Steering control device and steering control method

Abstract

A steering control device (1) comprises: an emergency determination unit (63) configured to determine whether or not there is an emergency for which an emergency avoidance operation is to be performed; and a workload adjustment unit (61, 72) configured to adjust a workload required for a driver to turn a steered wheel. The workload adjustment unit (61, 72) is configured to execute an emergency adjustment process for adjusting the workload in accordance with the result of the determination as to whether or not there is an emergency. The emergency adjustment process includes a reduction process for reducing the workload in an early stage after the emergency determination unit (63) has determined that there is an emergency, as compared to a case when it is not determined that there is an emergency.

Description

[Technical Field]

[0001] The present disclosure relates to a steering control device and a steering control method. [Background technology]

[0002] Conventionally, there is a steer-by-wire steering device in which the power transmission path between an operation unit to which a steering wheel is connected and a steering unit that steers the steered wheels is separated. For example, as described in Patent Document 1, a steering control device that controls such a steering device changes the angle ratio of the steering angle of the steered wheels to the steering angle of the steering wheel depending on the driving conditions of the vehicle.

[0003] Patent Document 2 discloses a vehicle that employs a joystick in addition to or instead of a steering wheel as an operating member operated by the driver. When a joystick is used as the operating member, it is possible to reduce the amount of operation required to steer the steered wheels compared to when a steering wheel is used as the operating member, thereby improving convenience for the driver. A reaction torque corresponding to the amount of operation by the driver is applied to the joystick. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Patent Publication No. 2021-30837 [Patent Document 2] Japanese Patent Application Publication No. 8-34353 Summary of the Invention [Problem to be solved by the invention]

[0005] For example, a driver may perform an emergency avoidance operation by quickly operating an operating member to avoid a collision with an obstacle in front of the vehicle. It is desirable that the emergency avoidance operation be an easy operation so that the steered wheels can be steered quickly. [Means for solving the problem]

[0006] One aspect of the present disclosure provides a steering control device for controlling a steering device of a vehicle. The steering device has a structure in which a power transmission path between an operation unit having an operation member and a steering unit configured to steer steered wheels is mechanically separated. The steering control device includes: a target steering corresponding value calculation unit configured to calculate a target steering corresponding value, which is a target value of a convertible value that can be converted into a steering angle of the steered wheels, based on the operation amount of the operation member; a steering control signal generation unit configured to generate a steering control signal for operating the steering unit based on the target steering corresponding value; an emergency determination unit configured to determine whether an emergency situation requires an emergency avoidance maneuver; and a workload adjustment unit configured to adjust the workload of the driver required to steer the steered wheels. The workload adjustment unit is configured to execute an emergency adjustment process that adjusts the workload in accordance with the determination result of whether an emergency situation exists. The emergency adjustment process includes a reduction process that reduces the workload in an early stage after the emergency determination unit determines that an emergency situation exists, compared to when an emergency situation does not exist.

[0007] Another aspect of the present disclosure provides a steering control method for controlling a steering device of a vehicle. The steering device has a structure in which a power transmission path between an operation unit having an operation member and a steering unit configured to steer the steered wheels is mechanically separated. The steering control method includes: calculating a target steering correspondence value, which is a target value of a convertible value that can be converted into a steering angle of the steered wheels, based on the operation amount of the operation member; generating a steering control signal for operating the steering unit based on the target steering correspondence value; determining whether an emergency situation requires an emergency avoidance maneuver; and adjusting the workload of the driver required to turn the steered wheels. Adjusting the workload includes executing an emergency adjustment process that adjusts the workload in accordance with the determination result of whether an emergency situation exists. The emergency adjustment process includes a reduction process that reduces the workload in an early stage after it is determined that an emergency situation exists, compared to when it is not determined that an emergency situation exists. [Brief explanation of the drawings]

[0008] [Figure 1] 1 is a schematic configuration diagram of a steering device of a first embodiment and a steering control device that controls the steering device. [Figure 2] FIG. 2 is a block diagram of the steering control device of FIG. 1. [Figure 3] 3 is a flowchart showing an example of a processing procedure for emergency determination by an emergency determination unit in FIG. 2; [Figure 4] 3 is a flowchart showing an example of a processing procedure for completion determination by an emergency determination unit in FIG. 2; [Figure 5] 3 is a flowchart showing an example of a processing procedure for calculating a target reaction force by a target reaction force calculation unit in FIG. 2. [Figure 6] 3A and 3B are diagrams showing examples of a normal state map and an emergency state map provided in the target steering angle calculation unit of FIG. 2. [Figure 7] 3 is a flowchart showing an example of a processing procedure for calculating a target steering-corresponding angle by a target steering-corresponding angle calculation unit in FIG. 2. [Figure 8]10A and 10B are diagrams showing an example of a normal state map and an emergency state map provided in a target steering corresponding angle calculation unit of the second embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0009] (First embodiment) A first embodiment of the steering control device will be described below with reference to the drawings. (Overall composition) As shown in Fig. 1, a steering control device 1 controls a steer-by-wire steering device 2. The steering device 2 changes the traveling direction of the vehicle by steering steered wheels 3 in response to an operation by the driver. The steering device 2 includes an operation unit 4 that is operated by the driver, and a steering unit 5 that steers the steered wheels 3. The steering device 2 has a structure in which the power transmission paths between the operation unit 4 and the steering unit 5 are mechanically separated.

[0010] The operation unit 4 includes an operation lever 11, which is an operation member operated by the driver, and a base 12 that supports the operation lever 11 so that it can tilt. In this embodiment, the base 12 supports the operation lever 11 so that it can tilt laterally, i.e., in the left-right direction, of the vehicle, and the operation lever 11 tilts in the left-right direction when operated by the driver. In other words, the amount of operation by the driver is represented by the tilt angle of the operation lever 11 (hereinafter referred to as the lever tilt angle θl). In other embodiments, the base 12 may support the operation lever 11 so that it can tilt in the fore-and-aft direction of the vehicle. The operation unit 4 includes an inclination angle sensor 13 that detects the lever inclination angle θl. The lever inclination angle θl is detected as a positive value when the operation lever 11 tilts to the right and a negative value when the operation lever 11 tilts to the left, but the opposite may also be true.

[0011] The operation unit 4 also includes an operation actuator 15 that applies an operation reaction force, which is a force that resists the operation of the operation lever 11 by the driver. The operation actuator 15 of this embodiment includes an operation motor 16 and a link mechanism 17 that transmits the rotation of the operation motor 16 to the operation lever 11. The link mechanism 17 is configured, for example, by a plurality of gears and link members. The operation actuator 15 transmits the rotation of the operation motor 16 to the link mechanism 17, and applies an operation reaction force to the operation lever 11 by converting this rotation in the link mechanism 17. In other embodiments, the rotation of the operation motor 16 may be directly transmitted to the operation lever 11, and the configuration of the operation actuator 15 can be changed as appropriate.

[0012] The steering unit 5 includes a pinion shaft 21, a rack shaft 22 connected to the pinion shaft 21, a rack housing 23 that accommodates the rack shaft 22 so that it can reciprocate, and a rack-and-pinion mechanism 24 that has the pinion shaft 21 and the rack shaft 22. The rack-and-pinion mechanism 24 is configured such that pinion teeth 21a formed on the pinion shaft 21 mesh with rack teeth 22a formed on the rack shaft 22. As a result, the pinion shaft 21 rotates in response to the reciprocating motion of the rack shaft 22. Tie rods 26 are connected to both ends of the rack shaft 22 via ball joints 25. The ends of the tie rods 26 are connected to a knuckle (not shown) to which the steered wheels 3 are assembled.

[0013] Furthermore, steering unit 5 is equipped with steering actuator 31 that applies a steering force to rack shaft 22 that steers steerable wheels 3. Steering actuator 31 is equipped with, for example, steering motor 32 and a power transmission mechanism 33 that transmits the torque of steering motor 32 to rack shaft 22. Power transmission mechanism 33 is equipped with a belt mechanism 34 and a ball screw mechanism 35. Steering actuator 31 transmits the rotation of steering motor 32 to ball screw mechanism 35 via belt mechanism 34, and applies the steering force to steerable wheels 3 by converting it into reciprocating motion of rack shaft 22 by ball screw mechanism 35.

[0014] In the steering device 2 configured as above, a steering force is applied from the steering actuator 31 in response to the operation of the control lever 11 by the driver. This causes the rack shaft 22 to reciprocate, changing the steering angle θi of the steered wheels 3. In other words, the steering actuator 31 steers the steered wheels 3 in response to the operation of the driver. At this time, the operation actuator 15 applies an operation reaction force to the operation lever 11. In other words, in the steering device 2, the force applied by the driver required to operate the operation lever 11 is changed by the operation reaction force applied by the operation actuator 15.

