JP2006036124A - Steering device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To facilitate steering of a driver when stopping a variable gear ratio actuator and stabilize vehicle behavior. <P>SOLUTION: The steering device has a VGRS actuator 7 to vary a steering gear ratio which is a steering angle ratio applied to a steering wheel 13 with respect to a turning angle of front wheels 18, 19 and a EPS actuator 10 which outputs PS assist torque to the steering wheel 13. A control unit 20 changes PS assist characteristics in accordance with a stop position of the VGRS actuator 7 when the VGRS actuator 7 stops by failure. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention belongs to a technical field of a steering apparatus including a variable gear ratio actuator that varies a steering gear ratio and a power assist actuator that assists a driver in steering.

In the conventional steering device, at least a part of the steering torque necessary for performing the gear ratio variable control by the variable gear ratio actuator is compensated by the assist torque of the power assist actuator, so that the driver of the gear ratio variable control is compensated. An increase in steering burden is prevented (see, for example, Patent Document 1).
JP-A-11-78945

  However, in the above prior art, when the variable gear ratio actuator stops at an angle deviating from the steering neutral position, a deviation occurs between the steering wheel neutral position and the tire neutral position, so that the driver corresponds to the tire neutral position. It becomes difficult to quickly sense the steering angle. Therefore, the driver's steering operation tends to be delayed, and accordingly, the vehicle behavior may be disturbed.

  The present invention has been made paying attention to the above problems, and an object of the present invention is to provide a steering device that facilitates the driver's correction rudder when the variable gear ratio actuator is stopped and can stabilize the vehicle behavior. is there.

In order to achieve the above object, the present invention provides:
A variable gear ratio actuator that varies a steering gear ratio that is a ratio of a steered wheel turning angle to a steering angle applied to a steering operation means;
A power assist actuator that outputs a steering assist force to the steering operation means;
In a steering device with
When the variable gear ratio actuator stops, steering assist force characteristic changing means is provided for changing the steering assist force characteristic of the power assist actuator in accordance with the stop position of the variable gear ratio actuator.

  In the steering device of the present invention, the driver can recognize the deviation of the steering neutral position after the variable gear ratio actuator stops by the steering assist force, so that the driver can easily perform the steering and the vehicle behavior can be stabilized. .

  Hereinafter, the best mode for carrying out the present invention will be described based on the first embodiment.

First, the configuration will be described.
FIG. 1 is a system block diagram of a vehicle to which the steering device of the first embodiment is applied.
The steering wheel (steering operation means) 13 is connected to the upper end of the upper column shaft 14a so as to face the driver in a vehicle interior (not shown). A steering angle sensor 2 that detects a driver steering angle is provided between the steering wheel 13 and the upper column shaft 14a.

  The steering gear 15 is configured by a rack and pinion type steering device including a steering gear box 16 integrally formed at the lower end of the lower column shaft 14 b and a rack shaft 17. The rack shaft 17 is fixed to a vehicle front portion (not shown) so as to be slidable in the left-right direction. Both ends of the rack shaft 17 are connected to front wheels (steering wheels) 18 and 19 via tie rods not shown.

  An actuator for a variable gear ratio steering system (hereinafter, the variable gear ratio steering system is abbreviated as VGRS) 7 which is a variable gear ratio actuator is provided in the upper column shaft 14a, and rotates the upper column shaft 14a by motor rotation. Increase speed. Thus, the steering gear ratio (hereinafter abbreviated as gear ratio), which is the ratio of the driver steering angle applied to the steering wheel 13 to the steering angle of the front wheels 18 and 19, is variably controlled. The VGRS actuator 7 is provided with a motor rotation angle sensor 3 that detects a motor rotation angle.

  The gear ratio is set based on a gear ratio characteristic determined in advance according to the vehicle speed. The gear ratio characteristics are light and good in the low to medium speed range by reducing the gear ratio in the low to medium speed range to make the steering response quick, and in the high speed range to increase the gear ratio and making the steering response slow. It is set so as to achieve both a steering feeling and a gentle and stable steering feeling in a high speed range.

