Vehicle Hands-Off State Detection Device

Abstract

To provide an un-gripping state determination device improved so as to reduce the possibility of erroneous determination of whether a driver is in an un-gripping state of not, even when an output error of a steering torque sensor occurs due to a factor such as an assembly error of a steering device.SOLUTION: An un-gripping state determination device includes: a torque application device configured to apply control torque to a steering transmission system between a steering wheel and a steered wheel; a steering torque sensor provided in the steering transmission system between the steering wheel and the torque application device; and a control unit configured to determine an un-gripping state in which a driver is not gripping the steering wheel, when steering torque Ts detected by the steering torque sensor is in a first predetermined range (equal to or more than a lower limit value Tr-α and equal to and less than an upper limit value Tr+α); wherein the control unit variably sets the first predetermined range, based on the steering torque detected by the steering torque sensor in a situation where it is determined that the torque is not input to the steering torque sensor.SELECTED DRAWING: Figure 2

Description

Technical Field

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[0005]

[0001] The present invention relates to a released state determination device for vehicles such as automobiles.

Background Art

[0002] As an automatic driving device for vehicles such as automobiles, steering assistance devices such as a lane keeping support device, a lane departure suppression device, and a lane change support device that control the lateral position of the vehicle with respect to the lane by automatic steering are well known.

[0003] Steering assistance by the steering assistance device may be performed on the premise that the driver is holding the steering wheel. When the driver is not holding the steering wheel, since the situation where the magnitude of the steering torque is small continues, it is known to determine whether the driver is in a released state without holding the steering wheel based on the steering torque detected by the steering torque sensor.

[0004] For example, in Patent Document 1 below, when it is continuously determined a predetermined number of times that the magnitude of the steering torque detected by the steering torque sensor is less than the reference value, a released state determination technique for determining that the driver has released the steering wheel is described. According to this released state determination technique, it is possible to detect the released state of the driver without requiring an expensive sensor such as a touch sensor.

Prior Art Documents

Patent Documents

[0005]

Patent Document 1

Summary of the Invention

[0006] 〔Problems to be Solved by the Invention〕 When the vehicle is traveling in a straight line and neither automatic steering nor driver steering is being performed, no torque acts on the steering torque sensor, so the steering torque detected by the steering torque sensor is 0.

[0007] However, if there are errors in the assembly of the steering system or steering torque sensor, an output error may occur in which the steering torque detected by the steering torque sensor is a value other than zero, even when the vehicle is driving straight and neither automatic steering nor driver steering is being performed. In addition, misalignment of the steering wheel alignment or the left-right weight balance of the vehicle can also cause output errors in the steering torque sensor.

[0008] If the steering torque sensor output error occurs due to the factors described above, the magnitude of the steering torque detected by the steering torque sensor may exceed the standard value due to the output error, which can lead to a misjudgment that the driver is not hands-free even when they are.

[0009] The present invention provides an improved hands-free state determination device that can reduce the risk of misjudging whether or not the driver is hands-free, even if an output error occurs in the steering torque sensor due to factors such as assembly errors in the steering system.

[0010] [Means for solving the problem and the effects of the invention] According to the present invention, a vehicle hands-free state determination device (100) is provided, which includes a torque application device (EPS device 12) configured to apply control torque to a steering transmission system (34) between a steering wheel (14) and steering wheels (front wheels 16FL, 16FR), a steering torque sensor (38) provided in the steering transmission system between the steering wheel and the torque application device, and a control unit (steering support ECU 50) configured to determine (S110) that the driver is in a hands-free state, not gripping the steering wheel, when the steering torque (Ts) detected by the steering torque sensor is within a first predetermined range (lower limit Tr-α or more and upper limit Tr+α or less).

[0011] The control unit is configured to perform a first predetermined variable setting (S50, S80) based on the steering torque (Ts) detected by the steering torque sensor (38) when it is determined that no torque is being input to the steering torque sensor (38) (S10 to S40, or S10, S25, S35 and S40).

