Steering system for a vehicle

Abstract

A steering system for a vehicle capable of suppressing discomfort of a driver in the case where the driver performs a quick steering operation is provided. The steering system for a vehicle includes a steering mechanism mechanically separated from a steering member and configured to steer a wheel by moving a rack, a steering actuator configured to apply a driving force to the steering mechanism, and a controller configured to calculate a target position of the rack and control the steering actuator so that a position of the rack matches the target position thereof. The controller is configured to execute target position correction control in which the controller corrects the target position of the rack in accordance with a steering angular velocity and / or a steering angular acceleration of the steering member.

Description

Technical Field

[0001] This invention relates to a steering system for vehicles. Background Technology

[0002] Traditionally, there are steer-by-wire systems that include: a steering member configured to receive steering inputs; and a steering mechanism mechanically separated from the steering member and configured to steer the wheels by moving a rack.

[0003] For example, Patent Document 1 discloses a steering system for a vehicle, comprising: a steering mechanism configured to change the direction of a steerable wheel; and a steering device supported by a stationary member and not mechanically connected to the steering mechanism.

[0004] List of cited references

[0005] Patent documents

[0006] [Patent Document 1] JP2002-225733A Summary of the Invention

[0007] Technical issues

[0008] In a steering system where the steering member and 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 this time, the shaft of the steering member is twisted, causing the movement of the rack to be delayed relative to the steering operation. Conversely, in a steering system with steer-by-wire, the torque generated by the steering operation is transmitted to the rack of the steering mechanism via an electrical signal. Therefore, compared to a steering system where the steering member and steering mechanism are mechanically connected, the movement of the rack is less likely to be delayed relative to the steering operation.

[0009] However, if the rack movement is too sensitive to steering input, the wheels may be turned quickly immediately after a quick steering input by the driver, which could cause driver discomfort.

[0010] In view of the above background, the object of the present invention is to provide a steering system for a vehicle that can suppress driver discomfort when the driver performs a rapid steering operation.

[0011] Solution to the problem

[0012] To achieve this objective, one aspect of the present invention provides a steering system (1) for a vehicle (2), the steering system comprising: a steering member (10) configured to receive a steering operation; a steering angle sensor (32) configured to detect the steering angle of the steering member; a steering mechanism (11) mechanically separated from the steering member and configured to steer a wheel (3) by moving a rack (26); a steering actuator (12) configured to apply a driving force to the steering mechanism; and a rack position sensor (33) for the rack position... A sensor is configured to detect the position of the rack; and a controller (15) is configured to calculate a target position of the rack based on the steering angle of the steering member and to control the steering actuator such that the position of the rack detected by the rack position sensor matches the target position of the rack, wherein the controller is configured to perform target position correction control in which the controller corrects the target position of the rack based on the steering angular velocity and / or steering angular acceleration of the steering member to delay the movement of the rack in response to a change in the steering angle of the steering member.

[0013] According to this aspect, when the steering angular velocity and / or steering angular acceleration of the steering component increase due to the driver's rapid steering operation, the target position of the rack is corrected so that the rack's movement in response to changes in the steering angle of the steering component can be delayed. Therefore, it is possible to prevent the wheels from being rapidly steered immediately after a rapid steering operation, thereby suppressing driver discomfort.

[0014] In the foregoing, preferably, in the target position correction control, the controller corrects the target position of the rack immediately after initiating the steering operation in the prescribed direction.

[0015] Typically, the steering angular velocity and / or steering angular acceleration of the steering components may increase immediately after a steering operation is initiated in the specified direction. Taking this possibility into account, the target position of the rack is corrected immediately after the steering operation is initiated in the specified direction. Therefore, it is possible to reliably prevent the wheels from being rapidly steered immediately after a rapid steering operation, thereby effectively suppressing driver discomfort.

[0016] In the above aspects, preferably, the steering operation includes a turning operation as an operation in a direction away from the predetermined neutral position and a return operation as an operation in the direction of the neutral position, and in the target position correction control, the controller corrects the target position of the rack immediately after the return operation begins.

