JP7537487B2 - Neutral steering angle determination device, neutral steering angle determination method and program - Google Patents

Description

The present invention relates to a neutral steering angle determination device, a neutral steering angle determination method, and a program for determining a neutral steering angle at which the direction of the vehicle's wheels is parallel to the vehicle's traveling direction.

Technology is known that determines the neutral steering angle at which the direction of the vehicle's wheels is parallel to the vehicle's traveling direction. Patent Document 1 discloses a technology that learns the neutral steering angle by statistically processing the detection value of a sensor that detects the angle of the steering wheel when the vehicle is traveling straight and the steering wheel is not being steered.

JP 2017-105277 A

However, because actual roads have curves and cross slopes, the vehicle may not maintain a driving state in which it is moving straight and the steering wheel is not being turned. As a result, the number of detection values required for statistical processing may not be obtained, and learning of the neutral steering angle may not be completed.

Therefore, the present invention was made in consideration of these points, and aims to determine the neutral steering angle regardless of the steering state of the vehicle.

In a first aspect of the present invention, a neutral steering angle determination device is provided that includes a first acquisition unit that acquires a lateral acceleration applied in a vehicle width direction perpendicular to the traveling direction of the vehicle, a second acquisition unit that acquires the vehicle speed of the vehicle, a third acquisition unit that acquires the yaw rate of the vehicle, a fourth acquisition unit that acquires the steering angle of the vehicle, a first term represented by the product of the lateral acceleration and a first coefficient, a second term represented by the product of a ratio of the yaw rate to the vehicle speed and a second coefficient, and a third term represented by a third coefficient indicating an offset amount from a neutral steering angle at which the direction of the wheels of the vehicle is parallel to the traveling direction, and a first determination unit that determines the first coefficient, the second coefficient, and the third coefficient based on a function value of a model function representing the steering angle and the steering angle acquired by the third acquisition unit, and a second determination unit that determines the neutral steering angle according to the third coefficient determined by the first determination unit.

The first determination unit may determine the first coefficient, the second coefficient, and the third coefficient that minimize the sum of squares of the difference between the function value of the model function and the steering angle acquired by the third acquisition unit.

The first determination unit may determine the first coefficient, the second coefficient, and the third coefficient if the vehicle speed of the vehicle acquired by the second acquisition unit is equal to or greater than a threshold value.

The first determination unit may not determine the first coefficient, the second coefficient, and the third coefficient if the vehicle speed of the vehicle acquired by the second acquisition unit is less than the threshold value.

The first determination unit may determine the first coefficient, the second coefficient, and the third coefficient if the vehicle speed is equal to or greater than a threshold at which the lateral acceleration occurs in the vehicle, and the turning curvature of the vehicle, which is the ratio of the yaw rate to the vehicle speed, is equal to or greater than a lower limit curvature at which the road on which the vehicle is traveling is determined to be a curve and is equal to or less than an upper limit curvature at which the vehicle can turn.

The first determination unit may determine each coefficient using a recursive least squares method based on the newly acquired lateral acceleration, vehicle speed, yaw rate, and steering angle, and the most recently acquired lateral acceleration, vehicle speed, yaw rate, and steering angle.

The first determination unit may determine each coefficient by using the steering angle obtained when the orientation of the vehicle and the traveling direction are parallel as an initial value of the third coefficient in the recursive least squares method.

The first determination unit may determine each coefficient using the steering angle acquired when the vehicle is steered so that the orientation of the vehicle is parallel to the traveling direction when no goods are loaded on the vehicle as the initial value.

In a second aspect of the present invention, a neutral steering angle determination method is provided, which includes a step of acquiring a lateral acceleration applied in a vehicle width direction perpendicular to the traveling direction of the vehicle, a step of acquiring the vehicle speed of the vehicle, a step of acquiring the yaw rate of the vehicle, a step of acquiring a steering angle of the vehicle, and a first term expressed by the product of the lateral acceleration and a first coefficient, a second term expressed by the product of a ratio of the yaw rate to the vehicle speed and a second coefficient, and a third term expressed only by a third coefficient indicating an offset amount from a neutral steering angle at which the direction of the wheels of the vehicle is parallel to the traveling direction, and includes a step of determining the first coefficient, the second coefficient, and the third coefficient based on a function value of a model function representing the steering angle and the acquired steering angle, and a step of determining the neutral steering angle according to the determined third coefficient.

