Zero point estimation device, zero point estimation method, and zero point estimation program

Abstract

To provide a zero point estimation device capable of estimating a zero point of a hitch angle sensor 74 even if a vehicle is not under a direct advance.SOLUTION: A PU 52 learns a zero point of a steering angle θt detected by a steering sensor 70 during a direct advance of a vehicle. The PU 52 stores the steering angle θt sampled each time as steering angle data 54b for control on the basis of the learned zero point. The PU 52 samples a hitch angle β, synchronizing with the steering angle data 54b for control when the vehicle executes drive of changing a travel direction. The PU 52 learns the zero point of the hitch angle β on the basis of the similarity between the steering angle θt and the hitch angle β.SELECTED DRAWING: Figure 2

Description

[Technical Field]

[0001] The present invention relates to a zero point estimation device, a zero point estimation method, and a zero point estimation program. [Background technology]

[0002] For example, Patent Document 1 listed below describes an articulated vehicle equipped with a trailer towed by a tractor. In this document, a device for controlling the articulated vehicle uses the detection value of a hitch angle sensor that detects the hitch angle, which is the angle between the fore-and-aft direction of the tractor and the fore-and-aft direction of the trailer. The device also estimates the zero point of the hitch angle sensor when the vehicle is traveling straight ahead. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] U.S. Patent No. 9,290,202 Summary of the Invention [Problem to be solved by the invention]

[0004] In the case of the above-mentioned device, it is essential that the articulated vehicles travel straight ahead in order to estimate the zero point. [Means for solving the problem]

[0005] The means for solving the above problems and their effects will be described below. 1. A zero point estimation device applied to a vehicle equipped with a first sensor and a second sensor, wherein the first sensor is a sensor that detects a physical quantity that changes in accordance with yaw movement of the vehicle, and the second sensor is a sensor that detects a physical quantity that changes in accordance with yaw movement of the vehicle and is different from a physical quantity that is a detection target of the first sensor, the first sensor has undergone zero point correction and is configured to execute a first acquisition process, a second acquisition process, and a zero point estimation process, wherein the first acquisition process is a process of acquiring a plurality of first detection values ​​sampled at mutually different timings while the vehicle is traveling, including changes in direction of travel, the first detection values ​​being detection values ​​of the first sensor, the second acquisition process is a process of acquiring a plurality of second detection values ​​sampled in synchronization with the sampling timing of the first detection values ​​that are the acquisition target of the first acquisition process, the second detection values ​​being detection values ​​of the second sensor, and the zero point estimation process is a process of estimating the zero point of the second sensor using as input the plurality of first detection values ​​acquired by the first acquisition process and the plurality of second detection values ​​acquired by the second acquisition process.

[0006] The first sensor and the second sensor are both sensors that detect physical quantities that change in response to the yaw motion of the vehicle. Therefore, the transitions of the detection values ​​of the sensors when the vehicle travels, including changes in direction of travel, tend to trace similar figures. Therefore, the multiple first detection values ​​and the multiple second detection values ​​contain information about the similarity. Therefore, in the above configuration, the zero point is estimated using the multiple first detection values, which are detection values ​​of the first sensor that have been zero-point corrected, and the multiple second detection values ​​that are sampled synchronously. This allows the zero point of the second detection values ​​to be estimated using the information about the similarity. Therefore, in the above configuration, the zero point of the second sensor can be estimated even when the vehicle is not traveling straight.

[0007] 2. The zero point estimation device according to 1 above, wherein the plurality of first detection values ​​acquired by the first acquisition process include values ​​sampled at timings when the steering angle of the vehicle is different from one another.

[0008] 3. The zero point estimation device according to 1 or 2 above, wherein the plurality of first detection values ​​acquired by the first acquisition process include two first detection values ​​whose magnitudes differ from each other by a threshold or more. In the above configuration, the plurality of first detection values ​​includes two first detection values ​​whose magnitudes differ from each other by a threshold or more. Therefore, compared to a case where two first detection values ​​whose magnitudes differ from each other by a threshold or more are not included, a large difference occurs between the plurality of first detection values. Therefore, compared to a case where only one of the above is included, the signal-to-noise ratio can be improved.

[0009] 4. A zero point estimation device described in any one of 1 to 3 above, wherein the multiple first detection values ​​acquired by the first acquisition process include values ​​sampled when the vehicle is turning right and values ​​sampled when the vehicle is turning left.

[0010] In the above configuration, the plurality of first detection values ​​include a value sampled when the vehicle turns right and a value sampled when the vehicle turns left. Therefore, compared to a case where only one of the values ​​sampled when the vehicle turns right and the values ​​sampled when the vehicle turns left is included, a large difference occurs between the plurality of first detection values. Therefore, compared to a case where only one of the values ​​sampled when the vehicle turns right and the values ​​sampled when the vehicle turns left is included, the signal-to-noise ratio can be improved.

[0011] 5. A zero point estimation device described in any one of items 1 to 4 above, wherein the vehicle is a tractor capable of manipulating the steering angle of the steered wheels, a trailer towed by the tractor can be connected to the tractor, either the first sensor or the second sensor is a hitch angle sensor, the hitch angle sensor detects the hitch angle, which is the angle between the fore-and-aft direction of the tractor and the fore-and-aft direction of the trailer, and sampling of the first detection value to be acquired by the first acquisition process is configured to be performed on the condition that a predetermined period of time has elapsed after the vehicle starts moving.

[0012] When a vehicle starts moving, it is not clear what the hitch angle will be. Therefore, immediately after the vehicle starts moving, the similarity between the detection value of the hitch angle sensor and the detection values ​​of the other sensors is likely to be lost. Therefore, in the above configuration, the zero point is estimated using the first detection value sampled after a predetermined period of time has elapsed since the vehicle started moving. This makes it possible to estimate the zero point using the first detection value sampled in a state in which the waveforms drawn by the multiple first detection values ​​and the waveforms drawn by the multiple second detection values ​​are similar.

