Steering system for a vehicle

Abstract

Provided is a steer-by-wire steering system for a vehicle that can prevent the vehicle from suddenly accelerating in a direction that is not intended for driving even when the steering angle of a steering member is changed while the vehicle is parked. When the steered angle deviates from a prescribed relationship with the steering angle (ST2: YES), a control unit drives a steering actuator to make the steered angle closer to the prescribed relationship with the steering angle (ST16, ST17, ST20, ST21) immediately or when a trigger condition is satisfied, and sets an upper limit on the speed or acceleration of the vehicle (ST7).

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 operation by a driver; 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 the ignition switch is subsequently turned on, the wheels will be turned by the steering actuator until the steering angle of the wheels coincides with 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.

[0003] List of cited references

[0004] Patent documents

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

[0006] Technical issues

[0007] However, the maximum output of the steering actuator may decrease due to a malfunction in the steering actuator or overheating of the electric motor of the steering actuator. In this case, according to the invention disclosed in Patent Document 1, the vehicle may begin to move before the wheels are turned to a steering angle corresponding to the steering angle of the steering member. Furthermore, if the driver suddenly presses the accelerator pedal, the vehicle may suddenly accelerate in a direction unpredictable by 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 prevent the vehicle from suddenly accelerating in a direction unpredictable by the driver, 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 steering system for the vehicle comprising: a steering member (10) configured to receive a steering operation; a steering mechanism (11) mechanically separated from the steering member and configured to steer a wheel (3) via movement of the steering mechanism; a steering angle sensor (21) detecting a steering angle (β) of the steering member; a steering angle sensor (32) detecting a steering angle (α) of the wheel; a steering actuator (12) configured to provide a driving force to the steering mechanism; and a reaction force actuator (13) for providing a driving force to the steering mechanism. The actuator is configured to apply a reaction force to the steering member in response to the steering operation; and a control unit (15) controls the operation of the steering actuator to make the steering angle in a predetermined relationship with the steering angle, and controls the operation of the reaction force actuator to make the reaction force correspond to the steering state of the wheel, wherein when the steering angle deviates from the predetermined relationship with the steering angle (ST2: yes), immediately or when a triggering condition is met, the control unit drives the steering actuator to make the steering angle closer to the predetermined relationship with the steering angle (ST16, ST17, ST20, ST21), and sets an upper limit (ST7) on the speed or acceleration of the vehicle.

[0011] Therefore, when the steering angle deviates from the prescribed relationship with the steering angle, an upper limit is set on the vehicle's speed or acceleration. By limiting the vehicle's speed or acceleration in this way, sudden acceleration in directions unpredictable by the driver is prevented.

[0012] Preferably, the control unit is configured to acquire the maximum output (ST3) of the steering actuator, and when the maximum output of the steering actuator is equal to or greater than a predetermined value (ST4: yes), the control unit does not set the upper limit for the speed or acceleration of the vehicle.

[0013] If an upper limit is set on the vehicle's speed or acceleration whenever the steering angle deviates from the specified relationship with the steering angle, then even when the wheels can be properly driven to the steering angle corresponding to the steering angle of the steering member, the vehicle is prevented from accelerating as the driver desires. According to this arrangement, since no upper limit is set on the vehicle's speed or acceleration when the maximum output of the steering actuator is equal to or greater than the specified value, unnecessary restrictions on the vehicle's acceleration as desired by the driver can be avoided.

[0014] Preferably, the control unit calculates the maximum correction angle (α) based on the maximum output of the steering actuator. cmaxThe maximum correction angle is given as the maximum change in the steering angle that can be achieved within a specified time period (ST5), and even when the maximum output of the steering actuator is less than the specified value (ST4: no), as long as the steering angle deviates from the specified relationship with the steering angle by the amount of deviation (α) dev If the speed or acceleration of the vehicle is equal to or less than the maximum correction angle (ST6: Yes), the control unit will not set the upper limit for the speed or acceleration of the vehicle.

[0015] Since no upper limit is set on the vehicle's speed or acceleration when the deviation of the steering angle from the specified relationship is equal to or less than the maximum correction angle, any undesirable limitation on the vehicle's acceleration can be reliably avoided.

