JP7180867B2 - vehicle steering system - Google Patents

Description

The present invention relates to a vehicle steering system.

Conventionally, in a steer-by-wire system in which a steering mechanism and a steering mechanism are mechanically separated, there is known a device for preventing collision with a rack end at the steering limit. For example, in the vehicle steering control device disclosed in Patent Document 1, an angle near the maximum steering angle, which is the limit steering angle at which the steered wheels can be steered, is set as the upper limit angle, and the steering command angle calculated value is the upper limit angle. When the limit start angle smaller than is exceeded, the rate of change of the steering command angle calculated value is limited.

JP 2014-133521 A

In the prior art disclosed in Patent Document 1, the rate of change in the actual steering angle is moderated near the rack end to prevent the actual steering angle from reaching the rack end angle. However, as a result of limiting the steering angle, the relationship between the steering angle and the steering angle changes, and when the steering angle returns to the neutral side, the relationship between the steering angle and the steering angle does not return to the normal state. There is a risk.

SUMMARY OF THE INVENTION The present invention has been made in view of the above problems, and an object of the present invention is to provide a steer-by-wire system in which the upper limit of the steering angle is appropriately limited while maintaining the relationship between the steering angle and the steering angle. The object of the present invention is to provide a steering system for a vehicle.

The present invention is a vehicle steering apparatus of a steer-by-wire system in which a steering mechanism and a steering mechanism are mechanically separated and electrically connected, and detects a vehicle state including a vehicle speed (V). Applies to vehicles equipped with a detection device (50). This vehicle steering system includes a steering angle sensor (22), a steering angle sensor (42), a steering actuator (43), a steering actuator (23), and a controller (30).

A steering angle sensor detects a steering angle (θs) of a steering wheel (21). The steering angle sensor detects the steering angle (θt) of the steerable wheels (48). The steering actuator is controlled to generate a steering angle corresponding to the steering angle. The steering actuator is mechanically connected to the steered wheels and is controlled according to the steering angle so as to apply reaction torque in the direction opposite to the steering direction to the steered wheels. The control unit controls driving of the steering actuator and the steering actuator. When the steering angle reaches a predetermined limit angle (θ LIM ) during steering, the control unit controls the steering actuator so that the steering angle does not exceed the limit angle, and the absolute value of the _reaction torque is increased to control the steering actuator to impede steering by the driver.

According to the vehicle speed detected by the vehicle state detection device, the control unit keeps the limit angle constant in a region where the vehicle speed is equal to or lower than a predetermined speed (V1), and when the vehicle speed exceeds the predetermined speed, the vehicle speed increases. The limit angle is changed so that the limit angle decreases accordingly.

The vehicle steering system of the present invention controls the steering actuator to limit the steering angle, and controls the steering actuator to limit the steering angle. Therefore, this vehicle steering system can appropriately limit the upper limit of the steering angle while maintaining the relationship between the steering angle and the steering angle.

1 is a block diagram of a vehicle steering system according to one embodiment; FIG. 4 is a time chart of steering angle limiting processing according to one embodiment; 4 is a time chart showing processing for changing the limit angle according to the vehicle state; A map that defines the relationship between vehicle speed and limit angle. 4 is a flowchart of steering angle limiting processing according to one embodiment;

(one embodiment)
An embodiment of a vehicle steering system will be described below with reference to the drawings. The vehicle steering system of this embodiment is applied to a steer-by-wire system in which a steering mechanism and a steering mechanism are mechanically separated and electrically connected. First, referring to FIG. 1, the configuration of a vehicle steering system according to one embodiment will be described. The vehicle steering system 10 includes a steering angle sensor 22, a steering actuator 23, a control section 30, a steering angle sensor 42, a steering actuator 43, and the like.

