Vehicle behavior estimation method, vehicle behavior detection device, and steering system

Abstract

In one embodiment of a vehicle behavior estimation method, a vehicle behavior detection method, and a steering system of the present invention, a vehicle comprises a motor that imparts steering torque to wheels through a movable member. A normative travel state of the vehicle obtained from driver's steering operation information and the actual travel state of the vehicle are compared to output a first deviation. A normative shaft force occurring at the movable member and obtained from the vehicle travel speed and the wheel steering angle and an estimated shaft force occurring at the movable member and obtained from the motor current value are compared to output a second deviation. The first and second deviations are compared to estimate the vehicle behavior. The detection accuracy of vehicle behavior can be improved as a result.

Description

Technical Field

[0001] The present invention relates to a vehicle behavior estimation method, a vehicle behavior detection device, and a steering system.

Background Art

[0002] The turning behavior control device of the vehicle in Patent Document 1 calculates a target yaw rate based on the steering angle and the vehicle speed, and determines that it is in an understeer state when the actual yaw rate input from the yaw rate sensor is lower than the target yaw rate, and determines that it is in an oversteer state when the actual yaw rate is higher than the target yaw rate.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] By the way, when detecting understeer or oversteer, which is a vehicle behavior, based on the yaw rate deviation, which is the deviation between the reference yaw rate obtained from the steering angle of the wheels, the vehicle speed, etc., and the yaw rate actually occurring in the vehicle, the yaw rate deviation also occurs due to disturbances such as unevenness of the road surface on which the vehicle is traveling. For this reason, in the detection of vehicle behavior based on the yaw rate deviation, there is a problem that the detection accuracy is reduced due to disturbances.

[0005] The present invention has been made in view of the conventional situation, and its object is to provide a vehicle behavior estimation method, a vehicle behavior detection device, and a steering system that can improve the detection accuracy of a vehicle understeer or oversteer ..

Means for Solving the Problems

[0006] A vehicle behavior estimation method, a vehicle behavior detection device, and a steering system according to the present invention, in one embodiment, This is applicable to a vehicle equipped with a motor that applies steering torque to the vehicle's wheels via a movable member, and the From the steering operation information of the vehicle driver and a first physical quantity relating to the vehicle's speed 、 The aforementioned vehicle As a standard driving condition Determine the reference yaw rate, and compare it with the actual yaw rate occurring in the vehicle. Actual driving conditions Yorate By comparing the above, the reference yaw rate and the actual yaw rate The system outputs a first deviation which is the deviation from the first physical quantity and the second physical quantity relating to the steering angle of the wheel to determine the reference axial force generated in the movable member, and the system outputs the first deviation which is the deviation from the first physical quantity and the second physical quantity relating to the steering angle of the wheel to determine the estimated axial force generated in the movable member from the third physical quantity relating to the current value of the motor to determine the reference axial force and the estimated axial force By comparing the above, the reference axial force and the estimated axial force Output the second deviation, which is the deviation from the first deviation. By comparing the first deviation and the second deviation, the system estimates whether the vehicle is understeering or oversteering. In the process of estimating whether the vehicle is understeering or oversteering, a behavior detection signal is output to indicate that the vehicle is understeering or oversteering when the absolute value of the first deviation is greater than a positive first threshold, and a disturbance detection signal is output to indicate that the vehicle is not understeering or oversteering when the absolute value of the first deviation is less than or equal to the first threshold. When the amplitude or frequency of the second deviation exceeds the second threshold, a disturbance affecting the first deviation is present, and a disturbance detection signal is output to indicate that no disturbance affecting the first deviation is present when the amplitude or frequency of the second deviation is less than or equal to the second threshold. The system then compares the behavior detection signal and the disturbance detection signal. The system outputs a final behavior detection signal indicating whether the vehicle is understeering or oversteering. In the process of outputting the final behavior detection signal, if the behavior detection signal indicates that the vehicle is understeering or oversteering, and the disturbance detection signal indicates that no disturbance affecting the first deviation has occurred, the final behavior detection signal is output as a signal indicating that the vehicle is understeering or oversteering. If the behavior detection signal indicates that the vehicle is understeering or oversteering, but the disturbance detection signal indicates that a disturbance affecting the first deviation has occurred, the final behavior detection signal is output as a signal indicating that the vehicle is not understeering or oversteering, thereby invalidating the determination of understeer or oversteer based on the first deviation. . [Effects of the Invention]

[0007] According to the present invention, a vehicle understeer or oversteer This can improve the detection accuracy. [Brief explanation of the drawing]

[0008] [Figure 1] This is a schematic diagram of a vehicle equipped with a steer-by-wire steering system. [Figure 2] This is a functional block diagram showing the procedure for estimating vehicle behavior. [Figure 3] This is a time chart illustrating the changes in yaw rate deviation and axial force deviation in areas of uneven road surface. [Modes for carrying out the invention]

[0009] Hereinafter, embodiments of the vehicle behavior estimation method, vehicle behavior detection device, and steering system according to the present invention will be described with reference to the drawings. Figure 1 is a schematic diagram showing one embodiment of a vehicle 100 equipped with a steer-by-wire steering system 200. Vehicle 100 is a four-wheeled automobile equipped with a pair of front wheels 101 and 102, and a pair of rear wheels 103 and 104.