[0013] 6. A zero point estimation device described in any one of 1 to 5 above, wherein the zero point estimation process is a process of calculating the zero point by converting the magnitude of the first detection value into the magnitude of the second detection value according to the ratio between the amount of change in the first detection value indicated by the plurality of first detection values ​​and the amount of change in the second detection value indicated by the plurality of second detection values.

[0014] The braking system 64 includes at least one of a device that slows down the rotation of the wheels by frictional force and a device that slows down the rotation of the wheels by converting the power of the wheels into electric energy. The device that slows down the rotation of the wheels by converting into electric energy may be shared with the rotating electric machine of the drive system. The braking system 64 may also include a braking control device that controls the device that slows down the rotation of the wheels. In this case, the "control device 50 controls the braking system 64" is referred to as the "control device 50 controls the braking system 64." 4 "Operate" means that the control device 50 outputs a command signal to the braking control device.

[0015] 7. The zero point estimation device described in 6 above, wherein the zero point estimation process includes a ratio coefficient calculation process that calculates a ratio coefficient, which is the ratio of the difference between the two first detection values ​​and a predetermined first detection value, and a process that calculates an estimate of the second detection value based on the product of the difference between the two second detection values ​​and the ratio coefficient, wherein the predetermined first detection value is a detection value that is not the zero point among the multiple first detection values, and the two second detection values ​​are the second detection values ​​corresponding to the two first detection values.

[0016] The product of the difference between the second detection values ​​and the ratio coefficient is a conversion of the magnitude of the predetermined first detection value into the magnitude of the corresponding second detection value, i.e., an estimate of the second detection value corresponding to the predetermined first detection value.

[0017] 8. A zero point estimation device described in any one of 1 to 7 above, configured to execute a zero point correction process and an operation process, wherein the zero point correction process is a process of correcting the second detection value according to the zero point estimated by the zero point estimation process, and the operation process is a process of operating a specified device based on the second detection value corrected by the zero point correction process.

[0018] In the above configuration, by operating a predetermined device based on the second detection value corrected by the zero point correction process, it is possible to suppress the influence of errors in the second detection value on the operation of the device. 9. A zero point estimation device described in any one of 1 to 8 above, which executes an instruction process to instruct a user of the vehicle to drive the vehicle under predetermined driving conditions, the predetermined driving conditions being driving conditions that change the direction of travel of the vehicle, and which executes the first acquisition process when driving the vehicle after the instruction process.

[0019] In the above configuration, by executing the instruction process, it is possible to increase the reliability that appropriate driving conditions are met for the zero point estimation process. 10. A zero point estimation device described in any one of 1 to 9 above, wherein the vehicle is a tractor capable of manipulating the steering angle of the steered wheels, a trailer towed by the tractor can be connected to the tractor, the first sensor and the second sensor are any two of three sensors: a steering angle sensor, a yaw rate sensor, and a hitch angle sensor, and the hitch angle sensor is a sensor that detects a hitch angle, which is the angle between the fore-and-aft direction of the tractor and the fore-and-aft direction of the trailer.

[0020] 11. A zero point estimation method comprising a step of executing each of the processes in the zero point estimation device according to any one of 1 to 10 above. 12. A zero point estimation program that causes a computer to execute each of the processes in the zero point estimation device described in any one of 1 to 10 above. [Brief explanation of the drawings]

[0021] [Figure 1] 1 is a perspective view showing the configuration of an articulated vehicle according to a first embodiment. [Figure 2] FIG. 2 is a block diagram showing the configuration of a control system according to the embodiment. [Figure 3] 3 is a flowchart showing a procedure of a process executed by a control device according to the embodiment. [Figure 4] 3 is a flowchart showing a procedure of a process executed by a control device according to the embodiment. [Figure 5] 3 is a time chart illustrating a zero point estimation method according to the embodiment. [Figure 6] 3 is a flowchart showing a procedure of a process executed by a control device according to the embodiment. [Figure 7] 4 is a time chart for explaining the effect of the embodiment. [Figure 8] 10 is a flowchart showing a procedure of a process executed by a control device according to a second embodiment. [Figure 9] 10 is a flowchart showing a procedure of a process executed by a control device according to a third embodiment. [Figure 10] 3 is a flowchart showing a procedure of a process executed by a control device according to the embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0022] First Embodiment The first embodiment will be described below with reference to the drawings. "Configuration of articulated vehicles" As shown in FIG. 1, the articulated vehicle 10 has a tractor 20 and a trailer 30. FIG. 1 shows an example of the tractor 20 as a pickup truck, which is a type of small freight vehicle. The tractor 20 has front wheels 22 and rear wheels 24. The front wheels 22 include two wheels, a right front wheel and a left front wheel, and the rear wheels 24 include two wheels, a right rear wheel and a left rear wheel. FIG. 1 also shows an example of the trailer 30 as a box-shaped trailer. The trailer 30 has wheels 32. The wheels 32 include two wheels, a right wheel and a left wheel.

[0023] The trailer 30 is connected to the rear of the tractor 20 via a ball joint 40. The ball joint 40 is a member that connects the trailer 30 to the tractor 20 so that the trailer 30 can rotate about an axis 42. The axis 42 extends along the height direction of the tractor 20.

[0024] Figure 2 shows some of the components provided on the tractor 20. As shown in Figure 2, the tractor 20 is equipped with a control device 50. The control device 50 operates a steering system 60, a drive system 62, and a braking system 64 to control the control variables of the articulated vehicle 10, which is the control target. The control variables include vehicle speed, traveling direction, and hitch angle. The hitch angle is the angle between the fore-and-aft direction of the tractor 20 and the fore-and-aft direction of the trailer 30.

