JP7574559B2 - Steering control device - Google Patents

Description

The present invention relates to a steering control device that improves the straight-line stability of a vehicle.

A conventional steering control device is known, for example, from the device described in Patent Document 1. In the steering control device (vehicle steering device) of Patent Document 1, a target yaw rate is set based on the steering angle at the start of sudden braking on a μ-split road, and an actuator for driving the steering mechanism is controlled so that the actual yaw rate detected by the yaw rate detection means is guided to the target yaw rate.

In addition, in the steering control device (lateral stability control device) of Patent Document 2, when a lateral disturbance occurs, the steering angle of the driver is calculated, and a target rotational angular velocity to be targeted is calculated using this steering angle and vehicle information. Then, the rotational angular velocity of the vehicle is adjusted to the target rotational angular velocity, so that the rotational moment generated by the lateral disturbance is attenuated (improving straight-line stability).

Patent No. 3673455 Patent No. 5145128

However, in both Patent Documents 1 and 2, the control (feedback control) is based on the rotational angular velocity (yaw rate), so control is only performed after a change occurs in the vehicle's traveling direction, and in principle, offsets and wobble from the target trajectory are unavoidable. For example, on a μ-split road or a road subject to lateral disturbances, a yaw rate occurs while driving, and even if control is applied to suppress the yaw rate, the yaw rate will occur again, resulting in a repeated cycle.

In view of the above problems, an object of the present invention is to provide a steering control device capable of suppressing the occurrence of offset and wobble.

To achieve the above objective, the present invention employs the following technical means.

In a first disclosure, there is provided a steering control device for controlling a steering unit (20) that steers a vehicle (10),
A vehicle speed detection unit (111) for detecting a vehicle speed when the vehicle is traveling;
a tire action force detection unit (112) for detecting a tire longitudinal force, which is a force in the longitudinal direction as a tire action force acting on a tire of a vehicle;
a target steering amount calculation unit (122) for determining a target steering amount when the sum of a yaw rate generated by a vehicle speed and a difference between longitudinal forces of left and right tires and a yaw rate generated by steering becomes zero;
and a steering amount control unit (131) that controls the steering unit so as to achieve a target steering amount.
In a second disclosure, there is provided a steering control device for controlling a steering unit (20) that steers a vehicle (10),
A vehicle speed detection unit (111) for detecting a vehicle speed when the vehicle is traveling;
a tire action force detection unit (11 3 ) for detecting a tire lateral force acting in a lateral direction of the tire as a tire action force acting on a tire of a vehicle;
a target steering amount calculation unit (122) for determining a target steering amount when a sum of a yaw rate generated by a vehicle speed and a resultant force of tire lateral forces at each tire and a yaw rate generated by steering becomes zero;
and a steering amount control unit (131) that controls the steering unit so as to achieve a target steering amount.

The present developers have discovered that it is possible to predict the possible yaw rate from the tire forces acting on the tires of the vehicle (10). In this disclosure, a resultant force is calculated from the vehicle speed and tire forces, and the yaw rate generated by this resultant force is predicted. The steering amount control unit (131) then calculates (sets) a target steering amount for canceling out this yaw rate, and controls the steering unit (20). In other words, feedforward control of the steering amount relative to the predicted yaw rate is possible, and the occurrence of offset and wobble of the vehicle (10) can be suppressed.

The symbols in parentheses for each of the above means indicate the corresponding relationship with the specific means described in the embodiments below.

1 is a block diagram showing a steering control device in a first embodiment. FIG. FIG. 1 is an explanatory diagram showing a vehicle traveling on a μ-split road; 4 is a graph showing a longitudinal force difference and a yaw rate relative to a vehicle speed. 4 is a graph showing yaw rate relative to steering angle and vehicle speed. FIG. 11 is an explanatory diagram for explaining how steering control for canceling out yaw rate generated by longitudinal forces enables driving without offset or wobble. 4 is a flowchart showing control operations performed by a detection unit, a calculation unit, and a control unit. 4 is a graph showing the behavior of a vehicle under conventional control and under this control. FIG. 4 is an explanatory diagram showing an offset amount by steering amount control in the first embodiment. FIG. 11 is a block diagram showing a steering control device according to a second embodiment. FIG. 2 is an explanatory diagram showing a vehicle traveling on a cross gradient. FIG. 11 is an explanatory diagram for explaining how steering control for canceling a yaw rate caused by a lateral force enables driving without offset or wobble. 4 is a flowchart showing control operations performed by a detection unit, a calculation unit, and a control unit. FIG. 11 is an explanatory diagram showing an offset amount by steering amount control in the second embodiment. FIG. 13 is a block diagram showing a warning device according to a third embodiment.

