Road surface condition detection device, and power steering device equipped with the road surface condition detection device.

Abstract

To determine a road surface state corresponding to various operations and operation conditions with high accuracy.SOLUTION: A road surface state detection device 80 includes: a steering angle detection part 51 for detecting a steering angle θs of a steering wheel 21; a shaft force detection part 58 for detecting shaft force fr of a steering shaft 41 of a steering part 24 for steering wheels 23 and 23; a yaw rate detection part 63 for detecting a yaw rate Yr generated on a vehicle 10; a first road surface condition determination part 81 for determining a road surface condition of a road surface Rd in contact with the wheels 23 and 23 on the basis of the value of the axial force fr to the steering wheel θs; and a second road surface condition determination part 82 for determining a road surface condition of the road surface Rd in contact with the wheels 23 and 23 on the basis of the value of the yaw rate Yr to the steering angle θs.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to a road surface condition detection device and a power steering device equipped with the road surface condition detection device. [Background technology]

[0002] In recent years, development of a so-called steer-by-wire power steering device in which the steering wheel and the steering unit are mechanically separated has progressed. This type of steer-by-wire power steering device is known from, for example, Patent Document 1.

[0003] The steer-by-wire power steering device of Patent Document 1 controls the steering attitude so that the steering angle detected by a steering angle sensor approaches a target steering angle, and when traveling on a low-friction road surface, the steering attitude control is disabled and the steering angle of the steering section is controlled based on the steering of the driver. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] JP 2001-106110 A Summary of the Invention [Problem to be solved by the invention]

[0005] In general, vehicle driving conditions are diverse, and it is necessary to accurately determine road surface conditions corresponding to such driving conditions.

[0006] An object of the present invention is to provide a technology that can determine road surface conditions corresponding to various operations and driving situations with higher accuracy. [Means for solving the problem]

[0007] As a result of intensive research, the inventors have found that the state quantity by which the driver of a vehicle feels a decrease in road friction changes depending on the operation and driving situation. For example, the driver recognizes that the frictional force (road friction) between the road surface and the steered wheels has decreased in the following three cases.

[0008] In the first state, when the vehicle is traveling at a low speed (for example, when the vehicle speed is below approximately 20 km / h) and the steering wheel is turned further (steered in the direction of increasing the steering angle), the driver feels that the steering torque of the steering wheel has become too small, and recognizes that road friction has decreased.

[0009] In the second state, when the vehicle is traveling at high speed (for example, when the vehicle speed is about 50 km / h or more) and the steering angle is increasing, the driver feels that the yaw rate generated in the vehicle has become excessive, and recognizes that road friction has decreased.

[0010] In the third state, when the steering angle is increasing while the vehicle is accelerating, the driver perceives that the road friction has decreased by feeling that the steering torque has become too small and the yaw rate has become too large.

[0011] The present invention has been completed based on the knowledge that the state quantity by which the driver feels a decrease in road surface friction changes depending on the operation and driving conditions.

[0012] According to the present disclosure, there is provided a road surface condition detection device including a steering angle detection unit that detects the steering angle of a steering wheel, an axial force detection unit that detects the axial force of a steering shaft of a steering unit that steers the wheels, a yaw rate detection unit that detects a yaw rate generated in a vehicle, a first road surface condition judgment unit that judges the road surface condition of the road surface on which the wheels contact based on a value of the axial force with respect to the steering angle, and a second road surface condition judgment unit that judges the road surface condition of the road surface on which the wheels contact based on the value of the yaw rate with respect to the steering angle. Effect of the Invention

[0013] The present invention can provide a technology that can determine road surface conditions corresponding to various operations and driving situations with higher accuracy. [Brief description of the drawings]

[0014] [Figure 1] 1 is a schematic diagram of a power steering device according to a first embodiment of the present invention. [Diagram 2] 2 is a control flowchart of a control unit shown in FIG. 1. [Diagram 3] FIG. 3(a) is an explanatory diagram of the first map shown in FIG. 2, and FIG. 3(b) is an explanatory diagram of the second map shown in FIG. [Figure 4] FIG. 5 is a schematic diagram of a power steering device according to a second embodiment of the present invention. [Diagram 5] 5 is a control flowchart of a control unit shown in FIG. [Figure 6] FIG. 6(a) is an explanatory diagram of the first map shown in FIG. 5, and FIG. 6(b) is an explanatory diagram of the second map shown in FIG. [Figure 7] FIG. 11 is a schematic diagram of a power steering device according to a third embodiment of the present invention. [Figure 8] 8 is a control flowchart of a control unit shown in FIG. 7. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0015] DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below with reference to the accompanying drawings. Note that the embodiments shown in the accompanying drawings are merely examples of the present invention, and the present invention is not limited to these embodiments.

