Road surface friction coefficient estimation device and steering device

Abstract

Provided is a road surface friction coefficient estimation device and a steering device that can appropriately estimate a road surface friction coefficient even during normal travel in which a time response delay is small and a tire generated force is small. The road surface friction coefficient estimation device includes a wheel acting force sensor (200) that detects an acting force on a wheel, a moment calculation portion that calculates a moment Mtz around a plumb axis at a ground load center of a tire on the basis of an output of the wheel acting force sensor, and a friction coefficient estimation portion (300) that estimates a friction coefficient of a road surface on which the tire is grounded on the basis of the moment.

Description

TECHNICAL FIELD

[0001] The present application relates to a road surface friction coefficient estimation device that estimates a road surface friction coefficient on which a vehicle travels, and a steering device that steers the vehicle. BACKGROUND

[0002] For example, in a vehicle such as an automobile, when the road surface friction coefficient is low, it is necessary to estimate the road surface friction coefficient in order to call the attention of a user such as a driver, or to control the vehicle.

[0003] Conventionally, when a tire slips due to steering or drive / braking force, the road surface friction coefficient can be estimated based on the degree of slip.

[0004] Further, it has been proposed to estimate the road surface friction coefficient even during constant-speed straight traveling when slip is unlikely to occur, for example, by performing high-speed Fourier transform analysis on information from an acceleration sensor of the vehicle body.

[0005] As a conventional technique related to estimation of the road surface friction coefficient, it is described in Patent Document 1 that the road surface friction coefficient is determined by detecting the up-and-down direction acceleration acting on the spring of the suspension, and calculating the power spectral density in the frequency region.

[0006] Further, it is described in Patent Document 2 that the front-and-rear force, lateral force, up-and-down force, and the like acting on the ground surface are detected based on the six-component force acting on the tire, and the friction force is maintained near the peak value in antilock control and traction control.

[0007] Patent Document 1: Japanese Patent Application Laid-Open No. H6-135214

[0008] Patent Document 2: Japanese Patent Application Laid-Open No. 2002-39744 SUMMARY

[0009] The technique described in Patent Document 1 estimates the road surface friction coefficient based on the acceleration on the upper side of the spring of the vehicle, and high-speed Fourier transform processing is required, so that the time response delay becomes large when the change in the road surface friction coefficient is detected. Further, the device becomes complex in configuration because high-speed Fourier transform is performed.

[0010] The technique described in Patent Document 2 controls the tire generated force to be close to the peak value of the friction force when the tire generated force approaches the limit in antilock control and traction control, and the like, and does not consider monitoring the road surface friction coefficient when the tire generated force is small in normal traveling.

[0011] In view of the above problems, it is an object of the present application to provide a road surface friction coefficient estimation device and a steering device that can appropriately estimate the road surface friction coefficient even in normal traveling when the time response delay is small and the tire generated force is small.

[0012] The present application solves the above problems by the following solution.

[0013] The invention according to the technical solution 1 provides a road surface friction coefficient estimation device, characterized by comprising: a wheel acting force sensor that detects an acting force on a wheel; a moment calculation section that calculates a moment around a plumb axis at a ground load center of a tire based on an output of the wheel acting force sensor; and a friction coefficient estimation section that estimates a friction coefficient of a road surface on which the tire is grounded based on the moment.

[0014] A moment caused by some acting force is generated around a plumb axis passing through a ground load center in a wheel (tire) almost all the time, and it is related to a friction coefficient of a road surface.

[0015] According to the present application, by estimating a friction coefficient based on a moment around a plumb axis at a ground load center of a tire, which has a correlation with a friction coefficient of a road surface, even in normal driving when a tire generates a small force, such as constant speed straight driving, a friction coefficient of a road surface can be appropriately estimated.

[0016] In addition, by estimating a road surface friction coefficient based on an acting force acting on a wheel, a time response delay is small relative to, for example, road surface friction coefficient estimation based on behavior in a spring of a vehicle, and a high-speed Fourier transform process is not required, so the calculation burden can be reduced and the configuration of the device can be simplified.

[0017] The invention according to the technical solution 2 is the road surface friction coefficient estimation device according to the technical solution 1, characterized by estimating a friction coefficient based on the moment acquired when driving on a road surface that becomes a reference and the moment acquired when driving on a road surface on which a friction coefficient is estimated.

[0018] Accordingly, a friction coefficient of a road surface on which a vehicle is currently driving can be appropriately estimated based on a moment acquired when driving on a road surface that becomes a reference (for example, a dry paved road) and a moment acquired most recently.

[0019] The invention according to the technical solution 3 is the road surface friction coefficient estimation device according to the technical solution 2, characterized by comprising: a road surface type recognition section that recognizes a road surface type in which a vehicle is driving, and determines whether or not the vehicle is driving on the road surface that becomes a reference based on a recognition result of the road surface type recognition section.

[0020] Accordingly, it is possible to appropriately recognize that a vehicle is driving on a road surface that becomes a reference, detect a moment when driving on the road surface that becomes a reference, and perform learning correction of a determination condition with high precision.

[0021] The invention according to the technical solution 4 is the road surface friction coefficient estimation device according to any one of the technical solutions 1 to 3, characterized in that the road surface friction coefficient estimation device has a notification unit that notifies a user when the estimated friction coefficient is less than or equal to a predetermined value.

[0022] Accordingly, the user can be made aware of the situation in which the friction coefficient is low, and safety can be improved by promoting cautious driving.

[0023] The invention according to the technical solution 5 provides a steering device, characterized by including: an actuator that operates a steering wheel of a vehicle; and a steering control unit that controls a force generated by the actuator, the steering control unit changing the control of the actuator in accordance with an estimation result of a friction coefficient obtained by the road surface friction coefficient estimation device according to any one of the technical solutions 1 to 4.

[0024] Accordingly, when the friction coefficient of the road surface is low, the running stability of the vehicle can be ensured and safety can be improved, for example, by changing the control of the force generated by the actuator unit so that an excessive slip angle or yaw rate does not occur.

[0025] As explained above, according to the present invention, it is possible to provide a road surface friction coefficient estimation device and a steering device that can appropriately estimate the friction coefficient of the road surface even when the time response delay is small and the tire generated force is small during normal running. BRIEF DESCRIPTION OF DRAWINGS

[0026] Figure 1 is a diagram schematically showing the structure of an embodiment of the road surface friction coefficient estimation device and the steering device to which the present invention is applied.

[0027] Figure 2a , Figure 2b is a diagram showing a hub unit in the embodiment.

[0028] Figure 3 is a sectional view of a sensing body in a six-component force detection device of the embodiment, taken along a plane including a central axis and viewed.

[0029] Figure 4 is a perspective view schematically showing the arrangement of strain gauges in the six-component force detection device of the embodiment.

[0030] Figure 5a , Figure 5b , Figure 5c is a diagram showing the arrangement of strain gauges and the structure of a bridge circuit of a force detection system in the six-component force detection device of the embodiment.

