Vehicle steering system

Abstract

A steering device for a vehicle capable of suppressing a sense of discomfort felt by a driver when the driver performs a quick steering operation. The steering device for a vehicle includes a steering mechanism that is mechanically separated from a steering member and steers wheels by moving a rack, a steering actuator that applies a driving force to the steering mechanism, and a control device that calculates a target position of the rack and controls the steering actuator to match the position of the rack with the target position of the rack, and the control device is configured to be able to execute target position correction control that corrects the target position of the rack in response to the steering angular velocity and / or steering angular acceleration of the steering member. [Representative diagram] Figure 2

Description

[Technical field]

[0001] The present invention relates to a steering device for a vehicle. [Background technology]

[0002] 2. Description of the Related Art Steer-by-wire steering devices are known that include a steering member that receives a steering operation and a steering mechanism that is mechanically separated from the steering member and steers the wheels by moving a rack.

[0003] For example, Patent Document 1 discloses a vehicle steering device that includes a steering mechanism that changes the direction of steered wheels, and a steering means that is supported by a stationary member without being mechanically connected to the steering mechanism. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] JP 2002-225733 A Summary of the Invention [Problem to be solved by the invention]

[0005] In a steering device in which the steering member and the steering mechanism are mechanically connected, the torque generated by the steering operation is transmitted to the rack of the steering mechanism via the shaft of the steering member. At that time, the shaft of the steering member is twisted, causing a delay in the displacement of the rack relative to the steering operation. In contrast, in a steer-by-wire steering device, the torque generated by the steering operation is transmitted to the rack of the steering mechanism by an electric signal. Therefore, compared to a steering device in which the steering member and the steering mechanism are mechanically connected, the displacement of the rack is less likely to be delayed relative to the steering operation.

[0006] However, if the responsiveness of the rack displacement to the steering operation is too high, when the driver performs a quick steering operation, the wheels may be rapidly steered immediately after the steering operation, which may cause the driver to feel uncomfortable.

[0007] In view of the above background, an object of the present invention is to provide a steering device for a vehicle that can suppress the sense of discomfort felt by the driver when the driver performs a quick steering operation. [Means for solving the problem]

[0008] In order to solve the above problem, one aspect of the present invention is a steering device (1) for a vehicle (2), comprising: a steering member (10) that receives a steering operation; a steering angle sensor (32) that detects a steering angle of the steering member; a steering mechanism (11) that is mechanically separated from the steering member and steers wheels (3) by moving a rack (26); a steering actuator (12) that applies a driving force to the steering mechanism; a rack position sensor (33) that detects a position of the rack; and a control device (15) that calculates a target position of the rack based on the steering angle of the steering member and controls the steering actuator to match the position of the rack detected by the rack position sensor with the target position of the rack, and the control device may be capable of executing target position correction control that corrects the target position of the rack in accordance with the steering angular velocity and / or steering angular acceleration of the steering member in order to delay displacement of the rack in accordance with a change in the steering angle of the steering member.

[0009] According to this aspect, when the steering angular velocity and / or steering angular acceleration of the steering member increases due to a quick steering operation by the driver, the target position of the rack can be corrected and the displacement of the rack according to the change in the steering angle of the steering member can be delayed. Accordingly, the wheels can be prevented from being rapidly steered immediately after the quick steering operation, and therefore the discomfort felt by the driver can be suppressed.

[0010] In the above aspect, in the target position correction control, the control device may correct the target position of the rack immediately after the start of the steering operation in a predetermined direction.

[0011] In general, immediately after the start of a steering operation in a predetermined direction, there is a high possibility that the steering angular velocity and steering angular acceleration of the steering member will increase. By taking such a possibility into consideration and correcting the target position of the rack immediately after the start of a steering operation in a predetermined direction, it becomes easier to prevent the wheels from being rapidly steered immediately after a quick steering operation, and it is possible to effectively suppress the discomfort felt by the driver.

[0012] In the above aspect, the steering operation includes a turning operation, which is an operation in a direction away from a predetermined neutral position, and a return operation, which is an operation in a direction toward the neutral position, and in the target position correction control, the control device may correct the target position of the rack immediately after the start of the return operation.

[0013] In general, when performing a return steering operation, the driver is more likely to become inattentive than when performing a forward steering operation, and therefore there is a high possibility that the steering angular velocity and steering angular acceleration of the steering member will increase excessively. By taking such a possibility into consideration and correcting the target position of the rack immediately after the start of a return steering operation, it is possible to prevent the wheels from being rapidly steered immediately after an excessively quick steering operation, and effectively suppress the discomfort felt by the driver.