[0010] The steering system 200 includes a steering operation input device 300 through which a steering operation of a driver of the vehicle 100 is input via a steering wheel 310, a steering device 400 including a steering motor 410 that applies a steering torque to wheels of the vehicle 100 (specifically, the front wheels 101 and 102), and a steering control device 500. Here, the steering operation input device 300 and the steering device 400 are mechanically separated.

[0011] The steering operation input device 300 includes a steering wheel 310, a steering shaft 320, a reaction force motor 330, and an operation angle sensor 340. The steering wheel 310 is a steering operation input member operated by a driver of the vehicle 100.

[0012] The reaction force motor 330 is an actuator for pseudo-applying a steering reaction torque to the steering wheel 310. The operation angle sensor 340 is a sensor that detects an operation angle θ [deg] of the steering wheel 310.

[0013] The steering device 400 includes a steering mechanism 420. The steering mechanism 420 changes the steering angle of the front wheels 101 and 102 by converting the rotational motion of the steering motor 410 into a linear motion of a rack bar 421 by a rack and pinion method.

[0014] That is, the steering motor 410 applies a steering torque to the front wheels 101 and 102 via a rack bar 421 which is a movable member. Further, the steering device 400 includes a rack stroke sensor 430 that detects a rack stroke RS [mm] which is a stroke amount of the rack bar 421 correlated with the steering angle of the front wheels 101 and 102, a motor rotation angle sensor 440 that detects a rotation angle θm [deg] of the steering motor 410, and a motor current sensor 450 that detects a current value Cm [Arms] of the steering motor 410.

[0015] The steering control device 500 is an electronic control device equipped with an MCU (Micro Controller Unit) 510, and controls the operation of the steering system 200 by controlling the reaction force motor 330 and the steering motor 410, which are actuators included in the steering system 200. Note that the MCU 510 can be rephrased as a microcomputer, a processor, a processing device, an arithmetic device, etc.

[0016] The MCU 510 calculates control signals for the reaction force motor 330 and the steering motor 410 by performing arithmetic processing on various signals acquired from the outside, and outputs the calculated control signals. Here, the steering control device 500 can include a pre-driver, an inverter, etc. for controlling the energization of the reaction force motor 330 and the steering motor 410. Also, separately from the steering control device 500, a system including a drive circuit including a pre-driver, an inverter, etc. can be provided.

[0017] The vehicle 100 further includes wheel speed sensors 621 - 624 for detecting the wheel speeds WS1 - WS4, which are the rotational speeds of the wheels 101 - 104 respectively, a longitudinal acceleration sensor 630 for detecting the longitudinal acceleration G of the vehicle 100, and a yaw rate sensor 640 for detecting the yaw rate γ [deg / s] generated in the vehicle 100. Then, the MCU 510 of the steering control device 500 acquires the output signals of the operation angle sensor 340, the rack stroke sensor 430, the motor rotation angle sensor 440, the motor current sensor 450, the wheel speed sensors 621 - 624, the longitudinal acceleration sensor 630, and the yaw rate sensor 640.

[0018] Here, an overview of the control content of the steering system 200 (specifically, the reaction force motor 330 and the steering motor 410) by the MCU 510 of the steering control device 500 will be described. The MCU 510 calculates a target rack stroke RStg (in other words, the target value of the steering angle), which is the target value of the stroke amount of the rack bar 421, based on the information of the operation angle θ of the steering wheel 310. The MCU 510 then determines the control signal for the steering motor 410 based on the deviation between the actual rack stroke RS detected by the rack stroke sensor 430 and the target rack stroke RStg, i.e., the steering angle control error, and outputs the determined control signal to the drive circuit of the steering motor 410. In this embodiment, the actual rack stroke RS is detected using the rack stroke sensor 430. However, the stroke amount of the rack bar 421 may also be determined from the motor rotation angle θm detected by the motor rotation angle sensor 440. Alternatively, the actual rack stroke RS may be determined using a detector provided on the pinion gear that detects the rotation angle of the pinion shaft.

[0019] Furthermore, the MCU510 calculates the reaction torque command value TRtg, which is the target value of the reaction torque TR, based on information such as the vehicle speed VS [km / h] obtained from the wheel speeds WS1-WS4 and the steering wheel 310 operating angle θ. Furthermore, the MCU510 can obtain the wheel speed signals WS1-WS4 from the wheel speed sensors 621-624 to determine the vehicle speed VS, and can also obtain information on the vehicle speed VS determined by other in-vehicle control devices based on the wheel speed signals WS1-WS4 via the in-vehicle network.

[0020] The MCU510 then outputs a control signal based on the reaction force torque command value TRtg to the drive circuit of the reaction force motor 330. In this way, the MCU510 controls the operation of the steering system 200 by controlling the steering torque applied to the front wheels 101 and 102, and the reaction torque applied to the steering wheel 310.