[0015] The steering control device 1 is connected to the operation motor 16 and the steering motor 32, and controls the operation of the operation motor 16 and the steering motor 32. The steering control device 1 is also connected to the alarm 37, and controls the operation of the alarm 37. The alarm 37 may be a device that outputs a physical quantity that the driver can recognize with the five senses, such as a display panel or a speaker.

[0016] The detection results of various sensors are input to steering control device 1. The various sensors include, for example, tilt angle sensor 13, vehicle speed sensor 41, and rotation angle sensor 42. Vehicle speed sensor 41 detects vehicle speed V, which is the traveling speed of the vehicle. Rotation angle sensor 42 detects rotation angle θt of the rotation shaft of steering motor 32 as a relative angle within a range of 360°. The detection results of these sensors are examples of state variables. Steering control device 1 controls the operation of operation motor 16, steering motor 32, and alarm 37 based on the input state variables.

[0017] (Steering control device 1) The configuration of the steering control device 1 will be described in detail below. As shown in Fig. 2, the steering control device 1 includes a microcomputer 51, an operation drive circuit 52, and a turning drive circuit 53. The microcomputer 51 outputs an operation control signal Ms and a turning control signal Mt. The operation drive circuit 52 supplies power to the operation motor 16 based on the operation control signal Ms, and the turning drive circuit 53 supplies power to the turning motor 32 based on the turning control signal Mt.

[0018] The microcomputer 51, which is a processing circuit, can be configured as (1) one or more processors that operate according to a computer program (software), (2) one or more dedicated hardware circuits such as an application-specific integrated circuit (ASIC) that executes at least some of the various processes, or (3) a combination thereof. The processor includes a CPU and memory such as RAM and ROM, and the memory stores program code or instructions configured to cause the CPU to execute processes. Memory, i.e., non-transitory computer-readable medium, includes any available medium that can be accessed by a general-purpose or dedicated computer. Various controls by the microcomputer 51 are performed by the CPU executing programs stored in the memory at predetermined calculation cycles.

[0019] A typical PWM inverter having a plurality of switching elements such as FETs, IGBTs, etc. is employed for operation drive circuit 52 and steering drive circuit 53. The operation control signal Ms and steering control signal Mt are gate on / off signals that define the on / off state of each switching element.

[0020] When microcomputer 51 outputs an operation control signal Ms to operation drive circuit 52, power corresponding to the operation control signal Ms is supplied from the on-board power supply to operation motor 16. This causes operation motor 16 to rotate, and an operation reaction force is applied to operation lever 11 as described above. In this way, steering control device 1 controls the motor torque generated by operation motor 16 through the power supply to operation motor 16, and applies an operation reaction force to operation lever 11. Furthermore, when microcomputer 51 outputs a steering control signal Mt to steering drive circuit 53, power corresponding to the steering control signal Mt is supplied from the on-board power supply to steering motor 32. This causes steering motor 32 to rotate, and a steering force is applied to steered wheels 3 as described above. In this way, steering control device 1 controls the motor torque generated by steering motor 32 through the power supply to steering motor 32, and turns steered wheels 3.

[0021] (Microcomputer 51) Microcomputer 51 outputs an operation control signal Ms and a steering control signal Mt by having each of the following control blocks execute calculation processing at each predetermined calculation cycle. The vehicle speed V, lever inclination angle θl, and rotation angle θt are input to microcomputer 51. Microcomputer 51 generates and outputs the operation control signal Ms and the steering control signal Mt based on these state variables. Microcomputer 51 includes a reaction force control unit 54 that generates the operation control signal Ms, and a steering control unit 55 that generates the steering control signal Mt.

[0022] (Reaction force control unit 54) The reaction force control unit 54 includes a target operation reaction force calculation unit 61 that calculates a target operation reaction force T*, an operation control signal generation unit 62 that generates an operation control signal Ms, and an emergency determination unit 63 that outputs an emergency state signal Se that indicates whether or not an emergency situation exists in which an emergency avoidance operation is to be performed.

[0023] The vehicle speed V and the lever tilt angle θl are input to the emergency determination unit 63. Based on these state variables, the emergency determination unit 63 performs emergency determination to determine whether or not an emergency exists, and completion determination to determine whether or not an emergency avoidance maneuver has been completed. An emergency avoidance maneuver refers to, for example, quickly operating the operating lever 11 to avoid a collision with an obstacle present in front of the vehicle.

[0024] Emergency determination unit 63 has an emergency flag F. When the value of emergency flag F is "1", it indicates that an emergency situation in which an emergency avoidance operation is required exists, and when the value is "0", it indicates that an emergency situation in which an emergency avoidance operation is not required exists. Emergency state signal Se is a signal that indicates the value of emergency flag F. Emergency determination unit 63 changes the value of emergency flag F in accordance with the results of the emergency determination and the completion determination. Emergency determination unit 63 then outputs emergency state signal Se to target operation reaction force calculation unit 61, steering control unit 55, and annunciator 37. The emergency state signal Se, which indicates that the value of emergency flag F is "1", is configured to cause annunciator 37 to perform an announcing operation that an emergency situation exists. Emergency determination and completion determination will be described later.

[0025] The vehicle speed V, the lever tilt angle θl, and the emergency state signal Se are input to the target operation reaction force calculation unit 61. Based on these state variables, the target operation reaction force calculation unit 61 calculates a target operation reaction force T*, which is a target value of the operation reaction force, and outputs it to the operation control signal generation unit 62. The calculation of the target operation reaction force T* will be described later.

[0026] The operation control signal generating unit 62 generates an operation control signal Ms based on the target operation reaction force T*. The operation control signal generating unit 62 uses any known technology to generate the operation control signal Ms that causes the operation motor 16 to generate a torque corresponding to the target operation reaction force T*.

[0027] (Steering control unit 55) The steering control unit 55 includes a steering response angle calculation unit 71 that calculates the steering response angle θp, a target steering response angle calculation unit 72 that calculates the target steering response angle θp*, and a steering control signal generation unit 73 that generates the steering control signal Mt.

[0028] Rotation angle θt of steering motor 32 is input to steering response angle calculation unit 71. Steering response angle calculation unit 71 calculates an integrated angle by, for example, counting the number of rotations of steering motor 32 from the midpoint and integrating rotation angle θt with the midpoint set as zero degrees. Then, steering response angle calculation unit 71 calculates steering response angle θp by multiplying this integrated angle by a conversion coefficient based on the reduction ratio of belt mechanism 34, the lead of ball screw mechanism 35, and the rotational speed ratio of rack and pinion mechanism 24. In other words, steering response angle θp corresponds to the pinion angle, which is the rotation angle of pinion shaft 21, and the midpoint is the rotation angle of pinion shaft 21 when the vehicle is traveling straight. As described above, pinion shaft 21 rotates in response to the reciprocating motion of rack shaft 22, and therefore the rotation angle of pinion shaft 21, i.e., steering corresponding angle θp, corresponds to a steering corresponding value that is an actual value of a convertible value that can be converted into steering angle θi of steered wheels 3, and steering corresponding angle calculation section 71 corresponds to a steering corresponding value calculation section. The steering corresponding angle θp calculated by steering corresponding angle calculation section 71 is output to steering control signal generation section 73.

[0029] Vehicle speed V, lever tilt angle θl, and emergency state signal Se are input to target turning corresponding angle calculation unit 72. Target turning corresponding angle calculation unit 72 calculates target turning corresponding angle θp*, which is a target value of steering corresponding angle θp, based on these state variables. In other words, target turning corresponding angle θp* corresponds to a target turning corresponding value, which is a target value of a convertible value that can be converted into steering angle θi of steered wheels 3, and target turning corresponding angle calculation unit 72 corresponds to a target turning corresponding value calculation unit. The calculation process of target turning corresponding angle θp* by target turning corresponding angle calculation unit 72 will be described later. Target turning corresponding angle θp* is output to steering control signal generation unit 73.

[0030] The steering-corresponding angle θp and the target steering-corresponding angle θp* are input to steering control signal generation section 73. Based on these state quantities, steering control signal generation section 73 of the present embodiment generates a steering control signal Mt so as to gradually reflect changes in the target steering-corresponding angle θp* in the steering angle θi.

[0031] More specifically, the steering control signal generating section 73 includes a subtractor 74, a guard processing section 75, and a feedback control section 76. In the following, the term feedback may be abbreviated as "F / B."

[0032] The turning corresponding angle θp and the target turning corresponding angle θp* are input to the subtractor 74. The subtractor 74 calculates the difference Δθp by subtracting the turning corresponding angle θp from the target turning corresponding angle θp*. The difference Δθp is output to the guard processing unit 75.

