JP2015123864A - Steering control apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To realize a compact steering mechanism for steering a steering wheel.SOLUTION: As a steering-angle ratio characteristic representing a relation between a steering angle of a steering wheel and a turning angle of a turn-steering wheel, at least two characteristics, that is, a travel-time steering-angle ratio characteristic and a stop-time steering-angle ratio characteristic, are set. The stop-time steering-angle ratio characteristic is set at a steering-angle ratio characteristic associated with the travel-time steering-angle ratio characteristic until the steering angle reaches a threshold, and is set at a steering-angle ratio characteristic so that a steering-angle ratio increases when the steering angle exceeds the threshold. If a turning-wheel status at starting of power supply is consistent with a turning-wheel status at stopping of the power supply, steering-angle ratio control is performed by selecting the travel-time steering-angle ratio characteristic and the stop-time steering-angle ratio characteristic, or else recovery mode control is performed.

Description

  The present invention relates to a steering control device, and more particularly, to reduce the size of a steering mechanism that turns steered wheels according to steering of a steering wheel by a driver.

  As this type of conventional technology, the steering angle of the steering wheel and the vehicle speed are detected, and the target variable turning angle of the turning variable device is calculated based on the steering angle and the vehicle speed. Along with this, an invention is known in which the steering feeling is quick on the low speed side and slow on the high speed side by increasing the steering angle ratio, which is the ratio of the steered wheel to the steering angle of the steering wheel. (For example, refer to Patent Document 1). That is, in the invention described in Patent Document 1, the steering angle ratio becomes small and the steering feeling becomes quick when the vehicle is traveling at a constant speed or when the vehicle is stopped. Can do.

JP 2008-137612 A

However, since the technique described in Patent Document 1 is configured to reduce the steering angle ratio by reducing the steering angle ratio when the vehicle is stopped as described above, for example, the steering mechanism is driven by an electric motor. In the case of the configuration, a large electric motor capable of generating a large torque is required.
In other words, in the invention described in Patent Document 1, when selecting an electric motor to be mounted, it is assumed that the motor torque necessary for turning to a position near the full turning position can be generated at the time of stationary operation. However, there is an unsolved problem that the electric motor is inevitably increased in size, which hinders downsizing of the steering mechanism.

  The present invention has been made paying attention to such an unsolved problem of the conventional technology, and aims to reduce the size of a steering mechanism that steers steered wheels according to steering of a tearing wheel by a driver. It is an object of the present invention to provide a steering control device that can perform this.

  In order to solve the above-described problem, an aspect of the steering control device according to the present invention provides a steering angle ratio characteristic and a stoppage as a steering angle ratio characteristic indicating a relationship between a steering angle of a steering wheel and a turning angle of a steered wheel. At least two characteristics are set, including the hour steering angle ratio characteristic. The steering angle ratio characteristic when the vehicle is stopped is set to the steering angle ratio characteristic along the driving angle ratio characteristic until the steering angle reaches the threshold value, and the steering angle ratio increases when the steering angle exceeds the threshold value. Set to the steering angle ratio characteristic. Furthermore, when the start-time steering state at the start of power supply is different from the stop-time steering state at the time of power supply stop, the steering angle ratio of the start-time steering state is maintained and the steering angle is set to the steering angle. There is also provided a return mode control unit that performs return mode processing to be proportional to.

  According to the present invention, when the vehicle stops traveling, the steering control is performed in the same manner as the steering ratio characteristic during traveling of the vehicle until the steering angle reaches the threshold, and when the steering angle exceeds the threshold, the steering angle ratio increases. Since the change in the turning angle with respect to the steering angle is small, even if the driver steers the steering wheel greatly when the vehicle stops running, the turning by the turning mechanism can be small, so the maximum driving force required for the turning mechanism Becomes smaller. Therefore, it can contribute to size reduction of a steering mechanism.

  Furthermore, when the start-time steering state at the start of power supply is different from the stop-time steering state at the time of power supply stop, the steering angle ratio of the start-time steering state is maintained and the steering angle is set to the steering angle. Proportional to realize the steering state intended by the driver.

1 is a schematic view showing a configuration of a vehicle to which a steering control device according to the present invention is applied. It is a flowchart which shows an example of the steering reaction force control processing procedure performed with the steering reaction force control part which can be applied to this invention. It is a characteristic diagram which shows the relationship between a steering angle and a steering reaction force. It is a block diagram which shows an example of the steering control apparatus which can be applied to this invention. It is a figure which shows the installation state of a steering state warning light, Comprising: (a) is a perspective view which shows an instrument panel, (b) is a front view which shows a display part. It is a characteristic diagram which shows a steering angle ratio characteristic, Comprising: (a) is a characteristic diagram which shows a steering angle ratio characteristic at the time of driving, (b) is a characteristic diagram which shows a steering angle ratio characteristic at the time of a stop. It is a flowchart which shows an example of the steering angle control processing procedure performed in the target turning angle calculating part which can be applied to this invention. It is a flowchart which shows the specific process sequence of the initialization process of FIG. It is a flowchart which shows the specific process sequence of the steering angle ratio characteristic control process of FIG. It is a characteristic diagram explaining operation | movement when steering is performed at the time of the control stop of 1st Embodiment. It is a time chart explaining operation | movement when steering is not performed at the time of control stop of 1st Embodiment. It is a characteristic diagram which shows the other example of a steering angle ratio characteristic at the time of a stop.

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

  The vehicle 1 also includes a steering actuator 8, a steering actuator rotation angle sensor 9, an output side steering shaft 10, a steering torque sensor 11, a pinion gear 12, a pinion angle sensor 13, a rack shaft 14, a tie rod 15, The tie rod axial force sensor 16 and wheels 17FR, 17FL, 17RR, 17RL are provided. Here, the steering mechanism SM is configured by the steering actuator 8, the output side steering shaft 10, the pinion gear 12, the pinion angle sensor 13, the rack shaft 14, and the tie rod 15 constituting the driving force transmission unit.

This steering mechanism SM has a configuration of a steer-by-wire system SBW in which the steering wheel 2 and the steered wheels 17FR and 17FL are mechanically separated and the steered wheels 17FR and 17FL are steered by the steered actuator 8. .
Further, the vehicle 1 includes a drive shaft 20 that rotationally drives the front wheels 17FR and 17FL, for example, and the vehicle 1 is driven forward or reversely by a rotational drive source such as an engine or an electric motor (not shown). Move forward or backward. The drive format of the vehicle 1 is not limited to the front wheel drive format, and a rear wheel drive format or a four-wheel drive format can be applied.

In addition, the vehicle 1 includes a vehicle state parameter acquisition unit 21, wheel speed sensors 24 FR, 24 FL, 24 RR, 24 RL, a control / drive circuit unit 26, and a mechanical backup 27.
The steering wheel 2 is configured to rotate integrally with the input side steering shaft 3, and transmits a steering input by the driver to the input side steering shaft 3.

The input-side steering shaft 3 includes a steering reaction force actuator 6, and applies a steering reaction force by the steering reaction force actuator 6 to the steering input input from the steering wheel 2.
The steering angle sensor 4 is provided on the input side steering shaft 3 and detects the rotation angle of the input side steering shaft 3, that is, the steering angle θs of the steering wheel 2 by the driver. Then, the steering angle sensor 4 outputs the detected rotation angle of the input side steering shaft 3, that is, the steering angle θs, to the control / drive circuit unit 26.

The steering torque sensor 5 is installed on the input side steering shaft 3 and detects the rotational torque of the input side steering shaft 3, that is, the steering torque Ts to the steering wheel 2. Then, the steering torque sensor 5 outputs the detected steering torque Ts to the control / drive circuit unit 26.
In the steering reaction force actuator 6, a gear that rotates integrally with the motor shaft is engaged with a gear formed in a part of the input side steering shaft 3, and is operated by the steering wheel 2 in accordance with an instruction from the control / drive circuit unit 26. A reaction force is applied to the rotation of the input side steering shaft 3.

