Steering system

Abstract

To provide a steering system that is able to detect an anomaly in a steering shaft caused by a load in a bending direction.SOLUTION: In the present invention, a controller is configured to perform: an input determination process S101 of determining whether an external force is input to a vehicle or not, based on longitudinal acceleration; a position specification process S102 of, when the external force is input, specifying an input tire which is a tire to which the external force is input among the plurality of tires, based on an air pressure of each of the tires 81 to 84; a load calculation process S103 of, when the input tire is a tire of a steered wheel 91, 92, calculating vehicle deceleration or acquiring information on the deceleration, and calculating a load received by the input tire due to the external force, based on a difference between the longitudinal acceleration and the deceleration; and an anomaly determination process S104 of determining whether there is an anomaly in a steered shaft 511 or not, based on the load and a steered angle.SELECTED DRAWING: Figure 5

Description

Technical Field

[0001] The present invention relates to a steering system.

Background Art

[0002] In a rack and pinion type steering device, a rack gear of a rack bar and a pinion gear of a pinion shaft are engaged with each other. As the rack bar moves, a tie rod moves and a steering wheel is steered. The rack bar is one of the steering shafts (steering rods). Further, for example, Japanese Unexamined Patent Application Publication No. 2019-104488 discloses a steering system that detects an abnormality in a transmission device that transmits the output of an electric motor to a steering shaft.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] A technique for detecting an abnormality in a steering shaft due to a bending load applied to the steering shaft such as a rack bar has not been established. The bending direction is a direction orthogonal to the axial direction of the steering shaft. When a bending load is applied to the steering shaft, an abnormality such as the steering shaft being bent may occur. For example, an abnormality due to a bending load on the rack bar is, for example, deformation, breakage of the rack gear portion of the rack bar, or poor engagement between the rack bar and the pinion shaft. As a result, the rack and pinion mechanism may lock or become free.

[0005] For example, in a system where a steering wheel and a rack bar are mechanically connected, a driver may be able to sense an abnormality in the rack bar by operating the steering wheel. However, even in this system, there is a possibility that the driver may not notice an abnormality (including a state that is likely to become abnormal) in the rack bar. In particular, in a system such as a steer-by-wire type system where the steering wheel and the rack bar are not mechanically connected, due to the configuration, it is highly likely that the driver will not notice an abnormality in the rack bar by operating the steering wheel. An object of the present invention is to provide a steering system capable of detecting an abnormality in a steering shaft due to a load in the bending direction.

Means for Solving the Problems

[0006] The steering system of the present invention includes a steering shaft, a steering motor that applies a driving force to the steering shaft, and a conversion mechanism that converts the rotation of the steering motor into axial movement of the steering shaft, a steering actuator that steers a steered wheel, a steering angle sensor that detects the steering angle of the steered wheel, an acceleration sensor that detects a longitudinal acceleration that is the acceleration of the vehicle in the longitudinal direction, a tire pressure sensor that detects the air pressure of each tire, and one or more processors, and a controller configured to acquire information on the steering angle, information on the longitudinal acceleration, and information on the air pressure. The controller is configured to execute an input determination process for determining the presence or absence of an external force input to the vehicle based on the longitudinal acceleration, a position identification process for identifying an input tire, which is the tire to which the external force is input among a plurality of the tires, based on the air pressure of each tire when the external force is input, a load calculation process for calculating the deceleration of the vehicle or acquiring information on the deceleration and calculating the load received by the input tire due to the external force based on the difference between the longitudinal acceleration and the deceleration when the input tire is the tire of the steered wheel, and an abnormality determination process for determining the presence or absence of an abnormality in the steering shaft based on the load and the steering angle.

Effects of the Invention

[0007] According to the present invention, when an external force is input to a tire, for example, by mounting onto a curb or the like, the input tire is identified and the load on the input tire is calculated. The load in the bending direction applied to the steering shaft is affected by the load in the front-rear direction and the steering angle. The greater the load in the front-rear direction, the greater the load in the bending direction applied to the steering shaft. Also, the greater the offset of the steering shaft with respect to the input tire, the greater the moment arm and the greater the load in the bending direction applied to the steering shaft. The offset of the steering shaft corresponds to the steering angle. The controller determines the presence or absence of an abnormality in the steering shaft based on the load and the steering angle. Thus, according to the present invention, it is possible to detect an abnormality in the steering shaft due to the load in the bending direction.

Brief Description of the Drawings

[0008]

Figure 1

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Figure 10

Figure 11

Best Mode for Carrying Out the Invention

[0009] Hereinafter, as a mode for carrying out the present invention, a steering system 1 which is an embodiment of the present invention will be described in detail with reference to the drawings. It should be noted that the present invention can be implemented in various forms with various changes and improvements based on the knowledge of those skilled in the art in addition to the following examples. Each drawing is a conceptual diagram.

[0010] As shown in FIG. 1, the steering system 1 of the present embodiment includes a controller 10, a steering device 51, and an operating device 52. The controller 10 is an electronic control unit (ECU) or a computer including one or more processors 10a and one or more memories 10b. The controller 10 is communicably connected to various sensors. For example, the controller 10 is communicably connected to an acceleration sensor 21, a plurality of air pressure sensors 22, a plurality of vehicle height sensors 23, a pressure sensor 24, a steering angle sensor 25, etc. mounted on the vehicle. Note that communication inside the vehicle is performed by CAN (car area network or controllable area network).

[0011] The acceleration sensor 21 detects the longitudinal acceleration which is the acceleration in the longitudinal direction of the vehicle. The acceleration sensor 21 transmits the detection result to the controller 10. The plurality of air pressure sensors 22 detect the air pressures of the corresponding tires 81 to 84 for the plurality of tires 81, 82, 83, 84 of the vehicle. Each air pressure sensor 22 transmits the detection result to the controller 10.

[0012] The vehicle height sensor 23 detects a physical quantity related to the vehicle height. Specifically, the vehicle height sensor 23 detects the change amount of the vehicle height, that is, the vehicle height stroke. Based on the detection result of the vehicle height sensor 23, the controller 10 can determine the direction of the change in the vehicle height, that is, whether it is an upward change or a downward change, for example, based on the sign (plus or minus) of the detected current.

