Vehicle vibration damping method and vehicle vibration damping device

Abstract

Provided is a vehicle vibration-damping method that reduces vibrations of a vehicle (100) capable of independently controlling a front wheel drive source (10F), which generates a driving force and a braking force at front wheels (4FL, 4FR), and a rear wheel drive source (10R), which generates a driving force at rear wheels (4RL, 4RR), wherein, when a change in the steering angle over time due to the turning of the vehicle (100) is within a prescribed range, the front wheel drive source (10F) generates a braking force at the front wheels (4FL, 4FR) and the rear wheel drive source (10R) generates, at the rear wheels (4RL, 4RR), a driving force that cancels out all or part of the braking force generated at the front wheels (4FL, 4FR).

Description

[Technical Field]

[0001] The present invention relates to a vehicle vibration damping method and a vehicle vibration damping device. [Background Art]

[0002] The following Patent Document 1 describes a technology for suppressing rolling of a vehicle body by independently generating drive torque at a right front wheel, a left front wheel, a right rear wheel, and a left rear wheel. [Prior Art Documents] [Patent Documents]

[0003] [Patent Document 1] Japanese Unexamined Patent Application Publication No. 2005-312190 [Summary of the Invention] [Problem to be Solved by the Invention]

[0004] However, the configuration that independently controls the right front wheel, left front wheel, right rear wheel, and left rear wheel has the problem that the increase in the number of parts causes an increase in weight and an increase in cost. An object of the present invention is to reduce vibration in the yaw direction of a vehicle by controlling front wheel torque. [Means for Solving the Problem]

[0005] According to one aspect of the present invention, there is provided a vehicle vibration damping method for reducing vibration of a vehicle that can independently control a front wheel drive source that generates driving force and braking force at front wheels and a rear wheel drive source that generates driving force at rear wheels. In the vehicle vibration damping method, when a temporal change in a steering angle accompanying turning of the vehicle is within a predetermined range, braking force is generated at the front wheels by the front wheel drive source, and driving force that offsets all or part of the braking force of the front wheels is generated at the rear wheels by the rear wheel drive source. [Advantageous Effects of the Invention]

[0006] According to the present invention, vibration in the yaw direction of a vehicle can be reduced by controlling front wheel torque. The objectives and advantages of the present invention are embodied and achieved using the elements and combinations thereof set forth in the claims. Both the general description above and the detailed description below are merely illustrative and descriptive, and should be understood not to limit the invention in any way that would be limited by the claims. [Brief explanation of the drawing]

[0007] [Figure 1] This is a schematic diagram of a vehicle equipped with a vehicle vibration damping device according to an embodiment. [Figure 2] This is a block diagram showing an example of the controller's functional configuration. [Figure 3] This is a block diagram showing an example of the functional configuration of the limit coefficient calculation unit. [Figure 4] (a) to (d) are explanatory diagrams illustrating examples of setting limiting coefficients. [Figure 5] This is a block diagram showing an example of the functional configuration of the target torque determination unit. [Figure 6] (a) is a schematic diagram of the vehicle body coordinate system and the front wheel coordinate system, and (b) is a schematic diagram of the front wheel braking force and rear wheel driving force. [Figure 7] This is a schematic diagram of the simulation results. [Figure 8] This is a flowchart of an example of a vehicle vibration damping method according to an embodiment. [Modes for carrying out the invention]

[0008] (composition) Figure 1 is a schematic diagram of a vehicle equipped with a vehicle vibration damping device according to an embodiment. The vehicle 100 includes a steering angle measuring device 1, a steering device 2, wheel speed measuring devices 3FR, 3FL, 3RR and 3RL, a right front wheel 4FR, a left front wheel 4FL, a right rear wheel 4RR and a left rear wheel 4RL, front wheel drive shafts 5FR and 5FL, rear wheel drive shafts 6RR and 6RL, a yaw rate sensor 7, a controller 8, a power converter 9, a front wheel drive source 10F, a rear wheel drive source 10R, and a battery 11. In the following description, the right front wheel 4FR and the left front wheel 4FL may be collectively referred to as "front wheel 4F," and the right rear wheel 4RR and the left rear wheel 4RL may be collectively referred to as "rear wheel 4R." The steering angle measuring device 1 measures the steering angle δf of the steering wheel 2a that steers the steering wheels (i.e., the front wheels 4F) to change the direction of travel of the vehicle 100, and outputs it to the controller 8.

[0009] In the following description, the ratio Gstr = δf / θ of the rotation angle δf of the steering wheel 2a operated by the driver to the steering angle θ of the front wheel 4F relative to the vehicle 100 will be referred to as the "steering gear ratio". In a steer-by-wire system in which the steering wheel 2a and the front wheel 4F are mechanically separated, the steering gear ratio Gstr can be variably controlled, and the steering gear ratio Gstr is determined, for example, according to the steering angle δf and the state of the vehicle 100. The steering angle measuring device 1 may measure the steering angle θ of the front wheel 4F instead of the steering angle δf of the steering wheel 2a. In this case, the steering angle δf should be replaced with Gstr × steering angle θ in the description below.

[0010] Furthermore, if the vehicle 100 is equipped with a steering support system that automatically controls the steering angle θ of the front wheels 4F, the steering angle measuring device 1 may acquire command values ​​of the steering angle δf and steering angle θ generated by the steering support system instead of measured values ​​of the steering angle δf and steering angle θ. Furthermore, the units of the physical quantities acquired by the steering angle measuring device 1 are not limited to angles; the device may also detect the steering angle δf, the angular velocity which is the first time derivative of the steering angle θ, or the angular acceleration which is the second time derivative.

