JPH07291138A - Steering device for vehicle - Google Patents

Abstract

PURPOSE:To return wheels to steering neutral positions in a stop of a vehicle and to prevent a driver from suffering a feeling of physical disorder in restarting after the stop of the vehicle in an electric assist type steering device. CONSTITUTION:In a rear wheel steering device, in which a rear wheel steering mechanism 8 is driven by means of an electric motor 12, rear wheels 3, 4 are returned to steering neutral positions by means of a centering spring 13 when excitation to the motor 12 is stopped, and the rear wheel target steering angle is computed for controlling the rear wheel steering mechanism 8 so that it provides a target steering angle, the excitation to the electric motor 12 is stopped if a vehicle speed V is lowered to 0 (zero), and on the other hand, the excitation to the electric motor 12 is carried out when the vehicle is restarted so as to be started from a stopping condition, while the present steering angles of the rear wheels are set to the initial target steering angles.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a vehicle steering system, and more particularly to a so-called electric assist type steering system in which a wheel steering mechanism is driven by an electric drive means.

[0002]

2. Description of the Related Art Conventionally, as a steering device for a vehicle, a wheel steering mechanism for steering wheels has been electrically driven.
So-called electrically assisted steering devices are generally well known. Further, in this type of steering device, it is well known that the wheels are returned to the steering neutral position when the amount of electricity supplied to the electric drive means of the wheel steering mechanism is reduced to a predetermined value. . For example, not only the front wheels but also the rear wheels can be steered according to the steering wheel operation.
In a wheel steering vehicle (so-called 4WS vehicle), a rear wheel steering device that steers rear wheels is mounted in addition to the front wheel steering device used in a normal 2WS vehicle. When the steering mechanism for the rear wheels is driven by an electric drive unit such as an electric motor, and the amount of electricity supplied to the electric drive unit is reduced to a predetermined value, for example, when the vehicle is stopped.
(For example, when the energization amount is reduced to 0 (zero), that is, when the energization is cut off, etc.), the rear wheels are returned to the steering neutral position by the returning means using the biasing force of the spring or the like, and the vehicle is It is known to restore the normal 2WS state.

By adopting such a configuration, the amount of electricity supplied to the drive motor of the rear wheel steering mechanism is reduced (or the electricity supply is cut off) when the vehicle is not running or when it is not needed.
It is possible to suppress the electric power load on the battery, and particularly to prevent deterioration of the battery when the vehicle is left in a so-called stationary state when the vehicle is stopped. Further, by forcibly returning the rear wheels to the 2WS state at the time of stationary operation where the motor torque of the drive motor is originally maximized, it becomes unnecessary to control the drive motor, and therefore the motor can be downsized. This makes it possible to contribute to the cost reduction of the system.

For example, in Japanese Unexamined Patent Publication No. 1-285463, when the vehicle is in a stopped state and there is no change in the steering angle of the steering wheel, the amount of electricity supplied to the drive motor of the rear wheel steering mechanism is gradually reduced to a certain time. By shutting off the power supply with, the rear wheels are prevented from being continuously assisted even when the rear wheels are steered, parked and the engine is started, and therefore over-discharge of the battery can be prevented. It is disclosed. In addition, for example, actual Kaihei 4-595
In Japanese Patent Laid-Open No. 75-75, it is set such that the rear wheels are steered by the electric motor only when the vehicle speed is a certain value or less, and the steering angle sensor is operated while the vehicle speed (low speed) is the certain value or less. If sensors such as the vehicle speed sensor and the like detect an abnormality, the rear wheels are returned to the steering neutral position and the vehicle is operated normally.
It is disclosed that the safety is secured when an abnormality occurs by returning to the WS state.

In the electric assist type steering apparatus, when the wheel steering mechanism is driven to steer the wheels, the target steering angle value at the time of steering is calculated and obtained by this calculation. The wheel steering mechanism is controlled so that the target value is achieved. For example, in a 4WS vehicle, a method of controlling the steering angle of the rear wheels (that is, a method of controlling the steering ratio of the front and rear wheels) will be described.
(Steering angle sensitive type) or by associating with front wheel steering angle and vehicle speed
(Vehicle speed sensitive type), whose target value is set, has already been put to practical use.

Further, recently, in addition to the front wheel steering angle and the vehicle speed, the front wheel steering angular velocity and the yaw rate are detected, each of these parameters is applied to a predetermined map to obtain a signal operation value, and the signal operation value is calculated based on the operation value. A target yaw rate is set according to the vehicle's running conditions (steering wheel steering angle, vehicle speed, etc.) and road conditions, and the rear wheel steering angle is set to this yaw rate. Various types have been proposed, such as those to be controlled. Incidentally, for example, in Japanese Patent Laid-Open No. 4-135978,
In a vehicle stopped in a stationary state, when the engine is restarted, the target steering angle of the rear wheels is gradually increased,
It is disclosed that the vibration of the vehicle body is prevented from occurring due to the rear wheel steering.

[0007]

As described above, in the so-called electric assist type steering device, the target steering angle of the wheel at each time is set according to various conditions during traveling, but the vehicle is temporarily driven. When restarting after stopping, the target steering angle of the wheel is generally different when stopping and when starting to run again, and when the steering control when restarting and starting to stop There is a problem that the driver feels uncomfortable due to the influence of the target steering angle. That is, taking a case of a 4WS vehicle as an example, as shown in FIG. 11, for example, when the vehicle speed becomes 0 (zero) when the target value of the rear wheel steering angle θr is θo when the vehicle is stopped, If the wheel steering device is provided with a returning means for returning to the steering neutral position, the rear wheels are forcibly returned to the steering neutral position by the operation of the returning means. At this time, the rear wheels may not accurately return to the steering neutral position depending on the friction between the rear tires and the road surface.

