Vehicle braking method and vehicle braking device

Abstract

To provide a vehicle braking method and a vehicle braking device that are unlikely to cause a large change in a pitch angle velocity during a period until a target pitch angle is achieved.SOLUTION: Calculations are performed for: a vehicle body pitch angle gain, determined from vehicle specifications, according to vehicle deceleration for each braking force distribution ratio between front and rear wheels; target braking force frequency, derived from a target braking force change rate and target braking force; target deceleration corresponding to the target braking force; and a target braking force distribution ratio between the front and rear wheels, corresponding to the target pitch angle gain and the target braking force frequency, derived from the vehicle body pitch angle gain corresponding to the target deceleration. Then, braking force of the vehicle front and rear wheels is controlled to achieve the calculated target braking force distribution ratio between the front and rear wheels.SELECTED DRAWING: Figure 2

Description

Technical Field

[0001] The present invention relates to a braking method and a braking device for a vehicle that can control the braking forces of the front wheels and the rear wheels of the vehicle respectively.

Background Art

[0002] Patent Document 1 proposes a vehicle braking system that detects the pitch angle of a vehicle (vehicle body) during braking and controls the braking force ratio of the front wheels and the rear wheels using the difference from a preset target pitch angle.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] However, in the vehicle braking system described in Patent Document 1, the frequency response characteristics of the pitch angle generated in the vehicle are not considered, so a large pitch angular velocity change occurs before the target pitch angle is achieved. An object of the present invention is to provide a vehicle braking method and a vehicle braking device in which a large pitch angular velocity change hardly occurs before the target pitch angle is achieved.

Means for Solving the Problems

[0005] According to one aspect of the present invention, in a vehicle capable of controlling the braking forces of the front and rear wheels of the vehicle respectively, a target braking force of the vehicle is calculated based on the amount of braking operation by the driver in the vehicle or the magnitude of the required deceleration in the automatic driving state, a target pitch angle of the vehicle is calculated or set, and in a vehicle braking method of controlling the braking forces of the front and rear wheels of the vehicle according to the target braking force so that the target pitch angle is achieved, the frequency response characteristics of the pitch angle of the vehicle obtained from the specifications of the vehicle are calculated for each front-rear distribution ratio of the braking forces of the front and rear wheels of the vehicle according to the deceleration of the vehicle, a target braking force change speed which is the differential value of the target braking force and a target braking force frequency are calculated from the target braking force, a target deceleration of the vehicle corresponding to the target braking force is calculated, a front-rear distribution ratio of the target braking forces of the front and rear wheels of the vehicle corresponding to the target pitch angle and the target braking force frequency is calculated from the frequency response characteristics of the pitch angle of the vehicle corresponding to the target deceleration, and the braking forces of the front and rear wheels of the vehicle are controlled so that the front-rear distribution ratio of the target braking force is achieved.

Effect of the Invention

[0006] According to the present invention, since the frequency response characteristics of the pitch angle of the vehicle are considered, it is possible to control the front-rear distribution ratio of the braking force in a feed-forward manner, whereby the target pitch angle is quickly achieved and a large change in the pitch angular velocity is unlikely to occur until it is achieved.

Brief Description of the Drawings

[0007]

Figure 1

Figure 2

Figure 3

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Figure 6

Figure 7

Figure 8

Figure 9

Figure 10

Figure 11

Figure 12

Mode for Carrying Out the Invention

[0008] Hereinafter, embodiments of the present invention will be described with reference to the drawings. It should be noted that each drawing is schematic and may be different from the actual one. In addition, the embodiments of the present invention shown below are examples of devices and methods for embodying the technical idea of the present invention, and the technical idea of the present invention does not specify the structure, arrangement, etc. of the components as the following. The technical idea of the present invention can be variously modified within the technical scope defined by the claims described in the claims.

[0009] The vehicle braking system according to the embodiment shown in FIG. 1 controls the operating state of the braking devices 2 provided on the front wheels 1F and the rear wheels 1R. The braking devices 2 provided on the front wheels 1F and the rear wheels 1R are so-called disc brakes, which brake by clamping a disc rotor (rotor) 3 attached to the wheel with brake pads 4. In each braking device 2, inside the caliper, the brake pad 4 is arranged in a stationary state on one end face side of the rotor 3, and the brake pad 4 arranged on the opposite end face side is pressed against the rotor 3 to obtain a braking force. For this purpose, inside the caliper, a piston that reciprocates in the separating and contacting direction between the brake pad 4 and the rotor 3 according to the hydraulic pressure (oil pressure) is arranged. This piston moves in the direction of pressing the brake pad 4 against the rotor 3 when the hydraulic pressure applied to the pressure receiving surface on the side opposite to the brake pad 4 side is in a positive pressure (pressurized state). That is, each braking device 2 is provided with a hydraulic braking mechanism 7.

