JP2004034740A - Steering device for vehicle - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To solve such a problem that steering stability of a vehicle is not always improved when a ratio of a steering amount of a steering wheel with respect to an operation amount of a steering member such as a steering wheel, namely a steering ratio, is uniformly varied in a condition that visibility ahead of the vehicle is poor in a steering device for vehicle. <P>SOLUTION: When the vehicle travels at middle speed although the visibility is poor, a map A of an ordinary steering ratio is adopted (steps S2 and S6). When the visibility is poor and only a visual field of short distance is obtained and the vehicle travels at low speed, a map B whereby the steering ratio is reduced is adopted (step S4), and quick steering is achieved and thereby prompt obstacle avoidance can be achieved. When the vehicle travels at high speed although the visibility is poor, a map C whereby the steering is increased is adopted (step S7), and dull steering is achieved and thereby vehicle steering stability at high speed traveling can be achieved. <P>COPYRIGHT: (C)2004,JPO

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a vehicle steering device that steers steered wheels in response to an operation of a steering member.
[0002]
2. Description of the Related Art
As a steering device of this type, a steering ratio variable mechanism that varies a steering amount of a steered wheel with respect to an operation amount of a steering member is provided, and when the vehicle is traveling on a rough road, the steering ratio is reduced, That is, there is a steering device that changes to the quick side (for example, see Japanese Patent Application Laid-Open No. 60-131366).
Further, there is a steering device that changes the steering ratio to a larger side, that is, a dull side when the vehicle travels on a rough road such as an uneven road (for example, see Japanese Patent Application Laid-Open No. H11-227622).
[0003]
However, these steering devices have a problem that the vehicle behavior is easily disturbed because the steering ratio is uniformly changed regardless of, for example, the vehicle speed.
On the other hand, there is a steering device that executes a torque applying control that applies a steering torque independently of steering by a driver when visibility is low, and when visibility is good but the driver's awakening degree is low (for example, see Japanese Patent Application Laid-Open Publication No. H11-163873). 2001-151137).
However, in this steering device, only the operation reaction force of the steering member is changed, and the steering characteristics of the vehicle itself are not changed at all. Therefore, the degree of improvement in steering (steering stability) is small.
[0004]
The present invention has been made in view of the above problems, and an object of the present invention is to provide a vehicular steering apparatus that can surely improve the steerability in accordance with a road condition ahead or the like.
[0005]
Means for Solving the Problems and Effects of the Invention
In order to achieve the above object, an invention according to claim 1 is a vehicle steering apparatus including a steering mechanism that steers a steered wheel in accordance with steering of a steering member. Turning ratio varying means for varying the ratio of the road, road condition detecting means for detecting the road condition ahead of the vehicle, running condition detecting means for detecting the running condition of the vehicle including at least the vehicle speed, road condition detecting means and And a control unit for changing the turning ratio by the turning ratio variable means based on a signal from the traveling state detecting means. In the present invention, the steering ratio is changed in consideration of the road condition (for example, visibility or road surface condition) ahead of the vehicle and the vehicle speed, so that the steering stability can be reliably improved.
[0006]
Further, according to the present invention, the control unit includes a data map for determining a steering ratio from the detected vehicle speed in a case where the road condition is poor and a case where the road condition is good. Alternatively, as in claim 3, the control unit may include an arithmetic expression for determining the steering ratio from the detected vehicle speed, when the road condition is poor and when the road condition is good. In these cases, the steering ratio according to the road condition can be realized by using a data map or an arithmetic expression prepared in advance.
[0007]
Further, according to the present invention, the road condition detecting means detects the visibility of the road ahead of the vehicle and a road surface state of the road ahead of the vehicle. A road surface state detecting means, and a visibility emphasis mode for changing a turning ratio by a turning ratio variable means based on signals from the visibility detecting means and the running state detecting means, and a road surface state detecting means and The control unit includes a mode selection unit that can select any one of a road surface condition emphasis mode for changing a turning ratio by a turning ratio variable unit based on a signal from the traveling state detection unit. The turning ratio may be changed based on the mode selected by the selection unit.
[0008]
For example, if the condition of rain is regarded as a state of poor visibility, an obstacle can be recognized only at a position relatively close to the traveling direction of the vehicle, and quick steering is required because the obstacle must be detoured immediately. It is considered preferable. On the other hand, if it is assumed that the rainy state is a road surface state in which the tires easily slip, dull (dull) steering in which the steered wheels do not respond too sensitively to the operation of the steering member is considered preferable. Therefore, in the present invention, for example, the driver selects a mode in which the visibility or the road surface condition is prioritized, and controls the steering ratio according to the selected mode.
