JP3673455B2 - Vehicle steering system - Google Patents

Abstract

PROBLEM TO BE SOLVED: To add an attitude controlling function to a steering device for vehicle wherewith an operating member and a steering mechanism are coupled mechanically. SOLUTION: A steering wheel 20 is coupled mechanically with the steering mechanism 10 through a clutch 30. Normally the clutch 30 is in engaged condition, and a steering control part 50 makes drive control of a steering motor 40 in accordance with the operating torque sensed by a torque sensor 36 and gives a steering assist force to the steering mechanism 10. When quick braking on a μ-split road surface is sensed, the steering control part 50 puts the clutch in disengaged condition and makes drive control of the steering motor 40 for holding the actual yaw rate sensed by a yaw rate sensor 38 to the target value. The target yaw rate is decided on the basis of the steering angle or actual yaw rate immediately before the quick braking on the μ-split road surface is sensed.

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a vehicle steering apparatus in which an operation member such as a steering wheel and a steering mechanism are mechanically linked.
[0002]
[Prior art]
The situation in which the vehicle is suddenly braked on the so-called μ-split road surface is a typical traveling scene in which the vehicle posture is disturbed. A μ-split road is a road surface where the friction coefficient of the road surface is significantly different between the right and left sides of the vehicle. For example, the right wheel is on a dry asphalt road and the left wheel is on the ice surface. . When the braking mechanism of the vehicle is operated on such a μ-split road surface, a large braking force is generated on the high μ (high friction coefficient) side, and a large yaw moment is generated promptly, thereby disturbing the vehicle posture. Arise. Therefore, the driver performs so-called counter steering, applies a yaw moment in the reverse direction to the vehicle, and stabilizes the vehicle posture.
[0003]
On the other hand, recently, there is no mechanical connection between the steering wheel and the steering mechanism for steering the steering wheel, and the steering wheel operation direction and operation amount are detected. There has been proposed a vehicle steering device (so-called steer-by-wire system) in which a driving force from an actuator such as an electric motor is applied (see, for example, JP-A-9-142330).
[0004]
In the vehicle steering apparatus having such a configuration, the relationship between the operation of the steering wheel and the operation of the steering mechanism can be freely changed by electrical control. Accordingly, if the target yaw rate or the target lateral acceleration corresponding to the operation torque or the operation angle of the steering wheel is obtained and the operation of the steering mechanism is controlled based on these, the vehicle attitude can be controlled. That is, even if the vehicle behavior becomes unstable due to the braking operation on the μ-split road surface, the disturbance of the vehicle posture can be suppressed.
[0005]
In order to reduce a driver's steering burden, an electric power steering device that applies a steering assist force to a steering mechanism in accordance with an operation of a steering wheel is widely used. However, in this type of device, the steering wheel and the steering mechanism are mechanically coupled, and there is no example in which attitude control is performed as in the steer-by-wire system. That is, the disturbance of the vehicle behavior that occurs during braking on the μ-split road surface must be suppressed solely by the vehicle posture re-establishment by the driver's operation of the steering wheel.
[0006]
[Problems to be solved by the invention]
Accordingly, an object of the present invention is to provide a vehicle steering apparatus with improved added value by adding a posture control function to a vehicle steering apparatus in which an operation member and a steering mechanism are mechanically coupled. is there.