[0021] Furthermore, the MCU510 has a function to estimate vehicle behavior according to a predetermined procedure and to provide vehicle behavior notification to the driver of vehicle 100, informing them of the estimated vehicle behavior. In other words, the MCU510 is a control unit that executes a vehicle behavior estimation method and constitutes a vehicle behavior detection device.

[0022] Here, the vehicle behavior is the understeer (U / S) or oversteer (O / S) of vehicle 100 during turns. In a steer-by-wire steering system 200, the steering force of the steering wheel 310 does not change even if the vehicle 100 is understeering or oversteering, making it difficult for the driver to recognize understeer or oversteer. Therefore, the MCU510 estimates whether the vehicle 100 is understeering or oversteering, and warns the driver if the vehicle 100 is understeering or oversteering, prompting the driver to take corrective action such as steering.

[0023] Figure 2 is a functional block diagram showing the procedure for estimating vehicle behavior in the MCU510. The functional block diagram in Figure 2 is broadly divided into three parts: a first block 700 that outputs the yaw rate deviation Dγ [deg / s] as the first deviation; a second block 800 that outputs the axial force deviation DAF [kN] as the second deviation; and a third block 900 that compares the output of the first block 700 and the output of the second block 800 and outputs an understeer or oversteer detection signal as a control signal to turn vehicle behavior notification on or off.

[0024] Here, the first block 700, which calculates the yaw rate deviation Dγ, calculates the yaw rate deviation Dγ, which is the deviation between the reference yaw rate γn and the actual yaw rate γa, and outputs a binary signal indicating whether the vehicle 100 is understeering or oversteering by comparing the yaw rate deviation Dγ with the threshold Dγth. Meanwhile, the second block 800, which calculates the axial force deviation DAF, calculates the axial force deviation DAF[kN], which is the deviation between the reference axial force AFn[kN] and the estimated axial force AFe[kN] of the rack bar 421. By comparing the axial force deviation DAF with the threshold THaf, it outputs a binary signal indicating whether or not a disturbance affecting the yaw rate deviation Dγ is occurring.

[0025] The disturbances that affect the yaw rate deviation Dγ include, for example, the condition of the road surface on which vehicle 100 is traveling, and more specifically, the unevenness of the road surface. Then, the third block 900 performs a logical operation on the binary signal output by the first block 700 and the binary signal output by the second block 800 to output a binary signal indicating whether or not understeer or oversteer is occurring.

[0026] In the first block 700, the detection of understeer or oversteer based on the yaw rate deviation Dγ may result in false detections due to disturbances such as uneven road surfaces causing the yaw rate deviation Dγ to be generated. Therefore, the third block 900 compares the understeer or oversteer detection result in the first block 700 with the disturbance detection result in the second block 800 to perform the final understeer or oversteer detection, thereby suppressing false detections caused by disturbances.

[0027] The following describes the detailed structure of each of the three blocks: Block 1 (700), Block 2 (800), and Block 3 (900). The first block 700 includes a first coefficient setting unit 701, a reference yaw rate setting unit 702, a phase control unit 703, a second coefficient setting unit 704, a third coefficient setting unit 705, a first multiplication unit 706, a second multiplication unit 707, a deviation calculation unit 708, and a comparison unit 709.

[0028] The first coefficient setting unit 701 acquires the vehicle speed VS signal and sets the time coefficient Tf, which is a characteristic value of the response delay of the vehicle behavior to steering, based on the vehicle speed VS. The reference yaw rate setting unit 702 acquires the vehicle speed VS signal and the target rack stroke RStg (in other words, the target steering angle) signal as steering operation information, and based on these, it calculates the basic reference yaw rate γnb, which is the basic value of the reference yaw rate γn.

[0029] In other words, the reference yaw rate setting unit 702 determines the basic reference yaw rate γnb as the reference driving state of the vehicle 100 from the steering operation information and a first physical quantity relating to the vehicle's speed. Furthermore, the reference yaw rate setting unit 702 can determine the basic reference yaw rate γnb based on the vehicle speed VS and the steering wheel 310 operating angle θ as steering operation information.

[0030] The phase control unit 703 acquires the signal of the time coefficient Tf set by the first coefficient setting unit 701 and the signal of the basic reference yaw rate γnb obtained by the reference yaw rate setting unit 702, and delays the phase of the basic reference yaw rate γnb according to the time coefficient Tf. The second coefficient setting unit 704 sets the longitudinal acceleration of the vehicle 100 [m / s²] detected by the longitudinal acceleration sensor 630. 2 The signal is acquired, and a coefficient of change DC is set according to the change characteristics of the yaw rate γ when vehicle 100 decelerates.

[0031] Furthermore, the third coefficient setting unit 705 acquires the longitudinal acceleration signal [m / s²] of the vehicle 100 detected by the longitudinal acceleration sensor 630 and sets the coefficient of change AC according to the change characteristics of the yaw rate γ when the vehicle 100 accelerates. The first multiplier unit 706 then obtains the signal of the phase-controlled basic reference yaw rate γnb output by the phase control unit 703, and the deceleration coefficient DC set by the second coefficient setting unit 704, multiplies the basic reference yaw rate γnb by the deceleration coefficient DC, and outputs the multiplication result as the deceleration-corrected basic reference yaw rate γnb.

