Vehicle vibration reduction method and vehicle vibration reduction device

Abstract

A vehicle vibration reduction method for reducing vibration of a vehicle (100) capable of independently controlling a front wheel drive source (10F) for generating a driving force and a braking force on front wheels (4FL, 4FR) and a rear wheel drive source (10R) for generating a driving force on rear wheels (4RL, 4RR), in a case where a change over time of a steering angle accompanying turning of the vehicle (100) is within a predetermined range, the front wheel drive source (10F) generates the braking force on the front wheels (4FL, 4FR), and the rear wheel drive source (10R) generates the braking force on the rear wheels (4RL, 4RR) by the rear wheel drive source (10R) when the change over time of the steering angle accompanying turning of the vehicle (100) is within the predetermined range. A rear wheel drive source (10R) causes rear wheels (4RL, 4RR) to generate a driving force that cancels all or part of the braking force generated by 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] In Patent Document 1 described below, there is a technique for suppressing the roll of a vehicle body by independently generating driving torques for the right front wheel, the left front wheel, the right rear wheel, and the left rear wheel.

[0003] Prior Art Documents

[0004] Patent Document

[0005] Patent Document 1: Japanese Unexamined Patent Application Publication No. 2005-312190

[0006] Problems to be Solved by the Invention

[0007] However, a structure for independently controlling the right front wheel, the left front wheel, the right rear wheel, and the left rear wheel has problems of weight increase and cost increase due to an increase in the number of components. Summary of the Invention

[0008] An object of the present invention is to reduce vibration of a vehicle in the yaw direction by controlling the torque of the front wheels.

[0009] According to one aspect of the present invention, there is provided a vehicle vibration damping method for reducing vibration of a vehicle capable of independently controlling a front wheel drive source that generates driving force and braking force for the front wheels and a rear wheel drive source that generates driving force for the rear wheels. In the vehicle vibration damping method, when the temporal change in the steering angle accompanying turning of the vehicle is within a specified range, the front wheel drive source causes the front wheels to generate braking force, and the rear wheel drive source causes the rear wheels to generate driving force that cancels all or part of the braking force of the front wheels.

[0010] Advantages of the Invention

[0011] According to the present invention, by controlling the front wheel torque, vibration of the vehicle in the yaw direction can be reduced.

[0012] The objects and advantages of the present invention will be embodied and achieved by the elements and combinations thereof shown in the scope of the claims. The above general description and the following detailed description are merely exemplary and explanatory, and should not be construed as limiting the present invention as defined in the scope of the claims. Brief Description of the Drawings

[0013] Figure 1 is a schematic structural diagram of a vehicle equipped with the vehicle vibration damping device of the embodiment.

[0014] Figure 2 is a block diagram of a functional configuration example of a controller.

[0015] Figure 3It is a block diagram of a functional structure example of a limiting coefficient operation unit.

[0016] Figure 4 (a) to (d) are explanatory diagrams of setting examples of limiting coefficients.

[0017] Figure 5 It is a block diagram of a functional structure example of a target torque determination unit.

[0018] Figure 6 (a) is a schematic diagram of a vehicle body coordinate system and a front wheel coordinate system, and (b) is a schematic diagram of a front wheel braking force and a rear wheel driving force.

[0019] Figure 7 It is a schematic diagram of a simulation result.

[0020] Figure 8 It is a flowchart of an example of a vehicle vibration damping method according to an embodiment. Detailed Embodiment

[0021] (Configuration)

[0022] Figure 1 It is a schematic structural diagram of a vehicle equipped with a vehicle vibration damping device according to an embodiment. Vehicle 100 includes: a steering angle measurement device 1, a steering device 2, wheel speed measurement 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 storage battery 11. In the following description, the right front wheel 4FR and the left front wheel 4FL may be collectively referred to as "front wheels 4F", and the right rear wheel 4RR and the left rear wheel 4RL may be collectively referred to as "rear wheels 4R".

[0023] The steering angle measurement device 1 measures the steering angle δf of the steering wheel 2a that steers the steering wheel (i.e., the front wheels 4F) for changing the traveling direction of the vehicle 100 and outputs it to the controller 8.

[0024] In the following description, the ratio Gstr = δf / θ of the rotation angle δf of the steering wheel 2a operated by the driver of the vehicle 100 to the steering angle θ of the front wheels 4F is expressed as the "steering gear ratio". In a steer-by-wire system in which the steering wheel 2a and the front wheels 4F are mechanically separated, the steering gear ratio Gstr can be variably controlled. For example, the steering gear ratio Gstr is determined according to the steering angle δf and the state of the vehicle 100. The steering angle measurement device 1 may also measure the steering angle θ of the front wheels 4F instead of the steering angle δf of the steering wheel 2a. In this case, in the following description, the steering angle δf can be replaced by Gstr × steering angle θ.