Then, when the driver starts the vehicle again from this stopped state and turns the steering wheel so that the rear wheel steering angle θr takes a new target value θb in the opposite direction to the target value θo at the time of stop, The rear wheels will be steered toward the new target value θb after being steered by a slight amount in the direction of the previous target value θo (when stopped) (see K section in FIG. 11). . In FIG. 11, the white circle (○) indicates the target rear wheel steering angle θo when the vehicle is stopped, the black circle (●) indicates the actual rear wheel steering angle θa when the vehicle is stopped, and the × mark. Shows new target rear wheel steering angles θb when restarting and starting. In other words, for the driver, the rear wheels are once steered in the direction opposite to the direction in which the steering wheel was turned and steered.
There was a problem that I felt a sense of discomfort for a moment at the beginning of turning this handle. It should be noted that this problem can occur even if the rear wheels are accurately returned to the steering neutral position when the vehicle is stopped. When the vehicle is stopped in a so-called stationary state, the steering wheel is generally operated in the opposite direction when restarting and starting.

The present invention has been made in view of the above problems, and in a so-called electric assist type steering device,
An object of the present invention is to provide a steering device for a vehicle that can return the wheels to the steering neutral position when the vehicle is stopped and can prevent the driver from feeling uncomfortable when restarting after the vehicle is stopped.

[0010]

Therefore, the invention according to claim 1 of the present application (hereinafter referred to as the first invention) drives a wheel steering mechanism for steering the wheels and the wheel steering mechanism. Electric drive means, return means for returning the wheels to the steering neutral position when the amount of electricity supplied to the electric drive means is reduced to a predetermined value, and the target steering angle of the wheels is calculated to calculate the target steering angle. In a vehicle steering system including a control means for controlling the wheel steering mechanism so as to form an angle, the control means controls the electric drive means when the vehicle speed of the vehicle decreases to a preset predetermined vehicle speed. When the vehicle speed exceeds the predetermined vehicle speed from the predetermined vehicle speed or less while the current amount is reduced to the predetermined value, the electric drive amount to the electric drive means is increased and the wheel is driven. Current rudder angle of the first target In which it was to be set in the corner. In this specification, the term "reduce the energization amount" includes the case of reducing the energization amount to 0 (zero) (that is, the case of stopping the energization amount). The term "increase" also includes the case of increasing the energization amount from 0 (zero) to a certain energization amount (that is, changing the energization stop state to the energization ON state).

The invention according to claim 2 of the present application (hereinafter,
In the first invention, the control means includes a filter processing means for smoothing a target steering angle value, and the vehicle speed is the predetermined vehicle speed. Alternatively, the filter value of the filter processing means is set so that the target steering angle value can be made smoother when the vehicle speed exceeds the predetermined vehicle speed from a lower state.

[0012]

According to the first aspect of the present invention, since the control means is provided, when the vehicle speed of the vehicle drops to a predetermined vehicle speed set in advance, the amount of electricity supplied to the electric drive means is set to the predetermined value. When the vehicle speed exceeds the predetermined vehicle speed from the predetermined vehicle speed or below while decreasing
(That is, when the vehicle starts after restarting after stopping), increase the amount of electricity supplied to the electric drive means and set the current steering angle of the wheels to the first target steering angle. You can That is, after the restart, when the driver performs the steering wheel operation so that the wheel steering angle takes a new target value in the opposite direction to the target value at the time of stop, the wheel is from the current steering angle at the time of stop, The steering wheel is steered toward the new target steering angle value. Therefore, as in the past,
It is possible to prevent the driver from feeling uncomfortable at the beginning of turning the steering wheel, because the driver will not be slightly steered in the direction of the previous target value (when stopped). In this case, it is possible to reduce the amount of electricity supplied to the drive motor of the wheel steering mechanism (or cut off the electricity supply) when the vehicle is not running, such as when the vehicle is stopped, to reduce the power load on the battery, and in particular, It is possible to prevent the deterioration of the battery when the vehicle is left in a so-called stationary state when the vehicle is stopped. Furthermore, at the time of stationary steering when the motor torque of the drive motor is originally maximized, the wheels are returned to the steering neutral position. Since the drive motor does not need to be controlled, the motor can be downsized, and the system cost can be reduced.

Further, according to the second invention of the present application, basically, the same effect as that of the first invention can be obtained. Moreover, in addition, the control means includes a filter processing means for smoothing the target rudder angle value, and when the vehicle speed exceeds the predetermined vehicle speed from the predetermined vehicle speed or lower state (that is, When the vehicle restarts after the vehicle has stopped), the filter value of the filter processing means is set so that the target steering angle value is smoothed. It is possible to prevent the driver from feeling uncomfortable.

[0014]

Embodiments of the present invention will now be described in detail with reference to the accompanying drawings. FIG. 1 is an explanatory plan view showing an outline of a steering mechanism of an automobile according to this embodiment. This vehicle is, for example, a rear wheel drive type four wheel drive vehicle (4WS
Car). As shown in FIG. 1, the vehicle has, as its steering mechanism, a front wheel steering mechanism 6 that steers left and right front wheels 1 and 2, and a rear wheel steering mechanism 8 that steers left and right rear wheels 3 and 4. It has and. The front wheel steering mechanism 6 is the same as that well known in the related art, and is mechanically connected to the steering wheel 5 to steer the left and right front wheels 1 and 2 in accordance with the steering wheel operation by the driver.

Further, the rear wheel steering mechanism 8 is usually provided with rear left and right wheels so that a predetermined target rear wheel steering angle corresponding to a front wheel steering angle θf (hereinafter referred to as front wheel steering angle) is obtained, as described later. Steer wheels 3 and 4. The rear wheel steering mechanism 8 has a steering ratio θs expressed as a ratio of the rear wheel steering angle θr to the front wheel steering angle θf.
A turning ratio variable mechanism 9 for setting and changing
The turning ratio variable mechanism 9 is controlled by a 4WS control unit 10 mounted on the vehicle. Since the turning ratio varying mechanism 9 is the same as a well-known one, the detailed description and illustration of its internal structure will be omitted.