[0017] Typically, drivers are more likely to be careless, and therefore the steering angular velocity and / or steering angular acceleration of the steering components are more likely to increase excessively during a return maneuver compared to when performing a turn. Taking this possibility into account, the target position of the rack is corrected immediately after the return maneuver begins. This prevents the wheels from being rapidly turned immediately after an overly quick steering maneuver, effectively reducing driver discomfort.

[0018] In the foregoing, preferably, in the target position correction control, the controller prohibits the correction of the target position of the rack during the turning operation.

[0019] Typically, drivers are more likely to be cautious, and therefore the steering angular velocity and / or steering angular acceleration of the steering components are less likely to increase excessively during turning operations compared to when performing a return maneuver. Taking this impossibility into account, the target position of the rack is prohibited from being corrected during turning operations, thus preventing unnecessarily deterioration in the responsiveness of the rack to steering operations.

[0020] In the foregoing, preferably, in the target position correction control, the controller calculates the target position of the rack based on the steering angle of the steering member, calculates a correction amount for the target position of the rack based on 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.

[0021] Based on this, by calculating the correction amount based on the steering angular acceleration of the steering component, an appropriate correction amount can be calculated based on the change in the steering angular velocity of the steering component.

[0022] In the foregoing, preferably, the controller calculates the correction amount such that the correction amount increases as the steering angular acceleration of the steering member increases.

[0023] Based on this, the correction amount increases with the speed of the steering operation, which also increases the delay in rack movement. Therefore, it is possible to reliably prevent the wheels from being quickly turned immediately after a rapid steering operation, thereby effectively suppressing driver discomfort.

[0024] In the foregoing, preferably, the controller limits the correction amount to a predetermined upper limit or less.

[0025] If the correction amount increases indefinitely, the delay in rack movement may become excessive, and it may become impossible to determine whether the delay is caused by the target position correction control or by a steering system malfunction. Conversely, if the correction amount is limited to an upper limit or less, a steering system malfunction can be easily identified once the correction amount exceeds the upper limit. Therefore, excessively high reliability of steering system components (sensors, etc.) is not required.

[0026] In the above aspects, preferably, the steering member is configured to be steered in a direction away from or in the direction of the predetermined neutral position, and the controller is configured to set the upper limit based on the steering direction of the steering member, the steering angle of the steering member, and the vehicle speed.

[0027] Based on this, the upper limit can be set to an appropriate value according to the vehicle's driving status.

[0028] In the foregoing, preferably, the controller is configured to switch between a non-executing mode and an executing mode, wherein in the non-executing mode the controller does not perform the target position correction control in response to the steering operation, and in the executing mode the controller performs the target position correction control in response to the steering operation.

[0029] Based on this, it is possible to determine whether to execute target position correction control in response to steering input based on the driver's preferences, vehicle driving conditions, and other factors. This improves the convenience of the steering system.

[0030] In the foregoing, preferably, the controller is configured to perform the target position correction control in response to each steering operation.

[0031] According to this aspect, since it is possible to reliably prevent the wheels from being turned too quickly immediately after a rapid steering operation, driver discomfort can be suppressed more reliably.

[0032] Advantages of the invention

[0033] Therefore, based on the above aspects, driver discomfort can be suppressed when the driver performs a rapid steering maneuver. Attached Figure Description

[0034] [ Figure 1 This diagram shows a schematic representation of a steering system according to an embodiment of the present invention.

[0035] [ Figure 2 [A block diagram of a steering controller according to an embodiment of the present invention is shown.]

[0036] [ Figure 3 This diagram illustrates a correspondence diagram for calculating the correction amount according to an embodiment of the present invention.

[0037] [ Figure 4 The graph shows the relationship between the steering angle and the rack position when the steering operation is performed in non-executing mode according to an embodiment of the present invention.

[0038] [ Figure 5 The graph shows the relationship between the steering angle and the rack position under normal operation in the execution mode according to an embodiment of the present invention.