[0025] In addition, in the case where a steering assist system for automatically controlling the steering angle θ of the front wheels 4F is mounted in the vehicle 100, the steering angle measuring device 1 may also obtain the steering angle δf generated by the steering assist system and the command value of the steering angle θ in place of the measured values of the steering angle δf and the steering angle θ.

[0026] In addition, the unit of the physical quantity obtained by the steering angle measuring device 1 is not limited to an angle, and the first-order time differential (i.e., angular velocity) and the second-order time differential (i.e., angular acceleration) of the steering angle δf and the steering angle θ may also be detected.

[0027] The steering device 2 includes 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 device 2 and measures the change in the angle of the steering shaft 2b accompanying the rotational operation of the steering wheel 2a by the driver. In a normal vehicle, the rotation of the steering shaft 2b is converted into a change in the angle of the front wheels 4F relative to the vehicle 100 by the steering device. On the other hand, in a steer-by-wire system, the steering shaft may be omitted.

[0028] Wheel speed measuring devices 3FR, 3FL, 3RR, and 3RL (hereinafter sometimes collectively referred to as "wheel speed measuring devices 3") measure the wheel speeds ωFR, ωFL, ωRR, and ωRL of the right front wheel 4FR, the left front wheel 4FL, the right rear wheel 4RR, and the left rear wheel 4RL, respectively, and output them to the controller 8. Front-wheel drive shafts 5FR and 5FL are respectively provided at positions corresponding to the right front wheel 4FR and the left front wheel 4FL, and transmit the driving force and the braking force generated by the front-wheel drive source 10F to the right front wheel 4FR and the left front wheel 4FL. A rotational freedom is provided between the front-wheel drive shafts 5FR and 5FL and the front wheels 4F, and the steering angle θ of the front wheels 4F can be changed by the steering device 2. Rear-wheel drive shafts 6RR and 6RL are respectively provided at positions corresponding to the right rear wheel 4RR and the left rear wheel 4RL, and transmit the driving force and the braking force generated by the rear-wheel drive source 10R to the right rear wheel 4RR and the left rear wheel 4RL. In the case of a vehicle capable of rear-wheel steering, a rotational freedom is provided between the rear wheels 4R and the rear-wheel drive shafts 6RR and 6RL, and the steering angle of the rear wheels 4R can be changed.

[0029] The yaw rate sensor 7 is fixed at a position in the vehicle 100 having a high rigidity and close to the center of gravity, and measures the time change rate (i.e., yaw rate γr) of the yaw angle of the vehicle 100 and outputs it to the controller 8.

[0030] The controller 8 is an electronic control unit (ECU: Electronic Control Unit) that independently controls the driving force and braking force generated by the front wheels 4F and the driving force and braking force generated by the rear wheels 4R. The controller 8 includes a processor 8a and peripheral components such as a storage device 8b. The processor 8a can be, for example, a CPU (Central Processing Unit) and an MPU (Micro-Processing Unit). The storage device 8b can include a semiconductor storage device, a magnetic storage device, an optical storage device, etc. The functions of the controller 8 described below can be realized, for example, by causing the processor 8a to execute a computer program stored in the storage device 8b.

[0031] Based on the steering angle δf, the wheel speeds ωFR, ωFL, ωRR, and ωRL, and the yaw rate γr respectively obtained from the steering angle measurement device 1, the wheel speed measurement device 3, and the yaw rate sensor 7, the controller 8 determines the target generated torques of the front-wheel drive source 10F and the rear-wheel drive source 10R, and outputs them to the power converter 9.

[0032] The power converter 9 converts the power supplied from the storage battery 11 electrically connected to the power converter 9 into power supplied to the front-wheel drive source 10F and the rear-wheel drive source 10R to achieve the target generated torques indicated by the controller 8. In addition, the front-wheel drive source 10F and the rear-wheel drive source 10R are used as generators, and the power converter 9 supplies regenerative power to the storage battery 11 for charging. In Figure 1 this figure, a single power converter 9 is shown for the front-wheel drive source 10F and the rear-wheel drive source 10R, but the power converter 9 can supply power independently so that the front-wheel drive source 10F and the rear-wheel drive source 10R can independently generate braking force and driving force.

[0033] The front-wheel drive source 10F and the rear-wheel drive source 10R respectively generate driving force and braking force for the front wheels 4F and the rear wheels 4R. For example, the front-wheel drive source 10F and the rear-wheel drive source 10R can each include an electric motor and a speed reducer connected to its rotating shaft. The electric motor is connected to the power converter 9 and converts the power supplied from the power converter 9 into the rotational force of the rotor of the electric motor. Alternatively, the electric motor is used as a generator, and power is extracted from the rotational force and used for charging the storage battery 11. The speed reducer converts the torque generated in the rotor into the driving torque and braking torque of the front-wheel drive shafts 5FR and 5FL and the rear-wheel drive shafts 6RR and 6RL by changing the rotational speed between the rotor and the front-wheel drive shafts 5FR and 5FL and the rear-wheel drive shafts 6RR and 6RL. In addition, the power sources of the front-wheel drive source 10F and / or the rear-wheel drive source 10R are not limited to electric motors, and can be, for example, internal combustion engines.