  A motor for an electric motor power steering system which is a power assist actuator (hereinafter, electric motor power steering system is abbreviated as EPS) 10 is provided on the lower column shaft 14b, and the driver steers the motor by rotating the motor relative to the lower column shaft 14b. Outputs PS assist torque (steering assist force) to assist torque.

  The PS assist torque is set based on a PS assist characteristic determined in advance according to the steering torque. The PS assist characteristic is set such that the PS assist torque increases as the absolute value of the steering torque applied to the upper column shaft 14a by the rotation of the steering wheel 13 increases. The steering torque is detected by a torque sensor 4 provided between the upper column shaft 14a and the lower column shaft 14b.

  The control unit 20 receives the vehicle speed from the vehicle speed sensor 1, the driver steering angle from the steering angle sensor 2, the motor rotation angle from the motor rotation angle sensor 3, and the steering torque from the torque sensor 4. The drive of the VGRS actuator 7 and the EPS actuator 10 is controlled according to the sensor value.

  2 is a control block diagram of the control unit 20. The control unit 20 includes a VGRS target steering angle calculation unit 5, a VGRS command current calculation unit 6, an EPS target torque calculation unit 8, and an EPS command current calculation unit 9. And a straight traveling state determination unit (straight traveling state determination means) 11 and a VGRS failure determination unit 12.

  The VGRS target rudder angle calculation unit 5 calculates the VGRS target rudder angle based on the output of the vehicle speed sensor 1 and the output of the steering angle sensor 2. The VGRS command current calculation unit 6 calculates the VGRS command current value based on the output of the VGRS target rudder angle calculation unit 5, and drives the VGRS actuator 7 so that the current flowing through the VGRS actuator 7 approaches the VGRS command current value. .

  The EPS target torque calculation unit 8 is based on the output of the steering angle sensor 2, the output of the motor rotation angle sensor 3, the output of the torque sensor 4, the output of the straight traveling state determination unit 11, and the output of the VGRS fail determination unit 12. Calculate the target torque. The EPS command current calculator 9 calculates an EPS command current value based on the output of the EPS target torque calculator 8 and drives the EPS actuator 10 so that the current flowing through the EPS actuator 10 approaches the EPS command current value.

  The straight traveling state determination unit 11 sets a straight traveling state flag based on the output of the vehicle speed sensor 1 and the output of the steering angle sensor 2. The straight traveling state determination unit 11 sets a straight traveling state flag to 1 when determining that the vehicle is traveling straight, and sets the straight traveling state flag to zero when determining that the vehicle is not traveling straight.

  The VGRS fail determination unit 12 sets a VGRS fail flag from the output of the motor rotation angle sensor 3 and the output of the VGRS target rudder angle calculation unit 5. The VGRS fail determination unit 12 sets the VGRS fail flag to 1 when determining that an abnormality has occurred in the VGRS actuator 7, and sets the VGRS fail flag to zero when determining that the VGRS actuator 7 is normal. .

  FIG. 3 is a control block diagram of the EPS target torque calculation unit 8. The EPS target torque calculation unit 8 includes a basic target torque calculation unit 81 and a target torque correction unit (steering assist force characteristic changing means) 82. ing. The basic target torque calculation unit 81 calculates, for example, an EPS basic target torque from a PS assist map set in advance according to the steering torque, and outputs it to the target torque correction unit 82.

  The target torque correction unit 82 includes a gear ratio change rate torque correction unit 821, a tire neutral steering angle deviation torque correction unit 822, and a motor rotation angle deviation torque correction unit 823.

The gear ratio change rate torque correction unit 821 calculates the gear ratio from the gear ratio change rate from the gear ratio changed by the VGRS control to the gear ratio at the time of VGRS motor stop (mechanical steering gear ratio of the vehicle) before and after the VGRS motor stop. The change rate correction gain _Kgear is calculated.

  The tire neutral steering angle deviation torque correction unit 822 calculates a tire neutral steering angle deviation correction gain from the deviation between the motor rotation angle when the VGRS actuator 7 is stopped and the driver steering angle and the steering direction of the steering wheel 13. .

  The motor rotation angle deviation torque correction unit 823 calculates a motor rotation angle deviation correction gain from the deviation between the motor rotation command value and the actual motor rotation angle value from the motor rotation angle sensor 3 after the VGRS actuator is stopped.