Below, several embodiments for implementing the present invention will be described with reference to the drawings. In each embodiment, parts corresponding to matters described in the preceding embodiment will be given the same reference numerals, and duplicated descriptions may be omitted. In each embodiment, when only a part of the configuration is described, other previously described embodiments may be applied to the other parts of the configuration. In addition to combinations of parts that are specifically specified as being possible in each embodiment, it is also possible to partially combine embodiments even if not specified, as long as there is no particular problem with the combination.

First Embodiment
The steering control device 100A of this embodiment will be described with reference to Figs. 1 to 8. As shown in Figs. 1 and 2, the steering control device 100A is mounted on a vehicle 10 and controls a steering unit 20 that steers the vehicle 10, thereby improving straightness when traveling on a road with different friction coefficients for the left and right tires, such as a µ-split road. Fig. 2 shows an example of a µ-split road in which the left tire of the vehicle 10 is a high µ road and the right tire is a low µ road. The high µ road is assumed to be, for example, a normal asphalt road, and the low µ road is assumed to be, for example, a frozen road.

The steering unit 20 of the vehicle 10 steers the tires by changing the direction of the left and right tires by moving a steering shaft provided between the left and right tires on the front wheel side in the axial direction by a steering actuator provided in the control unit 130 described later. A steering wheel is connected to the steering shaft, and during normal driving, the tires are steered by the driver's operation of the steering wheel.

As shown in FIG. 1, the steering control device 100A includes a detection unit 110, a calculation unit 120, and a control unit 130.

The detection unit 110 detects the vehicle speed and tire longitudinal force, and includes a vehicle speed detection unit 111 and a tire longitudinal force detection unit 112.

The vehicle speed detection unit 111 is a sensor that detects the speed of the vehicle 10 while it is traveling, and outputs the detected vehicle speed signal to the resultant force calculation unit 121 (tire front-rear force difference calculation unit 121a) of the calculation unit 120.

The tire longitudinal force detection unit 112 corresponds to the tire action force detection unit of the present disclosure, and is a sensor that detects the tire action force acting on each tire. In this embodiment, for example, a case where the vehicle is traveling on a μ-split road is described as an example, and here, the tire action is a force in the longitudinal direction (hereinafter, the longitudinal force (FIG. 5(a))).

The tire longitudinal force detection unit 112 is attached to a predetermined portion (a portion around the tire) related to each tire of the vehicle 10, and detects the force acting on each tire, that is, the tire longitudinal force, by the amount of strain at the predetermined portion during driving. The predetermined portion can be, for example, a joint between a suspension member and a lower arm in a suspension. The tire longitudinal force detection unit 112 may estimate the amount of strain using the amount of displacement occurring at the joint. The tire longitudinal force detection unit 112 outputs data on the amount of strain (or displacement), that is, data on the longitudinal force occurring in each tire, to the resultant force calculation unit 121 (tire longitudinal force difference calculation unit 121a) of the calculation unit 120.

The calculation unit 120 is a part that calculates the yaw rate based on the difference between the longitudinal forces of the left and right tires, and the target steering amount, and has a tire longitudinal force difference calculation unit 121a as a resultant force calculation unit 121, a target steering amount calculation unit 122, etc.

The tire longitudinal force difference calculation unit 121a calculates the difference between the longitudinal forces of the left and right tires using longitudinal force data (strain or displacement) for each tire. When calculating the longitudinal force difference, the longitudinal force difference for at least one tire on each side is calculated. For example, if the vehicle 10 is a four-wheeled vehicle, the longitudinal force difference for the left and right tires (two tires) on the driven side may be calculated, or the longitudinal force difference between the left and right tires may be calculated using the longitudinal forces for all tires (four tires).