[0025] Steering system 60 includes a steering actuator that steers the steered wheels. The steered wheels are, for example, front wheels 22 shown in FIG. 1. Note that steering system 60 may also include a steering control device that operates the steering actuator. In this case, "control device 50 operates steering system 60" means that control device 50 outputs a command signal to the steering control device.

[0026] The drivetrain 62 includes at least one of an internal combustion engine and a rotating electric machine as a thrust generating device for the vehicle. The drivetrain 62 may also include a drive control device that controls the internal combustion engine and the rotating electric machine. In this case, "the control device 50 operates the drivetrain 62" means that the control device 50 outputs a command signal to the drive control device.

[0027] The braking system 64 includes at least one of a device that decelerates the rotation of the wheels by frictional force and a device that decelerates the rotation of the wheels by converting the power of the wheels into electrical energy. The device that decelerates the rotation of the wheels by converting it into electrical energy may be shared with the rotating electric machine of the drive system. The braking system 64 may also include a braking control device that controls the device that decelerates the rotation of the wheels. In this case, "the control device 50 operates the braking system 62" means that the control device 50 outputs a command signal to the braking control device.

[0028] To control the control variable, the control device 50 refers to the steering angle θt of the steered wheels detected by the steering angle sensor 70 and the yaw rate yr detected by the yaw rate sensor 72. The steering angle θt is a value in which either the right turn or the left turn has a positive sign and the other has a negative sign. The steering angle θt is the turning angle of the tires. Note that, for example, if the steering system 60 is equipped with a rack and pinion mechanism, the steering angle sensor 70 may be a sensor that detects the pinion angle. In this case, however, the control device 50 performs a process to convert the pinion angle into the turning angle of the tires. For convenience of explanation, the turning angle of the tires obtained by the above conversion process will be considered to be the detection value of the steering angle sensor 70 below.

[0029] The control device 50 also references the hitch angle β detected by the hitch angle sensor 74 and the wheel speeds ωw1 to ωw4 detected by the wheel speed sensor 76. The hitch angle β can take on either a positive or negative sign depending on the angle between the direction in which the tractor 20 moves from rear to front and the direction in which the trailer 30 moves from rear to front. For example, the sign of the hitch angle β may be set to positive when the direction in which the trailer 30 moves from rear to front deviates counterclockwise by less than 180° from the direction in which the tractor 20 moves from rear to front. The wheel speeds ωw1 and ωw2 are the rotational speeds of the right front wheel 22 and the left front wheel 22, respectively. The wheel speeds ωw3 and ωw4 are the rotational speeds of the right rear wheel 24 and the left rear wheel 24, respectively. The control device 50 sets the control of the control amount depending on the operation state of the user interface 80. The user interface 80 is used to communicate the user's intentions to the control device 50, such as selecting either automatic driving or manual driving.

[0030] The control device 50 includes a PU 52 and a storage device 54. The PU 52 is a software processing device including at least one of a CPU, a GPU, a TPU, etc. The storage device 54 stores a steering angle zero point estimation program 54a and a reverse assist program 54c.

[0031] Steering angle zero point estimation program 54a prescribes commands to cause PU 52 to execute zero point correction processing for steering angle θt detected by steering angle sensor 70. Zero point correction processing is processing to compensate for the difference between steering angle θt and zero. Zero point correction processing includes processing to calculate the difference between steering angle θt when articulated vehicle 10 is traveling straight and zero. Zero point correction processing also includes processing to correct the sequentially sampled steering angle θt using the calculated difference and store the result in storage device 54 as control steering angle data 54b. Control steering angle data 54b is data related to steering angle θt for which zero point correction has been performed.

[0032] The reverse assist program 54c prescribes commands for the processing to be executed by the PU 52 when automatically reversing the combination vehicle 10. This processing is executed using the control hitch angle data 54d, the steering angle θt, and the wheel speeds ωw1 to ωw4 as inputs to the storage device 54. In more detail, the PU 52 sets a target traveling trajectory, and then operates the steering system 60, drive system 62, and braking system 64 to control the traveling trajectory of the combination vehicle 10 to the target traveling trajectory.

[0033] Here, the control hitch angle data 54d is data obtained by performing zero point correction on the hitch angle β detected by the hitch angle sensor 74. The process related to the zero point correction of the hitch angle will be described in detail below.

[0034] "Hitch angle zero point correction processing" Figures 3 and 4 show the procedure for the hitch angle zero point estimation process. The process shown in Figures 3 and 4 is realized by the PU 52 repeatedly executing the hitch angle zero point estimation program 54e stored in the storage device 54, for example, at a predetermined interval. Note that, below, the step numbers of each process are represented by numbers preceded by "S."

[0035] In the series of processes shown in Figures 3 and 4, the PU 52 first acquires the vehicle speed SPD, which is the traveling speed of the combination vehicle 10 (S10). The vehicle speed SPD is calculated each time by the PU 52 based on the wheel speeds ωw1 to ωw4. The vehicle speed SPD may be, for example, a value obtained by converting the average value of the wheel speeds ωw1 to ωw4 into a translational speed. Next, the PU 52 determines whether the permission flag F is "1" (S12). The permission flag F is set to "1" if sampling of the steering angle θt and the hitch angle β is permitted to be used as input for zero-point learning of the hitch angle β. The permission flag F is set to "0" if the sampling is not permitted.

[0036] When the PU 52 determines that the permission flag F is "0" (S12: NO), it determines whether the logical product of the following conditions (A) and (B) is true (S14). Condition (A): Zero-point learning of the steering angle θt has been performed, and control steering angle data 54b is being updated sequentially. Condition (A) is a condition that a reference signal used for learning the hitch angle β is available.

