Vehicle steering assist device

Abstract

To provide a steering assist device improved so as to reduce the possibility of erroneous determination of whether a driver is not holding a steering handle.SOLUTION: A steering assist device for a vehicle includes: a torque applying device configured to apply control torque to a steering transmission system between a steering handle and a steering wheel; a steering torque sensor provided in the steering transmission system between the steering handle and the torque application device; and a control unit configured to determine that, when torque Ts detected by the steering toque sensor is lower than a reference value Tsc, a driver is not holding the steering handle. When it is determined that the torque is input from a steering-wheel side to the steering torque sensor, the control unit sets the reference value to a large value, compared to when it is determined that the torque is input to the steering torque sensor from a steering-handle side.SELECTED DRAWING: Figure 2

Description

[Technical Field]

[0001] The present invention relates to a steering assist device for a vehicle such as an automobile. [Background technology]

[0002] A well-known driving assistance system for vehicles such as automobiles is a steering assistance system that controls the lateral position of the vehicle relative to the lane by automatic steering. This type of steering assistance system includes a lane keeping assistance system, a lane departure prevention system, and a lane change assistance system.

[0003] When a steering assist device performs steering assistance, the driver is required to grip the steering wheel. When the driver is not gripping the steering wheel, a situation in which the steering torque is small continues. Therefore, it is known to determine whether the driver is not gripping the steering wheel and has let go of it based on the steering torque detected by a steering torque sensor.

[0004] For example, Patent Document 1 listed below describes a hands-off determination technique that determines that the driver has let go of the steering wheel if the steering torque detected by a steering torque sensor is determined to be less than a reference value a predetermined number of times in succession. This hands-off determination technique makes it possible to detect the driver's hands-off state without requiring an expensive sensor such as a touch sensor. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Japanese Patent Publication No. 2020-117025 Summary of the Invention

[0006] [Problem to be solved by the invention] In order to prevent the driver's hands-off state from being overlooked, the reference value needs to be set to a large value. However, if the reference value is set to a large value, it is likely that the driver will be erroneously determined to be in a hands-off state even though the driver is holding the steering wheel. Conversely, if the reference value is set to a small value, it is likely that the driver will be erroneously determined to be not in a hands-off state even though the driver is actually in a hands-off state.

[0007] For example, the steering assist device includes a torque applying device such as an electric power steering device, which applies a control torque for steering the steered wheels to a steering transmission system between the steering wheel and the steered wheels, located closer to the steered wheels than the steering torque sensor. Automatic steering in the steering assist device is achieved by applying a control torque to the steering transmission system by the torque applying device. Therefore, even if the driver has their hands off the steering wheel, the control torque may momentarily exceed a reference value, making it impossible to detect the driver's hands off the steering wheel. A similar situation occurs when a road disturbance causes torque to be input from the steered wheels to the steering transmission system.

[0008] The present invention provides an improved steering assist device that can reduce the risk of erroneous determination of whether the driver is in a hands-off state by changing the magnitude of a reference value depending on whether the torque input to the steering torque sensor is from the steering wheel side.

[0009] [Means for solving the problems and effects of the invention] According to the present invention, there is provided a steering assist device (100) including a torque imparting device (EPS device 12) configured to impart a control torque to a steering transmission system (34) between a steering wheel (14) and steered wheels (front wheels 16FL, 16FR), a steering torque sensor (38) provided in the steering transmission system between the steering wheel and the torque imparting device, and a control unit (steering assist ECU 50) configured to determine (S420) that the driver is not gripping the steering wheel when the torque (Ts) detected by the steering torque sensor is less than a reference value (Tsc) (S400).

[0010] When the control unit determines that torque is input to the steering torque sensor from the steering wheel side (S140), it sets the reference value to a larger value (S150, S300, S360) compared to when it determines that torque is input to the steering torque sensor from the steering wheel side (S120).

[0011] During automatic steering in which a control torque is applied to the steering transmission system by a torque application device, or during torque input due to a road disturbance, i.e., when torque is input to the steering torque sensor from the steering wheel side, the steering torque may momentarily increase even if the driver has his / her hands off the steering wheel. Therefore, in order to prevent an erroneous determination that the driver has his / her hands off the steering wheel, it is necessary to set the reference value to a large value. However, when torque is input to the steering torque sensor from the steering wheel side, if the reference value is set to a large value, it is likely that the driver will be erroneously determined to have his / her hands off the steering wheel even if he / she is holding the steering wheel. Therefore, it is necessary to avoid setting the reference value to a large value.