  When the VGRS fail flag output from the VGRS fail determination unit 12 is 1, the target torque correction unit 82 obtains the gear ratio change rate correction gain, tire neutral steering angle obtained by the three torque correction units 821, 822, and 823. Based on the deviation correction gain and the motor rotation angle deviation correction gain, the EPS basic target torque is corrected to obtain the EPS target torque, which is output to the EPS command current calculator 9.

Next, the operation will be described.
[PS assist control processing]
FIG. 4 is a flowchart showing the flow of PS assist control processing executed by the control unit 20, and each step will be described below.

  In step S1, the basic target torque calculator 81 reads the steering torque of the driver from the torque sensor 4, and the process proceeds to step S2.

  In step S2, the basic target torque calculator 81 calculates the EPS basic target torque from the steering torque read in step S1, and the process proceeds to step S3.

  In step S3, the VGRS failure determination unit 12 detects a failure of the VGRS actuator 7, and detects a failure of the VGRS. If it is determined that the VGRS actuator 7 has stopped due to an abnormality, the process proceeds to step S4. If it is determined that the VGRS actuator 7 is normal, the process proceeds to step S12.

For example, the VGRS fail determination unit 12 compares the VGRS target rudder angle output from the VGRS target rudder angle calculation unit 5 with the motor rotation angle, and the motor rotation despite the output and change of the target rudder angle. When the time during which the angle does not change continues for the set time _Tf or longer, it is determined that an abnormality has occurred in the VGRS actuator 7 and has stopped.

In step S4, the gear ratio change rate torque correction unit 821 uses the following equation (1) from the gear ratio G _VGRS before the actuator stop and the gear ratio after the actuator stop G _base to _{obtain the} gear ratio change rate G _fail. 'Is calculated.
G _fail '= (G _base -G _VGRS ) / G _base (1)
Subsequently, the gear ratio change rate correction gain K _gear is calculated with reference to the gear ratio change rate correction gain map shown in FIG. 5, and the process _proceeds to step S5.

In step S5, the tire neutral steering angle deviation torque correction unit 822 calculates the tire neutral steering angle θ _tN after the actuator is stopped using the following equation (2) (corresponding to the tire neutral position detecting means).
Tire neutral steering angle θ _tN = −θ _mtr (θ _mtr : Motor rotation angle)… (2)
Here, the “tire neutral steering angle” is a steering angle at which the tire goes straight. When the VGRS actuator 7 is rotated and stopped, the steering wheel 13 is rotated by the same angle in the opposite direction to the rotation direction. The steered position is the tire neutral steering angle.

Subsequently, the driver's steering direction is detected from the time change of the driver steering angle θ _str (corresponding to the steering direction detection means), and the detected steering direction, the tire neutral steering angle θ _tN, and the driver steering angle θ _str are detected. Based on the tire neutral steering angle deviation correction gain map of FIG. 6, the tire neutral steering angle deviation correction gain K _tN is calculated, and the process _proceeds to step S6.

In step S6, the target torque correction unit 82 determines whether or not the driver steering angle θ _str exceeds the tire neutral steering angle θ _tN after the actuator is stopped. If YES, the process proceeds to step S7, and if NO, the process proceeds to step S8.

In step S7, the target torque correction unit 82 performs the correction torque calculation 2 from the tire neutral steering angle deviation correction gain _KtN, and the process _proceeds to step S11.

The correction torque calculation 2, if the driver steering angle theta _str exceeds the tire neutral steering angle theta _tN, to facilitate the driver to recognize the tire neutral steering angle theta _tN, using equation (3) below, Calculate the corrected EPS target torque.
EPS target torque after correction =
EPS basic target torque × tire neutral steering angle deviation correction gain K _tN (3)
That is, by multiplying the EPS basic target torque by the correction gain, the PS assist torque is changed so as to be light in the direction approaching the tire neutral position and heavy in the direction away from the tire neutral position. This facilitates the driver to steer to the tire neutral steering angle _θtN .

In step S8, the EPS target torque calculation unit 8 performs a correction torque calculation 1 from the gear ratio change rate correction gain K _gear and the tire neutral steering angle deviation correction gain K _tN, and the process proceeds to step S9.