[0016] <Example 1> A power steering device 20 according to a first embodiment will be described with reference to FIGS. 1 to 3. FIG.

[0017] As shown in Fig. 1, a vehicle 10 is equipped with a power steering device 20. This power steering device 20 includes a steering unit 22 that generates a steering input (also called steering force or steering torque) to a steering wheel 21, and a turning unit 24 that steers left and right steerable wheels 23, 23 (wheels 23, 23, including tires). The left and right steerable wheels 23, 23 may be any wheels that can be steered by the turning unit 24, and may include front wheels, rear wheels, or both.

[0018] The power steering device 20 is a so-called steer-by-wire power steering device in which the steering wheel 21 and the steered section 24 are mechanically separated or separable, and the left and right steerable wheels 23, 23 can be steered by operating a steering actuator 44 in accordance with the amount of steering of the steering wheel 21.

[0019] The steering section 22 includes a steering wheel 21 steered by the driver, a steering shaft 31 connected to the steering wheel 21, and a reaction force applying actuator 32 that applies a steering reaction force to the steering wheel 21. This steering reaction force is applied from the reaction force applying actuator 32 (first actuator 32) to the steering wheel 21 in accordance with the steering resistance (road reaction force) that the left and right steered wheels 23, 23 receive from the road surface Rd, and can be referred to as a reaction torque (torque resisting the steering torque).

[0020] Here, steering the steering wheel 21 in the direction to increase the steering angle θs by the driver is referred to as an "increasing steering operation." Steering the steering wheel 21 in the direction to decrease the steering angle θs (towards the neutral direction) by the driver after the increasing steering operation is referred to as an "returning operation."

[0021] The reaction force adding actuator 32 generates a steering reaction force (reaction torque) that resists the steering input (steering torque) of the steering wheel 21 steered by the driver, and applies the steering reaction force to the steering wheel 21, thereby giving the driver a steering feel. The reaction force adding actuator 32 includes a reaction force adding motor 33 (first motor 33) that generates the steering reaction force, and a reaction force transmission mechanism 34 that transmits the steering reaction force to the steering shaft 31. The reaction force adding motor 33 is formed of an electric motor. Hereinafter, the reaction force adding motor 33 will be appropriately abbreviated to "reaction force motor 33".

[0022] The steering section 24 includes a steering shaft 41 extending in the vehicle width direction, left and right steerable wheels 23, 23 connected to both ends of the steering shaft 41 via tie rods 42, 42 and knuckles 43, 43, and a steering actuator 44 that applies steering power to the steering shaft 41.

[0023] The steering actuator 44 (second actuator 44) is made up of a steering motor 45 that generates steering power, and a steering power transmission mechanism 46 that transmits the steering power to the steering shaft 41. The steering motor 45 (second motor 45) is constituted by, for example, an electric motor. The steering power generated by the steering motor 45 is transmitted to the steering shaft 36 by the steering power transmission mechanism 46. As a result, the steering shaft 41 slides in the vehicle width direction.

[0024] Furthermore, the power steering device 20 includes a steering angle detection unit 51 that detects the steering angle θs of the steering wheel 21, a steering torque detection unit 52 that detects the steering torque generated in the steering shaft 31, a reaction motor rotation angle detection unit 53 that detects the rotation angle of the reaction motor 33, and a reaction motor current detection unit 54 that detects the current value of the reaction motor 33. The reaction motor rotation angle detection unit 53 is formed of, for example, a resolver provided in the reaction motor 33.

[0025] Furthermore, power steering device 20 is equipped with a steering motor rotation angle detection section 55 which detects the rotation angle of steering motor 45, a steering motor current detection section 56 which detects the current value of steering motor 45, a stroke detection section 57 which detects the stroke amount from the neutral position of steering shaft 41, and an axial force detection section 58 which detects the axial force fr of steering shaft 41. Steering motor rotation angle detection section 55 is constituted by a resolver provided in steering motor 45, for example.

[0026] There is a correlation between the stroke amount of the steered shaft 41 and the steering angle of the steered wheels 23, 23. The steering angle of the steered wheels 23, 23 can be indirectly obtained based on the detected stroke amount. Note that this steering angle can be indirectly obtained from the rotation angle of the steering motor 45 detected by the steering motor rotation angle detection unit 55.

[0027] In addition, the axial force fr can be indirectly obtained (estimated) from the steering angle θs of the steering wheel 21 detected by the steering angle detection unit 51, the rotation angle of the steering motor 45 detected by the steering motor rotation angle detection unit 55, and the current value of the steering motor 45 detected by the steering motor current detection unit 56.

[0028] Furthermore, the power steering device 20 includes a vehicle speed detection unit 61 that detects the traveling speed Vs (vehicle speed Vs) of the vehicle 10, an acceleration detection unit 62 that detects the acceleration of the vehicle 10, a yaw rate detection unit 63 that detects the yaw rate Yr generated in the vehicle 10, various other detection units 64, a warning generation unit 65 that issues a warning to the driver of the vehicle 10, and a control unit 66.