In the present embodiment, the rear wheel steering mechanism 8 is constructed as a so-called electric assist type that is driven electrically. That is, an electric motor 12 as an electric drive unit is arranged near the rear wheel steering rod 11, and a pinion 12p fixed to an output shaft 12s of the electric motor 12 is on the rear wheel steering rod 11. When the electric motor 12 is driven, the rear wheel steering rod 11 is driven in the vehicle width direction via the pinion 12p and the rack 11a, and the left and right rear wheels 3, 4 are engaged. Is being steered. Further, in this embodiment, a centering spring 13 is provided as a returning means for returning the left and right rear wheels 3 and 4 in the steered state to the steering neutral position in a predetermined case. The centering spring 13 is composed of, for example, a coil spring that surrounds a part of the rear wheel steering rod 11 coaxially, and when the rear wheel steering rod 11 moves from the steering neutral position to the left or right, A biasing force is applied to the rear wheel steering rod 11 in a direction to return it to the steering neutral position.

The 4WS control unit 10 is
Although not specifically shown, for example, a microcomputer is configured as a main part and is connected to various sensors so that signals can be exchanged. Then, the vehicle speed V from the vehicle speed sensor 15 and the yaw rate ψv from the yaw rate sensor 16 are
The steering ratio θs from the steering ratio sensor 17 corresponds to the front wheel steering angle sensor 1
8 to the front wheel steering angle θf, the rear wheel steering angle sensor 20 to the rear wheel steering angle θr, and the vertical acceleration sensor 19 to detect the vertical acceleration acting on the vehicle body. The longitudinal acceleration / deceleration sensor 21 for detecting the directional acceleration / deceleration inputs signals to the longitudinal acceleration / deceleration Gh. The control unit 1
0 is more preferably a control program for rear wheel steering control that determines the target steering ratio θstg based on the vehicle speed V, the yaw rate φv, and the front wheel steering angle θf and controls the steering ratio variable mechanism 9, and its control. The maps and the like required for are input and stored in advance.

Next, an outline of the rear wheel steering control will be described with reference to FIG.
~ It demonstrates, referring to the flowchart of FIG. This rear wheel steering control more preferably corrects the vehicle speed response term to the opposite phase side in order to improve the turning performance when driving on rough roads, and also controls the yaw rate correction term so as to ensure running stability when driving on rough roads. The gain of is greatly corrected. Also,
More preferably, the vehicle speed sensor 15 and the yaw rate sensor 1
When an abnormality occurs in either one of 9 and in both cases, a vehicle speed response term and a yaw rate correction term are provided so that turning traveling stability, straight traveling stability, etc. can be secured. Is to be corrected. This rear wheel steering control includes a subroutine for the sensor abnormality determination process shown in FIG. 2 and a subroutine for the rough road determination process shown in FIG.
The basic routine of the rear wheel steering control shown in FIG. 4 is included, and the sensor abnormality determination process and the rough road determination process are performed for a predetermined time.
The interrupt process is performed every (for example, 60 seconds). In the flow charts described above, reference symbol S
i (i = 1, 2, 3, ...) Indicates each step.

First, the subroutine of the sensor abnormality determination processing will be described with reference to FIG. This sensor abnormality determination processing is performed by the vehicle speed sensor 15 and the yaw rate sensor 1.
6 is a process of determining whether or not 6 is normal and setting the flag F. When this process is started while the vehicle is traveling, various signals (vehicle speed V from the vehicle speed sensor 15 and yaw rate ψv from the yaw rate sensor 16) necessary for this process are read for a predetermined time (for example, 1 second). The detection signals are stored in the memory (step S1), and then the read detection signals are analyzed to determine whether or not the sensors 15 and 16 are normal (step S2). In this analysis, for example, whether there is a detection signal, whether the detection signal is an abnormal value, whether the detection signal is constant despite the traveling state in which the detection signal should fluctuate, etc. By the analysis, it is determined whether the sensors 15 and 16 are normal or abnormal.

Next, using this analysis result, it is judged whether or not the yaw rate sensor 16 is normal (step S
3) If the determination result is Yes, then it is determined whether the vehicle speed sensor 15 is normal (step S4). If the vehicle speed sensor 15 is also normal, step S5 is performed.
At, the flag F is set to 1. When the vehicle speed sensor 15 is abnormal, the flag F is set to 2.
(Step S6). On the other hand, the determination result of step S3 is No.
If it is, it is determined in step S7 whether or not the vehicle speed sensor 15 is normal. If the vehicle speed sensor 15 is normal, the flag F is set to 3 in step S8. F
Is set to 4 (step S9). The data of the flag F is stored in the memory while being updated. Step S above
After S5, S6, S8, and S9, this process ends, and when the timing of each interrupt process from the next time is reached, the same process is performed.
(Subroutine in FIG. 2) is executed.

Next, the rough road discrimination processing subroutine will be described with reference to FIG. In this rough road determination process, the number of times the vertical acceleration Gv becomes abnormally high during the predetermined time T0 is counted, and the count value I is the threshold value I0.
Depending on whether or not the above is the case, it is a process of determining whether or not the road on which the vehicle is traveling is a bad road and setting the bad road flag Fak. When this process is started, a flag Ft for identifying the operating state of the timer T and a counter I (whose count value is I) are reset to 0 (step S20), and then the vertical acceleration sensor 19 The vertical acceleration Gv is read (step S21). Next, it is determined whether the flag Ft is 1 (step S22), and the flag Ft = 0 is initially set.
Therefore, the process proceeds to step S23, the timer T (whose time is T) is reset and then started, and the flag Ft is set to 1 (S23). However, since the flag Ft = 1 after the next time, the process proceeds from step S22 to step S24.

In step S24, the vertical acceleration G
It is determined whether or not the absolute value of v is equal to or greater than a predetermined value Gv0 that rarely occurs when the vehicle travels on a normal road. If the determination result is Yes, the counter I is incremented by 1 (step S25). ), And then the process proceeds to step S26. When the determination result of step S24 is No, step S25 is skipped and the process proceeds to step S26. Next, in step S26,
The time T measured by the timer T is a predetermined time T0 (for example, 10
(Seconds) or more is determined. If the time measured by the timer T does not reach the predetermined time T0, step S26
Then, the process returns to step S21, and steps S21 to S26 are repeatedly executed. Then, when the measured time T becomes the predetermined time T0 or more, the process proceeds to step S27, it is determined whether or not the count value I of the counter I is a predetermined threshold value I0 or more, and if the count value I ≧ I0 Is
The rough road flag Fak is set to 1 as a rough road
(Step S28) On the other hand, when the count value I <I0, it is determined that the road is not a bad road and the bad road flag Fak is reset to 0 (step S29).

