JP5333801B2 - Steering force control device - Google Patents

Description

  The present invention relates to a steering force control device, and more particularly to a technique for controlling a steering assist force when the posture of a vehicle becomes unstable.

2. Description of the Related Art In recent years, electric power steering capable of controlling a steering force by applying a steering assist force by the force of an electric motor has been adopted in power steering of vehicles.
Since the electric power steering has a larger friction due to the resistance of the electric motor than the hydraulic power steering, etc., and the steering is difficult to return to the neutral position, the steering wheel is moved to the neutral position by using the difference between the left and right wheel speeds during steering operation. There is a technique for controlling an electric power steering so that a steering assist force is applied in a direction to return to (see Patent Document 1).

That is, since the wheel speed on the inner wheel side is small and the wheel speed on the outer wheel side is large when the vehicle is turning, this technology controls to apply the steering assist force toward the outer wheel side where the wheel speed is large. For example, a steering assist force in the right direction is added during left turn when the steering is operated in the left direction.
Also, oversteer and understeer are judged by comparing the actual yaw rate and the target yaw rate, and the stability control (hereinafter referred to as ESC) that stabilizes the vehicle behavior by adding braking force to the wheel that is optimal for approaching the target vehicle behavior. There are vehicles equipped with. As a control of the electric power steering in the vehicle equipped with the ESC, a configuration is disclosed in which the steering assist force by the electric power steering is suppressed as the difference between the actual yaw rate and the target yaw rate increases, and the braking force control by the ESC is prioritized. (Patent Document 2).

Japanese Patent No. 3525541 JP 09-39762 A

  First, in the technique disclosed in Patent Document 1, for example, when braking is performed while traveling on a so-called μ split road surface having different road surface friction coefficients (μ) on the left and right sides of the vehicle, a low friction coefficient (hereinafter referred to as a low μ) is used. ) Since the wheel speed of the wheel that is in contact with the road surface is lower than the wheel that is in contact with the high friction coefficient (hereinafter referred to as “high μ”) road surface, the steering assist force is added to the high μ road surface side. It becomes.

However, since the braking force works strongly on the wheels on the high μ road surface, if the vehicle deflects toward the high μ road surface and the steering assist force is added to the high μ road surface side, the high μ road surface side There is a risk that the vehicle will be deflected toward the vehicle.
In the technique disclosed in Patent Document 2, the steering assist force is suppressed as the tendency of oversteer and understeer increases, and oversteer and understeer are eliminated by ESC. There is a problem that it becomes difficult for the driver to stabilize the posture of the vehicle, and the driver feels uncomfortable.

Furthermore, since ESC is a control that requires relatively expensive sensors such as a steering angle sensor and a yaw rate sensor, it cannot be applied to a vehicle that does not include such sensors. There's a problem.
The present invention has been made to solve such a problem, and the object of the present invention is to provide a steering assist force appropriately when the vehicle posture becomes unstable with a simple configuration with a minimum configuration. In addition, it is an object to provide a steering force control device that can promote stabilization of the posture of a vehicle by a steering operation.

  In order to achieve the above object, in the steering force control device according to claim 1, a steering means for changing the direction of the wheel according to the operation of the driver, and a steering assist force can be added to the operation of the steering means. Steering assistance means, wheel speed detection means for detecting the wheel speed of each wheel of the vehicle, and detecting lock of the vehicle wheel based on the wheel speed detected by the wheel speed detection means, thereby preventing the lock. The anti-lock brake control means for controlling the brake of the wheel so as to apply a braking force while the wheel speed detected by the wheel speed detecting means is used to determine the difference between the left and right wheel speeds in the pair of left and right wheels and A rate of change is calculated, and when the difference between the left and right wheel speeds of the wheel is greater than a predetermined wheel speed difference or the rate of change of the left and right wheel speed difference is greater than a predetermined rate of change, Wheel speed out of wheels When the steering assist means is controlled to add the steering assist force to the lower wheel side, and the anti-lock brake control means is controlled on the left and right wheels of the wheel during the predetermined time, And a steering assist control means for ending the addition of the steering assist force.