[0039] [ Figure 6 The graph shows the relationship between the steering angle and the rack position when performing rapid operation in the execution mode according to an embodiment of the present invention.

[0040] [ Figure 7 The graph shows the relationship between the steering angle and the rack position when performing further rapid operations in the execution mode according to an embodiment of the present invention.

[0041] [ Figure 8 The graph shows the relationship between the steering angle and the steering angular acceleration during a turning operation according to an embodiment of the present invention.

[0042] [ Figure 9 The graph shows the relationship between the steering angle and steering angular acceleration during the return operation according to an embodiment of the present invention.

[0043] [ Figure 10 This diagram illustrates a steering model according to another embodiment of the invention. Detailed Implementation

[0044] The steering system 1 for a vehicle 2 according to an embodiment of the present invention will now be described. Figure 1 As shown, the steering system 1 includes a steer-by-wire (SBW) system. The vehicle 2 equipped with the steering system 1 is a four-wheeled vehicle comprising left and right front wheels 3 and left and right rear wheels (not shown in the figure). The left and right front wheels 3 are connected to the vehicle body 8 via their respective steering knuckles 7. Figure 1 (Only the lower outline is shown in the diagram) The support allows the steering angle of the front wheel 3 to be changed, and the front wheel 3 thus functions as a steerable wheel. The steering angle refers to the angle of the front wheel 3 relative to the longitudinal direction in the top view. The steering system 1 thus changes the steering angle of the front wheel 3.

[0045] The steering system 1 includes a steering member 10 rotatably mounted on the vehicle body 8, a steering mechanism 11 configured to steer the front wheels 3, a steering actuator 12 configured to apply a driving force to the steering mechanism 11, a reaction force actuator 13 configured to apply a reaction torque to the steering member 10, and a steering controller 15 configured to control the reaction force actuator 13 and the steering actuator 12. The steering system 1 may be a redundant system including multiple steering actuators 12, multiple reaction force actuators 13, and multiple steering controllers 15.

[0046] The steering member 10 is configured to receive steering inputs from the driver. The steering member 10 includes a steering shaft 18 rotatably supported by the vehicle body 8 and a steering wheel 19 disposed at an end of the steering shaft 18. The steering shaft 18 is rotatably supported by a steering column (not shown) disposed on the vehicle body 8 and has a rear end projecting rearward from the steering column. The steering wheel 19 is connected to the rear end of the steering shaft 18 so as to rotate integrally with the steering shaft 18.

[0047] The reaction force actuator 13 is composed of an electric motor and is connected to the steering shaft 18 via a gear mechanism. When the reaction force actuator 13 is driven, its driving force is transmitted to the steering shaft 18 as a rotational force. The reaction force actuator 13 is configured to rotate, thereby applying torque to the steering member 10. The torque applied to the steering member 10 by the reaction force actuator 13 in response to steering operation is referred to as the "reaction torque".

[0048] The steering mechanism 11 includes a rack 26 extending in the vehicle width direction. The rack 26 is supported by a gearbox (not shown), allowing it to move in the vehicle width direction. The left and right ends of the rack 26 are connected to steering knuckles 7, which support the left and right front wheels 3 respectively via tie rods 30. When the rack 26 moves from a predetermined reference position (the position where the direction of the left and right front wheels 3 is parallel to the front-rear direction: see...) Figure 1 When moving along the width of the vehicle, the steering angle of the front wheel 3 changes. The steering mechanism 11 is mechanically separated from the steering component 10.

[0049] The steering actuator 12 includes an electric motor. The steering actuator 12 moves the rack 26 along the vehicle width direction based on a signal from the steering controller 15, thereby changing the steering angle of the left and right front wheels 3.

[0050] The steering controller 15 consists of an electronic control unit (ECU) including a CPU, a storage unit, etc. The CPU is configured to control each part of the steering system 1 based on the program and data stored in the storage unit.