[0033] The difference Δθp is input to the guard processing unit 75. The guard processing unit 75 calculates a difference Δθpg by limiting the difference Δθp to a difference upper limit value Δθlim or less. The difference upper limit value Δθlim is a value corresponding to the upper limit speed of the steering speed of the steered wheels 3. The guard processing unit 75 of this embodiment calculates the difference upper limit value Δθlim based on the vehicle speed V, but the difference upper limit value Δθlim may be a fixed value set in advance. For example, the guard processing unit 75 is provided with a map or a function formula that indicates the relationship between the vehicle speed V and the difference upper limit value Δθlim, and calculates the difference upper limit value Δθlim according to the vehicle speed V by referring to the map or function formula.

[0034] The guard processing unit 75 compares the absolute value of the input difference Δθp with the calculated difference upper limit value Δθlim to determine which is larger. If the absolute value of the difference Δθp is equal to or smaller than the difference upper limit value Δθlim, the guard processing unit 75 outputs the input difference Δθp as is as the difference Δθpg after guard processing to the F / B control unit 76. On the other hand, if the absolute value of the difference Δθp is larger than the difference upper limit value Δθlim, the guard processing unit 75 maintains the sign of the input difference Δθp and outputs a value obtained by making the absolute value equal to the difference upper limit value Δθlim as the difference Δθpg after guard processing to the F / B control unit 76.

[0035] The difference Δθpg after guard processing is input to F / B control section 76. F / B control section 76 calculates the target turning torque by performing F / B calculation based on the difference Δθpg. As an example, a PID control calculation is used for the F / B calculation, but the F / B calculation is not limited to this and may be a PI control calculation or the like. Then, F / B control section 76 uses any well-known technology to generate a turning control signal Mt that causes turning motor 32 to generate the target turning torque.

[0036] As described above, difference Δθpg used in the F / B calculation is limited to not more than difference upper limit value Δθlim corresponding to the upper limit speed. Therefore, when power is supplied from steering drive circuit 53 to steering motor 32 in accordance with steering control signal Mt, steered wheels 3 are steered to steering angle θi corresponding to target steering-corresponding angle θp* at a steering speed not more than the upper limit speed. In other words, steering control signal generation section 73 generates steering control signal Mt so that the steering speed of steered wheels 3 is set to not more than the upper limit speed, thereby gradually reflecting changes in target steering-corresponding angle θp* in steering angle θi.

[0037] (Emergency Judgment Department 63) Next, the emergency determination and completion determination by the emergency determination unit 63 will be described in detail. When the value of the emergency flag F is "0," i.e., when there is no emergency in which an emergency avoidance operation is required, the emergency determination unit 63 performs an emergency determination based on the vehicle speed V and the lever tilt angle θl. When the value of the emergency flag F is "1," i.e., when there is an emergency, the emergency determination unit 63 performs a completion determination based on the lever tilt angle θl. The emergency determination unit 63 then changes the value of the emergency flag F in accordance with the result of the emergency determination or the completion determination, and outputs an emergency state signal Se that indicates the value of the emergency flag F.

[0038] (Emergency judgment) The emergency determination unit 63 determines that an emergency has occurred when all of the following conditions (a1) to (a3) ​​are met.

[0039] (a1) The vehicle speed V is equal to or greater than the high-speed determination threshold Vth. (a2) The absolute value of the lever tilt angle θl is less than the turning determination threshold θlth. (a3) The absolute value of the operation speed ωl of the operating lever 11 is equal to or greater than the abrupt operation determination threshold ωlth.

[0040] The high-speed determination threshold Vth is a vehicle speed V at which it can be determined that the vehicle is traveling at a relatively high speed, and is set in advance. The turning determination threshold θlth is a lever tilt angle θl at which it can be determined that the vehicle is not turning significantly, i.e., is traveling generally straight, and is set in advance. The sudden operation determination threshold ωlth is an operation speed ωl at which it can be determined that the driver is performing a quick operation, and is set in advance. The emergency determination unit 63 of this embodiment calculates the operation speed ωl by differentiating the lever tilt angle θl. In another embodiment, a speed sensor may be provided in the operation unit 4, and the operation speed ωl may be input from the speed sensor. The operation speed ωl is detected by detecting a rightward tilt of the operation lever 11 as a positive value and a leftward tilt of the operation lever 11 as a negative value, but the opposite may also be true. The emergency determination is performed based on the result of comparing the magnitude of a parameter indicating the vehicle's traveling state with a threshold as in (a1) above, and the result of comparing the magnitude of a parameter indicating the operation state of the operation unit 4 with a threshold as in (a2) and (a3) ​​above.

[0041] The emergency determination unit 63 sets the value of the emergency flag F to "1" when all of the conditions (a1) to (a3) ​​are met. Furthermore, when all of the conditions (a1) to (a3) ​​are met, the emergency determination unit 63 of this embodiment determines and stores the operation direction of the operating lever 11 due to the emergency avoidance operation based on the sign of the operation speed ωl. On the other hand, when at least one of the conditions (a1) to (a3) ​​is not met, the emergency determination unit 63 does not change the value of the emergency flag F.

[0042] Next, an example of the procedure for emergency determination by the emergency determination unit 63 will be described with reference to the flowchart shown in FIG. 3, upon acquiring various state variables (step 101), the emergency determination unit 63 calculates the operation speed ωl (step 102) and determines whether the vehicle speed V is equal to or greater than the high-speed determination threshold Vth (step 103). If the vehicle speed V is equal to or greater than the high-speed determination threshold Vth (step 103: YES), the emergency determination unit 63 determines whether the absolute value of the lever tilt angle θl is less than the turning determination threshold θlth (step 104). If the absolute value of the lever tilt angle θl is less than the turning determination threshold θlth (step 104: YES), the emergency determination unit 63 determines whether the absolute value of the operation speed ωl of the operating lever 11 is equal to or greater than the sudden operation determination threshold ωlth (step 105).

[0043] If the absolute value of the operation speed ωl of the operating lever 11 is equal to or greater than the sudden operation determination threshold ωlth (step 105: YES), the emergency determination unit 63 sets the value of the emergency flag F to "1" (step 106). Next, the operation direction of the operating lever 11 due to the emergency avoidance operation is determined and stored (step 107). After that, this process ends.

[0044] On the other hand, if the vehicle speed V is less than the high speed determination threshold Vth (step 103: NO), the emergency determination unit 63 ends this process without setting the value of the emergency flag F to "1." Similarly, if the absolute value of the lever tilt angle θl is equal to or greater than the turning determination threshold θlth (step 104: NO) and if the absolute value of the operation speed ωl of the operating lever 11 is less than the sudden operation determination threshold ωlth (step 105: NO), the emergency determination unit 63 also ends this process without setting the value of the emergency flag F to "1."

[0045] (completion judgment) The emergency determination unit 63 determines that the emergency avoidance operation has been completed when the following condition (b1) is met:

[0046] (b1) The operating lever 11 was operated in the opposite direction to the direction in which it was operated during the emergency avoidance operation. The emergency determination unit 63 determines whether a return direction operation has been performed in response to the emergency avoidance operation, based on the sign of the operation speed ωl. Specifically, the emergency determination unit 63 calculates the operation speed ωl based on the lever tilt angle θl, and detects the current operation direction based on the sign of this operation speed ωl. Then, if the detected operation direction is opposite to the operation direction of the stored emergency avoidance operation, it determines that a return direction operation has been performed. If the condition (b1) is met, the emergency determination unit 63 resets the value of the emergency flag F to "0." Furthermore, if the emergency determination unit 63 determines that a return direction operation has been performed, it erases the stored operation direction of the emergency avoidance operation. On the other hand, if the condition (b1) is not met, the emergency determination unit 63 does not change the value of the emergency flag F, and does not erase the stored operation direction.

[0047] Next, an example of a procedure for the completion determination performed by the emergency determination unit 63 will be described with reference to the flowchart shown in FIG. 4, upon acquiring various state variables (step 201), the emergency determination unit 63 calculates the operation speed ωl and detects the current operation direction of the operating lever 11 based on the sign of this operation speed ωl (step 202). Subsequently, it determines whether the current operation direction is opposite to the operation direction due to the emergency avoidance operation, i.e., whether an operation in the return direction is being performed (step 203).

[0048] If a return operation is being performed (step 203: YES), the emergency determination unit 63 resets the value of the emergency flag F to "0" (step 204). Then, the emergency determination unit 63 erases the stored operation direction resulting from the emergency avoidance operation (step 205) and ends this process. On the other hand, if a return operation is not being performed (step 203: NO), the emergency determination unit 63 ends this process without resetting the value of the emergency flag F to "0".

[0049] (Target operation reaction force calculation unit 61) Next, the calculation of the target reaction force T* by the target reaction force calculation unit 61 shown in FIG. 2 will be described in detail.