The steering reaction force actuator rotation angle sensor 7 detects the rotation angle θra of the steering reaction force actuator 6, that is, the rotation angle θra due to the steering input transmitted to the steering reaction force actuator 6, and supplies the detected rotation angle θra to the control / drive circuit unit 26. Output.
The steered actuator 8 has a gear that rotates integrally with a motor shaft of a steered motor 8a, which will be described later, meshed with a gear formed on a part of the output-side steering shaft 10, and an instruction from the control / drive circuit unit 26. Accordingly, the output side steering shaft 10 is rotated. Here, the turning torque generated by the turning motor 8a of the turning actuator 8 is smaller than the turning torque required for full turning at the time of turning when the vehicle 1 is stopped. Is set. For this reason, the turning actuator 8 is smaller and lighter than a turning actuator that sufficiently outputs the turning torque necessary for full turning at the time of stationary.

The turning actuator rotation angle sensor 9 detects the rotation angle of the turning actuator 8, that is, the rotation angle δm output by the turning actuator 8, and outputs the detected rotation angle δm to the control / drive circuit unit 26. To do.
The output side steering shaft 10 includes a steering actuator 8, and transmits the rotation input by the steering actuator 8 to the pinion gear 12.

The steering torque sensor 11 is installed on the output side steering shaft 10 and detects the rotational torque of the output side steering shaft 10, that is, the steering torque Tr of the wheels 17FR and 17FL via the rack shaft 14. Then, the turning torque sensor 11 outputs the detected rotational torque Tr of the output side steering shaft 10 to the control / drive circuit unit 26.
The pinion gear 12 meshes with a rack gear formed on the rack shaft 14 constituting the steering member, and transmits the rotation input from the output side steering shaft 10 to the rack shaft 14.

The pinion angle sensor 13 detects the rotation angle of the pinion gear 12, that is, the turning angle δr of the wheels 17FR and 17FL output via the rack shaft 14, and controls / drives the detected rotation angle of the pinion gear 12, that is, the turning angle δr. Output to the circuit unit 26.
The rack shaft 14 has spur teeth that mesh with the pinion gear 12, and converts the rotation of the pinion gear 12 into a linear motion in the vehicle width direction.

The tie rod 15 connects both ends of the rack shaft 14 and the knuckle arms 18 of the wheels 17FR and 17FL via ball joints 19, respectively.
The tie rod axial force sensor 16 is installed on each of the tie rods 15 installed at both ends of the rack shaft 14 and detects the axial force acting on the tie rod 15. The tie rod axial force sensor 16 outputs the detected axial force of the tie rod 15 to the control / drive circuit unit 26.

  The wheels 17FR, 17FL, 17RR, and 17RL are configured by attaching a tire to a tire wheel, and are supported by the vehicle body 1A via a suspension device (not shown). Among these, for the front wheels (steered wheels 17FR, 17FL), the knuckle arm 18 is swung by the tie rod 15, so that the directions of the steered wheels 17FR, 17FL with respect to the vehicle body 1A change.

  The vehicle state parameter acquisition unit 21 acquires the vehicle speed V based on a pulse signal indicating the rotation speed of the wheels output from the wheel speed sensors 24FR, 24FL, 24RR, 24RL provided in the wheels 17FR, 17FL, 17RR, 17RL. To do. Moreover, the vehicle state parameter acquisition part 21 acquires the slip ratio of each wheel based on the vehicle speed V and the rotational speed of each wheel. Then, the vehicle state parameter acquisition unit 21 outputs the acquired parameters to the control / drive circuit unit 26.

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

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

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

The mechanical backup 27 connects the input side steering shaft 3 and the output side steering shaft 10 in accordance with instructions from the control / drive circuit unit 26, and ensures transmission of force from the input side steering shaft 3 to the output side steering shaft 10. Mechanism.
The mechanical backup 27 can be configured by, for example, a cable type steering mechanism or an electromagnetic clutch mechanism.

  Here, with respect to the mechanical backup 27, the input side steering shaft 3 and the output side steering shaft 10 are normally connected from the control / drive circuit unit 26 when an ignition switch (not shown) is turned off. When a fastening instruction is input and the ignition switch is turned on, a non-fastening instruction for not connecting the input side steering shaft 3 and the output side steering shaft 10 is input.

Further, when it is necessary to perform a steering operation without passing through the steering angle sensor 4, the steering torque sensor 5, the steering actuator 8, etc. due to the occurrence of a failure in the steering system, the control / drive circuit unit 26 inputs the steering on the input side. A fastening instruction for connecting the shaft 3 and the output side steering shaft 10 is input.
As shown in FIG. 1, the control / drive circuit unit 26 includes a steering reaction force control unit 40 that controls the steering reaction force actuator 6 and a turning control unit 50 that controls the turning actuator 8.

The steering reaction force control unit 40 receives the steering angle θs detected by the steering angle sensor 4, and refers to the steering reaction force torque calculation map shown in FIG. 2 based on the input steering angle θs. TR is calculated, and the calculated steering reaction torque TR is supplied to the steering reaction force actuator 6 to control the steering reaction torque on the steering wheel 2.
Here, as shown in FIG. 3, in the steering reaction force torque calculation map, the steering angle θs is set as the horizontal axis, and the steering reaction force torque TR is set as the vertical axis. This steering reaction force characteristic control map is obtained when the steering wheel 2 is in the neutral position (straight running state) θs = 0 as shown by the solid line in FIG. 3 when the steering angle ratio characteristic control map during traveling is selected. The steering reaction torque TR is set to “0”.

When the steering wheel 2 is steered in the right turn direction from the neutral position, the steering reaction is increased in response to an increase in the positive direction of the steering angle θs from the steering reaction force torque + TRn at the neutral position in the first quadrant of FIG. right up to become the characteristic line L _R that torque TR is increased is selected. When the steering angle θs reaches the maximum right steering angle θ _Rmax1 , the steering reaction torque TR becomes the maximum positive value + TR _RMAX1 .

When the steering is _maintained at the maximum right _turn steering angle θ _Rmax1 , the steering reaction torque TR decreases to the steering reaction torque value + TR1 which is smaller than the steering reaction torque + TRn at the neutral position. The steering reaction force torque TR passes through 0 and changes to a predetermined value −TR _Lmin on the negative side of the fourth quadrant along the characteristic line L _{C1 in} which the force torque TR is diagonally lower left. Then, the steering reaction torque TR increases in the negative direction in response to a decrease of the steering angle θs along the characteristic line L characteristic line _R parallel to the left edge L _L.

When the steering angle θs goes to the left-turned state beyond the neutral position where the steering angle θs becomes “0”, the steering reaction torque TR responds to the increase in the steering angle θs in the negative direction along the characteristic line L _L of the third quadrant. Increase in the negative direction. Further, when the steering angle θs reaches the left-turn maximum steering angle θ _Lmax , the steering reaction torque TR becomes the negative maximum value −TR _Lmax1 .
When the steering is _maintained at this left- _turn maximum steering angle _θLmax1 , the steering reaction torque TR decreases to a steering torque value −TR1 smaller than the steering reaction torque −TRn at the neutral position, and then switched back to the neutral position. The steering reaction force torque TR changes along a characteristic line L _C2 that is diagonally to the upper right and passes through 0 to a predetermined value + TR _Rmin on the positive side of the second quadrant. Thereafter, the steering reaction force torque TR increases in the positive direction along with the characteristic line _LR in accordance with the decrease in the steering angle θs. When the steering reaction force torque TR stays at the neutral position where the steering angle θs becomes “0”, the steering reaction force torque TR is increased. Return to “0”.