[0016] Preferably, when the maximum output of the steering actuator is less than the predetermined value (ST4: No), and the deviation of the steering angle from the predetermined relationship is equal to or greater than the maximum correction angle (ST6: No), the control unit sets the upper limit on the speed or acceleration of the vehicle until the maximum output becomes equal to or greater than the predetermined value, or until the deviation becomes equal to or less than the maximum correction angle (ST6: Yes).

[0017] This prevents sudden acceleration of the vehicle until its direction of travel aligns with the driver's intended direction for a specified period. Once this alignment is achieved, the vehicle can accelerate as needed by the driver. Therefore, both steering and acceleration can be controlled according to the driver's requirements.

[0018] Preferably, the control unit calculates the maximum correction angle (α) based on the maximum output of the steering actuator. cmax The maximum correction angle is given as the maximum change value of the steering angle that can be achieved within a specified time period (ST5), and even when the maximum output of the steering actuator is less than the specified value (ST4: no), if the same-direction correction amount (α) is given as the correction amount required to bring the steering angle and the steering angle to the same side of the neutral point. devn If the speed or acceleration of the vehicle is equal to or less than the maximum correction angle (ST6: Yes), then the control unit will not set the upper limit for the speed or acceleration of the vehicle.

[0019] Since no upper limit is set on the vehicle's speed or acceleration if the correction amount is equal to or less than the maximum correction angle, which is required to bring the steering angle and the steering angle to the same side of the neutral point, it prevents unnecessary restrictions on the vehicle's expected acceleration.

[0020] Preferably, when the maximum output of the steering actuator is less than the predetermined value (ST4: No), and the same-direction correction amount is greater than the maximum correction angle (ST36: No), the control unit sets the upper limit on the vehicle's speed or acceleration until the steering angle and the steering angle are on the same side of the neutral point (ST31: No), until the maximum output becomes equal to or greater than the predetermined value (ST4: Yes), or until the same-direction correction amount becomes equal to or less than the maximum correction angle (ST36: Yes).

[0021] This prevents sudden acceleration of the vehicle until its direction of travel aligns with the driver's intended direction for a specified period. Once this alignment is achieved, the vehicle can accelerate as needed by the driver. Therefore, both steering and acceleration can be controlled according to the driver's requirements.

[0022] Beneficial effects of the invention

[0023] Therefore, the present invention provides a steering system for a vehicle that prevents the vehicle from suddenly accelerating in a direction unpredictable by the driver when the steering angle of the steering member is changed during parking. Attached Figure Description

[0024] [ Figure 1 ] Figure 1 This is a schematic diagram of a steering system according to an embodiment of the present invention.

[0025] [ Figure 2 ] Figure 2 This is a graph showing the output characteristics of the steering actuator.

[0026] [ Figure 3 ] Figure 3 This is a schematic diagram showing the relationship between the steering angle of the steering component and the steering angle of the front wheel.

[0027] [ Figure 4 ] Figure 4 This is a schematic diagram showing the relationship between the steering angle of the steering component and the steering angle of the front wheel.

[0028] [ Figure 5 ] Figure 5 This is a flowchart of the first part of the phase matching control process executed by the control unit.

[0029] [ Figure 6 ] Figure 6 This is a flowchart of the second part of the phase matching control process executed by the control unit.

[0030] [ Figure 7 ] Figure 7 It is a graph showing the relationship between the maximum output of the steering actuator and the maximum correction angle.

[0031] [ Figure 8 ] Figure 8 This is a timing diagram showing the change in the steering angle caused by the passive phase matching process.

[0032] [ Figure 9 ] Figure 9 This is a timing diagram showing the change in the steering angle caused by the active phase matching process.

[0033] [ Figure 10 ] Figure 10 This is the first part of a flowchart of a phase matching control process according to a modified embodiment of the present invention. Detailed Implementation

[0034] The following describes a steering system 1 for a vehicle 2 according to an embodiment of the present invention. For example... 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 is shown in the diagram) The steering system 1 provides support so that the steering angle α of the front wheel 3 can be changed, and the front wheel 3 thus functions as a steerable wheel. The steering angle α refers to the angle of the front wheel 3 relative to the fore-and-aft direction in the top view. Therefore, the steering system 1 changes the steering angle α of the front wheel 3.