[0029] The control unit 66 receives detection signals from the above-mentioned detection units 51-58, 61-64, respectively, and applies current to the reaction force adding actuator 32 and the steering actuator 44, and issues an operation signal to the warning generation unit 65. This control unit 66 includes a reaction force adding actuator control unit 71 that drives and controls the reaction force adding actuator 32, a steering actuator control unit 72 that drives and controls the steering actuator 44, and a warning drive control unit 73 that drives and controls the warning generation unit 65.

[0030] In the first embodiment, a road surface condition detection device 80 is configured by the steering angle detection unit 51, the axial force detection unit 58, the yaw rate detection unit 63, and a control unit 66. In this road surface condition detection device 80, the control unit 66 is characterized by including the warning drive control unit 73, a first road surface condition determination unit 81 that determines a first road surface condition, and a second road surface condition determination unit 82 that determines a second road surface condition.

[0031] The first road surface condition judgment unit 81 judges a first road surface condition of the road surface Rd on which the steered wheels 23, 23 are in contact, based on the value of the axial force fr detected by the axial force detection unit 58 relative to the steering angle θs detected by the steering angle detection unit 51.

[0032] The second road surface condition judgment unit 82 judges a second road surface condition of the road surface Rd on which the steered wheels 23, 23 are in contact, based on the value of the yaw rate Yr detected by the yaw rate detection unit 63 relative to the steering angle θs detected by the steering angle detection unit 51.

[0033] Next, referring to Fig. 1, the control by the control unit 66 will be described based on Fig. 2 and Fig. 3. The control unit 66 is configured by, for example, a microcomputer. An example of specific control by the control unit 66 configured by a microcomputer will be described as follows.

[0034] 2 is a control flowchart of the control unit 66, and shows a subroutine for executing the process of determining the first road surface condition and the second road surface condition and controlling the operation of the warning generating unit 65, among a series of controls of the control unit 66. This subroutine is executed by, for example, interrupt processing under a predetermined condition or time sharing processing.

[0035] When control unit 66 starts control, first, in step S01, it acquires steering angle θs (actual steering angle θs) actually detected by steering angle detection unit 51. Next, a first process series of steps S11 to S13 and a second process series of steps S21 to S23 are executed in parallel.

[0036] In the first process, first, in step S11, an axial force threshold value fs, which is a threshold value related to the axial force fr, is set from the value of the steering angle θs. This axial force threshold value fs is, for example, a first reference value for determining whether or not the road surface Rd on which the steered wheels 23, 23 are in contact is in a low friction state. This axial force threshold value fs is obtained by a predetermined first map (see FIG. 3(a)) or calculation that is set in advance.

[0037] 3(a) shows a first map for determining the axial force threshold fs for the steering angle θs, with the horizontal axis representing the steering angle θs and the vertical axis representing the axial force threshold fs. According to this first map, it can be seen that the axial force threshold fs increases as the steering angle θs increases.

[0038] In step S12 following step S11, the axial force fr (actual axial force fr) actually detected by axial force detection unit 58 is acquired. Note that this axial force fr may be a value indirectly found (estimated) from the steering angle θs of steering wheel 21 detected by steering angle detection unit 51, the rotation angle of steering motor 45 detected by steering motor rotation angle detection unit 55, and the current value of steering motor 45 detected by steering motor current detection unit 56.

[0039] Next, in step S13, a first road surface condition of the road surface Rd on which the steered wheels 23, 23 are in contact is judged, that is, whether or not the actual axial force fr is below the axial force threshold value fs is judged. This step S13 constitutes a first road surface condition judgement unit 81 that judges the first road surface condition of the road surface Rd on which the steered wheels 23, 23 are in contact.

[0040] On the other hand, in the second process, first, in step S21, a yaw rate threshold Ys, which is a threshold value related to the yaw rate Yr, is set from the value of the steering angle θs. This yaw rate threshold Ys is, for example, a second reference value for determining whether or not the road surface Rd on which the steered wheels 23, 23 are in contact is in a low friction state. This yaw rate threshold Ys is obtained by a predetermined second map (see FIG. 3(b)) or calculation.

[0041] 3B shows a second map for determining the yaw rate threshold Ys for the steering angle θs, with the horizontal axis representing the steering angle θs and the vertical axis representing the yaw rate threshold Ys. According to this second map, it can be seen that the yaw rate threshold Ys increases as the steering angle θs increases.

[0042] In step S22 following step S21, the yaw rate Yr actually detected by the yaw rate detection unit 63 (actual yaw rate Yr) is obtained.