[0031] Figure 6a , Figure 6b , Figure 6c is a diagram showing the structure of a bridge circuit of a moment detection system in the six-component force detection device of the embodiment.

[0032] Figure 7 is a diagram schematically showing a wheel center of a wheel, a tire ground contact load center, and a force thereof.

[0033] Figure 8 is a flowchart showing the operation of the road surface friction coefficient estimation device and the steering device of the embodiment.

[0034] Figure 9 is a flowchart showing learning correction of a threshold in the road surface friction coefficient estimation device of the embodiment.

[0035] (Explanation of Reference Numerals)

[0036] 1: steering device; 10: steering wheel; 20: steering shaft; 21: universal joint; 22: pinion; 30: rack shaft; 31: rack gear; 40: rack housing; 41: rack boot; 50: tie rod; 51: ball joint; 52: ball joint; 60: housing; 61: knuckle arm; W: wheel; 70: torque sensor; 80: actuator unit; 81: electric motor; 82: gear box; 90: steering control unit; 100: hub unit; 110: hub; 111: disc portion; 112: central portion; 113: drive shaft mounting portion; 114: outer tube portion; 115: bearing fixing ring; 120: bearing; 121: outer ring; 122: inner ring; 123: ball; 130: sensing portion; 131: disc portion; 132: outer tube portion; 133: bearing fixing ring; 140: mounting portion; 141: mounting tab; 200: six-component force detection device; 210: sensitive body; 211: cylindrical portion; 212: first flange; 212a: threaded hole; 213: second flange; 213a: threaded hole; 214: intermediate portion; 215: intermediate portion; R1-R8: chamfered portion; 221-224: uniaxial strain gauge of Fx detection system; 231-234: uniaxial strain gauge of Fy detection system; 241-244: uniaxial strain gauge of Fz detection system; 251-254: uniaxial strain gauge of Mx detection system; 261-264: uniaxial strain gauge of My detection system; 271-274: shear strain gauge of Mz detection system; F: focal point; B: hub bolt; 300: friction coefficient estimation unit; 301: information notification device; 310: vehicle speed sensor; 320: environment recognition unit; 321: stereo camera device. DETAILED DESCRIPTION

[0037] Hereinafter, an embodiment of a road surface friction coefficient estimation device and a steering device to which the present application is applied will be described.

[0038] The road surface friction coefficient estimation device and the steering device of the embodiment are provided in a vehicle such as a passenger car, for example, for steering front wheels that are steering wheels.

[0039] The steering device of the embodiment includes a pinion-assisted electric power steering (EPS) device.

[0040] Figure 1 This is a diagram schematically illustrating the structure of the vehicle yaw factor estimation device and steering device according to an embodiment.

[0041] The steering device 1 includes a steering wheel 10, a steering shaft 20, a rack shaft 30, a rack housing 40, a tie rod 50, a housing 60, a torque sensor 70, an actuator unit 80, a steering control unit 90, etc.

[0042] The steering wheel 10 is a ring-shaped operating component that allows the driver to input steering input by rotating it.

[0043] The steering wheel 10 is positioned in the vehicle's cabin facing the driver's seat.

[0044] The steering shaft 20 is a rotating shaft with one end mounted to the steering wheel 10, and is a rotating shaft that transmits the rotational motion of the steering wheel 10 to the rack and pinion mechanism that converts it into translational motion.

[0045] A universal joint 21 is provided in the middle of the steering shaft 20, which is capable of transmitting rotation when the steering shaft 20 is bent.

[0046] A pinion 22, which forms part of a rack and pinion mechanism, is formed at the end of the steering shaft 20 on the side opposite to the steering wheel 10.

[0047] The rack shaft 30 is a columnar component arranged along the vehicle width direction in the length direction (axial direction).

[0048] The rack shaft 30 is supported so that it can translate relative to the vehicle body in the width direction.

[0049] A rack 31 that meshes with a pinion 22 is formed on a portion of the rack shaft 30.

[0050] In response to the rotation of the steering shaft 20, the pinion 22 drives the rack 31, and the rack shaft 30 translates (goes straight) in the vehicle width direction.

[0051] The rack 31 is configured to be offset to the left or right in the vehicle width direction (usually the driver's side).

[0052] For example, when the vehicle is a so-called right-hand drive vehicle with the right front seat as the driver's seat, the rack 31 is configured to be biased towards the right side of the center when neutral.

[0053] The rack housing 40 is a generally cylindrical component that supports and houses the rack shaft 30, allowing it to be displaced relative to the vehicle width direction.

[0054] Rack cover shoes 41 are provided at both ends of the rack housing 40.

[0055] The rack cover shoe 41 is a member that prevents foreign matter such as dust from entering the rack housing 40 while allowing relative displacement of the tie rod 50 with respect to the rack housing 40.

[0056] The rack cover shoe 41 is formed in a flexible bellows shape, for example, from a resin material such as an elastomer.

[0057] The tie rod 50 is a shaft-like linkage member that links the end portion of the rack shaft 30 and the knuckle arm 61 of the housing 60, and rotates the housing 60 about the king pin axis in linkage with the translational motion of the rack shaft 30.

[0058] The end portion of the tie rod 50 on the inner side in the vehicle width direction is swingably connected to the end portion of the rack shaft 30 via the spherical joint 51.

[0059] The end portion of the tie rod 50 on the outer side in the vehicle width direction is connected to the knuckle arm 61 of the housing 60 via the spherical joint 52.

[0060] A correction screw mechanism (not shown) for adjusting the toe-in force is provided at the connection portion between the tie rod 50 and the spherical joint 52.

[0061] The housing (knuckle) 60 is a member that houses a hub bearing that rotatably supports the wheel W about the vehicle axis.

[0062] The housing 60 has the knuckle arm 61 that is formed so as to project to the front side or the rear side with respect to the vehicle axis.

[0063] The housing 60 is rotatably supported about a king pin axis that is a predetermined center axis of rotation.

[0064] For example, when the front suspension of the vehicle is a MacPherson strut type, the king pin axis is an imaginary axis that connects the center of a strut top mount bearing and the center of a spherical joint that connects the lower portion of the housing 60 and a transverse link (lower arm).

[0065] The housing 60 is rotated about the king pin axis and the wheel W is steered by pushing and pulling the housing 60 in the vehicle width direction by the rack shaft 30 via the tie rod 50.

[0066] The torque sensor 70 is a sensor that detects the torque acting on the steering shaft 20.

[0067] The torque sensor 70 is provided at the intermediate portion of the steering shaft 20.

[0068] The output of the torque sensor 70 is transmitted to the steering control unit 90.

[0069] The actuator unit 80 is a driving device that is rotationally driven in a region near the pinion gear 22 in the steering shaft 20 to perform power assistance when the vehicle is manually driven and to perform steering work when the vehicle is automatically driven.

[0070] The actuator unit 80 includes a motor 81, a gear box 82, and the like.

[0071] The motor 81 is an electric actuator that generates a driving force applied to the steering shaft 20.

[0072] The rotational direction and the output torque of the motor 81 are controlled by a steering control unit 90.