[0035] 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.

[0036] 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.

[0037] 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.

[0038] 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.

[0039] 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.

[0040] 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 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 is changed. The steering mechanism 11 is mechanically separated from the steering member 10.

[0041] 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.

[0042] 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 driven angle sensor 32 for detecting the driven angle α of the front wheels 3. In this embodiment, the driven 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 driven angle α of the front wheels 3 is determined by the rack position.

[0043] The control unit 15 comprises an electronic control unit including a CPU, a memory, and a storage device for storing programs. A steering angle sensor 21, a torque sensor 22, a first rotation angle sensor 23, a second rotation angle sensor 31, and a 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 the steering angle β, steering torque Ts, rotation angle θ of the reaction force actuator 13, rotation angle θ of the steering actuator 12, and steering angle α. Furthermore, the control unit 15 is connected to the vehicle speed sensor 33 and the gear position sensor 34, and acquires signals corresponding to the vehicle speed V and the transmission gear SP of the transmission unit 35.

[0044] 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.

[0045] 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.

[0046] 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".

[0047] Control unit 15 is connected to reaction force actuator 13 and steering actuator 12, and controls reaction force actuator 13 and steering actuator 12. Control unit 15 controls steering actuator 12 according to steering angle β, and controls reaction force actuator 13 according to steering angle α.

[0048] In addition, the control unit 15 is configured to manage the output characteristics of the steering actuator 12. Figure 2 This is a graph showing the output characteristics of the steering actuator 12. (Example) Figure 2 As shown, the output characteristics of the steering actuator 12 enable it to steer the front wheels 3 at a predetermined speed (steering angular velocity) using the steering torque T1 required to steer the front wheels 3 when the vehicle 2 is stationary. Therefore, when the vehicle 2 is stationary, by using the steering torque T1 required to steer the front wheels 3 at a predetermined speed (steering angular velocity), the steering actuator 12 can steer the front wheels 3 at a predetermined speed (steering angular velocity). Figure 2 The maximum output drives the steering actuator 12, and the control unit 15 is able to steer the front wheels 3 at a specified speed. The steering actuator 12 exhibits a higher (faster) steering angular velocity as the steering torque required to steer the front wheels 3 decreases.

[0049] On the other hand, in situations such as when the power system fails or when the steering actuator 12 is in a deteriorated state, the steering actuator 12 may not operate at its maximum output. A deteriorated state refers to a condition where the output of the steering actuator 12 is limited due to factors such as overheating. In this case, the control unit 15 obtains the maximum output that can be generated from the steering actuator 12 as a value less than the rated output of the steering actuator 12. Therefore, this maximum output is less than... Figure 2 The characteristic value (rated output torque) of the steering actuator 12 shown varies (e.g., 90%, 50%, etc.) depending on the operating conditions, temperature, etc. of the steering actuator 12. The maximum output can be obtained by using the output value of a sensor or by estimation.

[0050] 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 rate of change (change rate) of the steering angle α.

[0051] 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.

[0052] 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.

[0053] 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.

[0054] Figure 3 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 2As shown, the phase of the steering angle β and the phase of the turned angle α can deviate from each other in two different types: Type A, or opposite phase relationship, where the phase of the steering angle β and the phase of the turned angle α are opposite to each other; and Type B, or same phase relationship, where the phase of the steering angle β and the phase of the turned angle α are the same. The two phases are considered to be the same when only one of the phases of the steering angle β and the turned 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 the steering angle β is 0 and the turned angle α is not 0; Type B2, where the phase of the turned angle α is greater than the phase of the steering angle β; Type B3, where the phase of the turned angle α is less than the phase of the steering angle β; and Type B4, where the steering angle β is greater than 0 in any direction and the turned angle α is 0.

[0055] Figure 4 This is a schematic diagram showing the relationship between the steering angle β of the steering member 10 and the steering angle α of the front wheel 3, which includes a single anti-phase type and four in-phase types.