In the corrected torque calculation 1, when the driver steering angle θ _str does not exceed the tire neutral steering angle θ _tN , the PS assist characteristic is expressed by the following equation (4) in order to suppress the influence of the gear ratio sudden change immediately after the actuator stops. Then, the corrected EPS target torque is calculated.
EPS target torque after correction = EPS basic target torque × K _gear × | K _tN |… (4)

  In step S9, the motor rotation angle deviation correction unit 823 obtains a deviation between the motor rotation command value and the actual sensor value (output of the motor rotation angle sensor 3) (corresponding to the steering state detection means), and there is a deviation. Shifts to step S10, and if there is no deviation, shifts to step S12.

In step S10, the motor rotation angle deviation torque correction unit 823 refers to the motor rotation angle deviation gain map shown in FIG. 7 based on the driver steering angle θ _str , and calculates the deviation between the motor rotation angle command value and the actual sensor value. The motor rotation angle deviation correction gain K _mtr corresponding to the absolute value is obtained, the EPS target torque after deviation correction is calculated using the following equation (5), and the process proceeds to step S11.
EPS target torque after deviation correction = EPS basic target torque + (EPS target torque after correction−EPS basic target torque) × Motor rotation angle deviation correction gain K _mtr (5)
However, the motor rotation angle deviation correction gain K _mtr is changed only in the increasing direction.

  In step S11, the straight traveling state determination unit 11 determines whether or not the vehicle is traveling straight from the vehicle speed, the steering angle, and the motor rotation angle. When the vehicle is in a straight traveling state, the process proceeds to step S12. When the vehicle is not in a straight traveling state, the process proceeds to step S13.

Here, the straight _traveling state determination time threshold value T _N and the straight _traveling state determination steering threshold value θ _ntr that are determined in advance according to the vehicle speed are used, and the time _during which the steering angle is the tire neutral steering angle ± θ _ntr is the straight _traveling state. When the judgment steering threshold value T _N is exceeded, it is judged that the vehicle is in a straight traveling state.

  In step S12, the PS assist characteristic is returned to the normal state (PS assist characteristic before change due to actuator stop), and the process proceeds to step S13.

  In step S13, the EPS actuator 10 is operated with the finally obtained PS assist characteristic, and the process proceeds to return.

[PS assist characteristic change control logic according to gear ratio change rate G _fail ']
When the VGRS actuator 7 stops, the gear ratio from the driver steering angle θ _str to the actual tire steering angle changes before and after the stop. That is, if the tire turning angle is made larger than the driver steering angle θ _str by the VGRS actuator 7 and the vehicle stops while traveling with the gear ratio set to quick, the gear ratio changes to the original slow gear ratio. At this time, the driver feels uncomfortable due to a sudden change in gear ratio.

In the first embodiment, the gear ratio change rate correction gain is obtained from the gear ratio change rate correction gain map shown in FIG. 5 according to the change rate of the gear ratio until the driver steering angle θ _str passes through the tire neutral steering angle θ _tN . The PS assist characteristics are changed by calculating K _gear and multiplying this by EPS basic target torque.

The gear ratio change rate correction gain map in FIG. 5 shows that when the gear ratio changes from slow to quick before and after the stop of the VGRS actuator 7, the gear ratio change rate correction gain _Kgear is decreased, and conversely, the gear ratio decreases from quick. Is set to increase the gear ratio change rate correction gain _Kgear .

  That is, when the gear ratio becomes quicker as the VGRS actuator 7 stops, the driver's excessive steering can be suppressed by setting a heavier PS assist characteristic. Further, when the gear ratio becomes slower, the driver's steering burden can be reduced by using a lighter PS assist characteristic.

As shown in FIG. 5, the gear ratio change rate correction gain K _gear is provided with an upper limit value and a lower limit value in order to prevent an excessive EPS target torque from being set.

[PS assist characteristic change control logic according to tire neutral steering angle deviation]
If the vehicle stops while the VGRS actuator 7 is rotating during traveling, the driver may not know the tire neutral steering angle θ _{tN at} which the vehicle goes straight, and the vehicle behavior may become unstable accordingly.