Then, the tire longitudinal force difference calculation unit 121a uses the vehicle speed value (vehicle speed signal) and the longitudinal force difference to calculate (predict) the yaw rate (γ _F ) that may occur in the vehicle 10, that is, the rotational angular velocity ( FIG. 5( a )) about the vertical axis passing through the center of gravity of the vehicle 10. The tire longitudinal force difference calculation unit 121a outputs the calculated yaw rate to the target steering amount calculation unit 122.

The target steering amount calculation unit 122 calculates a target steering amount (δ) for canceling the yaw rate (γδ) that may occur due to the difference between the longitudinal forces of the tires (described in detail later). The target steering amount calculation unit 122 outputs the calculated target steering amount to the steering amount control unit 131 of the control unit 130.

The target steering amount calculation unit 122 calculates the target steering amount (δ) based on the amount of steering currently being performed by the driver using the steering wheel.

The control unit 130 is a part that controls the steering unit 20, and has a steering amount control unit 131 and a steering actuator, etc.

The steering amount control unit 131 calculates the torque required to achieve the target steering amount calculated by the target steering amount calculation unit 122, and controls the steering unit 20 by operating the steering actuator with this required torque.

The configuration of the steering control device 100A of this embodiment is as described above, and its operation and effects will be explained below with reference to Figures 3 to 8.

The developers discovered that on a μ-split road, as shown in Figure 3, it is possible to predict the yaw rate that will occur by detecting the difference in the longitudinal forces of the left and right tires.

That is, as shown in FIG. 3, when the yaw rate is γ _F , the difference between the longitudinal forces is ΔF, and the correction value associated with the vehicle speed is G _F (G _F is a function of the vehicle speed),

(Equation 1)
γ _F = _GF・ΔF
It can be expressed as:

On the other hand, as shown in Figure 4, a yaw rate is naturally generated by normal steering. When the yaw rate at this time is γ _δ , the steering angle is δ, and the correction value associated with the vehicle speed is G _δ (G _δ is a function of the vehicle speed),

(Equation 2)
γ _δ = G _δ δ
It can be expressed as:

Therefore, as shown in FIG. 5, if the sum of the yaw rate _γF generated by the difference between the tire longitudinal forces and the yaw rate _γδ generated by steering becomes zero, the vehicle 10 can travel straight even on a road with different friction coefficients on the left and right, such as a μ-split road.

(Equation 3)
γ _F + γ _δ =G _F・ΔF+G _δ・δ=0
The steering angle (target steering amount) required to go straight is

(Equation 4)
δ=-(G _F /G _δ )・ΔF
It becomes.

In this embodiment, steering control is performed in a feedforward manner based on the longitudinal force difference ΔF. Figure 6 shows a control flowchart executed by the steering control device 100A.

First, in step S100 of FIG. 6, in the detection unit 110, the vehicle speed detection unit 111 acquires the vehicle speed of the vehicle 10, and in step S110, the tire longitudinal force detection unit 112 acquires the longitudinal forces of each tire.

Next, in step S120, in the calculation unit 120, the tire longitudinal force difference calculation unit 121a calculates the longitudinal force difference ΔF between the left and right tires from the longitudinal forces of each tire.

Next, in step S130, in the calculation section 120, the target steering amount calculation section 122 calculates the target steering amount δ (Equation 4) using the difference ΔF between the longitudinal forces and the correction values G _F and G _δ .

Then, in step S140, in the control unit 130, the steering amount control unit 131 operates the steering actuator to control the steering unit 20 so as to obtain the target steering amount δ. The steering amount control unit 131 determines whether or not to control the steering unit 20 depending on the speed of the vehicle 10. For example, when the vehicle is stopped, no yaw rate occurs, so control of the steering unit 20 is prohibited.

When driving on a μ-split road without adopting this embodiment, as shown in FIG. 7, as the vehicle speed increases (FIG. 7(a)), a difference ΔF in the longitudinal forces of the left and right tires occurs between the high μ road side and the low μ road side (FIGS. 7(b) and (c)), and accordingly, a steering angle and yaw rate occur (FIGS. 7(d) and (e)). Then, depending on the vehicle speed, a lateral offset (left/right deviation from the straight-ahead direction) occurs due to the yaw rate (FIG. 7(f)).

