JPH1191539A - Friction state arithmetic unit and braking force control device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To compute a friction state without minutely exciting braking force at all times. SOLUTION: This device is composed of a wheel speed detection portion 20 detecting a wheel speed, a step response detection portion 21 detecting a wheel speed step response component when braking force changes in steps and detecting the time-varying characteristic of the component, road surface μgradient operation division 22 computing a road surface μ gradient based on a detected time-varying characteristic as compensating the characteristic vehicle speed dependency by the wheel speed, a target braking force operation portion 23 computing target braking force corresponding to the road surface μgradient, and a wheel cylinder hydraulic control portion 24 controlling a wheel cylinder pressure in steps so as to follow the target braking force. Since the time-varying characteristic of the wheel speed step response component and the road surface μgradient correlate with each other, a friction state can be computed without minutely exciting the braking force at all times.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a friction state calculating device and a braking / driving force control device. Or, based on the characteristics of the wheel speed response component of the wheel resonance system when changed in a pulsed manner,
The present invention relates to a friction state calculating device that calculates a friction state between a tire and a road surface, and a braking / driving force control device that controls a braking / driving force based on the calculated friction state.

[0002]

2. Description of the Related Art In recent years, research and development of preventive safety technology has been promoted due to an increase in the safety consciousness of automobiles, and a typical safety device such as an anti-lock brake system (AB) has been developed.
S) is already equipped on many passenger cars.

Under these circumstances, ABS control based on a new principle focusing on the resonance phenomenon of a tire has been proposed and studied (Japanese Patent Application No. 7-220920). The present technology provides a small excitation having a frequency component equal to the resonance frequency when the tire is gripping to the brake pressure, and the transmission gain of the tire resonance system at that time (small amplitude at the resonance frequency of the wheel speed / brake pressure). The present invention relates to a braking force control device that controls the average brake pressure based on the excitation amplitude of the braking force.

In the so-called S-μ characteristic (a change curve of the friction coefficient μ with respect to the slip ratio S), the transmission gain is represented by the gradient of the friction coefficient μ with respect to the slip ratio S (or the slip speed Δω) (hereinafter, “road surface μ gradient”). ), And is expected to be able to estimate a friction characteristic relating to the ease of slip between the tire and the road surface during braking based on the transmission gain.

[0005]

However, in the above prior art, when a predetermined condition for starting the antilock brake operation is satisfied, in order to detect the slip state immediately before the peak μ, it is necessary to always use the braking force. There is a problem that the brake pressure to be applied must be slightly excited.

The principle of the above-mentioned prior art is that a driving force control device for estimating a friction characteristic between a tire and a road surface by slightly exciting the driving force and controlling the driving force based on the estimated friction characteristic. However, in this case as well, the driving force must always be slightly excited.

Further, when the above-mentioned prior art is applied to estimating the road surface μ gradient during steady running or the like, when the driver does not step on the brake pedal, the braking force is minutely excited, or the driving force is minutely excited. Must be undesirable.

SUMMARY OF THE INVENTION The present invention has been made in view of the above-described circumstances, and a braking / driving force control device and a braking / driving force control device capable of controlling the braking / driving force with high precision without constantly exciting the braking / driving force. An object of the present invention is to provide a frictional state computing device capable of equally and highly accurately estimating a frictional state in various traveling states such as braking, driving, and steady traveling without micro-excitation.

[0009]

In order to achieve the above object, the invention according to claim 1 comprises a wheel speed detecting means for detecting a wheel speed, and a braking / driving force acting on a wheel being changed in a predetermined changing state. Braking / driving force controlling means, damping characteristic detecting means for detecting a damping characteristic of a wheel speed response component due to a predetermined change in the braking / driving force, and a friction state between the wheel and the road surface based on the damping characteristic. And an operation means for performing an operation.

According to a second aspect of the present invention, there is provided a wheel speed detecting means for detecting a wheel speed, a braking / driving force control means for changing a braking / driving force acting on a wheel in a predetermined change state, and a predetermined braking / driving force. Damping characteristic detecting means for detecting a damping characteristic of a response component of a wheel speed due to a change in the vehicle speed; calculating means for calculating a friction state between a wheel and a road surface based on the damping characteristic; and friction calculated by the calculating means. Target braking / driving force calculating means for calculating a target braking / driving force corresponding to the state; and braking / driving force controlling means for changing the target braking / driving force so that the braking / driving force acting on the wheels follows the target braking / driving force. It is comprised including.