[0037] Condition (B): This is a condition that the articulated vehicle 10 has traveled a predetermined distance or more since starting. If the logical product is determined to be true (S14: YES), the PU 52 determines whether or not a condition (C) that the vehicle speed SPD is equal to or greater than the lower limit speed SthL and equal to or less than the upper limit speed SthH is satisfied (S16). If the condition (C) is satisfied (S16: YES), the PU 52 assigns "1" to the permission flag F (S18).

[0038] Next, PU 52 samples steering angle θt (S20). This process includes storing the sampled value in an area of ​​memory device 54 that stores data for zero point learning. Here, steering angle θt is the value indicated by control steering angle data 54b stored in memory device 54. PU 52 also samples hitch angle β detected by hitch angle sensor 74 (S22). This process includes storing the sampled value in an area of ​​memory device 54 that stores data for zero point learning. The processes of S20 and S22 are performed synchronously. That is, the steering angle θt sampled in the process of S20 and the hitch angle β sampled in the process of S22 can be considered to be values ​​at the same detection timing.

[0039] Next, the PU 52 determines whether the absolute value of the steering angle θt sampled in the process of S20 is greater than the learning upper limit value θthH (S24). On the other hand, when the PU 52 determines that the permission flag F is "1" (S12: YES), it determines whether or not the above-mentioned condition (C) is not satisfied (S26). In other words, the PU 52 determines whether or not the logical sum of the fact that the vehicle speed SPD is less than the lower limit value SthL and greater than the upper limit value SthH is true. When the PU 52 determines that the condition (C) is satisfied (S26: NO), it proceeds to the processing of S20. On the other hand, when the PU 52 determines that the condition (C) is not satisfied (S26: YES) or when the determination in the processing of S24 is affirmative, it assigns "0" to the permission flag F and erases the data sampled by the processing of S20 and S22 (S28).

[0040] On the other hand, if the determination in the process of S24 is negative, the PU 52 determines whether the logical product of the following conditions (D) to (G) is true (S30). Condition (D): This is a condition that the steering angle θt stored in the storage device 54 by the processing of S20 has a value for turning right.

[0041] Condition (E): This is a condition that there is a predetermined number of sampled values ​​in which the absolute value of the steering angular velocity during a right turn is equal to or less than a specified value Δ in the steering angle θt stored in storage device 54 by the processing of S20. This processing is processing to determine whether there is a history of the steering angle becoming steady during a right turn.

[0042] Condition (F): This is a condition that the steering angle θt stored in the storage device 54 by the processing of S20 has a value for turning left. Condition (G): This is a condition that there is a predetermined number of sampled values ​​in which the absolute value of the steering angular velocity during a left turn is equal to or less than a specified value Δ in the steering angle θt stored in storage device 54 by the processing of S20. This processing is processing to determine whether there is a history of the steering angle becoming steady during a left turn.

[0043] When the PU 52 determines that the logical product of conditions (D) to (G) is true (S30: YES), it performs low-pass filter processing on the time-series data of the steering angle θt stored in the storage device 54 by the processing of S20 (S32). In FIG. 3, the time-series data is expressed as "θt(1), θt(2), ...". Here, the number in parentheses after "θt" is the sampling number. Sampling numbers that are adjacent to each other have adjacent sampling timings.

[0044] In addition, the PU 52 performs low-pass filtering on the time-series data of the hitch angle β stored in the storage device 54 by the process of S22 (S34). In Fig. 3, the time-series data is expressed as "β(1), β(2), ...".

[0045] The low-pass filter used in the process of S32 and the low-pass filter used in the process of S34 have the same cutoff frequency. In the processes of S32 and S34, a dead zone may be provided in which values ​​near the zero point are set to zero. In this case, however, the width of the dead zone must be the same for the processes of S32 and S34.

[0046] Next, PU 52 substitutes the maximum value of the low-pass filtered time-series data of the steering angle θt for the maximum steering angle θtmax and the minimum value for the minimum steering angle θtmin (FIG. 4: S36).Furthermore, PU 52 substitutes the maximum value of the low-pass filtered time-series data of the hitch angle β for the maximum hitch angle βmax and the minimum value for the minimum hitch angle βmin (S38).

[0047] Next, PU 52 divides the maximum steering angle θtmax by the value obtained by subtracting the minimum steering angle θtmin from the maximum steering angle θtmax, and assigns the result to ratio coefficient K (S40). Next, PU 52 calculates offset amount βoff0, which is the amount of deviation of the zero point of hitch angle β, using the following equation (c1) (S42).

[0048] βoff0=βmin-K·(βmin-βmax)…(c1) 5 shows an example of the calculation process of the offset amount βoff0. In the following description, the value on the right-turning side is assumed to be positive.

[0049] When the steering angle θt is a value for the right turn, the hitch angle β is a value for the left turn. When the steering angle θt is a value for the left turn, the hitch angle β is a value for the right turn. In Figure 5, the hitch angle β when the zero point is correct is shown by a dashed dotted line. In Figure 5, the solid line shows the hitch angle β when there is an error in the zero point. As shown in Figure 5, when there is no error in the zero point, the hitch angle β and the steering angle θt have similar waveforms, although they have opposite signs. Therefore, the ratio between the absolute values ​​of the maximum steering angle θtmax and the minimum hitch angle βmin can be considered to be equal to the ratio between "θtmax - θtmin" and "βmax - βmin."