[0034] Figure 2It is a block diagram of a functional structure example 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 limit coefficient calculation unit 23, and a target torque determination unit 24.

[0035] The frequency component extraction unit 20 extracts the frequency component FC of the steering angle δf. For example, the frequency component extraction unit 20 can 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 the amplification of high-frequency noise components contained in the input signal through the differential processing. The cut-off frequency fc1 of the low-pass filter processing can be set to be able to sufficiently remove high-frequency noise without affecting the yaw resonance frequency. In addition, in the steering angle measuring device 1, the differential processing can be omitted when the time change rate is directly detected.

[0036] In addition, for example, the frequency component extraction unit 20 can extract the desired frequency component FC as the target of the 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 there is a target frequency between these frequencies and the gain in the passband can be sufficiently obtained.

[0037] The vehicle speed calculation unit 21 calculates the vehicle speed V, which is the center-of-gravity speed of the vehicle body of the vehicle 100, based on the wheel speeds ωFR, ωFL, ωRR, and ωRL. The vehicle speed calculation unit 21 multiplies the average wheel speed ωF = (ωFR + ωFL) / 2 of the front wheels 4F by the wheel radius rF of the front wheels 4F to calculate the first vehicle speed VF = rF × ωF. In addition, the average wheel speed ωR = (ωrR + ωRL) / 2 of the rear wheels 4R is multiplied by the wheel radius RR of the rear wheels 4R to calculate the second vehicle speed VR = rR × ωR. The vehicle speed V = (VF + VR) / 2 is obtained by averaging the first vehicle speed VF and the second vehicle speed VR.

[0038] The target torque calculation unit 22 calculates the target braking torque amount NtF0 indicated to the front-wheel drive source 10F. Specifically, the target torque calculation unit 22 calculates a torque having a magnitude corresponding to the change rate of the yaw rate as the target braking torque amount NtF0. For example, the target braking torque amount NtF0 having a magnitude proportional to the change rate of the yaw rate is calculated.

[0039] Here, the yaw rate (hereinafter referred to as "steady-state yaw rate γs") in the case where the steering angle is in a steady state is given by the following formula (1) according to the equation of motion of a two-wheel model in which the right and left wheels of the front wheels 4F and the rear wheels 4R are approximated as one wheel located at the center of the axle.

[0040]

[0041] The constant l in Equation (1) is the wheelbase, and the constant k is the stability coefficient. The target torque calculation unit 22 calculates the target braking torque amount NtF0 based on the frequency component FC and the vehicle speed V according to the following Equation (2). When the time differential value αf = dδf / dt of the steering angle δf is extracted as the frequency component FC, Equation (2) is replaced by the following Equation (3).

[0042]

[0043] In addition, the constant A in Equations (2) and (3) is an arbitrary proportional constant gain, and an appropriate target braking torque amount NtF0 is determined using simulation or an actual vehicle.

[0044] By replacing the time differential value αf of the steering angle δf included in Equation (1) with the absolute value |αf|, treating the parameters other than αf as constants, multiplying by the proportional constant gain A, and reversing its sign, Equation (3) is obtained. Therefore, the target braking torque amount NtF0 calculated based on Equation (3) has a value proportional to the change rate of the yaw rate. In addition, the use of the absolute value |αf| is to generate the same control input regardless of the positive or negative of the steering direction.

[0045] In addition, when a band-pass filter is applied to the steering angle δf to extract the desired frequency component FC, a target braking torque amount NtF0 having a value proportional to the desired frequency component of the yaw rate can be obtained.

[0046] As described later, when braking force is generated at the front wheels 4F during a turn of the vehicle 100, a lateral force component in the direction opposite to the turning direction of the front wheels 4F with respect to the vehicle body is generated at the front wheels 4F. Therefore, a yaw moment in the direction to cancel the yaw moment generated on the vehicle body due to the steering during the turn of the vehicle 100 can be generated, and the gain of the yaw rate response with respect to the steering input (yaw rate gain) can be suppressed. As a result, the vibration of the vehicle body in the yaw direction can be reduced, and the vehicle behavior can be stabilized. In the following description, the case where the braking torque of the target braking torque amount NtF0 is generated to suppress the yaw rate gain is sometimes referred to as "control intervention based on the target braking torque amount NtF0". In addition, in this specification, the term "accompanying the turn of the vehicle" is used not only during the turn of the vehicle but also as a term indicating an event that occurs when switching from a straight-ahead state to a turning state or from a turning state to a straight-ahead state.