In a third aspect of the present invention, a program is provided that causes a processor mounted on a vehicle to function as a first acquisition unit that acquires a lateral acceleration applied in a vehicle width direction perpendicular to the traveling direction of the vehicle, a second acquisition unit that acquires the vehicle speed of the vehicle, a third acquisition unit that acquires the yaw rate of the vehicle, a fourth acquisition unit that acquires the steering angle of the vehicle, a first term represented by the product of the lateral acceleration and a first coefficient, a second term represented by the product of a ratio of the yaw rate to the vehicle speed and a second coefficient, and a third term represented by a third coefficient indicating an offset amount from a neutral steering angle at which the direction of the wheels of the vehicle is parallel to the traveling direction, and a first determination unit that determines the first coefficient, the second coefficient, and the third coefficient based on a function value of a model function representing the steering angle and the steering angle acquired by the third acquisition unit, and a second determination unit that determines the neutral steering angle according to the third coefficient determined by the first determination unit.

In a fourth aspect of the present invention, a neutral steering angle determination device is provided that has a first acquisition unit that acquires a lateral acceleration applied in the vehicle width direction of the vehicle detected by an acceleration sensor, a second acquisition unit that acquires a vehicle speed of the vehicle detected by a vehicle speed sensor, a third acquisition unit that acquires a yaw rate of the vehicle detected by a yaw rate sensor, a fourth acquisition unit that acquires a steering angle of the vehicle detected by a steering angle sensor, and a determination unit that determines a neutral steering angle, which is the steering angle at which the direction of the wheels of the vehicle is parallel to the traveling direction of the vehicle, based on the lateral acceleration, the vehicle speed of the vehicle, the yaw rate of the vehicle, and the steering angle of the vehicle.

The determination unit may include a first term corresponding to the lateral acceleration, a second term corresponding to a ratio of the yaw rate to the vehicle speed, and a third term corresponding to an offset amount from a neutral steering angle at which the orientation of the vehicle's wheels is parallel to the traveling direction, and may determine the neutral steering angle based on a function value of a model function representing the steering angle and the steering angle acquired by the fourth acquisition unit.

The determination unit may determine the value of the third term so that the degree of agreement between the function value of the model function and the steering angle acquired by the fourth acquisition unit is high, and may determine the neutral steering angle according to the determined third term.

The determination unit may determine the neutral steering angle when the vehicle speed is equal to or greater than a threshold value, and may not determine the neutral steering angle when the vehicle speed is less than the threshold value.

The determination unit may determine the neutral steering angle when the vehicle speed is equal to or greater than a threshold at which the lateral acceleration occurs in the vehicle and the turning curvature of the vehicle is within a predetermined range.

The present invention has the advantage that the neutral steering angle can be determined regardless of the steering state of the vehicle.

FIG. 2 is a diagram for explaining a configuration of a neutral steering angle determination device. FIG. 4 is a schematic diagram showing the steering wheel in a reference position. FIG. 4 is a schematic diagram showing the direction of wheels when the steering wheel is in a reference position. FIG. 13 is a diagram showing a state where the steering wheel is in an offset position displaced by an offset amount from a reference position. FIG. 2 is a schematic diagram of the orientation of the wheels when the steering wheel is in an offset position. FIG. 13 is a plot of the change in the determined neutral steering angle over time. 5 is a flowchart showing an example of a process for determining a neutral steering angle.

[Configuration of neutral steering angle determination device 1 according to the embodiment]
1 is a diagram for explaining the configuration of a neutral steering angle determination device 1. The neutral steering angle determination device 1 is mounted on a host vehicle 2. The host vehicle 2 is an autonomous vehicle. The host vehicle 2 determines the speed and steering angle of the host vehicle 2 so that the host vehicle 2 heads toward a target point set by a user or manager of the host vehicle 2, and drives the host vehicle 2. The host vehicle 2 is mounted with an acceleration sensor 3, a vehicle speed sensor 4, a yaw rate sensor 5, and a steering angle sensor 6.

The acceleration sensor 3 is a sensor that detects the acceleration applied to the host vehicle 2. The acceleration sensor 3 detects the lateral acceleration applied in the vehicle width direction perpendicular to the traveling direction. The acceleration sensor 3 may also detect the longitudinal acceleration applied in the traveling direction of the host vehicle 2. The acceleration sensor 3 may be any type of sensor, such as a frequency change type, a piezoelectric type, a piezo-resistance type, or a capacitance type.