  In the steering force control device according to claim 2, the steering means for changing the direction of the wheel according to the operation of the driver, the steering auxiliary means capable of adding a steering auxiliary force to the operation of the steering means, and each of the vehicles Wheel speed detecting means for detecting the wheel speed of the wheel, and detecting the lock of the wheel of the vehicle based on the wheel speed detected by the wheel speed detecting means, and applying the braking force while preventing the lock An anti-lock brake control means for controlling the brake of the left and right wheels, and when the brake of one of the left and right wheels is controlled by the anti-lock brake control means, the steering assist to the one wheel side for a predetermined time The steering assisting means is controlled to apply force, and when the anti-lock brake control means is controlled on the left and right wheels of the wheel during the predetermined time, the steering assisting means is applied. It is characterized by comprising: a steering assisting control means to terminate the addition of forces, the.

In a steering force control device according to a third aspect, in the first or second aspect, the steering assist control unit calculates a left and right wheel speed difference between a pair of left and right wheels from a wheel speed detected by the wheel speed detection unit, It is characterized in that the magnitude of the steering assist force is controlled according to the magnitude of the difference between the left and right wheel speeds.
According to a fourth aspect of the present invention, there is provided the steering force control apparatus according to the first or second aspect, further comprising a turning state detection unit that detects a turning state of the vehicle, wherein the steering assist control unit is detected by the turning state detection unit. Is turned inside the turn more than a predetermined turning state, the addition of the steering assist force to the inside of the turn is terminated.

According to the steering force control apparatus of the first aspect of the present invention using the above means, in the power steering capable of controlling the steering assist force, the difference between the left and right wheel speeds of the wheels is larger than the predetermined wheel speed difference or the left and right wheel speed difference. When the predetermined change rate is greater than the predetermined change rate, the steering assist force is applied to the wheel side having a low wheel speed for a predetermined time.
In other words, for example, when a predetermined difference between the left and right wheel speeds occurs when braking on a high μ road surface, that is, a μ split road surface that deflects to the high wheel speed side, the low μ road surface side that becomes the low wheel speed side The steering assist force is applied only during a predetermined time.

In this way, at the moment when the difference between the left and right wheel speeds occurs and the vehicle is about to deflect, the steering assist force is applied to the opposite side to the direction of deflection to provide the driver with steering information in a direction that stabilizes the vehicle posture. Can be given.
In addition, by adding the steering assist force to the low wheel speed side only for a predetermined time, the actual steering in the direction of stabilizing the vehicle behavior by the driver becomes an excessive operation, or the subsequent correction It is possible to prevent the steering from being hindered.

Furthermore, when control by the anti-lock brake control means is performed on both the left and right wheels of the wheel, excessive interference with the anti-lock brake control is prevented by terminating the addition of the steering assist force even during a predetermined time. Can be suppressed.
As a result, the steering information can prompt the driver to steer in the posture stabilization direction, and the vehicle's posture can be changed early by not excessively interfering with the steering operation in the actual posture stabilization direction. Can be stabilized.

Further, since the steering assist force control means is simple control based only on the wheel speed, any vehicle equipped with the wheel speed detection means can be applied inexpensively without increasing the cost.
As described above, with a simple configuration with a minimum configuration, it is possible to appropriately apply a steering assist force when the vehicle posture becomes unstable, and to promote stabilization of the vehicle posture by a steering operation.

According to the steering force control device of the second aspect, the anti-brake brake control means is provided in the power steering capable of controlling the steering assist force, and when the control by the anti-lock brake control means acts on one of the wheels. A steering assist force is applied to the one wheel side for a predetermined time.
That is, for example, at the time of braking on the μ split road surface where the vehicle is deflected to the high μ road surface side, that is, the high wheel speed side, the steering assist force is applied to the low wheel speed side on which the antilock brake control acts.

In addition, when control by the antilock brake control means is performed on both the left and right wheels of the wheel, excessive interference with the antilock brake control is prevented by terminating the addition of the steering assist force even during a predetermined time. Can be suppressed.
As a result, the steering information can prompt the driver to steer in the posture stabilization direction, and the vehicle's posture can be changed early by not excessively interfering with the steering operation in the actual posture stabilization direction. Can be stabilized.

Here, whether or not the anti-lock brake control is actuated on each wheel can be detected by a vibration change of the wheel speed, or can be detected by communication with a controller of the anti-lock brake control.
Moreover, since it is simple control using anti-lock brake control, it can be applied at low cost without an increase in cost if the vehicle is provided with anti-lock brake control means.