[0007]
[Means for Solving the Problems and Effects of the Invention]
In order to achieve the above object, the invention according to claim 1 comprises an operation member (20) for steering a vehicle, a steering mechanism (10) mechanically linked to the operation member, and the steering mechanism. Driving on the μ split road where the difference in friction coefficient between the left and right wheels running road surface is a certain value or more, the actuator (40) for applying a driving force to the vehicle, the yaw rate detecting means (38) for detecting the yaw rate of the vehicle Μ split road sudden braking detection means (37, 50, S1) for detecting sudden braking when the vehicle is in operation, first actuator control means (50, S2) for controlling the actuator in accordance with the operation of the operation member, In response to detecting sudden braking on the μ split road by the μ split road sudden braking detection means, the yaw rate is replaced with the control by the first actuator control means. It viewed including second actuator control means for controlling the actuator so as to cancel the yaw rate variations are detected by the detecting means and (50, S3, S4, S5 ) and said second actuator control means, sudden braking in the μ split road Means (S4) for setting the target yaw rate based on the steering angle at the start of the operation, and means for controlling the actuator (S5) so that the actual yaw rate detected by the yaw rate detection means is guided to the set target yaw rate. ) and a vehicle steering apparatus according to claim including Mukoto a. In addition, the alphanumeric characters in parentheses represent corresponding components in the embodiments described later. The same applies hereinafter.
[0008]
According to the above configuration, in a normal traveling scene, the steering assist force is applied to the steering mechanism by driving the actuator in accordance with the operation of the operation member. In contrast, when Kyusei dynamic on μ split road surface is detected, the driving actuator so as to cancel the yaw rate variation of the vehicle, thereby steering mechanism operates so as to suppress a yaw rate variation of the vehicle .
Thereby, even in the vehicle steering device in which the operation member and the steering mechanism are mechanically linked, it is possible to realize posture control for suppressing disturbance of the vehicle posture on the μ split road surface.
[0009]
Further , according to the present invention, the target yaw rate corresponding to the steering angle at the start of sudden braking on the μ-split road surface is set, and the actuator is driven so that the actual yaw rate detected by the yaw rate detecting means matches the target yaw rate. Is done. Accordingly, the vehicle can be braked while maintaining the behavior state of the vehicle at the time when the sudden braking on the μ split road surface is started.
[0010]
According to the second aspect of the present invention, there is provided an operation member (20) for steering the vehicle, a steering mechanism (10) mechanically linked to the operation member, and an actuator (40) for applying a driving force to the steering mechanism. ), A yaw rate detection means (38) for detecting the yaw rate of the vehicle, and a sudden braking when the vehicle is traveling on a μ-split road where the difference in friction coefficient between the road surfaces of the left and right wheels is a certain value or more. μ split road sudden braking detection means (37, 50, S1), first actuator control means (50, S2) for controlling the actuator according to the operation of the operation member, and μ split road sudden braking detection means In response to the detection of sudden braking on the μ split road, the yaw rate detection means detects instead of the control by the first actuator control means. Includes a second actuator control means and (50, S3, S4, S5 ) for controlling the actuator so as to cancel the Reto variation, the second actuator control means, said yaw rate detection means at the start of the sudden braking in μ split road Means (S4) for setting the actual yaw rate detected by the target yaw rate, and means (S5) for controlling the actuator so that the actual yaw rate detected by the yaw rate detection means is guided to the set target yaw rate. a car dual steering system you comprising.
[0011]
In the present invention, the operation of the actuator is controlled using the actual yaw rate at the start of the sudden braking on the μ split road surface as the target yaw rate. Thereby, at the time of braking on the μ split road surface, it is possible to suppress the yaw rate fluctuation during the braking period.
The invention according to claim 3 further includes a straight traveling state detecting means (S11) for detecting whether or not the vehicle is traveling straight, wherein the second actuator control means detects the straight traveling state of the vehicle. 3. The vehicle steering apparatus according to claim 1, wherein the actuator is controlled instead of the control by the first actuator control means on condition that the first actuator control means is provided. 3.
[0012]
According to the present invention, the attitude control for canceling the fluctuation of the yaw rate of the vehicle is performed only when the vehicle is in the straight traveling state. When the vehicle is passing a curve, if the vehicle speed decreases due to braking, the curvature of the locus drawn by the vehicle gradually changes even if the yaw rate of the vehicle is kept constant. Therefore, attitude control for a vehicle traveling on a curve is extremely complicated. Therefore, by adopting the configuration of the present invention, the posture control during sudden braking on the μ-split road surface is performed only when the vehicle is in a straight traveling state, the control content is simplified, easy to realize, and A practical vehicle steering apparatus can be provided.