According to a third aspect of the present invention, there is provided a wheel speed detecting means for detecting a wheel speed, a braking / driving force control means for changing a braking / driving force acting on a wheel in a stepwise manner, and a wheel speed detecting means. A step response detecting means for detecting a time change characteristic of a wheel speed step response component when the braking / driving force is stepwise changed by the braking / driving force control means from the wheel speed; Calculating means for calculating the frictional state between the tire and the road surface based on the time change characteristic of the wheel speed step response component.

A fourth aspect of the present invention is an application of the third aspect of the present invention to a braking / driving force control device. As shown in FIG. A step response detecting means for detecting a time change characteristic of a wheel speed step response component when a braking / driving force acting on a wheel is changed stepwise from a wheel speed detected by the wheel speed detecting means; Calculating means for calculating the frictional state between the tire and the road surface based on the time change characteristic of the wheel speed step response component detected by the response detecting means; and a target control corresponding to the frictional state calculated by the calculating means. Target braking / driving force calculating means for calculating the driving force; and braking / driving force control means for changing the braking / driving force so that the braking / driving force acting on the wheels follows the target braking / driving force. Are those that you configured.

According to a fifth aspect of the present invention, there is provided a wheel speed detecting means for detecting a wheel speed, a pulse-like braking / driving force for oscillating a frictional force generated between a tire and a road surface, and a pulse-like braking / driving force. A pulsed braking / driving force having a phase opposite to the vibration of the frictional force generated by the braking / driving force, a pulsed braking / driving force generating means for generating the wheel speed, and a wheel speed detected by the wheel speed detecting means. Pulse response detecting means for detecting an amplitude characteristic of a wheel speed pulse response component when a pulsed braking / driving force is applied by the pulse braking / driving force generating means; and a wheel speed pulse response detected by the pulse response detecting means. Calculating means for calculating a frictional state between the tire and the road surface based on the amplitude characteristics of the components.

The invention according to claim 6 is an application of the invention according to claim 5 to a braking / driving force control device. The structure of the invention is, as shown in FIG. 10, comprising wheel speed detection means for detecting wheel speed. A pulse response detecting means for detecting an amplitude characteristic of a wheel speed pulse response component when a pulse-like braking / driving force is applied from the wheel speed detected by the wheel speed detecting means; Calculating means for calculating a frictional state between the tire and the road surface based on the amplitude characteristic of the wheel speed pulse response component obtained, and a target for calculating a target braking / driving force corresponding to the frictional state calculated by the calculating means. Braking / driving force calculating means for controlling the braking / driving force such that the braking / driving force acting on the wheels follows the target braking / driving force, and vibrating the frictional force generated between the tire and the road surface. A braking / driving force control means for generating a loose braking / driving force, and a pulse-shaped braking / driving force having an opposite phase to the vibration of the frictional force generated by the pulse-shaped braking / driving force. It is composed.

The wheel speed detecting means according to the first aspect of the present invention detects the wheel speed, and the braking / driving force control means changes the braking / driving force acting on the wheels in a predetermined change state. The damping characteristic detecting means detects a damping characteristic of a response component of the wheel speed due to the predetermined change of the braking / driving force, and the calculating means calculates a friction state between the wheel and the road surface based on the damping characteristic.

The wheel speed detecting means according to the second aspect of the present invention detects the wheel speed, and the braking / driving force control means comprises:
The braking / driving force acting on the wheels is changed in a predetermined change state. The damping characteristic detecting means detects a damping characteristic of a response component of the wheel speed due to the predetermined change of the braking / driving force, and the calculating means calculates a friction state between the wheel and the road surface based on the damping characteristic. The target braking / driving force calculating means calculates a target braking / driving force corresponding to the frictional state calculated by the calculating means, and the braking / driving force control means causes the braking / driving force acting on the wheels to follow the target braking / driving force. The target braking / driving force is changed so that

As described above, according to the present invention, the braking / driving force acting on the wheel is changed in a predetermined change state, and the damping characteristic of the response component of the wheel speed due to the predetermined change in the braking / driving force is detected.
Since the friction state between the wheel and the road surface is calculated based on the damping characteristic, the friction state can be calculated with high accuracy in various running states such as braking, driving, and steady running. (Principles of the Inventions of Claims 3 and 4) The principles of the present invention will be described with reference to FIGS. here,
FIG. 2 is an equivalent dynamic model of a wheel resonance system composed of a vehicle body, wheels, and a road surface. FIG. 3 is a friction characteristic between a tire and a road surface that defines the vibration characteristics of the wheel resonance system of FIG. Is
3 shows a vibration model of a wheel resonance system.

First, as shown in FIG.
Consider the vibration phenomenon at the wheels when the vehicle equipped with 2 is traveling at the vehicle speed v.