The vehicle speed sensor 4 is a sensor that detects the vehicle speed of the host vehicle 2. The vehicle speed sensor 4 detects the vehicle speed of the host vehicle 2 according to the value obtained by multiplying the number of rotations of the wheel per unit time by the circumference of the wheel, for example. The vehicle speed sensor 4 may also detect the vehicle speed of the host vehicle 2 based on the number of rotations of the engine mounted on the host vehicle 2, the current gear position, and the circumference of the wheels of the host vehicle 2.

The yaw rate sensor 5 is a sensor that detects the yaw rate of the host vehicle 2. The yaw rate sensor 5 detects the yaw rate, which is the speed at which the rotational motion of the host vehicle 2 changes around the traveling direction while the host vehicle 2 is traveling.

The steering angle sensor 6 is a sensor that detects the steering angle of the host vehicle 2. For example, the steering angle sensor 6 is attached so that it detects 0 when the steering wheel of the host vehicle 2 is in the reference position and the direction of the wheels of the host vehicle 2 is parallel to the traveling direction X. However, the detection value of the steering angle sensor 6 may not be 0 even when the steering wheel is in the reference position due to the position and angle at which the steering angle sensor 6 is attached, manufacturing errors, etc. In addition, if the host vehicle 2 is an axle-suspended type, the direction of the wheels of the host vehicle 2 changes depending on the total weight of the items carried by the host vehicle 2, so even if the steering angle detected by the steering angle sensor 6 is 0, it may not be parallel to the traveling direction of the host vehicle 2. A case in which the direction of the wheels is not parallel to the traveling direction of the host vehicle 2 will be described using Figures 2 and 3.

Fig. 2 is a schematic diagram when the steering wheel 7 is at a reference position K. Fig. 3 is a schematic diagram showing the direction W of the wheels 8 when the steering wheel 7 is at the reference position K. As shown in Fig. 3, the direction W of the wheels 8 is not parallel to the traveling direction X of the host vehicle 2. The angle between the direction W of the wheels 8 and the traveling direction X is called an offset amount δ _offset , which represents the amount of deviation of the direction W of the wheels 8 from the traveling direction X.

If the vehicle 2 is steered without knowing the offset amount δ _offset , there is a risk that the vehicle will not be able to move to the set target point, or that an excessively large or small steering angle will be set. Therefore, the neutral steering angle determination device 1 determines the angle of the steering wheel 7 when the traveling direction X of the vehicle 2 and the direction W of the wheels 8 of the vehicle 2 are parallel to each other (hereinafter referred to as "neutral steering angle δ ₀ "). The configuration of the neutral steering angle determination device 1 will be described in detail below.

The neutral steering angle determination device 1 has a memory unit 11 and a control unit 12. The memory unit 11 is a storage medium including a ROM (Read Only Memory), a RAM (Random Access Memory), a hard disk, etc. The memory unit 11 stores a program executed by the control unit 12.

The control unit 12 is a computational resource including a processor such as a CPU (Central Processing Unit). The control unit 12 executes the programs stored in the storage unit 11 to realize the functions of a lateral acceleration acquisition unit 121, a vehicle speed acquisition unit 122, a yaw rate acquisition unit 123, a steering angle acquisition unit 124, a coefficient determination unit 125, and a neutral steering angle determination unit 126.

The lateral acceleration acquisition unit 121 is a first acquisition unit that acquires the lateral acceleration detected by the acceleration sensor 3. The vehicle speed acquisition unit 122 is a second acquisition unit that acquires the vehicle speed detected by the vehicle speed sensor 4. The vehicle speed acquisition unit 122 may acquire the vehicle speed of the host vehicle 2 by integrating the vertical acceleration detected by the acceleration sensor 3 over time. The yaw rate acquisition unit 123 is a third acquisition unit that acquires the yaw rate detected by the yaw rate sensor 5. The steering angle acquisition unit 124 is a fourth acquisition unit that acquires the steering angle detected by the steering angle sensor 6.

The coefficient determination unit 125 and the neutral steering angle determination unit 126 determine the neutral steering angle based on the lateral acceleration, the vehicle speed, the yaw rate, and the steering angle. The detailed process of determining the neutral steering angle is described below. Note that, for the sake of simplicity, the coefficient determination unit 125 and the neutral steering angle determination unit 126 are treated as separate determination units, but it is also possible to execute the processing of the coefficient determination unit 125 and the neutral steering angle determination unit 126 as a single determination unit.