[0013]
The invention according to claim 4 further includes a coupling mechanism (30) capable of switching between a coupling state in which the operating member and the steering mechanism are mechanically coupled and a released state in which the coupling is released. actuator control means, after switching the connection mechanism to the released state (S3), one of the claims 1 to 3, characterized in that for controlling the actuator in place of the control by the first actuator control means A vehicle steering apparatus according to claim 1.
[0014]
In this invention, the operation member and the steering mechanism are coupled via a coupling mechanism that can release the mechanical coupling between them. During sudden braking on the μ-split road surface, after the coupling between the operating member and the steering mechanism by the coupling mechanism is released, actuator control for stabilizing the vehicle posture is performed. As a result, the driver is not given the feeling that the operating member moves against his / her intention, so that the steering feeling can be improved.
[0015]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings.
FIG. 1 is an illustrative view showing a configuration of a vehicle steering apparatus according to an embodiment of the present invention. The vehicle steering device includes a steering mechanism 10 for causing a pair of steering wheels (normally front wheels) W (steering wheels) to perform a steering operation, and a clutch 30 for the steering mechanism 10. And a steering wheel 20 mechanically coupled. The clutch 30 can be switched between a connected state and a released state, and the mechanical connection between the steering wheel 20 and the steering mechanism 10 can be released by setting the released state.
[0016]
The steering mechanism 10 includes a steering shaft 11 that extends in the left-right direction of the vehicle body, and a knuckle arm that is coupled to both ends of the steering shaft 11 via tie rods 12 and 12 and supports the steered wheels W and W. 13 and 13. The steering shaft 11 is supported by the housing 14 and is slidable in the axial direction. A steering motor 40 as a steering actuator is coaxially incorporated in the middle of the steering shaft 11. When the steering motor 40 is driven, the rotation of the steering motor 40 is converted into the sliding of the steering shaft 11 by a motion conversion mechanism made of a ball screw or the like, and the steering wheels W and W are steered by the sliding of the steering shaft 11. Is achieved.
[0017]
A rack gear 11 a is formed on a part of the steering shaft 11, and a pinion gear 33 at the tip of a shaft 31 coupled to one side of the clutch 30 is engaged with the rack gear 11 a. A shaft 32 coupled to the other side of the clutch 30 is coupled to the steering wheel 20. Therefore, if the clutch 30 is in the connected state, the operation torque applied to the steering wheel 20 is mechanically transmitted to the steering shaft 11, and thereby the steering wheel W is steered.
[0018]
A shaft 32 that couples the steering wheel 20 and the clutch 30 is divided into an input shaft portion 32 </ b> A and an output shaft portion 32 </ b> B, which are connected via a torsion bar 35. The torsion bar 35 is made of an elastic body that twists according to an operation torque applied to the steering wheel 20. In relation to the torsion bar 35, a torque sensor 36 is provided for detecting an operation torque applied to the steering wheel 20 by detecting the amount of twist.
[0019]
The steering motor 40 is controlled by a steering control unit 50 including a microprocessor and the like. More specifically, the output of the torque sensor 36 is input to the steering control unit 50. Further, a rotary encoder 41 for detecting the rotational position of the steering motor 40 is disposed in association with the steering motor 40, and a detection signal of the rotary encoder 41 is input to the steering control unit 50. Yes. Further, a steering angle sensor 15 for detecting the actual turning angle of the steering mechanism 10 by detecting the axial position of the steering shaft 11 is provided in relation to the steering shaft 11. A detection signal of the steering angle sensor 15 is also input to the steering control unit 50. The steering control unit 50 is further input with detection signals from four wheel speed sensors 37 that detect the wheel speeds of the four wheels of the vehicle. Further, the steering control unit 50 receives an output signal of a yaw rate sensor 38 that detects the yaw rate of the vehicle.