In the dynamic model of the wheel resonance system shown in FIG.
The braking / driving torque T ₁ applied to the wheel (rim) 13 is caused by the spring element 14 caused by the torsion between the rim and the tread 15.
(Tire twist constant K) to the tread (belt) 15 and acts on the road surface via the tread surface. At this time, the wheel is as a base point a ground point between the tread and the road surface, are generated force T _L as the reaction of the braking and driving torque T ₁ from the road surface acts.

The generated force T _L is due to a frictional force between the tire and the road surface, and acts in a direction opposite to the direction of the braking / driving torque T ₁ . That is, when the driving torque T ₁ acts on the rim at the time of driving, the generated force _TL acts in the direction opposite to the wheel rotation direction (the direction of the rotation speed ω ₁ of the wheel 13), and the braking torque T ₁ during braking is reduced. If it works,
Acts in the direction of wheel rotation.

Here, when the vehicle is running at a certain speed v (the value converted into a rotating system is ω _v ), the brakes cause a slip between the tires and the road surface. generated force T _L generated between the tire and the road surface, to the slip ratio S ₁ represented by the following equation, it varies as a function relation of FIG. 3 (a region of the slip rate is positive). Note that ω ₂ is the rotation speed of the tread 15.

[0022]

(Equation 1)

Similarly, even when the driver accelerates by depressing the accelerator pedal from when the vehicle is running at a certain speed v, slip occurs between the tires and the road surface. T _L changes with respect to the slip ratio S ₂ represented by the following equation as shown in the functional relationship of FIG. 3 (a region where the slip ratio is negative).

[0024]

(Equation 2)

Here, assuming that the rotation direction of the wheels when the vehicle advances is the forward direction, the generated force _TL between the tire and the road surface can be expressed by the following equation.

At the time of braking: T _L = W _r Rμ (S ₁ ) (2) At the time of driving: T _L = W _r Rμ (S ₂ ) (3) where W _r is the wheel load and R is the dynamic load of the tire. The radius, μ, is the coefficient of friction between the tread 15 and the road surface. Note that μ
Is expressed as a function of the slip ratio S ₁ or S ₂ .

As shown by the S-μ curve in FIG. 3, when the slip ratio is 0, the generated force _TL is 0, but at a certain positive slip ratio, the generated force _TL during braking has a positive peak value. And at a certain negative slip ratio, the generated force _TL during braking
It can be seen that the relationship that takes a negative peak value holds. Also, at various operating points, the gradient of the generated force _TL with respect to the slip ratio takes a unique value, for example, a value near 0 at the peak value. (The frictional state) between the two.

The generated force T _L and the friction coefficient μ are expressed by (2)
, (3), the frictional state can be accurately expressed even by using the gradient of the friction coefficient μ with respect to the slip ratio. Further, the friction state can be expressed by using the slip speed instead of the slip rate. Hereinafter, the gradient of the generated force _TL with respect to the slip ratio (or the slip speed) and the gradient of the friction coefficient μ with respect to the slip ratio (or the slip speed) are collectively referred to as a road surface μ gradient.

In the dynamic model shown in FIG. 2, the braking / driving torque acting on the rim is changed to the average braking / driving torque T _1.
When excited around the amplitude [Delta] T _1, the excitation torque component appears as a vibration component [Delta] [omega ₁ around the wheel speed omega _1.

The vibration phenomenon of the wheel resonance system shown in FIG.
Consider a model shown in FIG. 4 equivalently modeled by the wheel rotation axis.

Here, as described above, the braking / driving force T ₁
Is acting through the surface of the tread 15 of the tire contact with the road surface in the road surface, the braking for driving force T ₁ is acting on the vehicle body 12 as a reaction from the fact road, equivalent body weight of the rotary shaft conversion The model 17 is connected to the side opposite to the wheel 13 via a friction element 16 between the tread of the tire and the road surface. This is the same as the large inertia under the wheels, that is, the weight of the vehicle body can be simulated by the mass on the side opposite to the wheels, as in the chassis dynamo device.

The wheel 13 including the tire rim in FIGS.
Spring element 1 of inertial between J _w, rim and tread 15
4, the spring constant is K, the inertia of the tread 15 is J _t , and the body 1
The inertia of the equivalent model 17 in terms of the rotation axis of the weight W of 2 is expressed by J _V
Then, the characteristics of the whole system are as shown in the following equations (4) to (6). In the following, the first-order derivative d / dt with respect to time will be described.
Is represented by “′”, and the second-order derivative d ² / dt ² with respect to time is represented by “”.