On the other hand, when the stop-time steering angle ratio characteristic control map is selected, as shown by the dotted line in FIG. 3, the steering angle θs changes to the positive predetermined value + θ1 that switches from the characteristic line L21 to L22 in FIG. upon reaching, it increases with the increase in the steering angle θs along large characteristic line L _R1 slope than the characteristic line L _R of the solid line shown. When the steering angle θ reaches the maximum right turn steering angle θ _Rmax , the maximum steering reaction torque + TR _Rmax2 is greater than the above-described maximum steering reaction torque + TR _Rmax1 .

When fixed steering to the right turn maximum steering angle theta _Rmax, the steering reaction torque TR is reduced to only large holding steering torque value + TR2 deltaTR than holding steering torque value + TR1. Thereafter, when returning to the neutral position side, the steering reaction torque TR changes along a characteristic line L _C3 parallel to the characteristic line L _C1 to a predetermined value −TR3 which is larger in the negative direction than the minimum value −TR _Lmin. The steering reaction force torque TR is maintained at the predetermined value −TR3 regardless of the decrease in the steering angle θs along the characteristic line L _L2 having a gentler slope than the line L _{L, and} the characteristic is obtained when the steering angle θs decreases beyond the predetermined value θ1. Back to the line _{L L.}

Then, steering angle θs is a left turn state beyond the neutral position, the steering angle θs exceeds a predetermined value -θ1 corresponding to the predetermined value .theta.1, the characteristic line of the large dotted illustrated slope than the characteristic line L _L The steering reaction torque TR increases along with the increase in the steering angle θs along L _L1 . When the steering angle θ reaches the left-turn maximum steering angle θ _Lmax , the maximum steering reaction force torque −TR _Lmax2 is greater than the maximum steering reaction force torque −TR _Lmax1 described above.

With fixed steering in this right turn maximum steering angle theta _Lmax, the steering reaction torque TR is reduced to only large predetermined value -TR2 deltaTR than holding steering torque value -TR1, switched back to a subsequent neutral position side, the characteristic line _{L C2} Along a characteristic line _LC4 parallel to the predetermined value + TR3 which is larger than the predetermined value + TR _{Rmin in the} positive direction. Then, the steering reaction torque TR regardless decrease of the steering angle θs along the characteristic line L characteristic line a gentle slope than _R L _R2 is maintained at a predetermined value -TR3, the steering angle θs exceeds a predetermined value -θ1 decrease Te is returning to the characteristic line L _R.

In this way, by creating the steering reaction force characteristic control map, the characteristic line shown in the solid line is selected in the state where the steering angle ratio characteristic control map during travel is selected, and the steering reaction force characteristic control map is selected according to the steering state of the steering wheel 2. The optimal steering reaction torque can be generated.
However, in the state where the steering angle ratio characteristic control map at the time of stop is selected, the steering angle δr is stopped with respect to the steering angle at the time of traveling in a state where the steering angle θ exceeds ± θ1, as will be described later. The turning angle at the time is limited to be small. Therefore, when the turning angle is in the restricted state, the driver can experience the restricted state of the turning angle by increasing the rate of increase of the steering reaction force torque as compared to during traveling.

  Then, the steering reaction force control unit 40 executes a steering reaction force control process shown in FIG. This steering reaction force control process is executed as a timer interrupt process at predetermined time intervals (for example, 10 msec). First, in step S1, the steering angle θs is read, and then the process proceeds to step S2 where the steering angle θs is “0”. It is determined whether or not. When the determination result is θs = 0, the process proceeds to step S3, the steering reaction torque TR is set to “0”, and then the process proceeds to step S4.

If the determination result in step S2 is that the steering angle θs is a value other than zero, the process directly proceeds to step S4.
In this step S4, it is determined whether the steering angle ratio characteristic control map during travel is selected or the steering angle ratio characteristic control map during stop is selected in the steering angle ratio characteristic control process of FIG.
If the determination result of step S4 is that the steering angle ratio characteristic control map during travel is selected, the process proceeds to step S5, the steering reaction force characteristic control map shown by the solid line in FIG. 3 is selected, and then the process proceeds to step S6. Based on the steering angle θs, the steering reaction force TR is calculated with reference to the steering reaction force characteristic control map shown by the solid line in FIG.

In step S7, a steering reaction force current Ir for driving the steering reaction force actuator 6 is calculated based on the steering reaction force TR calculated in step S6, and the calculated steering reaction force current Ir is output to the steering reaction force actuator 6. After that, the timer interrupt process is terminated and the program returns to the predetermined main program.
On the other hand, if the determination result of step S4 is that the stationary steering angle ratio characteristic control map is selected, the process proceeds to step S8 to select the steering reaction force characteristic control map shown by the broken line in FIG. 3, and then to step S9. Based on the steering angle θs, the steering reaction force TR is calculated with reference to the steering reaction force characteristic control map shown by the dotted line in FIG. 3, and then the process proceeds to step S7.

  The steering reaction force torque TR is not limited to the calculation based on the steering reaction force torque calculation map, and the steering reaction force torque TR may be calculated by calculation. That is, the steering reaction force Fr due to the lateral force acting on the steering reaction force control unit 40 in the direction of the rotation axis of the front wheels 17FR and 17FL from the steering torque Ts detected by the steering torque sensor 5 and the road surface detected by the tie rod axial force sensor 16 is applied. Then, the rotation angle δm of the steering actuator 8 and the steering angle θs of the steering wheel 2 detected by the steering angle sensor 4 are input from the steering actuator rotation angle sensor 9. Then, the steering reaction force control unit 40 calculates the target steering reaction force torque TR to be applied to the input side steering shaft 3 based on the steering torque Ts, the turning reaction force Fr, and the rotation angle δm of the turning actuator 8. May be. Further, the steering reaction torque TR calculated in FIG. 3 may be corrected according to the traveling state.

Moreover, the steering control part 50 is provided with the target turning angle calculating part 51 and the actuator control part 52, as shown in FIG.
The target turning angle calculation unit 51 receives the steering angle θs detected by the steering angle sensor 4 and the vehicle speed V acquired by the vehicle state parameter acquisition unit 21, and controls the turning actuator 8 based on the steering angle θs and the vehicle speed V. A target turning angle δ ^* for driving is calculated. The target turning angle calculation unit 51 includes a steering angle ratio characteristic selection unit 51A, a steering angle ratio control unit 51B, and a return mode control unit 51C.

Here, the target turning angle calculation unit 51 sets the steering angle ratio characteristic representing the relationship between the steering angle θs of the steering wheel 2 and the turning angles δr of the steered wheels 17FR and 17FL, as shown in FIG. An hour steering angle ratio characteristic control map and a stop hour steering angle ratio characteristic control map shown in FIG. 6B are stored. The target turning angle calculation unit 51 selects a traveling-time steering angle ratio characteristic control map and a stationary-time steering angle ratio characteristic control map based on whether the vehicle speed V representing the vehicle traveling state represents a traveling state or a stopped state. Then, the target turning angle δ ^* is calculated with reference to the control map selected based on the steering angle θs.

As shown in FIG. 6 (a), the steering angle ratio characteristic control map at the time of travel shows the steering angle ratio (= θs / δr) so that the target turning angle δ ^* increases in proportion to the increase in the steering angle θs. For example, a linear characteristic line L1 is set up to the full turning shown by the solid line as “1”. Thus, the reason why the characteristic line L1 is set linearly is that the road surface resistance with respect to the steered wheels 17FR and 17FL becomes small in the traveling state of the vehicle 1, and the steered force for steering the steered wheels 17FR and 17FL is reduced. This is because the steering torque that reaches the full steering can be generated even with the steering actuator 8 whose steering torque is smaller than the steering torque necessary for the full steering at the time of stationary as described above.