[0073] The gear box 82 includes a reduction gear train for reducing the rotational output of the motor 81 (increasing the torque) and transmitting it to the steering shaft 20.

[0074] The steering control unit 90 is a control device that provides the motor 81 with an instruction value of the rotational direction and the output torque.

[0075] The steering control unit 90 sets the instruction value given to the motor 81 on the basis of the torque input direction and the detected torque value of the torque sensor 70 when the vehicle is manually driven.

[0076] In addition, when the vehicle is automatically driven or when a drive assist control (for example, a lane keeping assist or the like) is performed, the steering control unit 90 sets the instruction value given to the motor 81 on the basis of an instruction given from an automatic drive control device (not shown).

[0077] In the embodiment, the wheel W is supported by a hub unit described below.

[0078] Figure 2a , Figure 2b is a view showing the hub unit in the embodiment, Figure 2a is a sectional view taken and observed with a plumb plane passing through an axle (a rotational center axis of the wheel), Figure 2b is a front view along the b-b line of Figure 2a .

[0079] As shown in Figure 2a , Figure 2b , the hub unit 100 includes a hub 110, a bearing 120, a sensing portion 130, a mounting portion 140, a six-component force detection device 200, and the like.

[0080] The hub 110 is a member that is fixed to a rim central portion of a wheel (not shown) and rotates around an axle with the wheel.

[0081] The hub 110 includes a disc portion 111, a central portion 112, a drive shaft mounting portion 113, an outer cylinder portion 114, a bearing fixing ring 115, and the like. ​

[0082] The disc portion 111 is formed substantially concentrically with the vehicle axle and is formed in a substantially flat plate shape.

[0083] In the disc portion 111, five hub bolts B for fastening the wheel hub are arranged at equal intervals on a predetermined pitch circle.

[0084] The central portion 112 is a cylindrical portion that protrudes from the central portion of the disc portion 111 to the vehicle width direction outer side.

[0085] The central portion 112 is inserted into a recess (not shown) provided in the wheel rim, and guides the wheel and the wheel hub 110 when the wheel is mounted, so that they can be concentrically mounted.

[0086] The drive shaft mounting portion 113 is a cylindrical portion that protrudes from the central portion of the disc portion 111 to the vehicle width direction inner side.

[0087] A spline hole portion that spline-engages with a spline shaft portion (not shown) of the drive shaft is formed on the inner diameter side of the drive shaft mounting portion 113.

[0088] In addition, the main portion of the drive shaft mounting portion 113 is inserted into the inner diameter side of the sensitive body 210 of the six-component force detection device 200.

[0089] The outer cylinder portion 114 is a cylindrical portion that protrudes from the outer peripheral portion of the disc portion 111 to the vehicle width direction inner side. The outer cylinder portion 114 is formed substantially concentrically with the vehicle axle.

[0090] The outer cylinder portion 114 is a portion in which the outer ring 121 of the bearing 120 is fixed.

[0091] In order to retain the outer ring 121, a portion in which the inner diameter increases in a stepped manner from the end portion on the vehicle width direction inner side to a width substantially the same as the width of the outer ring 121 is formed on the inner peripheral surface portion of the outer cylinder portion 114, and the outer ring 121 is fitted inside thereof.

[0092] The disc portion 111, the central portion 112, the drive shaft mounting portion 113, and the outer cylinder portion 114 described above are integrally formed, for example, by machining a workpiece that has been forged.

[0093] The bearing fixing ring 115 is a circular ring-shaped member that is fixed to the vehicle width direction inner side end portion of the outer cylinder portion 114 by, for example, a threaded stopper.

[0094] The bearing fixing ring 115 has substantially the same outer diameter as the outer cylinder portion 114 and an inner diameter smaller than the outer diameter of the outer ring 121 of the bearing 120, and retains the vehicle width direction inner side end portion of the outer ring 121 assembled in the outer cylinder portion 114 to prevent it from falling off.

[0095] The bearing 120 is, for example, a multi-row deep groove ball bearing that supports the wheel hub 110 so as to be rotatable around the axle, and includes an outer ring 121 formed with a raceway surface on the inner diameter side, an inner ring 122 formed with a raceway surface on the outer diameter side, and a steel ball 123 or the like as a rolling element assembled between them.

[0096] The inductor 130 is a member that is disposed on the inner diameter side of the outer cylinder portion 114 of the wheel hub 110 and fixes the inner ring 122 of the bearing 120.

[0097] The inductor 130 includes a disc portion 131, an outer cylinder portion 132, a bearing fixing ring 133, and the like.

[0098] The disc portion 131 is formed in a substantially flat plate shape substantially concentric with the axle. A circular opening into which the drive shaft mounting portion 113 of the wheel hub 110 is inserted is formed in the central portion of the disc portion 131.

[0099] A first flange 212 of a sensitive body 210 of a six-component force detection device 200 described later is fastened to the inner peripheral portion of the disc portion 131.

[0100] The outer cylinder portion 132 is a cylindrical portion that is protruded from the outer peripheral portion of the disc portion 131 to the inner side in the vehicle width direction. The outer cylinder portion 132 is formed substantially concentrically with the axle.

[0101] The outer cylinder portion 132 is a portion that fixes the inner ring 122 of the bearing 120.

[0102] In order to hold the inner ring 122, a portion in which the outer diameter is tapered from the end portion on the outer side in the vehicle width direction to a width substantially the same as the width of the inner ring 122 is formed in the outer peripheral surface portion of the outer cylinder portion 132, and this portion is inserted into the inner diameter side of the inner ring 122.

[0103] The disc portion 131 and the outer cylinder portion 132 described above are integrally formed, for example, by machining a workpiece that is forged.

[0104] The bearing fixing ring 133 is a ring-shaped member that is fixed to the end portion on the outer side in the vehicle width direction of the outer cylinder portion 132 by, for example, a threaded stopper.

[0105] The bearing fixing ring 133 has an outer diameter substantially the same as the inner diameter of the inner ring 122, and holds the end portion on the outer side in the vehicle width direction of the inner ring 122 assembled in the outer cylinder portion 132 to prevent it from falling off.

[0106] The mounting portion 140 is a plate-shaped member that is fixed to the housing 60.

[0107] On the outer peripheral portion of the mounting portion 140, for example, mounting tabs 141 are formed at four places, the mounting tabs 141 are formed so as to protrude toward the outer diameter side, and have bolt holes for fastening fixing bolts to the housing 60.

[0108] A circular opening into which the circular opening of the sensitive body 210 of the six-component force detection device 200 is inserted is formed in the central portion of the mounting portion 140. The second flange 213 of the sensitive body 210 is fastened to the inner peripheral portion of the circular opening.

[0109] The six-component force detection device 200 includes the sensitive body 210 formed in a substantially cylindrical shape and connecting the induction portion 130 and the mounting portion 140, and a plurality of strain gauges provided in the sensitive body 210 and a bridge circuit including the strain gauges.

[0110] Figure 3 is a sectional view of the sensitive body 210 in the six-component force detection device 200 of the embodiment, as viewed in a plane including the central axis.