[0033] _{J W θ w "= -T 1} + K (θ t -θ w) (4) J t θ t" = -K (θ t -θ w) + μW r R (5) J v ω v '= −μW _r R (6) where θ _w is the rotation angle of the wheel 13, θ _w "is the rotation angular acceleration of the wheel 13, θ _t is the rotation angle of the tread 15, and θ _t " is the rotation angular acceleration of the tread 15. is there. That is, ω ₁ = θ _w ′ (7) ω ₂ = θ _w ′ (8).

When the tire is gripping the road,
If the red 15 and the vehicle equivalent model 17 are directly connected
Considering the inertia of the vehicle equivalent model 17 and the tread 15
The inertia of the sum of the inertia and the inertia of the wheel 13 resonates.
Resonance frequency f of the wheel resonance system ₁Is

[0035]

(Equation 3)

## EQU1 ## This state is shown in FIG.
This corresponds to an operating point in a region where the road surface μ gradient before reaching (the maximum generated force) is positive.

Conversely, when the friction coefficient μ of the tire approaches the peak μ, the friction coefficient μ of the tire surface becomes the slip ratio S
, And the component accompanying the inertial vibration of the tread 15 does not affect the vehicle equivalent model 17. That is, the tread 15 and the vehicle equivalent model 17 are equivalently separated, and the tread 15 and the wheels 13 resonate. The resonance frequency f ₂ of the wheel resonance system at this time is

[0038]

(Equation 4)

## EQU1 ## In FIG. 3, this state corresponds to the region of the operating point where the road surface μ gradient becomes zero near the peak μ, and generally transitions to the region where the road surface μ gradient becomes negative instantaneously when the peak μ is reached. At this time, the tire locks during braking, and the tire spins during driving.

The magnitude relationship of each inertia is _{J t <J w <J v} (11), than this, become _{f 1 <f 2 (12)} . That is, when the tire locks or spins, the resonance frequency of the wheel resonance system shifts to the high frequency side. This change in the resonance frequency occurs sharply near the peak μ. By a change in the friction state between the thus tire and the road surface, the vibration characteristics of the wheel resonance system is changed, to the contrary, the response output of the vibration is the wheel resonance system (vibration component of the wheel speed omega ₁₎ Based on this, it is possible to estimate the friction state.

Therefore, in the present invention, the wheel resonance system is vibrated by changing the braking / driving force stepwise by the braking / driving force control means. For example, as shown in FIG. 5, when the master cylinder pressure is increased in accordance with the pedaling force of the driver, the wheel cylinder pressure is increased stepwise using a so-called ABS actuator or the like. After a certain wheel cylinder pressure is maintained for a certain time, the wheel cylinder pressure is reduced in a stepwise manner.

When such a suddenly increasing or decreasing braking / driving force is applied to the wheel, a sharp change in the wheel speed causes a twist angle (θ _t −θ _w ) between the tread and the wheel.
Is generated, the tread rotates and vibrates, and the frictional force generated between the tire and the road surface vibrates. Accordingly, a vibration component (wheel speed step response component) also occurs at the wheel speed. The wheel speed vibration continues without much attenuation when the tire is completely gripping the road surface, but abruptly attenuates when a slip occurs.

Here, when the slip ratio is 0.2, the road surface μ
On the road surface where the maximum value is 0.3, various initial vehicle speeds (10 rad
/ s, 20rad / s), various braking forces (μ = 0.1, 0.2
5 to 0.3) are shown in FIGS. 6 to 9, which show experimental results of temporal changes of the wheel speed and the vehicle speed actually detected when decelerating while applying stepwise. Various physical quantities in this experiment are as shown in the figure.

As shown in FIGS. 6 to 9, it can be seen that the time change characteristics of the wheel speed vibration are different depending on the difference in the braking torque, that is, the road surface μ. For example, comparing FIG. 7, FIG. 8 and FIG. 9 in which the initial vehicle speed is the same value (20 rad / s), the attenuation rate of the amplitude of the wheel speed vibration is μ = 0.1, 0.
It turns out that it becomes large in order of 25 and 0.3.
That is, as the road surface μ increases, the damping rate of the amplitude value of the wheel speed vibration increases, and the damping rate of the amplitude (included in the time change characteristic of the wheel speed step response component).
It has been suggested that the friction state can be determined from the above.

Further, the frequency of the damping vibration of the wheel speed is
It becomes smaller in the order of μ = 0.1, 0.25, 0.3, and it can be seen that the frequency of the damped vibration and the friction state are related. Therefore, the frequency of this damped vibration can be included as the time-change characteristic of the step response component of the wheel speed.