[0050] This means that the absolute value of the minimum hitch angle βmin is: θtmax·(βmax-βmin) / (θtmax-θtmin) Therefore, the minimum hitch angle without zero point error is given by the following formula:

[0051] θtmax·(βmin-βmax) / (θtmax-θtmin) =K·(βmin-βmax) The offset amount βoff0 is the difference between the sampled minimum hitch angle βmin and the minimum hitch angle without the zero point error, and is therefore equal to the right side of equation (c1).

[0052] 4, the PU 52 determines whether the offset amount βoff has already been calculated and stored (S44). If the PU 52 determines that the offset amount βoff has not yet been stored (S44: NO), the PU 52 assigns the offset amount βoff0 to the offset amount βoff (S46). Then, the PU 52 executes a process of displaying visual information to the effect that zero-point learning has been performed, as a process of notifying the user by operating the display device 82 shown in FIG. 2 (S48).

[0053] On the other hand, when the PU 52 determines that the offset amount βoff has already been stored (S44: YES), it updates the stored offset amount βoff (S50). Specifically, the PU 52 assigns the exponential moving average value of the already stored offset amount βoff and the offset amount βoff0 newly calculated by the processing of S42 to the offset amount βoff (S50). FIG. 4 shows an example in which the weighting coefficient of the already stored offset amount βoff is set to "α" and the weighting coefficient of the newly calculated offset amount βoff0 by the processing of S42 is set to "1-α", where "0<α<1".

[0054] When the processes of S28, S48, and S50 are completed, or when a negative determination is made in the processes of S14, S16, and S30, the PU 52 temporarily ends the series of processes shown in FIGS.

[0055] The procedure for updating the control hitch angle data 54d is shown in Fig. 6. The process shown in Fig. 6 is realized by the PU 52 repeatedly executing the hitch angle zero point estimation program 54e stored in the storage device 54, for example, at the sampling period of the hitch angle β.

[0056] In the series of processes shown in Fig. 6, the PU 52 first determines whether the offset amount βoff has already been stored (S60). If the PU 52 determines that the offset amount βoff has already been stored (S60: YES), the PU 52 acquires the most recent sampled value of the hitch angle β (S62). Next, the PU 52 assigns a value obtained by subtracting the offset amount βoff from the hitch angle β to the hitch angle β (S64). Then, the PU 52 updates the control hitch angle data 54d stored in the storage device 54 to the value calculated by the process of S64 (S66).

[0057] The PU 52 temporarily terminates the series of processes shown in FIG. 6 when the process of S66 is completed or when a negative determination is made in the process of S60. "Actions and Effects of the Present Embodiment" After detecting the zero point of the steering angle θt, the PU 52 calculates an offset amount βoff, which is the error in the zero point of the hitch angle β, based on the similarity between the waveform data of the steering angle θt and the waveform data of the hitch angle β. This makes it possible to detect the zero point of the hitch angle β even when the articulated vehicle 10 is not traveling straight ahead.

[0058] According to the present embodiment described above, the following actions and effects can be further obtained. (1) The PU 52 estimates the zero point of the hitch angle sensor 74 using both the hitch angle β sampled when the vehicle is turning right and the hitch angle β sampled when the vehicle is turning left. Therefore, compared to when only one of the hitch angle β sampled when the vehicle is turning right or the hitch angle β sampled when the vehicle is turning left is included, there is a large difference between the two hitch angles β. Therefore, the signal-to-noise ratio can be improved compared to when only one of the above is included.

[0059] (2) The PU 52 calculates the offset amount βoff based on the sampled values ​​of the steering angle θt and the hitch angle β in both the steady state of a right turn and the steady state of a left turn. This improves the accuracy of calculating the offset amount βoff compared to using sampled values ​​when the vehicle is not in a steady state.

[0060] Figure 7 shows the transitions of the steering angle θt, hitch angle β, ratio coefficient K, and offset amount βoff. However, the offset amount βoff is calculated without taking into account the above conditions (E) and (G). As shown in Figure 7, the offset amount βoff during period T1 when the turning is not steady deviates from the true value indicated by the dashed line in the figure.

[0061] (3) PU 52 calculates offset amount βoff based on sampled values ​​of steering angle θt and hitch angle β when the absolute value of steering angle θt is equal to or less than learning upper limit value θthH. This improves the accuracy of calculating offset amount βoff compared to using sampled values ​​when the absolute value of steering angle θt is greater than learning upper limit value θthH.

[0062] A period T2 in Fig. 7 shows a case where the offset amount βoff is calculated even when the absolute value of the steering angle θt is greater than the learning upper limit value θthH. As shown in Fig. 7, the offset amount βoff in the period T2 when the absolute value of the steering angle θt is large deviates from the true value indicated by the dashed dotted line in the figure.

[0063] (4) When condition (B) is satisfied, PU 52 performs sampling for zero point estimation. When articulated vehicle 10 starts moving, it is unclear what angle hitch angle β will be. Therefore, immediately after the start of movement, the similarity between the waveform depicted by the time series data of the detection values ​​of hitch angle sensor 74 and the waveform depicted by the time series data of the detection values ​​of steering angle sensor 70 is likely to be lost. In contrast, by setting condition (B), it is possible to estimate the zero point using values ​​sampled in a state in which the waveform depicted by the time series data of steering angle θt and the waveform depicted by the time series data of hitch angle β are similar.

[0064] (5) The PU 52 performs zero point correction on the hitch angle β sampled each time and updates the control hitch angle data 54d. The PU 52 then uses the control hitch angle data 54d when performing control using the hitch angle β, such as when executing the reverse assist program 54c. This makes it possible to suppress the influence of errors in the hitch angle sensor 74 on the control.

[0065] <Second embodiment> The second embodiment will be described below with reference to the drawings, focusing on the differences from the first embodiment.