[0051] Steering controller 15 is connected to steering angle sensor 32. Steering angle sensor 32 is configured to detect the rotation angle (hereinafter referred to as "steering angle θ") of steering member 10 relative to a predetermined neutral position and output steering angle θ to steering controller 15. In this embodiment, when steering member 10 is in the neutral position, steering angle θ is 0; when steering member 10 turns right from the neutral position, steering angle θ increases from 0; and when steering member 10 turns left from the neutral position, steering angle θ decreases from 0. However, in another embodiment, when steering member 10 turns left from the neutral position, steering angle θ can increase from 0, and when steering member 10 turns right from the neutral position, steering angle θ can decrease from 0.

[0052] The steering controller 15 is connected to the rack position sensor 33. The rack position sensor 33 is configured to detect the position of the rack 26 in the vehicle width direction (hereinafter referred to as "rack position P") and output the rack position P to the steering controller 15.

[0053] The steering controller 15 is connected to the vehicle speed sensor 34. The vehicle speed sensor 34 is configured to detect the speed of the vehicle 2 (hereinafter referred to as "vehicle speed V") and output the vehicle speed V to the steering controller 15.

[0054] (Target position correction control)

[0055] The steering controller 15 is configured to perform target position correction control, wherein the steering controller 15 corrects the target position T1 of the rack 26 based on the steering angle acceleration. For example, the target position correction control is performed periodically when the ignition switch of the vehicle 2 is on (when the steering system 1 is in operation). The target position correction control when the steering angle θ is greater than 0 (i.e., when the steering member 10 turns right from the neutral position) will be described below, 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 turns left from the neutral position) will be omitted.

[0056] Reference Figure 2 The steering controller 15 includes 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, a low-pass filter unit (LPF unit) 45, a correction amount calculation unit 46, a correction amount limiting unit 47, and a target position correction unit 48. These are functional elements used to perform target position correction control.

[0057] The target position calculation unit 41 of the steering controller 15 calculates the target position T1 of the rack 26 based on the steering angle θ and the vehicle speed V (V1, V2, ...). More specifically, the target position calculation unit 41 calculates the target position T1 by multiplying the steering angle θ by a reference gear ratio corresponding to the vehicle speed V. For example, the reference gear ratio is set to decrease as the vehicle speed V increases.

[0058] The steering angular velocity calculation unit 42 of the steering controller 15 calculates the steering angular velocity ω by differentiating the steering angle θ with respect to time. Incidentally, the steering angular velocity calculation unit 42 can apply a low-pass filter to the calculated steering angular velocity ω, thereby removing noise from the steering angular velocity ω (more specifically, noise generated by the differential calculation).

[0059] The steering direction determination unit 43 of the steering controller 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.

[0060] For example, when the steering angle θ is greater than 0 and the steering angular velocity ω is greater than 0, it can be estimated that the steering member 10 is located to the right of the neutral position and the steering member 10 is turning from left to right. In this case, the steering direction determination unit 43 determines that the steering direction Dr is a direction away from the neutral position. In the following text, the steering operation in the direction away from the neutral position is referred to as a "turning operation".

[0061] For example, when the steering angle θ is greater than 0 and the steering angular velocity ω is less than 0, it can be estimated that the steering member 10 is located to the right of the neutral position and the steering member 10 is turning from right to left. In this case, the steering controller 15 determines that the steering direction Dr is the direction of the neutral position. In the following text, the steering operation in the direction of the neutral position is referred to as the "return operation".

[0062] The steering angle acceleration calculation unit 44 of the steering controller 15 calculates the steering angle acceleration α1 by differentiating the steering angle velocity ω with respect to time.

[0063] The LPF unit 45 of the steering controller 15 performs low-pass filtering on the steering angular acceleration α1, thereby removing noise from the steering angular acceleration α1 (more specifically, noise generated by differential calculation). As a result, the LPF unit 45 generates a noise-removed steering angular acceleration α2.