Solid lines between blocks in FIG. 1 indicate mechanical connections, and dashed lines indicate electrical connections. A steering angle sensor 22 and a steering actuator 23 are mechanically connected to a steering wheel (steer) 21 and constitute a steering mechanism 20 . The steering angle sensor 42 and the steering actuator 43 are mechanically connected to a steered wheel (tire) 48 via a rack shaft 47 to constitute a steering mechanism 40 . The steering mechanism 20 and the steering mechanism 40 are electrically connected via the controller 30 . Accordingly, the steered wheels 21 are electrically connected to the steered wheels 48 via the controller 30 .

The steering angle sensor 22 detects the steering angle θs of the steered wheels 21 and outputs it to the controller 30 . The steering angle sensor 42 detects a steering angle θt of the steered wheels 48 and outputs the detected steering angle θt to the control unit 30 . The steering actuator 43 is controlled to generate a steering angle θt corresponding to the steering angle θs. The steering actuator 23 is controlled to apply a reaction torque Tr in a direction opposite to the steering direction to the steered wheels 21 according to the steering angle θs. The control unit 30 controls driving of the steering actuator 43 and the steering actuator 23 .

A vehicle in which the present embodiment is installed is equipped with a steering angle limiting device 46 , a vehicle state detection device 50 and an alarm device 60 . The turning angle limiting device 46 is provided at a position such as (a) or (b), for example, and is a stopper that mechanically limits the absolute value of the turning angle θt to a predetermined upper limit angle _{θMECH_LIM} or less.

The vehicle state detection device 50 detects vehicle states such as vehicle speed and acceleration. The control unit 30 acquires vehicle state information detected by the vehicle state detection device 50 . The alarm device 60 includes an indicator lamp and a buzzer provided on the instrument panel, vibration elements arranged on the steering wheel 21, and the like, and outputs an alarm according to a command from the control unit 30. FIG.

Next, before explaining the effects of this embodiment, the background of the technology for limiting the steering limit in the steer-by-wire system will be explained. In an electric power steering system (hereafter referred to as "EPS"), which is a typical conventional vehicle steering system, a steering wheel (steer) and a steerable wheel (tire) are mechanically connected to assist the driver's steering. Actuator is installed. On the other hand, in recent years, mass production of steer-by-wire systems, in which the steered wheels are mechanically separated from the steerable wheels and electrically connected, has begun, and in the future, the number will increase along with the commercialization of autonomous driving and the electrification of vehicles. it is conceivable that.

One of the problems with vehicle steering systems is "ensuring mechanical strength against collisions at the steering limit (for example, rack end)". That is, since there is a structural limit to the amount of steering of the steerable wheels, a limiting device (stopper) is required to stop the steering when the limit is approached during steering. Since this restriction device is expected to be subjected to many strong impacts, it is generally designed with high strength in consideration of material, weight and size. In the case of EPS, a larger force is applied due to the assist torque of the actuator.

Therefore, in EPS, as disclosed in Japanese Patent No. 2826687 and Japanese Patent Application Laid-Open No. 2006-160076, the actuator is driven in the direction opposite to the steering as the steering limit approaches, thereby reducing the load on the limiter. is being developed. However, since this technology generates a force in the direction opposite to the steering direction, the steered wheels tend to return to the center direction against the driver's intention due to disturbances such as unevenness such as falling objects and ruts on the road.

On the other hand, in the steer-by-wire system in which the steered wheels and the steered wheels are electrically connected, the ratio between the steering angle and the steered angle and the ratio between the steering force and the steered force can be freely changed. Taking advantage of this feature, the load on the mechanical stopper can be reduced by electrically controlling the steering actuator so that it is not steered any further when the steering angle approaches the steering limit. it is conceivable that.

By the way, in the conventional technology of Patent Document 1 (Japanese Patent Application Laid-Open No. 2014-133521), in the steer-by-wire system, the change speed of the actual steering angle is slowed near the rack end, and the actual steering angle reaches the rack end angle. to prevent However, as a result of limiting the steering angle, the relationship between the steering angle and the steering angle changes, and when the steering angle returns to the neutral side, the relationship between the steering angle and the steering angle does not return to the normal state. There is a risk.