To prevent this, in Example 1, after the driver steering angle theta _str passes the tire neutral steering angle theta _tN, the deviation between the driver steering angle theta _str and tire neutral steering angle theta _tN, depending on the steering direction The tire neutral steering angle deviation correction gain K _tN is calculated from the tire neutral steering angle deviation correction gain map shown in FIG. 6 and multiplied by the EPS basic target torque to change the PS assist characteristic.

Tire neutral steering angle deviation gain map of FIG. 6, the direction of steering at the time of approaching the tire neutral steering angle theta _tN, as the absolute value of the deviation between the driver steering angle theta _str and tire neutral steering angle theta _tN is large, the tire neutral steering the angular deviation correction gain K _tN increased, the direction of steering at the time away from the tire neutral steering angle theta _tN, as the absolute value of the deviation between the driver steering angle theta _str and tire neutral steering angle theta _tN is large, the tire neutral steering angle deviation The correction gain K _tN is set to be small.

In other words, by _reducing the steering in the direction approaching the tire neutral steering angle θ _tN and increasing the steering in the direction away from the tire neutral steering angle θ _tN , the driver can easily find the tire neutral steering angle θ _tN after the actuator stops. Yes.

As shown in FIG. 6, the tire neutral steering angle deviation correction gain K _tN is provided with an upper limit value and a lower limit value in order to prevent an excessive EPS target torque from being set.

[PS assist characteristic change control logic according to motor rotation angle deviation]
If the VGRS actuator 7 stops while turning around a corner, the PS assist characteristic corresponds to the gear ratio change rate G _fail 'because it stops at the position specified by the command if the steering is maintained at a fixed rudder angle. There is no need to change. On the other hand, if the motor does not rotate when the motor rotation angle command value is changed when turning, it is necessary to change to PS assist characteristics corresponding to the gear ratio change rate G _fail ′.

In the first embodiment, the motor rotation angle deviation gain map shown in FIG. 7 is used in accordance with the deviation between the motor rotation angle command value and the actual sensor value until the driver steering angle θ _str passes through the tire neutral steering angle θ _tN . From this, a motor rotation angle deviation correction gain K _mtr is calculated and multiplied by the corrected EPS target torque to limit the amount of change according to the gear ratio change rate G _fail ′ of the PS assist characteristic.

Motor rotational angle deviation gain map of FIG. 7, the absolute value of the difference between the motor rotation angle command value and the actual rotation angle is equal to or less than a predetermined value theta _a is smaller, so as to reduce the motor rotational angle deviation correction gain K _mtr Is set.

That is, during steering while the deviation between the motor rotation angle command value and the actual rotation angle is small, the amount of change according to the gear ratio change rate G _fail ′ of the PS assist characteristic is reduced, and the gear before and after the failure of the VGRS actuator 7 is reduced. the ratio changes, since the driver becomes a predetermined value theta _a more deviations much uncomfortable feeling, by changing to PS assist characteristic corresponding to the gear ratio change rate G _fail ', in the steering holding, VGRS actuator When 7 stops, it can suppress that a PS assist characteristic changes.

  Note that the horizontal axis in FIG. 7 may be the deviation of the driver steering angle before and after stopping the VGRS actuator.

[Return control logic to normal assist characteristics after tire neutral steering angle recognition]
Even if the driver can recognize the tire neutral steering angle θ _tN after changing the PS assist characteristic by stopping the actuator, if the PS assist characteristic change control is continued, the steering feeling is different from the normal state, so the driver feels uncomfortable. I will give it.

In the first embodiment, when the vehicle goes straight after stopping the actuator (a state where the straight running is continued for a predetermined time), the driver determines that the tire neutral steering angle θ _tN can be recognized, and returns the PS assist characteristic to the normal state. This prevents the driver from feeling uncomfortable.

  The flowchart showing the flow of the PS assist control process in FIG. 4 is executed based on the control logic described above.

[PS assist characteristic change control action]
When a failure occurs in the VGRS actuator 7 and stops, the flow proceeds from step S1, step S2, step S3, step S4, step S5, and step S6 in the flowchart of FIG.

That is, in step S4, a gear ratio change rate correction gain K _gear corresponding to the gear ratio change rate G _fail ′ is calculated. In step S5, a tire neutral steering angle deviation correction gain K _tN corresponding to the tire neutral steering angle θ _tN is calculated. Is calculated.