[0064] The correction calculation unit 46 of the steering controller 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 calculation unit 46 calculates the correction amount C by referring to the correction amount calculation correspondence diagram based on the steering angle θ, the steering angular acceleration α2, and the vehicle speed V (see...). Figure 3The correction amount C is calculated using the following method. The correction amount calculation correspondence diagram is a three-dimensional control correspondence diagram that defines the relationship between the steering angle θ, steering angular acceleration α2, and vehicle speed V and the correction amount C. In the correction amount calculation correspondence diagram, if the steering angular acceleration α2 is 0, the corresponding correction amount C is set to 0. Conversely, if the steering angular acceleration α2 is not 0, the corresponding correction amount C is set to a value greater than 0 based on the steering angular acceleration α2. For example, in the correction amount calculation correspondence diagram, the correction amount C increases as the steering angular acceleration α2 increases.

[0065] The correction limiting unit 47 of the steering controller 15 sets the upper limit Lim based on the steering direction Dr, the steering angle θ, and the vehicle speed V. For example, when the steering direction Dr is away from the neutral position (i.e., when the steering operation is a turning operation), the correction limiting unit 47 sets the upper limit Lim to 0. Furthermore, when the steering angle θ is less than a predetermined reference angle θr, the correction limiting unit 47 sets the upper limit Lim to 0. Conversely, when the steering direction Dr is in the neutral position (i.e., the steering operation is a return operation) and the steering angle θ is equal to or greater than the reference angle θr, the correction limiting unit 47 sets the upper limit Lim (Lim>0) based on the vehicle speed V.

[0066] The correction amount limiting unit 47 of the steering controller 15 compares the correction amount C with the upper limit Lim. If the correction amount C is equal to or less than the upper limit Lim, the correction amount limiting unit 47 outputs the correction amount C as is. On the other hand, if the correction amount C exceeds the upper limit Lim, the correction amount limiting unit 47 outputs the correction amount C after reducing it to the upper limit Lim. Thus, the correction amount limiting unit 47 limits the correction amount C to the upper limit Lim or less. Incidentally, when the upper limit Lim is set to 0 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.

[0067] The target position correction unit 48 of the steering controller 15 determines whether to output 0 or a correction amount C from the correction amount limiting unit 47. When the correction amount limiting unit 47 outputs 0, the target position correction unit 48 does not correct the target position T1 and outputs the target position T1 as is. Conversely, when the correction amount limiting unit 47 outputs a correction amount C, the target position correction unit 48 corrects the target position T1 by adding the correction amount C to the target position T1, thereby outputting the corrected target position T2. ​​This completes the target position correction control.

[0068] (Execution mode and non-execution mode)

[0069] The steering controller 15 is configured to switch between a non-execution mode in which the steering controller 15 performs target position correction control without responding to steering operations and an execution mode in which the steering controller 15 performs target position correction control in response to steering operations. For example, the steering controller 15 can switch between the non-execution mode and the execution mode based on the driver's operation or the driving state of the vehicle 2.

[0070] Figure 4 The relationship between the steering angle θ and the rack position P is shown when steering is performed in non-executable mode. During non-executable mode, the steering controller 15 controls the steering actuator 12 such that the rack position P matches the target position T1. In practice, the rack position P is slightly delayed relative to the target position T1, depending on the delay time from the output of the target position T1 to the movement of the rack 26.

[0071] Figure 5 , Figure 6 and Figure 7 The relationship between the steering angle θ and the rack position P is shown for normal operation, rapid operation, and further rapid operation in the execution mode. During the execution mode, the steering controller 15 controls the steering actuator 12 such that the rack position P matches the target position T1 or T2. In practice, the rack position P is slightly delayed relative to the target position T1 or T2, depending on the delay time from the output of the target position T1 or T2 to the movement of the rack 26.

[0072] Reference Figure 8 When performing a turning operation in execution mode, the steering angle acceleration is generated based on the speed of the turning operation immediately following its start and immediately following its end. Therefore, the correction calculation unit 46 calculates the correction amount C based on the steering angle acceleration and outputs the correction amount C to the correction amount limiting unit 47. As described above, when the turning operation is a cornering 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 does not correct the target position T1 but outputs the target position T1 as is.