Next, the basic routine of the rear wheel steering control will be described with reference to FIG. This basic routine is a routine that is repeatedly executed every minute time while the automobile is running. In order to facilitate understanding of the explanation of the basic routine of the rear wheel steering control, first, the target steering ratio θstg and the correction are based on the detected values of the vehicle speed V, the yaw rate ψv and the front wheel steering angle θf. Target turning ratio θs
A calculation process for calculating tg1 (process of step S54 described later) will be described with reference to FIG.

The target turning ratio θstg is calculated by the following equation. θstg = -G1 ・ f1 (V) ・ θsh + G2 ・ K2 (θ2) ・ J2 (│θd2│) ・ f2 (V) ・ θs
ψ-G3 ・ K3 (θ2) ・ f3 (V) ・ θsd + G4 ・ f4 (V)

In the above equation, the first term on the right side is the steering angle correction term,
The second term is a yaw rate feedback term, the third term is a steering angle change correction term, and the fourth term is a vehicle speed response term which is a base when performing rear wheel steering control according to the vehicle speed V. By setting the target steering ratio θstg as in the above formula, when the front wheels are steered from the straight running state based on the vehicle speed-sensitive rear wheel steering control, the rear wheels and the front wheels are initially in the steering state. This is a phase in which the steering direction is opposite to that of and to improve the turning performance, and then the yaw rate is generated and the rear wheels are steered to the same phase side where the front wheels are in the same direction and the direction stability is improved. Inversion control can be performed.

In the above equation, G1, G2, G3, and G4 are variable gain constants, and other variables are based on the vehicle speed V, the yaw rate ψv, and the front wheel steering angle θf, as shown in FIG. It is calculated as described below. Variables f1 (V), f2 (V), f3 (V), and f4 (V) shown in the respective terms on the right side are vehicle speed sensitive gains, and from the vehicle speed V, maps M10, M5, M
13 and M1, respectively. Map above M1
0 and M13 are characteristics in which the variables f1 (V) and f3 (V) are 0 in the low vehicle speed region and the high vehicle speed region, respectively, and have positive constant values in the medium vehicle speed region. Also, the map M5 has a variable f2
The characteristic is that (V) is 0 in the low vehicle speed region and is a positive constant value in the medium and high vehicle speed regions. Furthermore, the map M1
Is a characteristic in which the variable f4 (V) is changed to a large negative value in the low vehicle speed region, from the negative value to a positive value in the medium vehicle speed region according to the increase of the vehicle speed, and is set to a large positive value in the high vehicle speed region. .

The variable θsh of the first term on the right side is a steering angle correction value, and after offsetting the front wheel steering angle θf by the map M8 to θ1, a hysteresis is added to this θ1 by the map M11 and θ2. And the absolute value | θ2 | is calculated by the map M9. The offset of the map M8 is for the dead zone, and
The hysteresis of 11 is for preventing hunting. In the map M9, the variable θsh is 0 in the small steering angle region, a value proportional to the steering angle in the medium steering angle region, a positive constant value in the large steering angle region, and an abnormality occurs in the larger steering angle region. Is 0.

Next, the variable θsψ of the second term on the right-hand side is a yaw rate correction value, and after the yaw rate ψv is offset by the map M2 to be ψ1, the ψ2 obtained by adding hysteresis to this ψ1 by the map M3. , Map M4. This map M4 has a variable θsψ
Is a value proportional to ψ2 in the small yaw rate region, a positive constant value in the medium yaw rate region, and 0 in the large yaw rate region when an abnormality has occurred.

The variable K2 (θ2) of the second term on the right side is a steering angle sensitive gain, which is calculated from θ2 obtained in the map M11 by the map M6. This map M6 is the variable K2
(θ2) is a value that is substantially proportional to θ2 in the small front wheel steering angle region, and has a characteristic that the increase rate decreases as the front wheel steering angle increases. The variable J2 (| θd2 |) of the second term on the right side is the steering angle change rate sensitive gain, and is calculated by the map M7 from the absolute value | θd2 | of the differential value of θ2 obtained in the map M11.
In this map M7, the variable J2 (| θd2 |) is changed to | θd2 |
Is a relatively small value in the small front wheel steering angle change rate area, a relatively large value in the middle front wheel steering angle change rate area, and a smaller value in the large front wheel steering angle change rate area than the small front wheel steering angle change rate area. It is a characteristic.

The variable θsd of the third term on the right side is the steering angle change rate correction value and is the differential value θd of θ2 obtained in the map M11.
2 is calculated by the map M12. This map M1
2 is a characteristic in which the variable θsd is a value proportional to θd2 in the small front wheel steering angle change rate region, a positive constant value in the middle front wheel steering angle change rate region, and 0 as abnormal in the large front wheel steering angle change rate region. Is. The variable K3 (θ2) of the third term on the right side is the steering angle response gain, and is calculated from θ2 obtained in the map M11 to the map M.
Calculated by 14. This map M14 has a variable K3
(θ2) is a value that is substantially proportional to θ2 in the small front wheel steering angle region, and has a characteristic that the increase rate decreases as the front wheel steering angle increases.

The target turning ratio θstg is determined by adding / subtracting a signal operation value obtained by multiplying the constant by a variable for each term on the right side of the above equation. The addition / subtraction value is an abnormal value. If so, the target turning ratio θstg also becomes an abnormal value, so the target turning ratio θstg becomes a value within the basic permissible range (hatched area of the map M15) set according to the vehicle speed V by the map M15. The target turning ratio θstg is set to the corrected target turning ratio θstg1. still,
In this modification, when the target turning ratio θstg exceeds the upper limit value of the basic allowable range, it is corrected to the upper limit value at the vehicle speed V, and when it is less than the lower limit value of the basic allowable range, at the vehicle speed V. Is corrected to the lower limit of.