[0011] The steering system 2 consists of a steering wheel 2a, a steering shaft 2b connected thereto, and a steering mechanism (not shown) that can change the angle of the front wheels 4F relative to the vehicle 100. The steering angle measuring device 1 is connected to the steering system 2 and measures the change in the angle of the steering shaft 2b that occurs when the driver rotates the steering wheel 2a. In a typical vehicle, the rotation of the steering shaft 2b is converted by the steering system into a change in the angle of the front wheels 4F relative to the vehicle 100. On the other hand, in a steer-by-wire system... steering The shaft may be omitted.

[0012] The wheel speed measuring devices 3FR, 3FL, 3RR, and 3RL (hereinafter sometimes collectively referred to as "wheel speed measuring device 3") measure the wheel speeds ωFR, ωFL, ωRR, and ωRL of the right front wheel 4FR, left front wheel 4FL, right rear wheel 4RR, and left rear wheel 4RL, respectively, and output them to the controller 8. The front wheel drive shafts 5FR and 5FL are installed in positions corresponding to the right front wheel 4FR and left front wheel 4FL, respectively, and transmit the driving force and braking force generated by the front wheel drive source 10F to the right front wheel 4FR and left front wheel 4FL. There is rotational freedom between the front wheel drive shafts 5FR and 5FL and the front wheel 4F, allowing the steering device 2 to change the steering angle θ of the front wheel 4F. The rear wheel drive shafts 6RR and 6RL are installed in positions corresponding to the right rear wheel 4RR and left rear wheel 4RL, respectively, and transmit the driving force and braking force generated by the rear wheel drive source 10R to the right rear wheel 4RR and left rear wheel 4RL. In vehicles with rear-wheel steering, a degree of rotational freedom is provided between the rear wheel 4R and the rear-wheel drive shafts 6RR and 6RL, allowing for changes in the steering angle of the rear wheel 4R.

[0013] The yaw rate sensor 7 is fixed to a relatively rigid location within the vehicle 100, close to the center of gravity, and measures the yaw rate γr, which is the rate of change of the yaw angle of the vehicle 100 over time, and outputs it to the controller 8. Controller 8 is an electronic control unit (ECU) that independently controls the driving and braking forces generated on the front wheels 4F and the driving and braking forces generated on the rear wheels 4R. Controller 8 includes a processor 8a and peripheral components such as a memory device 8b. The processor 8a may be, for example, a CPU (Central Processing Unit) or an MPU (Micro-Processing Unit). The memory device 8b may include a semiconductor memory device, a magnetic memory device, an optical memory device, etc. The functions of Controller 8 described below are realized, for example, by the processor 8a executing a computer program stored in the memory device 8b. The controller 8 determines target generated torques for a front-wheel drive source 10F and a rear-wheel drive source 10R based on a steering angle δf, wheel speeds ωFR, ωFL, ωRR and ωRL, and a yaw rate γr respectively acquired from a steering angle measurement device 1, a wheel speed measurement device 3, and a yaw rate sensor 7, and outputs the determined target generated torques to a power converter 9.

[0014] The power converter 9 converts power supplied from a battery 11 electrically connected to the power converter 9 into power to be supplied to the front-wheel drive source 10F and the rear-wheel drive source 10R so as to achieve the target generated torque commanded from the controller 8. Further, the front-wheel drive source 10F and the rear-wheel drive source 10R are used as generators, and regenerative power is supplied to the battery 11 through the power converter 9 to charge the battery. Although FIG. 1 shows a single power converter 9 for the front-wheel drive source 10F and the rear-wheel drive source 10R, the power converter 9 can independently supply power such that the front-wheel drive source 10F and the rear-wheel drive source 10R can independently generate braking force and driving force.

[0015] The front-wheel drive source 10F and the rear-wheel drive source 10R generate driving force and braking force for front wheels 4F and rear wheels 4R, respectively. For example, the front-wheel drive source 10F and the rear-wheel drive source 10R may each include an electric motor and a speed reducer to which the rotation shaft of the electric motor is connected. The electric motor is connected to the power converter 9, and converts power supplied from the power converter 9 into rotational force of a rotor of the electric motor. Alternatively, the electric motor is used as a generator to extract electric power from rotational force, and the extracted electric power is used for charging the battery 11. The speed reducer converts the rotational speed between the rotor and front-wheel drive shafts 5FR, 5FL and rear-wheel drive shafts 6RR, 6RL, thereby converting the rotational torque generated at the rotor into driving torque and braking torque for the front-wheel drive shafts 5FR, 5FL and the rear-wheel drive shafts 6RR, 6RL. It should be noted that the power source of the front-wheel drive source 10F and / or the rear-wheel drive source 10R is not limited to an electric motor, and may be, for example, an internal combustion engine.