[0073] As mentioned above, even when performing a turning operation in execution mode, the target position T1 is not corrected. Therefore, regarding the turning operation, the rack position P in execution mode (see...) Figures 5 to 7 Matching rack position P in non-execution mode (see...) Figure 4 ).

[0074] See Figure 9When a return operation is performed in execution mode, the steering angle acceleration is generated based on the speed of the return operation immediately following its start and immediately following its end. Therefore, the correction calculation unit 46 calculates the correction amount C based on the steering angle acceleration and outputs the correction amount C to the correction amount limiting unit 47.

[0075] Immediately after the return operation begins, the steering angle θ is equal to or greater 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 less than the upper limit Lim, and when the correction amount C exceeds the upper limit Lim, the correction amount limiting unit 47 outputs the correction amount C after reducing it to the upper limit Lim. 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.

[0076] Immediately before the return operation ends, 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 correction unit 48 does not correct the target position T1 but outputs the target position T1 as is.

[0077] As described above, when performing a return operation in execution mode, the target position T1 is corrected immediately after the return operation begins. Therefore, regarding the return operation, the trajectory of the rack position P in execution mode (see...) Figures 5 to 7 The trajectory from rack position P in non-executive mode (see...) Figure 4 ) Shift. Therefore, the movement of rack 26 in execution mode is delayed relative to the movement of rack 26 in non-execution mode.

[0078] Immediately after the return operation begins in execution mode, the correction amount C of the target position T1 increases with the speed of the steering operation (see...). Figures 5 to 7 However, if the correction C at target position T1 exceeds the upper limit Lim, the correction C at target position T1 is limited to the upper limit Lim or less (see [link to relevant documentation]). Figure 7 ).

[0079] Additionally, the steering operation can be switched from a return operation to a turn operation while correcting the target position T1 of rack 26 (i.e., when the correction amount C is not 0). In this case, it is preferable to gradually decrease the correction amount C to 0 while moving rack 26, rather than immediately decreasing the correction amount C to 0 or decreasing the correction amount C without moving rack 26. In this case, the gradual decrease of correction amount C can be similar to the gradual increase of correction amount C immediately after the start of the return operation. The rate of decrease of correction amount C can be a function of the intensity (speed) of the steering operation. For example, the faster the steering operation, the greater the rate of decrease of correction amount C.

[0080] Furthermore, the gain for turning operations can be distinguished from the gain for returning operations. Also, when the correction amount C reaches the upper limit Lim, the upper limit Lim can be suddenly changed. In these cases, it is preferable to limit the rate of change of the correction amount C to below a specified rate of change.

[0081] (Effect)

[0082] As described above, the steering controller 15 performs target position correction control, wherein the steering controller 15 corrects the target position T1 of the rack 26 based on the steering angular acceleration. Therefore, when the steering angular acceleration increases due to a driver's rapid steering operation, the target position T1 of the rack 26 is corrected, thereby delaying the movement of the rack 26 in response to changes in the steering angle θ. This prevents the front wheels 3 from being rapidly steered immediately after a rapid steering operation, thus suppressing driver discomfort.

[0083] Typically, the steering angular velocity and / or steering angular acceleration of the steering component 10 may increase immediately after a steering operation is initiated in the specified direction. Taking this possibility into account, in the target position correction control, the steering controller 15 corrects the target position T1 of the rack 26 immediately after a steering operation is initiated in the specified direction. Therefore, it is reliably possible to prevent the front wheels 3 from being rapidly steered immediately after a rapid steering operation, thereby effectively suppressing driver discomfort.

[0084] Typically, drivers are more likely to be careless, and therefore the steering angular velocity and / or steering angular acceleration of the steering member 10 are more likely to increase excessively during a return maneuver compared to when performing a turn. Taking this possibility into account, in the target position correction control, the steering controller 15 corrects the target position T1 of the rack 26 immediately after the return maneuver begins. Therefore, it is possible to prevent the front wheels 3 from being rapidly steered immediately after an overly quick steering maneuver, thereby effectively suppressing driver discomfort.