[0032] Furthermore, the second multiplier unit 707 acquires the signal of the basic reference yaw rate γnb after deceleration correction output by the first multiplier unit 706, and the acceleration coefficient AC set by the third coefficient setting unit 705, multiplies the basic reference yaw rate γnb after deceleration correction by the acceleration coefficient AC, and outputs the multiplication result as the reference yaw rate γn. The deviation calculation unit 708 acquires the reference yaw rate γn signal output by the second multiplication unit 707 and the actual yaw rate γac signal detected by the yaw rate sensor 640, and outputs the result of subtracting the actual yaw rate γac from the reference yaw rate γn as the yaw rate deviation Dγ (Dγ = γn - γac) signal.

[0033] Here, the reference yaw rate γn is the reference driving state determined based on steering operation information, while the actual yaw rate γac detected by the yaw rate sensor 640 is the driving state that actually occurs in the vehicle 100. Therefore, the deviation calculation unit 708 is a functional unit that compares the standard driving state with the actual driving state and outputs a first deviation.

[0034] The comparison unit 709 acquires the yaw rate deviation Dγ signal and the threshold Dγth signal obtained by the deviation calculation unit 708, and by comparing the yaw rate deviation Dγ and the threshold Dγth, outputs a binary signal indicating whether or not the vehicle is in an understeer or oversteer state. In this case, a state where the output signal of the comparison unit 709 is 1 (High) indicates that understeer or oversteer has been detected. On the other hand, a state where the output signal of the comparison unit 709 is 0 (Low) indicates that understeer or oversteer has not been detected; in other words, it indicates a state of natural steer where the reference yaw rate γn and the actual yaw rate γac are approximate.

[0035] The yord rate deviation Dγ is calculated as a positive or negative value, and the threshold Dγth is set as well, with a positive first threshold Dγth1 and a negative second threshold Dγth2. The comparison unit 709 then sets the output signal to 0 (Low) if the yaw rate deviation Dγ is within the region between the first threshold Dγth1 and the second threshold Dγth2 (Dγth1 ≥ Dγ ≥ Dγth2).

[0036] Further, when the yaw rate deviation Dγ is greater than the first threshold value Dγth1 (Dγth1 < Dγ), the comparison unit 709 sets the output signal to 1 (High), and when the yaw rate deviation Dγ is less than the second threshold value Dγth2 (Dγth2 > Dγ), the comparison unit 709 also sets the output signal to 1 (High). In other words, when the absolute value of the yaw rate deviation Dγ is greater than the positive threshold value, the comparison unit 709 sets the output signal to 1 (High).

[0037] The upper part of FIG. 3 illustrates the correlation between the yaw rate deviation Dγ and the threshold values Dγth1 and Dγth2. The yaw rate deviation Dγ in FIG. 3 is in a state of periodically fluctuating under the influence of the unevenness of the road surface. The state where the yaw rate deviation Dγ is greater than the first threshold value Dγth1, the state where the yaw rate deviation Dγ is within the region sandwiched between the first threshold value Dγth1 and the second threshold value Dγth2, and the state where the yaw rate deviation Dγ is less than the second threshold value Dγth2 are periodically repeated. At this time, the output signal of the comparison unit 709 will alternately switch between 1 (High) and 0 (Low).

[0038] As described above, the first block 700 compares the reference yaw rate γn obtained from the rack stroke and the vehicle speed as the steering operation information with the yaw rate actually generated in the vehicle 100 to obtain the yaw rate deviation Dγ, and determines whether the vehicle 100 is understeering or oversteering based on the yaw rate deviation Dγ. On the other hand, the second block 800 includes a reference axial force calculation block 810, an estimated axial force calculation block 820, a deviation calculation unit 830, and a comparison unit 840.

[0039] The reference axial force calculation block 810 includes a basic reference axial force setting unit 811, a rack stroke speed calculation unit 812, a reference axial force intercept calculation unit 813, and an addition unit 814. The basic reference axial force setting unit 811 acquires the signals of the rack stroke RS and the vehicle speed VS, and based on these, obtains the basic reference axial force AFnb, which is the basic value of the reference axial force AFn generated in the rack bar 421.

[0040] The rack stroke velocity calculation unit 812 differentiates the rack stroke RS signal to obtain the rack stroke velocity ΔRS [mm / s], which is the amount of change in rack stroke per unit time.

[0041] The reference axial force intercept calculation unit 813 acquires the rack stroke speed ΔRS signal and the vehicle speed VS signal, and calculates the intercept ΔAF as a correction value for correcting the basic reference axial force AFnb. The summing unit 814 then acquires the signal for the basic reference axial force AFnb and the signal for the intercept ΔAF, adds the intercept ΔAF to the basic reference axial force AFnb, and outputs the final reference axial force AFn (AFn = AFnb + ΔAF). In this way, the reference axial force calculation block 810 determines the reference axial force AFn generated in the rack bar 421 from a first physical quantity relating to the vehicle speed 100 and a second physical quantity relating to the steering angles of the front wheels 101 and 102.