In this embodiment, the difference ΔF (resultant force) between the longitudinal forces of the left and right tires is calculated from the vehicle speed and the longitudinal tire forces (tire acting forces), and the yaw rate generated by this longitudinal force difference ΔF is predicted. The steering amount control unit 131 then calculates (sets) a target steering amount δ for canceling this yaw rate, and controls the steering unit 20. In other words, feedforward control of the steering amount relative to the predicted yaw rate is possible, and the occurrence of offset and wobble of the vehicle 10 can be suppressed (Figure 7(f)).

As shown in Figure 8, the results of a desk simulation showed that this embodiment was able to reduce the maximum offset compared to the conventional method.

The tire longitudinal force detection unit 112 also detects the longitudinal force acting on the tire using the amount of strain (or displacement) at a specific location related to the tire of the vehicle 10. This utilizes the fact that there is a correlation between the longitudinal force and the amount of strain (displacement) at a specific location, and allows the tire longitudinal force to be detected in a simple manner.

The target steering amount calculation unit 122 also calculates the target steering amount δ based on the current steering amount. This allows for highly accurate control, for example, when turning, by adding the target steering amount δ corresponding to the longitudinal force based on the steering amount at that time.

The steering amount control unit 131 also determines whether or not to control the steering unit 20 depending on the vehicle speed. For example, when the vehicle 10 is stopped, no yaw rate occurs, so unnecessary control operations can be eliminated.

Second Embodiment
A steering control device 100B of the second embodiment is shown in Fig. 9 to Fig. 13. The second embodiment improves straightness when traveling on a road with a transverse slope, for example. Fig. 10 shows a transverse slope in which the left side of the vehicle 10 is at a higher position and the right side is at a lower position as the vertical height position of the road surface with a transverse slope.

As compared to the first embodiment, in the steering control device 100B, as shown in FIG. 9, a tire lateral force detection unit 113 is provided instead of the tire longitudinal force detection unit 112. In addition, as the resultant force calculation unit 121, a tire resultant force calculation unit 121b is provided instead of the tire longitudinal force difference calculation unit 121a.

The tire lateral force detection unit 113 corresponds to the tire acting force detection unit of the present disclosure, and detects the tire lateral force acting laterally on the tire, for example, when the vehicle 10 travels on a transverse gradient, when turning, when it is subjected to a crosswind, etc. The tire lateral force detection unit 113 outputs the detected tire lateral force data to the tire resultant force calculation unit 121b. For example, on a road with a transverse gradient, the tire lateral force acts from the low road surface position to the high road surface position (FIG. 11(a)).

The tire lateral force detection unit 113, like the tire longitudinal force detection unit 112 in the first embodiment, detects the amount of strain or displacement of a specific part of the vehicle 10 related to the tire.

The tire resultant force calculation unit 121b calculates the resultant lateral force of each tire using the vehicle speed value (vehicle speed signal) and the lateral force data of each tire (strain amount, displacement amount). Then, the tire resultant force calculation unit 121b calculates (predicts) the yaw rate (γ _F ) ( FIG. 11( a )) that may occur in the vehicle 10 using the resultant lateral force. The tire resultant force calculation unit 121b outputs the calculated yaw rate to the target steering amount calculation unit 122.

The target steering amount calculation unit 122 calculates a target steering amount (δt) for canceling the yaw rate that may occur due to the resultant force of the tire lateral forces (described in detail later). The target steering amount calculation unit 122 outputs the calculated target steering amount to the steering amount control unit 131 of the control unit 130.

In this embodiment, the lateral force (resultant lateral force) on each tire is detected on a road with a transverse gradient in the following manner to predict the yaw rate, and the target steering amount δt is calculated based on the yaw rate.

That is, if the lateral force of the left front wheel is Ffl, the lateral force of the right front wheel is Ffr, the lateral force of the left rear wheel is Frl, the lateral force of the right rear wheel is Frr, the lateral force of the front wheel is Ff, and the lateral force of the rear wheel is Fr

(Equation 5)
Ff=Ffl+Ffr

(Equation 6)
Fr=Frl+Frr
It is.

In addition, when the distance from the center of gravity of the vehicle 10 to the front wheel axle is lf, the distance from the center of gravity of the vehicle 10 to the rear wheel axle is lr, and the correction value associated with the vehicle speed is G _F , the yaw rate γ generated by the resultant lateral force is

(Equation 7)
γ _F =G _F (lf・Ff−lr・Fr)
It is.