[0010] In this embodiment, in order to enable automatic driving, an electric booster 18 is used as a hydraulic pressure generating device that generates the hydraulic pressure to the pistons 6 of each braking device 2. This electric booster 18 is a hydraulic pump driven by an electric motor (electric actuator) not shown, and can pressurize the hydraulic pressure to the pistons of each braking device 2 to at least a positive pressure. The positive pressure is generally a state where the pressure is higher than the atmospheric pressure. When the electric motor is not driven, the hydraulic pressure is equivalent to the atmospheric pressure. In this embodiment, the electric booster 18 is mechanically or hydraulically connected to the brake pedal 16, and when the brake pedal 16 is depressed, a positive pressure hydraulic pressure corresponding to the depression amount of the brake pedal 16 is output. The operating state of the electric booster 18 is controlled by a booster controller 19.

[0011] On the hydraulic output side of the electric booster 18, a hydraulic pressure adjusting device 20 capable of individually adjusting the hydraulic pressure of the braking device 2 of each wheel is interposed between the braking device 2 of each wheel. This hydraulic pressure adjusting device 20 can individually hold, depressurize, or pressurize the hydraulic pressure of the braking device 2 of each wheel. As a result, braking force can be applied to each wheel or the braking force can be increased or decreased. Specifically, it has a hydraulic pressure adjusting function equivalent to that of an anti-skid control device (ABS) for reducing the wheel lock tendency and a vehicle behavior control device (VDC) for adjusting the behavior of the vehicle represented by the yaw rate and lateral acceleration. In this hydraulic pressure adjusting device 20, regardless of the output hydraulic pressure of the electric booster 18, the hydraulic pressure of the braking device 2 of each wheel can be adjusted. For example, by a switching valve provided in the hydraulic pressure adjusting device 20, the braking device 2 of each wheel can be connected (directly connected) to the electric booster 18 or disconnected from the electric booster 18. That is, in a state where the braking device 2 is directly connected to the electric booster 18, the output hydraulic pressure of the electric booster 18 is directly supplied to the braking device 2 (hydraulic braking mechanism 7). In a state where the braking device 2 is disconnected from the electric booster 18, the hydraulic pressure of the braking device 2 can be individually adjusted by the hydraulic pressure adjusting device 20. The operating state of this hydraulic pressure adjusting device 20 is controlled by a hydraulic pressure controller 21. In this embodiment, since each braking device 2 can adjust the braking force by hydraulic pressure, the hydraulic pressure controller 21 can be read as a braking force controller.

[0012] As described above, this vehicle is provided with an automatic driving controller 13 for enabling automatic driving. This automatic driving controller 13 is, for example, for achieving a driving state according to the driving route in conjunction with a navigation system (not shown), or for executing well-known following vehicle driving control, obstacle avoidance driving control, constant speed driving control, etc. Specifically, it is in charge of controlling the operating state of a drive source such as an engine or a driving electric motor (not shown) and the steering state of the steered wheels by a steering device, and outputs necessary control commands to a drive source controller and a steering controller (both not shown). Therefore, this vehicle is provided with control input acquisition means such as various sensors, cameras (image pick-up devices), and distance meters necessary for automatic driving. When it becomes necessary to decelerate the vehicle during automatic driving, the required deceleration of the vehicle is output as a required deceleration to a booster controller 19 and a hydraulic controller 21.

[0013] The hydraulic controller 21 is an electronic control unit (ECU: Electronic Control Unit) that controls the braking hydraulic pressure applied to the braking devices 2 (hydraulic braking mechanisms 7) of each wheel 1F, 1R by controlling the operating states of the actuators and valves within the hydraulic adjustment device 20. Therefore, this hydraulic controller 21 is equipped with a computer system having a high-level arithmetic processing capability. This computer system is configured to include a processor 14 that exhibits a high-level arithmetic processing capability and a storage device 15 that stores information such as programs and sensor signals, similar to a well-known computer system. The processor 14 is composed of, for example, a CPU (Central Processing Unit) or an MPU (Micro-Processing Unit). The storage device 15 is composed of a semiconductor storage device, a magnetic storage device, and an optical storage device. The storage device 15 may further include a register, a cache memory, and a memory used as a main memory. The arithmetic processing executed by the hydraulic controller 21 is realized, for example, by the processor 14 executing a computer program stored in the storage device 15 of the hydraulic controller 21. Also, the arithmetic processing executed by the hydraulic controller 21 may be executed by a functional logic circuit set in a general-purpose semiconductor integrated circuit. For example, the hydraulic controller 21 may have a programmable logic device such as a field programmable gate array. Note that other controllers also have equivalent configurations and functions. Also, data sharing and mutual communication can be performed between the controllers.