[0047] In addition, the target torque calculation unit 22 calculates the target drive torque amount NtR0 indicated for the rear-wheel drive source 10R. For example, the target braking torque calculation unit 22 converts the target braking torque amount NtF0 into the braking force at the tire contact point of the front wheels 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 wheels 4F. The target torque calculation unit 22 calculates the drive torque that generates a driving force at the tire contact point of the rear wheels 4R to cancel out 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 formula (4).

[0048]

[0049] The constant GmotR in formula (4) represents the rear-wheel drive system gear ratio. In the example of formula (4), the target drive torque amount NtR0 is calculated in such a way that the driving force generated by the target braking torque amount NtF0 at the rear wheels 4RF cancels out all of the braking force generated at the front wheels 4F, but the target drive torque amount NtR0 can also be calculated in such a way as to cancel out a part of the braking force generated by the target braking torque amount NtF0. That is, the driving force generated by the target drive torque amount NtR0 can be equal to, less than, or greater than the braking force generated by the target braking torque amount NtF0.

[0050] The target torque calculation unit 22 outputs the target braking torque amount NtF0 and the target drive torque amount NtR0 to the target torque determination unit 24.

[0051] The limit coefficient calculation unit 23 calculates the limit coefficient C that limits the target braking torque amount NtF0 according to the vehicle state of the vehicle 100. Figure 3 A block diagram showing a functional structure example of the limit coefficient calculation unit 23. The limit coefficient calculation unit 23 includes: a vehicle speed-dependent limit coefficient setting unit 30, a steady yaw rate calculation unit 31, a turning direction determination unit 32, a wheel speed difference-dependent limit coefficient setting unit 33, a yaw rate difference-dependent limit coefficient setting unit 34, and a limit coefficient setting unit 35.

[0052] The vehicle speed-dependent limit coefficient setting unit 30 sets the vehicle speed-dependent limit coefficient Cv according to the vehicle speed.

[0053] Figure 4(a) shows an example of setting the vehicle speed-dependent limit coefficient Cv. The vehicle speed-dependent limit coefficient Cv has a value in the range from "0" to "1". When the vehicle speed V is below the threshold V1 and when the vehicle speed V is above the threshold V4, the vehicle speed-dependent limit coefficient Cv is "0". In the range where the vehicle speed V is above the threshold V1 and below the threshold V2, as the vehicle speed V increases, the vehicle speed-dependent limit coefficient Cv increases from "0" to the value Cv1. In the range where the vehicle speed V is above the threshold V2 and below the threshold V3, as the vehicle speed V increases, the vehicle speed-dependent limit coefficient Cv changes from the value Cv1 to the value Cv2. In the range where the vehicle speed V is above the threshold V3 and below the threshold V4, as the vehicle speed V increases, the vehicle speed-dependent limit coefficient Cv decreases from the value Cv2 to "0".

[0054] Generally, it is known that in the frequency characteristics of the yaw rate response with respect to the steering input, when the vehicle speed V is low, the peak value of the gain at the yaw resonance frequency is small, and there is a phase delay in the yaw rate with respect to the steering. Therefore, if control intervention based on the target braking torque amount NtF0 is performed in the low vehicle speed region, it will encourage the delay in the vehicle response with respect to the steering. Therefore, the thresholds V1, V2, and the value Cv1 are determined in such a way that the control intervention based on the target braking torque amount NtF0 at low vehicle speeds is eliminated, or the target braking torque amount NtF0 becomes smaller. In addition, the thresholds V3, V4, and the value Cv2 are values for setting the maximum vehicle speed at which control intervention based on the target braking torque amount NtF0 is performed, and are set in the case where the speed is limited to an upper limit considering durability. The thresholds V1 to V4, the values Cv1, and Cv2 can be appropriately set, for example, based on vehicle parameters, simulations, and evaluations in an actual vehicle.

[0055] In addition, in Figure 4 the example of (a), Cv1 and Cv2 are set such that Cv1 > Cv2, but Cv1 can also be equal to or less than Cv2.

[0056] The stable yaw rate calculation unit 31 calculates the stable yaw rate γs based on the steering angle δf, the vehicle speed V, and vehicle parameters. For example, the stable yaw rate calculation unit 31 can calculate the stable yaw rate γs according to the above formula (1).

[0057] The turning direction determination unit 32 determines whether the turning direction obtained based on the driver's steering operation is consistent with the turning direction detected based on the yaw rate γr detected by the sensor. The rotation direction determination unit 32 outputs a determination result flag Ct. When the turning direction obtained based on the driver's steering operation is consistent with the turning direction detected based on the yaw rate γr, the value of the determination result flag Ct is set to "1", and in other cases, it is set to "0". For example, when the sign of the yaw rate γr detected by the sensor is consistent with the sign of the steady yaw rate γs, the turning direction determination unit 32 sets the value of the determination result flag Ct to "1", and in other cases, it is set to "0".

