated.

  In step S23, the counter control torque is turned ON to generate a periodic torque signal having an effective value of zero as shown in FIG. Although a rectangular wave is shown in FIG. 12, a sine wave may be used.

  In step S24, it is determined which direction of steering is counter steer from the sign of the side slip angular velocity. Next, it is determined from the driver input torque, the counter control torque, the rack axial force, and the like whether or not the driver's steering or counter control torque is in the counter steer direction. If the driver's steering or counter control torque is in the counter steer direction, the process proceeds to step S25, and if the driver's steering is not in the counter steer direction, the process proceeds to step S27.

  In step S25, the friction flag is set to “1”, and in step S27, the friction flag is set to “0”.

[Reaction force generation during steering]
The outputs generated by the operations of the counter control unit 84, the steering angle servo unit 81, the virtual steering model unit 82, and the torque generation unit 83 in this embodiment are represented by the equivalent model 12 in FIG. The driver feels a reaction force according to the output of the steering angle by inputting the skid angular velocity, the driver input torque, the rack axial force, and the like. In this embodiment, the reaction force positively guides to an appropriate counter steering angle.

  For example, consider a case where the vehicle is turning to the right and the driver input torque is equal to the rack axial force, that is, the driver is keeping the steering wheel 1 at a constant steering angle. FIG. 14 shows the counter control torque input when the driver input torque and the rack axial force are equal to each other on the right, and the state of generation of static friction and reaction force when the counter control torque is input. It is a graph.

  When the counter control torque as shown in FIG. 14A is input to the virtual steering model unit 82, the calculator 82e is in the opposite direction to the counter control torque as shown in FIG. Reproduce the static friction. However, when the driver input torque is generated in the counter steer direction (left direction), the counter control unit 80 sets the friction flag to “1”, so that the static friction is reduced or corrected to zero. Here, it is assumed that the static friction in the portion indicated by the alternate long and short dash line in FIG. 14B is corrected to zero. When the counter control torque and the static friction are combined, as shown in FIG. 14C, the counter control torque in the reverse counter steer direction (right direction) is canceled by the static friction, and the assist controller 8 counteracts the counter steer direction. The assist motor 6 is controlled so that a force is generated.

[Reaction force generation during turning]
When the counter-steering reaction force is generated during the steering operation as described above, the handle 1 rotates in the counter-steer direction if the driver input torque is constant. During the rotation of the handle 1, dynamic friction is generated not on the static friction but on the side opposite to the rotation direction of the handle 1. FIG. 15 is a graph showing the generation of counter control torque, dynamic friction and reaction force, and the steering angle when the handle 1 is rotating in the counter steer direction due to generation of the counter control torque.

  Consider a case where the driver input torque is equal to the rack axial force, but the handle 1 is steered in the counter steer direction by the counter control torque. At this time, counter control torque as shown in FIG. 15A is continuously input to the virtual steering model unit 82. The static / dynamic friction signal generator 82e reproduces the dynamic friction that is opposite to the steering direction of the handle 1 as shown in FIG. 15B and is smaller than the counter control torque. The generation direction of the dynamic friction does not change according to the generation direction of the counter control torque, but occurs in the direction opposite to the steering direction of the handle 1. At this time, the dynamic friction in the right direction occurs when the steering wheel 1 is steered in the counter steer direction (left direction), so the counter control unit 80 sets the friction flag to “1”. Therefore, the dynamic friction is reduced or corrected to zero. Here, it is assumed that the dynamic friction of the portion indicated by the alternate long and short dash line in FIG. 15B is corrected to zero. When the counter control torque and the static friction are combined, the counter control torque input in the counter steer direction is generated as a reaction force as shown in FIG. On the other hand, the counter control torque input in the reverse countersteer direction is generated as a reaction force if the steering direction of the handle 1 is the countersteer direction. If the steering direction of the handle 1 is the counter-counter steering direction, a part of the steering force cancels out with the dynamic friction, and a reaction force smaller than the value of the counter control torque input is generated.