[0014] This vehicle is provided with an automatic driving switch 11 for activating the automatic driving controller 13 to put the automatic driving into an active state. When the occupant turns on the automatic driving switch 11, the automatic driving is activated by the automatic driving controller 13 and the automatic driving is started. Also, this vehicle is provided with a driving characteristic selection switch 12 that can select the driving state of the vehicle, for example, the driving characteristics when the vehicle turns. This driving characteristic selection switch 12 can select, for example, a sports driving mode that can exhibit sharp turning characteristics such as winding road, an eco mode that suppresses the fuel consumption of the engine or the power consumption of the driving battery, a comfort mode that achieves a comfortable riding feeling, and the like. Also, this vehicle is provided with an accelerator sensor 5 that detects the depression state of the accelerator pedal 17 and a brake sensor 6 such as a pedal force sensor or a hydraulic pressure sensor that detects the depression state of the brake pedal 16, similar to a general vehicle.

[0015] Next, the arithmetic processing performed by the hydraulic controller 21 particularly during normal braking (deceleration during the automatic driving state) will be described using the flowchart of FIG. 2. This arithmetic processing is executed, for example, at a predetermined arithmetic cycle. First, in step S1, it is determined whether or not it is in a braking state (or whether there is a required deceleration from the automatic driving controller 11). If it is in a braking state (or there is a required deceleration), the process proceeds to step S2, and if not, the process returns. In step S2, it is determined whether or not VDC (or ABS) is non-intervening. If VDC (ABS) is non-intervening, the process proceeds to step S3, and if not, the process returns. In step S3, the driving characteristics (mode) selected by the driving characteristic selection switch 12 are read. Next, the process proceeds to step S4 to set the target pitch angle. As will be described later, this target pitch angle represents the frequency response characteristics of the pitch angle targeted during braking of the vehicle in terms of the gain for each frequency. Next, the process proceeds to step S5 to calculate the target braking force to be achieved by the vehicle from the output of the brake sensor 6 or the required deceleration.

[0016] Next, proceed to step S6, and calculate the maximum braking force achievable by the vehicle as described later. Note that this maximum braking force may be a fixed value. Next, proceed to step S7, and calculate the target braking force change rate from the differential value of the target braking force calculated in step S5. Next, proceed to step S8, and calculate the target braking force frequency as described later. This target braking force frequency is considered, for example, as a case where the target braking force changes periodically in a sine waveform with respect to the time axis, and estimates how the target braking force changes in terms of period (frequency) between the target braking force and the maximum braking force, with the target braking force change rate, which is the differential value of the target braking force, as the maximum speed. Next, proceed to step S9, and calculate the target deceleration by dividing the target braking force by the mass of the vehicle, for example. When a required deceleration is requested from the automatic driving controller 13, the required deceleration may be set as the target deceleration as it is. Next, proceed to step S10, and calculate the front-rear distribution ratio of the target braking force of the vehicle as described later. For the calculation of this front-rear distribution ratio of the target braking force, it is necessary to calculate and store in advance the frequency response characteristics (body pitch angle gain) of the pitch angle of the vehicle, particularly the body pitch angle, obtained from the specifications of the vehicle, for each front-rear distribution ratio of the braking force according to the deceleration of the vehicle. Details thereof will be described later. Next, proceed to step S11, output a control signal that achieves the front-rear distribution ratio of the target braking force of the vehicle obtained in step S10 to the hydraulic pressure adjustment device 20, and then return.