[0111] As shown in Figure 3 , the sensitive body 210 has a cylindrical portion 211, a first flange 212, a second flange 213, and the like.

[0112] The cylindrical portion 211 is a portion formed in a cylindrical shape in which the inner diameter and the outer diameter are substantially constant over a predetermined axial length, and is a portion to which the plurality of strain gauges described later are to be attached. The cylindrical portion 211 is disposed substantially concentrically with the axle.

[0113] The first flange 212 is a flat plate-shaped portion provided at one end portion of the cylindrical portion 211 and projects outward in the radial direction and inward in the radial direction with respect to the cylindrical portion 211.

[0114] The first flange 212 is used to fix the inner peripheral portion of the disc portion 131 of the induction portion 130, and is formed with a threaded hole 212a for fastening a bolt (not shown).

[0115] Further, an intermediate portion 214 is provided between the cylindrical portion 211 and the first flange 212, which is set so that the outer diameter and the inner diameter are intermediate between the two. The outer peripheral surface of the intermediate portion 214 is formed so as to increase in diameter in a stepped manner with respect to the outer peripheral surface of the cylindrical portion 211. Further, the inner peripheral surface of the intermediate portion 214 is formed so as to decrease in diameter in a stepped manner with respect to the inner peripheral surface of the cylindrical portion 211.

[0116] A chamfer portion (R1) is provided between the end surface of the second flange 213 side in the outer diameter side of the first flange 212 and the outer peripheral surface of the intermediate portion 214.

[0117] A chamfer portion (R2) is provided between the end surface of the second flange 213 side in the outer diameter side of the intermediate portion 214 and the outer peripheral surface of the cylindrical portion 211.

[0118] A chamfer portion (R3) is provided between the end surface of the second flange 213 side in the inner diameter side of the first flange 212 and the inner peripheral surface of the intermediate portion 214.

[0119] A chamfer (R4) is provided between the end face of the second flange 213 on the inner diameter side of the middle portion 214 and the inner circumferential surface of the cylindrical portion 211.

[0120] In each of the above-mentioned chamfered portions (R1 to R4), R1 and R3 are configured such that the positions of the sensing element 210 in the axial direction are approximately the same.

[0121] Additionally, R2 and R4 are configured to offset the position of the sensing element 210 in the axial direction so that R2 becomes the side of the second flange 213.

[0122] The second flange 213 is a flat plate portion provided at the end of the cylindrical portion 211 opposite to the first flange 212, and is formed to protrude outwards towards the outer diameter side and the inner diameter side relative to the cylindrical portion 211, respectively.

[0123] The second flange 213 is used to fix the inner peripheral edge of the mounting part 140 and has a bolt hole 213a for inserting a bolt (not shown).

[0124] like Figure 2a , Figure 2b As shown, the inner peripheral edge of the mounting portion 140 is configured to abut against the face of the second flange 213 on the side of the first flange 212, and is fastened by a bolt inserted into the bolt hole 213a of the second flange 213 from the inside in the vehicle width direction.

[0125] An intermediate portion 215 is provided between the cylindrical portion 211 and the second flange 213, such that the outer diameter and the inner diameter are centered between them. The outer peripheral surface of the intermediate portion 215 is formed such that its diameter increases in a trapezoidal shape relative to the outer peripheral surface of the cylindrical portion 211. In addition, the inner peripheral surface of the intermediate portion 215 is formed such that its diameter decreases in a trapezoidal shape relative to the inner peripheral surface of the cylindrical portion 211.

[0126] A chamfer (R5) is provided between the end face of the first flange 212 side on the outer diameter side of the second flange 213 and the outer peripheral surface of the intermediate portion 215.

[0127] A chamfer (R6) is provided between the end face of the first flange 212 on the outer diameter side of the middle portion 215 and the outer peripheral surface of the cylindrical portion 211.

[0128] A chamfer (R7) is provided between the end face of the first flange 212 side on the inner diameter side of the second flange 213 and the inner peripheral surface of the intermediate portion 215.

[0129] A chamfer (R8) is provided between the end face of the first flange 212 on the inner diameter side of the intermediate portion 215 and the inner circumferential surface of the cylindrical portion 211.

[0130] In each of the chamfered portions (R5 to R8), R5 and R7 are arranged so that the positions of the sensitive body 210 in the axial direction are substantially identical.

[0131] In addition, R6 and R8 are arranged so that the positions of the sensitive body 210 in the axial direction are offset so that R6 is on the side of the first flange 212.

[0132] Further, the thickness t1 of the first flange 212 and the thickness t2 of the second flange 213 are set to be sufficiently greater than the wall thickness t0 of the cylindrical portion 211.

[0133] The six-component force detection device 200 includes an Fx detection system, an Fy detection system, an Fz detection system, an Mx detection system, an My detection system, and an Mz detection system, each of which has a bridge circuit including a strain gauge provided in the cylindrical portion 211 of the sensitive body 210.

[0134] The Fx detection system detects a force Fx in the radial direction (hereinafter, referred to as the x-axis direction) acting on the cylindrical portion 211 of the sensitive body 210.

[0135] The Fy detection system detects a force Fy in the radial direction (hereinafter, referred to as the y-axis direction) orthogonal to the x-axis direction acting on the cylindrical portion 211 of the sensitive body 210.

[0136] The Fz detection system detects a force Fz in the axial direction (hereinafter, referred to as the z-axis direction) acting on the cylindrical portion 211 of the sensitive body 210.

[0137] The Mx detection system detects a moment Mx around the x-axis acting on the cylindrical portion 211 of the sensitive body 210.

[0138] The My detection system detects a moment My around the y-axis acting on the cylindrical portion 211 of the sensitive body 210.

[0139] The Mz detection system detects a moment Mz around the z-axis acting on the cylindrical portion 211 of the sensitive body 210.

[0140] Each of the above-described Fx detection system, Fy detection system, Fz detection system, Mx detection system, My detection system, and Mz detection system has a bridge circuit including four strain gauges.

[0141] Figure 4 is a perspective view schematically showing the arrangement of strain gauges in the six-component force detection device of the embodiment.

[0142] Figure 5a , Figure 5b , Figure 5c is a view showing the arrangement of strain gauges and the structure of a bridge circuit of a force detection system in the six-component force detection device of the embodiment. Figure 5a , Figure 5b , Figure 5cThe Fx detection system, the Fy detection system, and the Fz detection system are shown, respectively.

[0143] Figure 6a Figure 6b Figure 6c FIG. 6 is a diagram showing the structure of a bridge circuit of a moment detection system in a six-component force detection device according to an embodiment. Figure 6a Figure 6b Figure 6c The Mx detection system, the My detection system, and the Mz detection system are shown, respectively.

[0144] Further, in Figure 5a Figure 5b Figure 5c Figure 6a Figure 6b Figure 6c In the Figs. 6 to 8, the intermediate portions 214, 215, and the like are omitted from the illustrations.