[0056] Because the phase relationship between the steering angle β and the steering angle α may be interfered with when the ignition switch is off, the control unit 15 performs the following actions when the ignition switch is on and the control unit 15 is activated: Figure 5 and Figure 6 The phase matching control process is shown.

[0057] Figure 5 A flowchart of the first half of the phase-matching control process executed by control unit 15 at startup is shown, and Figure 6 The second half of the phase-matching control process is shown. (As shown) Figure 5 As shown, when activated, the control unit 15 acquires the steering angle β and the 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). 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.

[0058] When the phase of the steering angle β and the phase of the steering angle α deviate from each other (ST2: Yes), the control unit 15 acquires the maximum output of the steering actuator 12 (step ST3) and determines whether the maximum output is equal to or greater than a predetermined value (step ST4). The predetermined value is selected as the maximum output value that allows the front wheels 3 to be steered at a predetermined speed when the vehicle 2 is stationary, and may be, for example, 90% or 80% of the rated maximum output. The predetermined value may be a fixed value or a variable value that changes according to the state of the vehicle 2.

[0059] When the maximum output of the steering actuator 12 is less than the specified value (ST4: No), the control unit 15 calculates the maximum correction angle α that can be achieved within a specified time period when the vehicle 2 is stationary, based on the maximum output of the steering actuator 12. cmax Or the maximum change in steering angle α (step ST5). This specified time period is longest after the ignition switch is turned on, shorter after the gear SP is changed from the parking position "P" to the drive position "D", and even shorter when vehicle 2 begins to move. For example, as Figure 7 As shown in the graph, the maximum correction angle α is set at a specific time point. cmax Subsequently, in the control unit 15, the deviation amount α, given as the deviation of the phase relationship between the steering angle α and the steering angle β, is determined. dev Or whether the phase difference between the steering angle and the value obtained by multiplying the steering angle β by the gear ratio K is equal to or less than the aforementioned maximum correction angle α. cmax (Step ST6)

[0060] When the deviation of the steering angle α is α dev Greater than the maximum correction angle α cmax When (ST6: No), the control unit 15 performs a speed limiting operation by setting an upper limit on the vehicle speed V (step ST7), and the processing flow proceeds to... Figure 6 Step ST8 in the process. For example, the control unit 15 sets the upper limit of the vehicle speed V to 10 km / h. On the other hand, when the maximum output of the steering actuator 12 is equal to or greater than the specified value (ST4: Yes), and is affected by the deviation α of the steering angle α... dev Equal to or less than the maximum correction angle α cmax When (ST6: Yes) is active, control unit 15 enters... Figure 6 The step ST8 shown does not limit the vehicle speed. As a result, vehicle 2 is prevented from traveling at a speed V higher than the upper limit value until the determination result in step ST4 or step ST6 becomes yes. When the determination result in step ST2 becomes no, the vehicle speed limit is also released, but usually the determination result in step ST6 becomes yes before the determination result in step ST2 becomes no.

[0061] Thus, when the phase of the steering angle β and the phase of the steering angle α deviate from each other (ST2: Yes), if the maximum output of the steering actuator 12 is less than a specified value (ST4: No), and the deviation α of the steering angle α... dev Greater than the maximum correction angle α cmax(ST6: No), then the vehicle speed V is limited. The vehicle speed V is limited until the maximum output of the steering actuator 12 returns to the specified value, or until the phase of the steering angle α and the phase of the steering angle β are matched before the vehicle speed V reaches the predetermined speed. This prevents the vehicle 2 from traveling at high speed in a direction different from the direction desired by the driver.

[0062] like Figure 6 As shown, the control unit 15 acquires the vehicle speed V (step ST8) and determines whether the vehicle 2 is moving (step ST9). More specifically, when the vehicle speed V is higher than a predetermined threshold Vth, the control unit 15 determines that the vehicle 2 is moving; otherwise, it determines that the vehicle 2 is stationary. When it is determined that the vehicle 2 is stationary (ST9: no), the control unit 15 determines the type of phase deviation based on the steering angle β and the steering angle α (step ST10) to determine whether it is a case of opposite phase relationship (type A) (step ST11).