[0013] The vehicle height sensor 23 includes, for example, a lever mechanism and a variable resistor (not shown), and is configured to detect the vehicle height stroke based on the variation of the lever mechanism. In the present embodiment, the vehicle height sensors 23 are provided at each of the wheels 91 to 94 and measure the change in distance between the suspension arm and the vehicle body. Note that the vehicle height sensor 23 is not limited to the above, and may have other known configurations. Further, the vehicle height sensors 23 may be provided only at, for example, the steered wheels 91 and 92. Further, the vehicle height sensor 23 may be a sensor that detects the vehicle height.

[0014] The pressure sensor 24 detects the hydraulic pressure corresponding to the hydraulic pressure of the wheel cylinders 61, 62, 63, and 64 of the braking devices 71, 72, 73, and 74 provided at each of the plurality of wheels 91, 92, 93, and 94 of the vehicle. The braking devices 71 to 74 each include, for example, a brake rotor, a brake pad, and a piston that presses the brake pad against the brake rotor according to the hydraulic pressure of the wheel cylinders 61 to 64 (not shown). Based on the hydraulic pressure of the wheel cylinders 61 to 64, the braking force applied to each corresponding wheel 91 to 94 is determined.

[0015] The wheel cylinders 61 to 64 of each of the braking devices 71 to 74 are connected to a hydraulic pressure adjustment device 70 (not shown in the hydraulic circuit diagram) that adjusts the hydraulic pressure of the wheel cylinders 61 to 64 (hereinafter also referred to as "wheel pressure"). The hydraulic pressure adjustment device 70 includes, for example, a reservoir tank, a pressure regulating device having an electric motor, and a plurality of solenoid valves (not shown). The hydraulic pressure adjustment device 70 includes, for example, an ESC actuator and / or an electric cylinder. The hydraulic pressure adjustment device 70 is controlled by a brake ECU 70a.

[0016] The pressure sensor 24 may be provided for each of the wheel cylinders 61 to 64, for example, or may be provided one by one for the front-wheel system wheel cylinders 61 and 62 and the rear-wheel system wheel cylinders 63 and 64, or for either one of the two systems. When the pressure sensor 24 is not provided for each of the wheel cylinders 61 to 64, each wheel pressure is calculated by the brake ECU 70a based on the detection result of one pressure sensor 24 and the control content of an electromagnetic valve or the like. Further, the wheel pressure corresponds to the deceleration generated by braking the vehicle. The brake ECU 70a calculates the deceleration of the vehicle by hydraulic braking based on each wheel pressure.

[0017] The controller 10 receives the detection result of the pressure sensor 24, each wheel pressure calculated by the brake ECU 70a, and / or the deceleration calculated by the brake ECU 70a as information regarding the deceleration of the vehicle.

[0018] The steering angle sensor 25 is provided in the steering device 51 that steers the steered wheels 91 and 92 of the vehicle, and detects the steering angle of the steered wheels 91 and 92. The steered wheels 91 and 92 of the present embodiment are a pair of front wheels. The steering system 1 of the present embodiment is a steer-by-wire type steering system. Therefore, the steering device 51 and the operation device 52 are mechanically independent of each other. The controller 10 that functions as a steering ECU is communicably connected to the steering device 51 and the operation device 52. Note that the steering system 1 may include a steering ECU that controls the steering device 51 and the operation device 52 separately from the controller 10.

[0019] The operation device 52 includes a steering wheel 521, a steering shaft 522, a steering column 523, a reaction force applying mechanism 524, and an operation angle sensor 525. The steering wheel 521 is an operation member for the driver's steering operation. The steering shaft 522 is a shaft member to which the steering wheel 521 is attached at its tip. The steering column 523 rotatably holds the steering shaft 522 and is a member supported by the instrument panel reinforcement.

[0020] The reaction force applying mechanism 524 is a mechanism that applies a reaction force to the steering operation to the steering wheel 521 via the steering shaft 522, using the reaction force motor 526, which is an electric motor supported by the steering column 523, as a power source. The reaction force applying mechanism 524 has a general structure including a speed reducer or the like. A rotation angle sensor 526a is provided in the reaction force motor 526. The operation angle sensor 525 detects the operation angle of the steering wheel 521 as the steering operation amount.

[0021] Also, in the operation device 52, a torsion bar 527 is incorporated in the steering shaft 522, similar to a general so-called power steering system. The operation device 52 has an operation torque sensor 528 for detecting the operation torque as the operation force applied to the steering wheel 521 by the driver based on the amount of twist of the torsion bar 527.

[0022] Each of the wheels 91 to 94 is supported by the vehicle body so as to be steerable via a steering knuckle 539, which is a component of the suspension device. The steering device 51 integrally steers the pair of front wheels 91 and 92 by rotating the steering knuckle 539. The steering device 51 has a steering actuator 510 as a main component.

[0023] As shown in FIGS. 1 and 2, the steering actuator 510 includes a rack bar 511 as a steering shaft, a housing 512, a pinion shaft 513, tie rods 514, a steering motor 515, and a conversion mechanism 516. The rack bar 511 is a member whose both ends are respectively connected to the left and right steering knuckles 539 via the tie rods 514. In other words, the left end of the rack bar 511 is connected to the steering knuckle 539 of the left front wheel 91 via the left tie rod 514, and the right end of the rack bar 511 is connected to the steering knuckle 539 of the right front wheel 92 via the right tie rod 514.

[0024] The housing 512 supports the rack bar 511 so as to be movable left and right, and is a member fixedly held to the vehicle body. At each end of the housing 512, a boot 512a is provided to cover the connection portion between the rack bar 511 and the tie rod 514.