[0014] In the above aspect, in the target position correction control, the control device may prohibit correction of the target position of the rack when the cutting operation is being performed.

[0015] In general, when a steering operation is performed, the driver is more attentive and the steering angular velocity and steering angular acceleration of the steering member are less likely to increase excessively than when a steering return operation is performed. Therefore, by prohibiting correction of the target position of the rack when a steering operation is performed, it is possible to suppress an unnecessary decrease in the responsiveness of the rack displacement to the steering operation.

[0016] In the above aspect, in the target position correction control, the control device may calculate the target position of the rack in accordance with the steering angle of the steering member, calculate a correction amount for the target position of the rack in accordance with the steering angular acceleration of the steering member, and correct the target position of the rack by adding the correction amount to the target position of the rack.

[0017] According to this aspect, by calculating the correction amount according to the steering angular acceleration of the steering member, it is possible to calculate an appropriate correction amount according to a change in the steering angular velocity of the steering member.

[0018] In the above aspect, the control device may calculate the correction amount such that the correction amount increases as the steering angular acceleration of the steering member increases.

[0019] According to this aspect, the correction amount can be increased as the steering operation becomes quicker, and the delay in the rack displacement can be increased accordingly. This makes it easier to prevent the wheels from being rapidly steered immediately after a quick steering operation, and effectively reduces the discomfort felt by the driver.

[0020] In the above aspect, the control device may limit the correction amount to a predetermined upper limit value or less.

[0021] If the correction amount increases without limit, the delay in the rack displacement will become excessively large, and it may become impossible to determine whether the delay in the rack displacement is due to the target position correction control or an abnormality in the steering device. In contrast, if the correction amount is limited to an upper limit value or less, it can be easily determined that the steering device is in an abnormal state at the stage when the correction amount exceeds the upper limit value. As a result, there is no need to require excessively high reliability for the components of the steering device (sensors, etc.).

[0022] In the above aspect, the control device may set the upper limit value based on a steering direction of the steering member, the steering angle of the steering member, and a vehicle speed.

[0023] According to this aspect, the upper limit value can be set to an appropriate value depending on the running state of the vehicle.

[0024] In the above aspect, the steering member may be steered in a direction away from a predetermined neutral position or in a direction toward the neutral position, and the control device may be switchable between a non-execution mode in which the target position correction control is not executed in response to the steering operation, and an execution mode in which the target position correction control is executed in response to the steering operation.

[0025] According to this aspect, it is possible to determine whether or not to execute target position correction control for steering operation depending on the driver's preference, the vehicle running state, etc. Therefore, the convenience of the steering device is improved.

[0026] In the above aspect, the control device may always execute the target position correction control in response to the steering operation.

[0027] According to this aspect, it is possible to reliably prevent the wheels from being rapidly steered immediately after a quick steering operation, which makes it easier to prevent the driver from feeling uncomfortable. Effect of the Invention

[0028] According to the above aspect, when the driver performs a quick steering operation, the sense of discomfort felt by the driver can be suppressed. [Brief description of the drawings]

[0029] [Figure 1] FIG. 1 is a schematic diagram showing a steering device according to an embodiment of the present invention; [Diagram 2] FIG. 1 is a block diagram showing a steering control device according to an embodiment of the present invention; [Diagram 3] FIG. 4 is a schematic diagram showing a correction amount calculation map according to an embodiment of the present invention; [Figure 4] 1 is a graph showing the relationship between the steering angle and the rack position when a steering operation is performed during a non-execution mode in an embodiment of the present invention. [Diagram 5]1 is a graph showing the relationship between the steering angle and the rack position when a normal steering operation is performed during execution mode in one embodiment of the present invention. [Figure 6] 1 is a graph showing the relationship between steering angle and rack position when a quick steering operation is performed during execution mode in one embodiment of the present invention. [Figure 7] 1 is a graph showing the relationship between the steering angle and the rack position when a quicker steering operation is performed during execution mode in one embodiment of the present invention. [Figure 8] 1 is a graph showing the relationship between the steering angle and the steering angular acceleration when a turning operation is performed in one embodiment of the present invention. [Figure 9] 1 is a graph showing the relationship between the steering angle and the steering angular acceleration when a steering return operation is performed in one embodiment of the present invention. [Figure 10] FIG. 13 is a schematic diagram showing a steering system model according to another embodiment of the present invention; DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0030] Hereinafter, a steering device 1 of a vehicle 2 according to one embodiment of the present invention will be described. As shown in Fig. 1, the steering device 1 is a steer-by-wire (SBW) type steering device. The vehicle 2 on which the steering device 1 is provided is a four-wheeled automobile equipped with left and right front wheels 3 and left and right rear wheels (not shown). The left and right front wheels 3 are supported by a vehicle body 8 (only the outline of the lower part is shown in Fig. 1) via knuckles 7 so that the steering angle can be changed, and function as steered wheels. The steering angle refers to the angle of the front wheels 3 with respect to the fore-and-aft direction in a plan view. The steering device 1 changes the steering angle of the front wheels 3.

