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: A braking force distribution ratio between front and rear wheels is calculated in accordance with frequency of target braking force, so as to reduce a difference between a vehicle body pitch angle gain, which is determined from vehicle specifications and vehicle deceleration corresponding to the target braking force, and a target pitch angle gain. Then, the braking force of the vehicle front and rear wheels is controlled to achieve the calculated braking force distribution ratio between front and rear wheels.SELECTED DRAWING: Figure 2

Description

Technical Field

[0001] The present invention relates to a vehicle braking method and a braking device that can control the braking forces of the front wheels and rear wheels of a 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 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, since the frequency response characteristics of the pitch angle generated in the vehicle are not considered, 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 braking operation amount of 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, a difference between the gain in the frequency response characteristics of the pitch angle of the vehicle obtained from the deceleration of the vehicle according to the vehicle specifications and the target braking force and the gain in the frequency response characteristics of the target pitch angle is reduced, and the front-rear distribution ratio of the braking forces of the front and rear wheels of the vehicle is calculated according to the frequency of the target braking force, and the braking forces of the front and rear wheels of the vehicle are controlled so that the front-rear distribution ratio of the braking forces 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 becomes 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 less likely to occur until it is achieved.

Brief Description of the Drawings

[0007]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Figure 6

Figure 7

Figure 8

Figure 9

Figure 10

Figure 11

Figure 12

Embodiments for Carrying Out the Invention

[0008] Hereinafter, embodiments of the present invention will be described with reference to the drawings. Note 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 states 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 sandwiching a disc rotor (rotor) 3 attached to the wheel with brake pads 4. Each braking device 2 arranges the brake pad 4 in a stationary state on one end face side of the rotor 3 in the caliper, and presses the brake pad 4 arranged on the opposite end face side against the rotor 3 to obtain a braking force. For this reason, a piston that reciprocates in the direction of separating from and contacting the brake pad 4 and the rotor 3 according to the hydraulic pressure (oil pressure) is arranged in the caliper. 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 includes a hydraulic brake mechanism 7.