[0043] Next, in step S23, a second road surface condition of the road surface Rd on which the steered wheels 23, 23 are in contact is judged, that is, it is judged whether the actual yaw rate Yr exceeds the yaw rate threshold value Ys. This step S04 constitutes a second road surface condition judgement unit 82 that judges the second road surface condition of the road surface Rd on which the steered wheels 23, 23 are in contact.

[0044] When it is determined in step S13 that the actual axial force fr is below the axial force threshold value fs and / or when it is determined in step S23 that the actual yaw rate Yr is above the yaw rate threshold value Ys, that is, when it is determined that the road surface Rd is in a low friction state, the warning drive control unit 73 operates the warning generation unit 65 in the next step S31, and then this subroutine is terminated. As a result, the warning generation unit 65 issues a warning to the driver who is driving the vehicle 10.

[0045] On the other hand, if it is determined in step S13 that the actual axial force fr is not below the axial force threshold value fs, and if it is determined in step S23 that the actual yaw rate Yr is not above the yaw rate threshold value Ys, the subroutine is terminated without operating the warning generating unit 65.

[0046] As is clear from the above description, the power steering device 20 includes a road surface condition detection device 80. The road surface condition detection device 80 includes a first road surface condition determination unit 81 (step S13), a second road surface condition determination unit 82 (step S23), and a warning drive control unit 73 (step S31).

[0047] The above description of the first embodiment can be summarized as follows. The road surface condition detection device 80 includes a steering angle detection unit 51 that detects the steering angle θs of the steering wheel 21, an axial force detection unit 58 that detects the axial force fr of the steering shaft 41 of the steering unit 24 that steers the wheels 23, 23 (steerable wheels 23, 23), a yaw rate detection unit 63 that detects the yaw rate Yr generated in the vehicle 10, a first road surface condition judgment unit 81 that judges the road surface condition (first road surface condition) of the road surface Rd on which the wheels 23, 23 are in contact based on the value of the axial force fr with respect to the steering angle θs, and a second road surface condition judgment unit 82 that judges the road surface condition (second road surface condition) of the road surface Rd on which the wheels 23, 23 are in contact based on the value of the yaw rate Yr with respect to the steering angle θs.

[0048] Therefore, a first road surface condition can be determined based on the value of the axial force fr of the steered shaft 41 relative to the steering angle θs. A second road surface condition can be determined based on the value of the yaw rate Yr of the vehicle 10 relative to the steering angle θs. By having two types of road surface condition determination units, road surface conditions corresponding to various operations and driving situations can be determined with higher accuracy.

[0049] Moreover, by defining a state quantity that allows the driver to recognize that the road surface Rd is in a state of reduced friction, it is possible to determine whether the road surface is a low-friction surface based on the driver's recognition, so there is no need to actually measure the condition of the road surface Rd.

[0050] Furthermore, the first road surface condition judgment unit 81 judges the first road surface condition based on an axial force threshold value fs which is a threshold value related to the axial force fr. The second road surface condition judgment unit 82 judges the second road surface condition based on a yaw rate threshold value Ys which is a threshold value related to the yaw rate Yr.

[0051] In this way, by setting the axial force threshold fs and the yaw rate threshold Ys to a level that allows the driver to recognize that the road surface is in a state of reduced friction, it is possible to more clearly and reliably determine whether the road surface is low-friction based on the driver's perception.

[0052] Furthermore, at least one of the axial force threshold value fs and the yaw rate threshold value Ys is a value for determining whether or not the road surface Rd is in a low friction state.

[0053] Therefore, for example, in the case of the following three states, the road surface condition detection device 80 can determine that the frictional force (road surface friction) between the road surface Rd and the steered wheels 23, 23 has decreased.

[0054] First, when the steering wheel 21 is being turned further (the steering angle θs is increasing), the road surface condition detection device 80 determines that the road surface Rd is in a low friction state if the axial force fr falls below the axial force threshold value fs. The axial force is a state quantity that triggers the driver to determine that the friction force of the road surface has decreased and to perform corrective steering while the vehicle is traveling at low speed (for example, when the vehicle speed is about 20 km / h or less), and is particularly effective in that vehicle speed range.

[0055] Secondly, when the steering angle θs is increasing, if the yaw rate Yr exceeds the yaw rate threshold Ys, the road surface condition detection device 80 determines that the road surface Rd is in a low friction state. The yaw rate is a state quantity that triggers the driver to determine that the frictional force of the road surface has decreased and to perform corrective steering when the vehicle is traveling at high speed (for example, when the vehicle speed is about 50 km / h or more), and is particularly effective in this vehicle speed range.