[0012] According to the above configuration, when it is determined that torque is being input to the steering torque sensor from the steering wheel side, the reference value is set to a larger value compared to when it is determined that torque is being input to the steering torque sensor from the steering wheel side. Thus, it is possible to reduce the risk of erroneously determining that the driver is not in a hands-off state when torque is being input from the steering wheel side, and to reduce the risk of erroneously determining that the driver is in a hands-off state when torque is being input from the steering wheel side.

[0013] [Mode of the Invention] In one aspect of the present invention, the steering assist device (100) includes a steering angle detection device (steering angle sensor 36, rotary encoder 28A) configured to detect the steering angle by detecting the rotation angle of a member of the steering transmission system, and the control unit (steering assist ECU 50) is configured to determine (S140) whether or not torque is being input to the steering torque sensor from the steered wheel side, based on the relationship (FIG. 3) between the direction of change of the steering angle (θs, θp) detected by the steering angle detection device and the direction of the torque (Ts) detected by the steering torque sensor.

[0014] In another aspect of the present invention, the steering assist device (100) includes a first steering angle detection device (steering angle sensor 36) that detects the steering angle between the steering wheel and the steering torque sensor, and a second steering angle detection device (rotary encoder 28A) that detects the steering angle between the steered wheels and the steering torque sensor, and the control unit (steering assist ECU 50) is configured to determine (S290) whether torque is being input to the steering torque sensor from the steered wheels based on the relationship (FIG. 4) between the direction of change of the steering angle (θs) detected by the first steering angle detection device and the direction of change of the steering angle (θp) detected by the second steering angle detection device.

[0015] In another aspect of the present invention, the steering assist device (100) includes a steering angle detection device (steering angle sensor 36, rotary encoder 28A) configured to detect the steering angle by detecting the rotation angle of one of the members of the steering transmission system, with one rotation direction of the member being positive, and the steering torque sensor (38) is configured to detect torque with torque in one relative rotation direction being positive, and the control unit (steering assist ECU 50) is configured to determine (S350) whether torque is being input to the steering torque sensor from the steered wheel side, based on the sign of the product of the second-order differential value (θsdd, θpdd) of the steering angle detected by the steering angle detection device and the differential value (Tsd) of the torque detected by the steering torque sensor (FIG. 6).

[0016] In another aspect of the present invention, the torque applying device (EPS device 12) includes an electric motor (28) equipped with a rotary encoder (28A), and the steering angle detection device is configured to detect the steering angle using the output of the rotary encoder.

[0017] Other objects, other features and attendant advantages of the present invention will be readily apparent from the following description of the preferred embodiments of the present invention which will be given with reference to the accompanying drawings. [Brief explanation of the drawings]

[0018] [Figure 1] 1 is a schematic configuration diagram showing a steering assist device according to an embodiment. [Figure 2] 4 is a flowchart showing a hands-off determination control routine according to the first embodiment; [Figure 3] 1A is a diagram showing the relationship between the first steering angular velocity θsd and steering torque Ts and the steering input direction, and FIG. 1B is a diagram showing the relationship between the second steering angular velocity θpd and steering torque Ts and the steering input direction. [Figure 4] 10A and 10B are diagrams illustrating examples of changes in the first steering angular velocity θsd and the second steering angular velocity θpd when the steering input is from the upstream side (A) and when the steering input is from the downstream side (B). [Figure 5] 10 is a flowchart showing a main part of a hands-off determination control routine according to a second embodiment; [Figure 6] 1A and 1B are diagrams illustrating the relationship between the signs of the first steering angular acceleration θsdd and the second steering angular acceleration θpdd and the sign of the differential value Tsd of the steering torque Ts when the steering input is from the upstream side (A) and when the steering input is from the downstream side (B). [Figure 7] 10 is a flowchart showing a main part of a hands-off determination control routine according to a third embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0019] DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings.

[0020] 1, a steering assist device 100 according to an embodiment is applied to a vehicle 102 that includes a steering device 10, an electric power steering ECU 40, a steering assist ECU 50, a drive ECU 60, and a braking ECU 70. In this specification, the electric power steering will be referred to as EPS (short for Electric Power Steering) as necessary.

[0021] The EPS ECU 40, steering assist ECU 50, drive ECU 60, and braking ECU 70 are electronic control units that include microcomputers as their main components, and are connected to each other via a controller area network (CAN) 104 so that they can send and receive information. Each microcomputer includes a CPU, ROM, RAM, non-volatile memory, an interface, etc. The CPU performs various functions by executing instructions (programs, routines) stored in the ROM. These ECUs may be integrated into a single ECU.