What was suggested by the above experiment can be supported by the vibration model of FIG. That is,
The wheel resonance system is vibrated by the stepwise changing braking / driving force, and immediately after the stepwise change, the resonance frequency component of the wheel resonance system is output as a wheel speed step response component.

For example, when the tire is completely gripping the road surface, the vibration component of the frequency f ₁ continues with almost the same amplitude. However, as described above, as the peak approaches μ, the resonance frequency of the wheel resonance system increases. , the process proceeds to f ₂ of the higher frequency. Therefore, when the braking force increases stepwise and approaches the peak μ, the energy of the vibration shifts to the vibration component of the frequency f ₂ . At this time, as the time elapses, the frequency f ₁
Vibration component is attenuated, it can be observed that the oscillation component of the frequency f ₂ are amplified. Conversely, from this state, decreasing the step braking force, damped oscillation component of the frequency f ₂ is in the course of time, the vibration component of the frequency f ₁ is amplified.

The time change characteristics (damping characteristics and amplification characteristics) of such wheel speed step response components change in accordance with the frictional state (road surface μ gradient, μ value, etc.) between the tire and the road surface. Conversely, the friction state can be calculated based on the time change characteristics of the wheel speed step response component.

Therefore, in the present invention, focusing on the above fact,
The calculating means calculates the frictional state between the tire and the road surface based on the time change characteristic of the wheel speed step response component as described above. Here, as the friction state, it is desirable to calculate a road surface μ gradient having the highest correlation with the time change characteristic of the wheel speed step response component.

The time change characteristics of the wheel speed step response component include the damping rate of the damping vibration generated immediately after the stepwise change of the braking / driving force, its frequency, and the resonance frequency f _1.
Component attenuation rate, an increase rate of the components of the resonance frequency f _2, or the like can be used combinations thereof.

In the invention of claim 4, the target braking / driving force calculating means calculates the target braking / driving force corresponding to the friction state calculated by the calculating means. For example, in the case of control following the peak μ, if the calculated frictional state is far from the peak μ, the incremented target braking / driving force is applied to the peak μ.
In the case of the immediately preceding state, the decremented target braking / driving force is calculated. Then, the braking / driving force control means changes the braking / driving force such that the braking / driving force acting on the wheels follows the calculated target braking / driving force.

For example, when the braking force is controlled by adjusting the oil pressure of the wheel cylinder, the average braking force is determined by the ratio of the pressure increasing time during which the wheel cylinder pressure is increased and the pressure reducing time during which the wheel cylinder pressure is reduced, From a macroscopic perspective, smooth running of the vehicle body is possible. However, if a finer change is observed, the braking force changes stepwise when the wheel cylinder pressure is increased or decreased, and a step response component is generated in the wheel speed in accordance with the change.

That is, in the control of the average braking / driving force, it is generally possible to add a step-like change in the braking / driving force. In various running states such as driving and steady running, the friction state can be equally estimated with high accuracy. (Principle of Claim 5 and Claim 6) Next, Claim 5
The principle of the present invention will be described with reference to FIG.

When a pulsed braking / driving force is applied to a wheel, the tread via the wheel and the spring element tends to rotate and vibrate, so that the frictional force generated between the tire and the road surface vibrates. At this time, as shown in FIG. 11A, in a state where the tire is completely gripped on the road surface, when the braking / driving force is changed in a stepwise manner, the secondary system vibration corresponding to the damping coefficient of zero is generated. Since it can be approximated, the frictional force on the tire-road surface overshoots by the same step width as the changed braking / driving force. Also, when the frictional force on the tire-road surface reaches the maximum value due to overshoot, that is, when the value becomes twice the step width, the braking / driving force is returned to the initial state, and the friction on the tire-road surface is reduced. The force oscillates around an initial value of the braking / driving force with an amplitude twice the step width of the braking / driving force. The vibration of the frictional force has a small damping rate in the perfect grip state, and therefore, the wheel speed vibrations continue to have substantially the same amplitude.

However, as shown in FIG. 11 (b), if a slip occurs on the + side of the applied braking / driving force (in the same direction as the braking / driving force) at the time of pulse input, the road surface friction force is saturated. As the vibration of the frictional force is attenuated, the amplitude of the wheel speed vibration is also attenuated. Here, since the road surface frictional force when a slip occurs on the + side is smaller than twice the applied braking / driving force, the amplitude value of the wheel speed vibration vibrated by the road surface frictional force did not cause the slip. It is smaller than the amplitude at the time, and corresponds to the magnitude of the actually generated road surface frictional force. That is, the friction state between the tire and the road surface can be calculated based on the amplitude value of the wheel speed vibration.