[0058] By determining the turning direction in this way, control intervention based on the target braking torque amount NtF0 is performed only when the vehicle turning direction based on the target yaw rate estimated from the driver's steering operation is consistent with the vehicle turning direction based on the actual yaw rate of the vehicle 100 obtained by the sensor, thereby suppressing the yaw rate gain. On the contrary, when the turning directions are inconsistent, the yaw rate gain is not suppressed, thereby preventing the behavior of the vehicle 100 from being delayed with respect to the driver's operation.

[0059] When the wheel speed difference Δωfr = ωF - ωR between the front wheels 4F and the rear wheels 4R is too large (for example, when slip occurs in the front wheels 4F and / or the rear wheels 4R), the wheel speed difference-dependent limit coefficient setting unit 33 sets the front-rear wheel speed difference-dependent limit coefficient Cfr that limits the target braking torque amount NtF0. 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 from "0" to "1". The front-rear wheel speed difference-dependent limit coefficient Cfr is "1" when the wheel speed difference |Δωfr| is below the threshold value Δωfr1, and decreases from "1" to "0" as the wheel speed difference |Δωfr| increases in the range where the wheel speed difference |Δωfr| is above the threshold value Δωfr1 and below the threshold value Δωfr2, and is "0" when the wheel speed difference |Δωfr| is above the threshold value Δωfr2. The threshold values Δωfr1 and Δωfr2 can be appropriately set using vehicle parameters, simulations, and experiments on actual vehicles.

[0060] When the wheel speed difference Δωlrf between the right front wheel 4FR and the left front wheel 4FL is too large (for example, when slip occurs in either the right front wheel 4FR or the left front wheel 4FL), the wheel speed difference-dependent limit coefficient setting unit 33 sets the left-right wheel speed difference-dependent limit coefficient Clrf that limits the target braking torque amount NtF0. 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 from "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 value Δωlrf1, decreases from "1" to "0" as the wheel speed difference |Δωlrf| increases in the range where the wheel speed difference |Δωlrf| is greater than the threshold value Δωlrf1 and less than or equal to the threshold value Δωlrf2, and is "0" when the wheel speed difference |Δωlrf| is greater than the threshold value Δωlrf2. The threshold values Δωlrf1 and Δωlrf2 can be appropriately set using vehicle parameters, simulations, and experiments on an actual vehicle.

[0061] Similar to the setting method of the left - right wheel speed difference - dependent limit coefficient Clrf, the wheel speed difference - dependent limit coefficient setting unit 33 sets the left - right wheel speed difference - dependent limit coefficient Clrr of 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 too large (for example, when slip occurs in either the right rear wheel 4RR or the left rear wheel 4RL).

[0062] The yaw rate difference - dependent limit coefficient setting unit 34 sets the yaw rate difference - dependent limit coefficient Cy of the target braking torque amount NtF0 when the yaw rate difference Δγ = γs - γr between the steady - state yaw rate γs predicted based on the driver's steering operation and the yaw rate γr obtained by the yaw rate sensor 7 is too large (for example, when slip occurs in any one or all of the four wheels during turning and the driver cannot perform 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 from "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 value Δγ1, decreases from "1" to "0" as the yaw rate difference |Δγ| increases in the range where the yaw rate difference |Δγ| is greater than the threshold value Δγ1 and less than or equal to the threshold value Δγ2, and is "0" when the yaw rate difference |Δγ| is greater than the threshold value Δγ2. The threshold values Δγ1 and Δγ2 can be appropriately set using vehicle parameters, simulations, and experiments on an actual vehicle.

[0063] The limit coefficient setting unit 35 selects the minimum value among the vehicle speed-dependent limit coefficient Cv, the front and rear wheel speed difference-dependent limit coefficient Cfr, the left and right wheel speed difference-dependent limit coefficients Clrf, Clrr, and the yaw rate difference-dependent limit coefficient Cy, and calculates the product obtained by multiplying the selected minimum value by the determination result flag Ct as the limit coefficient C = Ct × min(Cv, Cfr, Clrf, Clrr, Cy). The limit coefficient setting unit 35 outputs the limit coefficient C to the target torque determination unit 24.

[0064] The target torque determination unit 24 calculates the limited target braking torque amount NtF and the target driving torque amount NtR by limiting the target braking torque amount NtF0 and the target driving torque amount NtR0 calculated by the target torque calculation unit 22 using the limit coefficient C.

[0065] Figure 5 is a block diagram of a functional structure example 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.

[0066] The target torque correction unit 40 calculates the product C × NtF0 obtained by multiplying the target braking torque amount NtF0 by the limit coefficient C. The rate limiter 41 limits the time change rate of the product C × NtF0. The output of the rate limiter 41 is subjected to a low-pass filter 42 with a cut-off frequency fc4 to calculate the target braking torque amount NtF.