[0012] According to the above configuration, a first predetermined range is variably set based on the steering torque detected by the steering torque sensor in situations where it is determined that no torque is being input to the steering torque sensor. The steering torque detected by the steering torque sensor in situations where it is determined that no torque is being input to the steering torque sensor is the output error of the steering torque sensor due to factors such as assembly errors in the steering system. Therefore, the first predetermined range can be variably set based on the output error of the steering torque sensor. Consequently, compared to the case where the first predetermined range is not variably set, the risk of misjudgment due to output errors in the steering torque sensor caused by factors such as assembly errors in the steering system can be reduced.

[0013] [Aspects of the Invention] In one embodiment of the present invention, the first predetermined range is a range of reference torque - predetermined value or greater and reference torque + predetermined value or less (Tr - α or greater and Tr + α or less), and the control unit (steering support ECU 50) is configured to make a variable setting of the first predetermined range (S50, S80) by setting the steering torque (Ts) detected by the steering torque sensor as the reference torque (Tr) when it is determined that no torque has been input to the steering torque sensor (38) (S10 to S40, or S10, S25, S35 and S40).

[0014] According to the above embodiment, the first predetermined range is the range between the reference torque minus a predetermined value and the reference torque plus a predetermined value, and the steering torque detected by the steering torque sensor in a situation where it is determined that no torque is being input to the steering torque sensor is set as the reference torque. Therefore, the first predetermined range can be set variably by variably setting the reference torque based on the steering torque detected by the steering torque sensor in a situation where it is determined that no torque is being input to the steering torque sensor.

[0015] In another embodiment of the present invention, the control unit (steering assist ECU 50) is configured to determine (S50) that when it determines that the vehicle (102) is traveling in a straight line, the vehicle is traveling in the center of the lane, and the road surface is not laterally inclined, torque is not being input to the steering torque sensor (38) from the side of the steering wheels (front wheels 16FL, 16FR).

[0016] When it is determined that the vehicle is traveling in a straight line, is in the center of the lane, and the road surface is not tilted laterally, no torque is applied to the steering torque sensor from the steering wheels. Therefore, according to the above embodiment, it is possible to determine a situation in which no torque is being input to the steering torque sensor from the steering wheels.

[0017] In another embodiment of the present invention, the control unit (steering assist ECU 50) is configured to determine (S50) that when it determines that the vehicle (102) is in a straight-ahead state, the magnitude of the lateral force acting on the vehicle is less than or equal to a reference value for lateral force determination, and the magnitude of the control torque is less than or equal to a reference value for control torque determination (S10 to S40, or S10, S25 and S35), that no torque is being input to the steering torque sensor (38) from the steering wheel (front wheels 16FL, 16FR).

[0018] When the vehicle is moving straight, the magnitude of the lateral force acting on the vehicle is less than or equal to the reference value for lateral force determination, and the magnitude of the control torque is less than or equal to the reference value for control torque determination, no torque is applied to the steering torque sensor from the steering wheel side. Therefore, according to the above embodiment, it is possible to determine a situation in which no torque is being input to the steering torque sensor from the steering wheel side.

[0019] In another embodiment of the present invention, the control unit (steering assist ECU 50) is configured to determine that no torque is being input to the steering torque sensor from the steering wheel (14) when, in a situation where no torque is being input to the steering torque sensor from the steering wheel side, the steering torque (Ts) detected by the steering torque sensor (38) is within a second predetermined range (lower limit Tr-β or greater and upper limit Tr+β or less) which is greater than a first predetermined range.

[0020] When no torque is being input to the steering torque sensor from the steering wheel side, and the driver is not performing any steering operations and is lightly holding the steering wheel, the magnitude of the steering torque detected by the steering torque sensor will not be a large value. According to the above embodiment, when the steering torque detected by the steering torque sensor is within a second predetermined range which is greater than a first predetermined range, it is determined that no torque is being input to the steering torque sensor from the steering wheel side. Therefore, it is possible to determine a situation where the driver is not performing any steering operations, is lightly holding the steering wheel, and no torque is being input to the steering torque sensor from the steering wheel side.