  FIG. 15C shows a change in the steering angle when the steering angle is “0” when the driver is turning to the right and the driver is keeping the steering wheel 1 at a constant steering angle. From time 0 to t1, since the reaction force is generated on the left, the handle 1 is steered to the left. From time t1 to t2, the steering wheel 1 continues to be steered to the left due to inertia, but a reaction force is generated to the right, so that the speed of change of the steering angle decreases. At time t2, the steering direction of the steering wheel 1 is reversed, and steering to the right side starts. From time t2 to t3, although the reaction force is generated to the right, the steering wheel 1 is steered to the right. Therefore, dynamic friction is generated, and the magnitude of the reaction force is smaller than the time t1 to t2, and the steering angle The speed of change of becomes smaller than time 0 to t1. From time t3 to t4, the steering wheel 1 continues to be steered to the right due to inertia, but the reaction force is generated to the left, so that the speed of change of the steering angle decreases. Thereafter, the steering angle change from time 0 to t4 is repeated, and if the counter steer steering angle is reached at time t13, the input of the counter control torque is terminated.

[Steering angle simulation]
FIG. 16 shows the result of simulating the change in the steering angle due to the action in the present embodiment. FIG. 16 (a) shows the state of the friction flag, and FIG. 16 (b) shows the state of the steering angle. This simulation was performed based on the following conditions.
1: Steady turning in the right direction.
2: The sum of the driver input torque and the rack shaft is zero (that is, in a balanced state).
3: The rear wheel starts to flow at time 0 [ms], the skid angular velocity becomes equal to or higher than a predetermined value, and counter control is started.
4: At time 200 [ms], the skid angular velocity becomes less than a predetermined value, and the counter control is terminated.
The steering angle in FIG. 16 (b) is shown by assuming that the steering angle during steady turning in the right direction is “0” and the left direction steering is positive.

  As shown in FIG. 16B, even if the driver input torque does not change, the steering angle is guided to an appropriate counter-steer steering angle. However, since the counter control torque has an effective value of zero, it does not hinder the driver's steering intervention. Further, when the input of the counter control torque is finished, the steering angular velocity becomes zero, so that the steering angle does not overshoot the counter steer steering angle and can be accurately guided to the counter steering angle.

  Next, the effect will be described.

  (5) When a strong oversteer of the vehicle is detected, a counter control torque, which is a periodic torque that repeats positive and negative effective values, is input to the virtual steering model unit 82. Therefore, even if the driver input torque does not change, the steering angle is guided to an appropriate countersteer steering angle. However, since the counter control torque has an effective value of zero, it does not hinder the driver's steering intervention. Further, when the input of the counter control torque is finished, the steering angular velocity becomes zero, so that the steering angle does not overshoot the counter steer steering angle and can be accurately guided to the counter steering angle.

  In this embodiment, the counter control torque of the assist controller 8 increases as the side slip angular velocity of the vehicle when the side slip angular velocity is greater than or equal to a predetermined value and the vehicle is about to enter strong oversteer increases. I tried to make it bigger.

[Calculation of friction flag and generation of counter control torque]
FIG. 17 is a flowchart showing the flow of processing executed in the counter control unit 84. Each step will be described below.

  In step S31, the side slip angular velocity of the vehicle is read.

  In step S32, it is determined whether or not the side slip angular velocity of the vehicle is greater than or equal to a predetermined value. This determines whether the vehicle is about to enter strong oversteer. When the absolute value of the side slip angular velocity is equal to or greater than a predetermined value, it is estimated that the vehicle is about to enter strong oversteer. Moreover, in order to prevent hunting of this judgment part, you may give the hysteresis characteristic generally used. If the skid angular velocity is greater than or equal to the predetermined value, the process proceeds to step S33, and if the skid angular velocity is less than the predetermined value, the process proceeds to step S37 to turn off the counter control torque so that the counter control torque is not generated.

  In step S33, the amplitude of the counter control torque is calculated so as to increase the amplitude of the counter control torque as the side slip angular velocity of the vehicle increases.

  In step S34, the counter control torque is turned ON, and a periodic torque signal having the amplitude calculated in step S33 and having an effective value of zero is generated.