[0067] In addition, the target torque correction unit 43 calculates the product C × NtR0 obtained by multiplying the target driving torque amount NtR0 by the limit coefficient C. The rate limiter 44 limits the time change rate of the product C × NtR0. The output of the rate limiter 44 is subjected to a low-pass filter 45 with a cut-off frequency fc4 to calculate the target driving torque amount NtR. Here, the change rate limit values and the cut-off frequency fc4 of the rate limiters 41 and 44 are set so as not to affect the frequency band to be controlled.

[0068] Refer to Figure 1 The controller 8 outputs the target braking torque amount NtF and the target driving torque amount 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 to achieve the target braking torque amount NtF and the target driving torque amount NtR indicated by the controller 8. The front-wheel drive source 10F and the rear-wheel drive source 10R respectively generate a braking force corresponding to the target braking torque amount NtF and a driving force corresponding to the target driving torque amount NtR on the front wheels 4F and the rear wheels 4R.

[0069] Next, a mechanism for suppressing the yaw behavior of the vehicle when applying the braking torque determined as described above to the front wheels during the steering of the vehicle 100 will be described. In the following description, the vehicle body has a bilaterally symmetric shape in the front-back and left-right directions, and a two-wheel model is used in which the right and left wheels of the front wheels 4F and the rear wheels 4R are approximated as one wheel located at the center of the axle.

[0070] Figure 6 (a) is a diagram showing 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 observed from each coordinate system. The vehicle body coordinate system (solid line) is a coordinate system in which the coordinate system origin is the wheel center, the x-axis is set in a direction parallel to the left-right center line of the vehicle body with the front direction as the positive direction, the y-axis is set in a direction orthogonal to the x-axis with the left direction as the positive direction, and the z-axis is set in a way that forms a right-handed system with these x-axis and y-axis. The front wheel coordinate system (dashed line) is a coordinate system in which the coordinate system origin is the wheel center, the x-axis is set in a direction parallel to the front-rear direction of the wheel with the front direction as the positive direction, the y-axis is set in a direction orthogonal to the x-axis with the left direction as the positive direction, and the z-axis is set in a way that forms a right-handed system with these x-axis and y-axis.

[0071] The vehicle body coordinate system and the front wheel coordinate system share the origin. Here, it is assumed that the front wheel coordinate system (dashed line) rotates counterclockwise by only δf / Gstr around the wheel center with respect to the vehicle body coordinate system (solid line). This represents a state in which the front wheels 4F are steered by only δf / Gstr with respect to the vehicle body.

[0072] The braking force is the product Kf×Sf of the front slip ratio Sf and the front traction coefficient Kf. The front slip ratio Sf = (rF×ωF - V) / V is obtained by dividing the difference between the product of the wheel speed ωF of the front wheels 4F and the wheel radius rF of the front wheels 4F and the x-direction component of the vehicle speed V by the vehicle speed V. In an actual vehicle, it takes a certain amount of time for the braking force to generate the front slip ratio Sf with respect to the indicated braking torque of the motor. Therefore, there is a delay in generating the braking force Kf×Sf that balances the target braking torque amount NtF, but since this delay is sufficiently small with respect to the frequency of the steering angle change (i.e., the frequency of the yaw behavior of the vehicle), the influence can be ignored.

[0073] The braking force Kf×Sf acts in the x-axis direction of the front-wheel coordinate system. However, if the front wheel 4F is steered by only the steering angle δf / Gstr with respect to the vehicle body, it includes the y-axis direction component of the vehicle body coordinate system (Kf×Sf×sin(δf / Gstr)≒Kf×Sf×δf / Gstr). The direction of this y-axis direction component (Kf×Sf×δf / Gstr) is opposite to the turning direction. Therefore, if a braking force is generated on the front wheel 4F during steering, a yaw moment can be generated in the direction that cancels the yaw moment generated on the vehicle body due to steering. At this time, since a braking force (Kf×Sf×cos(δf / Gstr)≒Kf×Sf) is generated on the front wheel 4F in the negative direction of the x-axis of the vehicle body coordinate system, longitudinal acceleration is generated. To prevent or reduce the deceleration of the vehicle 100 caused by the braking force of the front wheel 4F, as Figure 6 shown in (b), a driving force Kr×Sr = -Kf×Sf is generated on the rear wheel 4R with the target driving torque amount NtR. Kr and Sr are the rear traction coefficient and the rear slip ratio.

[0074] The following shows the simulation results in the case where a front-wheel braking torque is applied according to the steering angular velocity αf = dδf / dt. Figure 7 It shows the frequency characteristics of the gain of the yaw rate response with respect to the steering input. The dashed line 50 represents a comparative example of the gain without applying the front-wheel braking torque, and the solid line 51 represents the gain when the front-wheel braking torque is applied. It can be Figure 7 seen that near 0 Hz where the steering angular velocity is relatively slow, the difference in gain between the case without applying the front-wheel braking torque and the case with applying the front-wheel braking torque is small. On the other hand, near the yaw resonance frequency Fres, the peak can be suppressed by applying the front-wheel braking torque. From this, it can be known that compared with the case without applying the front-wheel braking torque, the change in the magnitude of the yaw response of the vehicle body is suppressed between the driver's steering near the yaw resonance frequency Fres and the stable steering near 0 Hz.