[0017] Before explaining the specific circuit configuration, operation, and effects in this arithmetic processing, the frequency response characteristics of the pitch angle generated in the vehicle, particularly the body pitch angle, will be explained. During braking (when the tires are braking), forces as shown in FIG. 3 act on the vehicle. The vehicle center of gravity O G is acted upon by a (front-rear) braking force Fx represented by the product value of the vehicle mass M and the braking deceleration a B . The line segment connecting the link instantaneous rotation center O LF of the front suspension and the contact point G F of the front tire is called the front suspension virtual link, and the angle of this front suspension virtual link with respect to the ground is called the anti-dive angle θ F . Also, the line segment connecting the link instantaneous rotation center O LR of the rear suspension and the contact point G RThe line segment connecting them is called the rear suspension virtual link, and the angle of this rear suspension virtual link with respect to the ground is called the anti-lift angle θ R Generally speaking, the anti-lift angle θ R is larger than the anti-dive angle θ F . Therefore, a compressive force acts on the instantaneous rotation center O LF of the front suspension link and the contact point G F of the front tire. When the rear distribution ratio of the front-to-rear braking force distribution ratio is α, this compressive force is expressed as (1 - α)·Fxcosθ F . Conversely, a tensile force acts on the instantaneous rotation center O LR of the rear suspension link and the contact point G R of the rear tire, and this tensile force is expressed as α·Fxcosθ R . The compressive force (1 - α)·Fxcosθ F at the front tire contact point G F is decomposed into the vehicle longitudinal direction and the height direction. The front wheel braking force Fx F that pulls the front tire contact point G F towards the rear of the vehicle is expressed as (1 - α)·Fx, and the force (1 - α)·Fxtanθ F that lifts the front tire contact point G F is generally called the anti-dive force. Similarly, when the tensile force α·Fxcosθ R at the rear tire contact point G R is decomposed into the vehicle longitudinal direction and the height direction, the rear wheel braking force Fx R that pulls the rear tire contact point G R towards the rear of the vehicle is expressed as α·Fx, and the force α·Fxtanθ R that pulls down the rear tire contact point G R is generally called the anti-lift force. The sum of the front wheel braking force Fx F and the rear wheel braking force Fx R is the braking force Fx

[0018] This vehicle was modeled as shown in Figure 4. Here, the symbol I P in the figure is the pitch moment of inertia of the vehicle body (vehicle), h is the height of the vehicle center of gravity O G , C F is the reduction coefficient of the front suspension, K F is the spring constant of the same, and LF is the vehicle center of gravity O G to the front tire contact point G F in the longitudinal vehicle length, C R is the damping coefficient of the rear suspension, K R is also the spring constant, L R is the vehicle center of gravity O G to the rear tire contact point G R in the longitudinal vehicle length, θ P is the vehicle body (vehicle) pitch angle, My is the pitch moment acting on the vehicle center of gravity O G Using these and the symbols in FIG. 3, the vehicle body pitch angle θ P and the pitch moment My are expressed by the following equation (1). As is clear from equation (1), the vehicle body pitch angle θ P is proportional to the braking deceleration a B (or the target braking force Fx) and has a second-order frequency response characteristic.

Equation

[0019] When the frequency response characteristics of this vehicle body pitch angle are represented by gain (Bode diagram), they appear as shown by the solid line in Fig. 5 (the figure is slightly exaggerated). As is clear from Fig. 5, the frequency response characteristics of the vehicle body pitch angle gain can be divided into three parts: near 0 Hz, where the vehicle body pitch angle gain is in a steady low-frequency band (the first frequency band in the figure); a vehicle body pitch resonance frequency band (the second frequency band) where the vehicle body pitch angle resonates at a frequency higher than this low-frequency band; and a high-frequency band (the third frequency band) where the vehicle body pitch angle gain shows a decreasing trend at a frequency higher than this vehicle body pitch resonance frequency band. The frequency in the vehicle body pitch angle gain can be considered, for example, as the operation speed of the brake pedal. In the low-frequency band where the brake pedal is operated slowly, it is not necessary to eliminate pitching of the vehicle (vehicle body) itself, but there is a requirement to reduce its gain. In the vehicle body pitch resonance frequency band, there is a requirement to suppress the resonance of the vehicle body pitching and make the gain equivalent to that in the low-frequency band. In the high-frequency band, while it is desired to suppress the vehicle body pitching, if the gain becomes negative, the vehicle body is felt not to follow the brake operation, so there is a requirement to increase the gain within an achievable range. Summing these up, the gain in the frequency response characteristics as shown by the dashed-dotted line in Fig. 5 is obtained as the target pitch angle. Therefore, it is desirable to make the vehicle body pitch angle gain approach the target pitch angle gain in each of the low-frequency band, the vehicle body pitch resonance frequency band, and the high-frequency band. Note that it is also possible to further divide or reduce the number of divisions of the frequency band of the vehicle body pitch angle gain, but for a real vehicle, sufficient effects are obtained with the above number of frequency band divisions.