[0050] The target reaction force calculation unit 61 first calculates the basic reaction force Tb, and then adjusts the basic reaction force Tb in accordance with the value of the emergency flag F to calculate the target reaction force T*. Specifically, the target operation reaction force calculation unit 61 calculates the angular axial force as a basic operation reaction force Tb. The angular axial force is a road surface reaction force that is thought to be applied to the steered wheels 3 from the road surface, and is an ideal value defined by an arbitrarily set vehicle model. The angular axial force is an axial force that does not reflect road surface information. Road surface information includes information on minute irregularities that do not affect the lateral behavior of the vehicle and steps that affect the lateral behavior of the vehicle. The angular axial force is calculated so that, for example, the greater the absolute value of the lever tilt angle θl, the greater the absolute value of the angular axial force. Furthermore, the angular axial force is calculated so that, for example, the greater the vehicle speed V, the greater the absolute value of the angular axial force.

[0051] The target reaction force calculation unit 61 adjusts the basic reaction force Tb by multiplying the basic reaction force Tb by a gain G. The target reaction force calculation unit 61 changes the gain G according to the value of the emergency flag F and the time t that has elapsed since it was determined that an emergency occurred. The target reaction force calculation unit 61 has a timer (not shown) that measures the time t that has elapsed since the value of the emergency flag F was changed from "0" to "1."

[0052] More specifically, when the value of the emergency flag F is "0," that is, when it is not determined that an emergency exists, the target operation reaction force calculation unit 61 sets the gain G to the normal gain Gn. The normal gain Gn is, for example, "1," but may be set to any value greater than zero.

[0053] When the value of the emergency flag F is "1" and the elapsed time t since it was determined that an emergency occurred is less than the predetermined time tth, the target operation reaction force calculation unit 61 calculates an early gain Gi based on the vehicle speed V and sets the gain G to the early gain Gi. The early gain Gi is calculated to be a value greater than zero and smaller than the normal gain Gn. For example, the early gain Gi is calculated to be a larger value as the vehicle speed V increases, but it may also be calculated to be a smaller value as the vehicle speed V increases.

[0054] When the value of the emergency flag F is "1" and the elapsed time t since it was determined that an emergency occurred is equal to or greater than a predetermined time tth, the target operation reaction force calculation unit 61 calculates a later gain Gl based on the vehicle speed V and sets the gain G to the later gain Gl. The later gain Gl is calculated to be equal to or greater than the normal gain Gn. For example, the later gain Gl is calculated to be a larger value as the vehicle speed V increases, but it may also be calculated to be a smaller value as the vehicle speed V increases.

[0055] The predetermined time tth is set in advance based on the stage of avoidance by an emergency avoidance operation. The avoidance stage is divided into an early stage in which the steered wheels 3 are steered to avoid a collision with an obstacle, for example, and a later stage in which further steering of the steered wheels 3 is no longer necessary. The predetermined time tth is set in advance based on the time it takes to move from the early stage to the later stage, and may be, for example, about 0.3 seconds.

[0056] The target reaction force calculation unit 61 calculates the target reaction force T* by multiplying the basic reaction force Tb by the gain G set in this way. That is, in the early stage, the target reaction force calculation unit 61 calculates a target reaction force T* having a smaller absolute value than when it is determined that an emergency does not exist. Then, in the later stage, the target reaction force calculation unit 61 calculates a target reaction force T* having an absolute value equal to or greater than the target reaction force T* when it is determined that an emergency does not exist. As a result, when it is determined that an emergency exists, the target reaction force T* is first calculated to be smaller, and then calculated to be larger again.

[0057] Here, the workload of the driver required to turn the steered wheels 3 is expressed as the product of the force resisting the operation reaction force and the amount of change in the lever tilt angle θl. Therefore, in the early stage, the target operation reaction force calculation unit 61 reduces the operation reaction force, thereby reducing the workload required to turn the steered wheels 3. In other words, the target operation reaction force calculation unit 61 corresponds to a workload adjustment unit, and executes emergency adjustment processing. The emergency adjustment processing includes a reduction processing, which includes a reduction target operation reaction force calculation processing, and a weighting processing.

[0058] As described above, after it is determined that an emergency exists and the value of the emergency flag F becomes "1," the gain G is changed to the early gain Gi or the later gain Gl, and the emergency adjustment process is executed. This emergency adjustment process is stopped by changing the gain G to the normal gain Gn after it is determined that the emergency avoidance maneuver has been completed and the value of the emergency flag F becomes "0."

[0059] Next, an example of a processing procedure in which the target reaction force calculation unit 61 calculates the target reaction force T* will be described with reference to the flowchart shown in FIG. 5, upon acquiring various state variables (step 301), the target reaction force calculation unit 61 calculates a basic reaction force Tb (step 302). Subsequently, it determines whether the value of the emergency flag F is "0" (step 303). If the value of the emergency flag F is "0" (step 303: YES), the gain G is set to the normal gain Gn (step 304), and the target reaction force T* is calculated using the normal gain Gn (step 305).

[0060] On the other hand, if the value of the emergency flag F is "1" (step 303: NO), the target operation reaction force calculation unit 61 determines whether the elapsed time t since it was determined that an emergency occurred is equal to or greater than a predetermined time tth (step 306). If the elapsed time t is less than the predetermined time tth (step 306: NO), the target operation reaction force calculation unit 61 calculates an early gain Gi based on the vehicle speed V (step 307). Next, the gain G is set to the early gain Gi (step 308), and the process proceeds to step 305 to calculate the target operation reaction force T* using the early gain Gi. The processing of steps 305, 307, and 308 corresponds to the reduction processing and the reduction target operation reaction force calculation processing.

[0061] If the elapsed time t is equal to or greater than the predetermined time tth (step 306: YES), the target operation reaction force calculation unit 61 calculates a later gain Gl based on the vehicle speed V (step 309). Next, the gain G is set to the later gain Gl (step 310), and the process proceeds to step 305, where the target operation reaction force T* is calculated using the later gain Gl. The processes of steps 305, 309, and 310 correspond to the weighting process. The processes of steps 305 to 310 correspond to the emergency adjustment process.

[0062] (Target steering angle calculation unit 72) Next, the calculation of the target turning-corresponding angle θp* by the target turning-corresponding angle calculation unit 72 shown in FIG. 2 will be described in detail.

[0063] The target steering-corresponding angle calculation unit 72 includes a memory 72a, which stores a normal state map 81 that is normal state calculation information and an emergency state map 82 that is emergency state calculation information.

[0064] As shown in Fig. 6, the normal state map 81 and the emergency state map 82 show the relationship between the lever tilt angle θl, the vehicle speed V, and the target steering-related angle θp*. In other words, the normal state map 81 and the emergency state map 82 are three-dimensional maps showing the relationship between the lever tilt angle θl and the vehicle speed V and the target steering-related angle θp*. In Fig. 6, the normal state map 81 is shown by a solid line, and the emergency state map 82 is shown by a dashed line.

[0065] In the illustrated example, in both the normal state map 81 and the emergency state map 82, when the lever tilt angle θl is zero degrees, the target steering-corresponding angle θp* is zero degrees. Both the normal state map 81 and the emergency state map 82 are set so that the absolute value of the target steering-corresponding angle θp* increases as the absolute value of the lever tilt angle θl increases. The absolute value of the target steering-corresponding angle θp* increases linearly based on the increase in the absolute value of the lever tilt angle θl. In other words, the angle ratio α of the steering angle θi of the steered wheels 3 to the lever tilt angle θl of the operating lever 11 does not change according to the absolute value of the lever tilt angle θl. However, in other embodiments, the absolute value of the target steering-corresponding angle θp* may increase, for example, nonlinearly based on the increase in the absolute value of the lever tilt angle θl. In other words, the angle ratio α may change according to the absolute value of the lever tilt angle θl. The angle ratio α is a value obtained by dividing the steering angle θi by the lever tilt angle θl (α=θi / θl).

[0066] Furthermore, both the normal state map 81 and the emergency state map 82 are set so that, for example, the smaller the vehicle speed V, the larger the absolute value of the target steering corresponding angle θp*. In other words, the angle ratio α changes according to the vehicle speed V. The amount of change in the absolute value of the target steering corresponding angle θp* with respect to the amount of change in the lever tilt angle θl and vehicle speed V in the emergency state map 82 is set so as to be smaller than the amount of change in the absolute value of the target steering corresponding angle θp* with respect to the amount of change in the lever tilt angle θl and vehicle speed V in the normal state map 81. As a result, the absolute value of the target steering corresponding angle θp* in the emergency state map 82 is smaller than the absolute value of the target steering corresponding angle θp* in the normal state map 81 at any lever tilt angle θl and vehicle speed V, except when the absolute value of the target steering corresponding angle θp* in the normal state map 81 is zero.

