Steering system for a vehicle

Abstract

Provided is a steer-by-wire steering system (1) for a vehicle (2) that appropriately brings the steering angle of a wheel into a prescribed relationship with the steering angle of a steering member (10) even when the steering angle of the steering member is changed while parked. When the steering angle of the wheel deviates from the prescribed relationship with the steering angle of the steering member (ST2: YES) when started, a control unit (15) uses a change in transmission gear from a park position (P) or a neutral position (N) to a travel position (D or R) as a trigger (ST8: YES) to drive at least one of a steering actuator (12) and a reaction force actuator (13) to bring the steering angle (α) of the wheel closer to the prescribed relationship with the steering angle (β) of the steering member (ST12).

Description

Technical Field

[0001] This invention relates to a steer-by-wire system for vehicles. Background Technology

[0002] A steer-by-wire system for a vehicle is known, comprising: a steering member, such as a steering wheel configured for driver operation; and a steering mechanism mechanically separated from the steering member and configured to change the steering angle of the wheels. The steering mechanism is driven by a steering actuator that generates a driving force to change the steering angle of the wheels. A reaction force actuator applies a reaction force to the steering member in response to steering operation. In such a steering system, when the steering angle of the steering member should deviate from a predetermined relationship with the steering angle of the wheels, because the steering member moves after the vehicle's ignition switch is turned off and then turned on, the wheels will be turned by the steering actuator until the steering angle of the wheels matches the steering angle of the steering member. See, for example, Patent Document 1. According to Patent Document 1, the steering timing of the wheels is preferably selected before the vehicle begins to move, more preferably before the engine is started. Patent Document 1 also teaches driving the wheels when all doors are closed, the transmission is in the parking range, and the brake pedal is depressed.

[0003] List of cited references

[0004] Patent documents

[0005] [Patent Document 1] JP2007-153109A Summary of the Invention

[0006] Technical issues

[0007] According to the invention disclosed in Patent Document 1, the wheels can be turned even when the ignition is on, regardless of the driver's intention to move forward. Therefore, the steering angle of the wheels may change before the vehicle begins to move forward and before the driver has fully checked the environment around the vehicle, which may cause some discomfort to the driver.

[0008] In view of this problem in the prior art, the main objective of the present invention is to provide a steer-by-wire system for vehicles that can properly maintain a prescribed relationship between the steering angle of the steering component and the steering angle of the wheels, even when the steering angle of the steering component changes while the vehicle is parked.

[0009] Solution to the problem

[0010] To achieve this objective, the present invention provides a steering system (1) for a vehicle (2), the vehicle being provided with a transmission device (35) configured to be operated by a driver and having at least a transmission gear (SP) including a parking position or neutral position and a driving position, the steering system for the vehicle comprising: a steering member (10) configured to receive steering operation; a steering mechanism (11) mechanically separated from the steering member and configured to steer the wheels (3) of the vehicle; a steering angle sensor (21) for detecting the steering angle (β) of the steering member; a steering angle sensor (32) for detecting the steering angle (α) of the wheels; a steering actuator (12) configured to provide a driving force to the steering mechanism; and a reaction force actuator (13) for detecting the steering angle (α) of the wheels. A force actuator is configured to apply a reaction force to the steering member in response to the steering operation; and a control unit (15) is configured to control the steering actuator to make the steering angle of the wheel in a predetermined relationship with the steering angle of the steering member, and to control the reaction force actuator to make the reaction force correspond to the steering state of the wheel, wherein, when the steering angle of the wheel deviates from the predetermined relationship with the steering angle of the steering member upon activation (ST2: Yes), the control unit is configured to use a change of the transmission gear from the parking position or the neutral position to the driving position as a trigger (ST8: Yes) to drive at least one of the steering actuator and the reaction force actuator to make the steering angle of the wheel closer to the predetermined relationship with the steering angle of the steering member (ST12). Here, the driving position may include a driving position, a reverse position, a first speed position, and a second speed position.

[0011] Therefore, by shifting the transmission gear from the parking or neutral position to the driving position, the steering angle of the wheels and the steering mechanism are brought closer to the specified relationship. Thus, the steering angle of the wheels and the steering mechanism can only approach the specified relationship when the driver actually intends to begin moving forward.

[0012] Preferably, when the direction of the steering angle of the steering member and the direction of the steering angle of the wheel are consistent with each other at startup (ST6: No), the control unit is configured to drive the steering actuator by using the operation applied to the steering member as a trigger (ST10, No) to make the steering angle of the wheel closer to the prescribed relationship with the steering angle of the steering member (ST11).

[0013] Therefore, by using the operation applied to the steering component as a trigger to make the steering angle of the wheel closer to the prescribed relationship with the steering angle of the steering component, the wheel steering is prevented from happening, and the driver will not expect this to happen.

[0014] Preferably, when the direction of the steering angle of the steering member and the direction of the steering angle of the wheel are consistent with each other at startup (ST6: No), after an event in which the steering actuator is started by using the operation applied to the steering member as a trigger, the control unit is configured to stop driving the steering actuator by using the operation of stopping the application to the steering member as a trigger (ST10: Yes).

[0015] Since the steering angle of the wheel remains constant by stopping the drive of the steering actuator after the operation of the steering component has stopped, the steering angle of the wheel is prevented from changing, while no operation is applied to the steering component, and thus the operator is prevented from feeling uncomfortable.

[0016] Preferably, when the direction of the steering angle of the steering member and the direction of the steering angle of the wheel are inconsistent with each other at startup (ST6: Yes), the control unit is configured to drive at least one of the steering actuator and the reaction force actuator to make the steering angle of the wheel closer to the prescribed relationship with the steering angle of the steering member (ST12), regardless of whether the steering member is operated.