From the above, with a simple configuration in cooperation with anti-lock brake control, an appropriate steering assist force can be added when the vehicle posture becomes unstable, and the stabilization of the vehicle posture by steering operation can be promoted. it can.
According to the steering force control device of claim 3, the wheel speed difference between the pair of left and right wheels is calculated, and the steering assist force applied to the wheel side having the lower wheel speed among the left and right wheels according to the wheel speed difference. By controlling the magnitude, the steering assist force according to the road surface μ can be obtained, and the posture of the vehicle can be more appropriately stabilized.

  According to the steering force control apparatus of the fourth aspect, when the turning state of the vehicle is equal to or greater than a predetermined value, the situation where the vehicle behavior tends to become unstable is avoided by stopping the addition of the steering assist force to the inside of the turn. can do.

It is a schematic block diagram of the steering force control apparatus in 1st Example of this invention. It is a flowchart which shows the attitude | position stabilization EPS control routine performed by steering ECU of the steering force control apparatus in 1st Example of this invention. FIG. 6 is a schematic diagram showing a state of the vehicle when posture stabilization EPS control is performed in the first embodiment of the present invention during μ-split road surface braking. It is a schematic block diagram of the steering force control apparatus in 2nd Example of this invention. It is a flowchart which shows the attitude | position stabilization EPS control routine performed by steering ECU of the steering force control apparatus in 2nd Example of this invention. It is a schematic diagram showing a state of the vehicle when posture stabilization EPS control in the second embodiment of the present invention is performed at the time of low μ road turning.

Hereinafter, embodiments of the present invention will be described with reference to the drawings.
First, the first embodiment will be described.
Referring to FIG. 1, there is shown a schematic configuration diagram of a steering force control apparatus in a first embodiment of the present invention.
As shown in the figure, the vehicle 1 is provided with a left front wheel 2L, a right front wheel 2R, a left rear wheel 4L, and a right rear wheel 4R.

The left front wheel 2L and the right front wheel 2R are steering wheels of the vehicle 1 and are connected to an electric power steering 10 (steering means, steering assist means) (hereinafter referred to as EPS 10) via a tie rod 6.
The electric power steering 10 mainly includes a steering gear box 12, a steering shaft 14, a steering wheel 16, and an electric motor 18.

  Specifically, a steering wheel 16 is connected to the steering gear box 12 via a steering shaft 14. The operation of the steering wheel 16 by the driver is transmitted to the steering gear box 12 via the steering shaft 14, and the tie rod 8 is actuated via the steering gear box 12 to change the directions of the left and right front wheels 2L, 2R. It is configured as follows.

In addition, the electric motor 18 is provided in the steering gear box 12, and the rotation of the electric motor 18 is input to the steering gear box 12 to generate a steering assist force in response to the operation of the steering wheel 16. .
On the other hand, each wheel 2L, 2R, 4L, 4R is provided with a brake 20L, 20R, 22L, 22R for applying a braking force to each wheel 2L, 2R, 4L, 4R. The brakes 20L, 20R, 22L, and 22R are adjusted in braking force to the wheels 2L, 2R, 4L, and 4R by supplying hydraulic pressure from a brake hydraulic unit 24 mounted on the vehicle.

Furthermore, wheel speed sensors 26L, 26R, 28L, and 28R for detecting wheel speeds are provided on the wheels 2L, 2R, 4L, and 4R, respectively.
The vehicle 1 is equipped with a steering ECU 30 electrically connected to the electric motor 18 and a braking system ECU 32 electrically connected to the brake hydraulic unit 24.

Each of the ECUs 30 and 32 includes an input / output device (not shown), a storage device (ROM, RAM, BURAM, etc.) incorporating a number of control programs, a central processing unit (CPU), a timer counter, and the like.
Further, the wheel speed sensors 26L, 26R, 28L, and 28R are electrically connected to the ECUs 30 and 32, respectively. Further, the steering ECU 30 and the braking system ECU 32 are also electrically connected to each other. In addition, each ECU30 and 32 may be independent.