[0021] Other objects, features, and associated advantages of the present invention will be readily apparent from the description of embodiments of the present invention, which will be described with reference to the following drawings. [Brief explanation of the drawing]

[0022] [Figure 1] This is a schematic diagram showing a hands-free state determination device according to an embodiment. [Figure 2] This is a flowchart showing the hands-free state determination control routine of the first embodiment. [Figure 3] It is a flowchart showing the release state determination control routine of the second embodiment. [Figure 4] It is a flowchart showing the release state determination control routine of the third embodiment. [Figure 5] It is a flowchart showing the release state determination control routine of the fourth embodiment. [Figure 6] It is a diagram showing an example of release state determination for a conventional case (A) where the reference value Tr is not variably set and a case (B) where the reference value Tr is variably set according to the present invention.

Mode for Carrying Out the Invention

[0023] Hereinafter, embodiments of the present invention will be described in detail with reference to the attached drawings.

[0024] As shown in FIG. 1, the release state determination device 100 according to the embodiment includes a steering device 10, an electric power steering ECU 40, and a steering assist ECU 50, and is applied to a vehicle 102 capable of automatic driving equipped with a drive ECU 60 and a brake ECU 70. In this specification, electric power steering is called EPS (abbreviation for Electric Power Steering) as necessary.

[0025] The EPS·ECU 40, the steering assist ECU 50, the drive ECU 60, and the brake ECU 70 are electronic control units (Electronic Control Unit) having a microcomputer as a main part, and are connected to be able to transmit and receive information to and from each other via a CAN (Controller Area Network) 104. Each microcomputer includes a CPU, a ROM, a RAM, a non-volatile memory, an interface, and the like. The CPU realizes various functions by executing instructions (programs, routines) stored in the ROM. These ECUs may be integrated into one ECU.

[0026] As shown in Figure 1, the steering system 10 includes an EPS device 12 connected to the EPS ECU 40, which is configured as a rack-and-pinion type EPS device driven in response to the driver's operation of the steering wheel 14. The rack bar 18 of the EPS device 12 is connected via tie rods 20L and 20R to the knuckle arms (not shown) of the steering wheels, the front wheels 16FL and 16FR. The steering wheel 14 is connected to the pinion shaft 26 of the EPS device 12 via a steering shaft 22 and a universal joint 24.

[0027] 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, for example a belt type, which converts the rotation and torque of the electric motor 28 into reciprocating displacement and force and transmits it to the rack bar 18. The EPS device 12 generates control torque by driving the rack bar 18 relative to the housing 32.

[0028] Therefore, the steering shaft 22, universal joint 24, pinion shaft 26, EPS device 12, and tie rods 20L and 20R constitute a steering transmission system 34 that transmits steering displacement and torque between the steering wheel 14 and the front wheels 16FL and 16FR. The EPS device 12 works in cooperation with the EPS ECU 40 to function as a torque application device that applies a control torque Tc to the steering transmission system 34.

[0029] The steering shaft 22 is equipped with a steering angle sensor 36 for detecting the steering angle θs, and the pinion shaft 26 is equipped with a steering torque sensor 38 for detecting the steering torque Ts. Although not shown in detail in Figure 1, the steering torque sensor 38 detects the steering torque Ts as a value proportional to the difference in rotation angles between the member on the steering wheel 14 side and the member on the EPS device 12 side with respect to an elastically torsion deformable torsion bar, i.e., the relative rotation angle. The steering torque sensor 38 may also be provided on the steering shaft 22.

[0030] Furthermore, the steering angle θs and steering torque Ts are assumed to be positive when the vehicle 102 turns left due to the driver's steering operation. The EPS device 12 may be a pinion-assist type or column-assist type EPS device, as long as it applies control torque to the steering transmission system 34 between the front wheels 16FL and 16FR and the steering torque sensor 38.