[0031] The steering device 1 has a steering member 10 rotatably provided on the vehicle body 8, a steering mechanism 11 that steers the front wheels 3, a steering actuator 12 that applies a driving force to the steering mechanism 11, a reaction force actuator 13 that applies a reaction torque to the steering member 10, and a steering control device 15 that controls the reaction force actuator 13 and the steering actuator 12. The steering device 1 may be a redundant system having a plurality of each of the steering actuators 12, the reaction force actuators 13, and the steering control devices 15.

[0032] The steering member 10 receives steering operations by the driver. The steering member 10 has a steering shaft 18 rotatably supported by the vehicle body 8, and a steering wheel 19 provided at one end of the steering shaft 18. The steering shaft 18 is rotatably supported by a steering column (not shown) provided on the vehicle body 8, and its rear end protrudes rearward from the steering column. The steering wheel 19 is coupled to the rear end of the steering shaft 18 and rotates integrally with the steering shaft 18.

[0033] The reaction force actuator 13 is an electric motor, and is connected to the steering shaft 18 via a gear. When the reaction force actuator 13 is driven, the driving force is transmitted to the steering shaft 18 as a rotational force. The reaction force actuator 13 applies torque to the steering member 10 by rotating. The torque that the reaction force actuator 13 applies to the steering member 10 in response to the steering operation is called "reaction force torque."

[0034] The steering mechanism 11 has a rack 26 extending in the vehicle width direction. The rack 26 is supported by a gear housing (not shown) so as to be movable in the vehicle width direction. The left and right ends of the rack 26 are connected to knuckles 7 that support the left and right front wheels 3, respectively, via tie rods 30. The steering angle of the front wheels 3 changes as the rack 26 moves in the vehicle width direction from a predetermined reference position (a position where the orientation of the left and right front wheels 3 is parallel to the front-rear direction: see FIG. 1). The steering mechanism 11 is mechanically separated from the steering member 10.

[0035] The steering actuator 12 is an electric motor. The steering actuator 12 moves a rack 26 in the vehicle width direction based on a signal from the steering control device 15, thereby changing the steering angle of the left and right front wheels 3.

[0036] The steering control device 15 is an ECU (Electronic Control Unit) including a CPU, a storage device, etc. The CPU controls each part of the steering device 1 based on the programs and data stored in the storage device.

[0037] The steering control device 15 is connected to a steering angle sensor 32. The steering angle sensor 32 detects the rotation angle of the steering member 10 relative to a predetermined neutral position (hereinafter referred to as "steering angle θ") and outputs it to the steering control device 15. In this embodiment, when the steering member 10 is in the neutral position, the steering angle θ is 0, and as the steering member 10 is steered to the right from the neutral position, the steering angle θ increases from 0, and as the steering member 10 is steered to the left from the neutral position, the steering angle θ decreases from 0. However, in other embodiments, the steering angle θ may increase from 0 as the steering member 10 is steered to the left from the neutral position, and the steering angle θ may decrease from 0 as the steering member 10 is steered to the right from the neutral position.

[0038] The steering control device 15 is connected to a rack position sensor 33. The rack position sensor 33 detects the position of the rack 26 in the vehicle width direction (hereinafter referred to as “rack position P”) and outputs it to the steering control device 15.

[0039] The steering control device 15 is connected to a vehicle speed sensor 34. The vehicle speed sensor 34 detects the speed of the vehicle 2 (hereinafter referred to as “vehicle speed V”) and outputs it to the steering control device 15.