[0067] When the value of emergency flag F is "0," target steering corresponding angle calculation unit 72 calculates target steering corresponding angle θp* corresponding to lever tilt angle θl and vehicle speed V by referring to normal state map 81. On the other hand, when the value of emergency flag F is "1," target steering corresponding angle calculation unit 72 calculates target steering corresponding angle θp* corresponding to lever tilt angle θl and vehicle speed V by referring to emergency state map 82. In other words, target steering corresponding angle calculation unit 72 switches the map depending on whether it is determined that an emergency exists or not. As a result, when it is determined that an emergency exists, target steering corresponding angle calculation unit 72 calculates target steering corresponding angle θp* having a smaller absolute value than target steering corresponding angle θp* when it is not determined that an emergency exists. In other words, after it is determined that an emergency exists, target steering corresponding angle θp* becomes less likely to change in response to changes in lever tilt angle θl due to driver operation.

[0068] As described above, the workload of the driver required to turn the steered wheels 3 is expressed as the product of the force resisting the operation reaction force and the amount of change in the lever inclination angle θl. Therefore, the target turning corresponding angle calculation unit 72 increases the amount of workload required to turn the steered wheels 3 by increasing the amount of change in the lever inclination angle θl required to turn the steered wheels 3. In other words, the target turning corresponding angle calculation unit 72 corresponds to a workload adjustment unit, and executes emergency adjustment processing. The emergency adjustment processing includes suppression target turning corresponding value calculation processing.

[0069] Next, an example of a processing procedure in which target turning-corresponding angle calculation unit 72 calculates target turning-corresponding angle θp* will be described with reference to the flowchart shown in FIG. When target steering-corresponding angle calculation unit 72 acquires various state quantities (step 401), it determines whether the value of emergency flag F is "0" (step 402). If the value of emergency flag F is "0" (step 402: YES), it calculates target steering-corresponding angle θp* using normal state map 81 (step 403).

[0070] On the other hand, when the value of emergency flag F is "1" (step 402: NO), target turning corresponding angle calculation unit 72 calculates target turning corresponding angle θp* using emergency map 82 (step 404). The processing of step 404 corresponds to the suppression target turning corresponding value calculation processing and the emergency adjustment processing.

[0071] Next, the operation and effects of this embodiment will be described. (1-1) The target operation reaction force calculation unit 61, which is a workload adjustment unit, executes emergency adjustment processing to adjust the workload required to steer the steered wheels 3 in accordance with the determination result of whether or not an emergency exists. The emergency adjustment processing includes a reduction processing to reduce the workload in an early stage after the emergency determination unit 63 has determined that an emergency exists, compared to when it is not determined that an emergency exists. Therefore, when it is determined that an emergency exists, the steered wheels 3 can be turned with a small workload. This makes it easy to perform emergency avoidance operations.

[0072] (1-2) The reduction process includes a reduced target operation reaction force calculation process that calculates the absolute value of the target operation reaction force T* to be smaller than when it is determined that an emergency does not exist. Therefore, by executing the reduction process, the force required to operate the operating lever 11 is reduced, and the workload required to steer the steered wheels 3 is reduced. This makes it easier to perform an emergency avoidance operation.

[0073] (1-3) The reduction target operation reaction force calculation process is a process for reducing the absolute value of the target operation reaction force T* based on the vehicle speed V. Therefore, when it is determined that an emergency situation exists, the operation reaction force can be suitably reduced in accordance with the vehicle speed V.

[0074] (1-4) If the operation reaction force is reduced when it is determined that an emergency exists, the lever tilt angle θl may become too large, which may cause the absolute value of the target steering response angle θp* to become too large. In this regard, the emergency adjustment process further includes a weighting process in a later stage following the earlier stage that calculates a target operation reaction force T* having an absolute value equal to or greater than the target operation reaction force T* calculated when it is not determined that an emergency exists. In other words, the operation reaction force becomes large in the later stage following the earlier stage. This prevents the lever tilt angle θl from becoming too large. This makes it easy to perform an appropriate emergency avoidance operation.

[0075] (1-5) The target operation reaction force calculation unit 61 determines that the avoidance stage due to the emergency avoidance operation has shifted from the early stage to the late stage based on the time t that has elapsed since it was determined that an emergency situation has occurred. Here, the angle ratio α of the change in the steering angle θi to the change in the lever tilt angle θl may differ depending on the vehicle model in which the steering device 2 is installed. Therefore, if the determination of whether or not the state has transitioned from the early stage to the later stage is based on, for example, the lever tilt angle θl, an optimal threshold value for the lever tilt angle θl must be considered for each vehicle model. In this regard, with the above configuration, the determination of whether or not the state has transitioned from the early stage to the later stage is based on the elapsed time t since it was determined that an emergency occurred. Therefore, it is possible to easily determine whether or not the state has transitioned from the early stage to the later stage for a wide range of vehicle models.

[0076] (1-6) If the operation reaction force is reduced when it is determined that an emergency exists, the lever tilt angle θl may become too large, which may cause the absolute value of the target steering-corresponding angle θp* to become too large. In this regard, the emergency adjustment process further includes a suppression target steering-corresponding value calculation process that calculates the target steering-corresponding angle θp* so that the amount of change in the steering angle θi relative to the amount of change in the operation of the operating lever 11 is smaller than when it is not determined that an emergency exists. Therefore, even if the lever tilt angle θl becomes too large, it is possible to prevent the absolute value of the target steering-corresponding angle θp* from becoming too large. This makes it easy to perform an appropriate emergency avoidance operation.

[0077] (1-7) The suppression target steering corresponding value calculation process is a process for calculating the target steering corresponding angle θp* based on the vehicle speed V. Therefore, when it is determined that an emergency situation exists, the target steering corresponding angle θp* can be calculated appropriately in accordance with the vehicle speed V.

[0078] (1-8) The steering control signal generator 73 generates the steering control signal Mt so that the change in the target steering corresponding angle θp* is gradually reflected in the steering angle θi. This suppresses abrupt changes in the steering angle θi, thereby suppressing disturbances in the behavior of the vehicle.

[0079] (1-9) Emergency determination unit 63 determines whether or not the emergency avoidance maneuver has been completed. Target operation reaction force calculation unit 61 and target steering response angle calculation unit 72 stop the emergency adjustment process after it is determined that the emergency avoidance maneuver has been completed. This makes it possible to prevent, for example, a sudden change in the operation reaction force during the emergency avoidance maneuver. This makes it possible to suppress any sense of discomfort felt by the driver.

[0080] (1-10) Normally, when an emergency avoidance operation is completed, the lever tilt angle θl of the operating lever 11 is returned to its original position. In light of this, the emergency determination unit 63 determines whether or not the emergency avoidance operation is completed based on whether or not the operating lever 11 is operated in the return direction opposite to the operating direction thereof due to the emergency avoidance operation. Therefore, it is possible to appropriately determine that the emergency avoidance operation has been completed.

[0081] (1-11) The emergency determination unit 63 determines whether or not an emergency has occurred based on the result of comparing the magnitude of a parameter indicating the vehicle's running state with a threshold value, and the result of comparing the magnitude of a parameter indicating the operation state of the operation unit 4 with a threshold value. Therefore, it is possible to appropriately determine whether or not an emergency has occurred depending on the running state of the vehicle and the operation state of the operation unit 4.

[0082] (Second embodiment) Next, a second embodiment of the steering control device will be described with reference to the drawings. For the sake of convenience, the same components as those in the first embodiment will be denoted by the same reference numerals, and the description thereof will be omitted.

[0083] As shown in Fig. 8, memory 72a of target steering corresponding angle calculation unit 72 of the present embodiment stores an emergency map 92 having a shape different from emergency map 82 of the first embodiment. Memory 72a also stores normal state map 81 of the first embodiment. In Fig. 8, normal state map 81 is indicated by a solid line, and emergency state map 92 is indicated by a dashed line.

[0084] Each of the normal map 81 and the emergency map 92 has a small operation range and a large operation range set as the range of the lever tilt angle θl. The small operation range is the range of the lever tilt angle θl from zero to the boundary value θlb, and the large operation range is the range of the lever tilt angle θl greater than the boundary value θlb. The boundary value θlb is the lever tilt angle θl at which the steering angle θi becomes somewhat large. In this embodiment, the boundary value θlb is the same as the turning determination threshold θlth, for example, but may be a value greater or smaller than the turning determination threshold θlth. In other embodiments, the boundary value θlb may be changed based on, for example, the vehicle speed V.