[0145] As shown in Figure 4 Figure 5a Figure 5b Figure 5c The Fx detection system has strain gauges 221 to 224. The strain gauges 221 to 224 are uniaxial strain gauges, and are attached to the outer peripheral surface of the cylindrical portion 211 so that their detection directions are parallel to the central axis direction of the cylindrical portion 211.

[0146] The strain gauge 221 is disposed in a region (a region close to the intermediate portion 214) of the outer peripheral surface of the cylindrical portion 211 on the first flange 212 side.

[0147] The strain gauge 222 is disposed on a straight line that passes through the strain gauge 221 and is parallel to the axial direction of the cylindrical portion 211, and is disposed in a region (a region close to the intermediate portion 215) of the outer peripheral surface of the cylindrical portion 211 on the second flange 213 side.

[0148] The strain gauge 223 is disposed at a position (a position symmetrical to the strain gauge 222 with respect to the central axis of the cylindrical portion 211) that is shifted by 180 degrees around the central axis of the cylindrical portion 211 with respect to the strain gauge 222.

[0149] The strain gauge 224 is disposed at a position (a position symmetrical to the strain gauge 221 with respect to the central axis of the cylindrical portion 211) that is shifted by 180 degrees around the central axis of the cylindrical portion 211 with respect to the strain gauge 221.

[0150] Further, as shown in Figure 5a ​​​​​​​​​​​​As shown, in the bridging circuit of the Fx detection system, strain gauges 221 to 224 are connected in a ring in sequence. The positive and negative terminals of the power supply are connected between strain gauges 222 and 223 and between strain gauges 221 and 224, respectively. The potential difference between strain gauges 221 and 222 and between strain gauges 223 and 224 is extracted as the output.

[0151] The Fy detection system includes strain gauges 231 to 234. Strain gauges 231 to 234 are uniaxial strain gauges, which are attached to the outer circumferential surface of the cylindrical part 211 with their detection direction parallel to the central axis of the cylindrical part 211.

[0152] The strain gauge 231 is configured to be offset by 90 degrees from the strain gauge 221 of the Fx detection system around the central axis of the cylindrical part 211.

[0153] The strain gauge 232 is configured to be offset by 90 degrees from the strain gauge 222 of the Fx detection system around the central axis of the cylindrical part 211.

[0154] Strain gauges 231 and 232 are arranged on the same straight line parallel to the axial direction of the cylindrical part 211.

[0155] The strain gauge 233 is positioned 180 degrees off from the central axis of the cylindrical part 211 relative to the strain gauge 232 (a position symmetrical to the strain gauge 232 relative to the central axis of the cylindrical part 211).

[0156] The strain gauge 234 is positioned 180 degrees off from the central axis of the cylindrical part 211 relative to the strain gauge 231 (a position symmetrical to the strain gauge 231 relative to the central axis of the cylindrical part 211).

[0157] In addition, such as Figure 5b As shown, in the bridging circuit of the Fy detection system, strain gauges 231 to 234 are connected in a ring in sequence. The positive and negative terminals of the power supply are connected between strain gauges 232 and 233 and between strain gauges 231 and 234, respectively. The potential difference between strain gauges 231 and 232 and between strain gauges 233 and 234 is extracted as the output.

[0158] The Fz detection system includes strain gauges 241 to 244. Strain gauges 241 to 244 are uniaxial strain gauges, which are attached to the outer circumferential surface of the cylindrical part 211 with their detection direction parallel to the central axis of the cylindrical part 211.

[0159] Strain gauge 241 is positioned between strain gauge 221 and strain gauge 222 in the Fx detection system.

[0160] The strain gauges 242, 243, 244 are arranged at positions that are 90 degrees, 180 degrees, and 270 degrees, respectively, out of phase around the center axis of the cylindrical portion 211, with respect to the strain gauge 241.

[0161] In addition, as shown in FIG. 2, in the bridge circuit of the Fz detection system, the strain gauges 241, 242, 244, 243 are connected in a ring shape, and the positive and negative poles of the power source are connected between the strain gauge 241 and the strain gauge 243 and between the strain gauge 242 and the strain gauge 244, respectively, and the potential difference between the strain gauge 241 and the strain gauge 242 and between the strain gauge 243 and the strain gauge 244 is extracted as an output. Figure 5c

[0162] As shown in FIG. 2, the Fy detection system includes strain gauges 231 to 234. The strain gauges 231 to 234 are uniaxial strain gauges, and are attached to the outer peripheral surface of the cylindrical portion 211 so that their detection directions are parallel to the center axis direction of the cylindrical portion 211. Figure 4 Figure 6a Figure 6b Figure 6c As shown in FIG. 2, the Mx detection system includes strain gauges 251 to 254. The strain gauges 251 to 254 are uniaxial strain gauges, and are attached to the outer peripheral surface of the cylindrical portion 211 so that their detection directions are parallel to the center axis direction of the cylindrical portion 211.

[0163] The strain gauge 251 is arranged adjacent to the strain gauge 231 of the Fy detection system in the center axis direction of the cylindrical portion 211.

[0164] The strain gauge 252 is arranged adjacent to the strain gauge 232 of the Fy detection system in the center axis direction of the cylindrical portion 211.

[0165] The strain gauges 251 and 252 are arranged on the same straight line parallel to the axial direction of the cylindrical portion 211.

[0166] The strain gauge 253 is arranged at a position that is 180 degrees out of phase around the center axis of the cylindrical portion 211 with respect to the strain gauge 252 (a position symmetrical to the strain gauge 252 with respect to the center axis of the cylindrical portion 211).

[0167] The strain gauge 254 is arranged at a position that is 180 degrees out of phase around the center axis of the cylindrical portion 211 with respect to the strain gauge 251 (a position symmetrical to the strain gauge 251 with respect to the center axis of the cylindrical portion 211).

[0168] In addition, as shown in FIG. 2, in the bridge circuit of the Mx detection system, the strain gauges 251, 253, 252, 254 are connected in a ring shape, and the positive and negative poles of the power source are connected between the strain gauge 251 and the strain gauge 253 and between the strain gauge 252 and the strain gauge 254, respectively, and the potential difference between the strain gauge 251 and the strain gauge 254 and between the strain gauge 253 and the strain gauge 252 is extracted as an output. Figure 6a

[0169] ​​​​​The My detection system includes strain gauges 261 to 264. Strain gauges 261 to 264 are uniaxial strain gauges and are attached to the outer circumferential surface of the cylindrical part 211 in such a way that their detection direction is parallel to the central axis direction of the cylindrical part 211.

[0170] The strain gauge 261 is arranged adjacent to the strain gauge 221 of the Fx detection system in the direction of the central axis of the cylindrical part 211.

[0171] The strain gauge 262 is arranged adjacent to the strain gauge 222 of the Fx detection system in the direction of the central axis of the cylindrical part 211.

[0172] Strain gauges 261 and 262 are arranged on the same straight line parallel to the axial direction of the cylindrical portion 211.

[0173] The strain gauge 263 is positioned 180 degrees off from the central axis of the cylindrical part 211 relative to the strain gauge 262 (a position symmetrical to the strain gauge 262 relative to the central axis of the cylindrical part 211).