[0009]
Further, according to the present invention, when the road condition detected by the road condition detecting means is poor, the vehicle speed signal detected by the traveling state detecting means is subjected to predetermined processing and given to the control unit. There are cases. In this case, for example, when the visibility is good and when the visibility is poor, the turning ratio can be obtained by using a common data map or a common arithmetic expression.
[0010]
BEST MODE FOR CARRYING OUT THE INVENTION
Preferred embodiments of the present invention will be described with reference to the accompanying drawings.
FIG. 1 is a schematic diagram showing a schematic configuration of a vehicle steering system according to an embodiment of the present invention. Referring to FIG. 1, the vehicle steering system includes a steering transmission system 30 from a steering member 1 such as a steering wheel to left and right steered wheels 5 for steering, and a mechanical connection between the steering member 1 and the steered wheels 5. It is configured as a so-called steer-by-wire (SBW) system, which eliminates various connections. In the vehicle steering system, the operation of the steering actuator 2 driven in response to, for example, a rotation operation of the steering member 1 is converted into a linear motion of the steering shaft 4 supported by the housing 3 in the vehicle width direction. Steering for converting the linear motion of the shaft 4 into the steering motion of the left and right steered wheels 5 is achieved.
[0011]
The steering actuator 2 is configured to include an electric motor such as a brushless motor. The driving force (rotational force of the output shaft) of the electric motor is linearly moved in the axial direction (vehicle width direction) of the steering shaft 4 by a motion conversion mechanism (for example, a ball screw mechanism) provided in association with the steering shaft 4. Is converted to The linear motion of the steering shaft 4 is transmitted to a tie rod 6 provided to protrude from both ends of the steering shaft 4, and further causes the knuckle arm 7 connected to the kingpin P via the tie rod 6 to rotate. Thereby, steering of the wheel 5 supported by the knuckle arm 7 is achieved. The steering shaft 4, the tie rod 6, the knuckle arm 7, and the like constitute a steering mechanism for steering the steered wheels 5 of the steering mechanism.
[0012]
The steering member 1 is connected to a steering shaft 8 rotatably supported on the vehicle body. The steering shaft 8 is provided with a reaction force actuator 9 for applying an operation reaction force to the steering member 1. The reaction force actuator 9 includes an electric motor such as a brushless motor having an output shaft integrated with the steering shaft 8.
An elastic member 10 composed of a spiral spring or the like is connected to an end of the steering shaft 8 opposite to the steering member 1. When the reaction force actuator 9 does not apply torque to the steering member 1, the elastic member 10 returns the steering member 1 to the straight steering position by the elastic force.
[0013]
In order to detect an operation input value of the steering member 1, an operation angle sensor 11 for detecting an operation angle of the steering member 1 is provided in association with the steering shaft 8. Further, the steering shaft 8 is provided with a torque sensor 12 for detecting a torque applied to the steering member 1. On the other hand, in connection with the steering shaft 4, a turning angle detection sensor 13 for detecting the turning angle of the steered wheels 5 is provided.
[0014]
The operation angle sensor 11, the torque sensor 12, and the turning angle sensor 13 are connected to a control device 14 as a control unit having a configuration including a microcomputer. The control device 14 is further connected to a vehicle speed sensor 15 for detecting a vehicle speed and a fog light switch 16 as visibility detection means.
The control device 14 generates an appropriate reaction force in the direction opposite to the operation direction of the steering member 2 based on the detected operation angle, the operation torque detected by the torque sensor 12, and the vehicle speed detected by the vehicle speed sensor 15. Then, the reaction force actuator 9 is controlled via the drive circuit 18.
[0015]
The control device 14 uses a normal map A (shown by a solid line in FIG. 2) and a normal map A as a vehicle speed-steering ratio data map for determining the steering ratio from the vehicle speed, as shown in FIG. A map B (shown by a broken line in FIG. 2) in which the steering ratio is lower than that of the map A and a map C (shown by a dashed line in FIG. 2) in which the steering ratio is higher than that of the normal map A are selectively used. The steering ratio is determined.
That is, the control device 14 detects the vehicle speed based on the vehicle speed (hereinafter, referred to as “detected vehicle speed”) detected by the vehicle speed sensor 15 as the traveling state detection sensor and on / off of the fog light switch 16 as the visibility detecting means. A preferable turning ratio map is selected according to the visibility, and a turning ratio according to the vehicle speed is set using the selected map.