[0010] In this embodiment, an electric booster 18 is used as a hydraulic pressure generating device that generates hydraulic pressure to the pistons 6 of each braking device 2 in order to enable automatic driving. 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 adjustment 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 adjustment 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 adjustment function equivalent to an anti-skid control device (ABS) that reduces the locking tendency of the wheels and a vehicle behavior control device (VDC) that adjusts the behavior of the vehicle represented by the yaw rate and lateral acceleration. In this hydraulic pressure adjustment 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 means of a switching valve provided in the hydraulic pressure adjustment 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), and in a state where the braking device 2 is disconnected from the electric booster 18, the hydraulic pressure of that braking device 2 can be individually adjusted by the hydraulic pressure adjustment device 20. The operation state of this hydraulic pressure adjustment 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 driving control for a preceding vehicle, obstacle avoidance driving control, constant speed driving control, etc. Specifically, it controls the operating state of a driving 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 driving source controller and a steering controller (both not shown). Therefore, this vehicle is provided with various sensors, cameras (image pick-up devices), distance meters, etc., which are control input acquisition means 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 hydraulic braking pressure applied to the braking device 2 (hydraulic braking mechanism 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 ability. This computer system is configured to include a processor 14 that exhibits a high-level arithmetic processing ability 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 an automatic driving controller 13 to put the automatic driving into an operating 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. Further, this vehicle is provided with a driving characteristic selection switch 12 capable of selecting 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 capable of exhibiting sharp turning characteristics such as a winding road, an eco mode for suppressing the fuel consumption of the engine or the power consumption of the driving battery, a comfort mode for achieving a comfortable ride, and the like. In addition, this vehicle is provided with an accelerator sensor 5 for detecting the depression state of the accelerator pedal 17 and a brake sensor 6 such as a pedal force sensor or a hydraulic pressure sensor for detecting 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 in the automatic driving state) will be described with reference to 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. This target pitch angle represents, as will be described later, 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 extract each frequency band component of the target braking force as described below. Next, proceed to step S7, and calculate the braking force front-rear distribution ratio that makes the pitch angle of the vehicle (the gain in the frequency response characteristic: hereinafter referred to as the vehicle body pitch angle gain) due to the target braking force in each frequency band extracted in step S6 approach the target pitch angle (the gain in the frequency response characteristic: hereinafter referred to as the target pitch angle gain) in the same frequency band (reduce the difference). In this embodiment, the frequency band in the frequency response characteristic of the vehicle body pitch angle is divided into three: a low frequency band where the vehicle body pitch angle gain is steady near 0 Hz, a vehicle body pitch resonance frequency band where the vehicle body pitches resonantly in a frequency band higher than this low frequency band, and a high frequency band where the vehicle body pitch angle gain shows a decreasing trend in a frequency band higher than this vehicle body pitch resonance frequency band. Next, proceed to step S8, and calculate the target braking force front-rear distribution ratio of the vehicle by integrating the braking force front-rear distribution ratios in each frequency band obtained in step S7. Next, proceed to step S9, output a control signal that achieves the target braking force front-rear distribution ratio of the vehicle obtained in step S8 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 vehicle body pitch angle, will be explained. During braking (when the tires are braking), a force as shown in FIG. 3 acts on the vehicle. The vehicle center of gravity O G is acted upon by a braking force Fx (front and rear) 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 R of the rear tire 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, the anti-lift angle θ R is larger than the anti-dive angle θF is larger than the instantaneous rotation center O of the front suspension link LF and the contact point G of the front tire F is subjected to a compressive force, which, when the rear distribution ratio of the braking force front-rear distribution ratio is α, is (1 - α)·Fxcosθ F is represented by. Conversely, the instantaneous rotation center O of the rear suspension link LR and the contact point G of the rear tire R is subjected to a tensile force, which is represented by α·Fxcosθ R The compressive force (1 - α)·Fxcosθ at the front tire contact point G F When 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 rearward of the vehicle F is represented by (1 - α)·Fx, and the force (1 - α)·Fxtanθ F that pulls up the front tire contact point G F is generally called the anti-dive force. Similarly, the tensile force α·Fxcosθ at the rear tire contact point G F When 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 rearward of the vehicle R is represented by 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 R and the rear wheel braking force Fx R is the braking force Fx. F and the rear wheel braking force Fx R The sum of is the braking force Fx.

[0018] This vehicle was modeled as shown in FIG. 4. Here, the symbol I in the figure P is the pitch moment of inertia of the vehicle body (vehicle), h is the height of the vehicle center of gravity O G of the vehicle, C F is the damping coefficient of the front suspension, K F is also the spring constant, L F is the longitudinal length of the vehicle from the vehicle center of gravity O G to the front tire contact point G F of the vehicle, C R is the damping coefficient of the rear suspension, K Ralso has the same spring constant, L R is the vehicle center of gravity O G to the rear tire contact point G R is the vehicle longitudinal length from, and 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. [Number]

[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 (and as described above), 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 of 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 on 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. It should be noted that it is also possible to further divide the frequency band of the vehicle body pitch angle gain or reduce the number of divisions, 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 this 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 F of the vehicle 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]

[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, in order to make the vehicle body pitch angle gain in Fig. 5 approach the target pitch angle gain (reduce the difference between the two), it is necessary to extract the target braking force in each frequency band of the low frequency band, the vehicle body pitch resonance frequency band, and the high frequency band, and set the braking force front-rear distribution ratio (rear side distribution ratio) α for the target braking force in each extracted frequency band. Furthermore, as it is, it does not become the command value of the braking force front-rear distribution ratio (rear side distribution ratio) α of the vehicle, so it is necessary to obtain the braking force front-rear distribution ratio (rear side distribution ratio) α of the vehicle by integrating the braking force front-rear distribution ratio (rear side distribution ratio) α for the target braking force in each frequency band. Here, if the braking force front-rear distribution ratio (rear side distribution ratio) α of the vehicle is set so that the vehicle body pitch angle gain coincides with the target pitch angle gain, by appropriately setting the target pitch angle gain, it becomes possible to adjust the pitching state actually occurring in the vehicle. For example, assuming that the normal target pitch angle gain in Fig. 7 is 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 passenger 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 passenger can feel the brisk behavior of the vehicle. For such a brisk behavior of the vehicle, there may be a case 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 simply reducing the normal target pitch angle gain, but also increasing the target pitch angle gain in the high frequency band period may be acceptable.