[0017] Therefore, when the direction of the steering angle of the steering component and the direction of the steering angle of the wheel are opposite to each other, when the gear shifts from the parking or neutral position to the driving position, the steering angle of the wheel is made closer to the specified relationship with the steering angle of the steering component, regardless of whether the steering component is operated.

[0018] Preferably, when the steering angle of the steering member and the steering angle of the wheel are opposite to each other at startup (ST6: Yes), after an event in which at least one of the steering actuator and the reaction force actuator is driven by using a change in the transmission gear as a trigger, the control unit is configured to stop the steering actuator or the reaction force actuator by using the alignment of the steering angle of the steering member and the steering angle of the wheel as a trigger (ST6: No).

[0019] Therefore, when the steering components are not operated, it prevents unnecessary changes in the steering angle of the steering components and / or the steering angle of the wheels, and prevents the vehicle from traveling in a direction not expected by the driver.

[0020] Preferably, the control unit is configured to drive the steering actuator under the condition that the direction of the steering angle of the steering member and the direction of the steering angle of the wheel are opposite to each other (ST6: Yes) and the transmission gear is in the parking position or the neutral position (ST8: No), so that when the steering member is operated (ST10: No), the steering angle of the wheel is closer to the prescribed relationship with the steering angle of the steering member (ST11).

[0021] Therefore, when the direction of the wheel's steering angle and the direction of the steering component's steering angle are opposite to each other, by using the operation of the steering component as a trigger, the wheel's steering angle can be made closer to the prescribed relationship with the steering component's steering angle without causing any discomfort to the driver.

[0022] Preferably, when the vehicle has started moving (ST4: yes) when the steering angle of the wheel deviates from the prescribed relationship with the steering angle of the steering member at startup, the control unit is configured to set an upper limit on the vehicle speed (ST13) until the steering angle of the wheel and the steering angle of the steering member are in the prescribed relationship.

[0023] This prevents vehicles from traveling at high speeds in directions other than those desired by the driver.

[0024] Preferably, when the vehicle has already started moving (ST4: Yes) due to the steering angle of the wheel deviating from the prescribed relationship with the steering angle of the steering member at startup, the control unit is configured to drive the steering actuator to bring the steering angle of the wheel closer to the prescribed relationship with the steering angle of the steering member (ST16), regardless of whether the steering member is operated, and release the upper limit of the vehicle speed once the steering angle of the wheel reaches the prescribed relationship with the steering angle of the steering member (ST2: No).

[0025] Therefore, when the steering mechanism is not operated, it prevents the vehicle from traveling at high speed in a direction different from the driver's desired direction.

[0026] Preferably, the control unit is configured to drive the steering actuator such that when the steering member is not operated (ST15: Yes), the rate of change of the steering angle of the wheel decreases as the vehicle speed increases (ST16).

[0027] Therefore, when the vehicle speed is low enough that a change in the wheel steering angle causes a very small change in vehicle behavior, the wheel steering angle changes at a relatively high rate. On the other hand, when the vehicle speed is high enough that a change in the wheel steering angle causes a significant change in vehicle behavior, the change in wheel steering angle is limited, thereby preventing the vehicle from exhibiting any unexpected behavior.

[0028] Preferably, the control unit is configured to drive the steering actuator such that when the steering member is operated (ST15: No), the steering angle of the wheel changes faster (ST17) than when the steering member is not operated (ST15: Yes).

[0029] Therefore, the wheel steering angle can be changed at high speed during steering operations because the driver can easily predict the vehicle's behavior at this time. This allows the wheel steering angle to initially maintain a predetermined relationship with the steering angle of the steering components.

[0030] Beneficial effects of the invention

[0031] Therefore, the present invention provides a steering system for a vehicle that can appropriately maintain a prescribed relationship between the steering angle of the wheels and the steering angle of the steering component, even when the steering angle of the steering component changes while the vehicle is parked. Attached Figure Description

[0032] [ Figure 1 ] Figure 1 This is a schematic diagram of a steering system according to an embodiment of the present invention.

[0033] [ Figure 2 ] Figure 2 This is a schematic diagram showing the relationship between the steering angle of the steering component and the steering angle of the front wheels.

[0034] [ Figure 3 ] Figure 3 It is a graph showing the relationship between the steering angle of the steering component and the steering angle of the front wheels.

[0035] [ Figure 4 ] Figure 4 This is a flowchart of phase matching control executed by the control unit at startup.

[0036] [ Figure 5 ] Figure 5 This is a timing diagram showing the change in steering angle caused by the passive phase matching process.

[0037] [ Figure 6 ] Figure 6 This is a timing diagram showing the change in steering angle caused by the active phase matching process.

[0038] [ Figure 7 ] Figure 7 This is a timing diagram illustrating an example of vehicle behavior under phase-matched control.

[0039] [ Figure 8 ] Figure 8 This is a timing diagram illustrating another example of vehicle behavior under phase-matched control.

[0040] [ Figure 9 ] Figure 9 This is a timing diagram illustrating yet another example of vehicle behavior under phase-matched control. Detailed Implementation

[0041] The following describes a steering system 1 for a vehicle 2 according to an embodiment of the present invention. 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 with 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 controlled by the vehicle body 8 via their respective steering knuckles 7. Figure 1 (Only the lower outline of the front wheel 3 is shown in the diagram.) The system provides support, allowing the steering angle α of the front wheel 3 to be changed, thus enabling the front wheel 3 to function as a steerable wheel. The steering angle α refers to the angle of the front wheel 3 relative to the longitudinal direction in the top view. Therefore, the steering system 1 changes the steering angle α of the front wheel 3.