[0042] The estimated axial force calculation block 820 includes a friction compensation unit 821, a friction compensation subtraction unit 822, an axial force conversion unit 823, a motor inertia compensation unit 824, and an estimated axial force correction unit 825. The friction compensation unit 821 acquires the motor rotation speed MRS [rpm] signal of the steering motor 410 and calculates the current value CMF [Arms] for mechanical friction based on the motor rotation speed MRS. The motor rotation speed MRS is determined based on the rotation angle θm [deg] of the steering motor 410 detected by the motor rotation angle sensor 440.

[0043] The friction compensation subtraction unit 822 acquires the motor current value Cm signal detected by the motor current sensor 450 and the mechanical friction current value CMF signal obtained by the friction compensation unit 821, subtracts the mechanical friction current value CMF from the motor current value Cm, and outputs the motor current value Cm with the mechanical friction component corrected. The axial force conversion unit 823 acquires the motor current value Cm signal output by the friction compensation subtraction unit 822, and calculates the basic estimated axial force AFeb estimated to occur in the rack bar 421 based on the acquired motor current value Cm. The conversion characteristics for determining the basic estimated axial force AFeb from the motor current value Cm are determined from the rated torque, rated current, and reduction ratio of the steering motor 410, as well as the specific stroke (rack gain) of the steering device 400.

[0044] The motor inertia compensation unit 824 acquires the motor rotation speed MRS signal of the steering motor 410 and calculates the axial force AFJ [kN] of the steering motor 410's inertia (moment of inertia) based on the motor rotation speed MRS. The estimated axial force correction unit 825 obtains the signal of the basic estimated axial force AFeb obtained by the axial force conversion unit 823 and the inertia component axial force AFJ obtained by the motor inertia compensation unit 824, subtracts the inertia component axial force AFJ from the basic estimated axial force AFeb, and outputs the final estimated axial force AFe (AFe = AFeb - AFJ). As described above, the estimated axial force calculation block 820 calculates the estimated axial force AFe from a third physical quantity related to the motor current value Cm of the steering motor 410 and a fourth physical quantity related to the motor rotation speed MRS of the steering motor 410.

[0045] The deviation calculation unit 830 then acquires the signal of the reference axial force AFn output by the addition unit 814 and the signal of the estimated axial force AFe output by the estimated axial force correction unit 825, and outputs the result of subtracting the estimated axial force AFe from the reference axial force AFn as the signal of the axial force deviation DAF (DAF = AFn - AFe). The comparison unit 840 acquires the axial force deviation DAF signal and the threshold THaf signal obtained by the deviation calculation unit 830, and outputs a binary signal indicating the presence or absence of disturbances such as unevenness in the road surface based on a comparison between the axial force deviation DAF and the threshold THaf. In other words, the comparison unit 840 sets a predetermined threshold for the axial force deviation DAF and compares the axial force deviation DAF with the predetermined threshold to determine whether or not there are disturbances such as unevenness in the road surface.

[0046] Figure 3 shows the fluctuations in yaw rate deviation Dγ and axial force deviation DAF when vehicle 100 is traveling on an uneven road surface. The axial force deviation DAF fluctuates periodically due to the influence of road surface irregularities, and the yaw rate deviation Dγ also fluctuates periodically due to the influence of road surface irregularities. In more detail, when there are bumps in the road surface, vertical vibrations occur in the vehicle body, causing the yaw rate sensor 640 to misdetect the actual yaw rate γa, resulting in a yaw rate deviation Dγ.

[0047] Furthermore, the first block 700 will misdetect understeer or oversteer if the yaw rate deviation Dγ fluctuates above the threshold Dγth (first threshold Dγth1, second threshold Dγth2). Therefore, in order to distinguish between changes in yaw rate deviation Dγ influenced by disturbances and changes in yaw rate deviation Dγ due to understeer or oversteer, the second block 800 determines the presence or absence of disturbances such as uneven road surface based on a comparison of the axial force deviation DAF and the threshold THaf.

[0048] Here, when the axial force deviation DAF and yaw rate deviation Dγ fluctuate due to the unevenness of the road surface, there is a characteristic that the fluctuation frequency of the axial force deviation DAF is higher than the fluctuation frequency of the yaw rate deviation Dγ. Therefore, the comparison unit 840 sets a frequency threshold THFaf to determine whether the fluctuation frequency of the axial force deviation DAF is higher than the fluctuation frequency of the yaw rate deviation Dγ, based on the fluctuation frequency of the yaw rate deviation Dγ.

[0049] The comparison unit 840 then determines that the axial force deviation DAF is fluctuating due to road surface irregularities if the frequency of the axial force deviation DAF is higher than the frequency threshold THFaf, in other words, if the frequency of the axial force deviation DAF is higher than the frequency of the yaw rate deviation Dγ, and sets the output signal to 0 (Low). In other words, a 0 (Low) output signal from the comparison unit 840 indicates that road surface irregularities have been detected as a disturbance; in other words, it indicates that the yaw rate deviation Dγ is fluctuating due to the influence of road surface irregularities.