Therefore, in the present invention, in order to actually detect the peak time of the road surface μ, the pulse braking / driving force generating means generates a pulse-shaped braking force for vibrating the frictional force generated between the tire and the road surface. Generates driving force. Here, the applied braking / driving force is pulsed, so that even if a large frictional force is applied so that the tire is momentarily slipped, the road surface frictional force in the opposite direction is immediately applied, so that the grip state is quickly increased. Can be returned to.

Further, in the present invention, after the pulse is generated, a pulse-shaped braking / driving force having an opposite phase to the vibration of the frictional force generated by the pulse-shaped braking / driving force is generated. When the opposite-phase pulse is generated as described above, the subsequent damping vibration of the frictional force is canceled by the opposite-phase pulse. For example, in the complete grip state, when the frictional force on the tire-road surface swings to the negative side and reaches the minimum value,
The braking / driving force is stepwise changed to the negative side by half the vibration amplitude of the frictional force, and when the frictional force returns to the initial value of the braking / driving force, the braking / driving force can be returned to the initial value. If the vibration stops completely. In this case, as shown in FIG.
In the vibration of the road surface frictional force and the accompanying wheel speed vibration, the vibration to the + side and the − side is generated only once, and the influence of the vibration on the vehicle traveling can be reduced.

Then, the calculating means calculates the friction state between the tire and the road surface based on the amplitude characteristic of the wheel speed pulse response component generated by the pulsed braking / driving force.

That is, the current friction state is a friction state separated from the friction state of the peak μ at which the maximum braking / driving force is attained by the braking / driving force corresponding to the amplitude value of the wheel speed vibration on the + side in FIG. Can be calculated. Note that the surplus braking / driving force obtained by subtracting the current braking / driving force from the maximum braking / driving force on the currently traveling road surface is an index indicating how much more braking / driving force can be applied. The frictional state can also be represented by the driving force. Of course, also in the present invention, the friction state may be a road surface μ gradient, a friction coefficient μ, or the like.

For example, as shown in FIG. 11 (a), when the amplitude value of the wheel speed vibration on the + side is an amplitude value corresponding to twice the applied braking / driving force, the friction state becomes It can be calculated that the driving force is at least twice the applied braking / driving force.

If the amplitude value of the wheel speed vibration on the + side in FIG. 11C is less than the amplitude value corresponding to twice the applied braking / driving force, it is considered that a slip has occurred on the + side. The friction state is calculated as a friction state (a state closer to the peak μ) in which the current marginal braking / driving force is the braking / driving force corresponding to the amplitude value in which the wheel speed vibration on the + side becomes smaller. it can. In the above description, it is assumed that the vehicle is shifted from the completely gripped state to the slip state discontinuously and then returns to the fully gripped state. In fact, there is very little grip, and there is a slight slip.

Therefore, the frictional force does not overshoot up to twice the applied braking force, and the frictional force is attenuated to some extent even if the slip does not completely occur. Therefore, the accuracy is further improved by obtaining the base damping characteristic in the case where the state does not shift to the complete slip state from the ratio of the minus side amplitude and the plus side amplitude, and correcting the above-mentioned margin braking / driving force.

In the present invention, the target braking / driving force calculating means calculates the target braking / driving force corresponding to the calculated frictional state. The braking / driving force control means generates a pulse-shaped braking / driving force as shown in FIG. 11C and a pulse-shaped braking / driving force having an opposite phase, and calculates the braking / driving force acting on the wheels. The braking / driving force is controlled so as to follow the set target braking / driving force.

[0064]

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, embodiments of a braking / driving force control device and a friction state calculating device of the present invention will be described in detail with reference to the drawings. (First Embodiment) In a first embodiment, the braking / driving force control device of the present invention is applied to an antilock brake control device for a vehicle. FIG. 12 shows the configuration of the device. Have been. As shown in the figure, the anti-lock brake control device according to the first embodiment includes a wheel speed detecting unit 20 that detects a wheel speed signal of each wheel, and a synchronization input from a detected wheel speed signal. A step response detecting unit 21 that detects a wheel speed step response component in synchronization with a signal and detects a time change characteristic of the component for each wheel, and a time change characteristic of the detected wheel speed step response component, A road μ gradient calculating unit 22 for calculating a road μ gradient α between each tire and the road surface; and a target for calculating a command of a target average braking force to be applied to each wheel based on the calculated road μ gradient α. A braking force calculation unit 23 and a wheel cylinder oil pressure control unit 24 that calculates a pressure increase / decrease command to a control valve for realizing a wheel cylinder pressure corresponding to each calculated target braking force for each wheel. Is done.