[0066] In the first embodiment, the zero point of the hitch angle β is estimated when the articulated vehicle 10 is driven arbitrarily. In contrast, in this embodiment, a driving sequence is provided for estimating the zero point. The procedure for the zero point estimation process according to this embodiment is shown in Fig. 8. The process shown in Fig. 8 is realized by the PU 52 repeatedly executing the hitch angle zero point estimation program 54e stored in the storage device 54, for example, at a predetermined interval.

[0067] In the series of processes shown in FIG. 8 , the PU 52 first determines whether the calibration mode is ON (S70). This process determines whether the user has selected driving for the zero point learning process for the hitch angle β. That is, when the zero point of the hitch angle β is learned by the processes of S40 and S42 described above, the PU 52 operates the display device 82 to notify the user of this. Therefore, if the zero point of the hitch angle β has not been learned, the user can understand from the information on the display device 82 that learning has not been performed. In this embodiment, the user can select to intentionally drive for the zero point learning. This can be achieved by operating the user interface 80 to select the calibration mode.

[0068] When the PU 52 determines that the calibration mode is ON (S70: YES), the PU 52 operates the display device 82 to specify a travel path (S72). Here, for example, a travel path that switches from a right turn to a left turn may be specified. Alternatively, for example, a travel path that switches from a left turn to a right turn may be specified.

[0069] 3 and 4. Then, the PU 52 determines whether or not learning is complete (S74). In other words, the PU 52 determines whether or not the processes up to S46 are complete. Here, if the user drives in a manner that results in a negative determination in the processes of S14, S16, and S30, or a positive determination in the process of S24, learning is not completed.

[0070] When the PU 52 determines that the learning is complete (S74: YES), the PU 52 executes a process of displaying visual information to the effect that the zero point learning has been completed, by operating the display device 82 shown in FIG. 2 (S76).

[0071] When the PU 52 makes a negative determination in the processes of S70 and S74, or when it completes the process of S76, it temporarily ends the series of processes shown in FIG. <Third embodiment> The third embodiment will be described below with reference to the drawings, focusing on the differences from the first embodiment.

[0072] In the first embodiment, the zero-point corrected steering angle θt is used as the reference signal. In contrast, in this embodiment, the zero-point corrected yaw rate yr is used as the reference signal. Note that the zero-point correction of the yaw rate yr is performed in the same manner as the zero-point correction of the steering angle θt.

[0073] Figures 9 and 10 show the procedure for the hitch angle zero point correction process according to this embodiment. The process shown in Figures 9 and 10 is implemented by the PU 52 repeatedly executing, for example, at a predetermined interval, the hitch angle zero point estimation program 54e stored in the storage device 54. Note that in Figures 9 and 10, the same step numbers are assigned to processes corresponding to those shown in Figures 3 and 4, and their description will be omitted.

[0074] 9 and 10, the PU 52 executes a process of sampling the yaw rate yr instead of the process of S20 (S20a). If the determination in the process of S24 is negative, the PU 52 determines whether the logical product of the following conditions (D1), (F1), (H), and (I) is true (S30a).

[0075] Condition (D1): This condition is that the yaw rate yr stored in the storage device 54 by the process of S20a has a value for turning right. Condition (F1): This condition is that the yaw rate yr stored in the storage device 54 by the process of S20a has a value for turning left.

[0076] Condition (H): The absolute value of the sampled value of the yaw rate yr during a right turn is equal to or less than a specified value Δ. Condition (I): The absolute value of the sampled value of the yaw rate yr during a left turn must be equal to or less than a specified value Δ.

[0077] When the PU 52 determines that the logical product is true (S30a: YES), it performs low-pass filtering on the time-series data of the yaw rate yr stored in the storage device 54 by the processing of S20a (S32a). In Fig. 9, the time-series data is expressed as "yr(1), yr(2), ...". In addition, the PU 52 executes the processing of S34.

[0078] The low-pass filter used in the process of S32a and the low-pass filter used in the process of S34 have the same cutoff frequency. In the processes of S32a and S34, a dead zone may be provided in which values ​​near the zero point are set to zero. In this case, however, the width of the dead zone must be the same for the processes of S32a and S34.

[0079] When completing the process of S34, the PU 52 substitutes the maximum value of the time series data of the yaw rate yr that has been subjected to the low-pass filter process into the maximum yaw rate yrmax and the minimum value into the minimum yaw rate yrmin (S36a: FIG. 10).

[0080] When completing the process of S38, the PU 52 assigns a value obtained by dividing the maximum yaw rate yrmax by a value obtained by subtracting the minimum yaw rate yrmin from the maximum yaw rate yrmax to the ratio coefficient K (S40a).

[0081] Thereafter, the PU 52 executes the processes of S42 to S50. <Correspondence> The correspondence between the matters in the above embodiment and the matters described in the "Means for Solving the Problem" column is as follows. Below, the correspondence is shown for each number of the means for solving the problem described in the "Means for Solving the Problem" column. [1, 10, 11] The first sensor corresponds to the steering angle sensor 70. The second sensor corresponds to the hitch angle sensor 74. The first acquisition process corresponds to the processes of S36 and S36a. The second acquisition process corresponds to the process of S38. The zero point estimation process corresponds to the processes of S40 to S46 and S50 in FIG. 4 and the processes of S40a, S42 to S46 and S50 in FIG. 10. [2, 3, 4] This corresponds to the acquisition of the maximum steering angle θtmax and the minimum steering angle θtmin in the process of S36. [5] This corresponds to the process of S14. [6] The ratio corresponds to "(βmi - βmax) / (θtmax - θemin)". [7] The ratio coefficient calculation process corresponds to the process of S40 and S40a. The estimated value of the second detection value corresponds to "K·(βmi-βmax)". The predetermined first detection value corresponds to the maximum steering angle θtmax. The predetermined second detection value corresponds to the minimum hitch angle βmin. "8" The zero point correction process corresponds to the process of S64. The operation process corresponds to the process realized by the PU 52 executing the command specified in the reverse assist program 54c. [9] The instruction process corresponds to the process of S72.