[0085] In the small operation range, the amount of change in the absolute value of the target steering corresponding angle θp* with respect to changes in the lever tilt angle θl and vehicle speed V in the emergency map 92 is set to be larger than the amount of change in the absolute value of the target steering corresponding angle θp* with respect to changes in the lever tilt angle θl and vehicle speed V in the normal operation map 81. In other words, in the small operation range, the angle ratio α when it is determined that an emergency exists is larger than the angle ratio α when it is not determined that an emergency exists. Also, in the large operation range, the amount of change in the absolute value of the target steering corresponding angle θp* with respect to changes in the lever tilt angle θl and vehicle speed V in the emergency operation map 92 is set to be smaller than the amount of change in the absolute value of the target steering corresponding angle θp* with respect to changes in the lever tilt angle θl and vehicle speed V in the normal operation map 81. In other words, in the large operation range, the angle ratio α when it is determined that an emergency exists is smaller than the angle ratio α when it is not determined that an emergency exists.

[0086] As in the first embodiment, when the value of emergency flag F is "0", target steering corresponding angle calculation unit 72 calculates target steering corresponding angle θp* by referring to normal state map 81. When the value of emergency flag F is "1", target steering corresponding angle calculation unit 72 calculates target steering corresponding angle θp* by referring to emergency state map 92.

[0087] Here, referring to the above condition (a2), when it is determined that an emergency exists, the absolute value of the lever tilt angle θl is less than the turning determination threshold θlth, i.e., less than the boundary value θlb. Therefore, in the early stage after it is determined that an emergency exists, even if the amount of change in the lever tilt angle θl due to the driver's operation is small, the target steering-corresponding angle θp* changes greatly.

[0088] As described above, the workload of the driver required to turn the steered wheels 3 is expressed as the product of the force resisting the operation reaction force and the amount of change in lever inclination angle θl. Therefore, target turning corresponding angle calculation unit 72 reduces the amount of workload required to turn the steered wheels 3 by reducing the amount of change in lever inclination angle θl required to turn the steered wheels 3. In other words, target turning corresponding angle calculation unit 72 corresponds to a workload adjustment unit, and executes emergency adjustment processing. The emergency adjustment processing includes reduction processing, which includes reduction target turning corresponding value calculation processing.

[0089] The processing procedure by which target steering corresponding angle calculation unit 72 calculates target steering corresponding angle θp* is the same as that in the first embodiment, and therefore description thereof will be omitted. Note that the processing of step 404 executed when lever tilt angle θl is within the small operation range, i.e., the processing of calculating target steering corresponding angle θp* using emergency map 92, corresponds to the reduction processing and the reduction target steering corresponding value calculation processing.

[0090] As described above, after it is determined that an emergency exists and the value of emergency flag F becomes "1", emergency adjustment processing is executed by calculating target steering response angle θp* using emergency map 92. This emergency adjustment processing is stopped when target steering response angle θp* is calculated using normal state map 81 after it is determined that an emergency avoidance operation has been completed and the value of emergency flag F becomes "0".

[0091] As described above, in this embodiment, in addition to the same functions and effects as those (1-1) to (1-11) of the first embodiment, the following functions and effects are achieved. (2-1) Target steering corresponding angle calculation unit 72, which is a workload adjustment unit, executes emergency adjustment processing to adjust the workload required to steer steered wheels 3 in accordance with the determination result of whether or not an emergency exists. Therefore, when it is determined that an emergency exists, steered wheels 3 can be turned with a small workload. This makes it easy to perform emergency avoidance operations.

[0092] (2-2) The reduction process includes a reduction target steering corresponding value calculation process that calculates the target steering corresponding angle θp* so that the amount of change in steering angle θi relative to the amount of change in the operation amount of operating lever 11 is larger than when it is not determined that an emergency exists. Therefore, by executing the reduction process, the amount of change in lever tilt angle θl required for emergency avoidance operation is reduced, thereby reducing the amount of work required to turn steered wheels 3. This makes it easier to perform emergency avoidance operation.

[0093] (2-3) The reduction target steering corresponding value calculation process is a process for calculating the target steering corresponding angle θp* based on the vehicle speed V. Therefore, when it is determined that an emergency situation exists, the target steering corresponding angle θp* can be suitably calculated in accordance with the vehicle speed V.

[0094] (2-4) An emergency avoidance maneuver is often necessary when the vehicle is not making a large turn, i.e., when traveling generally straight. In this regard, memory 72a of target steering corresponding angle calculation unit 72 stores normal state map 81 and emergency state map 92 that indicate the relationship between lever tilt angle θl and target steering corresponding angle θp*. Each of normal state map 81 and emergency state map 92 includes a small operation range, which is a range of lever tilt angle θl that includes zero, and a large operation range, which is a range of lever tilt angle θl whose absolute value is larger than that of the small operation range. In the small operation range, the amount of change in the absolute value of target steering corresponding angle θp* with respect to the amount of change in lever tilt angle θl in emergency state map 92 is set to be larger than the amount of change in the absolute value of target steering corresponding angle θp* with respect to the amount of change in lever tilt angle θl in the normal map. The reduction target steering corresponding value calculation process is a process that calculates target steering corresponding angle θp* based on lever tilt angle θl using emergency state map 92. Therefore, when it is determined that an emergency exists, the target steering response angle θp* can be calculated with a small calculation load so that the amount of change in the steering angle θi relative to the amount of change in the operation amount of the operating lever 11 is larger than when it is determined that an emergency exists.

[0095] (2-5) If the amount of change in the absolute value of the target steering-corresponding angle θp* relative to the amount of change in the lever tilt angle θl in the emergency map 92 is increased over the entire operation range of the operating lever 11, the absolute value of the target steering-corresponding angle θp* may become too large. In this regard, in a wide operation range, the amount of change in the absolute value of the target steering-corresponding angle θp* relative to the amount of change in the lever tilt angle θl in the emergency map 92 is set to be smaller than the amount of change in the absolute value of the target steering-corresponding angle θp* relative to the amount of change in the lever tilt angle θl in the normal map. Therefore, even if the absolute value of the lever tilt angle θl becomes large, the absolute value of the target steering-corresponding angle θp* can be prevented from becoming too large. This makes it easy to perform appropriate emergency operations.

[0096] The above-described embodiments can be modified as follows: The above-described embodiments and the following modifications can be combined with each other within the scope of technical compatibility. Although it is determined that an emergency exists when all of the above conditions (a1) to (a3) ​​are met, this is not limiting. For example, it may be determined that an emergency exists when conditions (a1) and (a3) ​​are met, without determining condition (a2) regarding the lever tilt angle θl. Furthermore, it may be determined whether or not an emergency exists using information other than the parameters indicating the operation state of the operation unit 4 and the parameters indicating the vehicle's traveling state. The other information may be, for example, a signal from a camera that detects obstacles. Furthermore, the other information may be information obtained by communication with other vehicles traveling nearby or with monitoring equipment installed on the road along which the vehicle is traveling.

[0097] Although it is determined that the emergency avoidance maneuver is complete when the above condition (b1) is met, this is not limiting. For example, it may be determined that the emergency avoidance maneuver is complete when the vehicle stops. Furthermore, it may be determined whether the emergency avoidance maneuver is complete using information other than the parameter indicating the operation state of the operation unit 4 and the parameter indicating the traveling state of the vehicle. The other information may be the distance traveled and the traveling time since it was determined that an emergency occurred. Furthermore, if a switch operated by the driver is provided in the driver's seat, the other information may be the on / off state of this switch.

[0098] Although the emergency adjustment process is stopped when the emergency determination unit 63 determines that the emergency avoidance maneuver is complete, this is not limiting. For example, the emergency adjustment process may be stopped when at least one of the conditions (a1) to (a3) ​​is not met. That is, for example, when at least one of the conditions (a1) to (a3) ​​is not met, the value of the emergency flag F may be reset to "0." In this case, the emergency determination unit 63 does not need to perform the completion determination.

[0099] In the second embodiment described above, the change in the absolute value of the target steering corresponding angle θp* with respect to the change in the lever tilt angle θl in the emergency map 92 may be greater than that in the normal map 81, even within the large operation range. Furthermore, the emergency map 92 may be set so that the absolute value of the target steering corresponding angle θp* does not change even if the absolute value of the lever tilt angle θl increases within the large operation range. In other words, when it is determined that an emergency exists, the target steering corresponding angle θp* when the lever tilt angle θl is a boundary value may be set as an upper limit angle, and the steered wheels 3 may not be steered any further. Note that even in this case, after it is determined that the emergency avoidance maneuver is completed, it becomes possible to steer the steered wheels 3 to an angle greater than the upper limit angle.