[0031] 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 the driving operation sensor 80 and vehicle condition sensor 90 described later. Furthermore, the EPS / ECU 40 can steer the front wheels 16FL and 16FR as needed by controlling the EPS device 12. Thus, the EPS / ECU 40 and the EPS device 12 function as an automatic steering system that automatically steers the front wheels as needed.

[0032] The steering assist ECU 50 is connected to a camera sensor 52 and a radar sensor 54. The camera sensor 52 and radar sensor 54 each include multiple camera devices and multiple radar devices, respectively. The camera sensor 52 and radar sensor 54 function as target information acquisition devices that acquire information on targets at least in front of the vehicle 102. LiDAR (Light Detection And Ranging) may be used instead of or in addition to the radar sensor 54.

[0033] Furthermore, a setting control 56 and a warning device 58 are connected to the steering assist ECU 50, and the setting control 56 is positioned to be operated by the driver. Although not shown in Figure 1, in this embodiment, the setting control 56 includes an LTA switch, and the steering assist ECU 50 performs LTA when the LTA switch is ON. Note that the LTA switch may be omitted. LTA stands for Lane Tracing Assist Control.

[0034] The warning device 58 is activated when it is determined that the driver is not holding the steering wheel 14 and is in a hands-free state, and issues a warning, that is, a warning that the driver is in a hands-free state. The warning device 58 may be any of the following: a visual warning device such as a display or warning lamp, an auditory warning device such as a warning buzzer, or a tactile warning device such as seat vibration, or any combination thereof.

[0035] The drive ECU 60 is connected to a drive unit 62, which accelerates the vehicle 102 by applying driving force to the drive wheels, which are not shown in Figure 1. Under normal circumstances, the drive ECU 60 controls the drive unit 62 so that the driving force generated by the drive unit 62 changes in accordance with the driver's driving operation, and when it receives a command signal from the steering support ECU 50, it controls the drive unit 62 based on the command signal.

[0036] The braking ECU 70 is connected to a braking device 72 that decelerates the vehicle 102 by applying braking force to the wheels, which are not shown in Figure 1. Under normal circumstances, the braking ECU 70 controls the braking device 72 so that the braking force generated by the braking device 72 changes in accordance with the driver's braking operation. When it receives a command signal from the steering support ECU 50, it performs automatic braking by controlling the braking device 72 based on the command signal.

[0037] The driving operation sensor 80 and the vehicle condition sensor 90 are connected to CAN 104. Information detected by the driving operation sensor 80 and the vehicle condition sensor 90 (referred to as sensor information) is transmitted to CAN 104. The driving operation sensor 80 includes a drive operation amount sensor and a brake operation amount sensor. The vehicle condition sensor 90 includes a vehicle speed sensor, a longitudinal acceleration sensor, a lateral acceleration sensor, and a yaw rate sensor, etc.

[0038] The steering support ECU 50 is a central control device that performs steering support control. In the embodiment, the steering support ECU 50 works in cooperation with other ECUs to perform LTA. Steering support control such as LTA is performed on the premise that the driver is holding the steering wheel 14. Therefore, in the first to fourth embodiments described below, the steering support ECU 50 performs hands-free state determination control to determine whether the driver has released the steering wheel 14. When the steering support ECU 50 determines that the hands-free state has occurred during the execution of LTA, it activates the alarm device 58 to issue an alarm and gradually reduces the LTA control amount to terminate LTA. Note that the control of LTA is well known in the art and does not constitute the essence of the present invention, so its explanation is omitted.

[0039] [First Embodiment] In the first embodiment, the ROM of the steering assist ECU 50 stores a program for hands-free state determination control corresponding to the flowchart shown in Figure 2. The hands-free state determination control according to the flowchart shown in Figure 2 is repeatedly executed at predetermined intervals by the CPU of the steering assist ECU 50 when the LTA switch of the setting control unit 56 (not shown in Figure 1) is on and LTA is being executed. This is also the case for the hands-free state determination control in other embodiments described later. Furthermore, at the start of the hands-free state determination control, the confidence level R, described later, is initialized to 0.