[0022] 1, the steering device 10 includes an EPS device 12 connected to an EPS ECU 40. The EPS device 12 is configured as a rack-and-pinion EPS device that is driven in response to the driver's operation of a steering wheel 14. A rack bar 18 of the EPS device 12 is connected to knuckle arms (not shown) of front wheels 16FL and 16FR, which are steered wheels, via tie rods 20L and 20R. The steering wheel 14 is connected to a pinion shaft 26 of the EPS device 12 via a steering shaft 22 and a universal joint 24.

[0023] In the illustrated embodiment, the EPS device 12 is a rack-assist type electric power steering device, and includes an electric motor 28 and a conversion mechanism 30, such as a belt type, that converts the rotation and torque of the electric motor 28 into a displacement and force in a reciprocating direction and transmits the displacement and force to the rack bar 18. The EPS device 12 generates a control torque by driving the rack bar 18 relative to a housing 32.

[0024] Therefore, the steering shaft 22, universal joint 24, pinion shaft 26, EPS device 12, and tie rods 20L, 20R constitute a steering transmission system 34 that transmits steering displacement and torque between the steering wheel 14 and the front wheels 16FL, 16FR. The EPS device 12 functions as a torque applying device that applies a control torque to the steering transmission system 34.

[0025] A steering angle sensor 36 that detects the steering angle θs is provided on the steering shaft 22, and a steering torque sensor 38 that detects the steering torque Ts is provided on the pinion shaft 26. A rotary encoder 28A that detects the rotation angle θm of a rotor (not shown) is provided on the electric motor 28 of the EPS device 12.

[0026] The steering angle sensor 36 is provided in the steering transmission system 34 between the steering wheel 14 and the steering torque sensor 38, and functions as a first steering angle detection device that detects a first steering angle θs. The EPS·ECU 40 calculates the steering angle θp as the rotation angle of the pinion shaft 26 on the EPS device 12 side relative to the steering torque sensor 38, based on the rotation angle θm detected by the rotary encoder 28A. Therefore, the rotary encoder 28A and the EPS·ECU 40 are provided in the steering transmission system 34 between the front wheels 16FL and 16FR and the steering torque sensor 38, and function as a second steering angle detection device 37 that detects a second steering angle θp.

[0027] 1, the steering torque sensor 38 detects the steering torque Ts as a value proportional to the difference in rotation angle between the member on the steering wheel 14 side and the member on the EPS device 12 side with respect to the elastically torsionally deformable torsion bar, i.e., the relative rotation angle. The rotation angle of the member on the steering wheel 14 side with respect to the torsion bar is the same as the first steering angle θs, and the rotation angle of the member on the EPS device 12 side with respect to the torsion bar is the same as the second steering angle θp.

[0028] The steering displacement and torque generated when the driver operates the steering wheel 14, i.e., the steering input, are transmitted from the steering wheel to the front wheels 16FL and 16FR via the steering transmission system 34. Therefore, in terms of the direction of transmission of the steering displacement and torque, the first steering angle detection device (steering angle sensor 36) is located upstream of the steering torque sensor 38, and the second steering angle detection device 37 is located downstream of the steering torque sensor 38.

[0029] It is assumed that the first steering angle θs, the second steering angle θp, and the steering torque Ts become positive values ​​when the driver's steering operation causes the vehicle 102 to turn left. Therefore, the steering torque Ts becomes positive when the relative rotation of the member on the steering wheel 14 side and the member on the EPS device 12 side with respect to the torsion bar corresponds to the direction in which the vehicle is turning left. In addition, the EPS device 12 may be a pinion assist type or a column assist type EPS device as long as it applies a control torque to the steering transmission system 34 between the front wheels 16FL and 16FR and the steering torque sensor 38.

[0030] The EPS-ECU 40 controls the steering assist torque and reduces the driver's steering burden by controlling the EPS device 12 in a manner known in the art based on the steering torque Ts and vehicle speed V detected by a driving operation sensor 80 and a vehicle state sensor 90 (described later). The EPS-ECU 40 also controls the EPS device 12 to steer the front wheels 16FL and 16FR as needed. Thus, the EPS-ECU 40 and the EPS device 12 function as an automatic steering device that automatically steers the front wheels as needed.

[0031] A camera sensor 52 and a radar sensor 54 are connected to the steering assist ECU 50. The camera sensor 52 and the radar sensor 54 each include a plurality of camera devices and a plurality of radar devices. The camera sensor 52 and the radar sensor 54 function as target information acquisition devices that acquire information about targets at least ahead of the vehicle 102. Note that a LiDAR (Light Detection And Ranging) may be used instead of or in addition to the radar sensor 54.

[0032] Furthermore, a setting operator 56 is connected to the steering assist ECU 50, and the setting operator 56 is provided in a position where it can be operated by the driver. Although not shown in FIG. 1 , in the embodiment, the setting operator 56 includes an LTA switch, and the steering assist ECU 50 executes LTA when the LTA switch is on. Note that the LTA switch may be omitted. Note that LTA stands for lane tracing assist control.