Next, the basic routine of the rear wheel steering control will be described with reference to the flowchart of FIG. When the system starts, first, various signals and data necessary for each processing in this basic routine (vehicle speed V, yaw rate ψv, front wheel steering angle θf, steering ratio θs, flags F, Fak, etc.)
Is read (step S40), then flag F = 1,
When both the vehicle speed sensor 15 and the yaw rate sensor 16 are normal (step S41: Yes), it is determined whether the rough road flag Fak = 1 (step S42), and the rough road flag Fak is determined.
If = 0 and the road is not a bad road, the process proceeds to step S43. If the bad road flag Fak = 1 and the road is a bad road, the process proceeds to step S44.

In step S43, line a of map M1 in FIG. 5 (this line a is adopted in normal control).
Is selected, and then the process proceeds to step S54. Step S44 is a case where the wheel speed sensor and the vehicle speed sensor 15 are normal and the vehicle is traveling on a rough road. In this step S44, in order to improve the turning ability, the line c of the map M1 of FIG. 5 (this line c is (A line in which the gain of the vehicle speed response term is increased in the opposite phase direction) is selected, and the gain coefficient G2 of the yaw rate correction term is set to 1.
Predetermined value α greater than 0 (for example, α = 1.1 to 1.5)
And G2, which is the default value, are set to α × G2, and then the process proceeds to step S54.

When the vehicle speed sensor 15 is abnormal and the yaw rate sensor 19 is normal, that is, when the flag F = 2,
Basically, the vehicle speed response term cannot be applied, but the yaw rate feedback term can be applied to ensure running stability when driving straight ahead. That is, in step S46, it is determined whether or not the vehicle is traveling straight ahead based on the front wheel steering angle θf. When traveling straight, the gain coefficient G4 of the vehicle speed response term is set to 0 in step S47, and the vehicle speed sensor 15 Since the detected value of the vehicle speed V cannot be applied due to the abnormality of, the vehicle speed V is set to the predetermined vehicle speed V0 in the medium speed range, and then the process proceeds to step S54.

When it is determined that the vehicle is not traveling straight as a result of the determination in step S46, the gain coefficient G4 = 0 and the gain coefficient G2 are set in step S48 so that the vehicle speed response term and the yaw rate feedback term are not applied. = 0 and the detected value of the vehicle speed V cannot be applied due to the abnormality of the vehicle speed sensor 15, the vehicle speed V is set to a predetermined vehicle speed V0 in the medium speed range, and then the process proceeds to step S54.

When the vehicle speed sensor 15 is normal and the yaw rate sensor 19 is abnormal, that is, when the flag F = 3,
The process proceeds from step S49 to step S50, and in S50, it is determined whether the bad road flag Fak = 1, that is, whether the road on which the vehicle is running is a bad road. If the road is a bad road, the process proceeds to step S52. If it is not a rough road, the process proceeds to step S51. When the vehicle is on a rough road, in S52, in the case of an FR vehicle such as the vehicle of the present embodiment, in order to improve running stability, line b of the map M1 in FIG. 5 is used.
(This is a line in which the gain in the in-phase direction is increased) is selected, and the gain coefficient G2 is set to G2 = 0 to prohibit the application of the yaw rate feedback term, and then the process proceeds to step S54. .

That is, when traveling on a rough road, in the case of an FR vehicle, oversteering tends to occur and traveling stability is reduced, so line b of the map M1 is selected. When driving on a rough road, in the case of an FF vehicle, the understeer tendency tends to occur, and the running stability decreases, so line c of the map M1 is selected in step S52. If the result of determination in step S50 is that the vehicle is not traveling on a rough road, line a of the map M1 is selected, the gain coefficient G2 of the yaw rate feedback term is set to G2 = 0, and then the routine proceeds to step S54. If both the vehicle speed sensor 15 and the yaw rate sensor 19 are abnormal and the flag F = 4, the gain coefficients G1, G2, G3, G4 are all set to 0 in step S53, and the target rear wheel steering ratio is set as system down. By holding θstg at 0, the rear wheel steering control is substantially stopped.

Next, as described above, step S5
4, the vehicle speed V, the yaw rate ψv, and the front wheel steering angle θf are applied to the processing of FIG. 5 to calculate the target turning ratio θstg and the corrected target turning ratio θstg1. Further, in step S55, the detected turning ratio is detected. A control signal for controlling θs to be the corrected target turning ratio θstg1 is output to the turning ratio variable mechanism 9. Then, after that, the process returns to step S40,
The rear wheel steering control shown in the flowchart of FIG. 4 is repeatedly executed every minute time.

Next, the operation of the rear wheel steering control described above will be described. When the vehicle speed sensor 15 and the yaw rate sensor 19 are normal and the vehicle is traveling on a rough road, the line c of the map M1 is selected and the gain coefficient G2 of the yaw rate feedback term is largely changed as shown in step S44. In addition to improving the turning ability in
Driving stability can be secured. When the vehicle speed sensor 15 is abnormal and the yaw rate sensor 19 is normal, the vehicle speed V is given a predetermined value V0 and the yaw rate feedback term can be applied when the vehicle travels straight ahead. It is possible to secure running stability at the time.

Further, when the vehicle speed sensor 15 is normal and the yaw rate sensor 19 is abnormal, or when the vehicle is traveling on a rough road, as shown in step S52, the FR vehicle has line b of the map M1.
And the line c of the map M1 for the FF vehicle, it is possible to ensure the traveling stability during traveling on a rough road, particularly the traveling stability during turning traveling.
Then, when the vehicle is traveling on this rough road, the gain coefficient G2 of the yaw rate feedback term is set to 0, so that the abnormal yaw rate ψv detected by the abnormal yaw rate sensor 19 is prevented from adding an abnormal value of the yaw rate feedback term. can do.