[0020]
However, for example, the wheel speed sensor 37 and the yaw rate sensor 38 do not need to be directly connected to the steering control unit 50, and other electronic control units (for example, an electronic device for controlling the antilock brake system) mounted on the vehicle. Data corresponding to detection outputs of these sensors may be input to the steering control unit 50 from a control unit or an electronic control unit for dynamic yaw rate control.
[0021]
The steering control unit 50 sets a voltage command value based on the input signals from the sensors, and gives a control signal corresponding to the set voltage command value to the drive circuit 42. As a result, current corresponding to the control signal is supplied from the drive circuit 42 to the steering motor 40, and as a result, torque for sliding the steering shaft 11 in the direction corresponding to the operation direction of the steering wheel 20 is generated from the steering motor 40. Is output.
On the other hand, the steering control unit 50 controls a drive circuit 39 for driving the clutch 30. The clutch 30 is normally in a connected state, and mechanically links the steering wheel 20 and the steering mechanism 10. As will be described later, the steering control unit 50 controls the clutch 30 to the released state as necessary when sudden braking on the μ-split road surface is detected.
[0022]
FIG. 2 is an illustrative view for explaining a state of braking on a so-called μ-split road surface. The μ-split road surface 70 is a high μ road surface 71 such as a dry asphalt road surface in the traveling direction 85 of the vehicle 80, and the road surface on the left side in the traveling direction 85 of the vehicle 80 is like an ice surface. This is a low μ road surface 72.
If the brake pedal is depressed while the right wheel of the vehicle 80 is on the high μ road surface 71 and the left wheel is on the low μ road surface 72, a yaw moment in the direction of arrow 81 is generated in the vehicle 80. In order to cancel the yaw moment in the direction of the arrow 81, the steering control unit 50 performs an attitude control operation.
[0023]
FIG. 3 is a flowchart for explaining a control operation by the steering control unit 50. FIG. 3 shows the processing at the time of sudden braking particularly on the μ split road surface.
The steering control unit 50 refers to the output from the wheel speed sensor 37, for example, and determines whether the vehicle is on the μ-split road surface according to whether or not the wheel speed difference between the left and right wheels of the vehicle exceeds a predetermined threshold value. It is determined whether or not the vehicle is in a braking state at step S1. On the μ-split road surface, the wheel speed of the wheel on the low μ road surface side quickly decreases as the braking pressure increases. On the other hand, the wheel speed of the wheel on the high μ road surface side gradually decreases as compared with the wheel on the low μ road surface side. Therefore, if the wheel speeds of the left and right wheels have a difference of a certain value or more, it can be considered that sudden braking is being performed on the μ split road surface.
[0024]
If it is determined that sudden braking on the μ-split road surface is being performed, the steering control unit 50 performs normal electric power steering control (step S2). In this case, normal electric power steering control refers to control for applying a steering assist force from the steering motor 40 to the steering mechanism 10 in accordance with the magnitude of the operation torque detected by the torque sensor 36. However, the steering control unit 50 gives a relatively small steering assisting force to the steering mechanism 10 near the steering angle midpoint based on the output of the steering angle sensor 15, and a large steering assisting force is steered when the steering angle is large. The drive circuit 42 is controlled to be generated from the motor 40. Further, the steering control unit 50 obtains the speed of the vehicle based on the output from the wheel speed sensor 37 and performs so-called vehicle speed sensitive control. That is, the steering motor 40 is controlled so that a small steering assist force is generated when the vehicle speed is high, and a large steering assist force is generated when the vehicle speed is low (including when the vehicle is stopped).
[0025]
If it is determined that sudden braking on the μ-split road surface is being performed (YES in step S1), the steering control unit 50 switches the clutch 30 to the released state (step S3). Thereby, the mechanical link between the steering wheel 20 and the steering mechanism 10 is released. Further, the steering control unit 50 determines a target yaw rate (step S4), and feedback-controls the steering motor 40 based on the determined target yaw rate (step S5). That is, the steering control unit 50 drives the drive circuit 42 to generate a required steering torque on the steering motor 40 based on the difference between the target yaw rate and the actual yaw rate (actual yaw rate) detected by the yaw rate sensor 38. Is given a control signal.