[0040] In step S10, the CPU determines whether the vehicle 102 is traveling in a straight line. If the CPU determines it is not, it proceeds to step S90; if it determines it is, it proceeds to step S20. In this case, the curvature of the lane is estimated based on the image of the front of the vehicle 102 captured by the camera sensor 52, and the inclination angle of the vehicle 102 in the direction of travel relative to the lane may be estimated. Furthermore, for example, if the absolute value of the curvature of the lane is less than or equal to the reference value (positive constant) for curvature determination and the absolute value of the inclination angle in the direction of travel is less than or equal to the reference value (positive constant) for inclination angle determination, it may be determined that the vehicle 102 is traveling in a straight line. Note that the determination of the inclination angle in the direction of travel may be omitted.

[0041] In step S20, the CPU determines whether or not the vehicle 102 is traveling in the center of the lane. If the CPU determines that the vehicle 102 is not traveling in the center of the lane, it proceeds to step S90; if it determines that the vehicle 102 is not traveling in the center of the lane, it proceeds to step S30. In this case, for example, the magnitude of the lateral displacement of the center of the vehicle 102 in the vehicle width direction relative to the center of the lane in the width direction may be estimated. Furthermore, if the magnitude of the lateral displacement is less than or equal to a reference value (positive constant) for displacement determination, it may be determined that the vehicle 102 is traveling in the center of the lane if this condition persists for a first reference time (positive constant) or longer.

[0042] In step S30, the CPU determines whether or not there is a lateral incline on the road surface. If the CPU determines that there is a lateral incline on the road surface, it proceeds to step S90; if it determines that there is a lateral incline on the road surface, it proceeds to step S40. In this case, it may be determined that there is no lateral incline on the road surface if the absolute value of the lateral acceleration Gy of the vehicle 102 detected by the lateral acceleration sensor of the vehicle state sensor 90 is less than or equal to the reference value (positive constant) for lateral acceleration, and the absolute value of the yaw rate Yr of the vehicle 102 detected by the yaw rate sensor is less than or equal to the reference value (positive constant) for yaw rate.

[0043] In step S40, the CPU determines whether the driver is lightly holding the steering wheel 14 without performing any steering operations. If the CPU determines that the driver is not holding the steering wheel 14, it proceeds to step S90; if it determines that the driver is not holding the steering wheel 14, it proceeds to step S50. In this case, the driver may be determined to be lightly holding the steering wheel 14 if the steering torque Ts detected by the steering torque sensor 38 remains within a second predetermined range between a lower limit of Trf-β and an upper limit of Trf+β for a second reference time (a positive constant) or longer. Note that β may be a positive constant greater than α in step S100 described later, and Trf is the previous value of the reference value Tr for determining the hands-free state, which is set in step S80 or S90 described later.

[0044] In step S50, the CPU calculates the average value Ta of the steering torque Ts detected by the steering torque sensor 38. In this case, the steering torque Ts used to calculate the average value Ta may be limited to the value from the present to a preset time ago or to a preset number of control cycles.

[0045] In step S60, the CPU calculates the confidence level R by adding 1 to the previous value of the confidence level R. The confidence level R may be reset to 0 when the vehicle 102 finishes its run.

[0046] In step S70, the CPU determines whether the confidence level R is greater than or equal to a reference value R0 (a positive integer). If the CPU makes a positive determination, in step S80, it sets the reference value Tr for the release state determination to the average value Ta calculated in step S50. Conversely, if the CPU makes a negative determination, it sets the reference value Tr for the release state determination to a pre-set reference value Tr0 (for example, 0).

[0047] In step S100, the CPU determines whether the steering torque Ts detected by the steering torque sensor 38 is within a first predetermined range, where α is a positive constant, and is greater than or equal to the lower limit Tr-α and less than or equal to the upper limit Tr+α. If the CPU makes a positive determination, in step S110, it determines that the driver has let go of the steering wheel and activates the warning device 58 to issue a warning indicating that the driver has let go of the steering wheel. Conversely, if the CPU makes a negative determination, in step S120, it does not determine that the driver has let go of the steering wheel, and if a warning has been issued, it stops the warning and then terminates this control. If no warning has been issued, the CPU terminates this control.