[0085] Typically, drivers are more likely to be cautious, and therefore, the steering angular velocity and / or steering angular acceleration of the steering member 10 are less likely to increase excessively during a turning maneuver compared to when performing a return maneuver. Taking this impossibility into account, in the target position correction control, the steering controller 15 prohibits correction of the target position T1 of the rack 26 during a turning maneuver. Therefore, it is possible to prevent unnecessarily deterioration in the responsiveness of the rack 26 to steering maneuvers.

[0086] Furthermore, in the target position correction control, the steering controller 15 calculates the correction amount C based on the steering angular acceleration α2. Therefore, an appropriate correction amount C can be calculated based on the change in the steering angular velocity ω of the steering member 10.

[0087] Furthermore, the steering controller 15 calculates a correction amount C such that C increases with the increase of the steering angle acceleration α2. Therefore, the correction amount C increases with the speed of the steering operation, which also increases the delay in the movement of the rack 26. Thus, it reliably prevents the front wheels 3 from being rapidly steered immediately after a rapid steering operation, thereby effectively suppressing driver discomfort.

[0088] Incidentally, if the correction amount C increases indefinitely, the delay in the movement of rack 26 may become excessive, and it may become impossible to determine whether the delay in the movement of rack 26 is caused by the target position correction control or by an abnormality in steering system 1. Therefore, steering controller 15 limits the correction amount C to an upper limit Lim or less. Thus, once the correction amount C exceeds the upper limit Lim, an abnormality in steering system 1 can be easily determined. Therefore, excessively high reliability of components (sensors, etc.) in steering system 1 is not required.

[0089] Furthermore, the steering controller 15 is configured to set the upper limit Lim based on the steering direction Dr, steering angle θ, and vehicle speed V. Therefore, the upper limit Lim can be set to an appropriate value according to the driving state of the vehicle 2.

[0090] Furthermore, the steering controller 15 is configured to switch between a non-execution mode where the steering controller 15 does not perform target position correction control and an execution mode where the steering controller 15 performs target position correction control. Therefore, whether to perform target position correction control can be determined based on the driver's preferences, the driving status of the vehicle 2, etc. This improves the convenience of the steering system 1.

[0091] (Improved implementation method)

[0092] In the above embodiment, the correction calculation unit 46 calculates the correction amount C by referring to the correction calculation diagram. On the other hand, in another embodiment, the correction calculation unit 46 can run a simulation using a steering model and calculate the correction amount C based on the simulation results.

[0093] Figure 10 An example of the steering model used in the simulation described above is shown. This steering model is based on electric power steering (EPS). The steering model includes a steering wheel 51, a steering shaft 52 connected to the steering wheel 51, a pinion 53 connected to the steering shaft 52, and a rack 54 meshing with the pinion 53.

[0094] exist Figure 10 In the steering model shown, the following equation (1) is satisfied.

[0095]

[0096] θ1: Angle of steering axis 52

[0097] θ2: Angle of pinion 53

[0098] I: Moment of inertia of rack 54

[0099] F: Frictional resistance

[0100] D: Damping coefficient

[0101] K1: Equivalent spring constant of steering shaft 52

[0102] K2: Equivalent spring constant between rack 54 and the road surface

[0103] By using the steering model described above, the parameters of the above equation (1) (e.g., I, F, D, K1 and K2) can vary according to the shape, size, driving state, etc. of the vehicle 2, and thus the optimal correction amount C can be determined.

[0104] In the above embodiment, the correction calculation unit 46 calculates the correction amount C based on the steering angular acceleration α2. On the other hand, in another embodiment, the correction calculation unit 46 may calculate the correction amount C based on the steering angular velocity ω, or it may calculate the correction amount C based on both the steering angular acceleration α2 and the steering angular velocity ω.

[0105] 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 can correct the target position T1 by multiplying the target position T1 by the correction ratio.