[0022] Therefore, according to the arithmetic processing in FIG. 2, a target pitch angle gain as shown in FIG. 7 is set or calculated according to the selected driving characteristic (mode), and a front-rear braking force distribution ratio that brings the target braking force in each of the low-frequency band, the vehicle body pitch resonance frequency band, and the high-frequency band closer to the target pitch angle gain is calculated in each frequency band, and these are integrated to calculate the target front-rear braking force distribution ratio of the vehicle. As a result, pitching of the vehicle close to the target pitch angle gain of the selected driving characteristic (mode) can be achieved by the hydraulic pressure (braking force) output from the hydraulic pressure adjustment device 20 to which a control signal for achieving this target front-rear braking force distribution ratio is input. 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, considering that 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 the target braking force corresponding to the brake sensor output at each sampling is stored side by side in the time axis direction for 5 sampling periods, the slope of this stored target braking force with respect to the time axis is in a proportional relationship with the operation speed of the brake pedal described above. Similarly, considering that the reading timing of the required deceleration output from the automatic driving controller 13 is equivalent to the output value sampling period of the brake sensor, the slope of the target braking force stored at each reading timing with respect to the time axis is in a proportional relationship with the operation speed of the brake pedal. Therefore, the frequency of the vehicle body pitch angle gain may be considered as the time change rate of the target braking force, and the target braking force used in the arithmetic processing includes the time change rate.

[0023] FIG. 8 is a block diagram of an arithmetic (digital) circuit that constitutes steps S6 to S8 of the arithmetic processing in FIG. 2. This arithmetic circuit includes a first low-pass filter 31 having a cut-off frequency corresponding to the lower limit frequency of the high-frequency band (for example, 2.5 Hz), a second low-pass filter 32 having a cut-off frequency corresponding to the upper limit frequency of the low-frequency band (for example, 0.5 Hz), a first adder / subtractor 33 that adds the signal of the target braking force calculated in step S5 of the arithmetic processing in FIG. 2 and subtracts the output signal of the first low-pass filter 31, a second adder / subtractor 34 that adds the output signal of the first low-pass filter 31 and subtracts the output signal of the second low-pass filter 32, a first ABS function unit 35 that outputs the absolute value of the output signal of the second low-pass filter 32, a second ABS function unit 36 that outputs the absolute value of the output signal of the second adder / subtractor 34, a third ABS function unit 37 that outputs the absolute value of the output signal of the first adder / subtractor 33, a first multiplier 38 that multiplies the output signal of the first ABS function unit 35 by a coefficient K1, a second multiplier 39 that multiplies the output signal of the second ABS function unit 36 by a coefficient K2, a third multiplier 40 that multiplies the output signal of the third ABS function unit 37 by a coefficient K3, a first adder 41 that adds the output signals of the first multiplier 38, the second multiplier 39, and the third multiplier 40, a second adder 42 that adds the output signals of the first ABS function unit 35, the second ABS function unit 36, and the third ABS function unit 37, a multiplier / divider 43 that multiplies the output signal of the first adder 41 and divides by the output signal of the second adder 42, and a limiter 44 that regulates the output signal of the multiplier / divider 43 between 0 and 1. The circuit is all digital, that is, it is constructed by software on a computer system.