  On the other hand, as shown in FIG. 6B, the steering angle ratio characteristic control map at the time of stopping is the time when the vehicle travels until the steering angle θs reaches a threshold value θsth set to about half of full steering from the neutral position. The steering angle ratio (= θs / δr) along the characteristic line L1 shown by the one-dot chain line in the steering angle ratio characteristic control map is set to a linear characteristic line L21 that is, for example, “1”. When the steering angle θs exceeds the threshold θsth, the steering angle ratio (= θs / δr) becomes about “0.3”, for example, and when the steering wheel 2 is steered to the full steering position, the steering actuator A linear characteristic line L22 is set such that the turning angle δr of the steered wheels 17FR and 17FL is δrmax ′ smaller than the full turning angle δrmax with the maximum turning torque generated at 8, that is, the maximum rack axial force FRmax.

  Further, as shown in FIG. 4, the target turning angle calculation unit 51 includes a turning state storage unit 51a constituted by, for example, a non-volatile memory, and a turning state warning unit 51c constituted by a turning state warning lamp 51b. Is connected. Here, as shown in FIGS. 5A and 5B, the steered state warning light 51b constituting the steered state warning unit 51c is disposed at a position visible from the driver in front of the driver's seat. ing. That is, the meter cluster 71 fixed to the upper surface of the steering column is provided in the cluster mounting recess 60a formed in the instrument panel 60 disposed on the front side of the driver's seat. In the meter cluster 71, a meter unit 77 including a speedometer 73, a tachometer 74, a fuel meter 75, a water temperature meter 76, and the like is disposed on the back substrate unit 72. Various warning lights 78 including a steered state warning lamp 51b are arranged below the meter section 77.

Further, the target turning angle calculation unit 51 executes the steering angle control process shown in FIG. 7 when an ignition switch (not shown) is turned on. In this steering angle control process, first, an initialization process is executed in step S10, and then the process proceeds to step S11, and after the steering ratio characteristic control process is executed, the process proceeds to step S12.
In this step S12, it is determined whether or not an ignition switch (not shown) is turned off. If the ignition switch (not shown) is kept on, the process returns to step S11, and the ignition switch is turned on. When the switch is turned off, the process proceeds to step S13.

In this step S13, the current steering angle θse and the turning angle δre are stored in the turning state storage unit 51a provided in the target turning angle calculation unit 51 as the steering state at the end, and then the process proceeds to step S14.
In this step S14, the mechanical backup 27 that mechanically locks the steering system mechanism between the steering wheel 2 and the steered wheels 17FR and 17FL is locked in a connected state, and then the process proceeds to step S15 to stop the system and then the system is stopped. The rudder control process is terminated.

Then, as shown in FIG. 8, the initialization process executed in step S10 is, first, in step S21, the steering angle θse and the turning angle representing the end-time turning state stored in the turning state storage unit 51a. After reading δre, the process proceeds to step S22.
In this step S22, the steering angle θsp and the turning angle δrp representing the current steered state are read, and then the process proceeds to step S23, the mechanical lock state by the mechanical backup 27 is released, and then the process proceeds to step S24.

In step S24, whether the steering state is changed due to a difference between the steering angle θse and the steering angle δre representing the end-time steering state and the steering angle θsp and the steering angle δrp representing the current steering state. If the turning state has not changed, the initialization process is terminated as it is, and the process proceeds to the steering ratio characteristic control process shown in FIG.
Further, when the result of determination in step S24 is that the steered state is changing, the process proceeds to step S25, and the coordinates of the steering angle θsp and the steered angle δre representing the current steered state are represented in FIG. 6 described above. It is determined whether or not the vehicle exists on the characteristic lines L21 and L22 represented by solid lines in the steering angle ratio characteristic control map. If the determination result of step S24 is that the coordinates of the steering angle θsp and the turning angle δre exist on the characteristic lines L21 and L22, the initialization process is terminated as it is and the process proceeds to the steering ratio characteristic control process shown in FIG. To do.

On the other hand, if the determination result in step S24 is that the coordinates of the steering angle θsp and the turning angle δre do not exist on the characteristic lines L21 and L22, the process proceeds to step S26, and a warning is given to the turning state warning lamp 51b. A signal is output to warn the driver that the current steered state has changed from the steered state at the end, and then the process proceeds to step S27.
In this step S27, a return mode turning angle calculation formula for calculating a return mode turning angle δri shown in the following equation (1) based on the current steering angle θsp and turning angle δrp is set, and then the process proceeds to step S28. To do.

δri = (δrp / θsp) θs (1)
In this step S28, the current steering angle θs is read, then the process proceeds to step S29, the return angle turning angle δri is calculated by substituting the steering angle θs into the equation (1), and then the process proceeds to step S30. .
In this step S30, it is determined whether or not the current steering angle θs is “0” representing the neutral position. If θs = 0, it is determined that the return mode process is to be terminated, and the process proceeds to step S31. After stopping the output of the warning signal to the steered state warning lamp 51b, the initialization process is terminated, and the process proceeds to the steering ratio characteristic control process of step S11 in FIG.

Further, when the determination result in step S30 is θs ≠ 0, the process proceeds to step S32, the stop-time steering angle ratio characteristic control map shown in FIG. 6 is selected, and then the process proceeds to step S33, where the steering angle θs. After the turning angle δr is read, the process proceeds to step S34.
In this step S34, it is determined whether or not the coordinates represented by the read steering angle θs and turning angle δr exceed the characteristic line L22. If the coordinates do not exceed the characteristic line L22, the process returns to step S28. Further, when the determination result in step S34 exceeds the characteristic line L22, the process proceeds to step S35, and after the steering angle θs is read, the process proceeds to step S36.

In this step S36, the target turning angle δ ^* is calculated with reference to the stop-time steering angle ratio characteristic control map based on the read steering angle θs, and then the process proceeds to step S37.
In step S37, the target turning angle δ ^* is output to the actuator control unit 52 shown in FIG. 4, and then the process proceeds to step S38 to determine whether or not the steering angle θs is “0”. If this determination result is θs = 0, it is determined that the return mode process is to be terminated, and the process proceeds to step S31. If θs ≠ 0, the process proceeds to step S39.

  In this step S39, it is determined whether or not the steering angle θs has reached the maximum steering angle θsmax. When the determination result is θs <θmax, the process returns to step S35, and when θs = θsmax is reached, the process proceeds to step S40, and whether or not the absolute value | V | of the vehicle speed V is greater than “0”. Determine. When this determination result is | V | = 0, the process returns to step S35, and when | V |> 0, the process proceeds to step S41.

In this step S41, the target turning angle δ ^* is calculated with reference to the traveling steering angle ratio characteristic control map shown in FIG. 6A, and then the process proceeds to step S42 to calculate the calculated target turning angle δ ^*. Is output to the actuator controller 52, and then the process proceeds to step S43.
In this step S43, it is determined whether or not the turning angle δr has reached the maximum turning angle δrmax. If δr <δrmax, the process returns to step S35, and if δr = δrmax, the return mode process is terminated. Then, the process proceeds to step S44, the output of the warning signal to the steered state warning lamp 51b is stopped, the initialization process is terminated, and the process proceeds to the steering ratio characteristic control process of FIG.

Here, in the processing of FIG. 8, the processing of step S21 to step S44 corresponds to the return mode control unit 51C.
In step S51, the steering angle ratio characteristic control process first reads the steering angle θs, the steering angle δr, the vehicle speed V, the steering torque Ts, and the steering torque Tr, and then proceeds to step S52.
In this step S52, it is determined whether or not the vehicle 1 is running or stopped by determining whether or not the absolute value of the vehicle speed V is greater than “0”. It is determined that the vehicle 1 is in the traveling state, the process proceeds to step S53, and the target turning angle δ is also obtained by referring to the steering angle ratio characteristic control map shown in FIG. 6A based on the steering angle θs. After calculating ^* , the process proceeds to step S54.

In this step S54, it is determined whether or not a steering angle deviation Δδ (= δ ^* −δr) obtained by subtracting the current steering angle δr from the target steering angle δ ^* exceeds a steering angle deviation threshold Δδs. To do. Here, the steering angle deviation threshold Δδs is set to a maximum value such that an increase in the steering angle δr cannot be detected by the driver.
If the determination result in step S54 is δ ^* −δr> Δδs, it is determined that the change in the target turning angle δ ^* is large, the process proceeds to step S55, and the steering angle deviation is added to the current turning angle δr. After the value obtained by adding the threshold value Δδs is set to the target turning angle δ ^* , the process proceeds to step S56.