[0016]
As described above, in the present embodiment, the turning ratio variable means for changing the ratio of the turning amount of the turning wheels 5 to the operation amount of the steering member 1 (turning ratio) is controlled by the execution program of the control device 14. Achieved softly.
On the other hand, an operation angle detected by the operation angle sensor 11 (hereinafter, referred to as “detected operation angle”) and a steering angle detected by the steering angle sensor 13 (hereinafter, referred to as “detected steering angle”) are input, The target steering angle is obtained from the detected operation angle and the set steering ratio, and the steering actuator 2 is feedback-controlled via the drive circuit 19 so that the detected steering angle approaches the target steering angle.
[0017]
FIG. 3 is a flowchart for explaining a routine process for determining a turning ratio, which is executed by the control device 14. Referring to FIG. 3, when fog light switch 16 is operated to be turned off, it is determined that visibility is good (NO in step S <b> 1), and turning ratio according to vehicle speed is determined using normal map A. Set (step S2).
On the other hand, when the fog lamp switch 16 is turned on, it is determined that the visibility is poor (YES in step S1). When it is determined that the visibility is poor, the turning ratio is set using the map A, B or C selected according to the vehicle speed.
[0018]
Specifically, when the vehicle is traveling at a low speed, that is, when the detected vehicle speed V is as low as less than a predetermined speed V1 (V <V1: V1 is, for example, 20 km) (YES in step S3), a steering ratio characteristic lower than that of the normal map A is obtained. The turning ratio is set using the map B that is provided (step S4).
When the vehicle is running at medium speed, that is, when the detected vehicle speed V is equal to or higher than the predetermined speed V1 and equal to or lower than the predetermined speed V2 (V1 ≦ V ≦ V2: V2 is, for example, 60 km / h) (YES in step S5), the normal map A is displayed. The turning ratio is set by using (Step S6).
[0019]
When the vehicle is traveling at high speed, that is, when the detected vehicle speed V exceeds the predetermined speed V2 (V2 <V) (NO in step S5), the turning ratio is determined using a map C having a turning ratio characteristic higher than that of the normal map A. It is set (step S7).
As described above, according to the present embodiment, a normal steering ratio is set when the vehicle is traveling at medium speed with poor visibility or when visibility is good.
Also, when visibility is poor and only a short distance field of view can be obtained, and when traveling at low speed, the steering ratio is set to the small side and quick steering is achieved, enabling quick obstacle avoidance. I do. Thus, even when the steering is quick, there is no possibility that the behavior of the vehicle becomes unstable during low-speed running.
[0020]
In addition, when the vehicle is traveling at high speed although visibility is low, the steering ratio is set to a large value, and the steering is dullly achieved, thereby ensuring the steering stability of the vehicle during high speed traveling.
4 to 6 show another embodiment of the present invention.
Referring to FIG. 4, the present embodiment is different from the embodiment of FIG. 1 in that a wiper switch 17 as road surface state detecting means is provided to control device 14 instead of fog lamp switch 16 as visibility detecting means. The point is that the controller 14 detects a road surface failure when the wiper switch 17 is turned on while being connected.
[0021]
As shown in FIG. 5, the control device 14 uses a normal map A (shown by a solid line in FIG. 5) and a normal map A as a vehicle speed-steering ratio data map for determining the steering ratio from the vehicle speed. A map D (shown by a dashed-dotted line in FIG. 5) in which the steering ratio is made higher than this and a map E (shown by a broken line in FIG. 5) in which the steering ratio is made even higher than this map D are selectively used. Thus, the steering ratio is determined.
FIG. 6 is a flowchart for explaining a routine process for determining a turning ratio, which is executed by the control device 14. Referring to FIG. 6, when wiper switch 17 is operated to be turned off, it is determined that the road surface condition is good (NO in step T1), and turning according to detected vehicle speed V is performed using normal map A. The ratio is set (step T2).
[0022]
On the other hand, when the wiper switch 17 is turned on, it is determined that the road surface condition is bad due to rain (YES in step T1).
Thus, even when it is determined that the road surface condition is bad, when the vehicle is running at low speed, that is, when the detected vehicle speed V is lower than the predetermined speed V1 (V <V1: V1 is, for example, 20 km) (YES in step T3), the vehicle is normally operated. A turning ratio is set using map A (step ST2).