[0020] Here, looking at the above formula (1), the braking force front-rear distribution ratio (rear-side distribution ratio) α is involved as a variable. Therefore, when the braking force front-rear distribution ratio (rear-side distribution ratio) α is changed, as shown in FIG. 6, in this embodiment, when the braking force front-rear distribution ratio (rear-side distribution ratio) α is decreased, the vehicle body pitch angle gain increases, and when it is increased, it decreases. Focusing on the front-side distribution ratio (1 - α) of the braking force front-rear distribution ratio, when the front-side distribution ratio (1 - α) is decreased, the vehicle body pitch angle gain decreases, and when it is increased, it increases. The increase and decrease of the vehicle body pitch angle gain due to the braking force front-rear distribution ratio (rear-side distribution ratio) α appear such that the vehicle body pitch angle gain moves parallelly in the vertical direction on the Bode diagram. Note that the above-described increase and decrease (behavior) of the vehicle body pitch angle gain with respect to the braking force front-rear distribution ratio (rear-side distribution ratio) α is related to the anti-lift angle θ R is limited to vehicles where the anti-lift angle θ F is larger than the anti-dive angle θ R When the anti-lift angle θ of the vehicle F is smaller than the anti-dive angle θ LF a tensile force acts on the link instantaneous rotation center O F of the front suspension and the ground contact point G LR of the front tire, and a compressive force acts on the link instantaneous rotation center O R of the rear suspension and the ground contact point G

[0021] of the rear tire. Therefore, when the braking force front-rear distribution ratio (rear-side distribution ratio) α is decreased, the vehicle body pitch angle gain decreases, and when it is increased, it increases. Focusing on the front-side distribution ratio (1 - α) of the braking force front-rear distribution ratio, when the front-side distribution ratio (1 - α) is decreased, the vehicle body pitch angle gain increases, and when it is increased, it decreases.Therefore, if the front-rear braking force distribution ratio (rear-side distribution ratio) α is appropriately set so that the vehicle body pitch angle gain in Fig. 5 can be made to match the target pitch angle gain (minimize the difference between the two), then by appropriately setting the target pitch angle gain, it becomes possible to adjust the pitching state actually occurring in the vehicle. For example, if the normal target pitch angle gain in Fig. 7 is assumed to be when the driving characteristics (mode) are not set, if the target pitch angle gain is made larger than this, the pitching occurring in the vehicle will become slightly larger, so the passengers can feel a comfortable ride. Therefore, when the comfort mode is selected, such a target pitch angle gain may be set. On the other hand, when the sports driving mode is selected, since it is desired to reduce the pitching occurring in the vehicle, by setting a target pitch angle gain smaller than the normal target pitch angle gain, the passengers can feel the crisp behavior of the vehicle. For such a crisp vehicle behavior, there may be cases where the followability of the vehicle body to the braking operation in the high-frequency band is required. Therefore, when the sports driving mode is selected, not only the normal target pitch angle gain may be simply reduced, but also the target pitch angle gain in the high-frequency band may be increased.

[0022] For example, in the board diagram of Fig. 5, assuming that the frequency of the current braking force, that is, the frequency of the target braking force, can be specified, the target value of the vehicle body pitch angle gain at that frequency is set from the target pitch angle gain in Fig. 7, and among the vehicle body pitch angle gains that change according to the front-rear braking force distribution ratio (rear-side distribution ratio) α, if the front-rear braking force distribution ratio (rear-side distribution ratio) α of the vehicle body pitch angle gain having the intersection of the target braking force frequency and the target pitch angle gain is set as the target front-rear braking force distribution ratio of the vehicle, then the pitching of the vehicle close to the target pitch angle gain of the selected driving characteristics (mode) can be achieved by the hydraulic pressure (braking force) output from the hydraulic pressure adjustment device 20 when a control signal for achieving this target front-rear braking force distribution ratio is input. Here, once again, looking at Equation (1), in addition to the above variables, the braking deceleration a B of the vehicle is intervening as a variable. Therefore, the vehicle body pitch angle gain for obtaining the intersection of the target braking force frequency and the target pitch angle gain depends not only on the front-rear braking force distribution ratio (rear-side distribution ratio) α but also on the braking deceleration aB also changes accordingly. Therefore, in this embodiment, the braking deceleration a B is used as the target deceleration, and the vehicle body pitch angle gain corresponding to the target deceleration is obtained in advance for each braking force front-rear distribution ratio (rear-side distribution ratio) α and mapped. A map of the vehicle body pitch angle gain corresponding to the target deceleration is selected, and the vehicle body pitch angle gain having an intersection with the target braking force frequency and the target pitch angle gain is extracted. The braking force front-rear distribution ratio (rear-side distribution ratio) α of the vehicle body pitch angle gain is set as the braking force front-rear distribution ratio of the vehicle. Here, the target braking force calculated by the arithmetic processing will be described. As described above, the target braking force is calculated from the output of the brake sensor 6 or the required deceleration from the automatic driving controller 13. For example, when the output value of the brake sensor 6 is read every 0.01 seconds and the arithmetic processing in FIG. 2 is performed every 5 sampling periods, if it is considered that the target braking forces corresponding to the brake sensor outputs at each sampling are arranged in the time axis direction for 5 sampling periods, the arranged and stored target braking forces have a slope with respect to the time axis. Similarly, if the reading timing of the required deceleration output from the automatic driving controller 13 is considered to be equivalent to the output value sampling period of the brake sensor, the target braking forces stored at each reading timing also have a slope with respect to the time axis. That is, the target braking force calculated by the arithmetic processing has a change rate.