On the other hand, when the determination result of step S54 is δ ^* −δr ≦ Δδs, it is determined that the correction of the target turning angle δ ^* is not necessary, and the process directly proceeds to step S56.
In step S56, the calculated target turning angle δ ^* is output to the actuator control unit 52, and then the timer interruption process is terminated and the process returns to the predetermined main program.
On the other hand, when the determination result in step S52 is | V | ≦ 0, it is determined that the vehicle 1 is in a stopped state, the process proceeds to step S57, and it is determined whether or not the turning angle δr has changed. To do. The determination result of step S57 is that the deviation Δδr between the turning angle δr (n-1) at the previous reading and the turning angle δr (n) at the current reading is equal to or larger than the set value Δδrs, and the turning angle δr is When it is determined that the change has occurred, the process proceeds to step S58, the road surface friction coefficient μ is calculated based on the turning angle δr and the turning torque Tr, and then the process proceeds to step S59.

In this step S59, it is determined whether or not the road surface friction coefficient μ is equal to or less than a preset low friction coefficient threshold μs (for example, μs = 0.7). If μ ≦ μs, the road surface is frozen road, snow road, It is determined that the road surface friction coefficient μ of the rainy road, gravel road, etc. is small and the turning force of the steered wheels 17FR and 17FL is small, and the process proceeds to step S53.
On the other hand, when the determination result of step S59 is μ> μs, the road is a dry concrete road or asphalt road, the road surface friction coefficient μ is large, and the turning force of the steered wheels 17FR and 17FL is increased, so that the turning actuator 8 It is determined that the load is large, and the process proceeds to step S60.

Further, when the determination result of step S57 indicates that the turning angle δr has not changed, the process directly proceeds to step S60.
In step S60, the target turning angle δ ^* is calculated based on the steering angle θs with reference to the stop-time steering angle ratio characteristic control map shown in FIG. 6B, and then the process proceeds to step S56.
In the steering angle ratio characteristic control process of FIG. 9, the processes of steps S51 and S52 correspond to the steering angle ratio characteristic selection unit 51A, and the processes of steps S53 to S60 correspond to the steering angle ratio control part 51B.

The actuator control unit 52 includes a turning angle deviation calculating unit 61 that calculates a turning angle deviation Δδ, a turning motor control unit 62, a current deviation calculating unit 63, and a motor current control unit 65.
The turning angle deviation calculation unit 61 subtracts the turning angle δr calculated based on the pinion rotation angle detected by the pinion angle sensor 13 from the target turning angle δ ^* output from the target turning angle calculation unit 51. The steering angle deviation Δδ is calculated, and the calculated steering angle deviation Δδ is output to the steered motor control unit 62.

The steered motor control unit 62 calculates the drive command current im ^* of the steered motor 8a constituting the actuator 8 so that the input steered angle deviation Δδ becomes zero, and the calculated drive command current im ^* Output to the deviation calculator 63.
The current deviation calculation unit 63 subtracts the motor current imr output from the motor current detection unit 64 that detects the motor current supplied to the steered motor 8a constituting the steered actuator 8 from the input drive command current im ^*. The current deviation Δi is calculated, and the calculated current deviation Δi is output to the motor current control unit 65.

The motor current control unit 65 performs feedback control so that the input current deviation Δi becomes zero, that is, the actual motor current imr follows the drive command current im ^*, and changes the turning motor drive current imr. Output to the rudder motor 8a.

(Operation)
Next, the operation of the above embodiment will be described.
Now, it is assumed that the vehicle 1 is stopped with an ignition switch (not shown) turned off.
When an ignition switch (not shown) is turned on in this stop state, the steering control processing of FIG. 7 is started by the target turning angle calculation unit 51 of the steering control unit 50, and first, initialization processing is executed. To do.

In this initialization process, as shown in FIG. 8, when an ignition switch (not shown) is turned off, the steering angle representing the steered state at the end of control stored in the steered state storage unit 51a. θse and the turning angle δre are read (step S21), and then the steering angle θep and the turning angle δrp representing the current turning state are read (step S22).
Next, in the initialization process, the locked state of the mechanical backup 27 that mechanically connects the steering wheel 2 and the rack shaft 14 is released (step S23), and the steering wheel 2 side and the rack shaft 14 side are separated.

  Next, in the initialization process, the steering angle θse and the turning angle δre at the end of the control are compared with the current steering angle θsp and the turning angle δrp, and whether or not there is a change in the turning state in which they are inconsistent. Is determined (step S24). At this time, when the steering angle θse and the turning angle δre at the end of the control coincide with the current steering angle θsp and the turning angle δrp, the steering is performed during a period when the ignition switch (not shown) is in the OFF state. It is judged that there is no steering process for rotating the wheel 2 and the steering angle ratio characteristic control at the time of stopping is possible, and the initialization process is finished as it is, and the routine proceeds to the steering angle ratio characteristic control process of FIG.

Further, when the steering angle θse and the turning angle δre at the end of the control are compared with the current steering angle θsp and the turning angle δrp, and there is a change in the turning state in which they do not match, the current steering is It is determined whether or not the coordinates represented by the angle θsp and the turning angle δrp are above any of the characteristic lines L21 and L22 on the stop-time steering angle ratio characteristic control map of FIG. 6B (step S25). ).
When the determination result indicates that the coordinates represented by the current steering angle θsp and the turning angle δrp are on any of the characteristic lines L21 and L22 on the stop-time steering angle ratio characteristic control map of FIG. Therefore, it is determined that the steering angle ratio characteristic control at the time of stopping is possible, the initialization process is terminated, and the process proceeds to the steering angle ratio characteristic control process of FIG.

  However, as shown in FIG. 10, the steering wheel θse and the turning angle δre at the end of the control are at the point Pe on the characteristic line L21, and the steering wheel is in the neutral direction during the period when the ignition switch (not shown) is in the OFF state. Is switched back to point Pp, the current steering angle θsp and the turning angle δrp do not match the steering angle θse and the turning angle δre at the end of the control, and the steering state is changed. Change occurs.

  When a change in the turning state occurs during a period in which an ignition switch (not shown) is in an off state, the turning state is changed by the target turning angle calculation unit 51 when the stop-time running control described later is started. It is not possible to predict how the turning angle will change because it is not grasped. For this reason, when a change in the steered state occurs, a return mode process for returning to a state in which the stop-time steering ratio characteristic control process can be started is executed.

In the return mode process, a warning signal is output to the steered state warning lamp 51b to warn the driver that the mode is the return mode (step S26).
Thereafter, the current steering angle θsp and turning angle δrp are substituted into the equation (1) to determine an equation for calculating the return mode turning angle δri represented by the characteristic line L3 in FIG. 10 (step S27). .

  Then, the current steering angle θs is read, and the return mode turning angle δri is calculated by substituting the steering angle θs into the equation (1). Therefore, the coordinates calculated and represented by the return mode steering angle δri and the steering angle θs move on the characteristic line L3 in FIG. The calculated return mode turning angle δri is output to the actuator controller 52, and the turning motor 8a is driven and controlled. Therefore, the return mode process can be performed without causing the driver to feel uncomfortable.

Then, when the steering wheel 2 is turned back to the neutral position side and the steering angle θs becomes “0”, it is determined that the steering angle ratio characteristic control at the time of stopping can be started, and the initialization process is terminated. The process proceeds to the steering angle ratio characteristic control process.
On the other hand, when the steering wheel 2 is increased to the full turning side, the steering angle θs increases, and the coordinates represented by the steering angle θs and the return mode turning angle δri exceed the characteristic line L2 in FIG. 6B, the target turning angle δ ^* is calculated according to the stop-time steering angle ratio characteristic control map of FIG. 6B (step S36), and the calculated target turning angle δ ^* is output to the actuator control unit 52. The steering actuator 8 is driven and controlled.