[0056] Thirdly, when the steering angle θs is increasing, the driver determines that the road surface Rd is in a low friction state when the axial force fr falls below the axial force threshold value fs and the yaw rate Yr exceeds the yaw rate threshold value Ys. The two indicators of the axial force and the yaw rate are state quantities that trigger the driver to determine that the frictional force of the road surface has decreased and to perform corrective steering when the vehicle is accelerating, and are particularly effective when the vehicle is accelerating.

[0057] Furthermore, the vehicle 10 is provided with a warning generating unit 65 that issues a warning to the driver of the vehicle 10 when the first road surface condition judgment unit 81 and / or the second road surface condition judgment unit 82 judges that the road surface Rd is in the low friction state.

[0058] Therefore, the warning generating unit 65 can issue a warning according to the judgment result that the road surface Rd is in a state of reduced friction by at least one of the first road surface condition judging unit 81 and the second road surface condition judging unit 82. Therefore, the driver can clearly and quickly judge that the road surface is in a state of reduced friction, regardless of the level of driving proficiency.

[0059] The power steering device 20 is a so-called steer-by-wire type power steering device in which the steering wheel 21 and the steered portion 24 are mechanically separated or separable from each other, and includes a road surface condition detection device 80.

[0060] In this way, in the steer-by-wire power steering device 20, the steering wheel 21 and the steered wheels 23, 23 are mechanically separated. Therefore, the driver cannot recognize the first road surface condition caused by the change in the axial force fr of the steered shaft 41. In contrast, by providing the road surface condition detection device 80 in the steer-by-wire power steering device 20, the driver can reliably recognize the first road surface condition, even though the steering wheel 21 and the steered wheels 23, 23 are mechanically separated.

[0061] <Example 2> Second Embodiment Next, a road surface condition detection device 80A according to a second embodiment and a power steering device 20A including this road surface condition detection device 80A will be described with reference to FIGS.

[0062] FIG. 4 is a schematic diagram of a power steering device 20A of the second embodiment, and is shown in correspondence with FIG. 1 which explains the power steering device 20 of the first embodiment. FIG. 5 is a control flowchart of a control unit 66A of the second embodiment, and is shown in correspondence with FIG. 2 which explains the control flowchart of the control unit 66 of the first embodiment. FIG. 6(a) is an explanatory diagram of a first map of the second embodiment, and is shown in correspondence with FIG. 3(a) which explains the first map of the first embodiment. FIG. 6(b) is an explanatory diagram of a second map of the second embodiment, and is shown in correspondence with FIG. 3(b) which explains the second map of the first embodiment.

[0063] The road surface condition detection device 80A of the power steering device 20A of the second embodiment is characterized in that at least one of the axial force threshold fs and the yaw rate threshold Ys varies based on the traveling speed Vs detected by the vehicle speed detection unit 61. The other basic configurations are common to the power steering device 20 of the first embodiment. The same reference numerals are used for the parts common to the power steering device 20 of the first embodiment, and detailed description thereof will be omitted.

[0064] In comparison with the control unit 66 in the first embodiment, the control unit 66A in the second embodiment has a function of a road surface condition detection device 80A, which is to change at least one of the axial force threshold fs and the yaw rate threshold Ys based on the traveling speed Vs.

[0065] When the control unit 66A of the second embodiment starts control, first in step S01, it acquires the detected steering angle θs (actual steering angle θs). Next, in step S02, it acquires the vehicle speed Vs (actual vehicle speed Vs) actually detected by the vehicle speed detection unit 61. Next, it executes a first process series of steps S11A to S13A and a second process series of steps S21A to S23A in parallel.

[0066] In the first process, first, in step S21A, an axial force threshold value fs, which is a threshold value related to the axial force fr, is set from the steering angle θs and the vehicle speed Vs. This axial force threshold value fs is a first reference value for determining whether or not the road surface Rd is in a low friction state. This axial force threshold value fs is obtained by a predetermined first map (see FIG. 6(a)) or calculation.

[0067] 6(a) shows a first map for determining the axial force threshold fs for the steering angle θs for each vehicle speed Vs1, Vs2, ... Vsn, with the horizontal axis representing the steering angle θs and the vertical axis representing the axial force threshold fs. Here, among the vehicle speeds Vs1, Vs2, ... Vsn detected by the vehicle speed detection unit 61, the value Vs1 is the slowest and the value Vsn is the fastest. According to this first map, it can be seen that the axial force threshold fs increases with an increase in the steering angle θs, and that the rate at which the axial force threshold fs increases with an increase in the steering angle θs increases increases as the vehicle speeds Vs1, Vs2, ... Vsn are faster.

[0068] In step S12A following step S11A, the axial force fr actually detected by the axial force detection unit 58 (actual axial force fr) is acquired, similarly to the first embodiment.