Therefore, the vehicle steering system 10 of the present embodiment aims to appropriately limit the upper limit of the steering angle without affecting the relationship between the steering angle and the steering angle in a steer-by-wire system. Therefore, the control unit 30 controls the steering actuator ₄₃ so that the steering angle θt does not exceed the limit angle _θLIM when the steering angle θt reaches a predetermined limit angle θLIM during steering. In addition, the control unit 30 controls the steering actuator 23 so as to increase the absolute value of the reaction torque Tr to prevent the driver from steering.

Next, a specific example of processing for limiting the turning angle θt to the limit angle _θLIM or less will be described with reference to the time chart of FIG. The horizontal axis in FIG. 2 is the time axis, and the vertical axis shows changes in the steering angle θs, the turning angle θt, the reaction torque Tr, and the warning device flag. Also, the symbols (*1) and (*2) denote locations cited in the description.

Here, the steering angle θs and the turning angle θt take positive and negative values depending on the direction of rotation of the steered wheels 21 or 48 . The steering torque that acts to increase the steering angle θs in the positive direction is defined as positive, and the steering torque that acts to increase the steering angle θs in the negative direction is defined as negative. However, since the positive and negative characteristics are basically symmetrical, FIG. 2 shows only the case where the steering angle θs and the turning angle θt are positive. At this time, the reaction torque Tr is generated in the negative direction.

Before the time ts, the vehicle is traveling straight, and the steered wheels 21 and the steered wheels 48 are in the neutral position. When the driver starts steering at time ts, the steering angle θs detected by the steering angle sensor 22 gradually increases. Then, the steering actuator 43 is controlled to generate the steering angle θt at a constant ratio to the steering angle θs, and the steering angle θt increases.

Further, the absolute value of the reaction torque Tr increases due to the driving of the steering actuator 23 as the steering angle θs increases. In the steer-by-wire system, the driver cannot directly sense the reaction force to the steering. To give an appropriate steering feeling.

The absolute value of the limit angle θ _LIM of the turning angle θt is preset to be smaller than the absolute value of the upper limit angle θ _{MECH_LIM} of the turning angle limiting device 46 . When the steering angle θt reaches the limit angle _θLIM at time te, the control unit 30 changes the angle ratio characteristic of the steering angle θt to the steering angle θs. The control unit 30 controls the steering actuator 43 so that the steering angle θt is fixed at the limit angle _θLIM and also controls the steering actuator 23 so as to increase the absolute value of the reaction torque Tr.

At this time, the reaction torque Tr abruptly changes from Tre to Trx as indicated by the block arrow (*1). Since the value of Trx is set to a value that hinders steering so that the driver cannot steer the vehicle any further, the steering angle θs is fixed at the value θsx at time te (*2). This value θsx is hereinafter referred to as a fixed angle. As a result, the steering angle θt and the steering angle θs after the time te are maintained at constant values at the limit angle _θLIM and the fixed angle θsx, respectively. That is, the relationship between the steering angle θs and the steering angle θt is maintained.

When the steering angle θs is fixed, the driver can intuitively feel that the steering limit has been reached from the feeling of gripping the steered wheels 21 . This feeling is similar to EPS. Furthermore, at the time te when the _steering angle θt reaches the limit angle θ _LIM , the alarm device flag turns from OFF to ON. to notify the driver. Therefore, the driver can reliably perceive that the steering limit has been reached by sight, hearing, or the like.

Next, with reference to FIGS. 3 and 4, a configuration for changing the limit angle _.theta.LIM according to the vehicle state will be described. Symbols (*3) and (*4) in FIG. 3 denote portions cited in the description. The limit angle θ _LIM of the turning angle θt is not only due to the structural limit of the vehicle, but also depending on the vehicle state and road surface conditions. be done.

The "vehicle state" includes vehicle speed, rapid acceleration or sudden stop state based on acceleration, climbing or descending state, shift position, and the like. The "road surface condition" includes the friction coefficient (μ) of the road surface and the like. It should be noted that the "state of the road on which the vehicle is running" may be broadly included in the "state of the vehicle." In this embodiment, it is assumed that the vehicle state detection device 50 can detect the operating state of the vehicle itself and also detect the condition of the road surface on which the vehicle is traveling.