In the present embodiment, the stepwise change of the braking force acting on the wheel is realized by changing the wheel cylinder pressure in a stepwise manner. Then, the step response detecting section 21 obtains, from the wheel cylinder oil pressure control section 24, a synchronization signal indicating the time point of the step change and the stepwise change amount ΔP of the wheel cylinder pressure. The step response detecting section 21 detects the time point of the step change based on the synchronization signal, and starts detecting the step response component of the wheel speed after a lapse of a predetermined time from the time point or a time delay in consideration of the time delay.

The means for detecting the time change characteristic of the step response detecting section 21 will be described in detail below. The detecting means determines which physical quantity is extracted as the time change characteristic of the wheel speed step response component, for example, as shown in FIG.
There are first to fourth modes shown in FIGS.

[0067] The first embodiment of FIG. 16 is for detecting a time variation characteristic of the resonance frequency f ₁ vibration component when the tire grip of the wheel speed step response component, from the wheel speed signal omega ₁ at the time of the step response detection, a band-pass filter 32a for passing only the frequency component of a predetermined band including the resonance frequency f ₁ during the tire grip, a full-wave rectifier 33 for rectifying the output signal of the filter, the low-frequency output signal of該全wave rectifier A low-pass filter 34 that outputs a DC-smoothed signal ω _d by passing only frequency components,
A divider 35 for dividing the output signal ω _{d of the} filter by a stepwise change amount ΔP of the wheel cylinder pressure, and a time for calculating a time change characteristic of a wheel speed step response component based on the output signal ω _d / ΔP. And a change characteristic calculation unit 36.

As shown in FIG. 16, the low-pass filter 3
4 performs DC smoothing of the input signal, so that the output signal ω
_d is an average amplitude value of the resonant frequency f ₁ near the wheel speed step response component. Therefore, the time change characteristic calculation unit 3
6 makes it possible to determine this time-varying characteristic of the amplitude value. Since this amplitude value varies depending on the stepwise change amount of the braking force, the stepwise change amount ΔP of the wheel cylinder pressure is used in order to extract a universal time change characteristic regardless of the change amount. By dividing the output signal ω _d by (the wheel cylinder pressure immediately after the change−the wheel cylinder pressure immediately before the change), a normalized amplitude value ω _d / ΔP is obtained.

As a specific calculation method of the time change characteristic,
For example, there is a method in which an average amplitude value at a first predetermined time and an average amplitude value at a next subsequent predetermined time are obtained, and a ratio of the average amplitude value is obtained as a time change characteristic. As another method, when the wheel speed step response component is attenuated, it is necessary for the amplitude A at the time of detecting the step response to attenuate to A / e (e is a constant larger than 1, for example, a natural constant). The extracted time T can be extracted as a time change characteristic.

[0070] In performing braking boosts the wheel cylinder pressure in steps, since the resonant frequency f ₁ component of the wheel speed step response decays characteristics corresponding to the gradient road surface mu, amplitude as a time change characteristics The decay rate will be required.

Further, in the second mode of FIG. 17, the main frequency of the wheel speed step response component is extracted as a time change characteristic, and the wheel speed step response component is converted into time series data discretized every predetermined sample time τ. On the other hand, FFT which transforms to frequency series data by performing fast Fourier transform
It comprises a processing unit 71 and an extraction unit 72 that extracts a main frequency at which the gain is maximum from the frequency sequence data.

When the braking is performed by increasing the wheel cylinder pressure in a stepwise manner, the characteristic damping vibration shown in FIGS. 6 to 9 becomes dominant in the wheel speed step response component. According to the second aspect, the main frequency of the damped oscillation is extracted.

Further, the third mode of FIG. 18 extracts a physical quantity relating to the main frequency of the wheel speed step response component as a time change characteristic similarly to the second mode. Frequency f ₁
High frequency cutoff filter 40 for blocking higher frequency components
And a pole detection unit 41 for detecting a first maximum point and a first minimum point based on a predetermined algorithm from time series data obtained by discretizing the filter output for each predetermined sample time τ.
And a time width detection unit 42 that detects a time width Δt between the detected first maximum point and the first minimum point.

Next, the detailed configuration of the road μ gradient calculating section 22 will be described with reference to the block diagram of FIG.

As shown in FIG. 14, the road surface μ gradient calculating unit 2
Reference numeral 2 denotes a vehicle speed estimating unit 26 that estimates a vehicle speed (vehicle speed) based on the wheel speeds of the right front wheel, the left front wheel, the right rear wheel, and the left rear wheel.
Μ gradient search unit 2 for searching the road μ gradient for each wheel based on the table 28 from the estimated vehicle speed and the time change characteristics of the detected wheel speed step response component of each wheel.
7 is comprised.