[0033] A drive device 62 that applies drive force to drive wheels not shown in Fig. 1 to accelerate the vehicle 102 is connected to the drive ECU 60. Under normal circumstances, the drive ECU 60 controls the drive device so that the drive force generated by the drive device 62 changes in response to the driving operation by the driver, and when a command signal is received from the steering assist ECU 50, the drive ECU 60 controls the drive device 62 based on the command signal.

[0034] The braking ECU 70 is connected to a braking device 72 that applies braking force to wheels not shown in Fig. 1 to decelerate the vehicle 102. The braking ECU 70 normally controls the braking device so that the braking force generated by the braking device 72 changes in response to the braking operation by the driver, and when it receives a command signal from the steering assist ECU 50, it controls the braking device 72 based on the command signal to perform automatic braking.

[0035] The driving operation sensor 80 and the vehicle state sensor 90 are connected to the CAN 104. Information detected by the driving operation sensor 80 and the vehicle state sensor 90 (referred to as sensor information) is transmitted to the CAN 104. The driving operation sensor 80 includes a driving operation amount sensor and a braking operation amount sensor. The vehicle state sensor 90 includes a vehicle speed sensor, a longitudinal acceleration sensor, a lateral acceleration sensor, a yaw rate sensor, etc.

[0036] The steering assist ECU 50 is a central control device that performs steering assist control. In the embodiment, the steering assist ECU 50 executes the LTA in cooperation with other ECUs. Steering assist control such as the LTA is performed on the premise that the driver is gripping the steering wheel 14. Therefore, in the first to third embodiments described below, the steering assist ECU 50 executes hands-off determination control that determines whether the driver is not gripping the steering wheel 14 but has let go. When the steering assist ECU 50 determines that the driver has let go of the steering wheel 14 while the LTA is being executed, it gradually reduces the control amount of the LTA and terminates the LTA. Note that the control of the LTA is well known in the technical field and is not part of the gist of the present invention, so a description thereof will be omitted.

[0037] [First embodiment] The first steering angle θs and the steering torque Ts become positive values ​​when the vehicle 102 turns left due to the driver's steering operation, i.e., when the first steering angle θs changes to the left turning direction and torque in the left turning direction is input to the steering torque sensor 38 from the upstream side. On the other hand, the first steering angle θs and the steering torque Ts become negative values ​​when the first steering angle θs changes to the right turning direction and torque in the right turning direction is input to the steering torque sensor 38 from the upstream side. In other words, the rate of change of the first steering angle θs and the steering torque Ts have the same sign when steering displacement and torque are input to the steering torque sensor 38 from the upstream side.

[0038] In contrast, when torque is input to the steering torque sensor 38 from the downstream side, regardless of whether the first steering angle θs changes to the left or right turning direction, the members of the steering torque sensor 38 are twisted in the direction opposite to when torque is input to the steering torque sensor from the upstream side. Therefore, when the steering input is from the downstream side, the rate of change of the first steering angle θs and the steering torque Ts have mutually different signs.

[0039] In the first embodiment, the ROM of the steering assist ECU 50 stores the map shown in Fig. 3(A). In Fig. 3(A) and Fig. 3(B) described below, the area hatched downward to the left is an area where it is determined that the steering input is from the upstream side, and the area hatched downward to the right is an area where it is determined that the steering input is from the downstream side. The cross-hatched area is an area where it is not possible to determine whether the steering input is from the upstream side or the downstream side, taking into account the offset of the steering torque sensor 38, etc.

[0040] The CPU calculates the derivative of the first steering angle θs as the rate of change of the first steering angle θs, i.e., the first steering angular velocity θsd. The CPU determines whether the steering input is from the upstream side by referring to a map based on the first steering angular velocity θsd and the steering torque Ts. The sign of the first steering angular velocity θsd indicates the direction of change of the first steering angle θs, and the sign of the steering torque Ts indicates the direction of the steering torque. Furthermore, when the CPU determines that the steering input is from the upstream side, it sets the reference value Tsc for determining whether the driver has let go to a standard value Tscs (a positive constant). On the other hand, when the CPU determines that the steering input is from the downstream side, it sets the reference value Tsc to an increased value Tsch that is greater than the standard value Tscs.

[0041] In the first embodiment, the ROM of the steering assist ECU 50 stores a program for hands-off determination control corresponding to the flowchart shown in Fig. 2. The CPU executes hands-off determination control in accordance with this program.