The steering ECU 30 has a general electric power steering control function for controlling a steering assist force for reducing the driver's steering torque, and further detects each of the wheel speed sensors 26L, 26R, 28L, 28R detected by the wheel speed sensors 26L, 26R, 28L, 28R. It has a function of controlling the steering assist force based on wheel speed, control of the braking system ECU 32, and the like.
Further, the braking system ECU 32 determines each wheel 2L, 2R based on each wheel speed detected by the wheel speed sensors 26L, 26R, 28L, 28R when the vehicle 1 is suddenly braked or when braking on a low μ road surface. 4L, 4R has a function to detect the lock, and perform a so-called anti-skid system (ABS control) that adjusts each brake 20L, 20R, 22L, 22R so as to give the optimum braking force while preventing the lock Yes.

Hereinafter, the operation of the steering force control apparatus according to the first embodiment of the present invention configured as described above will be described.
In the ABS control in the braking system ECU 32, the slip ratios of the wheels 2L, 2R, 4L, and 4R are calculated from the wheel speeds detected by the wheel speed sensors 26L, 26R, 28L, and 28R, and the slip ratio is optimal. The hydraulic pressure supplied from the brake hydraulic unit 24 to each brake 20L, 20R, 22L, 22R is controlled so as to be a value.

In the EPS control in the steering ECU 30, the electric power steering 10 is controlled so that a steering assist force is applied in the same direction as the driver's operation of the steering wheel 16 during normal driving.
The steering ECU 30 also applies a steering assist force in a direction to stabilize the posture of the vehicle 1 by the electric power steering 10 when the vehicle 1 is in a specific driving state in which the posture of the vehicle 1 becomes unstable. Stabilized EPS control (steering assist control means) is performed.

Specifically, FIG. 2 is a flowchart showing an attitude stabilization EPS control routine performed by the steering ECU 30 of the steering force control apparatus according to the first embodiment of the present invention, and will be described below with reference to the flowchart of FIG.
First, as shown in FIG. 2, the steering ECU 30 detects the turning state of the vehicle 1 in step S1. The turning state is detected from the wheel speed difference detected by the wheel speed sensors 28L and 28R of the rear wheels 4L and 4R, for example. That is, when the difference between the wheel speed of the left rear wheel 4L and the wheel speed of the right rear wheel 4R is equal to or smaller than a predetermined value, it is detected as a straight traveling state, and when it is equal to or larger than the predetermined value, it is detected as a turning state. Alternatively, the turning state can be detected by the torque sensor of EPS 10 or the assist current of EPS 10.

Subsequently, in step S2, it is determined whether or not a brake operation is performed by the driver.
If the determination result is false (No), that is, if the driver does not perform a brake operation, that is, a so-called brake off state, the process proceeds to step S14.
In step S14, the posture stabilization EPS control is ended, the duration time T from the start of the posture stabilization EPS control and the number N of the end of the posture stabilization EPS control, which are measured in the steering ECU 30, are reset. Return.

On the other hand, if the determination result in step S2 is true (Yes), that is, if the driver is performing a brake operation, that is, a so-called brake-on state, the process proceeds to step S3.
In step S <b> 3, it is determined whether or not the value of the number of times N of the posture stabilization EPS control measured in the steering ECU 30 is less than 1.
When the determination result is true (Yes), that is, when the number of times N of the end of the posture stabilization EPS control measured in the steering ECU 30 is less than 1, the process proceeds to step S4.

In step S4, the left and right wheel speed differences of the front wheels 2L and 2R are calculated from the wheel speeds detected by the wheel speed sensors 26L and 26R of the front wheels 2L and 2R, and the change rate of the front wheel left and right wheel speed differences is calculated. To do.
In step S5, the difference between the left and right wheel speeds of the front wheels 2L and 2R calculated in step S4 is greater than a preset predetermined wheel speed difference α, or the change rate of the left and right wheel speed difference is greater than a predetermined change rate β. It is determined whether or not. That is, in step S5, it is determined whether or not the road surface friction coefficient of one of the front wheels 2L and 2R is small and the posture of the vehicle 1 is in an unstable state.

If the determination result is true (Yes), that is, if the posture of the vehicle 1 is unstable, the process proceeds to step S6.
In step S6, a steering assist force is calculated. The direction of the steering assist force at this time is set to the lower side of the left and right front wheels 2L, 2R. That is, for example, if the wheel speed of the left front wheel 2L is lower than that of the right front wheel 2R, the steering assist force for leftward steering is set. Further, the steering assist force at this time is set by a map or the like corresponding to the difference between the left and right wheel speeds of the front wheels 2L and 2R. For example, the greater the left and right wheel speed difference, the greater the steering assist force. Is set. Further, the magnitude of the steering assist force may be adjusted with a map or the like according to the deceleration at the time of vehicle braking calculated from the wheel speed or the like.