[0042] The steering system 1 includes a steering member 10 rotatably mounted on the vehicle body 8, a steering mechanism 11 for steering the front wheels 3, a steering actuator 12 for applying driving force to the steering mechanism 11, a reaction force actuator 13 for applying a reaction torque T to the steering member 10, and a control unit 15 for controlling the reaction force actuator 13 and the steering actuator 12. The steering system 1 may be a redundant system comprising multiple sets of steering actuators 12, reaction force actuators 13, and control units 15, each of which is provided with a steering actuator 12, a reaction force actuator 13, and a control unit 15.

[0043] The steering member 10 receives steering input 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 the end of the steering shaft 18. The steering shaft 18 is rotatably supported by a steering column 20 disposed on the vehicle body 8, and the rear end of the steering shaft 18 protrudes rearward from the steering column 20. 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.

[0044] The reaction force actuator 13 includes an electric motor connected to the steering shaft 18 via a gear mechanism. 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 a rotational 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 called the reaction torque T.

[0045] The steering system 1 is also provided with a steering angle sensor 21, which detects the rotation angle of the steering shaft 18 about its central axis as the steering angle β. The steering angle sensor 21 may be a rotary encoder, which is known per se. Furthermore, the steering system 1 is provided with a torque sensor 22, which detects the torque applied to the steering shaft 18 as the steering torque Ts. The torque sensor 22 detects the steering torque Ts applied to the portion of the steering shaft 18 located between the steering wheel 19 and the reaction torque actuator 13. The steering torque Ts is determined by the operating torque applied by the driver to the steering wheel 19 and the reaction torque T applied by the reaction torque actuator 13 to the steering shaft 18. The torque sensor 22 may include a torque sensor known per se, such as a magnetostrictive torque sensor or a strain gauge; alternatively, the steering torque may be estimated based on the current value flowing through the electric motor of the reaction torque actuator 13.

[0046] The steering system 1 also includes a first rotation angle sensor 23 for detecting the rotation angle θ of the reaction force actuator 13. The first rotation angle sensor 23 may be a known solver or rotary encoder.

[0047] The steering mechanism 11 has a rack 26 extending in the lateral direction of the vehicle. The rack 26 is supported by a gearbox 27 so that it can move in the lateral direction of the vehicle. The left and right ends of the rack 26 are respectively connected to steering knuckles 7, which support the left and right front wheels 3 via corresponding tie rods 30. When the rack 26 moves in the lateral direction of the vehicle, the steering angle α of the front wheels 3 changes. The steering mechanism 11 is mechanically separated from the steering member 10.

[0048] The steering actuator 12 includes an electric motor. The steering actuator 12 moves the rack 26 in the lateral direction of the vehicle according to the signal from the control unit 15, and accordingly changes the steering angle α of the left and right front wheels 3.

[0049] The steering system 1 is also provided with a second rotation angle sensor 31 for detecting the rotation angle θ of the steering actuator 12. The second rotation angle sensor 31 may be a known solver or rotary encoder. In addition, the steering system 1 has a steering angle sensor 32 for detecting the steering angle α of the front wheels 3. In this embodiment, the steering angle sensor 32 includes a rack travel sensor for detecting the rack position (the position of the rack 26 in the lateral direction of the vehicle), and the steering angle α of the front wheels 3 is determined by the rack position.

[0050] The control unit 15 comprises an electronic control unit including a CPU, a memory, and a storage device for storing programs. Steering angle sensor 21, torque sensor 22, first rotation angle sensor 23, second rotation angle sensor 31, and steering angle sensor 32 are connected to the control unit 15. Based on signals from these sensors, the control unit 15 acquires signals corresponding to steering angle β, steering torque Ts, rotation angle θ of reaction force actuator 13, rotation angle θ of steering actuator 12, and steering angle α. Furthermore, the control unit 15 is connected to vehicle speed sensor 33 and gear position sensor 34, and acquires signals corresponding to vehicle speed V and transmission gear SP of transmission unit 35.

[0051] The transmission unit 35 is a device that changes the power transmission mode from the drive source mounted on the vehicle 2 to the wheels. For example, when the vehicle 2 is equipped with an internal combustion engine as the propulsion drive source, the transmission unit 35 is a device that changes the driving force transmission mode from the internal combustion engine to the driven wheels. Furthermore, when the vehicle 2 is equipped with an electric motor as the propulsion drive source, the transmission unit 35 is a power unit that changes the driving force transmission mode from the electric motor to the driven wheels.

[0052] In the case of an automatic transmission, the transmission unit 35 includes a parking position "P", a neutral position "N", a drive position "D", and a reverse position "R" as transmission gears SP representing different drive force transmission modes. The drive position "D" can have a single range, or it can have multiple ranges including a first speed, a second speed, etc. When the transmission unit 35 is a manual transmission, the transmission unit 35 has a neutral position "N", a drive position "D", and a reverse position "R". The drive position "D" can have multiple ranges, for example, from a first speed to a fifth speed. In the following text, the drive position "D" and the reverse position "R" are collectively referred to as driving positions.

[0053] The transmission gear SP of the transmission unit 35 is changed by the driver through a switching operation performed by a switching member such as a shift lever or shift button. The shift button may be a function button displayed on a touch panel display. The gear position sensor 34 acquires a signal corresponding to the transmission gear SP of the transmission unit 35 switched by the driver. The vehicle system equipped with the control unit 15 is configured to be engaged and disengaged only when the transmission unit 35 is in the parking position "P" or the neutral position "N".