[0040] (Target position correction control) The steering control device 15 is provided so as to be able to execute target position correction control for correcting the target position T1 of the rack 26 in accordance with the steering angular acceleration. For example, the target position correction control is executed periodically when the ignition switch of the vehicle 2 is turned on (when the steering device 1 is activated). Below, the target position correction control when the steering angle θ is greater than 0 (i.e., when the steering member 10 is steered to the right from the neutral position) will be described, and the description of the target position correction control when the steering angle θ is less than 0 (i.e., when the steering member 10 is steered to the left from the neutral position) will be omitted.

[0041] Referring to FIG. 2, the steering control device 15 includes, as functional elements for executing target position correction control, a target position calculation unit 41, a steering angular velocity calculation unit 42, a steering direction determination unit 43, a steering angular acceleration calculation unit 44, an LPF unit 45 (low-pass filter unit), a correction amount calculation unit 46, a correction amount limiting unit 47, and a target position correction unit 48.

[0042] The target position calculation unit 41 of the steering control device 15 calculates the target position T1 of the rack 26 based on the steering angle θ and the vehicle speed V (V1, V2, ...). Specifically, the target position calculation unit 41 calculates the target position T1 by multiplying the steering angle θ by a reference gear ratio according to the vehicle speed V. For example, the reference gear ratio is set to be smaller as the vehicle speed V becomes higher.

[0043] The steering angular velocity calculation unit 42 of the steering control device 15 calculates the steering angular velocity ω by differentiating the steering angle θ with respect to time. Note that the steering angular velocity calculation unit 42 may remove noise (noise generated by differential calculation) contained in the steering angular velocity ω by performing low-pass filter processing on the calculated steering angular velocity ω.

[0044] The steering direction determination unit 43 of the steering control device 15 determines the direction of the steering operation (hereinafter referred to as "steering direction Dr") based on the steering angle θ and the steering angular velocity ω.

[0045] For example, when the steering angle θ is greater than 0 and the steering angular velocity ω is greater than 0, it is estimated that the steering member 10 is to the right of the neutral position and is being steered from the left to the right. In such a case, the steering direction determination unit 43 determines that the steering direction Dr is a direction away from the neutral position. Hereinafter, such a steering operation in a direction away from the neutral position is referred to as a "turning operation."

[0046] For example, when the steering angle θ is greater than 0 and the steering angular velocity ω is less than 0, it is estimated that the steering member 10 is to the right of the neutral position and is being steered from the right to the left. In such a case, the steering control device 15 determines that the steering direction Dr is a direction approaching the neutral position. Hereinafter, such a steering operation in a direction approaching the neutral position is referred to as a "return operation."

[0047] The steering angular acceleration calculation unit 44 of the steering control device 15 calculates the steering angular acceleration α1 by differentiating the steering angular velocity ω with respect to time.

[0048] The LPF unit 45 of the steering control device 15 removes noise (noise generated by differential calculation) contained in the steering angular acceleration α1 by performing low-pass filtering on the steering angular acceleration α1. As a result, the LPF unit 45 generates the steering angular acceleration α2 from which noise has been removed.

[0049] The correction amount calculation unit 46 of the steering control device 15 calculates the correction amount C of the target position T1 based on the steering angle θ, the steering angular acceleration α2, and the vehicle speed V. For example, the correction amount calculation unit 46 calculates the correction amount C by referring to a correction amount calculation map (see FIG. 3) based on the steering angle θ, the steering angular acceleration α2, and the vehicle speed V. The correction amount calculation map is a three-dimensional control map that specifies the relationship between the steering angle θ, the steering angular acceleration α2, the vehicle speed V, and the correction amount C. In the correction amount calculation map, if the steering angular acceleration α2 is 0, the correction amount C is set to 0. On the other hand, in the correction amount calculation map, if the steering angular acceleration α2 is not 0, the correction amount C is set to a value larger than 0 according to the steering angular acceleration α2. For example, in the correction amount calculation map, the correction amount C increases as the steering angular acceleration α2 increases.

[0050] The correction amount limiting unit 47 of the steering control device 15 sets the upper limit value Lim based on the steering direction Dr, the steering angle θ, and the vehicle speed V. For example, when the steering direction Dr is a direction away from the neutral position (i.e., when the steering operation is a turning operation), the correction amount limiting unit 47 sets 0 as the upper limit value Lim. Also, when the steering angle θ is less than a predetermined reference angle θr, the correction amount limiting unit 47 sets 0 as the upper limit value Lim. On the other hand, when the steering direction Dr is a direction approaching the neutral position (i.e., when the steering operation is a turning-back operation) and the steering angle θ is equal to or greater than the reference angle θr, the correction amount limiting unit 47 sets the upper limit value Lim (Lim>0) according to the vehicle speed V.