[0063] In the case of an out-of-phase relationship (ST11: Yes), the control unit 15 acquires the transmission gear SP (step ST12) and determines whether the transmission gear SP is in drive position "D" or reverse position "R" (step ST13). If the driver has not yet operated the shift lever, and the transmission gear SP is still in park position "P" or neutral position "N" (ST13: No), or if the determination result of step ST11 is no, the control unit 15 acquires the steering angular velocity βdot (step ST14). The 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 ST15). For ease of description, the latter case will be referred to as the "βdot = 0" case in the following disclosure.

[0064] When the steering angular velocity βdot is 0 (ST15: 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 (ST15: No), the control unit 15 performs passive phase matching (step ST16). In the passive phase matching of step ST16, 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 turned angle α are closer to each other when the steering member 10 is steered (ST15: No). Here, "making the phase of the steering angle β and the phase of the turned angle α closer to each other" means making the steering angle β and the turned angle α closer to a predetermined relationship (the aforementioned 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 turned angle α.

[0065] In the passive phase matching of step ST16, the control unit 15 uses the event of operating the steering member 10 as a trigger (ST15: No) to drive the steering actuator 12 to bring the phase of the steering angle β and the phase of the steered angle α closer to each other. In this way, since the steered 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 without the driver's anticipation.

[0066] Figure 8 This is a timing diagram illustrating the change in the steering angle α during passive phase matching. (Example:) Figure 8 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 are turned in the same direction as the steering direction of the steering member 10.

[0067] See you again Figure 6 In the passive phase matching step ST16, the control unit 15 repeats the above process, or uses an event that stops the operation of the steering member 10 as a trigger (ST15: Yes) to stop the drive 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.

[0068] When the driver performs a gear shift operation to change the gear SP to drive position "D" or reverse position "R", the determination result in step ST13 becomes yes, and the control unit 15 performs anti-phase matching (step ST17). 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 the steering angle β and the phase of the turned angle α are closer to each other and enter the same phase, regardless of whether the steering member 10 is turning.

[0069] The anti-phase matching in step ST17 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 ST13. In other words, the control unit 15 begins anti-phase matching only 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.

[0070] Thus, when the driver triggers the action of changing 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 ST17, bringing the phases of the steering angle α and steering angle β closer to each other. Therefore, the phases of the steering angle α and steering angle β are closer to each other only when the driver intends to start the vehicle.

[0071] In this embodiment, the control unit 15 drives the steering actuator 12 to make the steering angle β and the driven angle α in phase. In the reverse phase matching (ST17) of this embodiment, the control unit 15 drives the steering actuator 12 with a target driven angle αt set to 0° (neutral position), and stops driving the steering actuator 12 once the driven angle α matches the target driven angle αt, and once the phase of the driven angle α becomes the same as the phase of the steering angle β. Here, the target driven 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.

[0072] When the control unit 15 has determined that the direction of the steering angle β and the direction of the steering angle α are consistent with each other (ST11: No), the steering actuator 12 is stopped from being driven. As a result, even when the steering member 10 is not operated (ST15: 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.

[0073] Unlike the passive phase matching in step ST16, the anti-phase matching in step ST17 is performed regardless of whether the steering member 10 has been operated. Therefore, when the direction of the steering angle β and the direction of the steering angle α are opposite to each other (ST11: Yes), the phase of the steering angle α and the phase of the steering angle β can immediately become closer to each other after the transmission gear SP is changed from the parking position "P" or the neutral position "N" to the driving position, regardless of the operation of the steering member 10.

[0074] When the control unit 15 performs anti-phase matching in step ST17, the type of phase deviation is subsequently determined to be anti-phase type in step ST11 (ST11: No). In this case, the control process executed by the control unit 15 proceeds to step ST14 and performs passive phase matching (ST16) to match the phase of the steering angle β and the phase of the steering angle α to each other when the steering member 10 is not steering (ST15: No).

[0075] Furthermore, when the directions of the steering angle β and the steering angle α are opposite to each other (ST11: Yes), passive phase matching in step ST16 is performed by using the operation of the steering member 10 (ST15: No) and the transmission gear SP being in the parking position "P" or neutral position "N" (ST13: No) as a trigger. In this way, when the directions of the steering angle β and the steering angle α are opposite to each other, by using the operation of the steering member 10 as a trigger, the phases of the steering angle α and the steering angle β can be brought closer to each other without causing any discomfort to the driver.