[12] The computer corresponds to the PU 52.

[0082] <Other embodiments> This embodiment can be modified as follows: This embodiment and the following modifications can be combined with each other within the scope of technical compatibility.

[0083] "About the first and second sensors" The combination of the first sensor and the second sensor is not limited to the example given in the above embodiment. For example, the first sensor may be the yaw rate sensor 72 and the second sensor may be the steering angle sensor 70.

[0084] The combination of the first sensor and the second sensor is not limited to a combination of any two of the steering angle sensor 70, the yaw rate sensor 72, and the hitch angle sensor 74. For example, the second sensor may be either an acceleration sensor that detects lateral acceleration or the wheel speed sensor 76. In that case, the first sensor may be either the steering angle sensor 70 or the yaw rate sensor 72. Note that, if the second sensor is a wheel speed sensor, the detected value to be subjected to zero point correction is the speed difference between the wheel speeds ωw1 and ωw2 of the front wheels or the speed difference between the wheel speeds ωw3 and ωw4 of the rear wheels. This is a physical quantity that has a correlation with the yaw rate, etc.

[0085] "About the first acquisition process and the second acquisition process" In the above embodiment, the maximum magnitude of the first detection value when turning left and the maximum magnitude of the first detection value when turning right, such as the maximum absolute value of the steering angle θt when turning left and right, are acquired. However, this is not limited to this. For example, without being particularly concerned with the maximum value, the first detection value when turning left and the first detection value when turning right may be acquired. Also, for example, the first detection value when turning left or right and the first detection value when traveling straight may be acquired. Furthermore, for example, two first detection values ​​having different magnitudes sampled when turning right or left may be sampled. In this case, it is preferable that the two first detection values ​​have a difference in magnitude (absolute value) of a threshold or more. Furthermore, it is not essential that the two first detection values ​​having a difference in magnitude of a threshold or more be first detection values ​​sampled during either a right turn or a left turn. The process of determining whether conditions (D) and (F) are met in the process of S30 in FIG. 3 is an example of a process of determining whether the magnitudes (absolute values) of the sampled values ​​differ by more than a threshold value.

[0086] In the above embodiment, the steering angle θt or the yaw rate yr and the hitch angle β are sampled in synchronization, and then their maximum and minimum values ​​are extracted. This means, for example, that the maximum and minimum values ​​of the steering angle θt or the yaw rate yr and the minimum and maximum values ​​of the hitch angle β are considered to be synchronized sampled values. However, this is not limiting, and logic may be used in which only values ​​sampled in synchronization with each other are extracted.

[0087] In the above embodiment, the hitch angle β obtained by the second acquisition process is a sensor value that has been subjected to low-pass filtering. However, this is not limited to this. For example, high-pass filtering may also be performed. When this modification is applied to the first embodiment, it is possible to compensate for the response delay of the change in the hitch angle β relative to the change in the steering angle θt.

[0088] The detected values ​​to be acquired are not limited to values ​​that have been subjected to low-pass filtering. The first acquisition process is not limited to a process of acquiring two detection values. For example, as described in the section "Regarding Zero Point Estimation Process," when an LDS is used, detection values ​​may be acquired sequentially.

[0089] "About zero point estimation processing" In the above embodiment, the ratio coefficient K is the ratio of the difference between the maximum and minimum values ​​of the first sensor to the maximum value, but this is not limiting. For example, it may be the ratio of the difference between the maximum and minimum values ​​of the first sensor to the minimum value.

[0090] It is not necessary to set the ratio coefficient K as the ratio of the difference between the maximum and minimum first detection values ​​to the maximum or minimum value. For example, as described in "Regarding the First Acquisition Process and the Second Acquisition Process," if the maximum and minimum values ​​are not acquired, the following can be done. That is, the ratio of the difference between two different first detection values ​​to the value of the two first detection values ​​that is not the zero point can be set as the ratio coefficient.

[0091] The process of converting the magnitude of a first detection value into the magnitude of a second detection value in accordance with the ratio between the amount of change in the first detection value indicated by a plurality of first detection values ​​and the amount of change in the second detection value indicated by a plurality of second detection values ​​is not limited to the process exemplified in the above embodiment. For example, the ratio between the difference between two different values ​​in the time-series data of the steering angle θt and the difference between the corresponding values ​​of the hitch angle β may be calculated multiple times by changing the two different values. The average value of each of these ratios may then be used in the process of conversion.

[0092] Alternatively, for example, the process may be such that a value is calculated by multiplying each of the steering angles θt(1), θt(2), ..., θt(n) by (βmin-βmax) / (θtmax-θtmin). In this case, the offset amount βoff may be the average value of the difference between each of these values ​​and the corresponding hitch angle β(1), β(2), ..., β(n).

[0093] The zero-point estimation process does not necessarily have to be a process of converting the magnitude of the first detection value into the magnitude of the second detection value in accordance with the ratio between the amount of change in the first detection value indicated by the plurality of first detection values ​​and the amount of change in the second detection value indicated by the plurality of second detection values. For example, the hitch angle β when the steering angle θt is zero may be used as the offset amount βoff.

[0094] Alternatively, for example, the hitch angle β estimated by inputting time series data of the steering angle θt and time series data of the corresponding hitch angle β into a trained model such as a linear dynamics system (LDS) may be used as the true value. In this case, the difference between the true value and the detected hitch angle β may be used as the offset amount βoff. Here, the training data for the trained model is data in which the zero-point-corrected steering angle θt and the non-zero-point-corrected hitch angle β are used as input variables, and the zero-point-corrected hitch angle β is used as the target variable. This trained model is a model that has learned the similarity between the waveform of the time series data of the steering angle θt and the waveform of the time series data of the hitch angle β. Furthermore, the output of the trained model may be the offset amount βoff instead of the hitch angle β.