[0051] The correction amount limiting unit 47 of the steering control device 15 compares the correction amount C with the upper limit value Lim. When the correction amount C is equal to or less than the upper limit value Lim, the correction amount limiting unit 47 outputs the correction amount C as is. On the other hand, when the correction amount C exceeds the upper limit value Lim, the correction amount limiting unit 47 reduces the correction amount C to the upper limit value Lim and outputs it. In this way, the correction amount limiting unit 47 limits the correction amount C to equal to or less than the upper limit value Lim. Note that when 0 is set as the upper limit value Lim as described above (i.e., when the steering operation is a turning operation or when the steering angle θ is less than the reference angle θr), the correction amount limiting unit 47 outputs 0 instead of the correction amount C.

[0052] The target position correction unit 48 of the steering control device 15 judges whether 0 or the correction amount C is output from the correction amount limiting unit 47. When 0 is output from the correction amount limiting unit 47, the target position correction unit 48 outputs the target position T1 as is without correcting it. On the other hand, when the correction amount C is output from the correction amount limiting unit 47, the target position correction unit 48 corrects the target position T1 by adding the correction amount C to the target position T1, and outputs the corrected target position T2. ​​With the above, the target position correction control is completed.

[0053] (Run and non-run modes) The steering control device 15 is provided to be switchable between a non-execution mode in which the target position correction control is not executed in response to the steering operation and an execution mode in which the target position correction control is executed in response to the steering operation. For example, the steering control device 15 may switch between the non-execution mode and the execution mode in response to the operation of the driver, or may switch between the non-execution mode and the execution mode in response to the running state of the vehicle 2.

[0054] 4 shows the relationship between the steering angle θ and the rack position P when a steering operation is performed during the non-execution mode. During the non-execution mode, the steering control device 15 controls the steering actuator 12 so that the rack position P coincides with the target position T1. However, the rack position P is slightly delayed with respect to the target position T1 depending on the delay time from the output of the target position T1 to the displacement of the rack 26.

[0055] 5 to 7 respectively show the relationship between the steering angle θ and the rack position P when a normal steering operation, a quick steering operation and an even quicker steering operation are performed during the execution mode. During the execution mode, the steering control device 15 controls the steering actuator 12 so as to make the rack position P coincident with the target position T1 or T2. However, the rack position P is slightly delayed with respect to the target position T1 or T2 depending on the delay time from the output of the target position T1 or T2 to the displacement of the rack 26.

[0056] 8, when a turning operation is performed during the execution mode, a steering angular acceleration occurs immediately after the start of the turning operation and immediately before the end of the turning operation according to the speed of the turning operation. Therefore, the correction amount calculation unit 46 calculates a correction amount C according to the steering angular acceleration and outputs it to the correction amount limiting unit 47. As described above, when the steering operation is a turning operation, the correction amount limiting unit 47 outputs 0 instead of the correction amount C. When the correction amount limiting unit 47 outputs 0, the target position correction unit 48 outputs the target position T1 as it is without correcting it.

[0057] As described above, even if a cutting operation is performed during the execution mode, the target position T1 is not corrected. Therefore, for a cutting operation, the rack position P during the execution mode (see FIGS. 5 to 7) coincides with the rack position P during the non-execution mode (see FIG. 4).

[0058] 9, when a steering-back operation is performed during the execution mode, a steering angular acceleration occurs immediately after the start and immediately before the end of the steering-back operation according to the speed of the steering-back operation. Therefore, the correction amount calculation unit 46 calculates a correction amount C according to the steering angular acceleration and outputs it to the correction amount limiting unit 47.

[0059] Immediately after the start of the steering-back operation, the steering angle θ is equal to or larger than the reference angle θr. Therefore, the correction amount limiting unit 47 outputs the correction amount C as is when the correction amount C is equal to or smaller than the upper limit value Lim, and outputs the correction amount C after reducing it to the upper limit value Lim when the correction amount C exceeds the upper limit value Lim. When the correction amount limiting unit 47 outputs the correction amount C, the target position correcting unit 48 corrects the target position T1 by adding the correction amount C to the target position T1, and outputs the corrected target position T2.