[0023]
When it is determined that the road surface condition is bad and when the vehicle is traveling at medium speed, that is, when the detected vehicle speed V is equal to or higher than the predetermined speed V1 and equal to or lower than the predetermined speed V2 (V1 ≦ V ≦ V2: V2 is, for example, 60 km / h) (step T3) (NO in step T4 and YES in step T4), the turning ratio is set using a map D having a turning ratio characteristic higher than that of the normal map A (step T5).
When it is determined that the road surface condition is bad and when the vehicle is traveling at high speed, that is, when the detected vehicle speed V exceeds the predetermined speed V2 (V2 <V) (NO in step T3 and NO in step S4), map D The turning ratio is set using a map E having a still higher turning ratio characteristic (step T6).
[0024]
According to the present embodiment, when the vehicle is traveling at a low speed although the road surface condition is poor, or when the road surface condition is good, the normal steering ratio is set.
Further, when the road surface condition is poor and the vehicle is traveling at a medium speed, the steering ratio is set to the large side, and the steering stability of the vehicle is ensured by achieving the dull steering. Also, when the road surface condition is poor and the vehicle is traveling at high speed, the steering ratio is set to a larger value to achieve more durable steering, thereby ensuring the steering stability of the vehicle at high speed traveling.
[0025]
7 and 8 show still another embodiment of the present invention. Referring to FIG. 7, the present embodiment is different from the embodiments of FIGS. 1 and 4 in that both a fog lamp switch 16 as visibility detecting means and a wiper switch 17 as road surface state detecting means are controlled by a control device. 14, and a mode selection switch 20 for selecting between the visibility emphasis mode and the road surface state emphasis mode is connected to the control device 14.
[0026]
Referring to FIG. 8, in the present embodiment, the mode selected by the driver (driver) is read (step P1), and if the visibility-oriented mode is selected (YES in step P2), The mode is placed in the visibility-oriented mode (step P3). If the road surface-oriented mode is selected (NO in step P2), the road state-oriented mode is entered (step P4).
In the visibility-oriented mode, the turning ratio is set based on the visibility and the vehicle speed in a flow similar to the flow shown in FIG. In the road surface state emphasis mode, the turning ratio is set based on the road surface state and the vehicle speed in a flow similar to the flow shown in FIG.
[0027]
Next, FIG. 9 shows still another embodiment of the present invention. Referring to FIG. 9, the present embodiment is different from the embodiment of FIG. 3 in that maps A, B, A and C are provided in steps S2, S4, S6 and S7 in FIG. The steering ratio is determined based on the calculation formulas K1 (V), K2 (V), K1 (V) and K3 (V) in steps S2, S4, S6 and S7, respectively. This is to determine the steering ratio. In this embodiment, the same operation and effect as those of the embodiment of FIG. 3 can be obtained. In the embodiments of FIGS. 6 and 8, similarly, an arithmetic expression may be used instead of the map.
[0028]
Next, FIG. 10 shows still another embodiment of the present invention. This embodiment is different from the embodiment of FIG. 9 in that a plurality of arithmetic expressions K1 (V), K2 (V) and K3 (V) are used in the embodiment of FIG. The aspect is that the calculation is performed using only the normal calculation formula K1 (V) corresponding to the case where the visibility is good.
Referring to FIG. 10, when fog light switch 16 is operated to be turned off, it is determined that visibility is good (NO in step R1), and the detected vehicle speed is reduced using a normal calculation formula K1 (V). A corresponding turning ratio is set (step R2).
[0029]
On the other hand, when the fog lamp switch 16 is turned on, it is determined that visibility is poor (YES in step R1).
As described above, when the visibility is determined to be poor and the vehicle is traveling at low speed, that is, when the detected vehicle speed V is lower than the predetermined speed V1 (V <V1: V1 is, for example, 20 km) (YES in step R3), the detected vehicle speed V is set to V After / G (G is a preset constant) (step R4), the steering ratio according to the detected vehicle speed is set using the normal arithmetic expression K1 (V) (step R2).
[0030]
Also, when it is determined that the visibility is poor and the vehicle is traveling at medium speed, that is, when the detected vehicle speed V is equal to or higher than the predetermined speed V1 and equal to or lower than the predetermined speed V2 (V1 ≦ V ≦ V2: V2 is, for example, 60 km / h) (step R5) YES), a turning ratio corresponding to the detected vehicle speed is set using the normal arithmetic expression K1 (V) (step R2).
When it is determined that visibility is low and the vehicle is traveling at high speed, that is, when the detected vehicle speed V is V2 <V (NO in step R5), the detected vehicle speed V is set to V · H (H is a preset constant). ) (Step R6), the steering ratio according to the detected vehicle speed is set using the normal arithmetic expression K1 (V) (step R2).