[0025] The pinion shaft 513 is arranged to intersect the rack bar 511, and includes a pinion gear 5A that meshes with a rack gear 5B formed on the rack bar 511. The pinion shaft 513 and the rack bar 511 constitute a rack and pinion mechanism. The pinion shaft 513 is configured to rotate in accordance with the movement of the rack bar 511 in the axial direction, that is, the left and right directions. A rotation angle sensor for detecting the rotation angle of the pinion shaft 513 is provided on the pinion shaft 513 as the steering angle sensor 25. The rotation angle of the pinion shaft 513 corresponds to the movement amount of the rack bar 511 in the left and right directions, and the movement amount of the rack bar 511 in the left and right directions corresponds to the steering angle of the steering wheels 91 and 92. That is, the steering angle of the steering wheels 91 and 92 can be calculated based on the rotation angle sensor that detects the rotation angle of the pinion shaft 513. Note that the steering angle sensor 25 may be a sensor that directly detects the movement amount of the rack bar 511.

[0026] The rack and pinion mechanism including the rack bar 511 and the pinion shaft 513 of the present embodiment is configured by using an existing system such as a power steering type steering system in which the pinion shaft 513 and the steering shaft 522 are mechanically connected, for example. The configuration of the present embodiment is configured as a steer-by-wire type steering system by eliminating the mechanical connection between the operation device 52 and the pinion shaft 513 in the existing configuration. That is, the steering system 1 of the present embodiment is a steer-by-wire type steering system that uses an existing rack and pinion mechanism as the steering angle sensor 25. It is also possible to provide a pinion assist motor as a steering motor in this rack and pinion mechanism.

[0027] The steering motor 515 is an electric motor that applies a driving force to the rack bar 511 via a conversion mechanism 516. The conversion mechanism 516 is a mechanism that converts the rotational motion of the steering motor 515 into the linear motion of the rack bar 511. The conversion mechanism 516 includes, for example, a large pulley 5a, a small pulley 5b, a belt 5c, and a transmission gear 5d. The belt 5c is wound around the large pulley 5a and the small pulley 5b. The transmission gear 5d is connected to the large pulley 5a. The small pulley 5b is connected to the output shaft of the steering motor 515 and rotates by the driving force of the steering motor 515. The rotation of the small pulley 5b is transmitted to the large pulley 5a via the belt 5c. Thereby, the transmission gear 5d connected to the large pulley 5a rotates. The transmission gear 5d meshes with a gear 51C formed on the rack bar 511. The conversion mechanism 516 is configured such that the rack bar 511 moves in the left - right direction by the rotation of the transmission gear 5d.

[0028] The controller 10 sets a target steering angle based on the operation amount of the steering wheel 521 or the command value in the automatic driving. The controller 10 controls the steering motor 515 based on the target steering angle and the actual steering angle (the detection result of the steering angle sensor 25) so that the difference between the target steering angle and the actual steering angle becomes small.

[0029] The pinion shaft 513 is provided at a position offset from the center in the vehicle width direction to one end side in the vehicle width direction. The steering motor 515 and the conversion mechanism 516 are provided at positions offset from the center in the vehicle width direction to the other end side in the vehicle width direction. In the present embodiment, the pinion shaft 513 is arranged on the right side of the center position in the left - right direction of the housing 512, and the steering motor 515 and the conversion mechanism 516 are arranged on the left side of the center position in the left - right direction of the housing 512. That is, with respect to the center position in the left - right direction of the rack bar 511, the rack gear 5B is located on the right side and the gear 51C is located on the left side. Note that the pinion shaft 513 and the rack gear 5B may be relatively arranged on the left side, and the steering motor 515 and the conversion mechanism 516 may be relatively arranged on the right side.

[0030] In this embodiment, when a load is applied to the right front wheel 92, the support point of the rack bar 511 with respect to the bending force is the pinion shaft 513 of the rack and pinion mechanism arranged relatively on the right side. That is, when a load is applied to the right front wheel 92, a bending load is applied to the portion of the rack bar 511 corresponding to the pinion shaft 513. On the other hand, when a load is applied to the left front wheel 91, the support point of the rack bar 511 with respect to the bending force is the conversion mechanism 516 arranged relatively on the left side. That is, when a load is applied to the left front wheel 91, a bending load is applied to the portion of the rack bar 511 corresponding to the conversion mechanism 516.

[0031] The rack gear 5B is formed in a portion where a cross section (hereinafter also referred to as an "axial orthogonal cross section") obtained by cutting the rack bar 511 in a plane orthogonal to the axis of the rack bar 511 is not circular but has a shape in which a part of the circular shape is cut off as shown in FIG. 3. In the portion 50b of the rack bar 511 where the rack gear 5B is located, there is a difference in the section modulus in the circumferential direction. The section modulus is the strength against the bending load. The section modulus against the load in the direction toward the rack gear 5B in the portion 50b (see, for example, the dashed arrow in FIG. 3) is smaller than that of other portions of the rack bar 511. That is, the rack bar 511 is relatively easy to deform with respect to the load in this direction. The gear 51C is formed over the entire circumferential direction of the rack bar 511, and there is almost no difference in the section modulus in the circumferential direction.

[0032] Also, as shown in FIG. 4, in many cases, the axial direction of the tie rod 514 is inclined with respect to the axial direction of the rack bar 511. In the present disclosure, this inclination angle is referred to as the tie rod inclination angle Ra. The tie rod inclination angle Ra changes according to the change in the vehicle height. Further, when an external force is input to the tire, the force is transmitted to the rack bar 511 via the tie rod 514. Regarding the force received by the rack bar 511, the force transmitted to the rack bar 511 can be decomposed into the axial force of the rack bar 511 and the bending force of the rack bar 511 (see the arrows in FIG. 4).

[0033] For example, when the right front wheel 92 rides up on a curb or the like while the vehicle is traveling forward, at the moment of riding up, a force acting rearward and upward is applied to the rack bar 511 via the tie rod 514. This force acts to bend the right end portion of the rack bar 511 rearward. The force input to the right front wheel 92 has a relatively large impact on the rack and pinion mechanism disposed relatively on the right side. The bending direction of the rack bar 511 is one of the directions orthogonal to the axis of the rack bar 511. The direction of the load (force) received by the rack bar 511 among the bending directions is affected by the tie rod inclination angle Ra. That is, the magnitude of the tie rod inclination angle Ra affects the direction of the load applied to the rack bar 511, that is, the direction of the load received by the rack bar 511.