[0016] FIG. 2 is a block diagram of an example functional configuration of the controller 8. The controller 8 includes a frequency component extraction unit 20, a vehicle speed calculation unit 21, a target torque calculation unit 22, a limiting coefficient calculation unit 23, and a target torque determination unit 24. The frequency component extraction unit 20 extracts the frequency component FC of the steering angle δf. For example, the frequency component extraction unit 20 may calculate the time differential value αf=dδf / dt of the steering angle δf, and extract the frequency component FC by applying a low-pass filter to the time differential value αf. The purpose of the low-pass filter is to suppress amplification of high-frequency noise components contained in an input signal through differential processing. The cut-off frequency fc1 of the low-pass filter processing may be set so as to sufficiently remove high-frequency noise without affecting the yaw resonance frequency. Note that when the steering angle measurement device 1 directly detects the time rate of change, the differential processing may be omitted.

[0017] Further, for example, the frequency component extraction unit 20 may extract a desired target frequency component FC of a steering input by applying a band-pass filter to the steering angle δf. The low-frequency side cut-off frequency fc2 and the high-frequency side cut-off frequency fc3 of the band-pass filter are set such that the target frequency exists between these frequencies and a sufficient gain is obtained in the pass band. The vehicle speed calculation unit 21 calculates a vehicle speed V, which is the center-of-gravity speed of the vehicle body of the vehicle 100, based on wheel speeds ωFR, ωFL, ωRR, and ωRL. The vehicle speed calculation unit 21 calculates a first vehicle speed VF=rF×ωF by multiplying an average wheel speed ωF=(ωFR+ωFL) / 2 of the front wheels 4F by a wheel radius rF of the front wheels 4F. Further, the vehicle speed calculation unit 21 calculates a second vehicle speed VR=rR×ωR by multiplying an average wheel speed ωR=(ωRR+ωRL) / 2 of the rear wheels 4R by a wheel radius rR of the rear wheels 4R. The first vehicle speed VF and the second vehicle speed VR are averaged to obtain a vehicle speed V=(VF+VR) / 2.

[0018] The target torque calculation unit 22 calculates a target braking torque amount NtF0 to be instructed to the front wheel drive source 10F. Specifically, the target torque calculation unit 22 calculates a torque having a magnitude corresponding to a rate of change of yaw rate as the target braking torque amount NtF0. For example, the target torque calculation unit 22 calculates the target braking torque amount NtF0 having a magnitude proportional to the rate of change of the yaw rate. Here, the yaw rate when the steering angle is steady (hereinafter referred to as "steady-state yaw rate γs") is given by equation (1) below, from the equation of motion of a two-wheel model in which the right and left wheels of the front wheel 4F and rear wheel 4R are approximated as one wheel located at the center of the axle.

[0019]

number

[0020] In equation (1), the constant l is the wheelbase and the constant K is the stability factor. The target torque calculation unit 22 calculates the target braking torque NtF0 based on the frequency component FC and the vehicle speed V according to the following equation (2). If the time derivative value αf = dδf / dt of the steering angle δf is extracted as the frequency component FC, then equation (2) can be replaced with the following equation (3).

[0021]

number

[0022] In equations (2) and (3), the constant A is an arbitrary proportionality constant gain, which is determined using simulations or actual vehicles to ensure that the target braking torque NtF0 is appropriate. Equation (3) is obtained by replacing the time derivative αf of the steering angle δf included in equation (1) with its absolute value |αf|, treating parameters other than αf as constants, multiplying by the proportionality constant gain A, and reversing the sign. Therefore, the target braking torque NtF0 calculated based on equation (3) has a value proportional to the rate of change of the yaw rate. The absolute value |αf| is used to generate the same control input regardless of the sign of the steering direction. Furthermore, by applying a bandpass filter to the steering angle δf and extracting the desired frequency component FC, a target braking torque NtF0 can be obtained that is proportional to the desired frequency component of the yaw rate.

[0023] As described later, when braking force is applied to the front wheels 4F during a turn of the vehicle 100, a lateral force component is generated on the front wheels 4F in the opposite direction to the turning direction, where the front wheels 4F are at a steering angle relative to the vehicle body. Therefore, a yaw moment can be generated that counteracts the yaw moment generated in the vehicle body due to steering during the turn of the vehicle 100, thereby suppressing the gain of the yaw rate response to the steering input (yaw rate gain). This reduces vibration of the vehicle body in the yaw direction and stabilizes the vehicle behavior. In the following description, the suppression of the yaw rate gain by generating a braking torque of target braking torque amount NtF0 may be referred to as "control intervention by target braking torque amount NtF0". Furthermore, in this specification, the phrase "associated with the turning of the vehicle" is used to mean that the event occurs not only during the turning of the vehicle, but also when transitioning from a straight-ahead state to a turning state or from a turning state to a straight-ahead state.

[0024] Furthermore, the target torque calculation unit 22 calculates the target drive torque amount NtR0 to instruct the rear wheel drive source 10R. For example, the target torque calculation unit 22 converts the target braking torque amount NtF0 into braking force at the tire contact point of the front wheel 4F by multiplying the target braking torque amount NtF0 by the front wheel drive system gear ratio GmotF and dividing by the wheel radius rF of the front wheel 4F. The target torque calculation unit 22 calculates the drive torque that will be generated at the tire contact point of the rear wheel 4R to counteract this braking force as the target drive torque amount NtR0. For example, the target torque calculation unit 22 calculates the target drive torque amount NtR0 according to the following equation (4).