[0054] The control unit 15 is connected to the reaction force actuator 13 and the steering actuator 12, and controls the reaction force actuator 13 and the steering actuator 12. The control unit 15 controls the steering actuator 12 according to the steering angle β, and controls the reaction force actuator 13 according to the steering angle α.

[0055] The control actions of the control unit 15 in SBW mode are described in detail below. The control unit 15 calculates a target steering angle αt that has a predetermined relationship with the actual steering angle β detected by the steering angle sensor 21. The control unit 15 can calculate the target steering angle αt (αt = β × K) by, for example, multiplying the steering angle β by a predetermined gear ratio K. The gear ratio K can be, for example, 0.01 to 0.5, and preferably 0.125. Then, the control unit 15 calculates a first current value A1 to be supplied to the steering actuator 12 based on the deviation Δα (= αt - α) between the target steering angle αt and the actual steering angle α, such that the steering angle α matches the target steering angle αt. That is, the control unit 15 performs feedback control of the steering actuator 12 based on the deviation Δα. As the deviation Δα increases, the first current value A1 supplied to the steering actuator 12 increases, and the output of the steering actuator 12 increases, resulting in an increase in the change in steering angle α.

[0056] The control unit 15 calculates the target reaction torque Tt to be generated by the reaction force actuator 13 based on the steering state of the front wheels 3, and in particular on the deviation Δα. The target reaction torque Tt can be calculated by multiplying Δα by a predetermined coefficient. Then, the control unit 15 calculates the second current value A2 to be supplied to the reaction force actuator 13 based on the calculated target reaction torque Tt. The second current value A2 to be supplied to the reaction force actuator 13 can be determined by referring to a predetermined mapping based on the target reaction torque Tt. Alternatively, the control unit 15 can determine the second current value A2 by referring to a predetermined mapping based on the deviation Δα. The values ​​of the target reaction torque Tt and the second current value A2 increase as the deviation Δα of the steering angle α increases.

[0057] Control unit 15 supplies a second current value A2 to reaction force actuator 13, and generates a driving force in reaction force actuator 13. The driving force generated by reaction force actuator 13 is supplied to steering shaft 18 as a reaction torque T opposite to the driver's operating input. As a result, the driver can receive a reaction force (resistance) against steering operation from steering wheel 19.

[0058] When the ignition switch of vehicle 2 is turned on, control unit 15 is activated, and when the ignition switch is turned off, control unit 15 is deactivated. Therefore, when the ignition switch is off, even if the steering member 10 rotates and the steering angle β changes, the steering angle α of the front wheel 3 does not change, and no reaction torque T is generated. Therefore, when the ignition switch is off, the steering angle β of the steering member 10 and the steering angle α of the front wheel 3 may deviate from the specified transmission ratio relationship described above. In the following disclosure, the two angles normalized by taking the transmission ratio into account are referred to as phase, and the angular deviation from the specified relationship between the steering angle α and the steering angle β is referred to as phase difference. Phase difference can occur in various different types.

[0059] Figure 2 This is a schematic diagram showing the phase relationship between the steering angle β of the steering component 10 and the steering angle α of the front wheel 3. For example... Figure 2 As shown, the phases of steering angle β and steering angle α can deviate from each other in two different types: Type A, or opposite phase relationship, where the phases of steering angle β and steering angle α are opposite to each other; and Type B, or same phase relationship, where the phases of steering angle β and steering angle α are the same. The two phases are considered to be the same when only one of the phases of steering angle β and steering angle α is 0, or within a specified small angle range of approximately 0. Therefore, Type B can be further divided into four types: Type B1, where steering angle β is 0 and steering angle α is not 0; Type B2, where the phase of steering angle α is greater than the phase of steering angle β; Type B3, where the phase of steering angle α is less than the phase of steering angle β; and Type B4, where steering angle β is greater than 0 in either direction and steering angle α is 0.

[0060] Figure 3 It is a graph showing the relationship between the steering angle β of the steering component 10 and the steering angle α of the front wheel 3, including a single anti-phase type and four in-phase types.

[0061] Because the phase relationship between steering angle β and steering angle α may be interfered with when the ignition switch is off, when the ignition switch is on and the control unit 15 is activated, the control unit 15 performs the following actions: Figure 4 The phase matching control process is shown.

[0062] Figure 4 A flowchart is shown of the phase-matching control process executed by control unit 15 at startup. (See attached diagram.) Figure 4 As shown, when activated, the control unit 15 acquires the steering angle β and steering angle α (step ST1) and determines whether there is any deviation between the phase of the steering angle β and the phase of the steering angle α (step ST2). In step ST2, it is determined whether the phase relationship between the steering angle β and the steering angle α deviates from the predetermined transmission ratio relationship (whether the phase relationship deviates from the predetermined transmission ratio relationship). Figure 3 The slant transmission ratio line K is shown. If the phase of the steering angle β and the phase of the steering angle α are in sync (ST2: No), the control unit 15 terminates the process.

[0063] If the phases of steering angle β and steering angle α deviate from each other (ST2: Yes), control unit 15 acquires vehicle speed V (step ST3) and determines whether vehicle 2 is moving (step ST4). More specifically, when vehicle speed V is higher than a predetermined threshold Vth, control unit 15 determines that vehicle 2 is moving; otherwise, it determines that vehicle 2 is stationary. When vehicle 2 is determined to be stationary (ST4: No), control unit 15 determines the type of phase deviation based on steering angle β and steering angle α (step ST5) to determine whether it is a case of opposite phase relationship (Type A) (step ST6).