[0031]
According to the present embodiment, since only one arithmetic expression needs to be stored, the structure of the control device 14 can be simplified. 9 and 10 can be applied to the embodiments shown in FIGS. 6 and 8.
The present invention is not limited to the above embodiments. For example, in each of the above embodiments, the turning ratio variable means is achieved in a software manner by the execution program of the control device 14. However, the present invention is not limited to this, and the planetary gear mechanism and other differences between the steering member 1 and the turning wheels 5 are provided. A steering transmission system for mechanical connection including a dynamic transmission mechanism may be interposed, and the steering ratio variable means may be configured as hardware by this differential transmission mechanism. In this case, for example, the turning ratio can be changed by controlling the rotation or stop of one element of the differential transmission mechanism by the electric motor.
[0032]
As the road surface condition detecting means, a raindrop sensor and road facility (infrastructure) side information can be used in addition to the wiper switch 17. In addition to the fog light switch 16, road facility (infrastructure) side information or image processing information of a vehicle-mounted camera can be used as the visibility detection means. In addition, various changes can be made within the scope of the claims of the present invention.
[Brief description of the drawings]
FIG. 1 is a schematic diagram showing a schematic configuration of a vehicle steering system according to an embodiment of the present invention.
FIG. 2 is a graph showing a vehicle speed-steering ratio map in the vehicle steering system shown in FIG. 1;
FIG. 3 is a flowchart illustrating a steering ratio setting process of the vehicle steering system in FIG. 1;
FIG. 4 is a schematic diagram showing a schematic configuration of a vehicle steering system according to another embodiment of the present invention.
5 is a graph showing a vehicle speed-steering ratio map in the vehicle steering system shown in FIG. 4;
FIG. 6 is a flowchart illustrating a steering ratio setting process of the vehicle steering system in FIG. 4;
FIG. 7 is a schematic diagram showing a schematic configuration of a vehicle steering system according to still another embodiment of the present invention.
FIG. 8 is a flowchart of mode selection in the vehicle steering system of FIG. 7;
FIG. 9 is a flowchart showing a steering ratio setting process according to still another embodiment of the present invention.
FIG. 10 is a flowchart showing a steering ratio setting process according to still another embodiment of the present invention.
[Explanation of symbols]
REFERENCE SIGNS LIST 1 steering member 2 steering actuator 4 steering shaft 5 steered wheel 8 steering shaft 9 reaction force actuator 11 operating angle sensor 12 torque sensor 13 steering angle sensor 14 control device (control unit)
15 Vehicle speed sensor 16 Fog light switch (visibility detection means. Road condition detection means)
17 Wiper switch (road surface condition detecting means; road condition detecting means)
A to E map (data map)
V detected vehicle speed (detected vehicle speed)
K1 (V), K2 (V), K3 (V) Formula

Claims (5)

In a vehicle steering device including a steering mechanism that steers a steered wheel according to steering of a steering member,
Turning ratio variable means for changing the ratio of the turning amount of the steered wheels to the operation amount of the steering member,
Road condition detecting means for detecting a road condition in front of the vehicle;
Traveling state detection means for detecting a traveling state of the vehicle including at least the vehicle speed,
A steering unit for changing a steering ratio by a steering ratio variable unit based on signals from the road condition detection unit and the traveling state detection unit. 2. The vehicle steering system according to claim 1, wherein the control unit includes a data map for determining a steering ratio based on the detected vehicle speed, when the road condition is bad and when the road condition is good. 2. The vehicle steering system according to claim 1, wherein the control unit includes an arithmetic expression for determining a steering ratio based on the detected vehicle speed when the road condition is poor and good. The road condition detecting means according to claim 1, 2 or 3, wherein the road condition detecting means detects visibility of a road ahead of the vehicle, and a road surface condition for detecting a road surface state of a road ahead of the vehicle. Detecting means,
Based on the visibility-oriented mode for changing the turning ratio by the turning ratio variable means based on the signals from the visibility detecting means and the running state detecting means, and based on the signals from the road surface state detecting means and the running state detecting means. A mode selection unit that can select one of road surface condition emphasis modes for changing the steering ratio by the steering ratio variable unit,
The control unit changes the steering ratio based on the mode selected by the mode selection unit. 5. The method according to claim 1, wherein when a road condition detected by the road condition detecting means is bad, a predetermined process is applied to a vehicle speed signal detected by the running condition detecting means and the result is given to a control unit. A vehicle steering system characterized by the above-mentioned.

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