[0042] <Hands-Off Determination Control Routine of the First Embodiment> The hands-off determination control according to the flowchart shown in Fig. 2 is repeatedly executed at predetermined time intervals by the CPU of the steering assist ECU 50 when an LTA switch (not shown in Fig. 1) of the setting operation device 58 is on and LTA is being executed. This also applies to the hands-off determination control of other embodiments described later. At the start of the hands-off determination control, the reference value Tsc for determining whether the driver has let go of the steering wheel is set to a standard value Tscs.

[0043] First, in step S110, the CPU calculates a first steering angular velocity θsd by calculating a differential value of the first steering angle θs.

[0044] In step S120, the CPU determines whether the steering input is from the upstream side by referring to the map shown in Fig. 3(A) based on the first steering angular velocity θsd and the steering torque Ts. If the CPU makes a positive determination, it sets the reference value Tsc for determining whether the driver has let go of the hands to the standard value Tscs in step S130. If the CPU makes a negative determination, it proceeds to step S140.

[0045] In step S140, the CPU determines whether the steering input is from the downstream side by referring to the map shown in Figure 3(A) based on the first steering angular velocity θsd and the steering torque Ts. If the CPU makes a negative determination, it maintains the reference value Tsc at its current value and temporarily terminates this control, but if the CPU makes a positive determination, it proceeds to step S150.

[0046] 2 based on the absolute value of the first steering angular velocity θsd. As shown in the figure, the reference value Tsc is set to a standard value Tscs when the absolute value of the first steering angular velocity θsd is less than Tsc1 (a positive constant), and is set to an increased value Tsch when the absolute value of the first steering angular velocity θsd is greater than Tsc2 (a positive constant greater than Tsc1). Furthermore, when the absolute value of the first steering angular velocity θsd is equal to or greater than Tsc1 and equal to or less than Tsc2, the reference value Tsc is set to increase as the absolute value of the first steering angular velocity θsd increases within the range of equal to or greater than the standard value Tscs and equal to or less than the increased value Tsch.

[0047] In step S400, the CPU determines whether the driver has released the steering wheel by determining whether the steering torque Ts has been determined to be less than the reference value Tsc a reference number of times (a certain positive integer). If the CPU makes a negative determination, it determines in step S410 that the driver is gripping the steering wheel and continues LTA control without interruption. In contrast, if the CPU makes a positive determination, it determines in step S420 that the driver has released the steering wheel and interrupts LTA control.

[0048] [First Modification] When torque acts on the steering torque sensor 38, the second steering angle θp changes in the opposite direction to the first steering angle θs. Therefore, the rate of change of the second steering angle θp and the steering torque Ts have different signs when the steering displacement and torque are input to the steering torque sensor 38 from the upstream side. On the other hand, the rate of change of the second steering angle θp and the steering torque Ts have the same sign when the steering input is from the downstream side.

[0049] In the first modified example, the ROM of the steering assist ECU 50 stores the map shown in FIG. 3(B). Although not shown in the figure, in step S110, the CPU calculates a derivative value of the second steering angle θp as a second steering angular velocity θpd. In addition, in step S120, the CPU determines whether the steering input is from the upstream side by referring to the map shown in FIG. 3(B) based on the second steering angular velocity θpd and the steering torque Ts. Furthermore, in step S140, the CPU determines whether the steering input is from the downstream side by referring to the map shown in FIG. 3(B) based on the second steering angular velocity θpd and the steering torque Ts.

[0050] According to the first embodiment and the first modified example, whether the steering input is from the downstream side is determined based on the relationship between the signs of the first steering angular velocity θsd and the steering torque Ts and the relationship between the signs of the second steering angular velocity θpd and the steering torque Ts. Therefore, whether the steering input is from the downstream side can be determined based on the first steering angular velocity θsd, the second steering angular velocity θpd, and the steering torque Ts.

[0051] [Second embodiment] Fig. 4(A) shows an example of changes in the first steering angular velocity θsd and the second steering angular velocity θpd when the driver performs a steering operation and the steering input is from the upstream side, and Fig. 4(B) shows an example of changes in the first steering angular velocity θsd and the second steering angular velocity θpd when the steering input is from the downstream side.

[0052] When the steering input is from the upstream side, the steering displacement is transmitted from the upstream side to the downstream side, so the first steering angle θs changes faster than the second steering angle θp. As shown in Fig. 4(A), near the start of the steering input (the origin) and near points P1 and P2 where the magnitude of the steering angular velocity changes from increasing to decreasing, the first steering angular velocity θsd and the second steering angular velocity θpd are 0 or very small values. However, near the origin and after passing near points P1 and P2, the first steering angular velocity θsd changes rapidly, but the change in the second steering angular velocity θpd is small.