[0076] If vehicle 2 starts driving without completing the phase matching of steering angle β and the steering angle α through passive phase matching in step ST16, then it is determined in step ST9 that vehicle 2 is driving (ST9: Yes).

[0077] Subsequently, the control unit 15 acquires the steering angular velocity βdot (step ST18) and determines whether the steering angular velocity βdot is 0 (step ST19). When the steering angular velocity βdot is 0 (ST19: Yes), the control unit 15 performs active phase matching (step ST20). 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 (ST19: Yes), after the vehicle 2 begins to move (ST9: Yes), the phase of the steering angle β and the phase of the steered 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 steered angle α.

[0078] Thus, regardless of whether the steering member 10 is operated, the control unit 15 performs active phase matching in step ST20, thereby preventing the vehicle 2 from traveling at high speed in a direction undesirable to the driver, even when the steering member 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.

[0079] Figure 9 This is a timing diagram showing the change in the steering angle α caused by active phase matching. (Example) Figure 9 As 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.

[0080] 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, so as to reduce the rate of change of the steering angle α compared with the normal steering angle control. As a result, the rate of change of the steering angle α becomes slower than normal, and the vehicle 2 is prevented from operating in a way that is not anticipated by the driver.

[0081] The deceleration gain G can be chosen to vary with vehicle speed V. More specifically, the deceleration gain G can be chosen to be relatively large when vehicle speed V is low and relatively small as vehicle speed V increases, such that the rate of change of the steering angle α decreases as vehicle speed V increases. As a result, when vehicle speed V is low and the effect of the change of the 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 the steering angle α on vehicle behavior is large, the steering angle changes at a relatively low rate. This prevents vehicle 2 from operating in an unexpected manner.

[0082] See you again Figure 6 When the driver steers the steering member 10 while the vehicle 2 is moving (ST9: Yes), and the steering angular velocity βdot is not 0 (ST19: No), the control unit 15 performs passive phase matching (step ST21). In the passive phase matching of step ST21, 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 (ST19: 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.

[0083] In the passive phase matching of step ST21, the control unit 15 drives the steering actuator 12 in such a way that the rate of change of the steering angle α is faster than that of the active phase matching (ST20) 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.

[0084] Phase matching control ends when the phase of steering angle β and the phase of the steering angle α are matched through passive phase matching in step ST16, active phase matching in step ST20, or passive phase matching in step ST21, and the determination result in step ST2 becomes negative.

[0085] The main features and advantages of the steering system 1 according to the foregoing embodiments are discussed below.

[0086] like Figure 5 As shown, at startup, if the steering angle α deviates from the specified relationship relative to the steering angle β (ST2: yes), and satisfies... Figure 6 If any of the triggering conditions shown in steps ST9, ST15, and ST17 occur, the control unit 15 drives the steering actuator 12 to bring the steering angle β closer to the prescribed relationship relative to the steering angle α (ST16, ST17, ST20, ST21), and sets an upper limit on the vehicle speed V (ST7). By limiting the vehicle speed V to an upper limit in this way, sudden acceleration of the vehicle 2 in directions unpredictable by the driver is prevented.

[0087] The control unit 15 acquires the maximum output (ST3) of the steering actuator 12 when activated or started, and does not set an upper limit value for the vehicle speed V when the maximum output of the steering actuator 12 is equal to or higher than a predetermined value (ST4: yes). Therefore, it does not prevent the vehicle from accelerating when it accelerates according to the driver's intention.

[0088] The control unit 15 calculates the maximum correction angle α based on the maximum output of the steering actuator 12 when activated. cmax The maximum correction angle is the maximum change in the steering angle α that can be achieved within a predetermined time period (ST5). Even if the maximum output of the steering actuator 12 is less than the specified value (ST4: No), as long as the deviation α relative to the specified relationship of the steering angle α is... dev Equal to or less than the maximum correction angle α cmax (ST6: Yes), the control unit 15 does not set an upper limit for the vehicle speed V. Therefore, it does not prevent the vehicle from accelerating when it accelerates reliably according to the driver's wishes.