The coefficient determination unit 125 is a first determination unit that determines the offset amount δ _offset by determining a coefficient of a model function that represents the steering angle. For example, the model function is a function that represents the steering angle using the lateral acceleration, the vehicle speed, and the yaw rate, and includes the offset amount δ _offset as a coefficient. The coefficient determination unit 125 determines the offset amount δ offset, which is one of the coefficients of the model function, based on the steering angle represented by the model function using the acquired lateral acceleration, the vehicle speed, and the yaw rate, and the steering angle detected by the steering angle sensor 6. Specifically, the coefficient determination unit 125 determines the offset amount δ _offset , which is one of the coefficients of the model function, so that the difference between the steering angle represented by the model function and the steering angle acquired by the steering angle acquisition unit 124 becomes small. In other words, the coefficient determination unit 125 determines the _offset amount δ _offset by determining a coefficient of a model function that represents the steering angle, including the lateral acceleration, the vehicle speed, and the yaw rate. Hereinafter, a method in which the coefficient determination unit 125 determines the offset amount δ _offset by determining the coefficient of the model function will be described.

式（１）のｌは、自車両２の前輪軸と後輪軸との距離を表すホイールベースである。Ｃ_ｆは前輪等価コーナリング係数を示す。コーナリング係数は、車輪８のコーナリングフォースを横滑り角と接地重量に対する係数とした値である。コーナリングフォースは、車輪８が道路と接触する箇所において進行方向Ｘに直交する車幅方向に発生する力である。Ｃ_ｒは後輪等価コーナリング係数である。Ｖは自車両２の車速である。ρは自車両２が走行中の道路の曲率又は走行中の軌道の曲率である。gは重力加速度である。θは自車両２が走行中の道路の横断勾配である。 First, a model showing a steering angle δ in a steady state where the host vehicle 2 travels at a constant speed and steering angle will be described. The steering angle δ in the steady state is expressed by the following equation (1) using a two-wheel model (equation of motion).

In formula (1), l is the wheelbase representing the distance between the front and rear wheel axles of the vehicle 2. _{C f} is the front wheel equivalent cornering coefficient. The cornering coefficient is a value obtained by taking the cornering force of the wheel 8 as a coefficient for the sideslip angle and the ground contact weight. The cornering force is a force generated in the vehicle width direction perpendicular to the traveling direction X at the point where the wheel 8 contacts the road. _{C r} is the rear wheel equivalent cornering coefficient. V is the vehicle speed of the vehicle 2. ρ is the curvature of the road on which the vehicle 2 is traveling or the curvature of the trajectory during traveling. g is the gravitational acceleration. θ is the transverse gradient of the road on which the vehicle 2 is traveling.

式（２）の第1項の（ρＶ^２＋ｇθ）は、横加速度に相当する。式（２）の第２項のρは、自車両２の旋回曲率であり、旋回曲率は車速Ｖに対するヨーレートの割合（ヨーレート／車速Ｖ）である。 When the function expressed by the formula (1) is transformed into a form that enables parameter estimation by the least squares method, the formula (1) is expressed by the following formula (2).

The first term ( ^ρV2 + gθ) in equation (2) corresponds to the lateral acceleration. The second term ρ in equation (2) is the turning curvature of the host vehicle 2, which is the ratio of the yaw rate to the vehicle speed V (yaw rate/vehicle speed V).

If the first term (1/ _Cf - 1/ _Cr ) in equation (2) is represented by the first coefficient _a1 , the lateral acceleration equivalent ( ^ρV2 + gθ) is represented by the first variable _u1 , the l in the second term is represented by the second coefficient _a2 , the turning curvature ρ is represented by the second variable _u2 , and the δ _offset in the third term is represented by the third coefficient _a3 , the function represented by equation (1) can be expressed as the following equation (3) as a model function representing the steering angle δ.
y = a ₁ u ₁ + a ₂ u ₂ + a ₃ …(3)

As described above, the first term of the formula (3) is expressed by the product of the first coefficient _a1 and the first variable _u1 . The second term is expressed by the product of the second variable _u2 and the second coefficient _a2 . The third term is expressed only by the third coefficient _a3 indicating the offset amount δ _offset . The coefficient determination unit 125 determines the first coefficient _a1 , the second coefficient _a2 , and the third coefficient _a3 that minimize the sum of squares of the difference between the function value y of the model function having the first coefficient _a1 , the second coefficient _a2 , and the third coefficient _a3 as parameters and the acquired steering angle δ.