[0025]

number

[0026] In equation (4), the constant GmotR represents the rear-wheel drive gear ratio. In the example of equation (4), the target drive torque NtR0 was calculated so that the driving force generated by the rear wheel 4RF cancels out all of the braking force generated by the front wheel 4F with respect to the target braking torque NtF0. However, the target drive torque NtR0 may also be calculated so that it cancels out only a portion of the braking force generated by the target braking torque NtF0. That is, the driving force generated by the target drive torque NtR0 may be equal to, less than, or greater than the braking force generated by the target braking torque NtF0. The target torque calculation unit 22 outputs the target braking torque amount NtF0 and the target driving torque amount NtR0 to the target torque determination unit 24.

[0027] The limiting coefficient calculation unit 23 calculates a limiting coefficient C that limits the target braking torque amount NtF0 according to the vehicle state of the vehicle 100. Figure 3 is a block diagram of an example of the functional configuration of the limiting coefficient calculation unit 23. The limiting coefficient calculation unit 23 includes a vehicle speed-dependent limiting coefficient setting unit 30, a steady-state yaw rate calculation unit 31, a turning direction determination unit 32, a wheel speed difference-dependent limiting coefficient setting unit 33, a yaw rate difference-dependent limiting coefficient setting unit 34, and a limiting coefficient setting unit 35. The vehicle speed-dependent limit coefficient setting unit 30 sets the vehicle speed-dependent limit coefficient Cv according to the vehicle speed.

[0028] Figure 4(a) shows an example of setting the vehicle speed-dependent limiting coefficient Cv. The vehicle speed-dependent limiting coefficient Cv has a value in the range of "0" to "1". When the vehicle speed V is less than or equal to the threshold V1, or when the vehicle speed V is greater than or equal to the threshold V4, the vehicle speed-dependent limiting coefficient Cv is "0". In the range where the vehicle speed V is greater than or equal to the threshold V1 and less than or equal to the threshold V2, the vehicle speed-dependent limiting coefficient Cv increases from "0" to the value Cv1 as the vehicle speed V increases. In the range where the vehicle speed V is greater than or equal to the threshold V2 and less than or equal to the threshold V3, the vehicle speed-dependent limiting coefficient Cv changes from the value Cv1 to the value Cv2 as the vehicle speed V increases. In the range where the vehicle speed V is greater than or equal to the threshold V3 and less than or equal to the threshold V4, the vehicle speed-dependent limiting coefficient Cv decreases from the value Cv2 to "0" as the vehicle speed V increases.

[0029] Generally, in the frequency characteristics of the yaw rate response to steering input, it is known that when the vehicle speed V is low, the peak at the yaw resonance frequency of the gain is small, and the phase of the yaw rate in response to steering lags. Therefore, if control intervention using the target braking torque NtF0 is performed in the low vehicle speed range, it will exacerbate the lag in the vehicle response to steering. For this reason, thresholds V1, V2 and value Cv1 are determined so that control intervention using the target braking torque NtF0 is eliminated at low vehicle speeds, or the target braking torque NtF0 is reduced. Thresholds V3, V4 and value Cv2 set the maximum vehicle speed at which control intervention using the target braking torque NtF0 is performed, and are set when an upper limit on speed is set considering durability. Thresholds V1~V4 and values ​​Cv1 and Cv2 may be set as appropriate based on vehicle specifications, simulations, and actual vehicle evaluations. In the example in Figure 4(a), Cv1 and Cv2 are set such that Cv1 > Cv2, but Cv1 can be equal to or less than Cv2.

[0030] The steady-state yaw rate calculation unit 31 calculates the steady-state yaw rate γs based on the steering angle δf, the vehicle speed V, and the vehicle specifications. For example, the steady-state yaw rate calculation unit 31 may calculate the steady-state yaw rate γs according to equation (1) above. The turning direction determination unit 32 determines whether the turning direction determined from the driver's steering operation matches the turning direction detected from the yaw rate γr detected by the sensor. The turning direction determination unit 32 outputs a determination result flag Ct. The value of the determination result flag Ct is set to "1" when the turning direction determined from the driver's steering operation matches the turning direction detected from the yaw rate γr, and to "0" when they are different. For example, the turning direction determination unit 32 sets the value of the determination result flag Ct to "1" when the signs of the yaw rate γr detected by the sensor and the steady-state yaw rate γs match, and to "0" when they are different. By determining the turning direction in this way, control intervention using the target braking torque NtF0 is performed only when the vehicle turning direction based on the target yaw rate estimated from the driver's steering input matches the vehicle turning direction based on the actual yaw rate of the vehicle 100 acquired by the sensor, thereby suppressing the yaw rate gain. Conversely, when the turning directions do not match, the yaw rate gain is not suppressed, preventing a delay in the vehicle 100's behavior in response to the driver's input.

[0031] The wheel speed difference dependent limit coefficient setting unit 33 sets a front / rear wheel speed difference dependent limit coefficient Cfr to limit the target braking torque amount NtF0 when the wheel speed difference Δωfr=ωF-ωR between the front wheel 4F and the rear wheel 4R is excessive (for example, when slip occurs in the front wheel 4F and / or the rear wheel 4R). Figure 4(b) shows an example of setting the front / rear wheel speed difference dependent limit coefficient Cfr. The front / rear wheel speed difference dependent limit coefficient Cfr has a value in the range of "0" to "1". The front / rear wheel speed difference dependent limit coefficient Cfr is "1" when the wheel speed difference |Δωfr| is less than or equal to the threshold Δωfr1, and in the range where the wheel speed difference |Δωfr| is greater than or equal to the threshold Δωfr1 and less than or equal to the threshold Δωfr2, it decreases from "1" to "0" as the wheel speed difference |Δωfr| increases, and when the wheel speed difference |Δωfr| is greater than or equal to the threshold Δωfr2, 0 The threshold values ​​Δωfr1 and Δωfr2 may be set appropriately using vehicle specifications, simulations, and experiments with actual vehicles.