[0174] The strain gauge 264 is positioned 180 degrees off from the central axis of the cylindrical part 211 relative to the strain gauge 261 (a position symmetrical to the strain gauge 261 relative to the central axis of the cylindrical part 211).

[0175] In addition, such as Figure 6b As shown, in the bridging circuit of the My detection system, strain gauges 261, 263, 262, and 264 are connected in a ring in sequence. The positive and negative terminals of the power supply are connected between strain gauges 261 and 263 and between strain gauges 262 and 264, respectively. The potential difference between strain gauges 261 and 264 and between strain gauges 263 and 262 is extracted as the output.

[0176] The Mz detection system includes strain gauges 271 to 274. Strain gauges 271 to 274 are shear strain gauges and are attached to the outer circumferential surface of the cylindrical part 211 in such a way that their detection direction is circumferential to that of the cylindrical part 211.

[0177] Strain gauge 271 is positioned between strain gauges 241 and 242 in the Fz detection system.

[0178] Strain gauge 272 is positioned between strain gauge 242 and strain gauge 244 in the Fz detection system.

[0179] Strain gauges 273 and 274 are respectively positioned symmetrically to strain gauges 272 and 271 with respect to the central axis of the cylindrical part 211.

[0180] In addition, such as Figure 6cAs shown, in the bridge circuit of the Mz detection system, the strain gauges 271, 273, 274, 272 are connected in a ring, and the positive and negative poles of a power source are connected between the strain gauge 271 and the strain gauge 273 and between the strain gauge 272 and the strain gauge 274, respectively, and the potential difference between the strain gauge 271 and the strain gauge 272 and between the strain gauge 273 and the strain gauge 274 is extracted as an output.

[0181] The strain gauges of each of the above detection systems are configured such that the focal point F of each detection system substantially coincides with the center of the wheel (not shown) (the center of the tire width on the axle).

[0182] In the embodiment, a friction coefficient estimation unit 300 that estimates the friction coefficient of the road surface based on the output of the six-component force detection device 200 is provided.

[0183] For example, even in the case of straight-line driving at a constant speed on a flat road surface, the wheel FW of the vehicle is acted upon by a moment Mt Z around the plumb axis on the ground load center of the tire due to various forces.

[0184] Such a moment Mt Z is generated due to the influence of, for example, the camber angle, the conicity torque, and the ply steer.

[0185] The camber angle is the angle of inclination of the center axis of rotation of the wheel FW with respect to the road surface.

[0186] When the camber angle is present, the wheel FW generates a lateral force (camber thrust) that influences the moment Mt Z .

[0187] The conicity is the change in the diameter of the cone on the tread of the tire of the wheel FW.

[0188] Even if such a conicity is present, a lateral force is generated, as in the case where the camber angle is present, which influences the moment Mt Z (conicity torque).

[0189] The ply steer refers to a slight lateral force that is generated even if the camber angle and the slip angle of the wheel FW are zero, and in the case of a radial tire, is mainly caused by the direction of adhesion of the outermost tread belt (the direction of inclination of the belt layer cords).

[0190] Regarding the ply steer, it is said that the influence caused by the deformation of the tread of the tire following the movement of the outermost belt layer predominates, causing the moments Mt Z in the same direction in the left and right wheels.

[0191] The friction coefficient estimation unit 300 estimates the road surface friction coefficient based on the change in the moment Mt caused by these influences. Z

[0192] The friction coefficient estimation unit 300 can be input with the output of the six-component force detection device 200 provided in the left and right front wheels, and communicates with the steering control unit 90.

[0193] The function and operation of the friction coefficient estimation unit 300 will be described later in detail.

[0194] The friction coefficient estimation unit 300 is provided with an information notification device 301 that notifies a user such as the driver when the estimated friction coefficient is low.

[0195] As the information notification device 301, for example, an image display device, a voice output device, a warning lamp, or the like can be used.

[0196] A vehicle speed sensor 310 that detects the running speed (vehicle speed) of the vehicle is connected to the friction coefficient estimation unit 300.

[0197] An environment recognition unit 320 is communicably connected to the friction coefficient estimation unit 300.

[0198] The environment recognition unit 320 recognizes information about the environment, such as the shape of the road around the vehicle, various obstacles, and the like, based on the output of various sensors, road-to-vehicle communication, vehicle-to-vehicle communication, map data, and the like.

[0199] As one of the sensors, for example, a stereo camera device 321 is connected to the environment recognition unit 320.

[0200] The stereo camera device 321 has a pair of photographing devices (cameras) arranged apart in the vehicle width direction in a state in which the photographing ranges face the front of the vehicle, and an image processing section or the like that performs stereo image processing on the images photographed by each camera.

[0201] The environment recognition unit 320 detects the lateral position in the lane of the host vehicle based on the output of the stereo camera device 321, and transmits it to the steering control unit 90.

[0202] The steering control unit 90 has a function of performing lane-keeping assist control of the actuator unit 80 so that the lateral position in the lane is within a predetermined range around the center portion of the lane.

[0203] In addition, the environment recognition unit 320 has a function of discriminating the type of the road on which the vehicle is currently traveling (dry paved road, wet paved road, snow-covered road, ice-snow road, or the like) based on the output of the stereo camera device 321.

[0204] ​The friction coefficient estimation unit 300 has a function of calculating the tire ground load center position and the moment Mt around the plumb axis passing through the ground load center position based on the six-component force F at the wheel center detected by the six-component force detection device 200. Z

[0205] The moment Mt Z is a value related to the friction coefficient of the road surface.

[0206] The friction coefficient estimation unit 300 has a function as the moment calculation section and the friction coefficient estimation section of the present application.

[0207] Hereinafter, the calculation method of the ground load center position will be described.

[0208] Figure 7 is a diagram schematically showing the wheel center of the wheel, the tire ground load center, and the force acting thereon.

[0209] First, the six-component force detected at the wheel center O of the wheel and the six-component force at the tire ground load center, etc. are defined as follows.

[0210] • The six-component force observed at the wheel center O:

[0211] F = (F x , F Y , F Z ), M = (M X , M Y , M Z )

[0212] • The six-component force at the tire ground load center:

[0213] Ft = (Ft X , Ft Y , Ft Z ), Mt = (Mt X , Mt Y , Mt Z )

[0214] • Let the position vector of the tire ground load center be r = (x, y, z) with the wheel center as the origin.

[0215] If it is assumed that no external force acts except the tire ground surface, it becomes as shown in Equation 1.

[0216] F = Ft... (Equation 1)

[0217] In addition, according to the definition of the moment, the following Equation 2 holds.

[0218] M = r x Ft + Mt... (Equation 2)

[0219] ​Here, unknown numbers and known numbers are arranged.

[0220] • If the camber angle is assumed to be within a sufficiently small range, then z = -R (R is the rolling radius of the tire and is a positive value).

[0221] • Will become Mt x = Mt y = 0 is defined as the center of the tire ground load.

[0222] Thus, unknown numbers are x, y, Mt z These three.