[0106] In the above embodiment, the target position correction unit 48 corrects the target position T1 immediately after the return operation begins. On the other hand, in another embodiment, the target position correction unit 48 can correct the target position T1 not only immediately after the return operation begins, but also immediately after the turning operation begins. Furthermore, in another embodiment, the target position correction unit 48 can correct the target position T1 immediately before the return operation and / or turning operation ends. Thus, the target position correction unit 48 can correct the target position T1 at any timing.

[0107] In the above embodiment, the steering controller 15 is configured to switch between a non-execution mode in which the steering controller 15 performs target position correction control without responding to a steering operation and an execution mode in which the steering controller 15 performs target position correction control in response to a steering operation. On the other hand, in another embodiment, the steering controller 15 may be configured to perform target position correction control in response to each steering operation. Therefore, since it is possible to reliably prevent the front wheels 3 from being rapidly steered immediately after a rapid steering operation, driver discomfort can be suppressed more reliably.

[0108] In the above embodiment, the rack position sensor 33 is configured to directly detect the rack position. On the other hand, in another embodiment, the rack position sensor 33 can indirectly detect the rack position based on the steering angle of the front wheel 3 or based on the lateral acceleration applied to the vehicle 2.

[0109] The specific embodiments of the present invention have been described above, but the present invention should not be limited to the above embodiments, and various modifications and changes can be made within the scope of the present invention.

[0110] List of reference numerals

[0111] 1: Steering System

[0112] 2: Vehicles

[0113] 3: Front wheel (example of a wheel)

[0114] 10: Steering components

[0115] 11: Steering mechanism

[0116] 12: Steering actuator

[0117] 15: Steering Controller (Example of a Controller)

[0118] 26: rack and pinion

[0119] 32: Steering angle sensor

[0120] 33: Rack and pinion position sensor

Claims

1. A steering system for a vehicle, the steering system for a vehicle comprising: A steering component configured to receive steering operations; A steering angle sensor, configured to detect the steering angle of the steering component; A steering mechanism, mechanically separate from the steering member and configured to steer the wheels by moving a rack; A steering actuator configured to apply a driving force to the steering mechanism; A rack position sensor, the rack position sensor being configured to detect the position of the rack; as well as A controller configured to calculate a target position of the rack based on the steering angle of the steering member, and to control the steering actuator such that the position of the rack detected by the rack position sensor matches the target position of the rack. The controller is configured to perform target position correction control, in which the controller corrects the target position of the rack based on the steering angular velocity and / or steering angular acceleration of the steering member, thereby delaying the movement of the rack in response to changes in the steering angle of the steering member. The steering operation includes a turning operation as an operation in a direction away from the predetermined neutral position and a returning operation as an operation in the direction of the neutral position. In the target position correction control, the controller corrects the target position of the rack immediately after initiating the return operation. In the target position correction control, the controller prohibits the correction of the target position of the rack during the turning operation.

2. The steering system for a vehicle according to claim 1, wherein, In the target position correction control, the controller calculates the target position of the rack based on the steering angle of the steering member, calculates the correction amount of the target position of the rack based on 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.

3. The steering system for a vehicle according to claim 2, wherein, The controller calculates the correction amount such that the correction amount increases as the steering angular acceleration of the steering component increases.

4. The steering system for a vehicle according to claim 3, wherein, The controller limits the correction amount to a specified upper limit or less.

5. The steering system for a vehicle according to claim 4, wherein, The steering member is configured to be steered in a direction away from or in the direction of the neutral position, and The controller is configured to set the upper limit based on the steering direction of the steering member, the steering angle of the steering member, and the vehicle speed.

6. The steering system for a vehicle according to claim 1, wherein, The controller is configured to switch between a non-executing mode and an executing mode, wherein in the non-executing mode the controller does not perform the target position correction control in response to the steering operation, and in the executing mode the controller performs the target position correction control in response to the steering operation.

7. The steering system for a vehicle according to claim 1, wherein, The controller is configured to perform the target position correction control in response to each steering operation.

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