Therefore, as shown in FIG. 3, when the vehicle state acquired from the vehicle state detection device 50 changes from the previous vehicle state, the control unit 30 changes the limit angle from the pre-change value θ _LIM1 (dashed line) to the post-change value θ LIM1 . Change the value θ _LIM2 (solid line). For example, the limit angle θ _LIM is changed to be smaller when the vehicle shifts from low-speed driving to high-speed driving, or when rain or snow begins to fall and the road surface changes from a dry state to a wet or frozen state. (*3).

FIG. 4 shows an example of a map that defines the relationship between the vehicle speed V and the limit angle θ _LIM . The limit angle θ _LIM is constant in the region where the vehicle speed V is equal to or lower than the speed V1, and when the vehicle speed V exceeds the speed V1, the limit angle θ _LIM decreases as the vehicle speed V increases.

Returning to FIG. 3, when the limit angle is changed from _θLIM1 to _θLIM2 , the timing at which the turning angle θt reaches the limit angle _θLIM is advanced from time te1 to time te2. As a result, the timing of increasing the absolute value of the reaction torque Tr is advanced, and the fixed angle θsx of the steering angle θs is reduced from θsx1 to θsx2 (*4). That is, the fixed angle θsx of the steering angle θs also changes following the change in the limit angle _θLIM .

Next, the turning angle limiting process according to this embodiment will be described with reference to the flowchart of FIG. The symbol "S" in the flow chart means step. The control unit 30 acquires vehicle state information detected by the vehicle state detection device 50 in S1, and sets a limit angle θ _LIM of the turning angle θt in accordance with the vehicle state in S2.

In S3, it is determined whether or not the absolute value |θs| of the steering angle is greater than or equal to the threshold value θs_th. If the absolute value |θs| of the steering angle is less than the threshold value θs_th and the result in S3 is NO, the process returns to before S1. If the absolute value |θs| of the steering angle is greater than or equal to the threshold value θs_th and S3 is YES, the process proceeds to S4. The threshold θs_th is a value obtained by converting the limit angle _θLIM of the steering angle θt by the angle ratio between the steering angle θs and the steering angle θt, and can be replaced with the fixed angle θsx in FIGS.

The control unit 30 changes the characteristic of the steering angle θt with respect to the steering angle θs in S4, and increases the steering torque Ts in the reaction force direction in S5. Further, in S6, the control unit 30 notifies the driver via the warning device 60 that the turning angle θt has reached the limit angle _θLIM .

In S7, it is determined again whether the absolute value |θs| of the steering angle is greater than or equal to the threshold value θs_th. If NO in S7, it means that the restricted state has been temporarily removed. In this case, the process returns to before S1, and the limit angle θ _LIM is set again based on the vehicle state at that time. If YES in S7, the process returns to before S4 to continue the restricted state. This routine is repeated until, for example, the ignition switch is turned off.

(effect)
(1) In the steer-by-wire system in which the steering mechanism and the steering mechanism are mechanically separated and electrically connected, the steering angle θt reaches the limit angle θ _LIM . When this occurs, the steering actuator 43 is controlled so as not to steer any further. Therefore, compared with the technology that generates a force in the direction opposite to the steering direction near the steering limit, it is possible to prevent the steering angle from changing against the driver's intention due to disturbance.