[0034] As shown by the dashed arrow in FIG. 3, when a load is applied to the rack gear 5B of the rack bar 511 having a relatively small section modulus, it is considered that abnormalities such as poor gear meshing, deformation and breakage of the rack bar 511 are likely to occur in the rack bar 511. In FIG. 3, when a force is applied to the rack bar 511 in the direction of the arrow from the upper left to the lower right, it is considered that an abnormality is relatively likely to occur.

[0035] The controller 10 can determine whether or not a load is applied toward the rack gear 5B based on the vehicle height information when the tire receives an external force by acquiring the relationship between the tie rod inclination angle Ra and the vehicle height and the relationship between the tie rod inclination angle Ra and the direction of the load. In the controller 10, the relationship between the tie rod inclination angle Ra and the vehicle height and the relationship between the tie rod inclination angle Ra and the direction of the load are preset. The controller 10 can specify the direction of the load applied to the rack bar 511 based on the detection result of the vehicle height sensor 23.

[0036] As described above, the steering system 1 of the present embodiment includes a rack bar 511, a steering motor 515 that applies a driving force to the rack bar 511, and a conversion mechanism 516 that converts the rotation of the steering motor 515 into the axial movement of the rack bar 511. The steering system 1 of the present embodiment also includes a steering actuator 510 that steers the steering wheels 91 and 92, a steering angle sensor 25 that detects the steering angle of the steering wheels 91 and 92, an acceleration sensor 21 that detects the longitudinal acceleration, which is the acceleration in the longitudinal direction of the vehicle, a tire pressure sensor 22 that detects the air pressure of each of the tires 81 to 84, and a controller 10 that has one or more processors 10a and is configured to acquire information on the steering angle, the longitudinal acceleration, and the air pressure. The steering system 1 of the present embodiment is a steer-by-wire type system in which the steering actuator 510 and the steering wheel 521 as an operation member are not mechanically connected.

[0037] (Abnormality Detection Control) The abnormality detection control by the controller 10 will be described. As shown in FIG. 5, the controller 10 is configured to execute an input determination process S101, a position identification process S102, a load calculation process S103, and an abnormality determination process S104 as the abnormality detection control based on the information acquired from various sensors.

[0038] The input determination process S101 is a process of determining the presence or absence of an external force input to the vehicle based on the longitudinal acceleration. The position identification process S102 is a process of identifying the input tire, which is the tire to which the external force is input among the plurality of tires 81 to 84, based on the air pressure of each of the tires 81 to 84 when an external force is input. The load calculation process S103 is a process of calculating the deceleration of the vehicle or acquiring the deceleration information when the input tire is one of the steering wheels 91 and 92, and calculating the load received by the input tire due to the external force based on the difference between the longitudinal acceleration and the deceleration. The abnormality determination process S104 is a process of determining the presence or absence of an abnormality in the rack bar 511 based on the load, the steering angle, and the detection result of the vehicle height sensor 23. In the present embodiment, the detection result of the vehicle height sensor 23 is used when it is desired to specify the direction of the load, and is not used when such specification is unnecessary.

[0039] With reference to FIG. 6, the abnormality detection control for detecting an abnormality due to the load on the rack gear 5B will be described. The controller 10 receives information on the longitudinal acceleration Gf from the acceleration sensor 21 (S201). The controller 10 determines whether the longitudinal acceleration Gf is greater than the acceleration threshold value Tg (S202). When the longitudinal acceleration Gf is less than or equal to the acceleration threshold value Tg (S202: No), the controller 10 determines that no abnormal external force is input, and returns the abnormality detection control to the first step (S201). When the longitudinal acceleration Gf is greater than the acceleration threshold value Tg (S202: Yes), the controller 10 determines that an abnormal external force has been input, and checks the air pressure information of each of the tires 81 to 84 (S203).

[0040] The controller 10 determines whether there are tires 81 to 84 in which the air pressure change rate Pa is greater than the air pressure threshold value Ta during a predetermined period (hereinafter referred to as the "determination target period") after the external force is input (S204). The change rate Pa is the amount of change in air pressure per unit time. Note that instead of the change rate Pa, the amount of change in air pressure may be set as a comparison element with the threshold value. When the air pressure change rate Pa of all the tires 81 to 84 is less than or equal to the air pressure threshold value Ta (S204: No), the controller 10 determines that no abnormal external force is applied to the tires 81 to 84, and returns the abnormality detection control to the first step.

[0041] When there are tires 81 to 84 in which the rate of change in air pressure Pa is greater than the air pressure threshold Ta (S204: Yes), the controller 10 determines whether the wheel provided with the tire to which an abnormal external force is input (hereinafter referred to as "input tire") is the predetermined steered wheel 92, that is, the right front wheel 92 in this example (S205). The detection results of each air pressure sensor 22 are associated with the positions of the tires 81 to 84 based on ID information and the like. Therefore, the controller 10 can recognize which tire position the detection result of the air pressure sensor 22 is the air pressure information of. When the tire rides up on a curb or the like, the tire is crushed, the volume of the tire becomes smaller, and the air pressure becomes larger. For example, when the air pressure of the input tire is increasing rapidly, it is considered highly likely that an abnormal external force has been applied.

[0042] When the wheel corresponding to the input tire is not the right front wheel 92 (S205: No), the controller 10 determines that there is no influence on the rack gear 5B and proceeds to process Z. Process Z will be described later. When the wheel corresponding to the input tire is the right front wheel 92 (S205: Yes), the controller 10 checks the information of each wheel pressure Pw when the external force is input in order to examine the influence on the rack gear 5B (S206). The controller 10 calculates the load L applied to the input tire by the external force based on the wheel pressure Pw and the longitudinal acceleration Gf (S207). It can also be said that the controller 10 estimates the assumed load that the input tire is assumed to have received by calculation. The load L can also be said to be the input load at the position of the input tire.