[0024] The output signal of the first adder / subtractor 33 of this arithmetic circuit is the high-frequency band component of the target braking force, the output signal of the second adder / subtractor 34 is the vehicle body pitch resonance frequency band component of the target braking force, and the output signal of the second low-pass filter 32 is the low-frequency band component of the target braking force. The coefficient K1 in the first multiplier 38 is a coefficient for making the vehicle body pitch angle gain in the low-frequency band approach the target pitch angle gain in the same frequency band, the coefficient K2 in the second multiplier 39 is a coefficient for making the vehicle body pitch angle gain in the vehicle body pitch resonance frequency band approach the target pitch angle gain in the same frequency band, and the coefficient K3 in the third multiplier 40 is a coefficient for making the vehicle body pitch angle gain in the high-frequency band approach the target pitch angle gain in the same frequency band. Therefore, the target braking force added by the first adder 41 is the overall value of the target braking force with the front-rear braking force distribution ratio adjusted so that the vehicle body pitch angle gain in each frequency band approaches the target pitch angle gain in the same frequency band. Therefore, by dividing this by the target braking force using the multiplier / division unit 43, the front-rear braking force distribution ratio of the vehicle can be obtained.

[0025] In this example, the coefficient K1 of the first multiplier 38, the coefficient K2 of the second multiplier 39, and the coefficient K3 of the third multiplier 40 are all fixed to constant values. These coefficients K1 to K3 were set as follows. For example, when the required deceleration is 2G, the target braking force is vibrated in a sine wave form, and for each of the low-frequency band component, the vehicle body pitch resonance frequency band component, and the high-frequency band component of this target braking force, the proportional constants that can make the vehicle body pitch angle gain match a specific target pitch angle gain are used as the coefficients K1 to K3. As is clear from the above formula (1), since the vehicle body pitch angle gain changes according to the vehicle deceleration, that is, the target braking force, if the coefficients K1 to K3 are constant, when the target braking force changes, the vehicle body pitch angle gain cannot be made to match a specific target pitch angle gain. That is, if the target braking force is greater than that at the time of setting the coefficients K1 to K3, the vehicle body pitch angle gain generated in the vehicle is greater than a specific target pitch angle gain, and if the target braking force is smaller, the vehicle body pitch angle gain is smaller than a specific target pitch angle gain. However, for the occupant, there is no sense of discomfort that the pitching generated in the vehicle is large when the target braking force is large and small when the target braking force is small. That is, although the actual vehicle body pitch angle gain increases or decreases according to the magnitude of the target braking force, the tendency is the same as the tendency in the frequency axis (horizontal axis) direction of the target pitch angle gain. Conversely, this means that the coefficients K1 to K3 for matching a specific target pitch angle gain are obtained in advance for each target braking force and mapped. For example, when calculating the front-rear distribution ratio of the braking force by the arithmetic circuit in FIG. 8, if the coefficients K1 to K3 corresponding to the target braking force are set as the coefficients of each multiplier, the vehicle body pitch angle gain of the pitching generated in the vehicle can be made to match a specific target pitch angle gain.

[0026] FIG. 9 shows the temporal changes in the vehicle body pitch angle, vehicle body pitch angular velocity, and front-rear braking force distribution during braking by the arithmetic processing of FIG. 2 and the arithmetic circuit of FIG. 8. FIG. 10 shows the temporal changes in the vehicle body pitch angle, vehicle body pitch angular velocity, and front-rear braking force distribution during braking in a conventional vehicle that does not control the front-rear braking force distribution ratio. The front-rear braking force distribution is indicated by the braking hydraulic pressure of the front wheels (solid line) and the braking hydraulic pressure of the rear wheels (broken line). The target braking force is assumed to increase in two stages according to the braking demand (G). As is clear from FIG. 9, in the vehicle braking system of the embodiment, by increasing the braking hydraulic pressure of the rear wheels at the initial stage of braking and the initial stage of braking increase, the fluctuation of the vehicle body pitch angular velocity can be suppressed. On the other hand, in the conventional vehicle shown in FIG. 10, the fluctuation of the vehicle body pitch angular velocity is large, and in particular, the sway-back vibration is repeated at a large speed. FIG. 11 shows the temporal changes in the rear-side braking force distribution ratio and the vehicle body pitch angle by the braking system of a conventional (non-braking force controlled) vehicle, the vehicle braking system of Patent Document 1, and the vehicle braking system of the embodiment when braking straight ahead at a magnitude of 0.5G from time 0. 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 braking force distribution ratio is set to be rapidly increased 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, the braking force rear-side distribution ratio and the vehicle body pitch angle, which are control outputs, may 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, and the vehicle braking system of the embodiment, indicated by 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.Braking was performed by applying a sine wave vibration of ±0.1 G to a target braking force of 0.5 G in 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 body pitch angle gain can be reduced compared to a conventional vehicle braking system. However, in the vehicle braking system of the embodiment, the gain increase (resonance) of the body pitch angle gain in the low frequency band with respect to the steady-state body pitch angle gain in the body pitch resonance frequency band can be suppressed to be equal to or less than that of a conventional vehicle braking system, while in the vehicle braking system of Patent Document 1, the resonance of the body pitch angle gain has increased.