Subsequently, in step S6, when the driver steering angle θ _str does not exceed the tire neutral steering angle θ _tN , the flow proceeds from step S6 to step S8 to step S9 to step S10 to step S11 to step S13. .

That is, in step S8, the corrected EPS target torque obtained by multiplying the EPS basic target torque by the absolute value of the gear ratio change rate correction gain K _gear and the tire neutral steering angle deviation correction gain K _tN is calculated, and in step S9. The motor rotation angle deviation correction gain K _mtr is calculated according to the deviation between the motor rotation angle command value and the actual rotation angle. In step S10, the correction gain K _mtr is set to the difference between the corrected EPS target torque and the EPS basic target torque. Multiply to calculate the corrected EPS target torque.

Therefore, since the PS assist characteristic is changed according to the gear ratio change rate G _fail ′, immediately after the actuator stops when the driver steering angle θ _str does not exceed the tire neutral steering angle θ _tN , the gear ratio sudden change due to the actuator stop becomes steering. The influence that it has can be suppressed.

In addition, since the PS assist characteristic is changed according to the tire neutral steering angle deviation, it is easy for the driver to recognize the tire neutral steering angle _θtN . Furthermore, since the PS assist characteristic is changed in accordance with the motor rotation angle deviation, it is possible to suppress the PS assist characteristic from changing during steering while the deviation between the motor rotation angle command value and the actual rotation angle is small.

If the driver steering angle θ _str exceeds the tire neutral steering angle θ _tN in step S6, the flow proceeds from step S6 to step S7 to step S11 to step S13. That is, in step S7, the corrected EPS target torque is calculated by multiplying the EPS basic target torque by the tire neutral steering angle deviation correction gain _KtN .

Therefore, since the PS assist characteristic is changed according to the tire neutral steering angle deviation, when the driver steering angle θ _str exceeds the tire neutral steering angle θ _tN , the driver recognizes the tire neutral steering angle θ _tN . Becomes easy.

After the actuator stops, when the driver recognizes the tire neutral steering angle θ _tN and the vehicle goes straight, in the flowchart of FIG. 4, step S1, step S2, step S3, step S4, step S5, step S6 → Step S7 → Step S11 → Step S12 → Step S13 or Step S1 → Step S2 → Step S3 → Step S4 → Step S5 → Step S6 → Step S8 → Step S9 → Step S10 → Step S11 → Step S12 → Step S13 It becomes the flow to go to.

That is, in step S11, it is determined that the vehicle is in a straight traveling state, and in step S12, the PS assist characteristic is returned to the normal state before the change, so the driver has recognized the tire neutral steering angle θ _tN , It is possible to prevent the driver from feeling uncomfortable due to the PS assist characteristic being changed.

[Steering neutral deviation due to actuator failure]
FIG. 8 is an explanatory diagram showing a steering neutral deviation when the variable gear ratio actuator is stopped.

  As shown in FIG. 8 (a), in a steering apparatus provided with a conventional variable gear ratio actuator, the steering wheel neutral position and the tire neutral position coincide with each other at normal times.

  Here, when the steering wheel is being steered left and right, if the variable gear ratio actuator fails and the actuator stops, when the steering wheel is returned to the neutral position, the motor is rotated and the tire is out of condition. (FIG. 8 (b)).

  When the tire is returned to the neutral position in this state, the steering wheel is cut in the opposite direction by the amount of rotation of the motor (FIG. 8 (c)), so that the driver can adjust the steering angle corresponding to the tire neutral position from the steering torque. It is difficult to feel quickly.

[PS assist characteristics change action when actuator fails]
On the other hand, in the steering device of the first embodiment, as shown in FIG. 9A, when the VGRS actuator 7 is stopped with the steering wheel 13 being steered to the left, the steering approaching the tire neutral steering angle θ _tN is performed. By _{reducing the} weight and increasing the steering away from the tire neutral steering angle θ _tN (FIG. 9B), the steering wheel 13 can be easily steered to the tire neutral steering angle θ _tN , and the driver can set the tire neutral steering angle θ _tN . It can be easily recognized. Therefore, the driver can easily steer.