[0223] If the unknown numbers of Equation 2 are summarized, the tire ground load center x, y and Mt z at that point are found as in Equation 3.

[0224] Equation 1

[0225]

[0226] Next, the operation of the road surface friction coefficient estimation device of the embodiment will be described.

[0227] Figure 8 is a flowchart showing the operation of the road surface friction coefficient estimation device and the steering device of the embodiment.

[0228] Hereinafter, each step will be described in order.

[0229] <Step S01: Judgment of vehicle speed, steering speed, and acceleration>

[0230] The friction coefficient estimation unit 300 acquires information on the vehicle speed V and the steering speed (time differential value of the steering angle) δdot based on information from the steering control unit 90 and the vehicle speed sensor 310.

[0231] In addition, the front-rear direction acceleration Gx of the vehicle is calculated by time-differentiating the vehicle speed V.

[0232] Further, the front-rear direction acceleration can also be detected using, for example, an acceleration sensor.

[0233] As a prerequisite condition for performing the friction coefficient estimation, the friction coefficient estimation unit 300 discriminates whether the vehicle speed V is a predetermined value (for example, 10 km / h) or more, and the steering speed δdot is -10 deg / s or more and 10 deg / s or less, and the front-rear direction acceleration Gx is -0.5 m / s 2 or more and 0.5 m / s 2 or less.

[0234] If the above conditions are satisfied, it proceeds to Step S02, and in other cases, the series of processing is ended (returns).

[0235] <Step S02: Calculate the moment Mt around the ground load center from the six-component force of the wheel Z >

[0236] The friction coefficient estimation unit 300 calculates the coordinate positions x, y of the ground load center of the tires of the left and right front wheels and the moment Mt around the plumb axis passing through the coordinate positions, based on the output of the six-component force detection device 200, by the above-described method Z .

[0237] Further, low-pass filter processing with a cut-off frequency of 5 Hz, for example, is performed on the output of the six-component force detection device 200.

[0238] Here, a third-order Butterworth filter can be used as the low-pass filter.

[0239] By performing this low-pass filter processing, the influence of unevenness such as joints and roughness on the road surface can be reduced.

[0240] After that, step S03 is entered.

[0241] <Step S03: Compare the moment Mt Z with a threshold value 1

[0242] The friction coefficient estimation unit 300 compares the moment Mt Z calculated in step S02 with a predetermined threshold value 1 set based on the moment Mt Z when driving on the road surface that becomes the reference, i.e., the dry paved road surface.

[0243] The threshold value 1 is a threshold value for discriminating between the dry paved road surface and the wet paved road surface.

[0244] If the moment Mt Z is equal to or less than the threshold value 1, step S04 is entered, and in other cases, the series of processing ends (returns).

[0245] <Step S04: Compare the moment Mt Z with a threshold value 2

[0246] The friction coefficient estimation unit 300 compares the moment Mt Z calculated in step S02 with a predetermined threshold value 2 set based on the moment Mt Z when driving on the road surface that becomes the reference, i.e., the dry paved road surface.

[0247] The threshold value 2 is a threshold value for discriminating between the wet paved road surface and the snow-covered road.

[0248] If the moment Mt ZIf equal to or less than threshold 2, proceed to step S05, and in other cases, proceed to step S06.

[0249] <Step S05: Alerting to wet road> Z

[0250] The friction coefficient estimation unit 300 compares the moment of force Mt calculated in step S02 with a predetermined threshold value 3 set in advance. Z Z The moment of force Mt calculated in step S02 is compared with a moment of force Mt based on driving on a road surface that becomes a reference, i.e., a dry paved road.

[0251] The threshold value 3 is a threshold value for discriminating between a snowy road and an icy road.

[0252] If the moment of force Mt calculated in step S02 is equal to or less than the threshold value 3, proceed to step S08, and in other cases, proceed to step S07. Z

[0253] <Step S06: Alerting to wet road>

[0254] The friction coefficient estimation unit 300 notifies the information notification device 301 of information for alerting to the fact that the road surface on which the vehicle is traveling is a wet road.

[0255] In addition, the friction coefficient estimation unit 300 transmits to the steering control unit 90 that the friction coefficient of the road surface has decreased to that of a wet road. The steering control unit 90 changes the content of the control of the force generated by the actuator unit 80 as necessary.

[0256] For example, on a wet road, control is performed to limit the force generated by the tires, the steering angle, the steering speed, the body yaw rate, and the like, so that tire slip does not occur, and excessive understeer behavior and oversteer behavior of the vehicle (the same in steps S07 and S08) do not occur.

[0257] After that, the series of processing ends (returns).

[0258] <Step S07: Alerting to snowy road>

[0259] The friction coefficient estimation unit 300 notifies the information notification device 301 of information for alerting to the fact that the road surface on which the vehicle is traveling is a snowy road.

[0260] In addition, the friction coefficient estimation unit 300 transmits to the steering control unit 90 that the friction coefficient of the road surface has decreased to that of a snowy road. The steering control unit 90 changes the content of the control of the force generated by the actuator unit 80 as necessary.

[0261] After that, the series of processing ends (returns).

[0262] ​​​<Step S08: Caution for icy road>

[0263] The friction coefficient estimation unit 300 notifies the information notification device 301 of information that cautions that the road surface on which the vehicle is currently traveling is an icy road.

[0264] In addition, the friction coefficient estimation unit 300 transmits to the steering control unit 90 that the friction coefficient of the road surface has decreased to that of an icy road. The steering control unit 90 changes the content of the control of the force generation by the actuator unit 80 as necessary.

[0265] After that, the series of processing is ended (return).

[0266] For example, the above-described threshold values 1 to 3 can be set in advance at the time of shipment of the vehicle or the like, but the torque Mt Z For example, it changes due to a change in tire radius caused by tire wear, a change in air pressure, tire replacement, a change in rim insertion, and a slight change in geometry caused by aging of a suspension bush or the like.

[0267] Therefore, in the present embodiment, for example, a dry paved road surface is taken as a road surface that becomes a reference, and the torque Mt Z is learned and corrected.

[0268] Figure 9 is a flowchart showing learning correction of the threshold values in the road surface friction coefficient estimation device of the embodiment.

[0269] Hereinafter, each step will be explained in order.

[0270] <Step Sll: Road surface state determination by stereo camera>

[0271] The friction coefficient estimation unit 300 determines the type of the road surface on which the vehicle is currently traveling based on information (recognition result of the stereo camera device 321) from the environment recognition unit 320.

[0272] After that, step S12 is entered.

[0273] <Step S12: Dry paved road surface determination>

[0274] The friction coefficient estimation unit 300 determines whether or not the road surface on which the vehicle is currently traveling is a dry paved road surface that becomes a reference for estimating the road surface friction coefficient.

[0275] If the road surface is a dry paved road surface, step S13 is entered, and in other cases, the processing is repeated from step Sll onward.