[0032] The wheel speed difference dependent limit coefficient setting unit 33 sets a left / right wheel speed difference dependent limit coefficient Clrf to limit the target braking torque amount NtF0 when the wheel speed difference Δωlrf between the right front wheel 4FR and the left front wheel 4FL is excessive (for example, when slip occurs in either the right front wheel 4FR or the left front wheel 4FL). Figure 4(c) shows an example of setting the left / right wheel speed difference dependent limit coefficient Clrf. The left / right wheel speed difference dependent limit coefficient Clrf has a value in the range of "0" to "1". The left / right wheel speed difference dependent limit coefficient Clrf is "1" when the wheel speed difference |Δωlrf| is less than or equal to the threshold Δωlrf1, and in the range where the wheel speed difference |Δωlrf| is greater than or equal to the threshold Δωlrf1 and less than or equal to the threshold Δωlrf2, it decreases from "1" to "0" as the wheel speed difference |Δωlrf| increases, and when the wheel speed difference |Δωlrf| is greater than or equal to the threshold Δωlrf2, 0 The threshold values ​​Δωlrf1 and Δωlrf2 may be set appropriately using vehicle specifications, simulations, and experiments with actual vehicles. The wheel speed difference-dependent limiting coefficient setting unit 33 sets the left-right wheel speed difference-dependent limiting coefficient Clrr to limit the target braking torque amount NtF0 when the wheel speed difference Δωlrr between the right rear wheel 4RR and the left rear wheel 4RL is excessive (for example, when slip occurs in either the right rear wheel 4RR or the left rear wheel 4RL), similar to the method for setting the left-right wheel speed difference-dependent limiting coefficient Clrf.

[0033] The yaw rate difference dependent limit coefficient setting unit 34 sets a yaw rate difference dependent limit coefficient Cy to limit the target braking torque amount NtF0 when the yaw rate difference Δγ = γs - γr between the steady yaw rate γs predicted from the driver's steering operation and the yaw rate γr acquired by the yaw rate sensor 7 is excessive (for example, when slip occurs in one or all of the four wheels during turning, and the driver cannot make the desired turn). Figure 4(d) shows an example of setting the yaw rate difference dependent limit coefficient Cy. The yaw rate difference dependent limit coefficient Cy has a value in the range of "0" to "1". The yaw rate difference dependent limit coefficient Cy is "1" when the yaw rate difference |Δγ| is less than or equal to the threshold Δγ1, and in the range where the yaw rate difference |Δγ| is greater than or equal to the threshold Δγ1 and less than or equal to the threshold Δγ2, it decreases from "1" to "0" as the yaw rate difference |Δγ| increases, and when the yaw rate difference |Δγ| is greater than or equal to the threshold Δγ2, 0 The threshold values ​​Δγ1 and Δγ2 may be set appropriately using vehicle specifications, simulations, and experiments with actual vehicles.

[0034] The limit coefficient setting unit 35 selects the minimum value from among the vehicle speed-dependent limit coefficient Cv, the front / rear wheel speed difference-dependent limit coefficient Cfr, the left / right wheel speed difference-dependent limit coefficients Clrf and Clrr, and the yaw rate difference-dependent limit coefficient Cy, and calculates the limit coefficient C = Ct × min(Cv, Cfr, Clrf, Clrr, Cy) by multiplying the selected minimum value by the determination result flag Ct. The limit coefficient setting unit 35 outputs the limit coefficient C to the target torque determination unit 24. The target torque determination unit 24 calculates the restricted target braking torque NtF and target driving torque NtR by limiting the target braking torque NtF0 and target driving torque NtR0 calculated by the target torque calculation unit 22 with a limiting coefficient C.

[0035] Figure 5 is a block diagram of an example of the functional configuration of the target torque determination unit 24. The target torque determination unit 24 includes target torque correction units 40 and 43, rate limiters 41 and 44, and low-pass filters (LPFs) 42 and 45. The target torque correction unit 40 calculates the product C × NtF0 by multiplying the target braking torque NtF0 by the limiting coefficient C. The rate limiter 41 limits the time rate of change of the product C × NtF0. A low-pass filter 42 with a cutoff frequency fc4 is applied to the output of the rate limiter 41 to calculate the target braking torque NtF.

[0036] Furthermore, the target torque correction unit 43 calculates the product C × NtR0 by multiplying the target drive torque amount NtR0 by the limiting coefficient C. The rate limiter 44 limits the time rate of change of the product C × NtR0. The output of the rate limiter 44 is subjected to a low-pass filter 45 with a cutoff frequency fc4 to calculate the target drive torque amount NtR. Here, the rate of change limit values ​​of the rate limiters 41 and 44 and the cutoff frequency fc4 are set so as not to affect the frequency band to be controlled. Refer to Figure 1. The controller 8 outputs the target braking torque NtF and the target driving torque NtR to the power converter 9. The power converter 9 supplies power to the front wheel drive source 10F and the rear wheel drive source 10R in order to realize the target braking torque NtF and the target driving torque NtR commanded by the controller 8. The front wheel drive source 10F and the rear wheel drive source 10R generate braking force corresponding to the target braking torque NtF and driving force corresponding to the target driving torque NtR for the front wheels 4F and the rear wheels 4R, respectively.