[0053] In contrast, when the steering input is from the downstream side, the steering displacement is transmitted from the downstream side to the upstream side, so the second steering angle θp changes faster than the first steering angle θs. As shown in Fig. 4(B) , in the vicinity of the origin and points Q1 and Q2, the first steering angular velocity θsd and the second steering angular velocity θpd are 0 or very small values. However, after passing the vicinity of the origin and points P1 and P2, the second steering angular velocity θpd changes rapidly, but the change in the first steering angular velocity θsd is small.

[0054] In the second embodiment, the CPU calculates the second-order differential of the first steering angle θs as the first steering angular acceleration θsdd, and calculates the second-order differential of the second steering angle θp as the second steering angular acceleration θpdd. The sign of the first steering angular acceleration θsdd represents the direction of change of the first steering angular velocity θsd, and the sign of the second steering angular acceleration θpdd represents the direction of change of the second steering angular velocity θpd. The CPU determines whether the steering input is from the upstream side based on the magnitudes of the first steering angular acceleration θsdd and the second steering angular acceleration θpdd after passing near the origin and near points P1 and P2.

[0055] In the second embodiment, the ROM of the steering assist ECU 50 stores a program for hands-off determination control corresponding to the flowchart shown in Fig. 5. The CPU executes the hands-off determination control in accordance with this program. At the start of the hands-off determination control, the flag Fd is initialized to 0. At the start of the hands-off determination control, the reference value Tsc for determining whether the driver has let go of the steering wheel is set to the standard value Tscs. <Hands-Off Determination Control Routine of the Second Embodiment>

[0056] First, in step S210, the CPU calculates the first steering angular acceleration θsdd by calculating the second derivative of the first steering angle θs, and calculates the second steering angular acceleration θpdd by calculating the second derivative of the second steering angle θp.

[0057] In step S220, the CPU determines whether flag Fd is 1, i.e., whether the situation allows determination of the steering input direction in steps S270 and S290, which will be described later. If the CPU makes a positive determination, it proceeds to step S250, and if the CPU makes a negative determination, it proceeds to step S230.

[0058] In step S230, the CPU determines whether the absolute value of the first steering angular acceleration θsdd is less than a first reference value θsdd1 (positive constant) and whether the absolute value of the second steering angular acceleration θpdd is less than a first reference value θpdd1 (positive constant). If the CPU makes a positive determination, it sets flag Fd to 1 in step S240, and if the CPU makes a negative determination, it temporarily terminates this control.

[0059] In step S250, the CPU determines whether the absolute value of the first steering angular acceleration θsdd is greater than the second reference value θsdd2 and whether the absolute value of the second steering angular acceleration θpdd is greater than the second reference value θpdd2. The second reference values ​​θsdd2 and θpdd2 are positive constants greater than the first reference values ​​θsdd1 and θpdd1, respectively. If the CPU makes a positive determination, it resets flag Fd to 0 in step S260. If the CPU makes a negative determination, it proceeds to step S270.

[0060] In step S270, the CPU determines whether the absolute value of the first steering angular acceleration θsdd is equal to or greater than a third reference value θsdd3 (a positive constant greater than θsdd1) and whether the absolute value of the second steering angular acceleration θpdd is less than a third reference value θpdd3 (a positive constant). If the CPU makes a negative determination, it proceeds to step S290, and if the CPU makes a positive determination, it proceeds to step S280.

[0061] In step S280, the CPU determines that the steering input is from the upstream side, and sets the reference value Tsc for determining whether the driver has let go to the standard value Tscs.

[0062] In step S290, the CPU determines whether the absolute value of the first steering angular acceleration θsdd is less than a fourth reference value θsdd4 (a positive constant) and whether the absolute value of the second steering angular acceleration θpdd is equal to or greater than a fourth reference value θpdd4 (a positive constant greater than θpdd1). If the CPU makes a negative determination, it maintains the reference value Tsc at its current value and temporarily terminates this control, but if the CPU makes a positive determination, it proceeds to step S300.

[0063] In step S300, the CPU determines that the steering input is from the downstream side and sets the reference value Tsc to the increased value Tsch. After completing step S280 or S300, the CPU advances this control to step S400.

[0064] According to the second embodiment, it is determined whether the steering input is from the downstream side based on the magnitude of the absolute value of the first steering angular acceleration θsdd and the magnitude of the absolute value of the second steering angular acceleration θpdd. Therefore, it is possible to determine whether the steering input is from the downstream side based on the first steering angular acceleration θsdd and the second steering angular acceleration θpdd without requiring the steering torque Ts.

[0065] [Third embodiment] 6A shows the relationship between the signs of the first steering angular acceleration θsdd and the second steering angular acceleration θpdd and the sign of the derivative value Tsd of the steering torque Ts when the driver performs a steering operation and the steering input is from the upstream side. FIG. 6B shows the relationship between the signs of the first steering angular acceleration θsdd and the second steering angular acceleration θpdd and the sign of the derivative value Tsd of the steering torque Ts when the steering input is from the downstream side.