[0043] The load L is calculated based on the difference between the longitudinal acceleration Gf and the deceleration Gd. The deceleration Gd is calculated based on each wheel pressure Pw. For example, the deceleration of one wheel is calculated based on the wheel pressure Pw, the wheel cylinder diameter of the caliper, the friction coefficient of the brake pad, the braking effective radius / tire dynamic load radius, and the estimated road surface friction coefficient. The arithmetic expression is, for example, the deceleration of one wheel = wheel pressure × wheel cylinder diameter of the caliper × friction coefficient of the brake pad × (braking effective radius / tire dynamic load radius) × estimated road surface friction coefficient.

[0044] For each of the wheels 91 to 94, a deceleration is calculated, and based on this, the deceleration Gd of the entire vehicle is calculated. The controller 10 may acquire information on the deceleration Gd from the brake ECU 70a. That is, the controller 10 may receive information on the deceleration Gd calculated by the brake ECU 70a.

[0045] The load L is calculated based on the longitudinal acceleration Gf, the deceleration Gd, and the assumed vehicle weight W. For example, the load L can be calculated by multiplying the difference between the longitudinal acceleration Gf and the deceleration Gd by the assumed vehicle weight W. The calculation formula is L = (Gf - Gd) × W. The assumed vehicle weight W is the weight of the vehicle and is set based on an initial setting value (for example, the weight of the vehicle only) stored in the controller 10. The controller 10 sets, for example, a value obtained by adding the weight of the occupants and / or the weight of the luggage to the initial setting value as the assumed vehicle weight W. Note that the controller 10 may set the initial setting value as the assumed vehicle weight W as it is.

[0046] Based on the detection results of the seat sensors 27 provided in each seat, the controller 10 grasps the number and / or weight of the occupants, and adds the occupant weight to the initial setting value according to the detection results of the respective seat sensors 27. As a result, it becomes possible to calculate the load L based on a weight closer to the actual situation, and it becomes possible to improve the calculation accuracy of the load L and, consequently, the abnormality detection accuracy. Further, the controller 10 may add the weight of the luggage acquired by the function of the luggage weight detection means or by the user's setting or the like to the assumed vehicle weight W. The seat sensor 27 is, for example, a load sensor that detects a change in load or a capacitance-type sensor that detects a change in capacitance.

[0047] The controller 10 determines whether the calculated load L is greater than the load threshold value Tl (S208). When the load L is less than or equal to the load threshold value Tl (S208: No), the controller 10 determines that a load large enough to cause an abnormality is not applied to the input tire, and returns the abnormality detection control to the first step. When the load L is greater than the load threshold value Tl (S208: Yes), the controller 10 checks the vehicle height information within the determination target period (S209).

[0048] During the determination target period, the controller 10 determines whether the vehicle height stroke Ch exceeds the vehicle height threshold Th (S210). The vehicle height stroke Ch corresponds to the direction of the load. Based on the knowledge obtained through simulations, tests, etc., in this embodiment, when the vehicle height stroke Ch is small, it can be determined that the direction of the load is not the direction towards the rack gear 5B. Note that the relationship between the vehicle height stroke Ch or the vehicle height Hv and the direction of the load on the rack bar 511 varies depending on the vehicle configuration.

[0049] If the vehicle height stroke Ch is less than or equal to the vehicle height threshold Th during the determination target period (S210: No), the controller 10 determines that the direction of the load is not the direction corresponding to the rack gear 5B, and returns the abnormality detection control to the first step. In step S210, the controller 10 may be set to compare the maximum value of the vehicle height stroke Ch during the determination target period with the vehicle height threshold Th. The controller 10 can calculate the vehicle height Hv at that time based on the initial set vehicle height and the vehicle height stroke Ch. That is, the vehicle height stroke Ch can be converted into the vehicle height Hv.

[0050] If the vehicle height stroke Ch exceeds the vehicle height threshold Th during the determination target period (S210: Yes), the controller 10 checks the steering angles Sa of the steered wheels 91 and 92 during the determination target period (S211). The steering angle Sa corresponds to the stroke of the rack bar 511. The larger the steering angle Sa, the larger the stroke of the rack bar 511 to one side. The stroke of the rack bar 511 is the amount of movement when the rack bar 511 moves axially to one side from the neutral position. In other words, the stroke of the rack bar 511 is the amount of movement of the left end of the rack bar 511 from the neutral position to the left when the rack bar 511 moves to the left, and the amount of movement of the right end of the rack bar 511 from the neutral position to the right when the rack bar 511 moves to the right. The neutral position of the rack bar 511 is the position where the vehicle goes straight.

[0051] When the vehicle is turning, the rack bar 511 protrudes on one side (either the left or the right) and retracts on the other side. When the tire on the side where the rack bar 511 protrudes is the input tire, the greater the protrusion of the rack bar 511, the greater the moment length and the greater the bending load applied to the rack bar 511. Therefore, the controller 10 determines whether the steering angle Sa within the determination target period is greater than the steering angle threshold Ts (S212). Although the steering angle Sa may change while an external force is being applied, by the controller 10 checking the steering angle Sa within the determination target period, such a change also becomes a determination target.

[0052] If the steering angle Sa is less than or equal to the steering angle threshold Ts within the determination target period (S212: No), the controller 10 determines that the influence of the external force on the rack bar 511 is small and returns the abnormality detection control to the first step. If the steering angle Sa exceeds the steering angle threshold Ts within the determination target period (S212: Yes), the controller 10 determines the presence or absence of an abnormality in the rack bar 511 based on a preset abnormality determination map M1, the steering angle Sa, and the vehicle height information (S213). The vehicle height information is the vehicle height stroke Ch of the wheel corresponding to the input tire, i.e., the right front wheel 92, or the vehicle height Hv based on the vehicle height stroke Ch.