[0027] Thus, in this embodiment, the front-rear braking force distribution ratio is calculated according to the frequency of the braking force so as to reduce the difference between the body pitch angle gain obtained from the vehicle deceleration corresponding to the vehicle specifications and the target braking force and the target pitch angle gain, and the braking forces of the front and rear wheels of the vehicle are controlled so that the front-rear braking force distribution ratio is achieved, whereby it becomes possible to feed-forward control the front-rear braking force distribution ratio, and thereby the target pitch angle is quickly achieved and a large pitch angular velocity change is less likely to occur until it is achieved.

[0028] Also, the body pitch angle gain and the target pitch angle gain are compared, and when the body pitch angle gain is larger than the target pitch angle gain, the front-rear braking force distribution ratio is set so that the body pitch angle gain decreases, and / or when the body pitch angle gain is smaller than the target pitch angle gain, the front-rear braking force distribution ratio is set so that the body pitch angle gain increases. Thereby, the difference between the body pitch angle gain and the target pitch angle gain can be surely reduced, and for example, when the magnitude relationship between the body pitch angle gain and the target pitch angle gain differs depending on the frequency band, the target braking force in each frequency band is extracted, and the front-rear braking force distribution ratios in each frequency band obtained for the extracted target braking force are integrated to set the front-rear braking force distribution ratio of the vehicle.

[0029] In addition, the vehicle body pitch angle corresponding to the front-rear braking force distribution ratio is determined by the anti-dive angle of the front suspension and the anti-lift angle of the rear suspension. When the anti-lift angle is larger than the anti-dive angle, increasing the front-side distribution ratio of the front-rear braking force distribution ratio increases the vehicle body pitch angle gain and / or decreasing the rear-side distribution ratio decreases the vehicle body pitch angle gain. When the anti-dive angle is larger than the anti-lift angle, increasing the front-side distribution ratio of the front-rear braking force distribution ratio decreases the vehicle body pitch angle gain and / or decreasing the rear-side distribution ratio increases the vehicle body pitch angle gain. Thereby, the difference between the vehicle body pitch angle gain and the target pitch angle gain can be surely reduced.

[0030] In addition, by dividing the frequency of the target braking force into a predetermined frequency band and calculating the front-rear braking force distribution ratio of the vehicle by integrating the front-rear braking force distribution ratios calculated in each frequency band, even when the magnitude relationship between the vehicle body pitch angle gain and the target pitch angle gain differs depending on the frequency band, the difference between the vehicle body pitch angle gain and the target pitch angle gain can be surely reduced.

[0031] In addition, 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.

[0032] In addition, by setting the target pitch angle (gain) so that the vehicle body pitch angle gain in the vehicle body pitch resonance frequency band is equal to that in the low frequency band, the resonance of pitching can be reduced and made equivalent to the suppressed steady pitching. In addition, by setting the target pitch angle (gain) so as to increase the vehicle body pitch angle gain in the high frequency band, pitching can occur during braking even in the high frequency band.

[0033] In the above-described embodiment, only the example of generating and adjusting the braking force of each wheel hydraulically has been described in detail. However, instead of this, 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. Further, in the above-described embodiment, the target pitch angle (gain) is set according to the selected running 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.