That is, as shown in FIG. 10, when the driver steering angle θ _str is steered in a direction approaching the tire neutral steering angle θ _tN , the driver steering angle is reduced by making the driver's steering force lighter than normal characteristics. It is possible to easily guide θ _str to the tire neutral steering angle θ _tN . Further, when the driver steering angle θ _str is steered away from the tire neutral steering angle θ _tN , the driver steering angle θ _str is made to be heavier than the normal characteristic so that the driver steering angle θ _{str is changed} to the tire neutral steering angle. It is difficult to keep away from θ _tN .

Next, the effect will be described.
In the steering device of the first embodiment, the effects listed below can be obtained.

  (1) When the VGRS actuator 7 stops, the target torque correction unit 82 that changes the PS assist characteristics from the normal characteristics according to the stop position of the VGRS actuator 7 is provided. Can be recognized by the driver by the PS assist torque, and the vehicle behavior can be stabilized by facilitating the driver's steering.

(2) A steering direction detection for detecting the steering direction of the steering wheel 13 and a tire neutral position detecting means for detecting a tire neutral position where the front wheels 18 and 19 are in a straight traveling state are provided. Since the PS assist torque in the direction away from the PS assist torque in the direction approaching the tire neutral steering angle θ _tN is reduced, the steering wheel 13 is more easily steered to the tire neutral steering angle θ _tN , and the vehicle is It becomes easy to return to the straight running state.

(3) Tire neutral position detecting means for detecting the tire neutral position where the front wheels 18 and 19 are in a straight traveling state is provided, and the target torque correction unit 82 has a large deviation between the tire neutral steering angle _θtN and the driver steering angle _θstr. As the assist torque change amount increases, the driver can more easily find the tire neutral steering angle θ _tN .

(4) The target torque correction unit 82 increases the amount of change in assist torque with respect to the assist torque in the normal state as the gear ratio change rate G _fail ′ when the VGRS actuator 7 is stopped increases. The influence of sudden changes on steering feel can be suppressed, and steering can be performed more smoothly.

(5) target torque correcting unit 82, when the deviation between the motor rotation command value and the actual rotational angle is less than or equal to the predetermined value theta _a, to reduce the assist torque change amount with respect to the assist torque in the normal state, holding at a constant steering angle When the deviation between the motor rotation command value and the actual rotation angle is small, such as during steering, the change amount of the PS assist characteristic is suppressed even when the VGRS actuator 7 is stopped, so that the driver does not feel uncomfortable.

  (6) Since the target torque correction unit 82 sets a limit value for the amount of change in the steering assist force with respect to the normal characteristics, the vehicle behavior can be stabilized by setting an excessive EPS target torque. The supply to the actuator 10 can be prevented.

(7) Tire neutral position detecting means for detecting the tire neutral position where the front wheels 18 and 19 are in a straight traveling state is provided, and the target torque correcting unit 82 is PS assist after passing the tire neutral steering angle θ _tN after stopping the VGRS actuator. Since the characteristic is changed, it becomes easy for the driver to recognize the tire neutral steering angle θ _tN .

(8) Tire neutral position detecting means for detecting the tire neutral position where the front wheels 18 and 19 are in the straight traveling _state is provided, and the target torque correction unit 82 changes the PS assist characteristic until the tire neutral steering angle θ _tN is passed. Therefore, even immediately after the actuator is stopped, the influence of the gear ratio sudden change on the steering feeling can be suppressed, and the steering can be performed more smoothly.

(9) A straight-running state determining unit 11 that determines the straight-running state of the vehicle is provided, and the target torque correcting unit 82 returns the PS assist characteristic to the normal state when the straight-running state continues for a predetermined time or longer after the PS assist characteristic is changed. Therefore, it is possible to prevent the driver from feeling uncomfortable by continuing to change the PS assist characteristic even though the driver has recognized the tire neutral steering angle _θtN .

(Other examples)
Although the best mode for carrying out the present invention has been described based on the first embodiment, the specific configuration is not limited to the first embodiment, and each claim of the claims Design changes and additions are permitted without departing from the spirit of the invention.

  For example, in the first embodiment, the PS assist torque is controlled based only on the steering torque. However, the PS assist characteristic may be a characteristic according to the vehicle speed, the steering angular speed, or the like, for example.