Further, when the steering angle θt reaches the limit angle θ _LIM , the control unit 30 increases the absolute value of the reaction torque Tr in the direction opposite to the steering direction to control the steering actuator 23 so as to prevent the driver from steering. do. As a result, the steering limit can be intuitively communicated to the driver. In addition, in contrast to the technique of Patent Document 1 (Japanese Patent Application Laid-Open No. 2014-133521) that controls only the steering actuator, the upper limit of the steering angle θt is set appropriately while maintaining the relationship between the steering angle θs and the steering angle θt. can be limited to

(2) The mechanical steering angle limiter 46 is preferably provided as a backup in the event that the steering actuator 43 is steered by a disturbance greater than the torque generated by the steering actuator 43 . Here, the absolute value of the limit angle θ _LIM of the turning angle θt is set smaller than the absolute value of the upper limit angle θ _{MECH_LIM} of the turning angle limiting device 46 . As a result, since the electrical restriction by the steering actuator 43 is applied before the mechanical steering restriction, the steering angle limiter 46 is not collided with, or the impact is considerably reduced even if it collides. do. Therefore, fatigue of the turning angle limiting device 46 can be suppressed, and the mechanical requirement specifications regarding strength and fatigue can be relaxed.

(3) Based on the vehicle state and road surface conditions, the control unit 30 changes the limit angle θ _LIM to a smaller value when the vehicle is traveling at high speeds or on wet or icy roads, for example. In this manner, when the vehicle is likely to slip, the limit angle θ _LIM is reduced to prevent further turning, thereby promoting stable vehicle driving.

(4) Further, the control unit 30 notifies the driver that the steering angle θt has reached the limit angle _θLIM by means of an alarm device 60 such as an indicator lamp, a buzzer, or a vibrating element. Therefore, the driver can reliably perceive that the steering limit has been reached by sight, hearing, etc., in addition to the feeling of the hand gripping the steering wheel 21 .

(Other embodiments)
The vehicle steering system 10 of the present invention may be applied to a vehicle that does not have the mechanical steering angle limiting device 46, the vehicle state detection device 50, or the warning device 60. FIG. Unless an exceptionally large disturbance occurs, the mechanical steering angle limiter 46 may be omitted. For example, instead of the vehicle state detection device 50, the driver may manually switch the limit angle θ _LIM when driving in rain or snow.

The present invention is not limited to such embodiments, and can be embodied in various forms without departing from the scope of the invention.

10... vehicle steering device,
21... steering wheel, 22... steering angle sensor, 23... steering actuator,
30 ... control unit,
42... Steering angle sensor, 43... Steering actuator, 48... Steering wheel.

Claims (4)

A steer-by-wire system vehicle steering apparatus in which a steering mechanism and a steering mechanism are mechanically separated and electrically connected , and is a vehicle state detection device (50) for detecting a vehicle state including a vehicle speed (V). ), and
a steering angle sensor (22) for detecting a steering angle (θs) of a steering wheel (21);
a turning angle sensor (42) for detecting a turning angle (θt) of a turning wheel (48);
a steering actuator (43) controlled to generate a steering angle corresponding to the steering angle;
a steering actuator (23) mechanically connected to the steered wheels and controlled to apply reaction torque in a direction opposite to the steering direction to the steered wheels according to a steering angle;
a control unit (30) for controlling driving of the steering actuator and the steering actuator;
with
When the turning angle reaches a predetermined limit angle (θ _LIM ) during steering,
The control unit controls the steering actuator so that the steering angle does not exceed the limit angle and increases the absolute value of the reaction torque to prevent the driver from steering. death,
The control unit, according to the vehicle speed detected by the vehicle state detection device,
When the vehicle speed exceeds the predetermined speed, the limit angle is changed so that the limit angle decreases as the vehicle speed increases. vehicle steering system. The vehicle state detection device is capable of further detecting the condition of the road surface on which the vehicle is running,
2. The vehicle steering system according to claim 1, wherein the control unit changes the limit angle according to road conditions detected by the vehicle condition detection device. Applied to a vehicle equipped with a steering angle limiting device (46) for mechanically limiting the absolute value of the steering angle to a predetermined upper limit angle (θ _{MECH_LIM} ) or less,
3. The vehicle steering system according to claim 1, wherein the absolute value of the limit angle is set smaller than the absolute value of the upper limit angle of the steering angle limiter. When the steering angle reaches the limit angle,
The vehicle steering system according to any one of claims 1 to 3, wherein the controller notifies the driver that the steering angle has reached the limit angle by means of an alarm device (60).

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