The coefficient determination unit 125 determines each coefficient while the host vehicle 2 is traveling. Specifically, the coefficient determination unit 125 determines each coefficient when the vehicle speed is equal to or greater than a threshold at which lateral acceleration occurs in the host vehicle 2 and the turning curvature ρ is within a predetermined range. The specific value of the threshold is 30 kilometers per hour, but is not limited to this. The predetermined range is equal to or greater than the lower limit curvature at which the road on which the host vehicle 2 is traveling is determined to be a curved road and equal to or less than the upper limit curvature at which the host vehicle 2 can turn. The specific value of the lower limit curvature is, for example, 1/2000 meters, and the specific value of the upper limit curvature is, for example, 1/100 meters. However, the specific values of the upper limit curvature and the lower limit curvature may be set appropriately and are not limited to this. As a result, the coefficient determination unit 125 can determine each coefficient of the model function that takes into account the lateral acceleration and the turning curvature while the host vehicle 2 is traveling on a curved road at a speed at which lateral acceleration occurs in the host vehicle 2.

When lateral acceleration is not generated, such as when driving at low speed, or when driving in a straight line, if the coefficients of the model function that takes lateral acceleration and turning curvature into consideration are determined, there is a risk that the coefficients will be determined incorrectly. Therefore, if the vehicle speed is less than the threshold value or the turning curvature ρ is outside a predetermined range, the coefficient determination unit 125 does not determine the coefficients of the model function that takes lateral acceleration and turning curvature into consideration. In other words, if the vehicle speed is less than the threshold value or the turning curvature ρ is outside a predetermined range, the coefficient determination unit 125 determines the coefficients of the model that do not take lateral acceleration and turning curvature into consideration.

上付きのかっこ内のｎは、データの時系列番号を示す。また、λは１である。式（４）及び（５）のハット付きθは、時刻ｎにおいて関数値yと操舵角δとの差の二乗和を最小化する各係数の最適解である。係数決定部１２５は、横加速度、車速、ヨーレート及び操舵角δが新たに取得される毎に、式（４）及び（５）を用いて各係数を決定する。 The coefficient determination unit 125 determines each coefficient using the recursive least squares method based on the newly acquired lateral acceleration, vehicle speed, yaw rate, and steering angle δ and the most recently acquired lateral acceleration, vehicle speed, yaw rate, and steering angle δ. Specifically, the coefficient determination unit 125 determines each coefficient using the following equations (4) and (5).

The n in the superscript parentheses indicates the time series number of the data. Also, λ is 1. The hatched θ in the formulas (4) and (5) is the optimal solution of each coefficient that minimizes the sum of squares of the difference between the function value y and the steering angle δ at time n. The coefficient determination unit 125 determines each coefficient using the formulas (4) and (5) every time the lateral acceleration, the vehicle speed, the yaw rate, and the steering angle δ are newly acquired.

The coefficient determination unit 125 may determine each coefficient by setting the steering angle δ acquired when the direction W of the wheels 8 and the traveling direction X are parallel to each other as the initial value of the third coefficient _a3 . Specifically, the coefficient determination unit 125 determines each coefficient by setting the steering angle δ acquired when the steering wheel 7 is steered so that the direction W of the wheels 8 and the traveling direction X are parallel to each other in a state where no articles are loaded on the host vehicle 2 as the initial value of the third coefficient _a3 . More specifically, the coefficient determination unit 125 determines each coefficient by setting the steering angle δ acquired when the host vehicle 2 is stopped so that the direction W of the wheels 8 and the traveling direction X are parallel to each other at the time of shipment, maintenance, or inspection of the host vehicle 2 as the initial value of the third coefficient _a3 . The initial value of the third coefficient _a3 is determined by an experiment or the like and stored in the storage unit 11.

In this way, the coefficient determination unit 125 can determine each coefficient by setting a value close to the actual offset amount δ _offset as the initial value, and therefore the time until the coefficients converge can be shortened compared to the case where this is not the case. Also, the coefficient determination unit 125 may determine each coefficient by setting the value of the wheelbase l stored in the storage unit 11 as the initial value of the second coefficient _a2 .

The offset amount δ _offset may be determined by a method different from the method of determining the coefficient when the sum of squares of the difference between the steering angle represented by the above-mentioned model function and the steering angle acquired by the steering angle acquisition unit 124 is minimum as the offset amount δ _offset . For example, the coefficient determination unit 125 determines the coefficient when the difference between the steering angle represented by the above-mentioned model function and the steering angle acquired by the steering angle acquisition unit 124 is equal to or less than a threshold value as the offset amount δ _offset . The coefficient determination unit 125 may also determine the coefficient when the ratio between the steering angle represented by the above-mentioned model function and the steering angle acquired by the steering angle acquisition unit 124 is within a predetermined range as the offset amount δ _offset . The predetermined range is a range including 1, and is, for example, a range equal to or greater than a value obtained by subtracting a predetermined value from 1 and equal to or less than a value obtained by adding a predetermined value to 1. The coefficient determination unit 125 may determine the coefficient by which the steering angle represented by the model function has a higher degree of agreement with the steering angle acquired by the steering angle acquisition unit 124 as the offset amount δ _offset .