When the vehicle speed sensor 15 is normal and the yaw rate sensor 19 is abnormal, when the vehicle is not traveling on a bad road,
As shown in step S51, the line a of the map M1 is selected and the gain coefficient G2 of the yaw rate correction term is selected.
Is set to 0, the vehicle speed response term can be set to an appropriate value, and it is possible to prevent the abnormal yaw rate ψv from being added to the abnormal yaw rate feedback term.

The following modified examples, in which a part of the above-mentioned embodiment is modified, can be considered. 1) Instead of the rough road discrimination processing described above, a rough road can be discriminated from the change state of the left and right driven wheel speeds detected by the wheel speed sensors of the driven wheels. 2) Instead of the vehicle speed sensor 15, a wheel speed sensor that detects the wheel speed of the left and right driven wheels may be provided, and the vehicle speed may be detected from the average value of the left and right driven wheel speeds. 3) Instead of the yaw rate sensor 19, a wheel speed sensor that detects the wheel speed of the left and right driven wheels is provided, and the yaw rate is detected using the absolute value of the difference between the left and right driven wheel speeds and the tread of the vehicle. It can also be configured to. 4) The target rear wheel turning angle θr is calculated by an arithmetic expression of θr = KG1 (V) × θf + KG2 (V) × ψv instead of the arithmetic expression for calculating the rear wheel turning ratio in the above embodiment. Good. Note that KG1 (V) corresponds to the vehicle speed sensitive gain f (V) in the vehicle speed sensitive term of the map M1, and K
G2 (V) is a vehicle speed response gain having a predetermined characteristic in the yaw rate feedback term. 5) The above-mentioned embodiment was applied to the rear-wheel drive type automobile, but it can be applied to the front-wheel drive type automobile as well.

By the way, in the vehicle according to this embodiment, as described above, the steering mechanism 8 for the rear wheels 3 and 4 is electrically driven.
When it is driven by the (electric motor 12) and the amount of electricity to the electric motor 12 is reduced to a predetermined value, for example, when the vehicle is stopped (for example, when the amount of electricity is reduced to 0 (zero), that is, When the power is cut off, the rear wheels 3 and 4 are forcibly returned to the steering neutral position by the returning means (the biasing force of the centering spring 13) to return the vehicle to the normal 2WS state. By adopting such a configuration, the amount of electricity supplied to the electric motor 12 of the rear wheel steering mechanism 8 is reduced (or the electricity supply is cut off) when the vehicle is not running or when it is unnecessary, and the power load on the battery is suppressed. In addition, it is possible to prevent deterioration of the battery particularly when the vehicle is left in a so-called stationary state when the vehicle is stopped. Furthermore, by forcibly returning the rear wheels 3 and 4 to the 2WS state at the time of stationary operation in which the motor torque of the electric motor 12 is originally maximized, it becomes unnecessary to control the electric motor 12. Motor 12
It is possible to reduce the size of the device, and it is possible to contribute to the cost reduction of the system.

In this embodiment, in such a so-called electric rear wheel steering system, the rear wheels 3 and 4 are returned to the 2WS state when the vehicle is stopped, and the vehicle is restarted after the vehicle is stopped. It is prevented that the driver feels uncomfortable under the influence of the rear wheel target steering angle when the rear wheel control is stopped, or more preferably, the rear wheels 3 and 4 are forced to be forced when the vehicle is stopped. In order to prevent the driver from feeling uncomfortable due to vibration of the vehicle body that should have been stationary when the vehicle was returned to the steering neutral position,
Steering control of the rear wheels 3 and 4 is performed.

The rear wheel control when the vehicle according to the present embodiment is stopped and when the vehicle is restarted and started after the stop will be described with reference to the flowcharts of FIGS. 6 and 7. It should be noted that this control is executed, for example, by interrupt processing at predetermined time intervals during the above-mentioned normal rear wheel steering control. Alternatively, it may be executed when deceleration above a certain level occurs or when the vehicle speed is below a certain level. When the vehicle starts running and the system starts, the target rear-wheel steering angle (that is, the target steering ratio θstg, and finally the corrected target steering ratio θstg1 according to the above-mentioned rear-wheel steering control program (see FIGS. 2 to 5). ) Is performed (step S71), and the detected turning ratio θs detected by the turning ratio sensor 17 is calculated.
The rear wheel steering angle is controlled so that the corrected target turning ratio θstg1 becomes.

Then, in step S72, it is determined whether or not the vehicle speed V is less than or equal to a preset first predetermined vehicle speed,
If this is YES, the power supply to the electric motor 12 is stopped (step S78). In this embodiment, the first predetermined vehicle speed is set to 0 (zero) km / hr, for example. However, the rotation of a gear-shaped (serrated) rotation detection plate (tooth-shaped rotor) that rotates integrally with the wheel is detected by an electromagnetic pickup arranged near the outer peripheral portion of the tooth-shaped rotor, a so-called electromagnetic pickup type. With the wheel speed sensor of, the complete speed is 0 (zero) km.
/ Hr is difficult to detect accurately, generally 2 to 2.
The detection limit is up to about 5 km / hr. Therefore, in this case, the vehicle speed 0 (zero) km / hr is determined by the estimation based on the calculation process of the detection data of the wheel speed sensor. On the other hand, if the decision result in the step S72 is NO, a step S73 decides whether or not the vehicle deceleration is equal to or more than a predetermined value (that is, the degree of deceleration of the vehicle is larger than the predetermined value). If YES, then in step S74, it is determined whether or not the current rear wheel steering angle θr is equal to or greater than a predetermined value.

If the decision result in the step S74 is NO, that is, if the current rear wheel steering angle is not so large, then in a step S75, the vehicle speed V is larger than the first predetermined vehicle speed by the second predetermined value. It is determined whether the vehicle speed is equal to or lower than the vehicle speed. In this embodiment, the second predetermined vehicle speed is set to, for example, 2 km / hr, which is almost the detection limit of the wheel speed sensor. If the determination result is YES (that is, the vehicle speed V is low and the vehicle is decelerating to some extent), more preferably, the target rear wheel steering angle is set to 0 (zero) in step S77. It has become so.