[0053] As shown in FIG. 7, the abnormality determination map M1 of this example is a map with the steering angle on the horizontal axis and the vehicle height on the vertical axis. Regarding the horizontal axis, the greater the value of the steering angle is from the origin O towards the right side (+), the greater the protrusion of the rack bar 511 to the right side, and the greater the protrusion of the rack bar 511 to the left side as it goes from the origin O towards the left side (-). The controller 10 can grasp the protruding direction of the rack bar 511 based on the detection result of the steering angle sensor 25. Since the abnormality determination map M1 is set to determine the presence or absence of an abnormality in the rack gear 5B, the case where the rack bar 511 protrudes to the right from the neutral position becomes the target case for abnormality determination.

[0054] Regarding the vertical axis, the lower the value of the vehicle height Hv is from the origin O (towards the lower side (-)), the greater the amount by which the vehicle sinks, i.e., the amount of bounce. The higher the value of the vehicle height Hv is from the origin O (towards the upper side (+)), the greater the amount by which the vehicle rises, i.e., the amount of rebound. For example, when a tire rides up on a curb or the like, the input tire fluctuates vertically, and the vehicle height detected by the wheel corresponding to the input tire also fluctuates vertically. The determination target period is set to a period longer than the assumed fluctuation period of the vertical fluctuation of the vehicle height caused by an external force. In the present embodiment, it is assumed that an external force is continuously input for a predetermined period due to one collision or ride-up.

[0055] In the abnormality determination map M1, areas determined to be abnormal by the controller 10 are set in the first quadrant and the fourth quadrant. A first area A1 is set in the first quadrant, and a second area A2 is set in the fourth quadrant. When the horizontal axis is X and the vertical axis is Y, in each of the areas A1 and A2, a delivery lower limit value ≤ X ≤ a delivery upper limit value and a vehicle height lower limit value ≤ Y ≤ a vehicle height upper limit value are set. Note that the delivery upper limit value and the vehicle height upper limit value may not be set. The range of the steering angle corresponding to each of the areas A1 and A2 corresponds to a first predetermined range, and the range of the vehicle height Hv or the vehicle height stroke Ch corresponding to each of the areas A1 and A2 corresponds to a second predetermined range. That is, in the load calculation process S103, when the load L is greater than the load threshold value, the steering angle Sa is a value within the first predetermined range, and the vehicle height stroke Ch or the vehicle height Hv is a value within the second predetermined range during the determination target period, the controller 10 determines that there is an abnormality in the rack bar 511. Note that the XY coordinates used for the determination may be (Sa, Hv) or (Sa, Ch).

[0056] The controller 10 determines whether the coordinates (Sa, Hv) have become values within the first area A1 or the second area A2 during the determination target period (S213). When the coordinates (Sa, Hv) have become values within the first area A1 or the second area A2 (S213: Yes), the controller 10 determines that there is an abnormality in the rack bar 511, sets an abnormality flag, and executes the processing at the time of abnormality (S214).

[0057] The processing in case of an abnormality is, for example, processing to notify the driver that there is an abnormality in the rack bar 511, such as turning on a warning lamp, displaying a warning on the display, or giving a warning by voice. On the other hand, when the coordinates (Sa, Hv) do not become values within the first area A1 or the second area A2 (S203: No), the controller 10 determines that there is no abnormality in the rack bar 511 and returns the abnormality detection control to the first step.

[0058] Note that the order of comparison between various information and the threshold value can be changed as appropriate. For example, the order of step S210 and step S212 may be swapped. Further, the controller 10 may omit the comparison between the steering angle Sa and the steering angle threshold value Ts and the comparison between the vehicle height stroke Ch and the vehicle height threshold value Th, and execute the comparison between the coordinates (Sa, Hv) and the abnormality determination map M1. That is, in the abnormality detection control, steps S210 and S212 may be omitted. Also, the vertical axis of the abnormality determination map M1 may be the vehicle height stroke Ch instead of the vehicle height Hv.

[0059] (Regarding process Z) As described above, in the abnormality detection control, when the input tire is not the right front tire 92 (S205: No), the controller 10 executes process Z. As shown in FIG. 8, in process Z, the controller 10 determines whether the input tire is the left front tire 91 (S301). When the input tire is not the left front tire 91 (S301: No), the controller 10 determines that there is no influence on the rack bar 511 due to an external force, and returns the abnormality detection control to the first step (S201).

[0060] When the input tire is the left front tire 91 (S301: Yes), the controller 10 calculates the load L based on the longitudinal and lateral accelerations Gf, the deceleration Gd, and the assumed vehicle weight W, similar to steps S206 and S207 (S302). The controller 10 determines whether the load L is greater than the load threshold value Tl2 (S303). When the load L is less than or equal to the load threshold value Tl2 (S303: No), the controller 10 determines that a load sufficient to cause an abnormality is not applied to the input tire, and returns the abnormality detection control to the first step.

[0061] When the load L is greater than the load threshold value Tl2 (S303: Yes), the steering angle Sa during the determination period is confirmed (S304). The controller 10 determines whether the steering angle Sa within the determination period is greater than the steering angle threshold value Ts2 (S305). When the steering angle Sa is less than or equal to the steering angle threshold value Ts2 (S305: No), it is determined that the influence on the part of the rack bar 511 on the converter mechanism 516 side is small, and the abnormality detection control is returned to the first step. The input of the external force to the left front wheel 91 affects the portion corresponding to the converter mechanism 516, which is the relatively left support point of the rack bar 511. As described above, the input of the external force to the right front wheel 92 affects the portion 50b corresponding to the pinion shaft 513, which is the relatively right support point of the rack bar 511.

[0062] When the steering angle Sa is greater than the steering angle threshold value Ts2 (S305: Yes), the controller 10 determines that there is an abnormality in the rack bar 511 because the bending load on the support point of the rack bar 511, that is, the portion corresponding to the converter mechanism 516, is large. Then, the controller 10 sets an abnormality flag and executes abnormality processing as in step S214 (S306). The controller 10 may store an abnormality determination map M2 in which a third area A3, which is an abnormality determination area, is set, as shown in FIG. 9, for example. Regarding the portion of the rack bar 511 corresponding to the converter mechanism 516, unlike the rack gear 5B, the section modulus of the rack bar 511 is substantially the same throughout the circumference. Therefore, the controller 10 can determine the presence or absence of an abnormality according to the magnitude of the load L and the magnitude of the steering angle Sa regardless of the vehicle height stroke Ch or the vehicle height Hv.