[0050] On the other hand, the comparison unit 840 determines that there are no road surface irregularities that would affect the yaw rate deviation Dγ if the frequency of the axial force deviation DAF is below the frequency threshold THFaf, and sets the output signal to 1 (High). In other words, a high output signal from the comparison unit 840 indicates that road surface irregularities as disturbances have not been detected. In other words, the yaw rate deviation Dγ is not affected by disturbances and is fluctuating due to the behavior of the vehicle 100, i.e., understeer or oversteer.

[0051] The comparison unit 840 sets an amplitude threshold THAaf to determine the amplitude of the axial force deviation DAF, and sets the output signal to 0 (Low) when the amplitude of the axial force deviation DAF exceeds the amplitude threshold THAaf, and sets the output signal to 1 (High) when the amplitude of the axial force deviation DAF is less than or equal to the amplitude threshold THAaf. In other words, the comparison unit 840 can determine the presence or absence of road surface irregularities as disturbances by comparing the amplitude of the axial force deviation DAF with the amplitude threshold THAaf.

[0052] Furthermore, the comparison unit 840 can determine the presence or absence of road surface irregularities as disturbances by comparing the amplitude of the axial force deviation DAF with the amplitude threshold THAaf, and by comparing the frequency of the axial force deviation DAF with the frequency threshold THFaf. In this case, the comparison unit 840 determines that the axial force deviation DAF is fluctuating due to road surface irregularities when the amplitude of the axial force deviation DAF exceeds the amplitude threshold THAaf and the frequency of the axial force deviation DAF is higher than the frequency threshold THFaf, and sets the output signal to 0 (Low).

[0053] The comparison unit 840 then determines that there are no irregularities on the road surface and sets the output signal to 1 (High) when at least one of the following conditions is met: the amplitude of the axial force deviation DAF is less than or equal to the amplitude threshold THAaf, and the frequency of the axial force deviation DAF is less than or equal to the frequency threshold THFaf. As described above, the comparison unit 840 (second block 800) determines the presence or absence of road surface irregularities as disturbances based on the amplitude and / or frequency of the axial force deviation DAF.

[0054] The third block 900 has a logical AND operation unit 910. The logical AND operation unit 910 receives the binary signal output by the comparison unit 709 of the first block 700 and the binary signal output by the comparison unit 840 of the second block 800, performs a logical AND operation on these signals, and outputs a binary signal as the result of the operation.

[0055] As mentioned above, the comparison unit 709 sets the output signal to 1 (High) when it detects understeer or oversteer based on the yaw rate deviation Dγ. On the other hand, the comparison unit 840, based on a comparison of the axial force deviation DAF and the threshold THaf, determines that the axial force deviation DAF is fluctuating due to unevenness in the road surface (in other words, unevenness in the road surface is occurring as a disturbance), and sets the output signal to 0 (Low). At this time, the output signal of the logical AND operation unit 910 becomes 0 (Low).

[0056] In other words, even if the comparison unit 709 detects understeer or oversteer based on the yaw rate deviation Dγ, if the comparison unit 840 detects unevenness in the road surface as a disturbance, the output signal of the logical AND operation unit 910 will be 0 (Low), indicating that understeer or oversteer has not been detected. In other words, if the comparison unit 840 detects road surface irregularities as a disturbance, the yaw rate deviation Dγ is considered to be caused by the disturbance, and the detection result of understeer or oversteer is ultimately invalidated.

[0057] On the other hand, if the comparison unit 709 detects understeer or oversteer based on the yaw rate deviation Dγ and the output signal of the comparison unit 709 is 1 (High), and the comparison unit 840 does not detect any unevenness in the road surface and the output signal of the comparison unit 840 is 1 (High), then the output signal of the logical AND operation unit 910 will also be 1 (High). In other words, if understeer or oversteer is detected based on the yaw rate deviation Dγ, and no road surface irregularities are detected, the output signal of the logical AND operation unit 910 will be 1 (High), indicating that understeer or oversteer has been detected.

[0058] In other words, when the MCU510 does not detect road surface irregularities as disturbances, it determines whether there is understeer or oversteer based on the yaw rate deviation Dγ. Therefore, according to the vehicle behavior estimation method performed by the MCU510, when a yaw rate deviation Dγ occurs due to the influence of road surface irregularities, false detection of understeer or oversteer is suppressed, and the accuracy of understeer or oversteer detection is improved.

[0059] The MCU510 provides the output signal of the logical AND operation unit 910, which indicates whether or not understeer or oversteer has been detected (in other words, the understeer / oversteer detection signal), as an on / off control signal to the alarm lamp 650, which acts as an alarm device. The warning lamp 650 lights up when the output signal of the logical AND operation unit 910 is 1 (High), notifying the driver of the vehicle 100 of the occurrence of understeer or oversteer.

[0060] In other words, when the MCU 510 detects the occurrence of understeer or oversteer, it activates the warning lamp 650, which is a warning device provided by the vehicle 100. The illumination of the warning lamp 650 allows the driver of the vehicle 100 to recognize the occurrence of understeer or oversteer, and for example, to take action to correct the understeer or oversteer. Here, the MCU510 can prevent false detection of understeer or oversteer due to road surface irregularities, and therefore can provide accurate information regarding understeer or oversteer to the driver of vehicle 100.