[0064] In the case of an out-of-phase relationship (ST6: Yes), control unit 15 acquires the transmission gear position SP (step ST7) and determines whether the transmission gear position SP is in drive position "D" or reverse position "R" (step ST8). If the driver has not yet operated the shift lever, and the transmission gear position SP is still in park position "P" or neutral position "N" (ST8: No), or if the determination result of step ST6 is no, control unit 15 acquires the steering angular velocity βdot (step ST9). Control unit 15 determines whether the steering angular velocity βdot is 0 (degrees / second) or within a predetermined small speed range that can be considered 0 (degrees / second) (step ST10). For ease of description, the latter case will be referred to as the "βdot=0" case in the following disclosure.

[0065] When the steering angular velocity βdot is 0 (ST10: Yes), the control unit 15 repeats the above process. When the steering member 10 is operated or steered by the driver and the steering angular velocity βdot is not 0 (ST10: No), the control unit 15 performs passive phase matching (step ST11). In the passive phase matching of step ST11, at least one of the steering actuator 12 and the reaction force actuator 13 is driven such that the phase of the steering angle β and the phase of the steering angle α are closer to each other when the steering member 10 is steered (ST10: No). Here, "making the phase of the steering angle β and the phase of the steering angle α closer to each other" means making the steering angle β and the steering angle α closer to the specified relationship (the above-mentioned transmission ratio relationship). This phase matching is characterized as "passive" because phase matching only occurs during the execution of specific actions such as steering operations. In this embodiment, the control unit 15 drives the steering actuator 12 to match the phase of the steering angle β and the phase of the steering angle α.

[0066] In the passive phase matching of step ST11, the control unit 15 uses the event of operating the steering member 10 as a trigger (ST10: No) to drive the steering actuator 12 to bring the phases of the steering angle β and the steering angle α closer to each other. In this way, since the steering angle α is brought closer to the steering angle β in phase by using the operation of the steering member 10 as a trigger, the front wheels 3 are prevented from turning unexpectedly by the driver.

[0067] Figure 5 This is a timing diagram illustrating the change in steering angle α during passive phase matching. (For example...) Figure 5 As shown, in passive phase matching, the control unit 15 drives the steering actuator 12 to gradually reduce the deviation Δα (=αt-α) between the target steering angle αt set according to the steering angle β and the actual steering angle α. Even when the steering member 10 turns in a direction closer to the phase of the steering angle α, if the steering speed of the steering member 10 is equal to or higher than the predetermined steering speed, the control unit 15 drives the steering actuator 12 so that the front wheels 3 turn in the same direction as the steering direction of the steering member 10.

[0068] See you again Figure 4 In the passive phase matching step ST11, the control unit 15 repeats the above process, or uses an event that stops the operation of the steering member 10 as a trigger (ST10: Yes) to stop driving the steering actuator 12. As a result, the steering angle α remains constant when the steering member 10 is not operated, thereby preventing the driver from feeling any discomfort.

[0069] When the driver performs a gear shift operation to change the transmission gear SP to drive position "D" or reverse position "R", the determination result in step ST8 becomes yes, and the control unit 15 performs anti-phase matching (step ST12). Anti-phase matching is a control process in which at least one of the steering actuator 12 and the reaction force actuator 13 is driven such that the phase of steering angle β and the phase of steering angle α are brought closer to each other and enter the same phase, regardless of whether the steering member 10 is turning.

[0070] The anti-phase matching in step ST12 is triggered by the event that the transmission gear SP changes from the parking position "P" or neutral position "N" to the drive position "D" or reverse position "R" during the determination process in step ST8. In other words, the control unit 15 begins anti-phase matching after the transmission gear SP has changed from the parking position "P" or neutral position "N" to the drive position. Anti-phase matching can begin immediately after this condition is met, or it may have a certain time delay.

[0071] Thus, when the driver triggers the change of the transmission gear SP from the parking position "P" or neutral position "N" to the driving position, the control unit 15 performs anti-phase matching in step ST12, bringing the phases of steering angle α and steering angle β closer together. Therefore, the phases of steering angle α and steering angle β are closer together only when the driver intends to start the vehicle.

[0072] In this embodiment, the control unit 15 drives the steering actuator 12 to make the steering angle β and steering angle α in phase. In the anti-phase matching (ST12) of this embodiment, the control unit 15 drives the steering actuator 12 with a target steering angle αt set to 0° (neutral position), and stops driving the steering actuator 12 once the steering angle α matches the target steering angle αt, and once the phase of the steering angle α becomes the same as the phase of the steering angle β. Here, the target steering angle αt can be set to any value, as long as it is within a specific range of 0° that is in phase with the steering angle β.

[0073] When the control unit 15 has determined that the directions of the steering angle β and the steering angle α are consistent with each other (ST6: No), the steering actuator 12 is stopped from being driven. As a result, even when the steering member 10 is not operated (ST10: Yes), unnecessary changes in the steering angle α and / or steering angle β are prevented, and the vehicle 2 is prevented from traveling in a direction not desired by the driver.

[0074] Unlike the passive phase matching in step ST11, the anti-phase matching in step ST12 is performed regardless of whether the steering member 10 has been operated. Therefore, when the directions of steering angle β and steering angle α are opposite to each other (ST6: Yes), the phases of steering angle α and steering angle β can immediately approach each other after the transmission gear SP is changed from the parking position "P" or neutral position "N" to the driving position, regardless of the operation of the steering member 10.