[0075] Generally, it is known that the vehicle characteristics with small changes in the frequency characteristics of the yaw rate gain will increase the sense of stability in the functional test. Therefore, according to the present invention, the steering stability during high-speed driving with a higher resonance peak can be improved.

[0076] In the present invention, the target braking torque amount NtF is set by multiplying the steering angular velocity αf = dδf / dt by a gain because the higher the frequency of the steering input, the larger the target braking torque amount NtF is proportional to the angular frequency. Therefore, if the gain is set in such a way that the yaw rate gain is reduced to a desired value at the yaw resonance frequency Fres, the vibration damping effect based on the lateral force generated by braking can be improved.

[0077] In addition, by setting the target braking torque amount NtF corresponding to the steering angular velocity αf = dδf / dt, the vibration damping effect becomes higher as the steering frequency becomes higher. Similarly, by setting the target braking torque amount NtF based on the component extracted by applying a band-pass filter to the steering angle δf, the yaw rate gain in any frequency band can be reduced.

[0078] (Operation)

[0079] Figure 8 It is a flowchart showing an example of the vehicle vibration damping method of the embodiment.

[0080] 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.

[0081] 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. In addition, the target drive torque amount NtR0 for generating a driving force that cancels all or part of the braking force generated by the target braking torque amount NtF0 at the front wheels 4F at the rear wheels 4R is calculated. In step S6, the limit coefficient calculation unit 23 calculates the wheel speed differences Δωfr, Δωlrf, and Δωlrr. In step S7, the limit coefficient calculation unit 23 calculates the yaw rate difference Δγ. In step S8, the limit coefficient calculation unit 23 calculates the limit 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.

[0082] In step S9, the target torque determination unit 24 calculates the limited target braking torque amount NtF and the target drive torque amount NtR by limiting the target braking torque amount NtF0 and the target drive torque amount NtR0 calculated in step S5 with the limit coefficient C. In step S10, the power converter 9, the front wheel drive source 10F, and the rear wheel drive source 10R respectively cause the front wheels 4F and the rear wheels 4R to generate a braking force corresponding to the target braking torque amount NtF and a driving force corresponding to the target drive torque amount NtR. Then the process ends.

[0083] (Effect of the Embodiment)

[0084] (1) The controller 8 reduces the vibration of the vehicle 100 that can independently control the front-wheel drive source that generates driving force and braking force for the front wheels 4F and the rear-wheel drive source that generates driving force for the rear wheels 4R. When the time change of the steering angle accompanying the turning of the vehicle 100 is within a specified range, the controller 8 causes the front-wheel drive source to generate a braking force for the front wheels 4F, and causes the rear-wheel drive source to generate a driving force that cancels all or part of the braking force of the front wheels 4F.

[0085] The braking force generated by the front wheels 4F has a lateral force component relative to the vehicle body due to the steering of the front wheels 4F. By generating such a lateral force component in accordance with the turning motion of the vehicle body based on steering, a yaw moment in the direction opposite to the turning direction can be generated, and the yaw rate can be controlled without independently controlling the torque of the right and left wheels. In addition, by applying a driving torque that generates a driving force balanced with the braking force generated by the front wheels 4F to the rear wheels 4R, the acceleration and deceleration in the longitudinal direction of the vehicle body can be suppressed.

[0086] (2) The controller 8 can cause the front wheels to generate a braking force proportional to the time derivative of the steering angle.

[0087] Thus, the higher the steering frequency, the more the movement of the vehicle 100 in the yaw direction relative to the steering angle can be suppressed. If the difference in yaw rate gain between this yaw resonance frequency and 0 Hz (i.e., a steady steering angle input) is small, the damping property of the yaw movement is high. If the movement in the yaw direction of the lateral force generated by the front-wheel braking force proportional to the time derivative of the steering angle is damped, the more high-frequency components are included in the steering input (i.e., the faster the steering), the more a damping effect proportional to the input angular frequency can be obtained. As a result, by reducing the yaw rate gain at the yaw resonance frequency and not generating a front-wheel braking force for a steady steering angle input, it is possible to achieve damping of the yaw movement based on the reduction of the yaw rate gain difference.

[0088] (3) The controller 8 can cause the front wheels to generate a braking force proportional to the magnitude of a specified frequency component of the steering angle.

[0089] Thus, it is possible to apply a front-wheel braking input proportional to the frequency component extracted by applying a band-pass filter that extracts the component near the yaw resonance frequency to the time component of the steering angle input. As a result, it is possible to limit near the yaw resonance frequency and suppress the peak of the yaw rate gain, and at the same time, achieve damping of the yaw movement that has no influence on other frequency bands.