[0026]
The target yaw rate set in step S4 is determined based on the actual turning angle output by the turning angle sensor 15 immediately before or immediately after the sudden braking on the μ split road surface is detected (preferably immediately before). Also good. The target yaw rate may be set equal to the actual yaw rate output by the yaw rate sensor 38 at the timing immediately before or immediately after the sudden braking on the μ split road surface is detected (preferably immediately before).
[0027]
In this way, during the period in which sudden braking on the μ split road surface is detected, the target yaw rate determined based on the steering angle (steering angle) at the start of sudden braking, or at the start of sudden braking. The steering motor 40 is controlled so that the target yaw rate set equal to the actual yaw rate is achieved. As a result, fluctuations in the yaw rate of the vehicle are suppressed, so that the vehicle posture can be stabilized. In addition, in this embodiment, since the attitude control as described above is performed after the clutch 30 is switched to the released state, the sense that the steering mechanism 10 is being driven against the intention is given to the steering wheel 20. Will not be given to the driver through. Thereby, the steering feeling is not impaired.
[0028]
FIG. 4 is a flowchart for explaining the operation of the vehicle steering apparatus according to the second embodiment of the present invention. In the description of this embodiment, reference is again made to FIGS. 1 and 2 described above. Also, in FIG. 4, steps in which processing similar to the steps shown in FIG. 3 is performed are denoted by the same reference numerals as in FIG. 3.
In this embodiment, the steering control unit 50 determines whether or not the vehicle is traveling straight (step S11). For example, the steering control unit 50 determines that the vehicle is traveling straight based on the fact that the output of the steering angle sensor 15 is stable near the midpoint of the steering angle. If the wheel is not in a straight traveling state, the processes of steps S1, S3, S4, and S5 are not performed, and normal electric power steering control (step S2) is performed. That is, only when the vehicle is in a straight traveling state, during sudden braking on the μ split road surface (step S1), the clutch 30 is switched to the released state (step S3), and the vehicle attitude is controlled by yaw rate feedback control (step S3). Steps S4 and S5) are performed.
[0029]
When such a configuration is adopted, the control content by the steering control unit 50 is simplified, and it becomes easy to introduce attitude control to the vehicle steering apparatus in which the steering wheel 20 and the steering mechanism 10 are mechanically coupled. . That is, when braking is performed while the vehicle is traveling on a curve, even if the yaw rate of the vehicle is kept constant, the trajectory drawn by the vehicle cannot have a constant curvature as the vehicle speed decreases. Gradually grows. Therefore, considering the case where sudden braking is performed on a curved μ-split road surface, it is necessary to change the target yaw rate over time in consideration of not only the yaw rate but also the vehicle speed. Therefore, the control content by the steering control unit 50 becomes complicated, and introduction of posture control may be difficult.
[0030]
In this embodiment, the above-mentioned problem is avoided by limiting the posture control during sudden braking on the μ split road surface only when the vehicle is traveling straight ahead.
While the two embodiments of the present invention have been described above, the present invention can also be implemented in other forms. For example, in the above-described embodiment, the clutch 30 is interposed between the steering wheel 20 and the steering mechanism 10 so that the connection between the steering wheel 20 and the steering mechanism 10 can be released as necessary. Without providing the clutch 30, the steering wheel 20 and the steering mechanism 10 may be mechanically connected at all times. In this case, the process of step S3 in FIGS. 3 and 4 is omitted.
[0031]
In the above-described embodiment, the steering motor 40 is controlled so as to generate a steering torque that achieves the target yaw rate at the time of sudden braking on the μ split road surface. However, the deviation between the target yaw rate and the actual yaw rate is determined. On the basis of setting the target turning angle, even if the steering motor 40 is controlled so that the deviation between the target turning angle and the actual turning angle detected by the turning angle sensor 15 is led to zero. Good.