The neutral steering angle determination unit 126 is a second determination unit that determines the neutral steering angle δ ₀ according to the third coefficient a _3. For example, the neutral steering angle determination unit 126 sets the third coefficient a ₃ determined by the coefficient determination unit 125 to the neutral steering angle δ _0. FIG. 4 is a diagram showing the steering wheel 7 at an offset position M that is shifted from the reference position K by an offset amount δ _offset . FIG. 5 is a schematic diagram showing the direction W of the wheels 8 when the steering wheel 7 is at the offset position M. As shown in FIG. 5, when the steering wheel 7 is at the offset position M, the direction W of the wheels 8 and the traveling direction X are parallel to each other.

FIG. 6 is a diagram plotting the time change of the determined neutral steering angle δ _0. The horizontal axis of FIG. 6 indicates time t, and the vertical axis indicates the determined neutral steering angle δ _0. Time T0 is the time when the host vehicle 2 starts traveling. The host vehicle 2 traveled on a curved road from time T0 to time T2. After time T2, the host vehicle 2 traveled on a straight road. Note that the road on which the host vehicle 2 travels has a transverse gradient of a predetermined angle.

A solid line 9 is a graph showing a time change of the neutral steering angle δ ₀ determined by the neutral steering angle determination unit 126 of the neutral steering angle determination device 1 according to the embodiment. The neutral steering angle determination unit 126 started the process of determining the neutral steering angle δ ₀ from time T0. The neutral steering angle determination unit 126 sequentially determined the neutral steering angle δ ₀ by using the recursive least squares method even while the host vehicle 2 was traveling on a curved road. The neutral steering angle δ ₀ determined by the neutral steering angle determination unit 126 converged to the first neutral steering angle δ 1 at time T1.

The dashed line 10 is a graph showing the time change of the neutral steering angle δ ₀ determined by the device according to the comparative example. Unlike the neutral steering angle determination device 1, the device according to the comparative example cannot determine the neutral steering angle unless the steering wheel is not steered while the comparative vehicle equipped with the device according to the comparative example is moving straight. Therefore, the device according to the comparative example cannot execute the process of determining the neutral steering angle δ ₀ before the time T2 when the comparative vehicle starts moving straight. The device according to the comparative example determined the neutral steering angle δ ₀ after the time T3 when the number of steering angles δ that can be statistically processed has been acquired after the time T2. The neutral steering angle δ ₀ determined by the device according to the comparative example converged to the second neutral steering angle δ 2, which has a larger absolute value than the first neutral steering angle δ 1, due to the influence of the cross gradient of the road. In this way, the coefficient determination unit 125 of the neutral steering angle determination device 1 according to the embodiment can determine a more appropriate neutral steering angle δ ₀ at an earlier time than the time when the device according to the comparative example determines the neutral steering angle δ ₀ .

(Modification)
The processing of the coefficient determination unit 125 and the neutral steering angle determination unit 126 may be performed by one determination unit. In this case, the one determination unit determines the neutral steering angle based on the lateral acceleration detected by the acceleration sensor 3, the vehicle speed detected by the vehicle speed sensor 4, the yaw rate detected by the yaw rate sensor 5, and the steering angle detected by the steering angle sensor 6. Specifically, the one determination unit first executes the processing executed by the coefficient determination unit 125 to determine the third coefficient _a3 of the model function. Next, the one determination unit determines the neutral steering angle _δ0 according to the third coefficient _a3 .

[Processing Executed by Neutral Steering Angle Determination Device 1]
Fig. 7 is a flowchart showing an example of a process for determining the neutral steering angle δ _0. The process according to the flowchart in Fig. 7 is executed at a predetermined interval while the host vehicle 2 is traveling. The predetermined interval is, for example, a processing cycle of the control unit 12, and a specific value is 100 milliseconds. It is assumed that the yaw rate, the vehicle speed, the lateral acceleration, and the steering angle δ are detected.

The coefficient determination unit 125 determines whether the acquired yaw rate is within a predetermined range (step S1). Specifically, the coefficient determination unit 125 determines whether the yaw rate is equal to or greater than the lower limit curvature and equal to or less than the upper limit curvature. If the yaw rate is less than the lower limit curvature or greater than the upper limit curvature (No in step S1), the coefficient determination unit 125 repeats step S1 until the yaw rate is equal to or greater than the lower limit curvature and equal to or less than the upper limit curvature.