[0276] <Step S13: Vehicle speed, steering speed, and acceleration determination>

[0277] As in step S01, as a precondition for performing the friction coefficient estimation, the friction coefficient estimation unit 300 discriminates whether the vehicle speed V is a predetermined value (for example, 10 km / h) or more, and the steering speed δdot is -10 deg / s or more and 10 deg / s or less, and the front-rear direction acceleration Gx is -0.5 m / s 2 or more and 0.5 m / s 2 or more.

[0278] If the above condition is satisfied, the processing proceeds to step S14, and in other cases, the processing returns to step S11 and the subsequent processing is repeated.

[0279] <Step S14: Calculation of moment Mt around the center of gravity of the wheel based on the six-component force Z

[0280] As in step S02, the friction coefficient estimation unit 300 calculates the coordinate positions x, y of the center of gravity of the tires of the left and right front wheels and the moment Mt around the plumb axis passing through the coordinate positions based on the output of the six-component force detection device 200 Z .

[0281] Subsequently, the processing proceeds to step S15.

[0282] <Step S15: Setting of thresholds 1 to 3 based on the moment Mt Z

[0283] The friction coefficient estimation unit 300 sets the thresholds 1 to 3 for the above road surface friction coefficient estimation based on the moment Mt Z calculated in step S14.

[0284] For example, the thresholds 1 to 3 can be set by multiplying the moment Mt Z , respectively, by a predetermined coefficient.

[0285] Subsequently, the series of processing ends.

[0286] As explained above, according to the present embodiment, the following effects can be obtained.

[0287] (1) By estimating the friction coefficient based on the moment Mt Z around the plumb axis at the center of gravity of the tire, even in normal driving in which the tire generates a small force, such as constant-speed straight driving, the road surface friction coefficient can be appropriately estimated with a small time response delay.

[0288] (2) By setting the thresholds 1 to 3 based on the moment Mt Z obtained when driving on a dry paved road and the moment Mt Z ​​By comparison, the friction coefficient of the road on which the vehicle is currently running can be appropriately estimated.

[0289] (3) By using the moment Mt acquired when the stereoscopic camera device 321 recognizes that the vehicle is running on a dry paved road Z By setting the reference and based on this, setting thresholds 1 to 3, learning correction of the determination condition can be performed with high precision.

[0290] (4) By notifying the user when it is estimated that the vehicle is running on a wet road, a snow-covered road, or an icy road, the user can be made aware of the situation in which the friction coefficient is low, and cautious driving can be promoted to improve safety.

[0291] (5) When the friction coefficient of the road is low, by, for example, changing the control of the actuator unit 80 to generate a force so that an excessive slip angle or yaw rate does not occur, the running stability of the vehicle can be ensured to improve safety.

[0292] (Variation)

[0293] The present application is not limited to the embodiments described above, and various modifications and changes can be made, which are also within the technical scope of the present application.

[0294] (1) The structure of the road surface friction coefficient estimation device, the steering device, and the vehicle is not limited to the above-described embodiments and can be appropriately changed.

[0295] (2) The structure of the sensor for detecting the force acting on the wheel (six-component force detection device 200 in the embodiment) is one example, and the configuration of the sensitive body, the arrangement of the strain gauges, and the like can be appropriately changed.

[0296] (3) In the embodiment, the output of the road surface friction coefficient estimation device is used to control the steering device, but the estimation result of the road surface friction coefficient can also be used for other purposes.

[0297] For example, it can also be used to control a drive force generation device, an anti-lock brake device, a behavior control device, or the like. In addition, when the vehicle is automatically driven, the content of the automatic driving scenario including the target running track of the vehicle, the target vehicle speed, and the like by automatic driving can be changed.

[0298] (4) The method of identifying the road surface to be the reference is not limited to the method of using the stereoscopic camera device as in the embodiment, and can be appropriately changed.

[0299] For example, when the ego vehicle is running on a paved road based on the ego vehicle position information and the map data, and no raindrops are detected by the raindrop sensor or there is no rainfall according to weather information or the like, it can also be recognized as a dry paved road.

Claims

1. A device for estimating the coefficient of road surface friction, characterized in that, include: Wheel force sensor detects the force exerted on the center of the wheel; The torque calculation unit calculates the torque around the plumb axis at the center of the tire's ground load based on the output of the wheel force sensor. as well as The friction coefficient estimation unit estimates the friction coefficient of the road surface in contact with the tire based on the torque. The torque calculation unit calculates the torque based on the following equation 3. The friction coefficient estimation section makes the following estimation: When the absolute value of the torque is greater than the first threshold, the friction coefficient of the road surface is presumed to be equivalent to the friction coefficient of the reference road surface used as a dry paved road surface. When the absolute value of the torque is equal to or less than the first threshold, the friction coefficient of the road surface is presumed to be lower than that of the reference road surface. in, x is the x-axis coordinate when the position vector of the tire's ground load center is r = (x, y, z), with the wheel center as the origin. y is the y-axis coordinate when the position vector of the tire's ground load center is r = (x, y, z) with the wheel center as the origin. Mt Z The torque is the force about the plumb line at the center of the tire's ground load. Ft X Let x be the axial force in the x-axis direction among the six components of force at the center of the tire's ground load. Ft Y Let y be the axial force in the y-axis direction among the six components of force at the center of the tire's ground load. Ft Z Let be the axial force in the z-axis direction among the six components of force at the center of the tire's ground load. M X Let x be the torque about the x-axis among the six force components observed at the center of the wheel. M Y Let the torque about the y-axis be one of the six force components observed at the center of the wheel. M Z Let the torque about the z-axis be one of the six force components observed at the center of the wheel. R is the tire rolling radius.

2. The road surface friction coefficient estimation device according to claim 1, characterized in that, When the absolute value of the torque is equal to or less than a second threshold smaller than the first threshold, the friction coefficient estimation unit estimates that the friction coefficient of the road surface is less than or equal to the friction coefficient of the snow-covered road.

3. The road surface friction coefficient estimation device according to claim 1, characterized in that, The road surface friction coefficient estimation device includes: The road surface type identification unit identifies the type of road surface the vehicle is traveling on, and the friction coefficient estimation unit corrects the first threshold based on the torque calculated when the road surface type identification unit identifies the type as dry paved road surface.

4. The road surface friction coefficient estimation device according to claim 2, characterized in that, The road surface friction coefficient estimation device includes: The road surface type recognition unit identifies the type of road surface the vehicle is traveling on. The friction coefficient estimation unit corrects the first threshold and the second threshold based on the torque calculated by the road surface type identification unit when the road surface type is identified as a dry paved road surface.

5. The road surface friction coefficient estimation device according to claim 2 or 4, characterized in that, The road surface friction coefficient estimation device has a notification unit that notifies the user when the friction coefficient estimation unit estimates that the friction coefficient of the road surface is less than or equal to the friction coefficient of the snow-covered road.

6. A steering device, characterized in that, include: Actuator, used to operate the vehicle's steering wheel; as well as The steering control unit controls the force generated by the actuator. The steering control unit changes the control of the actuator based on the estimated friction coefficient obtained by the road friction coefficient estimation device according to any one of claims 1 to 5.

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