Thereafter, when the steering angle θs becomes “0”, the output of the warning signal to the steered state warning lamp 51b is stopped, and then the process proceeds to the steering angle ratio characteristic control process of FIG.
On the other hand, when the steering angle θs reaches the maximum steering angle θsmax, when the vehicle 1 has started traveling, the target rotation is referred to with reference to the steering angle ratio characteristic control map during traveling shown in FIG. The steering angle δ ^* is calculated, and the calculated target steering angle δ ^* is output to the actuator control unit 52 to drive-control the steering actuator 8.

Then, when the turning angle δr reaches the full turning angle δrmax, the output of the warning signal to the turning state warning lamp 51b is stopped, and the process proceeds to the steering angle ratio characteristic control process of FIG.
As described above, when the vehicle 1 starts running and the turning angle δr reaches the full turning angle δrmax or the steering angle θs reaches “0”, the return mode by the initialization process is terminated and the steering is performed. Return to control the return mode turning angle δri without giving the driver a sense of incongruity when the turning state changes while the ignition switch (not shown) is in the OFF state by shifting to the angle ratio characteristic control process. Mode can be performed. Moreover, in the steered state in the return mode, the steered state warning lamp 51b is turned on, so that the driver can be surely recognized that the return mode is set.

  Further, in this return mode, when the steering angle ratio characteristic control map is selected and the steering angle ratio characteristic control is started, the steering reaction force characteristic indicated by the dotted line in FIG. 3 is controlled. In a state where the value exceeds ± θs1, the steering reaction force is increased compared to the steering reaction force characteristic shown in the solid line at normal time, the steering reaction force is increased during full turning, The steering reaction force is increased, and the driver can feel that the steering angle ratio is being reduced.

  Next, a case where the steering angle θs becomes “0” when the vehicle 1 stops and the steering angle ratio characteristic control process of FIG. 9 is started will be described with reference to FIGS. 11 (a) and 11 (b). . That is, as shown in FIG. 11B, it is assumed that the vehicle is stopped on a high friction coefficient road having a road surface friction coefficient μ larger than a set value μs like a dry concrete road with a vehicle speed V being zero at time t1. In this stopped state, the steering wheel 2 is not steered, the steering wheel 2 is in the neutral position, and the steered motor 8a constituting the steered actuator 8 turns the steered wheels 17FR and 17FL into a straight traveling state. It is assumed that the rotation stops at the rotation angle δm at which the angle δr is “0”.

  When the vehicle 1 is stopped, the steering angle ratio characteristic control process shown in FIG. 9 is executed by the target turning angle calculation unit 51 in the turning control unit 50. In this steering angle ratio characteristic control process, first, the steering angle θs, the steering angle δr, the vehicle speed V, the steering torque Ts, and the steering torque Tr are read (step S51). Next, since the vehicle speed V is zero, the process proceeds from step S52 to step S57, and since the steering wheel 2 is in the neutral position and the turning angle δr has not changed, the process proceeds to step S60.

Therefore, the stop-time steering angle ratio characteristic control map shown in FIG. 6B is selected, and the target turning angle δ ^* is calculated with reference to the stop-time steering angle characteristic control map based on the steering angle θs. At this time, as shown in FIG. 6 (b), the steering angle ratio characteristic control map at the time of stopping is the steering angle ratio characteristic during traveling shown in FIG. 6 (a) until the steering angle θs reaches the threshold value θsth from zero. A characteristic line L21 having a steering angle ratio (= θs / δr) of “1” similar to the characteristic line L1 of the control map is set.

Therefore, the target turning angle δ ^* coincides with the steering angle θs, and δ ^* = 0. This target turning angle δ ^* is output to the actuator controller 52. In this actuator controller 52, the turning motor 8a constituting the turning actuator 8 is stopped when the rotation angle δm is “0”.
Therefore, the turning angle deviation Δδ output from the turning angle deviation calculating unit 61 is also “0”, and the motor current command value im ^* output from the turning motor control unit 62 is also “0”. At this time, since the steered motor 8a is stopped and the motor current detection value imr is also “0”, the current deviation Δi output from the current deviation calculating unit 63 is also “0”. As a result, the motor current im output from the motor current control unit 65 is also controlled to “0”, and the steered motor 8a continues to be stopped.

  In the non-steering state when the vehicle 1 is stopped, in the steering reaction force control process of FIG. 2 executed by the steering reaction force control unit 40, the steering angle θs is “0” in the steering reaction force torque calculation map shown in FIG. Therefore, the steering reaction torque TR is set to “0”. For this reason, the steering reaction force actuator 6 also maintains the stopped state, the steering reaction force applied to the steering wheel 2 becomes “0”, and the steering wheel 2 is not rotated by the steering reaction force torque.

From this state, when the steering wheel 2 is turned to the right, for example, at the time point t2, the steering angle θs increases in the positive direction from “0” at the neutral position as shown in FIG.
At this time, the target turning angle δ ^* calculated with reference to the stop-time steering angle ratio characteristic control map of FIG. 9 is also the same as the characteristic line L1 of the driving-time steering angle ratio characteristic control map. (= Θs / δr) is maintained at “1” and increases. For this reason, the steered wheels 17FR and 17FL are steered in a state where the steering angle θs of the steering wheel 2 and the steered angles δr of the steered wheels 17FR and 17FL coincide with each other, and the stationary operation is performed.

  At the same time, the steering reaction force control unit 40 calculates the steering reaction force torque TR required at the time of upsetting based on the steering torque Ts, the turning reaction force Fr, and the rotation angle δm of the turning actuator 8, and calculates the calculated steering reaction force. A steering reaction force actuator current ir corresponding to the force torque TR is calculated. This steering reaction force actuator current ir is supplied to the steering reaction force actuator 6, and the steering reaction force actuator 6 generates a steering reaction force torque for the steering wheel 2.

In this way, the steered wheels 17FR and 17FR are steered to change the steered angle δr, the process proceeds from step S17 to step S18 in the steered angle ratio characteristic control process, and the steered angle δr and the steered torque are changed. A road surface friction coefficient μ is calculated based on Tr. Here, since the vehicle is stopped on the high friction coefficient road, the steering torque Tr becomes a large value, so that the road surface friction coefficient μ becomes a value larger than the set value μs, and the process proceeds from step S19 to step S20. The calculation of the target turning angle δ ^* by the hour steering angle ratio characteristic control map is continued, and the stationary turning is continued.

  Thereafter, when the steering angle θs exceeds the threshold θsth at the time point t3, the steering angle ratio (= θs / δr) is changed to “0.0” by switching from the characteristic line L21 to the characteristic line L22 in the stationary steering angle ratio characteristic control map. It is suppressed to about 3 ″. For this reason, the increase amount of the turning angle δr becomes smaller than the increase amount of the steering angle θs, and the stationary operation is continued in a state where the turning torque generated by the turning motor 8a constituting the turning actuator 8 is suppressed. Is done.

Thereafter, if the steering of the steering wheel 2 is stopped before the steering angle θs reaches the full turning state, the increase in the turning angle δr of the steered wheels 17FR and 17FL is also stopped accordingly. Thereafter, when the vehicle 1 is moved forward or backward as shown in FIG. 11B at time t5, the absolute value | V | of the vehicle speed V increases from “0” accordingly.
Therefore, in the steering angle control process of FIG. 7 executed by the steering control unit 50, the process proceeds from step S12 to step S13, and the target steering angle ratio characteristic control map shown in FIG. The turning angle δ ^* (n) is calculated. For this reason, the target turning angle δ ^* (n) is the steering angle ratio (= θs / δr) with respect to the target turning angle δ ^* (n-1) calculated in the previous stop-time steering angle ratio characteristic control map. ) Increases rapidly.