On the other hand, normal steering also naturally generates a yaw rate. When the yaw rate at this time is γ _δ , the steering angle is δ, and the correction value associated with the vehicle speed is G _δ,

(Equation 8)
γ _δ = G _δ δ
It can be expressed as:

Therefore, as shown in FIG. 11, if the sum of the yaw rate _γF generated by the resultant tire lateral force and the yaw rate _γδ generated by steering becomes zero, the vehicle 10 can travel straight even on a road on which the vehicle is subjected to a lateral force, such as a cross-slope road.

(Equation 9)
γF+γδ=G _F (lf・Ff−lr・Fr)+G _δ・δ=0
Then, the steering angle required to go straight (target steering amount δt) is

(Equation 10)
δt=-(G _F /G _δ )・(lf・Ff−lr・Fr)
It becomes.

In this embodiment, steering control is performed in a feedforward manner based on the lateral force (resultant lateral force). Figure 12 shows a control flowchart executed by the steering control device 100B.

First, in step S100 of FIG. 12, in the detection unit 110, the vehicle speed detection unit 111 acquires the vehicle speed of the vehicle 10, and in step S111, the tire lateral force detection unit 113 acquires the lateral force of each tire.

Next, in step S121, in the calculation unit 120, the tire resultant force calculation unit 121b calculates the resultant lateral force from the lateral forces of each tire.

Next, in step S130, in the calculation section 120, the target steering amount calculation section 122 calculates the target steering amount δt (Equation 10) using the resultant lateral force and each of the correction values G _F and G _δ .

Then, in step S140, in the control unit 130, the steering amount control unit 131 operates the steering actuator to control the steering unit 20 so as to obtain the target steering amount δt. The steering amount control unit 131 determines whether or not to control the steering unit 20 depending on the speed of the vehicle 10. For example, when the vehicle is stopped, no yaw rate is generated, so control of the steering unit 20 is prohibited.

In this embodiment, the tire lateral force (resultant lateral force) is calculated from the vehicle speed and tire lateral force (tire acting force), and the yaw rate generated by this resultant lateral force is predicted. The steering amount control unit 131 then calculates (sets) a target steering amount δt for canceling this yaw rate, and controls the steering unit 20. In other words, feedforward control of the steering amount relative to the predicted yaw rate is possible, and the occurrence of offset and wobble of the vehicle 10 can be suppressed.

As shown in Figure 13, the results of a desk simulation showed that this embodiment was able to reduce the maximum offset compared to the conventional method.

The tire lateral force detection unit 113 also detects the lateral force acting on the tire using the amount of strain (or displacement) at a specific location related to the tire of the vehicle 10. This utilizes the fact that there is a correlation between the lateral force and the amount of strain (displacement) at a specific location, and allows tire lateral force to be detected in a simple manner.

Third Embodiment
14 shows a warning device 101 according to the third embodiment. The warning device 101 issues a warning to a driver (passenger) regarding steering of the vehicle 10 by a warning unit 140. The warning device 101 includes a vehicle speed detection unit 111 as a detection unit 110, a tire acting force detection unit, a resultant force calculation unit 121 as a calculation unit 120, a yaw rate prediction calculation unit 123, and the like.

The vehicle speed detection unit 111 is the same as in the first embodiment. The tire action force detection unit is, for example, the tire longitudinal force detection unit 112 described in the first embodiment, or the tire lateral force detection unit 113 described in the second embodiment. The resultant force calculation unit 121 detects the resultant force (tire action force) acting on the tire. The resultant force calculation unit 121 can be the tire longitudinal force difference calculation unit 121a of the first embodiment, or the tire resultant force calculation unit 121b of the second embodiment, and calculates, for example, the tire longitudinal force difference ΔF, or a resultant force acting on the tire, such as a lateral force.

The yaw rate prediction calculation unit 123 predicts the yaw rate generated in the vehicle 10 from the resultant force acting on the tires, as in the first and second embodiments. Then, when the predicted yaw rate exceeds a predetermined value, the warning unit 140 is activated. The warning unit 140 issues a warning about steering to the driver, for example, by sound or image. The warning about steering is, for example, to warn of the possibility of the vehicle 10 swaying or offset driving on a straight road when a yaw rate occurs.