[0063] (Effect of this embodiment) According to this embodiment, when an external force is input to tires 81 to 84 by climbing onto a curb or the like, the input tire is identified and the load on the input tire is calculated. The bending load applied to the rack bar 511 is affected by the longitudinal load L and the steering angle Sa. The greater the longitudinal load L, the greater the bending load applied to the rack bar 511. Also, the greater the extension of the rack bar 511 with respect to the input tire, the greater the moment length, and the greater the bending load applied to the rack bar 511. The extension of the rack bar 511 corresponds to the steering angle Sa. The controller 10 determines the presence or absence of an abnormality in the rack bar 511 based on the load L and the steering angle Sa. Thus, according to this embodiment, an abnormality in the rack bar 511 due to the bending load can be detected. In particular, since the steering system 1 of this embodiment is a steer-by-wire type steering system, it is difficult for the driver to detect an abnormality in the rack bar 511. However, according to this embodiment, an abnormality in the rack bar 511 can be detected.

[0064] In this embodiment, the controller 10 determines the presence or absence of an abnormality in the rack bar 511 based on vehicle height information as well. In this embodiment, a rack bar 511 having a rack gear 5B that meshes with a pinion gear 5A is adopted as the steering shaft. The controller 10 is configured to acquire information on the vehicle height of the vehicle. The controller 10 is configured to determine the presence or absence of an abnormality in the rack bar 511 based on the load L, the steering angle Sa, and the vehicle height stroke Ch in the abnormality determination process S104.

[0065] The influence that the rack bar 511 receives due to the bending load varies depending on the tie rod inclination angle Ra and the extension of the rack bar 511. The magnitude of the tie rod inclination angle Ra affects the direction of the load applied to the rack bar 511, and since the extension of the rack bar 511 corresponds to the moment length, it affects the magnitude of the load applied to the rack bar 511. Also, since a rack gear 5B is formed on the rack bar 511, the strength against the bending load, that is, the section modulus, varies in the circumferential direction of the rack bar 511.

[0066] The vehicle height stroke Ch corresponds to the tie rod inclination angle Ra, and the tie rod inclination angle Ra corresponds to the direction of the load. Also, the steering angle Sa corresponds to the stroke of the rack bar 511. Therefore, based on the vehicle height stroke Ch (or vehicle height Hv) and the steering angle Sa when an external force is applied, the direction and magnitude of the load applied to the rack bar 511 can be calculated. Thus, according to the present embodiment, it is possible to accurately detect an abnormality of the rack bar 511 due to a load being applied to the rack bar 511 in the bending direction, taking into account the section modulus of the rack gear 5B. According to the present embodiment, by estimating the direction of the load and determining whether a load is applied to the rack gear 5B, it is possible to more accurately determine the presence or absence of an abnormality of the rack bar 511.

[0067] Also, in the load calculation process S103, the assumed vehicle weight W is set in consideration of the weight of the occupant using the detection result of the seat sensor 27. The steering system 1 includes seat sensors 27 arranged on one or more seats for detecting the presence or absence of an occupant. The controller 10 calculates the load L based on the longitudinal acceleration Gf, deceleration Gd, and assumed vehicle weight W in the load calculation process S103. The controller 10 sets the assumed vehicle weight W to a value obtained by adding the weight of the occupant based on the detection result of the seat sensor 27. Thereby, the load L corresponding to the occupancy state can be calculated.

[0068] (Others) The present invention is not limited to the above-described embodiment. For example, the present invention can be applied not only to a steer-by-wire type steering system but also to a system in which the steering actuator 510 and the operating device 52 are mechanically connected, such as a power steering type steering system. The present invention can also be applied to a steering system 1 in which, for example, the steering wheel 521 and the pinion shaft 513 are mechanically connected. In this case, for example, a pinion assist motor is connected to the pinion shaft 513. In this case, the pinion assist motor corresponds to the "steering motor", and the pinion shaft 513 corresponds to the "conversion mechanism".

[0069] Further, the steering shaft may be not only the rack bar 511 but also a ball nut type shaft member. In this case, the conversion mechanism becomes a ball nut mechanism. Also, one or more electric motors that apply a driving force to the steering shaft may be composed of, for example, any one or more of a rack assist motor, a pinion assist motor, and a column assist motor. The conversion mechanism may be configured to correspond to the steering motor, and as a result, any mechanism that transmits the driving force of the steering motor to the steering shaft may be used. Further, the present invention can also be applied to an autonomous vehicle.

[0070] Also, the steering actuator 510 may be a so-called dual pinion assist type device that moves the rack bar 511 with two rack and pinion mechanisms. That is, two pinion shafts 513 may be arranged on the left and right sides of the rack bar 511, and a pinion assist motor that rotates the pinion shaft 513 may be provided on each pinion shaft 513. Further, in other words, the steering actuator 510 includes two rack and pinion mechanisms (conversion mechanisms) spaced apart on the left and right and two pinion assist motors (steering motors). In this case, regardless of whether the input tire corresponds to either the right front wheel 92 or the left front wheel 91, the support point becomes one of the pinion shafts 513, and a load may be applied toward the rack gear 5B. In this case, the controller 10 may determine the presence or absence of an abnormality, for example, by an abnormality determination map M3 in which abnormality determination areas A4 and A5 are also set in the second and third quadrants as shown in FIG. 11.

[0071] Also, when the external force input to the left steering shaft affects the support point on the relatively right side, as shown in FIG. 11, abnormality determination areas may be set not only in the first and fourth quadrants but also in the second and third quadrants. Similarly, when the external force input to the right steering shaft affects the support point on the relatively left side, abnormality determination areas may be set not only in the second and third quadrants but also in the first and fourth quadrants.