Further, in the above-described embodiment, the sudden braking operation on the μ split road surface is detected based on the difference between the wheel speeds of the left and right wheels exceeding a certain threshold value. When the actual turning angle detected by the engine 15 and / or the actual yaw rate detected by the yaw rate sensor 38 change suddenly from a substantially constant state, it may be determined that sudden braking on the μ split road surface has been performed. Good.
[0032]
In this case, it is preferable to determine the target yaw rate during the sudden braking period on the μ split road surface based on the value of the turning angle or the actual yaw rate immediately before the turning angle or the actual yaw rate changes suddenly.
In addition, various design changes can be made within the scope of matters described in the claims.
[Brief description of the drawings]
FIG. 1 is an illustrative view showing a configuration of a vehicle steering apparatus according to an embodiment of the present invention;
FIG. 2 is an illustrative view for explaining a state of braking on a so-called μ-split road surface.
FIG. 3 is a flowchart for explaining a control operation by a steering control unit.
FIG. 4 is a flowchart for explaining the operation of a vehicle steering apparatus according to a second embodiment of the invention.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 10 Steering mechanism 11 Steering shaft 11a Rack gear 15 Steering angle sensor 20 Steering wheel 30 Clutch 33 Pinion gear 35 Torsion bar 36 Torque sensor 37 Wheel speed sensor 38 Yaw rate sensor 39 Drive circuit 40 Steering motor 42 Drive circuit 50 Steering control part

Claims (4)

An operating member for steering the vehicle;
A steering mechanism mechanically linked to the operating member;
An actuator for applying a driving force to the steering mechanism;
Yaw rate detection means for detecting the yaw rate of the vehicle;
Μ split road sudden braking detection means for detecting sudden braking when traveling on a μ split road where the difference in friction coefficient between the road surfaces of the left and right wheels is a certain value or more;
First actuator control means for controlling the actuator according to an operation of the operation member;
In response to the sudden braking on the μ split road being detected by the μ split road sudden braking detecting means, the yaw rate fluctuation detected by the yaw rate detecting means is canceled in place of the control by the first actuator control means. look including a second actuator control means for controlling the actuator,
The second actuator control means is configured to set a target yaw rate based on a steering angle at the start of sudden braking on the μ split road, and to guide the actual yaw rate detected by the yaw rate detection means to the set target yaw rate. vehicle steering system and means for controlling said actuator so wither characterized containing Mukoto. An operating member for steering the vehicle;
A steering mechanism mechanically linked to the operating member;
An actuator for applying a driving force to the steering mechanism;
Yaw rate detection means for detecting the yaw rate of the vehicle;
Μ split road sudden braking detection means for detecting sudden braking when traveling on a μ split road where the difference in friction coefficient between the road surfaces of the left and right wheels is a certain value or more;
First actuator control means for controlling the actuator according to an operation of the operation member;
In response to the sudden braking on the μ split road being detected by the μ split road sudden braking detecting means, the yaw rate fluctuation detected by the yaw rate detecting means is canceled in place of the control by the first actuator control means. And second actuator control means for controlling the actuator,
The second actuator control means has means for setting the actual yaw rate detected by the yaw rate detection means at the start of sudden braking on the μ split road as a target yaw rate and the actual yaw rate detected by the yaw rate detection means. car dual steering apparatus you; and a means for controlling the actuator as directed to the target yaw rate. It further includes a straight traveling state detection means for detecting whether the vehicle is traveling straight,
The second actuator control means controls the actuator in place of the control by the first actuator control means on the condition that the straight movement state detection means detects the straight movement state of the vehicle. The vehicle steering apparatus according to claim 1 or 2 . A coupling mechanism capable of switching between a coupling state in which the operation member and the steering mechanism are mechanically coupled and a released state in which the coupling is released;
Said second actuator control means, after switching the connection mechanism to the released state, any of claims 1 to 3 in place of the control by the first actuator control means, characterized in that for controlling the actuator The vehicle steering device according to claim 1.

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