In step S7, it is determined whether or not a steering assist force is applied in the same direction as the turning direction detected in step S1.
In the subsequent step S8, it is determined whether or not the ABS control performed by the braking system ECU 32 is acting on both the left and right wheels of the front wheels 2L and 2R.
Further, in step S9, it is determined whether or not the control continuation time T of the posture stabilization EPS control is equal to or shorter than a predetermined time Ta.

If any one of these steps S3, S5, and S7 to S9 is false (No), the process proceeds to step S12.
In step S12, it is determined whether or not the duration T from the start of the posture stabilization EPS control measured in the steering ECU 30 is not zero. That is, it is determined whether or not the posture stabilization control is currently being executed.

If the determination result is false (No), that is, if the posture stabilization EPS control is not currently being executed, the routine is returned.
On the other hand, if the determination result in step S12 is true (Yes), that is, if the posture stabilization EPS control is currently being executed, the process proceeds to step S13.
In step S13, the posture stabilization EPS control is ended, the duration T from the start of the posture stabilization EPS control measured in the steering ECU 30 is reset, and further, the posture stabilization EPS control end count N is set to 1. The added value is set as the new end count N, and the routine is returned.

  That is, if the posture stabilization EPS control is performed once while the brake operation is being performed by the driver (step S3), the μ-split road surface with a small road surface friction coefficient of one of the front wheels 2L and 2R. When the vehicle 1 is in a stable state (step S5), when a steering assist force is already applied in the same direction as the turning direction (step S5). Step S7), when ABS control is acting on the left and right wheels of the front wheels 2L, 2R (Step S8), and when posture stabilization EPS control is continued for a predetermined time Ta (Step S9), posture stabilization The EPS control is terminated.

  On the other hand, when the determination results of steps S5 to S8 are all true (Yes), that is, while the brake operation is performed by the driver, the posture stabilization EPS control is not performed once (step S3). ), When the road surface friction coefficient of one of the front wheels 2L and 2R is small and the vehicle 1 is in an unstable posture (step S5), the steering assist force is not applied or the steering assist force is When it is added on the opposite side to the turning direction of the vehicle (step S7), when ABS control is acting only on the left or right of the front wheels 2L, 2R (step S8), the posture stabilization EPS control is performed. If the duration time T is within the predetermined time Ta (step S9), the process proceeds to step S10.

In step S10, a value obtained by adding the control period time Ts to the duration time T of the posture stabilization EPS control is set as a new control duration time T.
In subsequent step S11, the steering assist force calculated in step S6 is generated.
After step S11, the process returns to step S2 again, and the determinations of steps S3, S5, and S7 to S9 are repeated. While each determination result is true (Yes), the steering assist force calculated in step S5 is determined as S11. Will continue to be added.

Here, referring to FIG. 3, there is shown a schematic diagram showing the state of the vehicle when the posture stabilization EPS control in the first embodiment of the present invention is performed at the time of μ split road surface braking. A specific vehicle behavior when the posture stabilization EPS control in the first embodiment is performed will be described.
The vehicle 1 shown in FIG. 3 travels straight on a μ split road surface, and the left wheels 2L and 4L are in contact with the high μ road surface and the right wheels 2R and 4R are in contact with the low μ road surface.

When the vehicle 1 performs sudden braking, the wheel speed of the front wheels 2L, 2R first decreases more rapidly on the right front wheel 2R on the low μ road side, and ABS control by the braking system ECU 32 acts to prevent locking. To do.
Further, the braking force acting on the front wheels 2L, 2R is higher in the left front wheel 2L that is in contact with the high μ road surface, and the vehicle 1 is deflected to the high μ road surface side, that is, the left side.

On the other hand, the steering ECU 30 causes a difference between the left and right wheel speeds in the front wheels 2L and 2R due to a sudden decrease in the wheel speed of the right front wheel 2R. Is equal to or greater than the predetermined change rate β, the posture stabilization EPS control is started.
In the posture stabilization EPS control, a steering assist force is applied to the right front wheel 2R side where the wheel speed is low, that is, to the right. That is, the steering assist force is applied in a direction that stabilizes the posture of the vehicle 1 on the side opposite to the deflection direction of the vehicle 1.