In step S35, it is determined which direction of steering is counter steer from the sign of the side slip angular velocity. Next, it is determined from the driver input torque trq _g , the rack axial force and the counter control torque whether or not the driver steering or the counter control torque is in the counter steer direction. If the driver's steering or counter control torque is in the counter steer direction, the process proceeds to step S36, and if the driver's steering is not in the counter steer direction, the process proceeds to step S38.

  In step S36, the friction flag is set to "1", and in step S38, the friction flag is set to "0".

[Steering angle simulation]
FIG. 18 shows the result of simulating the change in the steering angle due to the action in the present embodiment. FIG. 18A shows the state of the friction flag, and FIG. 18B shows the state of the steering angle. The present embodiment is a simulation in the case where a skid angular velocity larger than the skid angular velocity of the vehicle in the simulation performed in the second embodiment is generated. Other conditions were the same as in Example 2 based on the following conditions.
1: Steady turning in the right direction.
2: The sum of the driver input torque and the rack shaft is zero (that is, in a balanced state).
3: The rear wheel starts to flow at time 0 [ms], the skid angular velocity becomes equal to or higher than a predetermined value, and counter control is started.
4: At time 200 [ms], the skid angular velocity becomes less than a predetermined value, and the counter control is terminated.
The steering angle in FIG. 18 (b) is shown by assuming that the steering angle during steady turning in the right direction is "0" and the left direction steering is positive.

  In FIG. 18B, the counter steer direction changes by about 23 [deg] at time 200 [ms]. On the other hand, in FIG. 16A of the second embodiment, the counter steer direction changes by about 12 [deg] at time 200 [ms]. With this action, even when the side slip angular velocity of the vehicle is large, it is possible to promptly guide to the counter steering angle.

  Next, the effect will be described.

  (6) The amplitude of the counter control torque is increased as the side slip angular velocity of the vehicle increases and the degree of strong oversteer increases. Therefore, even when the side slip angular velocity of the vehicle is large, the counter steering angle can be promptly guided.

  As mentioned above, although the vehicle steering device of the present invention has been described based on the first to third embodiments, the specific configuration is not limited to this embodiment, and each claim of the claims Design changes and additions are allowed without departing from the spirit of the invention.

  For example, in the first to third embodiments, the electric power steering is described in which the steering wheel 1 and the steered wheel 10 are mechanically coupled and the steering torque is assisted by the assist motor 6, as shown in FIG. You may apply to what is called a steer-by-wire which isolate | separated the handle | steering-wheel 1 and the steered wheel 10 mechanically. In this steer-by-wire, unlike the electric power steering, the steering shaft 22 connected to the steering wheel 1 side and the steered shaft 23 connected to the steered wheel 10 side are separated, and a reaction force is generated on the steering wheel 1 side. A reaction force motor 20 that causes the steered wheels 10 to generate a turning force, and a controller 24 that controls the reaction force motor 20 and the turning motor 21 based on the steering torque and the steering angle. The assist controller 24 doubles the torque input to the steering wheel 1 and performs an operation for generating a turning torque for the steered wheels 10, a torque generation unit 24b for calculating a driver input torque, a virtual A virtual steering model 24c that outputs a steering angle, a steering angle servo 24d that outputs a motor command value to a reaction force motor, a steering gear ratio calculation unit 24e that calculates a turning angle with respect to the steering angle, and a steering motor 21 And a turning angle servo 24f that outputs a motor command value. Since the specific operation of the steer-by-wire itself has already been publicly known, a description thereof will be omitted.