[0023] FIG. 8 is a block diagram of an arithmetic (digital) circuit constituting steps S6 to S10 of the arithmetic processing in FIG. 2. This arithmetic circuit includes a maximum braking force calculation unit 31 that calculates the maximum braking force Fx that can be achieved by the vehicle MAX a differentiator 32 that differentiates the target braking force Fx to calculate the target braking force change rate Fx', and the Fx calculated by the maximum braking force calculation unit 31 MAX , the target braking force change rate Fx' calculated by the differentiator 32, and a target braking force frequency calculation unit 33 that calculates the target braking force frequency f from the target braking force Fx, and a divider 34 that divides the target braking force Fx by the mass M of the vehicle to calculate the target deceleration Gx (= braking deceleration a B ), and the target braking force frequency f calculated by the target braking force frequency calculation unit 33, the target pitch angle gain g at the target braking force frequency f TPand a rear braking force distribution ratio calculation unit 35 that calculates the rear braking force distribution ratio (front-rear braking force distribution ratio) α from the target deceleration Gx. The circuit is all digital, that is, it is constructed by software on a computer system.

[0024] In the maximum braking force calculation unit 31 of this calculation circuit, the friction coefficient state of the road surface (μ in the figure) is multiplied by the mass M of the vehicle and the gravitational acceleration g to obtain the maximum braking force Fx that the vehicle can achieve. MAX Calculate. This maximum braking force Fx MAX Since it is the braking force corresponding to the maximum deceleration that the vehicle can achieve on the road surface, it can be read as the braking force corresponding to the maximum deceleration. Note that for the maximum braking force Fx MAX For example, when μ = 1, Fx MAX = M·g may be used. In the target braking force frequency calculation unit 33, the target braking force frequency f is calculated as follows. As shown in FIG. 9, assuming that the target braking force Fx changes periodically with a sine wave, the maximum speed at time t = 0 is the target braking force change speed Fx', and the one-sided amplitude of the sine wave is represented by (Fx MAX - Fx) and the angular velocity ω is set to Fx' / (Fx MAX - Fx), then from ω = 2πf, the target braking force frequency f is obtained as f = Fx' / 2π·(Fx MAX - Fx). In the rear braking force distribution ratio calculation unit 35, the rear braking force distribution ratio (front-rear braking force distribution ratio) α is calculated as follows. As described above, in this embodiment, since the vehicle body pitch angle gain corresponding to the target deceleration Gx is obtained in advance for each rear braking force distribution ratio (front-rear braking force distribution ratio) α and mapped, first, a map of the vehicle body pitch angle gain corresponding to the target deceleration Gx calculated by the differentiator 32 is selected. In step S4 of the calculation process in FIG. 2, since the frequency response characteristics of the target pitch angle gain according to the running characteristics (mode) are set, the target pitch angle gain g PT of the target braking force frequency f in this frequency response characteristic is obtained. As shown in FIG. 10, the selected map of the vehicle body pitch angle gain stores the frequency response characteristics for each rear braking force distribution ratio (front-rear braking force distribution ratio) α. Therefore, the target braking force frequency f and the target pitch angle gain g PTExtract the frequency response characteristics of the vehicle body pitch angle gain having the intersection point, and set the braking force rear distribution ratio (front-rear braking force distribution ratio) α of the frequency response characteristics to the target front-rear braking force distribution ratio of the vehicle.