[0069] Next, in step S13A, a first road surface condition of the road surface Rd on which the steered wheels 23, 23 are in contact is judged, that is, whether or not the actual axial force fr is below the axial force threshold value fs is judged, as in the above-mentioned embodiment 1. This step S13A constitutes a first road surface condition judgement unit 81A that judges the first road surface condition of the road surface Rd on which the steered wheels 23, 23 are in contact.

[0070] On the other hand, in the second process, first, in step S21A, a yaw rate threshold Ys, which is a threshold value related to the yaw rate Yr, is set from the steering angle θs and the vehicle speed Vs. This yaw rate threshold Ys is a second reference value for determining whether the road surface Rd is in a low friction state or not. This yaw rate threshold Ys is obtained by a predetermined second map (see FIG. 6(b)) or calculation that is set in advance.

[0071] Fig. 6(b) shows a second map for determining the yaw rate threshold Ys for the steering angle θs for each vehicle speed Vs1, Vs2, ... Vsn, with the horizontal axis representing the steering angle θs and the vertical axis representing the yaw rate threshold Ys. Here, the arrangement of the vehicle speeds Vs1, Vs2, ... Vsn is in the reverse order to that of the first map shown in Fig. 6(a). According to this second map, it can be seen that the yaw rate threshold Ys increases with an increase in the steering angle θs, and that the rate at which the yaw rate threshold Ys increases with an increase in the steering angle θs decreases as the vehicle speeds Vs1, Vs2, ... Vsn are faster.

[0072] In step S22A following step S21A, the yaw rate Yr actually detected by the yaw rate detection unit 63 (actual yaw rate Yr) is obtained, similarly to the first embodiment.

[0073] Next, in step S23A, the second road surface condition of the road surface Rd on which the steered wheels 23, 23 are in contact is judged, that is, whether or not the actual yaw rate Yr exceeds the yaw rate threshold value Ys is judged, as in the above-mentioned embodiment 1. This step S23A constitutes a second road surface condition judgement unit 82A that judges the second road surface condition of the road surface Rd on which the steered wheels 23, 23 are in contact.

[0074] When it is determined in step S13A that the actual axial force fr is below the axial force threshold value fs and / or when it is determined in step S23A that the actual yaw rate Yr is above the yaw rate threshold value Ys, that is, when it is determined that the road surface Rd is in a low friction state, the warning drive control unit 73 operates the warning generation unit 65 in the next step S31, and then this subroutine is terminated. As a result, the warning generation unit 65 issues a warning to the driver who is driving the vehicle 10.

[0075] On the other hand, if it is determined in step S13A that the actual axial force fr is not below the axial force threshold value fs, and if it is determined in step S23A that the actual yaw rate Yr is not above the yaw rate threshold value Ys, the subroutine is terminated without operating the warning generating unit 65.

[0076] As is clear from the above description, the power steering device 20A includes a road surface condition detection device 80A. The road surface condition detection device 80A includes a first road surface condition determination unit 81A (step S13A), a second road surface condition determination unit 82A (step S23A), and a warning drive control unit 73 (step S31).

[0077] The above description of the second embodiment can be summarized as follows. The road surface condition detection device 80A includes a vehicle speed detection unit 61 that detects the traveling speed Vs (vehicle speed Vs) of the vehicle 10. At least one of the axial force threshold fs and the yaw rate threshold Ys changes based on the traveling speed Vs.

[0078] In general, the driver's perception of a decrease in road friction can change according to the traveling speed Vs (vehicle speed Vs). In contrast, in the second embodiment, the axial force threshold fs and the yaw rate threshold Ys are changed based on the traveling speed Vs (vehicle speed Vs). For example, the higher the vehicle speed, the higher the axial force threshold fs can be set and the lower the yaw rate threshold Ys can be set. This makes it possible to judge road surface conditions corresponding to various operations and driving conditions with even greater accuracy. Other actions and effects are the same as those of the first embodiment.

[0079] <Example 3> Third Embodiment Next, a road surface condition detection device 80B according to a third embodiment and a power steering device 20B including this road surface condition detection device 80B will be described with reference to FIGS.

[0080] Fig. 7 is a schematic diagram of a power steering device 20B of the third embodiment, and corresponds to Fig. 4 which explains the power steering device 20A of the second embodiment. Fig. 8 is a control flowchart of a control unit 66B of the third embodiment, and corresponds to Fig. 5 which explains the control flowchart of the control unit 66A of the second embodiment.

[0081] The road surface condition detection device 80B of the power steering device 20B of the third embodiment is characterized in that (1) a warning generating unit 65B generates different warnings for a first road surface condition and a second road surface condition, and (2) when the second road surface condition is a low friction condition, a steering reaction force in a direction to correct the slip of the steered wheels 23, 23 is applied to the steering wheel 21. The other basic configurations are common to the power steering device 20 of the first embodiment. The reference numerals are used for the parts common to the power steering device 20A of the second embodiment, and detailed description thereof will be omitted.