[0089] When the maximum output of the steering actuator 12 is less than the specified value (ST4: No), and the deviation α relative to the specified relationship of the steering angle α is... dev Greater than the maximum correction angle α cmax When (ST6: No), the control unit 15 sets an upper limit value for the vehicle speed V until the maximum output becomes equal to or greater than the specified value (ST4: Yes), or the deviation α dev Become equal to or less than the maximum correction angle α cmax (ST6: Yes). Therefore, any sudden acceleration of vehicle 2 is prevented until the driver's expected direction and the vehicle 2's direction of travel are aligned with each other for a predetermined period of time. Once the driver's expected direction and the vehicle 2's direction of travel are aligned with each other for the predetermined period of time, the driver's desired acceleration of the vehicle becomes possible. Therefore, steering and acceleration can be performed according to the driver's needs.

[0090] The following reference Figure 10A modified steering system 1 according to the foregoing embodiment is described. This modified embodiment differs from the foregoing embodiment in a part of the phase matching control process, but is similar to the foregoing embodiment in other respects. Therefore, only the parts of the modified embodiment that differ from the foregoing embodiment are described below.

[0091] Figure 10 This is a flowchart of the first part of the phase matching control according to the modified implementation. The latter half of the phase matching control is... Figure 6 The aforementioned implementation method is the same. For example... Figure 10 As shown, when it is determined in step ST2 that the phase of the steering angle β and the phase of the steering angle α deviate from each other (yes), the control unit 15 then determines whether the phase deviation between the steering angle β and the steering angle α is of the opposite phase type (step ST31). In the case of an opposite phase type deviation (ST31: yes), the control flow proceeds to step ST3. In the case of a same phase type deviation (ST31: no), the control flow proceeds to... Figure 8 The step ST8 is shown. Therefore, when the phase deviation is not of the anti-phase type, the vehicle speed V is not limited in step ST6.

[0092] Steps ST3 to ST5 are the same as the corresponding steps in the aforementioned embodiments. After step ST5, the control unit 15 corrects the steering angle α to be in phase with the steering angle β; in other words, the control unit 15 calculates the same-phase correction amount α. devn The same-direction correction amount is given as the amount of correction required to place the steering angle α on the same side as the steering angle β relative to the neutral position, and the same-direction correction amount α is determined. devn Is it equal to or less than the maximum correction angle α? cmax (Step ST36). Same-direction correction amount α devn It is the deviation angle of the steering angle α relative to the 0° position (neutral position).

[0093] When the same direction correction amount α dev Greater than the maximum correction angle α cmax When (ST36: No), the control unit 15 limits the vehicle speed by setting an upper limit value for the vehicle speed V (step ST7), and then enters... Figure 6 The step ST8 is shown. On the other hand, when the determination result in step ST6 indicates the same-direction correction amount α... dev Equal to or less than the maximum correction angle α cmax When (ST6: Yes) is active, control unit 15 enters... Figure 6 The steps shown in ST8 do not limit the vehicle speed.

[0094] In this modified embodiment, even if the maximum output of the steering actuator 12 is less than a specified value (ST4: No), as long as the steering angle α is placed in the same direction as the steering angle β, the required same-direction correction amount α will still be applied. devn Equal to or less than the maximum correction angle α cmax (ST36: Yes), the control unit 15 does not set an upper limit for the vehicle speed V. Therefore, when the vehicle accelerates reliably according to the driver's wishes, it does not prevent the vehicle from accelerating.

[0095] When the maximum output of the steering actuator 12 is less than the specified value (ST4: No), and the same direction correction amount α dev Greater than the maximum correction angle α cmax When (ST36: No), the control unit 15 sets an upper limit value for the vehicle speed V until the steering angle α becomes the same direction as the steering angle β (ST31: No), the maximum output becomes equal to or greater than the specified value (ST4: Yes), or the same-direction correction amount α... devn Become equal to or less than the maximum correction angle α cmax (ST36: Yes). Therefore, any sudden acceleration of vehicle 2 is prevented until the driver's expected driving direction and the actual driving direction of vehicle 2 are aligned for a predetermined time period. Once the driver's expected driving direction and the actual driving direction of vehicle 2 are aligned for the predetermined time period, the driver can accelerate vehicle 2 as needed. Thus, the steering and acceleration of vehicle 2 can be performed according to the driver's needs.