[0090] (4) The controller 8 can limit the braking force at least according to the speed of the vehicle 100. Thereby, when the speed of the vehicle 100 is low, by limiting the braking torque of the front wheels 4F, excessive vibration damping at low speeds can be suppressed. Generally, the difference in yaw rate gain between stable steering and at the yaw resonance frequency is more obvious at higher speeds and smaller at lower speeds. Therefore, if front wheel braking force is generated during relatively early steering when the vehicle is traveling at a low speed, the steering response may be impaired. Therefore, if the front wheel braking force is limited when the vehicle speed is low and the front wheel braking force is increased as the vehicle speed increases, the vibration damping effect when traveling at high speeds can be improved without impairing the steering response at low speeds.

[0091] (5) The controller 8 can limit the magnitude of the time change amount of the braking force. Thereby, by limiting the time change in the case where there is a time variation in the target braking torque amount NtF0, a sharp change in the behavior of the vehicle 100 can be suppressed.

[0092] (6) The controller 8 can limit the braking force at least when the change direction of the steering angle is different from the turning direction of the vehicle 100. Thereby, it is possible to prevent a situation where the driver feels that they cannot turn as intended when the direction intended by the driver is different from the moving direction of the vehicle.

[0093] (7) The controller 8 can limit the braking force at least when the rotational speed difference between the front wheels 4F and the rear wheels 4R exceeds a first threshold value.

[0094] Thereby, when excessive slip occurs in either or both of the front wheels 4F and the rear wheels 4R due to the generation of the target braking torque amount NtF, the front wheel braking force can be limited. Thereby, the skidding of the four wheels can be reduced, and the instability of the vehicle's behavior can be suppressed.

[0095] (8) The controller 8 can limit the braking force at least when the rotational speed difference between the right wheel and the left wheel exceeds a second threshold value.

[0096] Thereby, when excessive slip occurs in either one of the right wheel or the left wheel of the front wheels 4F and either one of the right wheel or the left wheel of the rear wheels 4R due to the generation of the target braking torque amount NtF, or when excessive slip occurs simultaneously in either one of the right wheel or the left wheel of the front wheels 4F and the rear wheels 4R, the front wheel braking force can be limited. Thereby, the skidding of the four wheels can be reduced, and the instability of the vehicle's behavior can be suppressed.

[0097] (9) The braking force can be limited at least when the difference between the yaw rate calculated based on at least the steering angle and the yaw rate detected by the sensor exceeds a third threshold value.

[0098] Accordingly, when any one or all of the four wheels slip due to the generation of the target braking torque amount NtF and the driver cannot perform the desired turning, the front wheel braking force can be restricted. As a result, the slip of the four wheels can be reduced, and the instability of the vehicle behavior can be suppressed.

[0099] All examples and conditional terms described herein are for teaching purposes to help the reader understand the present invention and the concepts provided by the inventor for technological progress, and should be construed as not being limited to the above examples and conditions specifically described in this specification and the structures of the examples showing the superiority and inferiority of the present invention. The embodiments of the present invention have been described in detail, but it should be understood that various changes, substitutions, and modifications can be made thereto without departing from the spirit and scope of the present invention.

[0100] Symbol Explanation

[0101] 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 Right 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: Storage 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: Stable 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 for reducing vibration of a vehicle capable of independently controlling a front-wheel drive source that generates driving force and braking force for the front wheels and a rear-wheel drive source that generates driving force for the rear wheels, characterized in that when the time change of the steering angle accompanying the turning of the vehicle is within a specified range, the front-wheel drive source causes the front wheels to generate braking force, and the rear-wheel drive source causes the rear wheels to generate a driving force that cancels all or part of the braking force of the front wheels.

2. The vehicle vibration damping method according to claim 1, characterized in that the front wheels generate the braking force proportional to the time derivative of the steering angle.

3. The vehicle vibration damping method according to claim 1, characterized in that the front wheels generate the braking force proportional to the magnitude of a specified frequency component of the steering angle.

4. The vehicle vibration damping method according to claim 1, characterized in that at least the braking force is restricted according to the speed of the vehicle.

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

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

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

8. The vehicle vibration damping method according to claim 1, characterized in that when the rotational speed difference between the right wheels and the left wheels exceeds a second threshold value, at least the braking force is restricted.

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

10. A vehicle shock absorber that reduces the vibration of the vehicle, characterized in that, Comprising: a front-wheel drive source that causes the front wheels to generate driving force and braking force; a rear-wheel drive source that independently of the driving force and braking force generated by the front wheels causes the rear wheels to generate driving force; a controller that performs the following processing: when the time change of the steering angle accompanying the turning of the vehicle is within a specified range, a process of causing the front-wheel drive source to cause the front wheels to generate braking force; a process of causing the rear-wheel drive source to cause the rear wheels to generate a driving force that cancels all or part of the braking force of the front wheels.

Images