[0075] When the control unit 15 performs anti-phase matching in step ST12, it subsequently determines the type of phase deviation as anti-phase type in step ST6 (ST6: No). In this case, the control process executed by the control unit 15 proceeds to step ST9 and performs passive phase matching (ST11) to match the phase of steering angle β and the phase of steering angle α to each other when the steering member 10 is not steering (ST10: No).

[0076] Furthermore, when the directions of steering angle β and steering angle α are opposite to each other (ST6: Yes), passive phase matching in step ST11 is performed by using the operation of steering member 10 (ST10: No) as a trigger when the transmission gear SP is in the parking position "P" or neutral position "N" (ST8: No). In this way, when the directions of steering angle β and steering angle α are opposite to each other, by using the operation of steering member 10 as a trigger, the phases of steering angle α and steering angle β can be brought closer to each other without causing any discomfort to the driver.

[0077] If vehicle 2 starts moving without completing the phase matching of steering angle β and steering angle α through passive phase matching in step ST11, it is determined in step ST4 that vehicle 2 is moving (ST4: Yes). In this case, control unit 15 limits the vehicle speed by setting an upper limit value for vehicle speed V (step ST13). For example, control unit 15 sets the upper limit value of vehicle speed V to 10 km / h. Once the phase matching control process is completed, control unit 15 releases the upper limit value of vehicle speed V. Therefore, vehicle 2 is prevented from moving at a speed V higher than the upper limit value until the phase of steering angle β and the phase of steering angle α match each other, and the determination result in step ST2 becomes No, or in other words, until... Figure 4 The phase matching control shown is complete.

[0078] Thus, if vehicle 2 starts moving when the phases of steering angle β and steering angle α are out of sync (ST4: Yes), control unit 15 sets an upper limit for vehicle speed V until phase matching is complete (ST13). As a result, vehicle 2 is prevented from traveling at high speed in directions not desired by the driver.

[0079] Subsequently, the control unit 15 acquires the steering angular velocity βdot (step ST14) and determines whether the steering angular velocity βdot is 0 (step ST15). When the steering angular velocity βdot is 0 (ST15: Yes), the control unit 15 performs active phase matching (step ST16). Active phase matching is a control action that drives at least one of the steering actuator 12 and the reaction force actuator 13 such that even when the driver does not steer the steering member 10 (ST15: Yes), after the vehicle 2 begins to move (ST4: Yes), the phase of the steering angle β and the phase of the steering angle α gradually become synchronized. In this embodiment, the control unit 15 drives the steering actuator 12 to match the phase of the steering angle β with the phase of the steering angle α.

[0080] Thus, regardless of whether the steering component 10 is operated, the control unit 15 performs active phase matching in step ST16, thereby preventing the vehicle 2 from traveling at high speed in a direction undesirable to the driver, even when the steering component 10 is not operated. By performing active phase matching, the phase of the steering angle β and the phase of the steering angle α are always consistent after the vehicle 2 begins to move. Once the determination result in step ST2 becomes negative, the phase matching control ends. This releases the upper limit of the vehicle speed V.

[0081] Figure 6 This is a timing diagram showing the change in steering angle α due to active phase matching. (Example:) Figure 6As shown, once the vehicle speed V becomes higher than the predetermined threshold Vth, the control unit 15 initiates active phase matching and drives the steering actuator 12 to reduce the phase deviation between the steering angle β and the steering angle α.

[0082] At this time, when driving the steering actuator 12, the control unit 15 multiplies the deceleration gain G by the first current value A1 calculated from the deviation Δα between the target steering angle αt and the actual steering angle α, in order to reduce the rate of change of steering angle α compared to the normal steering angle control situation. As a result, the rate of change of steering angle α becomes slower than normal, and the vehicle 2 is prevented from operating in a way that is not desired by the driver.

[0083] The deceleration gain G can be chosen to vary with vehicle speed V. More specifically, when vehicle speed V is low, the deceleration gain G can be chosen to be a relatively large value, and it can also be chosen to be a small value, such that the rate of change of steering angle α slows down as vehicle speed V increases. As a result, when vehicle speed V is low and the effect of the change of steering angle α on vehicle behavior is small, the steering angle α changes at a relatively high rate. Conversely, when vehicle speed V is high and the effect of the change of steering angle α on vehicle behavior is large, the steering angle α changes at a relatively low rate. This prevents vehicle 2 from operating in an unexpected manner.

[0084] See you again Figure 4 When the driver steers the steering member 10 while the vehicle 2 is moving (ST4: Yes), and the steering angular velocity βdot is not 0 (ST15: No), the control unit 15 performs passive phase matching (step ST17). In the passive phase matching of step ST17, at least one of the steering actuator 12 and the reaction force actuator 13 is driven such that the phase of the steering angle β is matched with the phase of the steering angle α while the steering member 10 is not turning (ST15: No). In this embodiment, the control unit 15 drives the steering actuator 12 to match the phase of the steering angle β with the phase of the steering angle α.

[0085] In the passive phase matching of step ST17, the control unit 15 drives the steering actuator 12 in such a way that the steering angle α changes faster than in the case of active phase matching (ST16) performed when the steering member 10 is operated. As a result, since the driver can easily predict the behavior of the vehicle 2 in this situation, the steering angle α changes rapidly during the steering operation, and as a result, the phase of the steering angle β and the phase of the steering angle α can be matched in an early stage.

[0086] Phase matching control ends when the phase of steering angle β and the phase of steering angle α are matched through passive phase matching in step ST11, active phase matching in step ST16, or passive phase matching in step ST17, and the determination result in step ST2 becomes negative.

[0087] Then, see below. Figures 7 to 9 ,right Figure 4 An example of vehicle behavior during phase matching control is provided to illustrate this.