[0066] In the hatched area sloping downward to the left in Fig. 6(A), the first steering angular velocity θsd increases and the steering torque Ts also increases, so the first steering accelerating velocity θsdd and the derivative value Tsd of the steering torque are positive. In the hatched area sloping downward to the right in Fig. 6(A), the second steering angular velocity θpd decreases and the steering torque Ts also decreases, so the second steering accelerating velocity θpdd and the derivative value Tsd of the steering torque are negative.

[0067] Therefore, the signs of the first steering accelerating velocity θsdd and the steering torque derivative Tsd, which indicate the direction of change of the first steering angular velocity θsd and the steering torque Ts, respectively, are the same. Also, the signs of the second steering accelerating velocity θpdd and the steering torque derivative Tsd, which indicate the direction of change of the second steering angular velocity θpd, are also the same. Therefore, the product of the first steering accelerating velocity θsdd and the steering torque derivative Tsd and the product of the second steering accelerating velocity θpdd and the steering torque derivative Tsd are positive.

[0068] In contrast, in the region hatched downward to the left in FIG. 6(B), the first steering angular velocity θsd decreases, and therefore the first steering accelerating velocity θsdd is negative. However, because the members of the torque sensor 38 are twisted in the same direction as in the region hatched downward to the left in FIG. 6(A), the steering torque Ts increases, and the steering torque derivative Tsd is positive. Also, in the region hatched downward to the right in FIG. 6(B), the second steering angular velocity θpd increases, and therefore the second steering accelerating velocity θpdd is positive. However, because the members of the torque sensor 38 are twisted in the same direction as in the region hatched downward to the right in FIG. 6(A), the steering torque Ts decreases, and the steering torque derivative Tsd is negative.

[0069] Therefore, the first steering accelerating velocity θsdd and the steering torque derivative value Tsd have different signs, and the second steering accelerating velocity θpdd and the steering torque derivative value Tsd also have different signs. Therefore, the product of the first steering accelerating velocity θsdd and the steering torque derivative value Tsd and the product of the second steering accelerating velocity θpdd and the steering torque derivative value Tsd are negative.

[0070] In the third embodiment, the CPU calculates the second steering angular acceleration θpdd and also calculates the derivative value Tsd of the steering torque Ts. Furthermore, the CPU determines whether the steering input is from the upstream side based on the sign of the product of the second steering angular acceleration θpdd and the derivative value Tsd of the steering torque.

[0071] In the third embodiment, the ROM of the steering assist ECU 50 stores a program for hands-off determination control corresponding to the flowchart shown in Fig. 7. The CPU executes the hands-off determination control in accordance with this program. At the start of the hands-off determination control, the reference value Tsc for determining whether the driver has let go of the steering wheel is set to the standard value Tscs.

[0072] <Hands-Off Determination Control Routine of the Third Embodiment> First, in step S310, the CPU calculates the second derivative of the second steering angle θp to calculate the second steering angular acceleration θpdd, and in step S320, the CPU calculates the derivative Tsd of the steering torque Ts.

[0073] In step S330, the CPU determines whether the product of the first steering angular acceleration θsdd and the steering torque derivative Tsd is equal to or greater than a reference value α (a positive constant close to 0). If the CPU makes a negative determination, the control proceeds to step S350, and if the CPU makes a positive determination, the control proceeds to step S340.

[0074] In step S340, the CPU determines that the steering input is from the upstream side, and sets the reference value Tsc for determining whether the driver has let go to the standard value Tscs.

[0075] In step S350, the CPU determines whether the product of the second steering angular acceleration θpdd and the steering torque derivative Tsd is equal to or less than a reference value −α. If the CPU determines negative, it maintains the reference value Tsc at its current value and temporarily terminates this control. If the CPU determines positive, it proceeds to step S360.

[0076] In step S360, the CPU determines that the steering input is from the downstream side and sets the reference value Tsc to the increased value Tsch. After completing step S340 or S360, the CPU advances this control to step S400.

[0077] [Second Variation] In step S330, it is determined whether the product of the second steering angular acceleration θpd and the steering torque derivative Tsd is a positive value, and in step S350, it is determined whether the product of the second steering angular acceleration θpdd and the steering torque derivative Tsd is a negative value, i.e., α in the third embodiment is set to 0.

[0078] [Third Variation] Step S350 in the third embodiment is omitted, and if a negative determination is made in step S330, step S360 is executed.

[0079] [Fourth Variation] In the second modified example, step S350 is omitted, and if a negative determination is made in step S330, step S360 is executed.