[0061] The technical concepts described in the above embodiments can be used in appropriate combinations, as long as no contradictions arise. Furthermore, although the contents of the present invention have been specifically described with reference to preferred embodiments, it will be obvious to those skilled in the art that various modifications can be taken based on the basic technical concept and teachings of the present invention.

[0062] For example, the comparison unit 709 can distinguish and detect vehicle behavior as oversteer or understeer by determining whether the yaw rate deviation Dγ exceeds a first threshold Dγth1, and whether the yaw rate deviation Dγ falls below a second threshold Dγth2. Furthermore, the comparison unit 840 can be configured to invalidate the oversteer or understeer detection result when it detects an external disturbance such as unevenness in the road surface.

[0063] Furthermore, when the MCU510 can distinguish between oversteer and understeer and detect them separately, it can activate a warning system so that the driver can distinguish and recognize between oversteer and understeer. Furthermore, when the MCU510 can distinguish between oversteer and understeer and detect them, it can reflect the detection results in the steering control and automatically perform corrective steering for oversteer or understeer.

[0064] The warning device for informing the driver of vehicle 100 of the occurrence of oversteer or understeer is not limited to a warning lamp 650. For example, a warning buzzer, liquid crystal display device, voice guidance device, etc., can be used as the warning device. Furthermore, the steer-by-wire steering system 200 may be equipped with a backup mechanism that mechanically connects the steering wheel 310 to the front wheels 101 and 102 using a clutch or the like.

[0065] Furthermore, the steer-by-wire steering system 200 may be equipped with a first control device that outputs a control signal for the steering motor 410 and a second control device that outputs a control signal for the reaction force motor 330, separately. In the steering system 200, either the first control device or the second control device is equipped with a control unit that performs a vehicle behavior detection method and can function as a vehicle behavior detection device. Furthermore, an electronic control unit that does not have a control function for the steering system 200 (in other words, the reaction force motor 330 and the steering motor 410) can function as a vehicle behavior detection device by having a control unit that executes a vehicle behavior detection method. [Explanation of Symbols]

[0066] 100…Vehicle, 101,102…Front wheels, 200…Steering system, 300…Steering operation input device, 340…Operation angle sensor, 400…Steering device, 410…Steering motor, 421…Rack bar (movable member), 430…Rack stroke sensor, 500…Steering control device (vehicle behavior detection device), 510…Microcomputer (control unit)

Claims

1. A method for estimating vehicle behavior performed by a control unit mounted on a vehicle equipped with a motor that applies steering torque to the vehicle's wheels via a movable member, The control unit is, From the steering operation information of the vehicle's driver and a first physical quantity relating to the vehicle's speed, a reference yaw rate is determined as the reference driving state of the vehicle. The reference yaw rate is compared with the actual yaw rate, which represents the actual driving conditions that occur in the vehicle, and a first deviation, which is the difference between the reference yaw rate and the actual yaw rate, is output. The reference axial force generated in the movable member is determined from the first physical quantity and the second physical quantity relating to the steering angle of the wheel. The estimated axial force generated in the movable member is determined from the third physical quantity relating to the current value of the motor. The reference axial force and the estimated axial force are compared, and a second deviation, which is the difference between the reference axial force and the estimated axial force, is output. By comparing the first deviation and the second deviation, it is estimated whether the vehicle is exhibiting understeer or oversteer. In the process of estimating whether the vehicle is understeering or oversteering, When the absolute value of the first deviation is greater than a positive first threshold, a behavior detection signal is output indicating that the vehicle is understeering or oversteering, and when the absolute value of the first deviation is less than or equal to the first threshold, a behavior detection signal is output indicating that the vehicle is not understeering or oversteering. When the amplitude or frequency of the second deviation exceeds the second threshold, a disturbance detection signal is output to indicate that a disturbance affecting the first deviation is occurring, and when the amplitude or frequency of the second deviation is less than or equal to the second threshold, a disturbance detection signal is output to indicate that no disturbance affecting the first deviation is occurring. The behavior detection signal and the disturbance detection signal are compared to output a final behavior detection signal indicating whether the vehicle is understeering or oversteering. In the process of outputting the final behavior detection signal, When the behavior detection signal indicates that the vehicle is understeering or oversteering, and the disturbance detection signal indicates that no disturbance affecting the first deviation has occurred, the final behavior detection signal is output as a signal indicating that the vehicle is understeering or oversteering. Even if the behavior detection signal indicates that the vehicle is understeering or oversteering, if the disturbance detection signal indicates that a disturbance affecting the first deviation is occurring, the final behavior detection signal is output as a signal indicating that the vehicle is not understeering or oversteering, thereby invalidating the determination of understeer or oversteer based on the first deviation. A method for estimating vehicle behavior.

2. A vehicle behavior estimation method according to claim 1, The control unit is, The estimated axial force generated in the movable member is determined from the third physical quantity and the fourth physical quantity relating to the rotational speed of the motor. A method for estimating vehicle behavior.