[0048] According to the first embodiment, when the vehicle 102 is traveling in a straight line, the vehicle is traveling in the center of the lane, and the road surface is not laterally inclined, a positive determination is made in steps S10 to S30. Therefore, according to steps S10 to S30, it is possible to determine that no torque is being input to the steering torque sensor 38 from the side of the steering wheels, the front wheels 16FL and 16FR. Furthermore, when the torque Ts detected by the steering torque sensor is within a second predetermined range which is greater than a first predetermined range, and this situation continues for a second reference time or longer, a positive determination is made in step S40. Therefore, according to step S40, it is possible to determine that no torque is being input to the steering torque sensor from the side of the steering wheel 14.

[0049] [Second Embodiment] In the second embodiment, the ROM of the steering assist ECU 50 stores a program for hands-free state determination control corresponding to the flowchart shown in Figure 3. The hands-free state determination control according to the flowchart shown in Figure 3 is repeatedly executed by the CPU of the steering assist ECU 50 at predetermined intervals when the LTA switch of the setting operator 56 (not shown in Figure 1) is ON and LTA is being executed.

[0050] As can be seen from the comparison between Figure 3 and Figure 2, steps S10 and steps S40 to S120 are performed in the same manner as in the first embodiment, and if a positive determination is made in step S10, step S25 is performed.

[0051] In step S25, the CPU determines whether the magnitude of the lateral force acting on the vehicle 102 is less than or equal to the reference value of the lateral force. If the CPU determines it is negative, it proceeds to step S90; if it determines it is positive, it proceeds to step S35. In this case, the CPU may determine that the magnitude of the lateral force acting on the vehicle is less than or equal to the reference value of the lateral force when the absolute value of the lateral acceleration Gy of the vehicle 102 detected by the lateral acceleration sensor of the vehicle state sensor 90 is less than or equal to the reference value of the lateral acceleration (a positive constant), and the absolute value of the yaw rate Yr of the vehicle 102 detected by the yaw rate sensor is less than or equal to the reference value of the yaw rate (a positive constant).

[0052] The lateral acceleration Gy of the vehicle 102 may be replaced with an estimated lateral acceleration calculated based on the steering angle θs detected by the steering angle sensor 36 and the vehicle speed detected by the vehicle speed sensor. Furthermore, the determination of the yaw rate may be omitted.

[0053] In step S35, the CPU determines whether the absolute value of the control torque Tc applied by the EPS device 12 to the steering transmission system 34 is less than or equal to the control torque reference value Tc0 (a positive constant). If the CPU determines that it is not true, it proceeds to step S90; if it determines that it is true, it proceeds to step S40.

[0054] According to the second embodiment, when it is determined that the vehicle 102 is traveling in a straight line, the lateral force acting on the vehicle is below a reference value, and the magnitude of the control torque Tc is below a reference value, a positive determination is made in steps S10, S25, and S35. Therefore, according to steps S10, S25, and S35, it is possible to determine that no torque is being input to the steering torque sensor 38 from the side of the steering wheels, the front wheels 16FL and 16FR. Also, similar to the first embodiment, when the torque Ts detected by the steering torque sensor is within a second predetermined range which is greater than a first predetermined range, and this situation continues for a second reference time or longer, a positive determination is made in step S40. Therefore, it is possible to determine that no torque is being input to the steering torque sensor from the side of the steering wheel 14.

[0055] [Third Embodiment] In the third embodiment, the ROM of the steering support ECU 50 stores a program for reference value Tr calculation control corresponding to the flowchart shown in Figure 4. The reference value Tr calculation control according to the flowchart shown in Figure 4 is repeatedly executed at predetermined intervals by the CPU of the steering support ECU 50 when the LTA switch of the setting operator 56 (not shown in Figure 1) is ON and LTA is being executed.