[0072] Further, the abnormality determination maps M1 and M2 may be set for each load L, for example, for each of a plurality of ranks related to the load L set within a predetermined range. For example, in the controller 10, the range of the first load rank may be set as load threshold < load L ≦ L1, the second load rank may be set as L1 < L ≦ L2, and the third load rank may be set as L2 < L. In this case, the controller 10 may store an abnormality determination map when the load L is within the range of the first load rank, an abnormality determination map when the load L is within the range of the second load rank, and an abnormality determination map when the load L is within the range of the third load rank. According to this, for example, even if the stroke of the steering shaft (for example, the rack bar 511) is small, when the load L is extremely large, it can be set to determine that there is an abnormality in the steering shaft. That is, it becomes possible to perform abnormality determination according to the load L.

[0073] Further, a plurality of abnormality determination maps may be set so as to correspond to the magnitude of the section modulus of the steering shaft. For example, the controller 10 may store an abnormality determination map when a load is applied toward a portion where the section modulus is relatively small and an abnormality determination map when a load is applied toward a portion where the section modulus is relatively large. The abnormality determination map may be set according to the direction of the load. In this case, the controller 10 specifies the direction of the load based on the vehicle height information, selects an abnormality determination map according to the direction of the load, and determines the presence or absence of an abnormality. Also, in the present disclosure, "load" can be replaced with "force".

[0074] Note that the steering system 1 of the present disclosure can be rephrased as follows. That is, as shown in FIG. 10, the steering system 1 includes an input determination unit 111 that determines the presence or absence of an external force input to the vehicle based on information on the longitudinal acceleration Gf, and when there is an external force input, based on information on the air pressure of each tire, a position identification unit 112 that identifies an input tire, which is a tire to which the external force is input among the plurality of tires 81 to 84, and when the input tire is one of the steered wheels 91 and 92, a load calculation unit 113 that calculates the deceleration Gd of the vehicle or obtains information on the deceleration Gd, and calculates the load L received by the input tire due to the external force based on the difference between the longitudinal acceleration Gf and the deceleration Gd, and an abnormality determination unit 114 that determines the presence or absence of an abnormality in the steering shaft of the steering device 51 based on the load L and the steering angle Sa. The abnormality determination unit 114 determines the presence or absence of an abnormality in the rack bar 511 based on the load L, the steering angle Sa, and the vehicle height stroke Ch. The abnormality determination unit 114 determines that there is an abnormality in the rack bar 511 when the load L is greater than the load threshold value Tl, the steering angle Sa is within the first predetermined range, and the vehicle height stroke Ch or the vehicle height Hv is within the second predetermined range during a predetermined period after the external force is input (that is, within the determination target period). The load calculation unit 113 calculates the load L based on the longitudinal acceleration Gf, the deceleration Gd, and the assumed vehicle weight W, and sets the assumed vehicle weight W to a value obtained by adding the weight of the occupant based on the detection result of the seat sensor 27.

[0075] Also, the technology of the present disclosure can be described as follows. The controller 10 of the present disclosure includes one or more processors 10a and is configured to acquire information on the longitudinal acceleration Gf, which is the acceleration in the longitudinal direction of the vehicle, information on the air pressure of each tire of the vehicle, information on the deceleration Gd generated by braking of the vehicle, and information on the steering angle Sa of the steered wheels 91 and 92 of the vehicle. This controller 10 is configured to execute the input determination process S101, the position identification process S102, the load calculation process S103, and the abnormality determination process S104 as described above.

Explanation of Reference Numerals

[0076] 1… Steering system, 10… Controller, 10a… Processor, 21… Acceleration sensor, 22… Pneumatic sensor, 23… Vehicle height sensor, 25… Steering angle sensor, 27… Seat sensor, 510… Steering actuator, 511… Rack bar (steering shaft), 513… Pinion shaft, 515… Steering motor, 516… Conversion mechanism, 521… Steering wheel (operating member), 5A… Pinion gear, 5B… Rack gear.

Claims

1. A steering actuator that has a steering shaft, a steering motor that applies a driving force to the steering shaft, and a conversion mechanism that converts the rotation of the steering motor into axial movement of the steering shaft, and steers a steering wheel, A steering angle sensor that detects the steering angle of the steering wheel, An acceleration sensor that detects the longitudinal acceleration, which is the acceleration in the longitudinal direction of the vehicle, An air pressure sensor that detects the air pressure of each tire, A vehicle height sensor that detects the vehicle height stroke or the vehicle height of the vehicle, A controller having one or more processors, configured to acquire information on the steering angle, information on the longitudinal acceleration, information on the air pressure, and the detection result of the vehicle height sensor, A steer-by-wire type steering system including the above, in which the steering actuator and an operating member for a driver's steering operation are not mechanically connected, The steering shaft is a rack bar having a rack gear that meshes with a pinion gear, The controller, An input determination process for determining the presence or absence of an external force input to the vehicle based on the longitudinal acceleration, When there is an input of the external force, a position identification process for identifying an input tire, which is the tire among the plurality of tires to which the external force is input, based on the air pressure of each tire, When the input tire is the tire of the steering wheel, calculate the deceleration of the vehicle or obtain information on the deceleration, and calculate the load received by the input tire due to the external force based on the difference between the longitudinal acceleration and the deceleration, An abnormality determination process for determining the presence or absence of an abnormality of the steering shaft based on the load, the steering angle, and the detection result of the vehicle height sensor, Is configured to execute, In the abnormality determination process, when the load is greater than the load threshold value and the steering angle is within a first predetermined range and the vehicle height stroke or the vehicle height is within a second predetermined range from when the external force is input until a predetermined period elapses, the controller determines that there is an abnormality in the rack bar. Steering system.

2. Comprising a seat sensor arranged on one or more seats for detecting the presence or absence of an occupant. In the load calculation process, the controller calculates the load based on the longitudinal acceleration, the deceleration, and the assumed vehicle weight. The controller sets the assumed vehicle weight to a value obtained by adding the weight of the occupant based on the detection result of the seat sensor. The steering system according to claim 1.

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