[0096] The present invention has been described according to specific embodiments, but the invention is not limited to these embodiments and can be modified in various ways without departing from the scope of the invention. In the above embodiments, in step ST7, the control unit 15 sets an upper limit value for the vehicle speed V, but the control unit 15 can also set an upper limit value for the acceleration of the vehicle 2. This also prevents the vehicle 2 from moving with high acceleration in directions not anticipated by the driver. Furthermore, the control unit 15 can drive the steering actuator 12 immediately upon activation (after step ST2 and before step ST8). In addition, 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. Furthermore, 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.

[0097] List of reference numerals

[0098] 1: Steering system 2: Vehicle

[0099] 3: Front wheel 10: Steering component

[0100] 11: Steering mechanism 12: Steering actuator

[0101] 13: Reaction force actuator 15: Control unit

[0102] 21: Steering angle sensor; 32: Steering angle sensor

[0103] α: Steering angle

[0104] α dev :deviation

[0105] α devn : Same direction correction amount

[0106] α cmax Maximum correction angle

[0107] β: Steering angle

[0108] V: Vehicle speed

Claims

1. A steering system for a vehicle, the steering system for a vehicle comprising: A steering component configured to receive a steering operation; A steering mechanism, mechanically separated from the steering member and configured to steer the wheels via movement of the steering mechanism; 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 The control unit controls the operation of the steering actuator to make the steering angle have a predetermined relationship with the steering angle, and controls the operation of the reaction force actuator to make the reaction force correspond to the steering state of the wheel. Specifically, when the steering angle deviates from the predetermined relationship with the steering angle, immediately or upon meeting a triggering condition, the control unit drives the steering actuator to bring the steering angle closer to the predetermined relationship with the steering angle, and sets an upper limit on the vehicle's speed or acceleration. The control unit is configured to acquire the maximum output of the steering actuator, and when the maximum output of the steering actuator is equal to or greater than a predetermined value, the control unit does not set the upper limit for the speed or acceleration of the vehicle.

2. The steering system for a vehicle according to claim 1, wherein, The control unit calculates the maximum correction angle based on the maximum output of the steering actuator. The maximum correction angle is given as the maximum change in the steered angle that can be achieved within a specified time period. Even when the maximum output of the steering actuator is less than the specified value, the control unit does not set the upper limit on the speed or acceleration of the vehicle as long as the deviation of the steered angle from the specified relationship with the steering angle is equal to or less than the maximum correction angle.

3. The steering system for a vehicle according to claim 2, wherein, When the maximum output of the steering actuator is less than the specified value, and the deviation of the steering angle from the specified relationship is equal to or greater than the maximum correction angle, the control unit sets the upper limit on the vehicle's speed or acceleration until the maximum output becomes equal to or greater than the specified value, or until the deviation becomes equal to or less than the maximum correction angle.

4. The steering system for a vehicle according to claim 1, wherein, The control unit calculates the maximum correction angle based on the maximum output of the steering actuator. The maximum correction angle is given as the maximum change value of the steered angle that can be achieved within a specified time period. Even when the maximum output of the steering actuator is less than the specified value, the control unit does not set the upper limit on the speed or acceleration of the vehicle as long as the same-direction correction amount given as the correction amount required to bring the steered angle and the steering angle to the same side of the neutral point is equal to or less than the maximum correction angle.

5. The steering system for a vehicle according to claim 4, wherein, When the maximum output of the steering actuator is less than the specified value and the same-direction correction amount is greater than the maximum correction angle, the control unit sets the upper limit on the speed or acceleration of the vehicle until the steering angle and the steering angle are on the same side of the neutral point, until the maximum output becomes equal to or greater than the specified value, or until the same-direction correction amount becomes equal to or less than the maximum correction angle.

Images