[0037] Next, we will explain the mechanism by which the vehicle yaw behavior is suppressed when the braking torque determined above is applied to the front wheels while the vehicle 100 is being steered. In the following explanation, the vehicle body is assumed to be symmetrical in the front, rear, left, and right directions, and a two-wheel model is used in which the right and left wheels of the front wheels 4F and rear wheels 4R are approximated as single wheels located at the center of the axle. Figure 6(a) shows the relationship between the vehicle body coordinate system and the front wheel coordinate system, and the relationship between the axial components of the braking force as viewed from each coordinate system. The vehicle body coordinate system (solid line) is a coordinate system in which the origin of the coordinate system is the wheel center, the x-axis is set to be parallel to the left-right centerline of the vehicle body and the forward direction is positive, the y-axis is set to be perpendicular to the x-axis and the left direction is positive, and the z-axis is set to form a right-handed system with these x and y axes. The front wheel coordinate system (dotted line) is a coordinate system in which the origin of the coordinate system is the wheel center, the x-axis is set to be parallel to the front-rear direction of the wheel and the positive direction, the y-axis is set to be perpendicular to the x-axis and the left direction is positive, and the z-axis is set to form a right-handed system with these x and y axes.

[0038] The vehicle body coordinate system and the front wheel coordinate system share the same origin. Here, we assume that the front wheel coordinate system (dotted line) is rotated counterclockwise by δf / Gstr around the wheel center relative to the vehicle body coordinate system (solid line). This indicates that the front wheel 4F is steered by δf / Gstr relative to the vehicle body. The braking force is the product of the front slip ratio Sf and the front traction coefficient Kf, Kf × Sf. The front slip ratio Sf = (rF × ωF - V) / V is obtained by dividing the difference between the product of the front wheel speed ωF and the wheel radius rF of the front wheel 4F and the x-component of the vehicle speed V by the vehicle speed V. In a real vehicle, a certain amount of time passes before the front slip ratio Sf is generated in response to the motor's instructed braking torque. Therefore, there is a delay in generating the braking force Kf × Sf that balances the target braking torque NtF, but this delay is sufficiently small compared to the frequency of steering angle changes (i.e., the frequency of the vehicle's yaw behavior) and can be ignored. The braking force Kf × Sf acts in the x-axis direction of the front wheel coordinate system, but if the front wheel 4F is steered by an angle δf / Gstr relative to the vehicle body, it will include a component in the y-axis direction of the vehicle body coordinate system (Kf × Sf × sin(δf / Gstr) ≈ Kf × Sf × δf / Gstr). The direction of this y-axis component (Kf × Sf × δf / Gstr) is opposite to the direction of turning. Therefore, when a braking force is applied to the front wheel 4F during steering, a yaw moment is generated that counteracts the yaw moment generated in the vehicle body by steering. At this time, a braking force (Kf × Sf × cos(δf / Gstr) ≈ Kf × Sf) is applied to the front wheel 4F in the negative x-axis direction of the vehicle body coordinate system, resulting in longitudinal acceleration. To prevent or reduce the deceleration of the vehicle 100 due to the braking force of the front wheels 4F, a driving force Kr × Sr = -Kf × Sf is generated on the rear wheels 4R with a target driving torque amount NtR, as shown in Figure 6(b). Kr and Sr are the rear traction coefficient and rear slip ratio, respectively.

[0039] The following shows the simulation results when front wheel braking torque is applied according to the steering angular velocity αf = dδf / dt. Figure 7 shows the frequency characteristics of the gain of the yaw rate response with respect to the steering input. The dashed line 50 shows a comparative example of the gain when no front wheel braking torque is applied, and the solid line 51 shows the gain when front wheel braking torque is applied. As can be seen from Figure 7, around 0 Hz, where the steering angular velocity is relatively slow, the difference in gain between when no front wheel braking torque is applied and when front wheel braking torque is applied is small, while around the yaw resonance frequency Fres, the peak is suppressed by applying front wheel braking torque. This shows that, compared to when no front wheel braking torque is applied, the change in the magnitude of the vehicle's yaw response is suppressed between the driver's steering around the yaw resonance frequency Fres and steady steering around 0 Hz.

[0040] Generally, vehicle characteristics with small changes in the frequency response of yaw rate gain are known to increase stability in subjective tests. Therefore, according to the present invention, stability to steering during high-speed driving, where the resonance peak is high, is improved. In this invention, the target braking torque NtF is set by multiplying the steering angular velocity αf = dδf / dt by a gain. This means that as the frequency of the steering input increases, the target braking torque NtF increases in proportion to the angular frequency. Therefore, by setting the gain so that the yaw rate gain decreases to a desired value at the yaw resonance frequency Fres, the vibration damping effect due to the lateral force generated during braking can be enhanced. Furthermore, by setting a target braking torque NtF corresponding to the steering angular velocity αf = dδf / dt, the vibration damping effect increases as the steering frequency increases. Similarly, by setting the target braking torque NtF based on the component extracted by applying a bandpass filter to the steering angle δf, the yaw rate gain in any frequency band can be reduced.