If the yaw rate is within a predetermined range (Yes in step S1), the coefficient determination unit 125 determines whether the vehicle speed is equal to or greater than a threshold (step S2). If the vehicle speed is less than the threshold (No in step S2), the coefficient determination unit 125 repeats steps S1 and S2 until the vehicle speed is equal to or greater than the threshold. Note that the coefficient determination unit 125 may execute step S2 before step S1, or may execute steps S1 and S2 in parallel.

If the yaw rate is within a predetermined range and the vehicle speed is equal to or greater than the threshold (Yes in step S2), the coefficient determination unit 125 determines each coefficient of the model function expressed by equation (3) (step S3). Specifically, the coefficient determination unit 125 determines the first coefficient _a1 , the second coefficient _a2 , and the third coefficient _a3 that minimize the sum of squares of the difference between the function value y of the model function having the first coefficient _a1 , the second coefficient _a2 , and the third coefficient _a3 as parameters and the acquired steering angle δ.

The neutral steering angle determination unit 126 determines the neutral steering angle _δ0 in accordance with the third coefficient _a3 determined by the coefficient determination unit 125. Specifically, the neutral steering angle determination unit 126 determines the neutral steering angle δ0 shifted from the zero point by the _offset amount δoffset, taking the third coefficient _a3 as the offset amount _δoffset from the _zero point of the steering angle sensor (step S4).

[Effects of the neutral steering angle determination device 1]
As described above, the neutral steering angle determination device 1 determines the neutral steering angle by using the difference between the actual steering angle and a model function that uses the lateral acceleration as a parameter. The neutral steering angle determination device 1 determines the first, second and _third coefficients that minimize the sum of squares of the difference between the function value of the model function that represents the steering angle δ, which includes the first term expressed by the product of the first coefficient _a1 and the lateral acceleration, the second term expressed by the product of the ratio of the yaw rate to the vehicle speed (turning curvature ρ) and the second coefficient _a2 , and the third term expressed only by the third coefficient that indicates the offset amount from the neutral steering angle δ0 at which the direction of the wheels 8 of the vehicle 2 is parallel to the traveling direction X, and the steering angle δ detected by the steering angle sensor.

As a result, the neutral steering angle determination device 1 can determine the neutral steering angle δ ₀ even when the vehicle 2 is traveling on a curved road or a road with a cross gradient. In other words, the neutral steering angle determination device 1 can determine the neutral steering angle δ ₀ regardless of the steering state of the vehicle. As a result, the neutral steering angle determination device 1 can determine the neutral steering angle δ _{0 earlier than a device that determines the neutral steering angle δ 0 only} when the steering wheel 7 is not operated while traveling straight, and can determine an appropriate neutral steering angle δ _0. Such a special effect is realized by using, as a parameter, the lateral acceleration that changes depending on the state of the road on which the vehicle 2 is traveling, i.e., whether the road is a curved road or has a cross gradient. Furthermore, the neutral steering angle determination device 1 according to the embodiment can further improve the accuracy by determining the neutral steering angle according to a third coefficient that minimizes the square sum of the difference between the function value of the model function representing the steering angle δ and the steering angle δ detected by the steering angle sensor.

Although the present invention has been described above using embodiments, the technical scope of the present invention is not limited to the scope described in the above embodiments, and various modifications and changes are possible within the scope of the gist of the invention. For example, all or part of the device can be configured by distributing or integrating functionally or physically in any unit. In addition, new embodiments resulting from any combination of multiple embodiments are also included in the embodiments of the present invention. The effect of the new embodiment resulting from the combination also has the effect of the original embodiment.

REFERENCE SIGNS LIST 1 Neutral steering angle determination device 11 Memory unit 12 Control unit 121 Lateral acceleration acquisition unit 122 Vehicle speed acquisition unit 123 Yaw rate acquisition unit 124 Steering angle acquisition unit 125 Coefficient determination unit 126 Neutral steering angle determination unit 2 Vehicle 3 Acceleration sensor 4 Vehicle speed sensor 5 Yaw rate sensor 6 Steering angle sensor 7 Steering wheel 8 Wheels

Claims (9)