[0060] Just before the end of the steering back operation, the steering angle θ is less than the reference angle θr. As described above, when the steering angle θ is less than the reference angle θr, the correction amount limiting unit 47 outputs 0 instead of the correction amount C. When the correction amount limiting unit 47 outputs 0, the target position correcting unit 48 outputs the target position T1 as is without correcting it.

[0061] As described above, when a steering-back operation is performed during the execution mode, the target position T1 is corrected immediately after the start of the steering-back operation. Therefore, for the steering-back operation, the trajectory of the rack position P during the execution mode (see Figs. 5 to 7) changes with respect to the trajectory of the rack position P during the non-execution mode (see Fig. 4). Accordingly, the displacement of the rack 26 during the execution mode lags behind the displacement of the rack 26 during the non-execution mode.

[0062] Immediately after starting the steering-back operation in the execution mode, the correction amount C of the target position T1 increases as the steering operation becomes quicker (see Figs. 5 to 7). However, when the correction amount C of the target position T1 exceeds the upper limit Lim, the correction amount C of the target position T1 is limited to be equal to or less than the upper limit Lim (see Fig. 7).

[0063] Incidentally, while correcting the target position T1 of the rack 26 (i.e., when the correction amount C is not 0), the steering operation may switch from a return operation to a turn-in operation. In such a case, it is preferable to gradually reduce the correction amount C to 0 while moving the rack 26, rather than immediately reducing the correction amount C to 0 or reducing the correction amount C without moving the rack 26. In such a case, the method of gradually reducing the correction amount C is similar to the method of gradually increasing the correction amount C immediately after the start of the return operation. The reduction rate of the correction amount C may be a function of the strength (speed) of the steering operation. For example, it is preferable that the reduction rate of the correction amount C increases as the steering operation becomes faster.

[0064] In addition, the gain for the turning operation may be separated from the gain for the returning operation. In addition, when the correction amount C reaches the upper limit value Lim, the upper limit value Lim may suddenly change. In such a case, it is preferable to limit the rate of change of the correction amount C to a predetermined value or less.

[0065] (effect) As described above, the steering control device 15 is provided to be capable of executing target position correction control for correcting the target position T1 of the rack 26 in accordance with the steering angular acceleration. This makes it possible to correct the target position T1 of the rack 26 and delay the displacement of the rack 26 in accordance with the change in the steering angle θ when the steering angular acceleration increases due to a quick steering operation by the driver. Accordingly, it is possible to prevent the front wheels 3 from being rapidly steered immediately after a quick steering operation, thereby suppressing the discomfort felt by the driver.

[0066] In general, immediately after the start of a steering operation in a predetermined direction, there is a high possibility that the steering angular velocity and steering angular acceleration of the steering member 10 will increase. In consideration of such a possibility, in the target position correction control, the steering control device 15 corrects the target position T1 of the rack 26 immediately after the start of a steering operation in a predetermined direction. This makes it easier to prevent the front wheels 3 from being rapidly steered immediately after a quick steering operation, and effectively suppresses the discomfort felt by the driver.

[0067] In general, when performing a return steering operation, the driver is more likely to become inattentive than when performing a forward steering operation, and there is a high possibility that the steering angular velocity and steering angular acceleration of the steering member 10 will increase excessively. In consideration of such a possibility, in the target position correction control, the steering control device 15 corrects the target position T1 of the rack 26 immediately after the start of a return steering operation. This makes it possible to prevent the front wheels 3 from being rapidly steered immediately after an excessively quick steering operation, and effectively suppresses the discomfort felt by the driver.

[0068] Generally, when a turning operation is performed, the driver is more careful and the steering angular velocity and steering angular acceleration of the steering member 10 are less likely to increase excessively than when a return operation is performed. Therefore, in the target position correction control, the steering control device 15 prohibits correction of the target position T1 of the rack 26 when a turning operation is performed. This makes it possible to suppress unnecessary reduction in the responsiveness of the displacement of the rack 26 to the steering operation.

[0069] In addition, in the target position correction control, the steering control device 15 calculates the correction amount C according to the steering angular acceleration α2. This makes it possible to calculate an appropriate correction amount C according to the change in the steering angular velocity ω of the steering member 10.

[0070] In addition, the steering control device 15 calculates the correction amount C so that the correction amount C increases as the steering angular acceleration α2 increases. This makes it possible to increase the correction amount C in response to an increase in the speed of the steering operation, thereby increasing the delay in the displacement of the rack 26. This makes it easier to prevent the front wheels 3 from being rapidly steered immediately after a quick steering operation, and effectively suppresses any discomfort felt by the driver.