[0082] In contrast to the warning generating unit 65 of the second embodiment, the warning generating unit 65B of the third embodiment is characterized in that it has two warning units, a first warning unit 101 and a second warning unit 102. The first warning unit 101 issues a warning in the case of a first road surface condition, and is configured, for example, so that the driver can visually recognize it (such as a flashing warning light), and is disposed in a position in the vehicle cabin where the driver can easily recognize it, for example, on the instrument panel. The second warning unit 102 issues a warning in the case of a second road surface condition, and is configured, for example, so that the driver can auditorily recognize it (such as a warning device such as a buzzer), and is disposed in the vehicle cabin.

[0083] The warning drive control unit 73B of the third embodiment is made up of a first warning drive control unit 103 that controls the drive of the first warning unit 101, and a second warning drive control unit 104 that controls the drive of the second warning unit .

[0084] In comparison with the control unit 66A of the second embodiment, the control unit 66B of the third embodiment has the functions of a road surface condition detection device 80B, which are: (1) to cause the warning generating unit 65B to generate different warnings for the first road surface condition and the second road surface condition, and (2) to cause the reaction force adding actuator 32 to generate a steering reaction force in a direction to correct the slip of the steered wheels 23, 23 when the second road surface condition is a low friction condition.

[0085] In the control flowchart of the control unit 66B of the third embodiment shown in FIG. 8, the control contents of steps S01, S02, S11A to S13A, and S21A to S23A are the same as the control contents of the control flowchart of the control unit 66A of the second embodiment shown in FIG. 5 above, and therefore the description thereof will be omitted.

[0086] If it is determined in step S13A that the actual axial force fr is below the axial force threshold fs, that is, if it is determined that the road surface Rd is in a low friction state, then in the next step S31A, the first warning drive control unit 103 activates the first warning unit 101, and then this subroutine is terminated. As a result, the first warning unit 101 issues a warning to the driver of the vehicle 10 that the road surface is in a first state. On the other hand, if it is determined in step S13A that the actual axial force fr is not below the axial force threshold fs, then this subroutine is terminated without activating the first warning unit 101.

[0087] When it is determined in step S23A that the actual yaw rate Yr is greater than the yaw rate threshold Ys, that is, when it is determined that the road surface Rd is in a low friction state, the second warning drive control unit 104 activates the second warning unit 102 in the next step S31B, and then the process proceeds to step S32. As a result, the second warning unit 102 issues a warning to the driver of the vehicle 10 that the road surface state is the second state. On the other hand, when it is determined in step S23A that the actual yaw rate Yr is not greater than the yaw rate threshold Ys, the second warning unit 102 is not activated and this subroutine is terminated.

[0088] In step S32 following step S31B, the reaction force adding actuator control section 71 drives and controls the reaction force adding actuator 32 to generate a steering reaction force from the reaction force adding actuator 32 in a direction to correct slip of the steered wheels 23, 23 against the road surface Rd.

[0089] As is clear from the above description, the power steering device 20B includes a road surface condition detection device 80B. The road surface condition detection device 80B includes a first road surface condition determination unit 81A (step S13A), a second road surface condition determination unit 82A (step S23A), a first warning drive control unit 103 (step S31A), a second warning drive control unit 104 (step S31B), and a reaction force addition actuator control unit 71.

[0090] The above description of the third embodiment can be summarized as follows. The warning generation unit 65B issues different types of warnings when the first road surface condition judgment unit 81 judges that the road surface Rd is in the low friction state and when the second road surface condition judgment unit 82 judges that the road surface Rd is in the low friction state.

[0091] Generally, the degree of danger to the driver differs depending on whether the road surface on which the vehicle is traveling is (1) a slippery surface or (2) an actual slippery surface, so it is preferable that the warning issued by warning generation unit 65B also differ.

[0092] The first road surface condition is a slippery road surface condition in which the driver recognizes that the road surface friction has decreased by feeling that the steering torque of the steering wheel 21 has become too small. The second road surface condition is a road surface condition that affects the vehicle motion in which the driver recognizes that the road surface friction has decreased by feeling that the yaw rate Yr generated in the vehicle 10 has become too large.

[0093] In response to this, when the warning generating unit 65B determines that the road surface conditions are the first conditions based on the change in the axial force fr, it drives the first warning unit 101 (for example, blinks a warning light). When the warning generating unit 65B determines that the road surface conditions are the second conditions of low friction based on the change in the yaw rate Yr, it drives the second warning unit 102 (for example, sounds an alarm such as a buzzer). In this way, the warnings issued by the warning generating unit 65B are different, so that the driver can quickly and easily recognize the degree of danger of the road surface conditions.