As a result, when the vehicle is stopped, the rear wheels 3, 4
Is returned to the steering neutral position while being steered according to the target steering angle before the electric motor 12 is de-energized and forcibly returned to the steering neutral position by the centering spring 13. Vibration will no longer occur in the vehicle body that should have been stopped and stopped,
It is possible to reliably prevent the occupant from feeling uncomfortable. In this case, it is possible to reduce the amount of electricity supplied to the drive motor of the rear wheel steering mechanism (or to cut off the electricity supply) when the vehicle is not running, for example, when the vehicle is not running, and to suppress the power load on the battery. It is possible to prevent the deterioration of the battery when the vehicle is left in a so-called stationary state when the vehicle is stopped, and further, in the stationary state where the motor torque of the drive motor is originally maximized, the rear wheel is driven by 2WS.
By returning to the state and eliminating the need for controlling the drive motor, the size of the motor can be reduced and the cost of the system can be reduced.

On the other hand, if the decision result in the step S73 or the step S75 is NO, a step S79 is carried out.
Then, it is determined whether or not the power supply to the electric motor 12 is stopped. When the determination result is YES, when the vehicle is restarted and starts (specifically, for example, the vehicle speed is detected. For example, in step S80, the current steering angle θr of the rear wheels 3 and 4 is set to the first target steering angle. That is, for example, as shown in FIG. 9, when the vehicle speed becomes 0 (zero) while the target value of the rear wheel steering angle θr is 0 (zero) when the vehicle is stopped, the rear wheels 3 and 4 are The steering neutral position is returned to the steering neutral position by the steering control according to the target steering angle, or by the biasing force of the centering spring 13 when this control is not in time, but the frictional state between the rear wheel tires 3 and 4 and the road surface, etc. Depending on the case, it may not return to the steering neutral position accurately.
(Actual steering angle value: θb). When the driver starts the vehicle again from this stopped state and turns the steering wheel so that the rear wheel steering angle θr takes a new target value θa different from the target value 0 (zero) at the time of stop, If there is, the rear wheels 3 and 4 once turn to a new target value θa after being slightly steered in the direction of the previous target value 0 (zero) (at the time of stop) (see J section in FIG. 9). It will be steered toward. In other words, for the driver, the rear wheels are once steered in the direction opposite to the direction in which the steering wheel was turned and the steering wheel was turned, so there was a problem that the driver felt a slight discomfort at the beginning of turning the steering wheel.

On the other hand, in this embodiment, as described above, the current actual steering angle θb of the rear wheels 3 and 4 is set to the first target steering angle in step S80. When the driver operates the steering wheel so that the rear wheel steering angle θr takes a new target value θa in the opposite direction to the target value 0 (zero) at the time of stop, for example, as shown in FIG. No. 4 is steered from the current steering angle θb at the time of stop toward the new steering angle target value θa. Therefore, unlike the conventional case, the steering wheel is not once steered a little in the direction of the previous target value (at the time of stopping), and it is possible to reliably prevent the driver from feeling uncomfortable when turning the steering wheel. Of.

In this embodiment, the target value of the rear wheel steering angle θr is set to 0 (zero) in advance when the vehicle is stopped, and the rear wheels 3 and 4 are returned to the steering neutral position by the steering control according to the target value. After stopping, the vehicle is stopped and the electric power to the electric motor 12 is cut off.
Even if it is not set to (zero), as described above, by setting the current steering angle θb at the time of stop to the first target steering angle at the time of restart, as shown in FIG. The steering angle is steered from the current steering angle θb to the new steering angle target value θa. Therefore, even in this case, as in the conventional case (see FIG. 11), once the previous (at the time of stop)
The steering wheel will not be slightly steered in the direction of the target value, that is, the rear wheel target rudder angle will not be affected when the rear wheel control is stopped when the vehicle restarts and starts running. It is possible to reliably prevent a feeling of strangeness at the beginning of cutting. When the vehicle is stopped in a so-called stationary state, the steering wheel is generally operated in the opposite direction when restarting and starting. In the graphs of FIGS. 8 to 11 above, white circles (○)
Is the target rear wheel steering angle when the vehicle is stopped, the black circle (●) is the actual rear wheel steering angle θa when the vehicle is stopped, and the X mark is the new target rear wheel when restarting and starting. The steering angles are shown respectively.

If the determination result in step S74 is YES (that is, if the current rear wheel steering angle is relatively large and is equal to or greater than the predetermined value), step S76
Then, it is determined whether or not the vehicle speed V is equal to or lower than a third predetermined vehicle speed (for example, 4 km / hr) which is higher than the second predetermined vehicle speed (2 km / hr), and if NO, skip to step S79. . On the other hand, the determination result in step S76 is YE.
In the case of S, more preferably, the target rear wheel steering angle is set to 0 (zero) in step S77.

In other words, when the current steering angles of the rear wheels 3 and 4 are large, the predetermined vehicle speed serving as a threshold value when setting the target rear wheel steering angle to 0 (zero) is high (from 2 km / hr). (4 km / hr) is set, and the time until the vehicle speed decelerates from this predetermined vehicle speed to the first predetermined vehicle speed (0 km / hr) when the vehicle decelerates.
(That is, the time from setting the target steering angles of the rear wheels 3 and 4 to zero until the centering spring 13 acts) can be lengthened accordingly. As a result, even if the current steering angle of the rear wheels 3 and 4 is large, the target steering angle of the rear wheels 3 and 4 must be reliably ensured before the centering spring 13 returns the steering wheels to the neutral position. It is possible to return to the steering neutral position while the steering control is performed according to.

Alternatively, or in addition to this, when the current rear wheel steering angle is relatively large and is equal to or larger than a predetermined value, it is more preferable that the driving speed of the electric motor 12 be high. You can Also in this case, similarly to the above, even when the current steering angles of the rear wheels 3 and 4 are large, the rear wheels 3 and 4 can be reliably returned to the steering neutral position by the centering spring 13. It becomes possible to return to the steering neutral position while being steered according to the target steering angle.