[0056] As can be seen from comparing Figure 4 with Figure 2, steps S10 to S80 are executed in the same manner as in the first embodiment, and once step S80 is completed, the control returns to step S10. Although not shown in Figure 4, steps S100 to S120 in the first and second embodiments are executed as a separate hands-off state determination routine from the routines of steps S10 to S80. The same applies to the fourth embodiment described later.

[0057] Furthermore, in the third embodiment, when the vehicle 102 has finished driving, the average value Ta of the steering torque Ts calculated in step S50 is stored in non-volatile memory. In addition, at the start of this control, prior to step S10, in step S5, the reference value Tr used for the determination in step S100 is set to the average value Ta stored in non-volatile memory.

[0058] [Fourth Embodiment] In the fourth embodiment, the ROM of the steering support ECU 50 stores a program for reference value Tr calculation control corresponding to the flowchart shown in Figure 5. The reference value Tr calculation control according to the flowchart shown in Figure 5 is repeatedly executed at predetermined intervals by the CPU of the steering support ECU 50 when the LTA switch of the setting operator 56 (not shown in Figure 1) is ON and LTA is being executed.

[0059] As can be seen from the comparison between Figure 5 and Figure 2, steps S10, S25, S35 and steps S40 to S80 are performed in the same manner as in the third embodiment, and if a positive determination is made in step S10, step S25 is performed.

[0060] Furthermore, in the fourth embodiment, similar to the third embodiment, when the vehicle 102 finishes driving, the average value Ta of the steering torque Ts calculated in step S50 is stored in non-volatile memory. In addition, at the start of this control, prior to step S10, in step S5, the reference value Tr used for the determination in step S100 is set to the average value Ta stored in non-volatile memory.

[0061] As can be seen from the above description, according to each embodiment, when it is determined that no torque is being input to the steering torque sensor 38, the average value Ta of the steering torque Ts detected by the steering torque sensor in that situation is calculated, and the reference value Tr is set to the average value Ta. Furthermore, a first predetermined range for determining the hands-off state is variably set based on the average value Ta so that it is between a lower limit value Tr-α and an upper limit value Tr+α.

[0062] In situations where it is determined that no torque is being input to the steering torque sensor 38, the steering torque Ts detected by the steering torque sensor is the output error of the steering torque sensor due to factors such as assembly errors in the steering system.

[0063] Therefore, according to each embodiment, the first predetermined range can be variably set based on the output error of the steering torque sensor. Accordingly, compared to the case where the first predetermined range is not variably set, the risk of misjudgment in determining whether or not the driver is hands-free can be reduced in situations where an output error occurs in the steering torque sensor due to factors such as assembly errors of the steering device.

[0064] For example, Figure 6 shows examples of hands-free state determination for a conventional case (A) where the reference value Tr is not variably set, and a case (B) where the reference value Tr is variably set according to the present invention. In Figure 6, the dashed line represents the average value Ta of the steering torque Ts detected by the steering torque sensor, where the average value Ta is ΔTs (ΔTs is a negative value), and the reference value Tr in case (A) is assumed to be 0, as with conventional hands-free state determination devices.

[0065] In case (A), even if the driver is hands-free, in the region where the steering torque Ts is smaller than the lower limit -α of a predetermined range (the hatched region), it is determined that the steering torque Ts exceeds the first predetermined range, and it is incorrectly determined that the driver is gripping the steering wheel 14.

[0066] In contrast, according to each embodiment, the reference value Tr is set to the average value Ta, and the first predetermined range for determining the hands-off state is set to a range of Tr-α or more and Tr+α or less. Therefore, even in the hatched area in case (A), it is determined that the steering torque Ts does not exceed the predetermined range, and it can be determined that the driver is hands-off.

[0067] In particular, according to each embodiment, the reliability R is calculated such that it increases the more times it is determined that no torque is being input to the steering torque sensor 38, and when the reliability R is equal to or greater than the reference value R0, the reference value Tr is set to the average value Ta. Therefore, compared to the case where the reference value Tr is set to the average value Ta without considering the number of times it is determined that no torque is being input to the steering torque sensor 38, the reference value Tr can be brought closer to the value of the steering torque Ts that the steering torque sensor 38 should actually output. Consequently, compared to the case where the reference value Tr is set to the average value Ta regardless of the reliability R, it is possible to accurately determine whether or not the driver is hands-free.