[0094] Furthermore, the steer-by-wire type power steering device 20 includes a reaction force adding actuator 32 that generates a steering reaction force resisting a steering input of the steering wheel 21 and adds it to the steering wheel 21, and a reaction force adding actuator control unit 71 that drives and controls the reaction force adding actuator 32. When the second road surface condition determination unit 82A determines that the vehicle is in the low friction condition, the reaction force adding actuator control unit 71 controls the reaction force adding actuator 82 to apply the steering reaction force to the steering wheel 21 in a direction that corrects slip of the steered wheels 23, 23 on the road surface Rd, thereby correcting the steering angle θs.

[0095] In this way, when the second road surface condition judgment unit 82 judges from the change in yaw rate Yr relative to the steering angle θs that the second road surface condition is low friction, a steering reaction force in a direction to correct the slip of the steered wheels 23, 23 is applied to the steering wheel 21, thereby changing the control amount of the steering actuator 44 which changes based on the steering angle θs and the steering torque, so that corrective steering can be performed quickly and the slip state of the steered wheels 23, 23 on the road surface Rd can be quickly eliminated.

[0096] The other functions and effects are the same as those of the first and second embodiments.

[0097] The shock absorber according to the present invention is not limited to the above embodiment, so long as the functions and effects of the present invention are achieved. For example, any two or all of the power steering devices 20, 20A, and 20B of the first to third embodiments can be combined. [Industrial Applicability]

[0098] The road surface condition detection devices 80, 80A, 80B of the present invention and the power steering devices 20, 20A, 20B including the road surface condition detection devices 80, 80A, 80B are suitable for installation in an automobile. [Explanation of symbols]

[0099] 10 Vehicles 20, 20A, 20B Power steering device 21 Steering Wheel 22 Steering section 23 wheels 24 Steering section 32 Reaction force actuator 44 Steering actuator 51 Steering angle detector 53 Reaction motor rotation angle detection unit 58 Axial force detector 61 Vehicle speed detection unit 63 Yaw rate detector 65,65B Warning generation section 66, 66A, 66B Control section 71 Reaction force added actuator control section 73,73B Warning drive control section 80, 80A, 80B Road surface condition detection device 81, 81A First road condition judgment section 82, 82A Second road condition judgment section 101 1st warning part 102 2nd warning section 103 First warning drive control unit 104 Second warning drive control section fr Axial force of steering shaft Rd road surface Vs Vehicle speed (vehicle speed) Yr Yaw rate generated by the vehicle θs Steering wheel angle

Claims

1. a steering angle detection unit that detects a steering angle of a steering wheel; an axial force detection unit that detects an axial force of a steering shaft of a steering unit that steers the wheels; a yaw rate detection unit that detects a yaw rate generated in the vehicle; a first road condition determination unit that determines a road condition of a road surface on which the wheels are in contact based on a value of the axial force with respect to the steering angle; a second road surface condition determination unit that determines a road surface condition of the road surface on which the wheels are in contact based on a value of the yaw rate with respect to the steering angle; Equipped with The first road surface condition determination unit determines a road surface condition based on an axial force threshold that is a threshold related to the axial force, the second road surface condition determination unit determines a road surface condition based on a yaw rate threshold that is a threshold related to the yaw rate; A road surface condition detection device, wherein the first road surface condition judgment unit and the second road surface condition judgment unit execute parallel processing.

2. A vehicle speed detection unit that detects a traveling speed of the vehicle is further provided, The road surface condition detection device according to claim 1 , wherein at least one of the axial force threshold value and the yaw rate threshold value varies based on the traveling speed.

3. 3. The road surface condition detection device according to claim 1, wherein at least one of the axial force threshold value and the yaw rate threshold value is a value for determining whether or not the road surface is in a low friction state.

4. 4. The road surface condition detection device according to claim 3, further comprising a warning generating unit that generates a warning to a driver who is driving the vehicle when the first road surface condition judgment unit and / or the second road surface condition judgment unit judges that the road surface is in the low friction state.

5. The warning generating unit is A case in which the first road surface condition determination unit determines that the road surface is in the low friction state; When the second road surface condition judgment unit judges that the road surface is in the low friction state, 5. The road surface condition detection device according to claim 4, wherein different types of warnings are issued.

6. A road surface condition detection device according to any one of claims 1 to 5, A power steering device, wherein the steering wheel and the steered portion are mechanically separated or separable from each other.

7. a reaction force applying actuator that generates a steering reaction force resisting a steering input of the steering wheel and applies the steering reaction force to the steering wheel; a reaction force adding actuator control unit that drives and controls the reaction force adding actuator, 7. The power steering device according to claim 6, wherein, when the second road surface condition judgment unit judges that the road surface is in the low friction condition, the reaction force adding actuator control unit controls the reaction force adding actuator to apply the steering reaction force to the steering wheel in a direction to correct slip of the wheels on the road surface, thereby correcting the steering angle.

Images