After the processing of step S77 is completed, or after the processing of step S80 is completed, or when the determination result in step S79 is NO, then
In step S81, filter processing for smoothing the target rudder angle value is performed. In this filtering process, for example, when calculating the target rudder angle value, the previous value and the current value are weighted respectively to obtain the target rudder angle value, and the filter value ( That is, the target rudder angle value can be changed). That is, the target rudder angle value can be made smoother by setting the weighting coefficient of the previous value larger (that is, setting the weighting coefficient of the current value smaller).
That is, for example, if the previous value of the target steering angle is θr (k−1), the current value is θr (k), and the weighting coefficients for the previous value and the current value are set to A and B (A + B = 1), respectively. , ΘrK can be represented by the following equation. θrK = A · θr (k−1) + B · θr (k) In this formula, by adjusting A and B, the filter value can be changed to change the degree to which the target steering angle value is blunted. By setting the weighting coefficient A of the previous value θr (k-1) to be larger (that is, the weighting coefficient B of the current value θr (k) to be smaller), the corrected target steering angle value θrK can be made smoother. You can

In this embodiment, when the vehicle speed V restarts after the vehicle stops and starts (when the vehicle speed V exceeds the first predetermined vehicle speed from the above-mentioned first predetermined vehicle speed or less), the rear wheels 3 , 4 are set so that the target rudder angle values of 4 are smoothed. By setting in this way, the rear wheel steering angle can be changed as gently as possible at the time of restart, and it is possible to prevent the driver from feeling uncomfortable.

When the processing in step S81 is completed, it is determined in step S82 whether or not the power supply to the electric motor 12 is stopped. If the result is YES, the power is supplied to the electric motor 12 in step S83. Done. Subsequently, in step S84, after the deceleration and vehicle speed conditions are satisfied, that is, the deceleration is equal to or more than a predetermined value (step S7).
(4: YES) and the vehicle speed becomes equal to or lower than the second predetermined vehicle speed (step S75: YES), the rear wheels 3, 4 are actually
It is determined whether or not the predetermined time required to return the steering angle of 0 to 0 (zero) has elapsed. If this is YES, the process returns to the first step S71 to estimate the vehicle speed as 0 (zero), After that, the same steps are repeated. Incidentally, the above step S
The same applies when the determination result in 82 is NO. If the decision result in the step S84 is NO, the process returns to the step S73, and thereafter, the same steps are repeatedly executed.

In the above embodiment, the vehicle speed is the first predetermined vehicle speed.
When the electric power is reduced to (0 (zero) km / hr), the electric power to the electric motor 12 is stopped. However, instead of completely reducing the amount of electric power to 0 (zero) in this way, a preset value is set. You may make it reduce to the predetermined value. Further, although the above-described embodiment is related to the so-called vehicle speed sensitive / yaw rate feedback type rear wheel steering control, the present invention is not limited to the above case, and various other types of rear wheel steering control are performed. It is also effectively applied to rudder control, for example, so-called complete yaw rate feedback type rear wheel steering control, in which the target yaw rate is calculated from the front wheel steering angle and the vehicle speed, and the rear wheel steering angle is controlled to achieve this target yaw rate. Is something that can be done. Further, although the above-mentioned embodiment is related to the rear wheel steering system for a 4WS vehicle, the present invention is
The present invention is not limited to such a case, and a so-called electric assist type can be effectively applied to a front wheel steering device of a vehicle.

[Brief description of drawings]

FIG. 1 is an explanatory plan view showing an outline of a steering mechanism for an automobile according to an embodiment of the present invention.

FIG. 2 is a flowchart showing a subroutine of a sensor abnormality determination process in the rear wheel steering control of the vehicle.

FIG. 3 is a flowchart showing a subroutine of rough road discrimination processing in the rear wheel steering control.

FIG. 4 is a flowchart showing a basic routine of the rear wheel steering control.

5 is a control block diagram showing a calculation process of a target turning ratio and a corrected target turning ratio in the flowchart of FIG.

FIG. 6 is a diagram showing a part of a flowchart for explaining rear wheel steering control when the vehicle is stopped and when the vehicle is restarted.

FIG. 7 is a diagram showing a part of a flowchart for explaining rear wheel steering control when the vehicle is stopped and restarted.

FIG. 8 is a diagram for explaining a rear wheel steering characteristic when the rear wheel steering mechanism according to the above-described embodiment is started and restarted.

FIG. 9 is a diagram for explaining a rear wheel steering characteristic when the rear wheel steering mechanism according to the conventional example starts and restarts.

FIG. 10 is a diagram for explaining a rear wheel steering characteristic when the rear wheel steering mechanism according to the modified example of the above-described embodiment is started and restarted.

FIG. 11 is a diagram for explaining a rear wheel steering characteristic when the rear wheel steering mechanism according to the conventional example starts and restarts.

[Explanation of symbols]

 3, 4 ... Rear wheel 8 ... Rear wheel steering mechanism 10 ... Control unit 12 ... Electric motor 13 ... Centering spring 15 ... Vehicle speed sensor 17 ... Turning ratio sensor

Claims (2)

[Claims] 1. A wheel turning mechanism for turning a wheel, an electric drive means for driving the wheel turning mechanism, and the wheel when the amount of electricity supplied to the electric drive means is reduced to a predetermined value. In the steering apparatus for a vehicle, there is provided a returning means for returning the steering wheel to a steering neutral position, and a control means for calculating a target steering angle of the wheel to control the wheel steering mechanism so that the target steering angle becomes the target steering angle. When the vehicle speed of the vehicle is reduced to a predetermined vehicle speed set in advance, the control means reduces the amount of electricity supplied to the electric drive means to the predetermined value, while the vehicle speed is set to the predetermined vehicle speed or lower than the predetermined value. When the vehicle speed is exceeded, the vehicle steering apparatus is characterized in that the amount of electricity supplied to the electric drive means is increased and the current steering angle of the wheels is set to a first target steering angle. 2. The control means includes a filter processing means for smoothing the target rudder angle value, and when the vehicle speed exceeds the predetermined vehicle speed from the predetermined vehicle speed or lower state. The vehicle steering system according to claim 1, wherein the filter value of the filter processing unit is set so that the target steering angle value is smoothed.