[0100] A dead zone may be set in the normal state map 81 and the emergency state maps 82, 92. Specifically, a range may be set near zero degrees of the lever tilt angle θl within which the target steering corresponding angle θp* remains zero degrees even if the absolute value of the lever tilt angle θl increases. Furthermore, the normal state map 81 and the emergency state maps 82, 92 may be two-dimensional maps that indicate the relationship between the target steering corresponding angle θp* and the lever tilt angle θl. In other words, the suppression target steering corresponding value calculation process and the reduction target steering corresponding value calculation process may be processes that calculate the target steering corresponding angle θp* without using the vehicle speed V. Furthermore, the normal state calculation information and the emergency state calculation information may not be maps but may be, for example, functional expressions.

[0101] In the second embodiment described above, the reduction process by target steering corresponding angle calculation unit 72 may calculate target steering corresponding angle θp* so that the amount of change in steering angle θi relative to the amount of change in lever tilt angle θl is larger than when it is not determined that an emergency exists, regardless of the absolute value of lever tilt angle θl.

[0102] The steering control signal generation unit 73 includes a guard processing unit 75, and generates a steering control signal Mt that gradually reflects changes in target steering-related angle θp* in the steering angle θi by setting the steering speed of the steered wheels 3 to be equal to or lower than the upper limit speed. However, this is not limiting, and the steering control signal generation unit 73 may include, for example, a filter processing unit that performs first-order lag filtering in addition to or instead of the guard processing unit 75. In this case, the filter processing unit performs first-order lag filtering on the input difference Δθp, thereby suppressing sudden changes in the difference Δθp. As a result, changes in the target steering-related angle θp* are gradually reflected in the steering angle θi. Note that the time constant of the filter, etc., may be changed based on the vehicle speed V.

[0103] Steering control signal generator 73 always generates steering control signal Mt so as to gradually reflect changes in target steering-related angle θp* in steering angle θi. However, this is not limiting, and steering control signal Mt may be generated so as to gradually reflect changes in target steering-related angle θp* in steering angle θi only when, for example, normal map 81 and emergency maps 82, 92 are switched between. In this case, steering control signal Mt may be generated so that difference Δθp caused by switching between maps disappears within a preset gradual-change time. Note that the gradual-change time may be calculated based on vehicle speed V.

[0104] Furthermore, the steering control signal generating section 73 may not be provided with the guard processing section 75, and may generate the steering control signal Mt so that a change in the target steering corresponding angle θp* is immediately reflected in the steering angle θi. While target operation reaction force calculation unit 61 calculated the angular axial force as basic operation reaction force Tb, this is not limiting, and for example, the current axial force may be calculated as basic operation reaction force Tb. The current axial force is the axial force actually transmitted from steering motor 32 to rack shaft 22, and includes road surface information. The current axial force can be calculated based on the actual current value supplied to steering motor 32. Alternatively, a distributed axial force obtained by adding the angular axial force and the current axial force at a predetermined ratio may be calculated as basic operation reaction force Tb. Furthermore, for example, a value proportional to the absolute value of lever tilt angle θl may be calculated as basic operation reaction force Tb, and the calculation of basic operation reaction force Tb can be changed as appropriate.

[0105] The target operation reaction force calculation unit 61 calculates the early gain Gi based on the vehicle speed V, but this is not limiting, and the early gain Gi may be a fixed value set in advance. Similarly, the later gain Gl may be a fixed value set in advance.

[0106] The target operation reaction force calculation unit 61 adjusted the basic operation reaction force Tb by multiplying the basic operation reaction force Tb by the gain G, but this is not limiting and the method of adjusting the basic operation reaction force Tb can be changed as appropriate. For example, the basic operation reaction force Tb may be adjusted by subtracting an adjustment value from the absolute value of the basic operation reaction force Tb. The adjustment value may be a preset fixed value or a value calculated based on the vehicle speed V.

[0107] Furthermore, the target operation reaction force calculation unit 61 may have normal operation calculation information and emergency operation calculation information that indicate, for example, the relationship between the lever tilt angle θl and the target operation reaction force T*. In this case, the target operation reaction force T* in the emergency operation calculation information can be set to be larger than the target operation reaction force T* in the normal operation calculation information. In this case, the target operation reaction force calculation unit 61 can directly calculate the target operation reaction force T* without calculating the basic operation reaction force Tb.

[0108] While it is determined that the avoidance stage due to the emergency avoidance operation has shifted from the early stage to the late stage based on the elapsed time t since it was determined that an emergency situation has occurred, this is not limiting. For example, it may be determined that the avoidance stage has shifted from the early stage to the late stage based on the amount of change in the lever tilt angle θl since it was determined that an emergency situation has occurred.

[0109] The emergency adjustment process does not have to include weighting. In other words, once it is determined that an emergency exists, the operation reaction force may remain small. In the first embodiment, the emergency adjustment process does not have to include the process of calculating the suppression target turning corresponding value. In other words, the target turning corresponding angle θp* may be calculated in the same manner whether or not it is determined that an emergency exists.

[0110] In the second embodiment, the emergency adjustment process does not have to include the reduction process, the reduction target reaction force calculation process, and the weighting process by the target reaction force calculation unit 61. In other words, the target reaction force T* may be calculated in the same way whether it is determined that an emergency exists or not.

[0111] The convertible value that can be converted into the steering angle θi of the steered wheels 3 is the rotation angle of the pinion shaft 21, but this is not limited to this. For example, the convertible value may be the stroke amount of the rack shaft 22 or the steering angle θi itself.

[0112] The microcomputer 51 does not have to notify the driver of an emergency via the alarm 37. Although the operating lever 11 is tiltably supported on the base 12, the present invention is not limited to this and may be supported, for example, slidably with respect to the base 12. In this case, the amount of operation by the driver is represented by the amount of sliding of the operating lever 11. The operating lever 11 may be used to control the driving / braking of the vehicle in addition to controlling the steering angle θi of the steered wheels 3.

[0113] Although the lever tilt angle θl is detected by the tilt angle sensor 13, this is not limiting, and the lever tilt angle θl may be detected based on, for example, the rotation angle of the operation motor 16. In this case, the operation unit 4 does not need to be equipped with the tilt angle sensor 13.

[0114] The operation unit 4 may be provided with a steering wheel, which is an operation member, instead of the operation lever 11. Also, the operation unit 4 may be provided with a steering wheel operated by the driver in addition to the operation lever 11. The steering device 2 has a linkless structure in which power transmission between the operation unit 4 and the steering unit 5 is separated, but this is not limited to this. When a steering wheel is provided, the steering device 2 may be provided with a structure in which power transmission between the operation unit 4 and the steering unit 5 can be separated by a clutch.

[0115] In the above embodiment, steering actuator 31 transmits the rotation of steering motor 32 to ball screw mechanism 35 via belt mechanism 34, but this is not limiting, and steering actuator 31 may be configured, for example, so that the rotation of steering motor 32 is transmitted to ball screw mechanism 35 via a gear mechanism. Also, steering actuator 31 may be configured so that steering motor 32 directly rotates ball screw mechanism 35. Furthermore, steering unit 5 may be configured to include a second rack-and-pinion mechanism, and steering actuator 31 may be configured so that the rotation of steering motor 32 is converted into reciprocating motion of rack shaft 22 by the second rack-and-pinion mechanism, thereby applying a steering force to steering unit 5.

Claims

1. A steering control device that controls a steering device of a vehicle, the steering device has a structure in which a power transmission path between an operation unit having an operation member and a steering unit configured to steer steered wheels is mechanically separated, The steering control device includes: a target steering corresponding value calculation unit configured to calculate a target steering corresponding value, which is a target value of a convertible value that can be converted into a steering angle of the steered wheels, based on an operation amount of the operating member; a steering control signal generation unit configured to generate a steering control signal that operates the steering unit based on the target steering corresponding value; an emergency determination unit configured to determine whether an emergency situation occurs in which an emergency avoidance operation is required; a workload adjustment unit configured to adjust the workload of a driver required to steer the steered wheels, the workload adjustment unit is configured to execute an emergency adjustment process to adjust the workload depending on a determination result of whether or not an emergency occurs; the emergency adjustment process includes a reduction process of reducing the workload in an early stage after the emergency determination unit has determined that an emergency exists, compared to a case where an emergency is not determined, the operation unit is configured to apply an operation reaction force to the operation member in accordance with the operation amount, The steering control device includes: a target reaction force calculation unit configured to calculate a target reaction force, which is a target value of the reaction force, based on the amount of operation; an operation control signal generation unit configured to generate an operation control signal for operating the operation unit based on the target operation reaction force; the workload adjustment unit includes the target operation reaction force calculation unit, the reduction process includes a reduction target reaction force calculation process that calculates the target reaction force having a smaller absolute value than when it is determined that the situation is not an emergency, A steering control device, wherein the emergency adjustment process further includes a weighting process in a later stage following the earlier stage to calculate the target operation reaction force having an absolute value greater than the target operation reaction force calculated in the earlier stage.