[0025] Hereinafter, the braking system of the vehicle according to the embodiment by the arithmetic processing of FIG. 2 and the arithmetic circuit of FIG. 8, the braking system in a conventional vehicle that does not control the front-rear distribution ratio of braking force, and the braking force characteristics of the vehicle braking system of Patent Document 1 above will be described. FIG. 11 shows the braking system of a conventional (non-braking force controlled) vehicle when braking straight ahead at a magnitude of 0.5G from time t0, the vehicle braking system of Patent Document 1 above, and the change over time of the rear-side distribution ratio of braking force and the vehicle body pitch angle by the vehicle braking system of the embodiment. The solid line indicates the vehicle braking system of the embodiment, the two-dot chain line indicates the vehicle braking system of Patent Document 1, and the broken line indicates the braking system of a conventional vehicle. As is clear from FIG. 11, in the vehicle braking system of the embodiment, since the rear-side distribution ratio of braking force is set rapidly and in a feed-forward manner, the vehicle body pitch angle can be rapidly converged to the target pitch angle. On the other hand, in the vehicle braking system of Patent Document 1, since the difference between the vehicle body pitch angle and the target pitch angle is fed back, it takes time to converge to the target pitch angle. If the feedback control gain is increased to accelerate the convergence to the target pitch angle in the vehicle braking system of Patent Document 1, there is a risk that the rear-side distribution ratio of braking force, which is the control output, and the vehicle body pitch angle will oscillate. FIG. 12 shows the frequency response characteristics during straight-ahead braking of the braking system of a conventional (non-braking force controlled) vehicle, the vehicle braking system of Patent Document 1 above, and the vehicle braking system of the embodiment, in terms of the vehicle body pitch angle gain. The solid line indicates the vehicle braking system of the embodiment, the two-dot chain line indicates the vehicle braking system of Patent Document 1, and the broken line indicates the braking system of a conventional vehicle. For braking, a sine wave vibration of ±0.1G was added to the target braking force of 0.5G magnitude to obtain the frequency response characteristics. Since both the vehicle braking system of the embodiment and the vehicle braking system of Patent Document 1 use the target pitch angle, the vehicle body pitch angle gain can be reduced compared to the braking system of a conventional vehicle.However, in the vehicle braking system of the embodiment, an increase (resonance) in gain with respect to the steady-state vehicle pitch angle gain in the low-frequency band of the vehicle pitch angle gain in the vehicle body pitch resonance frequency band can be suppressed to be equal to or less than that of a conventional vehicle braking system, whereas in the vehicle braking system of Patent Document 1, the resonance of the vehicle pitch angle gain has increased.

[0026] Thus, in this embodiment, the vehicle pitch angle gain obtained from the vehicle specifications is calculated for each braking force front-rear distribution ratio (rear-side braking force distribution ratio) α according to the vehicle deceleration, the target braking force frequency is calculated from the target braking force change speed and the target braking force, the target deceleration corresponding to the target braking force is calculated, the target pitch angle gain is calculated from the vehicle pitch angle gain corresponding to the target deceleration, and the target braking force front-rear distribution ratio (rear-side braking force distribution ratio) α corresponding to the target braking force frequency is calculated. By controlling the braking forces of the front wheels and rear wheels of the vehicle so that the target braking force front-rear distribution ratio is achieved, it becomes possible to feedforward control the braking force front-rear distribution ratio, whereby the target pitch angle is quickly achieved and a large change in pitch angular velocity is unlikely to occur until it is achieved.

[0027] Also, by calculating the target braking force frequency using the braking force equivalent to the maximum deceleration that the vehicle can achieve, the target braking force frequency can be accurately obtained. Further, by setting the target braking force change speed as the maximum speed in a sine wave, calculating the braking force equivalent to the maximum deceleration using the mass of the vehicle and the friction coefficient state of the road surface, setting the value obtained by subtracting the target braking force from the braking force equivalent to the maximum deceleration as the single amplitude in the sine wave, and calculating the target braking force frequency by dividing the maximum speed by the single amplitude, the target braking force frequency can be obtained more accurately.

[0028] Also, by comparing the vehicle pitch angle gain for each braking force front-rear distribution ratio corresponding to the target deceleration and setting the braking force front-rear distribution ratio of the vehicle pitch angle gain that can achieve the intersection of the target pitch angle gain and the target braking force frequency as the target braking force front-rear distribution ratio of the vehicle, the pitching generated in the vehicle can be brought closer to the target pitch angle.

[0029] Also, by setting the target pitch angle (gain) so as to reduce the vehicle body pitch angle gain in the low frequency band near 0 Hz, steady pitching in the low frequency band can be suppressed.