As a result, the driver is urged to steer in the stabilization direction from the steering information by the addition of the steering assist force.
When the posture stabilization EPS control is performed once (S3), when a turning operation or the like is performed and a steering assist force is applied in the same direction as the turning direction (S7), the posture stabilization EPS control is performed together with the right front wheel 2R. When ABS control also acts on the left front wheel 2L on the μ road side (S8), when a predetermined time Ta has elapsed from the start of the posture stabilization EPS control (S9), the posture stabilization EPS control is terminated and the normal Transition to EPS control.

Thus, in the steering force control apparatus according to the first embodiment of the present invention, when the posture of the vehicle 1 becomes unstable due to braking on the μ split road surface, the posture stabilization EPS control by the steering ECU 30 By adding a steering force in a direction that stabilizes the posture of the vehicle 1, it is possible to prompt the driver to steer in the stabilization direction using the steering information.
In the configuration of the first embodiment, the steering ECU 30 and the braking system ECU 32 are both simple controls using only the wheel speed sensors 26L, 26R, 28L, 28R, and at least the wheel speed sensors 26L, 26R, 28L, If it is a vehicle provided with 28R, it can be mounted inexpensively without an increase in cost.

Further, the addition of the steering assist force by the posture stabilization EPS control is limited to the predetermined time Ta, so that the driver's excessive operation by adding the steering assist force for a long time, the correction steering for the excessive operation, etc. It is possible to prevent obstruction.
Further, even during a predetermined time Ta, when a turning operation or the like is performed and a steering assist force is applied in the same direction as the turning direction, or the left front wheel 2L on the high μ road side together with the right front wheel 2R. In addition, when the ABS control is activated, the addition of the excessive steering assist force or excessive interference with the ABS control can be suppressed by terminating the posture stabilization EPS control. Further, since the posture stabilization EPS control can obtain a sufficient effect if it acts as steering information at an early stage when the posture of the vehicle becomes unstable, the posture stabilization EPS during one brake operation of the driver. The number of control interventions is limited to one, and when other control interventions or steering is performed in a direction that stabilizes the posture, the posture stabilization EPS control is excessively affected by immediately terminating the control. It is possible to prevent the posture of the vehicle from becoming unstable again.

Furthermore, when the wheel speed difference and the rate of change of the left and right wheels are equal to or less than the predetermined values α and β, the addition of the steering assist force is terminated to prevent the addition of the steering assist force on the high μ road, It is possible to prevent the posture stabilization EPS control from intervening in the wheel speed difference between the left and right front wheels 2L, 2R that is temporarily generated when braking is performed on a certain road surface.
From the above, it is possible to appropriately stabilize the posture of the vehicle by the steering operation by appropriately applying the steering assist force when the vehicle posture becomes unstable with the minimum simple configuration.

Next, a second embodiment will be described.
Referring to FIG. 4, there is shown a schematic configuration diagram of a steering force control device in a second embodiment of the present invention. In the second embodiment, the same components as those in the first embodiment are denoted by the same reference numerals and description thereof is omitted.
As shown in FIG. 4, in the second embodiment, in addition to the configuration of the first embodiment, a steering angle sensor 40 that detects the steering angle of the steering wheel 16, a yaw rate sensor 42 that detects the yaw rate of the vehicle 1, and the like. Is provided.

The vehicle 1 is mounted with a braking ECU 52 that controls the braking force of the vehicle 1 by adjusting the brakes 20L, 20R, 22L, and 22R via the steering ECU 50 that performs EPS control and the brake hydraulic unit 24.
The steering angle sensor 40 and the yaw rate sensor 42 are electrically connected to the braking system ECU 52 in the second embodiment.

The braking system ECU 52 has the same ABS control function as that of the first embodiment, and is optimal while adjusting the braking force by the brakes 20L, 20R, 22L, and 22R and stabilizing the posture of the vehicle. It has a so-called stability control (ESC) function that ensures braking force.
Hereinafter, the operation of the steering force control apparatus according to the second embodiment of the present invention configured as described above will be described.