  In the first embodiment, the steering gear ratio is variably controlled according to the vehicle speed and the steering angle. However, the steering gear ratio variable control including other conditions such as the steering angular speed may be used.

1 is a system block diagram of a vehicle to which a steering device according to a first embodiment is applied. 3 is a control block diagram of the control unit 20. FIG. 4 is a control block diagram of an EPS target torque calculation unit 8. FIG. 4 is a flowchart showing a flow of PS assist control processing executed by a control unit 20. It is a gear ratio change rate correction gain map. It is a tire neutral steering angle deviation correction gain map. It is a motor rotation angle deviation gain map. It is explanatory drawing which shows the steering neutral shift | offset | difference at the time of an actuator stop. It is explanatory drawing which shows the PS assist characteristic change effect | action of Example 1. FIG. It is explanatory drawing which shows the PS assist characteristic change effect | action of Example 1. FIG.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Vehicle speed sensor 2 Steering angle sensor 3 Motor rotation angle sensor 4 Torque sensor 5 Target steering angle calculation part 6 Command current calculation part 7 VGRS actuator 8 Target torque calculation part 81 Basic target torque calculation part 82 Target torque correction part 821 Torque correction part 822 Torque correction unit 823 Torque correction unit 9 Command current calculation unit 10 EPS actuator 11 Straight running state determination unit 12 Fail determination unit 13 Steering wheel 14a Upper column shaft 14b Lower column shaft 15 Steering gear 16 Steering gear box 17 Rack shafts 18, 19 Front wheels 20 control unit

Claims (9)

A variable gear ratio actuator that varies a steering gear ratio that is a ratio of a steered wheel turning angle to a steering angle applied to a steering operation means;
A power assist actuator that outputs a steering assist force to the steering operation means;
In a steering device with
A steering apparatus, comprising: a steering assist force characteristic changing unit that changes a steering assist force characteristic of the power assist actuator in accordance with a stop position of the variable gear ratio actuator when the variable gear ratio actuator stops. The steering apparatus according to claim 1, wherein
Steering direction detection means for detecting the steering direction of the steering operation means;
Tire neutral position detecting means for detecting a tire neutral position where the steering wheel is in a straight traveling state;
Provided,
The steering assisting force characteristic changing means reduces the steering assisting force when the steering direction is away from the steering assisting force when the steering direction is closer to the tire neutral position. The steering apparatus according to claim 1 or 2,
Provided a tire neutral position detection for detecting a tire neutral position where the steered wheel goes straight.
The steering assisting force characteristic changing means increases the amount of change in the steering assisting force as the deviation between the neutral position of the tire and the neutral position of the steering operating means increases. The steering apparatus according to any one of claims 1 to 3,
The steering assisting force characteristic changing means increases the change amount of the steering assisting force as the steering gear ratio change rate when the variable gear ratio actuator stops is larger. The steering apparatus according to any one of claims 1 to 4, wherein:
A steering state detection means for detecting the steering state of the driver is provided,
The steering assisting force characteristic changing means reduces the amount of change in the steering assisting force when the steering state is a steering holding state after stopping the variable gear ratio actuator. The steering apparatus according to any one of claims 1 to 5,
The steering assisting force characteristic changing means provides a limit value for the change amount of the steering assisting force. The steering apparatus according to any one of claims 1 to 6,
Provided is a tire neutral position detecting means for detecting a tire neutral position where the steering wheel is in a straight traveling state,
The steering assisting force characteristic changing means changes the steering assisting force characteristic after passing through the tire neutral position after stopping the variable gear ratio actuator. The steering apparatus according to any one of claims 3 to 6,
Provided is a tire neutral position detecting means for detecting a tire neutral position where the steering wheel is in a straight traveling state,
The steering assisting force characteristic changing means changes the steering assisting force characteristic after passing through the tire neutral position after stopping the variable gear ratio actuator. The steering apparatus according to any one of claims 1 to 8,
Providing straight running state judging means for judging straight running state of the vehicle,
The steering assisting force characteristic changing means returns the steering assisting force characteristic to the characteristic before the change when the straight traveling state continues for a predetermined time or longer after the steering auxiliary force characteristic is changed.

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