[0088] exist Figure 7 In the example shown, at time t1, the ignition switch is turned on and the control unit 15 is activated. At this time, the phase of the steering angle β of the steering member 10 and the phase of the steering angle α of the front wheels 3 are opposite to each other, because the steering member turns to the left and the front wheels turn to the right. When the transmission gear SP changes from the parking position "P" or neutral position "N" to the driving position at time t2, the control unit 15 uses the gear change as a trigger to start anti-phase matching (ST12).

[0089] Due to the anti-phase matching control action, the target steering angle αt is set to 0°, the steering actuator 12 is commanded to turn left, and the front wheels 3 turn left. At time point t3, the steering angle α becomes 0°, and the anti-phase matching is completed. From time point t2 to time point t3, the vehicle speed V remains at 0 km / h.

[0090] During the time interval between time point t2 and time point t3 when anti-phase matching is performed, the control unit 15 notifies the driver via visual display or sound that phase synchronization is in progress (phase matching is being performed).

[0091] exist Figure 8 In the example shown, at time point t11, the ignition switch is turned on and the control unit 15 is activated. At this time, the phase of the steering angle β of the steering member 10 and the phase of the steering angle α of the front wheel 3 are in phase, because the former has a smaller value to the right and the latter has a larger value to the right. At time point t12, the transmission gear SP changes from the parking position "P" or neutral position "N" to the driving position. Since this is in phase, anti-phase matching is not performed.

[0092] When it is determined that vehicle 2 starts driving at time t13, and the vehicle speed V is higher than the predetermined threshold Vth at time t14, the control unit 15 uses this as a trigger to set the upper limit value of the vehicle speed V. Since the steering component 10 does not steer at time t14, the control unit 15 starts active phase matching (ST16).

[0093] Due to the control action of active phase matching, the target steering angle αt is set to the value corresponding to the steering angle β, and the steering actuator 12 is commanded to turn left, causing the front wheels 3 to turn left. At time point t15, the actual steering angle α equals the target steering angle αt corresponding to the steering angle β, and active phase matching ends. During the time interval between time points t14 and t15, the control unit 15 notifies the driver via visual display or sound that phase matching is in progress (phase matching is being performed).

[0094] exist Figure 9 In the example shown, at time point t21, the ignition switch is turned on and the control unit 15 is activated. At this time, the steering angle β of the steering member 10 and the steering angle α of the front wheel 3 are in phase, because the former is 0° and the latter is a larger value to the right. At time point t22, the transmission gear SP changes from the parking position "P" or neutral position "N" to the driving position. Since they are in phase, anti-phase matching is not performed.

[0095] When it is determined that vehicle 2 starts driving at time t23 and the vehicle speed V is greater than the predetermined threshold Vth at time t24, the control unit 15 uses this as a trigger to set the upper limit value of the vehicle speed V. Since the steering component 10 does not steer at time t24, the control unit 15 initiates active phase matching (ST16).

[0096] Due to the active phase matching control action, the target steering angle αt is set to the value corresponding to the steering angle β (0°), the steering actuator 12 is commanded to turn left, and the front wheels 3 turn left. When the steering member 10 begins to turn right at time t25, the control unit 15 switches from active phase matching to passive phase matching (ST17). In passive phase matching, the control unit 15 causes the front wheels 3 to turn in the same direction as the steering member 10, causing the steering angle α of the front wheels 3 to increase to the right, but the phase deviation between the steering angle α and the steering angle β (or the deviation Δα between the actual steering angle α and the target steering angle αt set according to the steering angle β) decreases.

[0097] When the rotation of the steering member 10 stops at time t26, and the steering angle β begins to remain at a constant value without any steering operation, the control unit 15 reactivates active phase matching. A left turn command is given to the steering actuator 12, and the front wheels 3 turn left. When the steering member 10 begins to turn left at time t27, the control unit 15 switches from active phase matching to passive phase matching again. In passive phase matching, the control unit 15 causes the front wheels 3 to turn in the same direction as the steering member 10, so that the deviation Δα between the target steering angle αt and the actual steering angle α gradually decreases. Therefore, the front wheels 3 turn left, and at time t28, the steering angle α corresponds to the target steering angle αt, or the value corresponding to the steering angle β. As a result, the phase of the steering angle β and the phase of the steering angle α are matched, and phase matching control is completed.

[0098] During the time interval between time point t24 and time point 28, or during the time of performing active or passive phase matching, the control unit 15 notifies the driver via visual display or sound that phase matching is in progress (phase matching is being performed).

[0099] As described above, according to this embodiment, such as Figure 4 As shown, if the steering angle α deviates from the specified relationship relative to the steering angle β during startup (ST2: Yes), then by shifting the transmission gear SP from the parking position "P" or neutral position "N" to the driving position (ST8: Yes), the control unit 15 drives at least one of the steering actuator 12 and the reaction force actuator 13 (ST12) to bring the steering angle α closer to the specified relationship with the steering angle β. Therefore, the steering angles α and β can only be closer to the specified relationship when the driver intends to start the vehicle.

[0100] The present invention has been described according to specific embodiments, but the invention is not limited to such embodiments and can be modified in various ways without departing from the scope of the invention. In the foregoing embodiments, the control unit 15 is configured to drive the steering actuator 12 in anti-phase matching in step ST12, but the control unit 15 may drive the reaction force actuator 13 in addition to the steering actuator 12. Furthermore, the specific configuration, arrangement, quantity, angle, program, etc. of each component and part can be appropriately changed without departing from the spirit of the invention. In addition, all components shown in the above embodiments are not essential to the present invention and can be appropriately selected and omitted without departing from the spirit of the invention.