  In the ESC in the braking system ECU 52, the actual yaw rate (from the wheel speed detected by the wheel speed sensors 26L, 26R, 28L, and 28R, the steering angle detected by the steering angle sensor 40, and the yaw rate detected by the yaw rate sensor 42) is calculated. Oversteer, understeer, etc. are detected from the difference between the actual turning trajectory) and the target yaw rate (target turning trajectory), and the braking force of each wheel 2L, 2R, 4L, 4R is adjusted to achieve the target yaw rate. Further, in the ESC, the braking force of each wheel 2L, 2R, 4L, 4R is adjusted so as to suppress a sudden turn such as a spin.

Referring to FIG. 5, a posture stabilization EPS control routine performed by the steering ECU 50 of the steering force control apparatus according to the second embodiment of the present invention is shown in a flowchart, which will be described below with reference to the flowchart in FIG. . In this case as well, the same control contents as those in the first embodiment are denoted by the same reference numerals and description thereof is omitted.
As shown in FIG. 5, in the posture stabilization EPS control in the second embodiment, when the determination result in step S2 is false (No), that is, in the brake-off state, the diagram of the first embodiment. Step S21 which is not in 2 is added. This is because the ESC operates regardless of the driver's braking operation.

That is, even in the brake off state, if it is detected that the ESC is operating, the determination result is true (Yes), and the process proceeds to step S3.
In the second embodiment, the determination in step S8 shown in FIG. 2 of the first embodiment is performed to determine whether or not ABS control or ESC is acting on both the left and right wheels of the front wheels 2L and 2R. Has been changed.

That is, when ABS control and ESC are not acting on the front wheels 2L and 2R, or when ABS control and ESC are acting on both the left and right wheels of the front wheels 2L and 2R, the determination result is false (No), Proceed to step S12.
On the other hand, if ABS control or ESC is acting only on the left or right of the front wheels 2L, 2R, the determination result is true (Yes), and the process proceeds to step S9.

Further, if the vehicle is equipped with an ESC as in the second embodiment, the turning direction in step S1 can be detected and the turning state of the vehicle can be detected from information from the steering angle sensor 40 and the yaw rate sensor 42. It is.
Here, referring to FIG. 6, there is shown a schematic diagram showing the state of the vehicle when the posture stabilization EPS control in the second embodiment is performed at the time of turning on the low μ road surface. A specific vehicle behavior when the posture stabilization EPS control in the second embodiment is performed will be described.

The vehicle 1 shown in FIG. 6 is turning left on a low μ road surface.
For example, when the driver steers the steering wheel 16 further leftward and the rear wheels 4L and 4R slide sideways, the vehicle 1 enters a spin behavior toward the inside of the turn.
The braking system ECU 52 applies a braking force to the right front wheel 2R in order to prevent the vehicle 1 from spinning inside the turn due to ESC.

On the other hand, when the braking force is applied to the right front wheel 2R by ESC, the steering ECU 50 causes a difference in the left and right wheel speed between the front wheels 2L and 2R, and the wheel speed difference is greater than or equal to a predetermined wheel speed difference α or the wheel speed difference. When the change rate of becomes equal to or greater than the predetermined change rate β, posture stabilization EPS control is started.
In the posture stabilization EPS control, a steering assist force is applied to the right front wheel 2R side where the wheel speed is low, that is, to the right. That is, the steering assist force is applied to the side opposite to the spin behavior of the vehicle 1, that is, the direction in which the posture of the vehicle 1 is stabilized.

By adding the steering assist force, the driver is urged to steer in the stabilizing direction, and the actual steering becomes smooth. Further, the control amount of the ESC, that is, the braking force applied to the wheels is reduced by stabilizing the posture of the vehicle as the driver steers in the stabilization direction.
When ESC acts on the left front wheel 2L on the turning inner wheel side together with the right front wheel 2R, or when ABS control is performed on both the left and right wheels of the front wheels 2L and 2R, the posture is stable when the deceleration exceeds a predetermined deceleration. When the predetermined time Ta has elapsed from the start of the control EPS control, the posture stabilization EPS control is terminated and the process proceeds to normal EPS control.

As described above, in the steering force control apparatus according to the second embodiment of the present invention, posture stabilization EPS control can be applied to a vehicle equipped with ESC in substantially the same manner as in the first embodiment.
Even when the ESC acts on the left or right side of the front wheels 2L, 2R to produce a difference between the left and right wheels, the same effect as in the first embodiment can be obtained. 1 posture can be stabilized.