[0071] However, if the correction amount C increases without limit, the delay in the displacement of the rack 26 becomes excessively large, and it may become impossible to determine whether the delay in the displacement of the rack 26 is due to the target position correction control or an abnormality in the steering device 1. Therefore, the steering control device 15 limits the correction amount C to be equal to or less than the upper limit value Lim. This makes it possible to easily determine that the steering device 1 is in an abnormal state at the stage when the correction amount C exceeds the upper limit value Lim. Accordingly, there is no need to require excessively high reliability for the components (sensors, etc.) of the steering device 1.

[0072] In addition, the steering control device 15 sets the upper limit value Lim based on the steering direction Dr, the steering angle θ, and the vehicle speed V. This makes it possible to set the upper limit value Lim to an appropriate value depending on the traveling state of the vehicle 2.

[0073] In addition, the steering control device 15 is provided so as to be switchable between a non-execution mode in which the target position correction control is not executed and an execution mode in which the target position correction control is executed. This makes it possible to determine whether or not to execute the target position correction control depending on the driver's preference and the running state of the vehicle 2. This improves the convenience of the steering device 1.

[0074] (Modification) In the above embodiment, the correction amount calculation unit 46 refers to the correction amount calculation map to calculate the correction amount C. On the other hand, in other embodiments, the correction amount calculation unit 46 may perform a simulation using a steering system model and calculate the correction amount C based on the result of the simulation.

[0075] An example of a steering system model used in the above-mentioned simulation is shown in Fig. 10. This steering system model is set based on EPS (Electric Power Steering). This steering system model includes a steering wheel 51, a steering shaft 52 connected to the steering wheel 51, a pinion shaft 53 connected to the steering shaft 52, and a rack 54 engaged with the pinion shaft 53.

[0076] In the steering system model of FIG. 10, the following equation (1) holds true. TIFF0007636584000001.tif12169θ1: Angle of steering shaft 52 θ2: Angle of pinion shaft 53 I: Moment of inertia of rack 54 F: Frictional resistance D: Damping coefficient K1: equivalent spring constant of the steering shaft 52 K2: Equivalent spring constant between the rack 54 and the road surface

[0077] By using the steering system model as described above, the parameters (e.g., I, F, D, K1, and K2) of the above equation (1) can be changed according to the shape, size, driving conditions, etc. of the vehicle 2, and the optimal correction amount C can be determined.

[0078] In the above embodiment, the correction amount calculation unit 46 calculates the correction amount C based on the steering angular acceleration α2. On the other hand, in other embodiments, the correction amount calculation unit 46 may calculate the correction amount C based on the steering angular velocity ω, or may calculate the correction amount C based on both the steering angular acceleration α2 and the steering angular velocity ω.

[0079] In the above embodiment, the target position correction unit 48 corrects the target position T1 by adding the correction amount C to the target position T1. On the other hand, in another embodiment, the target position correction unit 48 may correct the target position T1 by multiplying the target position T1 by a correction rate.

[0080] In the above embodiment, the target position correction unit 48 corrects the target position T1 immediately after the start of a steering-back operation. On the other hand, in other embodiments, the target position correction unit 48 may correct the target position T1 not only immediately after the start of a steering-back operation but also immediately after the start of a turning operation. Furthermore, in other embodiments, the target position correction unit 48 may correct the target position T1 immediately before the end of a steering-back operation and / or a turning operation. In this way, the target position correction unit 48 may correct the target position T1 at any timing.

[0081] In the above embodiment, the steering control device 15 is provided to be switchable between a non-execution mode in which the target position correction control is not executed for the steering operation and an execution mode in which the target position correction control is executed for the steering operation. On the other hand, in another embodiment, the steering control device 15 may always execute the target position correction control for the steering operation. According to this aspect, it is possible to reliably prevent the front wheels 3 from being rapidly steered immediately after a quick steering operation, which makes it easier to suppress the discomfort felt by the driver.

[0082] In the above embodiment, the rack position sensor 33 directly detects the rack position. On the other hand, in other embodiments, the rack position sensor 33 may indirectly detect the rack position based on the steering angle of the front wheels 3, or may indirectly detect the rack position based on the lateral acceleration applied to the vehicle 2.