[0101] List of reference numerals

[0102] 1: Steering system 2: Vehicle

[0103] 3: Front wheel 10: Steering component

[0104] 11: Steering mechanism 12: Steering actuator

[0105] 13: Reaction force actuator 15: Control unit

[0106] 21: Steering angle sensor 32: Steering angle sensor

[0107] 35: Transmission unit

[0108] α: Steering angle

[0109] β: Steering angle

[0110] SP: Gearbox position

Claims

1. A steering system for a vehicle provided with a transmission device configured to be operated by a driver and having a transmission gear position including at least a parking position or a neutral position and a traveling position, the steering system for a vehicle comprising: a steering member configured to accept a steering operation; a steering mechanism mechanically separated from the steering member and configured to steer a wheel of the vehicle; a steering angle sensor that detects a steering angle of the steering member; a steering angle sensor that detects a steering angle of the wheel; a steering actuator configured to provide a driving force to the steering mechanism; a reaction force actuator configured to apply a reaction force to the steering member in response to the steering operation; and a control unit configured to control the steering actuator to make the steering angle of the wheel be in a prescribed relationship with the steering angle of the steering member, and to control the reaction force actuator to make the reaction force correspond to a steering state of the wheel, wherein when a direction of the steering angle of the steering member and a direction of the steering angle of the wheel are not consistent with each other at the start and the steering angle of the wheel deviates from the prescribed relationship with the steering angle of the steering member, the control unit is configured to drive at least one of the steering actuator and the reaction force actuator in response to a change of the transmission gear position from the parking position or the neutral position to the traveling position to make the steering angle of the wheel closer to the prescribed relationship with the steering angle of the steering member, and wherein when the direction of the steering angle of the steering member and the direction of the steering angle of the wheel are consistent with each other at the start and the steering angle of the wheel deviates from the prescribed relationship with the steering angle of the steering member, the control unit is configured to drive at least one of the steering actuator and the reaction force actuator in response to an operation applied to the steering member to make the steering angle of the wheel closer to the prescribed relationship with the steering angle of the steering member. When the direction of the steering angle of the steering member and the direction of the steering angle of the wheel are consistent with each other at the start and the steering angle of the wheel deviates from the prescribed relationship with the steering angle of the steering member, the control unit is configured to stop driving the steering actuator in response to a stop of the operation applied to the steering member after an event of starting to drive the steering actuator in response to the operation applied to the steering member.

2. The steering system for a vehicle according to claim 1, wherein, When the direction of the steering angle of the steering member and the direction of the steering angle of the wheel are opposite to each other at the start, the control unit is configured to stop the steering actuator or the reaction force actuator in response to a consistency of the direction of the steering angle of the steering member and the direction of the steering angle of the wheel after an event of driving at least one of the steering actuator and the reaction force actuator in response to a change of the transmission gear position.

3. The steering system for a vehicle according to claim 1, wherein, ​ 4. The steering system for a vehicle according to claim 1, wherein, The control unit is configured to drive the steering actuator when the steering angle of the steering member and the steering angle of the wheel are opposite to each other and the transmission gear is in the parking position or the neutral position, so that when the steering member is operated, the steering angle of the wheel is closer to the prescribed relationship with the steering angle of the steering member.

5. A steering system for a vehicle, the vehicle being provided with a transmission, the transmission being configured to be operated by a driver and having at least a transmission gear including a parking position or neutral position and a driving position, the steering system for the vehicle comprising: A steering component configured to accept steering operations; A steering mechanism, mechanically separate from the steering member and configured to steer the wheels of the vehicle; A steering angle sensor that detects the steering angle of the steering component; A steering angle sensor that detects the steering angle of the wheel; A steering actuator configured to provide driving force to the steering mechanism; A reaction force actuator, the reaction force actuator being configured to apply a reaction force to the steering member in response to the steering operation; as well as A control unit is configured to control the steering actuator to make the steering angle of the wheel have a predetermined relationship with the steering angle of the steering member, and to control the reaction force actuator to make the reaction force correspond to the steering state of the wheel. Wherein, when the steering angle of the wheel deviates from the prescribed relationship with the steering angle of the steering member upon startup, the control unit is configured to, in response to a change in the transmission gear from the parking position or the neutral position to the driving position, drive at least one of the steering actuator and the reaction force actuator to bring the steering angle of the wheel closer to the prescribed relationship with the steering angle of the steering member, and Wherein, when the vehicle has already started moving if the steering angle of the wheels deviates from the prescribed relationship with the steering angle of the steering component at startup, the control unit is configured to set an upper limit on the vehicle speed until the steering angle of the wheels and the steering angle of the steering component are in the prescribed relationship.

6. The steering system for a vehicle according to claim 5, wherein, When the vehicle has already started moving and the steering angle of the wheel deviates from the prescribed relationship with the steering angle of the steering member at startup, the control unit is configured to drive the steering actuator to bring the steering angle of the wheel closer to the prescribed relationship with the steering angle of the steering member, regardless of whether the steering member is operated, and to release the upper limit of the vehicle speed once the steering angle of the wheel reaches the prescribed relationship with the steering angle of the steering member.

7. The steering system for a vehicle according to claim 6, wherein, The control unit is configured to drive the steering actuator such that when the steering component is not operated, the rate of change of the wheel's steering angle decreases as the vehicle speed increases.

8. The steering system for a vehicle of claim 6, wherein, The control unit is configured to drive the steering actuator such that when the steering member is operated, the steering angle of the wheel changes faster than when the steering member is not operated.

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