[0041] (operation) Figure 8 is a flowchart of an example of a vehicle vibration damping method according to the embodiment. In step S1, the steering angle measuring device 1 detects the steering angle δf of the steering wheel 2a. In step S2, the frequency component extraction unit 20 extracts the frequency component FC of the steering angle δf. In step S3, the wheel speed measuring devices 3FR, 3FL, 3RR, and 3RL detect the wheel speeds ωFR, ωFL, ωRR, and ωRL. In step S4, the vehicle speed calculation unit 21 calculates the vehicle speed V based on the wheel speeds ωFR, ωFL, ωRR, and ωRL.

[0042] In step S5, the target torque calculation unit 22 calculates the target braking torque amount NtF0 based on the frequency component FC and the vehicle speed V. It also calculates the target drive torque amount NtR0 generated at the rear wheel 4R, which is the driving force that will offset all or part of the braking force generated at the front wheel 4F by the target braking torque amount NtF0. In step S6, the limiting coefficient calculation unit 23 calculates the wheel speed differences Δωfr, Δωlrf, and Δωlrr. In step S7, the limiting coefficient calculation unit 23 calculates the yaw rate difference Δγ. In step S8, the limiting coefficient calculation unit 23 calculates the limiting coefficient C based on the vehicle speed V, the wheel speed differences Δωfr, Δωlrf, Δωlrr, the yaw rate difference Δγ, the yaw rate γr detected by the sensor, and the steady yaw rate γs calculated from the steering operation.

[0043] In step S9, the target torque determination unit 24 limits the target braking torque NtF0 and target driving torque NtR0 calculated in step S5 by a limiting coefficient C, thereby calculating the limited target braking torque NtF and target driving torque NtR. In step S10, the power converter 9, the front wheel drive source 10F, and the rear wheel drive source 10R generate braking force corresponding to the target braking torque NtF and driving force corresponding to the target driving torque NtR for the front wheels 4F and rear wheels 4R, respectively. The process then ends.

[0044] (Effects of the embodiment) (1) The controller 8 reduces vibrations of the vehicle 100 by independently controlling the front wheel drive source that generates driving and braking forces to the front wheel 4F and the rear wheel drive source that generates driving force to the rear wheel 4R. When the time change of the steering angle accompanying the turning of the vehicle 100 is within a predetermined range, the controller 8 generates a braking force to the front wheel 4F using the front wheel drive source and generates a driving force to the rear wheel 4R using the rear wheel drive source that cancels out all or part of the braking force of the front wheel 4F.

[0045] The braking force generated at the front 4F has a lateral force component relative to the vehicle body due to the steering of the front 4F. By generating this lateral force component in conjunction with the turning motion caused by the steering of the vehicle body, a yaw moment opposite to the turning direction is generated, and the yaw rate can be controlled without independently controlling the torque of the right and left wheels. braking A force that balances Drive By applying the driving torque that generates force to the rear wheels (4R), acceleration and deceleration in the longitudinal direction of the vehicle can be suppressed.

[0046] (2) The controller 8 may generate a braking force on the front wheels that is proportional to the time derivative of the steering angle. As a result, the yaw motion of the vehicle 100 with respect to the steering angle can be suppressed as the steering frequency increases. If the difference in yaw rate gain between this yaw resonance frequency and 0 Hz (i.e., steady steering angle input) is small, the damping effect of the yaw motion is high. By damping the yaw motion using the lateral force from the front wheel braking force, which is proportional to the time derivative of the steering angle, the damping effect proportional to the angular frequency of the input can be obtained as the steering input contains higher frequency components (i.e., the faster the steering is performed). As a result, by reducing the yaw rate gain at the yaw resonance frequency and not generating front wheel braking force for steady steering angle input, damping of yaw motion can be achieved by reducing the difference in yaw rate gain.

[0047] (3) The controller 8 may generate a braking force on the front wheels that is proportional to the magnitude of a predetermined frequency component of the steering angle. This allows for the application of a bandpass filter to extract the component near the yaw resonance frequency from the time component of the steering angle input, and then applying a front-wheel braking input proportional to the extracted frequency component. As a result, it is possible to suppress yaw motion vibrations while limiting the yaw rate gain to the vicinity of the yaw resonance frequency and without affecting other frequency bands.

[0048] (4) The controller 8 may limit the braking force according to the speed of the vehicle 100. This allows for the suppression of excessive vibration at low speeds by limiting the braking torque of the front wheels 4F when the vehicle 100 is moving slowly. Generally, the difference in yaw rate gain between steady steering and the yaw resonance frequency becomes more pronounced at higher speeds and smaller at lower speeds. For this reason, if a braking force is generated on the front wheels when the vehicle is moving at a low speed and a relatively fast steering input is made, it may impair steering responsiveness. Therefore, by limiting the braking force on the front wheels when the vehicle speed is low and increasing the braking force on the front wheels as the vehicle speed increases, it is possible to enhance the vibration damping effect at high speeds without impairing steering responsiveness at low speeds.

[0049] (5) The controller 8 may limit the magnitude of the time variation of the braking force. By limiting the time variation when there is a time variation in the target braking torque NtF0, abrupt changes in the behavior of the vehicle 100 can be suppressed. (6) The controller 8 may limit the braking force at least when the direction of change in the steering angle is different from the turning direction of the vehicle 100. This prevents the driver from feeling that the vehicle is not turning as intended when the direction the driver intends to turn is different from the direction of the vehicle's movement.