Although the description of the embodiment of the steering force control device according to the present invention has been completed above, the embodiment is not limited to the above embodiment.
In the above embodiment, the attitude state of the vehicle 1 is detected from the difference between the left and right wheel speeds of the front wheels 2L and 2R or the rate of change of the left and right wheel speed difference. However, the present invention is not limited to this, and ABS control by the braking system ECUs 32 and 52 You may detect the attitude | position state of the vehicle 1 from ESC.

  For example, when ABS control or ESC is applied to one of the left and right front wheels 2L, 2R, control information indicating that ABS control or ESC has been applied to one of the left and right front wheels 2L, 2R is received from the braking system ECU 32, 52; The same effect can be obtained even when the steering assist force is added to the one front wheel side, and thereby a simpler configuration in cooperation with other controls can be achieved.

  Further, in addition to the above-described embodiment, a deceleration sensor or the like for detecting the deceleration of the vehicle is provided, or the deceleration of the vehicle is estimated from the wheel speed (deceleration detecting means). A steering assist force in the posture stabilization EPS control may be set. For example, when the vehicle is traveling on a high μ road surface and the deceleration during braking is equal to or greater than a predetermined value, the steering assist force is set low or the addition of the steering assist force is terminated to It is possible to prevent an excessive steering assist force from being applied during braking on a high μ road surface that is strongly influenced by behavior.

  Moreover, in the said embodiment, although the magnitude | size of steering assistance force is set by the map according to the left-right wheel speed difference, it is not restricted to the said right-left wheel speed difference. For example, a constant steering assist force may be added regardless of the left and right wheel speed difference.

1 Vehicle 2L Left front wheel (steering wheel)
2R right front wheel (steering wheel)
10 Electric power steering (steering means)
18 Electric motor (steering assist means)
20L, 20R, 22L, 22R Brake 24 Brake hydraulic unit 26L, 26R, 28L, 28R Wheel speed sensor (wheel speed detection means, deceleration detection means)
30, 50 Steering ECU (steering assist control means)
32, 52 Braking system ECU (anti-lock brake control means, stability control means)

Claims (4)

Steering means for changing the direction of the wheel according to the operation of the driver,
Steering assist means capable of adding a steering assist force to the operation of the steering means;
Wheel speed detection means for detecting the wheel speed of each wheel of the vehicle;
Anti-lock brake control means for detecting the lock of the vehicle wheel based on the wheel speed detected by the wheel speed detection means, and controlling the brake of the wheel so as to apply a braking force while preventing the lock;
From the wheel speed detected by the wheel speed detecting means, the left and right wheel speed difference between the pair of left and right wheels and the change rate of the left and right wheel speed difference are calculated, and the left and right wheel speed difference of the wheels is larger than a predetermined wheel speed difference. Or when the rate of change of the difference between the left and right wheel speeds is greater than a predetermined rate of change, the steering assist force is applied to the side of the left and right wheels having a lower wheel speed for a predetermined time. Steering assist control means for controlling the assisting means, and when the control by the antilock brake control means is performed on the left and right wheels of the wheel during the predetermined time; A steering force control device comprising: Steering means for changing the direction of the wheel according to the operation of the driver,
Steering assist means capable of adding a steering assist force to the operation of the steering means;
Wheel speed detection means for detecting the wheel speed of each wheel of the vehicle;
Anti-lock brake control means for detecting the lock of the vehicle wheel based on the wheel speed detected by the wheel speed detection means, and controlling the brake of the wheel so as to apply a braking force while preventing the lock;
When the brake of one of the left and right wheels is controlled by the anti-lock brake control means, the steering assistance means is controlled to apply the steering assistance force to the one wheel side for a predetermined time. A steering assist control means for terminating the addition of the steering assist force when the anti-lock brake control means is controlled on the left and right wheels of the wheel during the predetermined time. A steering force control device as a feature.   The steering assist control means calculates a left and right wheel speed difference between the pair of left and right wheels from the wheel speed detected by the wheel speed detection means, and the magnitude of the steering assist force is determined according to the magnitude of the left and right wheel speed difference. The steering force control device according to claim 1, wherein the steering force control device controls the steering force. A turning state detecting means for detecting a turning state of the vehicle;
The steering assist control means ends the addition of the steering assist force to the inside of the turn when the turning state detected by the turning state detecting means is turning inside the turning more than a predetermined turning state. The steering force control apparatus according to claim 1 or 2, characterized in that

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