[0083] Although the specific embodiment has been described above, the present invention is not limited to the above embodiment and its modified examples, and can be modified in a wide range of ways. [Explanation of symbols]

[0084] 1: Steering gear 2: Vehicle 3: Front wheel (example of a wheel) 10: Steering member 11: Steering mechanism 12: Steering actuator 15: Steering control device (an example of a control device) 26: Rack 32: Steering angle sensor 33: Rack position sensor

Claims

1. A steering device for a vehicle, comprising: A steering member that receives a steering operation; a steering angle sensor for detecting a steering angle of the steering member; a steering mechanism that is mechanically separated from the steering member and that steers the wheels by moving a rack; A steering actuator that applies a driving force to the steering mechanism; a rack position sensor for detecting a position of the rack; a control device that calculates a target position of the rack based on the steering angle of the steering member and controls the steering actuator so that the position of the rack detected by the rack position sensor coincides with the target position of the rack, the control device is capable of executing a target position correction control for correcting the target position of the rack in response to a steering angular velocity and / or a steering angular acceleration of the steering member in order to delay a displacement of the rack in response to a change in the steering angle of the steering member, In the target position correction control, the control device calculates the target position of the rack in accordance with the steering angle of the steering member, calculates a correction amount for the target position of the rack in accordance with the steering angular acceleration of the steering member, and corrects the target position of the rack by adding the correction amount to the target position of the rack.

2. 2. The steering device for a vehicle according to claim 1, wherein in the target position correction control, the control device corrects the target position of the rack immediately after the start of the steering operation in a predetermined direction.

3. The steering operation includes a turning operation which is an operation in a direction away from a predetermined neutral position, and a returning operation which is an operation in a direction toward the neutral position, 3. The vehicle steering system according to claim 2, wherein in the target position correction control, the control device corrects the target position of the rack immediately after the start of the returning operation.

4. A steering device for a vehicle, comprising: A steering member that receives a steering operation; a steering angle sensor for detecting a steering angle of the steering member; a steering mechanism that is mechanically separated from the steering member and that steers the wheels by moving a rack; A steering actuator that applies a driving force to the steering mechanism; a rack position sensor for detecting a position of the rack; a control device that calculates a target position of the rack based on the steering angle of the steering member and controls the steering actuator so that the position of the rack detected by the rack position sensor coincides with the target position of the rack, the control device is capable of executing a target position correction control for correcting the target position of the rack in response to a steering angular velocity and / or a steering angular acceleration of the steering member in order to delay a displacement of the rack in response to a change in the steering angle of the steering member, In the target position correction control, the control device corrects the target position of the rack immediately after the start of the steering operation in a predetermined direction, The steering operation includes a turning operation which is an operation in a direction away from a predetermined neutral position, and a returning operation which is an operation in a direction toward the neutral position, In the target position correction control, the control device corrects the target position of the rack immediately after the start of the steering-back operation, In the target position correction control, the control device prohibits correction of the target position of the rack when the turning operation is performed.

5. 2. The steering device for a vehicle according to claim 1, wherein the control device calculates the correction amount so that the correction amount increases as the steering angular acceleration of the steering member increases.

6. The steering system for a vehicle according to claim 5 , wherein the control device limits the amount of correction to a predetermined upper limit value or less.

7. The steering member is steered in a direction away from a predetermined neutral position or in a direction toward the neutral position, The vehicle steering device according to claim 6 , wherein the control device sets the upper limit value based on a steering direction of the steering member, the steering angle of the steering member, and a vehicle speed.

8. A steering device for a vehicle, comprising: A steering member that receives a steering operation; a steering angle sensor for detecting a steering angle of the steering member; a steering mechanism that is mechanically separated from the steering member and that steers the wheels by moving a rack; A steering actuator that applies a driving force to the steering mechanism; a rack position sensor for detecting a position of the rack; a control device that calculates a target position of the rack based on the steering angle of the steering member and controls the steering actuator so that the position of the rack detected by the rack position sensor coincides with the target position of the rack, the control device is capable of executing a target position correction control for correcting the target position of the rack in response to a steering angular velocity and / or a steering angular acceleration of the steering member in order to delay a displacement of the rack in response to a change in the steering angle of the steering member, The control device is a steering device for a vehicle that is switchable between a non-execution mode in which the target position correction control is not executed in response to the steering operation and an execution mode in which the target position correction control is executed in response to the steering operation.

9. 8. The vehicle steering device according to claim 1, wherein the control device constantly executes the target position correction control in response to the steering operation.

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