This improves safety by providing the driver with a steering warning based on the magnitude of the yaw rate based on the forces acting on the tires of the vehicle 10.

Other Embodiments
In the above-described embodiments, the tire longitudinal force detection unit 112 or the tire lateral force detection unit 113 for detecting the tire acting force is attached to a predetermined portion related to each tire (a portion around the tire), for example, a joint between a suspension member and a lower arm. However, the present invention is not limited to this, and other portions are also possible. The tire longitudinal force detection unit 112 or the tire lateral force detection unit 113 may be attached to, for example, the tread portion of the tire, the sidewall portion of the tire, the wheel axle portion of the tire, or the axle hub portion of the tire.

The disclosure in this specification and drawings is not limited to the illustrated embodiment. The disclosure includes the illustrated embodiment and modifications based thereon by those skilled in the art. For example, the disclosure is not limited to the combination of parts and/or elements shown in the embodiment. The disclosure can be implemented by various combinations. The disclosure can have additional parts that can be added to the embodiment. The disclosure includes the omission of parts and/or elements of the embodiment. The disclosure includes the substitution or combination of parts and/or elements between one embodiment and another embodiment. The disclosed technical scope is not limited to the description of the embodiment. Some disclosed technical scopes are indicated by the description of the scope of the claims, and should be interpreted as including all modifications within the meaning and scope equivalent to the description of the scope of the claims.

The control unit and the method described in this disclosure may be realized by a special-purpose computer provided by configuring a processor and memory programmed to execute one or more functions embodied in a computer program.

Alternatively, the control unit and the method described in this disclosure may be implemented by a special-purpose computer provided by configuring a processor with one or more dedicated hardware logic circuits.

Alternatively, the control unit and the method described in this disclosure may be implemented by one or more special-purpose computers configured by combining a processor and memory programmed to perform one or more functions, and a processor configured by one or more hardware logic circuits.

The computer program may also be stored on a computer-readable non-transitory tangible recording medium as instructions to be executed by a computer.

Here, the flowchart described in this embodiment, or the process of the flowchart, is composed of multiple sections (also referred to as steps), and each section is expressed as, for example, S110. Furthermore, each section can be divided into multiple subsections, while multiple sections can also be combined into one section. Furthermore, each section thus composed can be referred to as a device, module, or means.

10 Vehicle 20 Steering unit 100A, 100B Steering control device 101 Warning device 111 Vehicle speed detection unit 112 Tire longitudinal force detection unit (tire acting force detection unit)
113 Tire lateral force detection unit (tire acting force detection unit)
121 Resultant force calculation unit 122 Target steering amount calculation unit 123 Yaw rate prediction calculation unit 131 Steering amount control unit 140 Warning unit

Claims (5)

A steering control device that controls a steering unit (20) that steers a vehicle (10),
A vehicle speed detection unit (111) that detects the vehicle speed when the vehicle is traveling;
a tire action force detection unit (112) for detecting a tire longitudinal force, which is a force in the longitudinal direction as a tire action force acting on a tire of the vehicle;
a target steering amount calculation unit (122) that determines a target steering amount when a sum of a yaw rate generated by the vehicle speed and a difference between the longitudinal forces of the left and right tires and a yaw rate generated by steering becomes zero;
A steering control device comprising: a steering amount control unit (131) that controls the steering unit so as to achieve the target steering amount. A steering control device that controls a steering unit (20) that steers a vehicle (10),
A vehicle speed detection unit (111) that detects the vehicle speed when the vehicle is traveling;
a tire action force detection unit (11 3 ) for detecting a tire lateral force acting in a lateral direction of the tire as a tire action force acting on the tire of the vehicle;
a target steering amount calculation unit (122) for determining a target steering amount when a sum of a yaw rate generated by the vehicle speed and a resultant force of tire lateral forces at each tire and a yaw rate generated by steering becomes zero;
A steering control device comprising: a steering amount control unit (131) that controls the steering unit so as to achieve the target steering amount. 3. The steering control device according to claim 1, wherein the tire action force detection unit estimates the tire action force from an amount of strain in a portion related to the tire. The steering control device according to claim 3 , wherein the tire action force detection unit estimates the amount of strain using a displacement at a portion related to the tire. 5. The steering control device according to claim 1 , wherein the steering amount control unit determines whether or not to control the steering unit depending on the vehicle speed.