[0095] "About the control device" The control device is not limited to one equipped with a PU 52 and a storage device 54 and executing software processing. For example, it may be equipped with a dedicated hardware circuit, such as an ASIC, that performs hardware processing on at least a portion of what was software processed in the above embodiments. That is, the control device may have any of the following configurations (a) to (c): (a) equipped with a processing device that executes all of the above processing according to a program, and a program storage device, such as a storage device, that stores the program; (b) equipped with a processing device and program storage device that executes part of the above processing according to a program, and a dedicated hardware circuit that executes the remaining processing; or (c) equipped with a dedicated hardware circuit that executes all of the above processing. Here, there may be multiple software execution devices equipped with a processing device and a program storage device, and multiple dedicated hardware circuits.

[0096] "About the vehicle" Articulated vehicles are not limited to the vehicles illustrated in Figure 1. Vehicles are not limited to articulated vehicles. [Explanation of symbols]

[0097] 10...Articulated vehicle 20...Tractor 22...Front wheel 24...Rear wheel 30...Trailer 32...Wheel 40...ball joint 42...Axis 50...Control device

Claims

1. The present invention is applied to a vehicle equipped with a first sensor and a second sensor, the first sensor is a sensor that detects a physical quantity that changes in response to a yaw motion of the vehicle, the second sensor is a sensor that detects a physical quantity that changes in response to a yaw motion of the vehicle and is different from a physical quantity that is detected by the first sensor, the first sensor is zero-point corrected; configured to execute a first acquisition process, a second acquisition process, and a zero point estimation process; the first acquisition process is a process of acquiring a plurality of first detection values ​​sampled at mutually different timings while the vehicle is traveling, including changing its traveling direction; the first detection value is a detection value of the first sensor, the second acquisition process is a process of acquiring a plurality of second detection values ​​sampled in synchronization with sampling timings of the first detection values ​​to be acquired in the first acquisition process, the second detection value is a detection value of the second sensor, The zero point estimation process is a process of estimating the zero point of the second sensor using as input a plurality of first detection values ​​acquired by the first acquisition process and a plurality of second detection values ​​acquired by the second acquisition process.

2. 2. The zero point estimation device according to claim 1, wherein the plurality of first detection values ​​acquired by the first acquisition process include values ​​sampled at timings when the steering angle of the vehicle is different from one another.

3. 3. The zero point estimation device according to claim 1, wherein the plurality of first detection values ​​acquired by the first acquisition process include two first detection values ​​whose magnitudes differ from each other by a threshold or more.

4. The zero point estimation device according to any one of claims 1 to 3, wherein the plurality of first detection values ​​acquired by the first acquisition process include values ​​sampled when the vehicle is turning right and values ​​sampled when the vehicle is turning left.

5. the vehicle is a tractor capable of manipulating the steering angle of steered wheels, A trailer to be pulled by the tractor can be connected to the tractor, one of the first sensor and the second sensor is a hitch angle sensor; the hitch angle sensor is a sensor for detecting a hitch angle, which is an angle between the front-rear direction of the tractor and the front-rear direction of the trailer, The zero point estimation device according to any one of claims 1 to 4, wherein sampling of the first detection value to be acquired by the first acquisition process is performed on the condition that a predetermined period of time has elapsed after the vehicle starts traveling.

6. The zero point estimation device according to any one of claims 1 to 5, wherein the zero point estimation process is a process of calculating the zero point by converting the magnitude of the first detection value into the magnitude of the second detection value according to a ratio between an amount of change in the first detection value indicated by a plurality of the first detection values ​​and an amount of change in the second detection value indicated by a plurality of the second detection values.

7. The zero point estimation process includes: a ratio coefficient calculation process for calculating a ratio coefficient that is a ratio between a difference between the two first detection values ​​and a predetermined first detection value; calculating an estimated value of the second detection value according to a product of a difference between two of the second detection values ​​and the ratio coefficient; the predetermined first detection value is a detection value that is not a zero point among the plurality of first detection values, 7. The zero point estimation device according to claim 6, wherein the two second detection values ​​are the second detection values ​​corresponding to the two first detection values.

8. configured to perform a zero point correction process and an operation process; the zero point correction process is a process of correcting the second detection value in accordance with the zero point estimated by the zero point estimation process, The zero point estimation device according to any one of claims 1 to 7, wherein the operation process is a process of operating a predetermined device based on the second detection value corrected by the zero point correction process.

9. executes an instruction process to instruct a user of the vehicle to drive the vehicle under predetermined driving conditions; the predetermined driving condition is a driving condition that changes the traveling direction of the vehicle, 9. The zero point estimation device according to claim 1, wherein the first acquisition process is executed when the vehicle is being driven after the instruction process.

10. the vehicle is a tractor capable of manipulating the steering angle of steered wheels, A trailer to be pulled by the tractor can be connected to the tractor, the first sensor and the second sensor are any two of three sensors: a steering angle sensor, a yaw rate sensor, and a hitch angle sensor; 10. The zero point estimation device according to claim 1, wherein the hitch angle sensor is a sensor that detects a hitch angle, which is an angle formed between the front-rear direction of the tractor and the front-rear direction of the trailer.

11. A zero point estimation method comprising the step of executing each of the processes in the zero point estimation device according to any one of claims 1 to 10.

12. A zero point estimation program that causes a computer to execute each of the processes in the zero point estimation device according to any one of claims 1 to 10.

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