[0030] Also, by setting the target pitch angle (gain) so that the vehicle body pitch angle gain in the vehicle body pitch resonance frequency band is made equal to that in the low frequency band, the resonance of pitching of the vehicle can be reduced and made equal to the suppressed steady pitching. Also, by setting the target pitch angle (gain) so as to increase the vehicle body pitch angle gain in the high frequency band, pitching can be made to occur during braking even in the high frequency band.

[0031] In the above embodiment, only the example of generating and adjusting the braking force of each wheel hydraulically has been described in detail. Instead, the braking force of each wheel may be generated and adjusted by an electric actuator such as an electric motor, or the electric actuator may be used supplementarily for generating and controlling the braking force. Also, in the above embodiment, the target pitch angle (gain) is set according to the selected driving characteristics (mode) or increased or decreased according to the frequency. However, as described in Patent Document 1 above, the target pitch angle may be a fixed value, or the target pitch angle gain may be a constant value.

Explanation of Reference Numerals

[0032] 1F... front wheel, 1R... rear wheel, 2... braking device, 6... brake sensor, 7... hydraulic braking mechanism, 12... driving characteristics selection switch, 13... automatic driving controller, 14... processor, 15... storage device, 16... brake pedal, 20... hydraulic adjustment device, 21... hydraulic controller

Claims

1. In a vehicle capable of controlling the braking forces of the front and rear wheels of the vehicle respectively, calculate the target braking force of the vehicle based on the amount of braking operation of the driver in the vehicle or the magnitude of the required deceleration in the automatic driving state, calculate or set the target pitch angle of the vehicle, In a vehicle braking method for controlling the braking forces of the front and rear wheels of the vehicle according to the target braking force so that the target pitch angle is achieved, calculate the frequency response characteristics of the pitch angle of the vehicle obtained from the specifications of the vehicle for each front-rear distribution ratio of the braking forces of the front and rear wheels of the vehicle according to the deceleration of the vehicle, calculate the target braking force change speed which is the differential value of the target braking force and calculate the target braking force frequency from the target braking force, calculate the target deceleration of the vehicle according to the target braking force, calculate the front-rear distribution ratio of the target braking forces of the front and rear wheels of the vehicle according to the target pitch angle and the target braking force frequency from the frequency response characteristics of the pitch angle of the vehicle according to the target deceleration, and control the braking forces of the front and rear wheels of the vehicle so that the front-rear distribution ratio of the target braking force is achieved. A vehicle braking method characterized by this.

2. The vehicle braking method according to claim 1, characterized in that the target braking force frequency is calculated using the braking force equivalent to the maximum deceleration achievable by the vehicle.

3. The vehicle braking method according to claim 2, characterized in that the target braking force change speed is set as the maximum speed in a sine wave, the braking force equivalent to the maximum deceleration is calculated using the mass of the vehicle and the friction coefficient state of the road surface, the value obtained by subtracting the target braking force from the braking force equivalent to the maximum deceleration is set as the single amplitude in the sine wave, and the target braking force frequency is calculated by dividing the maximum speed by the single amplitude.

4. Compare the body pitch angle gains for each front-rear distribution ratio of the braking force in the frequency response characteristics according to the target deceleration, and set the front-rear distribution ratio of the braking force of the body pitch angle gain that can achieve the intersection of the target pitch angle gain and the target braking force frequency in the frequency response characteristics of the target pitch angle as the target front-rear distribution ratio of the braking force. The vehicle braking method according to claim 3, characterized by this.

5. In a vehicle capable of controlling the braking forces of the front and rear wheels of the vehicle respectively, In a vehicle braking device including a controller that calculates a target braking force of the vehicle based on a braking operation amount of a driver in the vehicle or a magnitude of a required deceleration in an automatic driving state, calculates or sets a target pitch angle of the vehicle, and controls braking forces of front and rear wheels of the vehicle according to the target braking force so that the target pitch angle is achieved, the controller calculates a frequency response characteristic of a pitch angle of the vehicle obtained from specifications of the vehicle for each front and rear braking force distribution ratio of the vehicle according to a deceleration of the vehicle, calculates a target braking force change speed that is a differential value of the target braking force and a target braking force frequency from the target braking force, calculates a target deceleration of the vehicle according to the target braking force, calculates a front and rear target braking force distribution ratio of the front and rear wheels of the vehicle according to the target pitch angle and the target braking force frequency from the frequency response characteristic of the pitch angle of the vehicle according to the target deceleration, and controls the braking forces of the front and rear wheels of the vehicle so that the front and rear target braking force distribution ratio is achieved. A vehicle braking device characterized by the above.

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