2. The steering control device according to claim 1, A steering control device, wherein the reduction target operation reaction force calculation process is a process for calculating the target operation reaction force based on a vehicle speed.

3. The steering control device according to claim 1 or 2, The target operation reaction force calculation unit is configured to determine that the stage of avoidance by emergency avoidance operation has shifted from the early stage to the late stage based on the elapsed time since it was determined that an emergency situation has occurred.

4. The steering control device according to any one of claims 1 to 3, The workload adjustment unit further includes the target steering corresponding value calculation unit, The emergency adjustment process further includes a suppression target steering corresponding value calculation process that calculates the target steering corresponding value so that the amount of change in the steering angle relative to the amount of change in the operation amount is smaller than when it is determined that an emergency is not occurring.

5. A steering control device that controls a steering device of a vehicle, the steering device has a structure in which a power transmission path between an operation unit having an operation member and a steering unit configured to steer steered wheels is mechanically separated, The steering control device includes: a target steering corresponding value calculation unit configured to calculate a target steering corresponding value, which is a target value of a convertible value that can be converted into a steering angle of the steered wheels, based on an operation amount of the operating member; a steering control signal generation unit configured to generate a steering control signal that operates the steering unit based on the target steering corresponding value; an emergency determination unit configured to determine whether an emergency situation occurs in which an emergency avoidance operation is required; a workload adjustment unit configured to adjust the workload of a driver required to steer the steered wheels, the workload adjustment unit is configured to execute an emergency adjustment process to adjust the workload depending on a determination result of whether or not an emergency occurs; the emergency adjustment process includes a reduction process of reducing the workload in an early stage after the emergency determination unit has determined that an emergency exists, compared to a case where an emergency is not determined, the operation unit is configured to apply an operation reaction force to the operation member in accordance with the operation amount, The steering control device includes: a target reaction force calculation unit configured to calculate a target reaction force, which is a target value of the reaction force, based on the amount of operation; an operation control signal generation unit configured to generate an operation control signal for operating the operation unit based on the target operation reaction force; the workload adjustment unit includes the target operation reaction force calculation unit, the reduction process includes a reduction target reaction force calculation process that calculates the target reaction force having a smaller absolute value than when it is determined that the situation is not an emergency, The workload adjustment unit further includes the target steering corresponding value calculation unit, The emergency adjustment process further includes a suppression target steering corresponding value calculation process that calculates the target steering corresponding value so that the amount of change in the steering angle relative to the amount of change in the operation amount is smaller than when it is determined that an emergency is not occurring.

6. The steering control device according to claim 5, A steering control device, wherein the reduction target operation reaction force calculation process is a process for calculating the target operation reaction force based on a vehicle speed.

7. The steering control device according to claim 5 or 6, The emergency adjustment process further includes, in a later stage following the earlier stage, a weighting process for calculating the target operation reaction force having an absolute value equal to or greater than the target operation reaction force calculated when it is not determined that an emergency exists.

8. The steering control device according to claim 7, The target operation reaction force calculation unit is configured to determine that the stage of avoidance by emergency avoidance operation has shifted from the early stage to the late stage based on the elapsed time since it was determined that an emergency situation has occurred.

9. The steering control device according to any one of claims 4 to 8, A steering control device, wherein the suppression target steering corresponding value calculation process is a process of calculating the target steering corresponding value based on a vehicle speed.

10. The steering control device according to any one of claims 1 to 3, The workload adjustment unit includes the target steering corresponding value calculation unit, The steering control device includes a reduction target steering corresponding value calculation process that calculates the target steering corresponding value so that the amount of change in the steering angle relative to the amount of change in the operation amount is larger than when it is not determined that an emergency exists.

11. The steering control device according to claim 10, A steering control device, wherein the reduction target steering corresponding value calculation process is a process of calculating the target steering corresponding value based on a vehicle speed.

12. The steering control device according to claim 10 or 11, The target steering corresponding value calculation unit includes a memory, the memory stores normal operation information and emergency operation information indicating a relationship between the operation amount and the target steering corresponding value, The operation amount is zero when the vehicle travels straight, each of the normal operation information and the emergency operation information includes a small operation range that is a range of the operation amount including zero, and a large operation range that is a range of the operation amount having an absolute value larger than that of the small operation range; In the small operation range, a change amount of the absolute value of the target steering corresponding value with respect to a change amount of the operation amount in the emergency calculation information is set to be larger than that in the normal operation information, The steering control device, wherein the reduction target steering corresponding value calculation process is a process of calculating the target steering corresponding value based on the operation amount using the emergency calculation information.

13. The steering control device according to claim 12, A steering control device wherein, in the large operation range, a change in the absolute value of the target steering corresponding value relative to a change in the operation amount in the emergency operation information is set to be smaller than that in the normal operation information.

14. A steering control device according to any one of claims 1 to 13, A steering control device, wherein the steering control signal generation unit is configured to generate the steering control signal that gradually reflects a change in the target steering corresponding value in the steering angle.

15. A steering control device according to any one of claims 1 to 14, the emergency determination unit is further configured to determine whether an emergency avoidance maneuver has been completed; The steering control device, wherein the workload adjustment unit is configured to stop the emergency adjustment process after the emergency determination unit determines that an emergency avoidance maneuver has been completed.

16. 16. The steering control device according to claim 15, The emergency determination unit is configured to determine whether or not an emergency avoidance operation has been completed based on whether or not an operation is performed in a return direction opposite to the operation direction of the operating member due to the emergency avoidance operation.

17. A steering control device according to any one of claims 1 to 16, The emergency determination unit is configured to determine whether an emergency exists based on the result of comparing a parameter indicating the vehicle's driving state with a threshold value, and the result of comparing a parameter indicating the operation state of the operation unit with a threshold value.

18. A steering control method for controlling a steering device of a vehicle, comprising: the steering device has a structure in which a power transmission path between an operation unit having an operation member and a steering unit configured to steer steered wheels is mechanically separated, The steering control method includes: calculating a target steering corresponding value that is a target value of a convertible value that can be converted into a steering angle of the steered wheels based on an operation amount of the operating member; generating a steering control signal for operating the steering unit based on the target steering corresponding value; Determining whether or not an emergency situation is occurring in which an emergency avoidance operation is required; adjusting the amount of driver work required to steer the steered wheels; adjusting the workload includes executing an emergency adjustment process to adjust the workload depending on a determination result of whether or not an emergency occurs; the emergency adjustment process includes a reduction process for reducing the workload in an early stage after it has been determined that an emergency exists, compared to when it has not been determined that an emergency exists; the operation unit is configured to apply an operation reaction force to the operation member in accordance with the operation amount, The steering control method includes: calculating a target operation reaction force, which is a target value of the operation reaction force, based on the operation amount; generating an operation control signal for operating the operation unit based on the target operation reaction force; adjusting the workload includes calculating the target operation reaction force; the reduction process includes a reduction target reaction force calculation process that calculates the target reaction force having a smaller absolute value than when it is determined that the situation is not an emergency, The steering control method, wherein the emergency adjustment process further includes a weighting process in a later stage following the earlier stage to calculate the target operation reaction force having a larger absolute value than the target operation reaction force calculated in the earlier stage.

19. A steering control method for controlling a steering device of a vehicle, comprising: the steering device has a structure in which a power transmission path between an operation unit having an operation member and a steering unit configured to steer steered wheels is mechanically separated, The steering control method includes: calculating a target steering corresponding value that is a target value of a convertible value that can be converted into a steering angle of the steered wheels based on an operation amount of the operating member; generating a steering control signal for operating the steering unit based on the target steering corresponding value; Determining whether or not an emergency situation is occurring in which an emergency avoidance operation is required; adjusting the amount of driver work required to steer the steered wheels; adjusting the workload includes executing an emergency adjustment process to adjust the workload depending on a determination result of whether or not an emergency occurs; the emergency adjustment process includes a reduction process for reducing the workload in an early stage after it has been determined that an emergency exists, compared to when it has not been determined that an emergency exists; the operation unit is configured to apply an operation reaction force to the operation member in accordance with the operation amount, The steering control method includes: calculating a target operation reaction force, which is a target value of the operation reaction force, based on the operation amount; generating an operation control signal for operating the operation unit based on the target operation reaction force; adjusting the workload includes calculating the target operation reaction force; the reduction process includes a reduction target reaction force calculation process that calculates the target reaction force having a smaller absolute value than when it is determined that the situation is not an emergency, adjusting the workload further includes calculating the target steering corresponding value; The emergency adjustment process further includes a suppression target steering corresponding value calculation process that calculates the target steering corresponding value so that a change in the steering angle relative to a change in the operation amount is smaller than when it is determined that an emergency does not exist.

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