[0080] According to the third embodiment and the second to fourth modifications, it is possible to determine whether the steering input is from the downstream side based on the second steering angular acceleration θpd and the steering torque derivative Tsd. Therefore, the first steering angle θs is not necessary, and the steering angle sensor 36 can be omitted.

[0081] As can be seen from the above description, according to each embodiment and each modified example, when it is determined that the steering input is from the downstream side, the reference value Tsc for determining whether the driver has let go of the hands is set to an increased value Tsch that is greater than the standard value Tscs. This reduces the risk of erroneously determining that the driver has let go of the hands when the steering input is from the downstream side, while reducing the risk of erroneously determining that the driver has let go of the hands when the steering input is from the upstream side.

[0082] In particular, according to the embodiment, the EPS device 12 serving as a torque applying device includes an electric motor 28 equipped with a rotary encoder 28A, and the second steering angle θp is detected using the output of the rotary encoder. Therefore, in steering assist control such as LTA, the rotary encoder used to control the steering angle of the front wheels 16FL and 16FR can be effectively used to detect the second steering angle θp. Therefore, for example, a steering angle sensor downstream of the steering torque sensor 38 that detects the rotation angle of the pinion shaft 26, i.e., the second steering angle θp, is not required.

[0083] Although the present invention has been described in detail above with reference to specific embodiments and modifications, it will be apparent to those skilled in the art that the present invention is not limited to the above-described embodiments and modifications, and that various other embodiments are possible within the scope of the present invention.

[0084] For example, in each of the above-described embodiments and variant examples, the steering assist control is LTA, but it may be any steering assist control that controls the lateral position of the vehicle relative to the lane by automatic steering, such as lane departure prevention control or lane change assist control.

[0085] In the first embodiment and the first modified example, in step S150, the reference value Tsc is calculated by referring to the map shown in step S140 of Fig. 2 based on the absolute value of the first steering angular velocity θsd. However, in step S150, the reference value Tsc may be set to the increased value Tsch regardless of the magnitude of the absolute value of the first steering angular velocity θsd.

[0086] Furthermore, the second steering angular acceleration θpd in the third embodiment and the second to fourth modified examples may be replaced with the first steering angular acceleration θsdd. [Explanation of symbols]

[0087] 10...Steering device, 12...EPS device, 14...Steering handle, 16FL, 16FR...Front wheels, 40...EPS ECU, 50...Steering assist ECU, 52...Camera sensor, 54...Radar sensor, 60...Drive ECU, 70...Braking ECU, 100...Steering assist device, 102...Vehicle

Claims

1. A steering assist device including: a torque applying device configured to apply a control torque to a steering transmission system between a steering wheel and steering wheels; a steering torque sensor provided in the steering transmission system between the steering wheel and the torque applying device; and a control unit configured to determine that a driver is not gripping the steering wheel when the torque detected by the steering torque sensor is less than a reference value, A steering assist device configured such that when the control unit determines that torque is being input to the steering torque sensor from the steering wheel side, the control unit sets the reference value to a larger value compared to when the control unit determines that torque is being input to the steering torque sensor from the steering handle side.

2. 2. The steering assist device according to claim 1, further comprising a steering angle detection device configured to detect the steering angle by detecting a rotation angle of a member of the steering transmission system, and the control unit configured to determine whether torque is being input to the steering torque sensor from the steered wheel side based on the relationship between the direction of change in the steering angle detected by the steering angle detection device and the direction of torque detected by the steering torque sensor.

3. 2. A steering assist device according to claim 1, comprising: a first steering angle detection device that detects a steering angle between the steering wheel and the steering torque sensor; and a second steering angle detection device that detects a steering angle between the steered wheel and the steering torque sensor, wherein the control unit is configured to determine whether torque is being input to the steering torque sensor from the steered wheel side based on the relationship between the direction of change of the steering angle detected by the first steering angle detection device and the direction of change of the steering angle detected by the second steering angle detection device.

4. 2. A steering assist device according to claim 1, wherein the steering assist device includes a steering angle detection device configured to detect the steering angle by detecting the rotation angle of one of the members of the steering transmission system, with one rotation direction of the member being positive, the steering torque sensor configured to detect torque with torque in one relative rotation direction being positive, and the control unit configured to determine whether torque is input to the steering torque sensor from the steered wheel side based on the sign of the product of a second-order differential value of the steering angle detected by the steering angle detection device and a differential value of the torque detected by the steering torque sensor.

5. 5. The steering assist device according to claim 4, wherein the torque applying device includes an electric motor equipped with a rotary encoder, and the steering angle detecting device is configured to detect the steering angle using an output of the rotary encoder.

Images