A first acquisition unit that acquires a lateral acceleration applied in a vehicle width direction perpendicular to a traveling direction of the vehicle;
A second acquisition unit that acquires a vehicle speed of the vehicle;
A third acquisition unit that acquires a yaw rate of the vehicle;
A fourth acquisition unit that acquires a steering angle of the vehicle;
a first determination unit which determines the first coefficient, the second coefficient, and the third coefficient by performing parameter estimation using a least squares method , the first coefficient, the second coefficient , and the third coefficient representing the steering angle and minimizing a sum of squares of a difference between a function value of a model function having the first coefficient, the second coefficient, and the third coefficient as parameters and the steering angle acquired by the fourth acquisition unit , the first coefficient, the second coefficient, and the third coefficient representing the steering angle and minimizing a sum of squares of a difference between a function value of a model function having the first coefficient, the second coefficient , and the third coefficient as parameters and the steering angle acquired by the fourth acquisition unit;
A second determination unit that determines the neutral steering angle in accordance with the third coefficient determined by the first determination unit;
A neutral steering angle determination device having the above structure. The first determination unit determines the first coefficient, the second coefficient, and the third coefficient when the vehicle speed of the vehicle acquired by the second acquisition unit is equal to or greater than a threshold value.
2. The neutral steering angle determining device according to claim 1. The first determination unit does not determine the first coefficient, the second coefficient, and the third coefficient when the vehicle speed of the vehicle acquired by the second acquisition unit is less than the threshold value.
3. The neutral steering angle determining device according to claim 2 . the first determination unit determines the first coefficient, the second coefficient, and the third coefficient when the vehicle speed is equal to or greater than a threshold at which the lateral acceleration occurs in the vehicle, and a turning curvature of the vehicle, which is a ratio of the yaw rate to the vehicle speed, is equal to or greater than a lower limit curvature at which a road on which the vehicle is traveling is determined to be a curve and is equal to or less than an upper limit curvature at which the vehicle can turn.
2. The neutral steering angle determining device according to claim 1. The first determination unit determines each coefficient by using a recursive least squares method based on the newly acquired lateral acceleration, the vehicle speed, the yaw rate, and the steering angle, and the most recently acquired lateral acceleration, the vehicle speed, the yaw rate, and the steering angle.
5. The neutral steering angle determining device according to claim 1. the first determination unit determines each coefficient by using the steering angle acquired when the orientation of the vehicle and the traveling direction are parallel as an initial value of the third coefficient in the recursive least squares method.
6. The neutral steering angle determining device according to claim 5 . the first determination unit determines each coefficient by using, as the initial value, the steering angle acquired when the vehicle is steered so that the orientation of the vehicle is parallel to the traveling direction in a state where no article is loaded on the vehicle.
7. The neutral steering angle determining device according to claim 6 . Executed by a processor installed in the vehicle,
acquiring a lateral acceleration applied in a vehicle width direction perpendicular to a traveling direction of the vehicle;
acquiring a vehicle speed of the vehicle;
obtaining a yaw rate of the vehicle;
obtaining a steering angle of the vehicle;
a step of determining, by performing parameter estimation using a least squares method, the first coefficient, the second coefficient, and the third coefficient , which represent the steering angle and minimize a sum of squares of a difference between the acquired steering angle and a function value of a model function having the first coefficient, the second coefficient , and the third coefficient as parameters, and which includes a first term represented by the product of a first coefficient corresponding to a cornering coefficient of the vehicle and the lateral acceleration, a second term represented by the product of a second coefficient indicating a wheel base of the vehicle and a ratio of the yaw rate to the vehicle speed, and a third term represented by a third coefficient indicating an offset amount from a neutral steering angle at which the direction of the wheels of the vehicle is parallel to the traveling direction ;
determining the neutral steering angle in accordance with the determined third coefficient;
A method for determining a neutral steering angle comprising the steps of: The processor installed in the vehicle
A first acquisition unit that acquires a lateral acceleration applied in a vehicle width direction perpendicular to a traveling direction of the vehicle;
A second acquisition unit that acquires a vehicle speed of the vehicle;
A third acquisition unit that acquires a yaw rate of the vehicle;
A fourth acquisition unit that acquires a steering angle of the vehicle;
a first determination unit that determines the first coefficient, the second coefficient, and the third coefficient by performing parameter estimation using a least squares method, the first coefficient, the second coefficient, and the third coefficient representing the steering angle and minimizing the sum of squares of the difference between a function value of a model function having the first coefficient, the second coefficient, and the third coefficient as parameters and the steering angle acquired by the third acquisition unit; and a second determination unit that determines the neutral steering angle in accordance with the third coefficient determined by the first determination unit.

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