[0068] Although the present invention has been described in detail above in terms of specific embodiments and modifications, it will be apparent to those skilled in the art that the present invention is not limited to the embodiments and modifications described above, and that various other embodiments are possible within the scope of the present invention.

[0069] For example, in each of the embodiments described above, the steering assistance control is LTA, but it may be any steering assistance 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 assistance control.

[0070] Furthermore, in this embodiment, LTA is performed on the premise that the driver is not hands-free, in other words, that the driver is holding the steering wheel. However, steering assistance control such as LTA may be performed regardless of whether the driver is hands-free or not, and the determination of whether the driver is hands-free or not may be made when the termination condition of the steering assistance control is met.

[0071] Furthermore, the first to fourth embodiments described above can be performed independently of each other. However, at least one of steps S20 and S30 of the first embodiment may be incorporated into the second embodiment. Conversely, at least one of steps S25 and S35 of the second embodiment may be incorporated into the first embodiment.

[0072] Similarly, at least one of steps S20 and S30 of the third embodiment may be incorporated into the fourth embodiment. Conversely, at least one of steps S25 and S35 of the fourth embodiment may be incorporated into the third embodiment.

[0073] Furthermore, in the first and third embodiments, if a negative determination is made in any of steps S10 to S40, the confidence level R may decrease or be reset to 0. Similarly, in the second and fourth embodiments, if a negative determination is made in any of steps S10, S25, S35, and S40, the confidence level R may decrease or be reset to 0. [Explanation of symbols]

[0074] 10...Steering system, 12...EPS system, 14...Steering wheel, 16FL, 16FR...Front wheels, 38...Steering torque sensor, 40...EPS ECU, 50...Steering assist ECU, 60...Drive ECU, 70...Braking ECU, 100...Hands-off condition detection device, 102...Vehicle

Claims

1. A vehicle hands-free state determination device includes: a torque application device configured to apply control torque to the steering transmission system between the steering wheel and the steering wheel; a steering torque sensor provided in the steering transmission system between the steering wheel and the torque application device; and a control unit configured to determine that the driver is in a hands-free state and not gripping the steering wheel when the steering torque detected by the steering torque sensor is within a first predetermined range, A vehicle hands-free state determination device, wherein the control unit is configured to perform a variable setting of the first predetermined range based on the steering torque detected by the steering torque sensor when it is determined that no torque is being input to the steering torque sensor.

2. A vehicle hands-free state determination device according to claim 1, wherein the first predetermined range is a range of reference torque - predetermined value or greater and reference torque + predetermined value or less, and the control unit is configured to make variable settings of the first predetermined range by setting the steering torque detected by the steering torque sensor as the reference torque in a situation in which it is determined that no torque is input to the steering torque sensor.

3. A vehicle hands-free state determination device according to claim 1, wherein the control unit is configured to determine that no torque is being input to the steering torque sensor from the steering wheel side when it determines that the vehicle is traveling in a straight line, the vehicle is traveling in the center of the lane, and the road surface is not tilted laterally.

4. A vehicle hands-free state determination device according to claim 1, wherein the control unit is configured to determine that no torque is being input to the steering torque sensor from the steering wheel side when it determines that the vehicle is in a straight-ahead state, the magnitude of the lateral force acting on the vehicle is less than or equal to a reference value for lateral force determination, and the magnitude of the control torque is less than or equal to a reference value for control torque determination.

5. A vehicle hands-free state determination device according to claim 1, wherein the control unit is configured to determine that no torque is being input to the steering torque sensor from the steering wheel side when the steering torque detected by the steering torque sensor is within a second predetermined range which is greater than the first predetermined range, in a state where no torque is being input to the steering torque sensor from the steering wheel side.

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