However, since the actual turning angle δr is smaller than the calculated target turning angle δ ^* (n), it is determined in step S14 that δ ^* −δr> Δδs. The steering angle δ ^* is suppressed to a value obtained by adding the set value Δδs to the current turning angle δr, and the target turning angle δ ^* is output to the turning angle deviation calculating unit 61 of the actuator control unit 52.
For this reason, the turning angle δr gradually increases as the vehicle starts, as shown by the one-dot chain line in FIG. 11A, and the turning angle δr is calculated with the target steering angle ratio characteristic control map. When δ ^* −δr ≦ Δδs comes close to the turning angle δ ^* , the process proceeds directly from step S14 to step S16. Therefore, the target turning angle δ ^* calculated in the running-time steering angle ratio characteristic control map is directly used as the actuator. It is supplied to the turning angle deviation calculation unit 61 of the control unit 52.

Therefore, thereafter, the steered angle δr of the steered wheels 17FR and 17FL is controlled according to the target steered angle δ ^* calculated by the travel-time steered angle ratio characteristic control map. In the traveling state of the vehicle 1, the road surface reaction force is sufficiently smaller than that at the time of stationary, so that it is possible to generate the turning torque that reaches the full turning state by the turning motor 8 a that suppresses the turning torque. .
Thus, the target turning angle δ ^* calculated with reference to the stop-time steering angle ratio characteristic control map is in a steering state in which the steering angle ratio is suppressed with respect to the steering angle θs, and the vehicle 1 moves forward or backward. When the vehicle starts running, it can be switched to the target turning angle δ ^* calculated in the steering angle ratio characteristic map during a short period of time, so the driver can smoothly and normally do not sense that the turning radius is limited. The turning radius can be shifted to. For this reason, it is possible to perform the steering control without giving the driver a sense of incongruity at the time of starting, which requires steering to avoid obstacles in the traveling direction at the time of starting the garage, parallel parking, or starting at the time of starting from the stationary state.

Further, in a state where the steering angle θs of the steering wheel 2 at the time of stationary is equal to or less than the threshold value θsth, the characteristic line L21 of the stop-time steering angle ratio characteristic control map shown in FIG. 6B is the travel shown in FIG. It is set equal to the characteristic line L1 of the hour steering angle ratio characteristic control map. For this reason, when the vehicle 1 starts traveling forward or backward, the target turning angle δ ^* calculated by the stop-time steering angle ratio characteristic control map and the target turning angle calculated by the driving-time steering angle ratio characteristic control map are used. The steering angle δ ^* becomes equal. Therefore, even when the vehicle starts traveling in the stationary state, the steered control can be continued without a sudden change in the calculated target steered angle δ ^* .

In this state, by turning the vehicle 1 forward or backward, the steered wheels 17FR and 17FL are steered in a short time to the maximum steered angle δrmax as the road surface reaction force decreases due to traveling. For this reason, the turning radius of the vehicle 1 immediately shifts to the turning radius of the full steering intended by the driver, and the driver does not feel uncomfortable.
Further, when the vehicle 1 is stopped on a low friction counting road surface such as a frozen road, a snowy road, a rainy road, a gravel road, etc., the steering angle ratio of FIG. In the characteristic control process, the process proceeds from step S57 to step S56 directly through step S60.

However, when the turning angle δr of the steered wheels 17FR and 17FL increases by steering the steering wheel 2, the process proceeds from step S57 to step S58, and the road surface is based on the steered angle δr and the steered torque Tr. The friction coefficient μ is calculated. When the road surface friction coefficient μ calculated at this time becomes equal to or less than the set value μs, the process proceeds from step S59 to step S53, and the target turning is performed with reference to the steering angle ratio characteristic control map during travel shown in FIG. The angle δ ^* is calculated.

On this low friction coefficient road surface, since the road surface reaction force is small, even the steering motor 8a in which the turning torque is suppressed can be steered to the maximum turning angle δrmax at which full turning is possible.
When the vehicle 1 is moved forward or backward from the stopped state on the low friction coefficient road surface and the vehicle speed V becomes V> 0, the target turning angle δ ^* is calculated with reference to the same steering angle ratio characteristic control map during traveling. Since the difference between the turning angle δr and the target turning angle δ ^* is smaller than the set value Δδs, the target turning angle δ ^* is output as it is to the turning angle deviation calculating unit 61 of the actuator control unit 52 and turned. 17FR and 17FL are steered.

Therefore, it is possible to start at the turning angle intended by the driver without greatly changing the turning angle δr of the steered wheels 17FR and 17FL even in the full turning state.
Thereafter, when the ignition switch (not shown) is turned off after the vehicle 1 is stopped, the steering angle θs and the steering angle δr at the time when the ignition switch is turned off in the steering angle control process of FIG. Is stored in the steered state storage unit 51a as the steering angle θse and the steered angle δre at the end of control (step S13).

Next, the mechanical backup 27 is operated so as to mechanically lock the steering system mechanism between the steering wheel 2 and the steered wheels 17FR and 17FL (step S14), and then the system is stopped (step S15).
Here, in the present embodiment, the steering angle sensor 4 corresponds to the steering state detection unit, the wheel speed sensors 7FL to 7RR and the vehicle state parameter acquisition unit 21 correspond to the traveling state detection unit, and the process of step S18 in FIG. Corresponds to the road surface friction coefficient detection unit.

(Effect of 1st Embodiment)
(1) A steering angle ratio characteristic representing a relationship between a steering angle of a steering wheel and a turning angle of a steered wheel by a steering control unit according to a traveling state of whether the vehicle 1 is at a stop or traveling. Control at least one of the steering angle ratio characteristic at the time of stopping and the steering angle ratio characteristic at the time of driving to control the steering mechanism for turning the steered wheels, and the steering angle ratio characteristic at the time of stop is until the steering angle reaches a threshold value. Is set to a steering angle ratio characteristic that conforms to the steering angle ratio characteristic during traveling, and is set to a steering angle ratio characteristic that increases the steering angle ratio when the steering angle exceeds a threshold value.

  For this reason, it is not necessary to generate an excessive steering torque even at the time of stationary, and therefore the maximum torque required for the steered motor 8a can be small. Therefore, it is advantageous for reducing the size and weight of the steered motor 8a itself. Moreover, since the steering angle ratio characteristic at the time of stop is set to the steering angle ratio characteristic along the steering angle ratio characteristic at the time of traveling until the steering angle of the steering wheel reaches the threshold value, the steering angle until the steering angle reaches the threshold value. When the vehicle is started in this steering state, the steering angle ratio characteristic does not change, and the switching from the stationary steering angle ratio characteristic to the traveling steering angle ratio characteristic can be performed smoothly.

(2) When the steering wheel is steered when the power supply is stopped (ignition switch is turned off), and the turning state when the power supply is stopped differs from the starting steering state when the power supply is started. The return mode control unit includes a return mode control unit that performs a return mode process for maintaining the steering angle ratio in the start-time steering state and making the turning angle proportional to the steering angle. For this reason, even if the turning state is changing, the turning control intended by the driver can be started without giving the driver a sense of incongruity.

(3) A warning generation unit that generates a warning until the return mode control process is completed is provided. Therefore, it is possible to warn the driver that the return mode process is being executed, and it is possible to suppress the steering until the driver enters the full turning state.
(4) The warning generation unit performs warning display that is visible to the driver. For this reason, the driver can visually recognize that the return mode processing is being performed.

(5) The return mode control unit ends the return mode process when the turning angle reaches the maximum turning angle or when the steering angle reaches the neutral position. For this reason, it is possible to shift from the return mode process to the steering control process for controlling the steering mechanism based on the steering angle ratio characteristic selected by the normal steering angle ratio characteristic selection unit without giving the driver a sense of incongruity.
(6) When the steering angle ratio characteristic selection unit selects the steering angle ratio characteristic when the vehicle is stopped and the turning angle is in a reduced state, the steering reaction force generated with respect to the steering wheel is compared with the normal time. The steering reaction force control unit is set to a large value. According to this configuration, the driver can experience that the turning angle is maintained in a reduced state by the steering angle ratio characteristic when the vehicle is stopped.