[0050] (7) The controller 8 may limit the braking force at least when the difference in rotational speed between the front wheel 4F and the rear wheel 4R exceeds a first threshold. This allows the braking force on the front wheels to be limited when excessive slip occurs in either or both of the front wheels (4F) and / or rear wheels (4R) due to the generation of the target braking torque amount NtF. This reduces slip in all four wheels and suppresses instability in the vehicle's behavior. (8) The controller 8 may limit the braking force at least when the difference in rotational speed between the right wheel and the left wheel exceeds a second threshold. This allows the front braking force to be limited when excessive slip occurs in either the right or left front wheel 4F and either the right or left rear wheel 4R, or when excessive slip occurs simultaneously in either the right or left wheel of both the front 4F and rear 4R, due to the generation of the target braking torque NtF. This reduces slip in all four wheels and suppresses instability in the vehicle's behavior.

[0051] (9) The braking force may be limited if the difference between the yaw rate calculated based on the steering angle and the yaw rate detected by the sensor exceeds a third threshold. This allows the front wheel braking force to be limited if the target braking torque NtF is generated, causing slippage in one or all of the four wheels and preventing the driver from making the desired turn. This reduces slippage in all four wheels and prevents the vehicle's behavior from becoming unstable.

[0052] All examples and conditional terms set forth herein are intended for educational purposes to help the reader understand the concepts given by the inventors for the advancement of the invention and the art, and should be interpreted without limitation to the examples and conditions specifically described herein, as well as the configuration of examples relating to demonstrating the superiority and inferiority of the invention. Although embodiments of the invention are described in detail, it should be understood that various changes, substitutions, and modifications are possible without departing from the spirit and scope of the invention. [Explanation of Symbols]

[0053] 1…Steering angle measuring device, 2…Steering device, 2a…Steering wheel, 2b…Steering shaft, 3…Wheel speed measuring device, 3FL, 3FR, 3RL, 3RR…Wheel speed measuring device, 4F…Front wheel, 4FL…Left front wheel, 4FR…Right front wheel, 4R…Rear wheel, 4RF…Rear wheel, 4RL…Left rear wheel, 4RR…Right rear wheel, 5FL…Front wheel drive shaft, 5FR…Front wheel drive shaft, 6RL…Rear wheel drive shaft, 6RR…Rear wheel drive shaft, 7…Yaw rate sensor, 8…Controller, 8a…Processor, 8b…Memory device, 9…Power converter, 10F…Front wheel Drive source, 10R...Rear wheel drive source, 11...Battery, 20...Frequency component extraction unit, 21...Vehicle speed calculation unit, 22...Target torque calculation unit, 23...Limiting coefficient calculation unit, 24...Target torque determination unit, 30...Vehicle speed dependent limiting coefficient setting unit, 31...Steady yaw rate calculation unit, 32...Turning direction determination unit, 33...Wheel speed difference dependent limiting coefficient setting unit, 34...Yaw rate difference dependent limiting coefficient setting unit, 35...Limiting coefficient setting unit, 40, 43...Target torque correction unit, 41, 44...Rate limiter, 42, 45...Low-pass filter (LPF), 100...Vehicle

Claims

1. A vehicle vibration damping method that reduces vehicle vibrations by independently controlling a front-wheel drive source that generates driving and braking forces to the front wheels and a rear-wheel drive source that generates driving force to the rear wheels, The front wheel drive source generates a braking force on the front wheels that is proportional to the magnitude of the time derivative of the steering angle during the turning of the vehicle, or proportional to the magnitude of a predetermined frequency component near the yaw resonance frequency of the steering angle. The rear-wheel drive source generates a driving force in the rear wheels that cancels out all or part of the braking force of the front wheels. A vehicle vibration damping method characterized by the following features.

2. The vehicle vibration damping method according to claim 1, characterized in that it limits at least the braking force according to the speed of the vehicle.

3. The vehicle vibration damping method according to claim 1, characterized in that the magnitude of the time change in the braking force is limited.

4. The vehicle vibration damping method according to claim 1, characterized in that at least the braking force is limited when the direction of change of the steering angle and the turning direction of the vehicle are different.

5. The vehicle vibration damping method according to claim 1, characterized in that the braking force is limited at least when the difference in rotational speed between the front wheel and the rear wheel exceeds a first threshold.

6. The vehicle vibration damping method according to claim 1, characterized in that the braking force is limited to at least the amount of the rotational speed difference between the right wheel and the left wheel when the difference in rotational speed exceeds a second threshold.

7. The vehicle vibration damping method according to claim 1, characterized in that the braking force is limited to at least the amount of the braking force when the difference between the yaw rate calculated based on the steering angle and the yaw rate detected by the sensor exceeds a third threshold.

8. A vehicle vibration damping device that reduces vehicle vibrations, A front-wheel drive source that generates driving and braking force for the front wheels, A rear-wheel drive source that generates driving force to the rear wheels independently of the driving force and braking force generated to the front wheels, A controller that performs the following processes: generating a braking force on the front wheels using the front wheel drive source that is proportional to the magnitude of the time derivative of the steering angle associated with the turning of the vehicle, or proportional to the magnitude of a predetermined frequency component near the yaw resonance frequency of the steering angle; and generating a driving force on the rear wheels using the rear wheel drive source that cancels out all or part of the braking force of the front wheels. A vehicle vibration damping device characterized by being equipped with the following features.

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