Description of Signs

[0034] 1F... front wheel, 1R... rear wheel, 2... braking device, 6... brake sensor, 7... hydraulic braking mechanism, 12... running characteristic 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 braking operation amount 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, Reduce the difference between the gain in the frequency response characteristic of the pitch angle of the vehicle obtained from the specifications of the vehicle and the deceleration of the vehicle corresponding to the target braking force and the gain in the frequency response characteristic of the target pitch angle, and calculate the front-rear distribution ratio of the braking forces of the front and rear wheels of the vehicle according to the frequency of the target braking force, and control the braking forces of the front and rear wheels of the vehicle so that the front-rear distribution ratio of the braking forces is achieved. A vehicle braking method characterized by the above.

2. Compare the gain in the frequency response characteristic of the pitch angle of the vehicle with the gain in the frequency response characteristic of the target pitch angle, and when the gain in the frequency response characteristic of the pitch angle of the vehicle is larger than the gain in the frequency response characteristic of the target pitch angle, set the front-rear distribution ratio of the braking force so that the gain in the frequency response characteristic of the pitch angle of the vehicle decreases, and / or when the gain in the frequency response characteristic of the pitch angle of the vehicle is smaller than the gain in the frequency response characteristic of the target pitch angle, set the front-rear distribution ratio of the braking force so that the gain in the frequency response characteristic of the pitch angle of the vehicle increases. The vehicle braking method according to claim 1, characterized by the above.

3. The pitch angle of the vehicle corresponding to the front-rear distribution ratio of the braking force is determined by the anti-dive angle of the front suspension and the anti-lift angle of the rear suspension, which are suspension geometry characteristics. When the anti-lift angle is larger than the anti-dive angle, increasing the front distribution ratio of the front-rear distribution ratio of the braking force increases the gain in the frequency response characteristic of the pitch angle and / or decreasing the rear distribution ratio decreases the gain in the frequency response characteristic of the pitch angle. When the anti-dive angle is larger than the anti-lift angle, increasing the front distribution ratio of the front-rear distribution ratio of the braking force decreases the gain in the frequency response characteristic of the pitch angle and / or decreasing the rear distribution ratio increases the gain in the frequency response characteristic of the pitch angle. The vehicle braking method according to claim 2, characterized by the above.

4. The method for braking a vehicle according to any one of claims 1 to 3, characterized in that the frequency of the target braking force is divided into a predetermined frequency band, and the front-rear braking force distribution ratios calculated in each frequency band are integrated to calculate the front-rear braking force distribution ratio of the front and rear wheels of the vehicle.

5. The method for braking a vehicle according to claim 4, characterized in that the target pitch angle is set so as to reduce the gain in the frequency response characteristic of the pitch angle of the vehicle in the low-frequency band near 0 Hz.

6. The method for braking a vehicle according to claim 5, characterized in that the target pitch angle is set so that the gain in the frequency response characteristic of the pitch angle of the vehicle in the vehicle body pitch resonance frequency band is made equal to that in the low-frequency band near 0 Hz.

7. The method for braking a vehicle according to claim 6, characterized in that the target pitch angle is set so as to increase the gain in the frequency response characteristic of the pitch angle of the vehicle in a frequency band higher than the vehicle body pitch resonance frequency band.

8. In a vehicle capable of controlling the braking forces of the front and rear wheels of the vehicle respectively, in the vehicle braking device provided with a controller that calculates the target braking force of the vehicle based on the braking operation amount of the driver in the vehicle or the magnitude of the required deceleration in the automatic driving state, calculates or sets the target pitch angle of the vehicle, and controls 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 controller calculates the front-rear braking force distribution ratio of the front and rear wheels of the vehicle according to the frequency of the target braking force so as to reduce the difference between the gain in the frequency response characteristic of the pitch angle of the vehicle obtained from the vehicle specifications and the deceleration of the vehicle corresponding to the target braking force and the gain in the frequency response characteristic of the target pitch angle, and controls the braking forces of the front and rear wheels of the vehicle so that the front-rear braking force distribution ratio is achieved.

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