(7) Each of the travel time steering angle ratio characteristic and the stop time steering angle ratio characteristic is set as a control map representing a relationship between the steering angle and the turning angle, and the steering angle ratio characteristic control unit is Based on the steering angle, the target turning angle is calculated with reference to the control map.
According to this configuration, the target turning angle according to the steering angle can be easily and quickly selected by selecting one of the traveling-time steering angle ratio characteristic control map and the traveling-time steering angle ratio characteristic control map according to the traveling state. Can be calculated.

(8) The steering mechanism has a configuration of a steer-by-wire system in which the steering wheel and the steered wheel are mechanically separated.
According to this configuration, the steering angle ratio characteristic can be easily adjusted without affecting the steering of the steering wheel.
(9) The steering mechanism includes an electric motor that generates a driving force for turning the steered wheel, and a driving force transmission unit that transmits the driving force generated by the electric motor to the steered wheel. Yes.
According to this configuration, the steering angle ratio can be easily adjusted by controlling the electric motor by the steering control unit.

(Modification 1)
In the said 1st Embodiment, although the steering angle ratio characteristic at the time of a stop demonstrated the case where it has the linear characteristic line L22 as shown in FIG. 7, it is not limited to this, FIG. As shown in FIG. 12, the change rate (dθs / dδr) of the steering angle ratio may be reduced as time passes so as to be a quadratic curve L24 that increases as time passes.

(effect)
Thus, by making the characteristic line L24 a quadratic curve, the change in the steering angle ratio at the switching point between the characteristic line L21 and the quadratic curve L24 can be smoothed, and the driver can detect the change in the steering angle ratio. Can be difficult.
(Modification 2)
In the first embodiment, the case where the present invention is applied to the vehicle 1 provided with the steer-by-wire type steering mechanism SM has been described. However, the present invention is not limited to this, and the steering wheel 2 and the front wheels 17FR and 17FL include An electric power steering apparatus that is mechanically connected and is configured to apply a steering torque generated by steering the steering wheel 2 to the front wheels 17FR and 17FL and a steering assist torque generated by a steering assist motor. The present invention can be applied even to an automobile provided. That is, a steering angle ratio variable mechanism that varies the steering angle ratio using a plurality of gears is provided, and the steering angle ratio variable mechanism is controlled by the steering control unit in the same manner as in the first embodiment, so that The steering torque generated at the time of turning can be reduced, which can contribute to the miniaturization of the steering assist motor.

(Modification 3)
In the first embodiment, the vehicle speed V is obtained based on the wheel speed detection signals supplied from the wheel speed sensors 24FL to 24RR. However, the present invention is not limited to this. It is also possible to detect the generated longitudinal acceleration and integrate the longitudinal acceleration to calculate the vehicle speed V. Moreover, you may make it judge the stop state and running state of the vehicle 1 based on the longitudinal acceleration.

(Modification 4)
Furthermore, in the first embodiment, the case where the tie rod axial force detected by the tie rod axial force sensor 16 is detected as the steering reaction force has been described. However, the present invention is not limited to this, and the front wheel 17FR is not limited thereto. Further, a hub lateral force sensor may be incorporated in 17FL and the turning reaction force Fr due to the lateral force acting in the direction of the rotation axis of the front wheels 17FR, 17FL may be detected.

  DESCRIPTION OF SYMBOLS 1 ... Vehicle, 1A ... Vehicle body, 2 ... Steering wheel, 3 ... Input side steering shaft, 4 ... Steering angle sensor, 5 ... Steering torque sensor, 6 ... Steering reaction force actuator, 7 ... Steering reaction force actuator rotation angle sensor, 8 DESCRIPTION OF SYMBOLS ... Steering actuator, 8a ... Steering motor, 9 ... Steering actuator rotation angle sensor, 10 ... Output side steering shaft, 11 ... Steering torque sensor, 12 ... Pinion gear, 13 ... Pinion angle sensor, 14 ... Rack shaft, 15 Tie rod, 16 tie rod axial force sensor, 17FR, 17FL, 17RR, 17RL ... wheel, 18 ... knuckle arm, 19 ... ball joint, 20 ... drive shaft, 21 ... vehicle state parameter acquisition unit, 24FR, 24FL, 24RR, 24RL ... wheel speed sensor, 26 ... drive circuit unit, 27 ... mechanical bag Up, SM ... steering mechanism, SBW ... steer-by-wire system, 40 ... steering reaction force control unit, 50 ... steering control unit, 51 ... target turning angle calculation unit, 51A ... steering angle ratio characteristic selection unit, 51B ... steer Angle ratio control unit, 51C ... return mode control unit, 51a ... steering state storage unit, 51b ... steering state warning light, 51c ... steering state warning unit, 52 ... actuator control unit, 61 ... steering angle deviation calculation unit , 62 ... Steering motor control unit, 63 ... Current deviation calculation unit, 64 ... Current sensor, 65 ... Motor current control unit

Claims (9)

A steering state detector for detecting the steering state of the steering wheel;
A running state detection unit for detecting the running state of the vehicle;
A steering mechanism for steering the steered wheels;
The steering angle ratio characteristic representing the relationship between the steering angle of the steering wheel and the turning angle of the steered wheel is divided into at least a steering angle ratio characteristic during traveling when the vehicle is traveling and a steering angle ratio characteristic when the vehicle is stationary. A steering angle ratio characteristic selecting unit that selects and selects either the traveling steering angle ratio characteristic or the stationary steering angle ratio characteristic based on the traveling state detected by the traveling state detection unit;
A steered state storage unit that stores the steered state when the power supply is stopped as the steered state when stopped
Rudder angle ratio control for controlling the steering mechanism based on the rudder angle ratio characteristic selected by the rudder angle ratio characteristic selector when the steered state at the start of power supply matches the steered state at the time of stop And
A return mode that maintains the steering angle ratio of the start-time steering state and makes the steering angle proportional to the steering angle when the start-time steering state at the start of power supply is different from the stop-time steering state A steering control apparatus comprising: a return mode control unit that performs processing.   The steering control device according to claim 1, wherein the return mode control unit includes a warning generation unit that issues a warning until the return mode process ends.   The steering control device according to claim 2, wherein the warning generation unit displays a warning that is visible to a driver.   The return mode control unit ends the return mode process when the turning angle reaches a maximum turning angle or when the steering angle reaches a neutral position. The steering control device according to any one of claims 1 to 3.   When the steering angle ratio characteristic is selected by the steering angle ratio characteristic selection unit and the turning angle is in a reduced state, the steering reaction force generated with respect to the steering wheel is increased compared to the normal time. The steering control device according to any one of claims 1 to 4, further comprising a steering reaction force control unit to be set.   Each of the traveling-time steering angle ratio characteristic and the stationary-time steering angle ratio characteristic is set as a control map representing a relationship between the steering angle and the turning angle, and the steering angle ratio characteristic control unit determines the steering angle. The steering control device according to any one of claims 1 to 5, wherein a target turning angle is calculated with reference to the control map.   The steering control according to any one of claims 1 to 6, wherein the steering mechanism has a configuration of a steer-by-wire system in which the steering wheel and the steered wheels are mechanically separated from each other. apparatus.   The steering mechanism includes an electric motor that generates a driving force for turning the steered wheel, and a driving force transmission unit that transmits the driving force generated by the electric motor to the steered wheel. The steering control device according to claim 7, wherein the steering control device is characterized in that:   The steering angle ratio characteristic when the vehicle is stopped is set to a quadratic curve that gradually increases the rate of change of the turning angle with respect to the steering angle when the steering angle exceeds the threshold value. The steering control device according to any one of 1 to 8.

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