1 is an overall system diagram of a vehicle equipped with a vehicle steering apparatus according to a first embodiment. FIG. 3 is a control block diagram of the assist controller according to the first embodiment. FIG. 3 is a control block diagram of a virtual steering model according to the first embodiment. FIG. 3 is a control block diagram of a torque generation unit according to the first embodiment. It is a figure explaining the counter steer based on Example 1. FIG. It is a figure explaining the hunting of the steering of the driver based on Example 1. FIG. 5 is a flowchart illustrating a flow of processing executed in a counter control unit according to the first embodiment. 4 is a flowchart illustrating a flow of processing executed in the assist controller according to the first embodiment. 4 is an equivalent model of control performed in the first embodiment according to the first embodiment. 6 is a control block diagram of an assist controller according to Embodiment 2. FIG. 10 is a flowchart illustrating a flow of processing executed in a counter control unit according to the second embodiment. It is a figure which shows the counter control torque based on Example 2. FIG. It is an equivalent model of the control performed in Example 2 based on Example 2. FIG. It is a figure which shows the mode of the reaction force at the time of steering of the steering wheel produced | generated by the counter control torque based on Example 2. FIG. It is a figure which shows the mode of the reaction force at the time of steering wheel steering which generate | occur | produces by the counter control torque based on Example 2. FIG. It is a figure which shows the result of having simulated the steering angle change based on Example 2. FIG. 10 is a flowchart illustrating a flow of processing executed in a counter control unit according to a third embodiment. It is a figure which shows the result of having simulated the steering angle change based on Example 3. FIG. It is a whole system figure of the vehicle carrying the vehicle steering device as another Example.

Explanation of symbols

2 Steering torque sensor 3 Steering angle sensor 5 Column shaft 6 Assist motor 8 Assist controller 10 Steering wheel 80 Counter control unit 81 Steering angle servo unit 82 Virtual steering model unit 82e Static / dynamic friction signal generation unit 82f Static / dynamic friction correction unit 83 Torque generator

Claims (8)

In the transmission element that transmits the steering torque to the steered wheel side, a resistance element that generates a force in a direction that hinders steering independently of the steering situation;
Steer state detecting means for detecting the steer state of the vehicle;
Counter steer determination means for determining whether the steering direction is steered in a counter steer direction opposite to the turning direction of the vehicle;
When the steering state detection means detects a strong oversteer that shows an oversteer tendency due to a predetermined condition of the vehicle and determines that the steering direction is the countersteer direction, the force generated by the resistance element is reduced or reduced to zero. Correction means for correcting;
A vehicle steering apparatus comprising: The vehicle steering apparatus according to claim 1,
The resistance element is a friction in a transmission element that transmits the steering torque to a steered wheel,
The vehicle steering apparatus characterized in that the correction means reduces or eliminates the friction. The vehicle steering apparatus according to claim 2,
An actuator for applying torque around the axis to the column shaft;
Steering torque detection means for detecting steering torque input to the column shaft;
Steering angle detection means for detecting a steering angle which is a rotation angle of the column shaft;
A driver input torque calculating means for calculating a driver input torque input to the steering wheel by the driver from the steering torque and the steering angle;
A virtual steering model for calculating a target steering angle of the column shaft from the driver input torque;
Steering angle control means for controlling the output of the actuator so that the steering angle of the column shaft follows the target steering angle;
With
The virtual steering model is
Friction signal generation means for reproducing the friction and outputting it as a friction signal;
The correction means;
Have
The vehicle steering apparatus according to claim 1, wherein the correction means outputs the friction signal when the friction is reduced or corrected to zero. The vehicle steering apparatus according to claim 3,
The vehicle steering apparatus according to claim 1, wherein the friction generating means generates at least one of a friction signal generated when the steering wheel is stopped and a dynamic friction generated when the steering wheel is rotated. In the vehicle steering device according to claim 3 or 4,
When a strong oversteer of the vehicle is detected, a counter control torque output means for generating a periodic torque signal that repeats positive and negative effective values is provided,
The virtual steering model calculates a target steering angle of the column shaft from the driver input torque and the periodic torque. The vehicle steering apparatus according to claim 5,
The counter control torque output means increases the amplitude of the periodic torque as the degree of strong oversteer increases. The vehicle steering apparatus according to any one of claims 1 to 6,
The vehicle steering apparatus according to claim 1, wherein the predetermined condition indicates a state in which a rear wheel starts losing grip force while the vehicle is turning.   When a strong oversteer of the vehicle is detected and the steering direction is determined to be the countersteer direction, the force in the direction that hinders steering independently of the steering situation is reduced in the transmission element that transmits the steering torque to the steered wheels. Alternatively, the vehicle steering control method is characterized by correcting to zero.

Images