3. A vehicle behavior estimation method according to claim 1, The control unit is, As the second threshold for comparison with the frequency of the second deviation, a frequency threshold for determining whether the fluctuation frequency of the second deviation is higher than the fluctuation frequency of the first deviation is set based on the fluctuation frequency of the first deviation. When the frequency of the second deviation is higher than the frequency threshold, the determination of understeer or oversteer based on the first deviation is invalidated. A method for estimating vehicle behavior.

4. A vehicle behavior detection device mounted on a vehicle, comprising a motor that applies steering torque to the vehicle's wheels via a movable member, and a warning device, The vehicle behavior detection device has a control unit, The control unit is, From the steering operation information of the vehicle's driver and a first physical quantity relating to the vehicle's speed, a reference yaw rate is determined as the reference driving state of the vehicle. The reference yaw rate is compared with the actual yaw rate, which represents the actual driving conditions that occur in the vehicle, and a first deviation, which is the difference between the reference yaw rate and the actual yaw rate, is output. The reference axial force generated in the movable member is determined from the first physical quantity and the second physical quantity relating to the steering angle of the wheel. The estimated axial force generated in the movable member is determined from the third physical quantity relating to the current value of the motor. The reference axial force and the estimated axial force are compared, and a second deviation, which is the difference between the reference axial force and the estimated axial force, is output. By comparing the first deviation and the second deviation, it is estimated whether the vehicle is exhibiting understeer or oversteer. In the process of estimating whether the vehicle is understeering or oversteering, When the absolute value of the first deviation is greater than a positive first threshold, a behavior detection signal is output indicating that the vehicle is understeering or oversteering, and when the absolute value of the first deviation is less than or equal to the first threshold, a behavior detection signal is output indicating that the vehicle is not understeering or oversteering. When the amplitude or frequency of the second deviation exceeds the second threshold, a disturbance detection signal is output to indicate that a disturbance affecting the first deviation is occurring, and when the amplitude or frequency of the second deviation is less than or equal to the second threshold, a disturbance detection signal is output to indicate that no disturbance affecting the first deviation is occurring. The behavior detection signal and the disturbance detection signal are compared to output a final behavior detection signal indicating whether the vehicle is understeering or oversteering. In the process of outputting the final behavior detection signal, When the behavior detection signal indicates that the vehicle is understeering or oversteering, and the disturbance detection signal indicates that no disturbance affecting the first deviation has occurred, the final behavior detection signal is output as a signal indicating that the vehicle is understeering or oversteering. Even if the behavior detection signal indicates that the vehicle is understeering or oversteering, if the disturbance detection signal indicates that a disturbance affecting the first deviation is occurring, the final behavior detection signal is output as a signal indicating that the vehicle is not understeering or oversteering, thereby invalidating the understeer or oversteer determination based on the first deviation. The warning device is activated when the final behavior detection signal indicates that the vehicle is understeering or oversteering. Vehicle behavior detection device.

5. A motor that applies steering torque to the vehicle's wheels via a movable member, Alarm device, Vehicle motion detection device, A steering system including, The vehicle behavior detection device has a control unit, The control unit is, From the steering operation information of the vehicle's driver and a first physical quantity relating to the vehicle's speed, a reference yaw rate is determined as the reference driving state of the vehicle. The reference yaw rate is compared with the actual yaw rate, which represents the actual driving conditions that occur in the vehicle, and a first deviation, which is the difference between the reference yaw rate and the actual yaw rate, is output. The reference axial force generated in the movable member is determined from the first physical quantity and the second physical quantity relating to the steering angle of the wheel. The estimated axial force generated in the movable member is determined from the third physical quantity relating to the current value of the motor. The reference axial force and the estimated axial force are compared, and a second deviation, which is the difference between the reference axial force and the estimated axial force, is output. By comparing the first deviation and the second deviation, it is estimated whether the vehicle is exhibiting understeer or oversteer. In the process of estimating whether the vehicle is understeering or oversteering, When the absolute value of the first deviation is greater than a positive first threshold, a behavior detection signal is output indicating that the vehicle is understeering or oversteering, and when the absolute value of the first deviation is less than or equal to the first threshold, a behavior detection signal is output indicating that the vehicle is not understeering or oversteering. When the amplitude or frequency of the second deviation exceeds the second threshold, a disturbance detection signal is output to indicate that a disturbance affecting the first deviation is occurring, and when the amplitude or frequency of the second deviation is less than or equal to the second threshold, a disturbance detection signal is output to indicate that no disturbance affecting the first deviation is occurring. The behavior detection signal and the disturbance detection signal are compared to output a final behavior detection signal indicating whether the vehicle is understeering or oversteering. In the process of outputting the final behavior detection signal, When the behavior detection signal indicates that the vehicle is understeering or oversteering, and the disturbance detection signal indicates that no disturbance affecting the first deviation has occurred, the final behavior detection signal is output as a signal indicating that the vehicle is understeering or oversteering. Even if the behavior detection signal indicates that the vehicle is understeering or oversteering, if the disturbance detection signal indicates that a disturbance affecting the first deviation is occurring, the final behavior detection signal is output as a signal indicating that the vehicle is not understeering or oversteering, thereby invalidating the understeer or oversteer determination based on the first deviation. The warning device is activated when the final behavior detection signal indicates that the vehicle is understeering or oversteering. Steering system.

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