Here, comparing the conditions of FIG. 6 and FIG. 8, the friction coefficient μ is the same as 0.25, but the initial vehicle speed in FIG. 6 is 10 rad / s, while the initial vehicle speed in FIG. The vehicle speed is 20 rad / s. When comparing the time change characteristics of the wheel speeds in FIGS. 6 and 8, the damping rate in FIG. 8 is larger than the damping rate in FIG. 6 and the main frequency of the damped vibration is different. That is, the same road surface μ
Even in the state described above, the time change characteristic of the wheel speed step response component depends on the vehicle speed.

Therefore, in order to compensate for such vehicle speed dependency, the table 28 in FIG. 14 is configured as a two-dimensional table, and the actual measured value of the road surface μ gradient with respect to the time change characteristic is stored for each vehicle speed. . That is, by searching for a table value corresponding to the time change characteristics of the estimated vehicle speed and the detected wheel speed step response component, the table value can be obtained as the road surface μ gradient.

The vehicle speed estimating unit 26 can be configured as a computing unit that selects the largest wheel speed among the wheel speeds of the wheels and outputs the wheel speed as the vehicle speed.
Further, the vehicle speed may be estimated based on the wheel speed at the start of braking.

Note that the step response detecting section 21
Depending on which of the configurations shown in FIGS.
Since the physical quantity of the time change characteristic detected differs,
Of course, the table 28 is changed accordingly. Further, the road surface μ gradient calculating unit 22 not only refers to one physical quantity detected in any of the modes of FIGS. 16 to 18 as a time change characteristic, but also comprehensively calculates a plurality of physical quantities detected in each mode. The determination may be made to determine the road μ gradient.

Next, an example of the configuration of the target braking force calculator 23 will be described.
FIG. As shown in FIG. 15, the target braking force calculation unit 2
3 is the road surface μ slope calculated by the road surface μ slope calculation unit 22
Distribution α and a predetermined reference gradient α_sAnd the difference Δα (= α
−α _s) And the difference Δα is equal to zero
Or the proportional gain G_PrAnd integral gain
G_Ir/ S (s is Laplace operator) proportional integral control
PI controller 30 that performs
Brake from the driver's pedaling force
Target average by removing positive values to prevent braking
Braking force command P_rAnd a positive value removing unit 31 that outputs
Is done. Note that the road μ gradient α that gives the peak μ is 0.
So α_sIs set to a positive value near 0,
Target average braking force command P for realizing_rBut
Is calculated.

The PI controller 30 can be configured as a PID controller including differential control, and further, a higher-order control such as a robust controller for performing so-called H∞ control or two-degree-of-freedom control. May be configured by a controller that performs the following.

In the configuration example shown in FIG. 15, the road surface μ gradient α
Is directly fed back. However, a wheel behavior amount (for example, a slip ratio or the like) corresponding to the calculated road surface gradient α is determined, and a target average for matching the wheel behavior amount to a predetermined target value is determined. It is also possible to configure the target braking force calculation unit 23 to calculate the braking force command _Pr .

Next, the structure of the brake unit that operates in accordance with the valve operation command output from the wheel cylinder oil pressure control unit 24 will be described with reference to FIG.

As shown in FIG. 20, the brake unit 45
A control valve 52, a master cylinder 48, a wheel cylinder 56, a reservoir 58, and an oil pump 60 are provided.

The brake pedal 46 is provided with a master cylinder 48 for increasing the pressure in accordance with the depression force of the brake pedal 46.
Is connected to the pressure-intensifying valve 50 of the control valve 52. The control valve 52 is connected to a reservoir 58 as a low pressure source via a pressure reducing valve 54. Further, a wheel cylinder 56 for applying the brake pressure supplied by the control valve to the brake disc is connected to the control valve 52. The control valve 52 supplies the brake pressure P _d by pedaling force of the driver, controls the opening and closing of the pressure increasing valve 50 and pressure reducing valve 54 on the basis of the pressure increase, pressure reduction command input from the wheel cylinder hydraulic pressure control unit 24 .

The control valve 52 is connected to the pressure increasing valve 5
0 is controlled to open only the wheel cylinder 5
The hydraulic pressure (wheel cylinder pressure) of the master cylinder 48 (master cylinder pressure) is proportional to the pressure obtained when the driver depresses the brake pedal 46.
To rise. Conversely, when the pressure is controlled so as to open only the pressure reducing valve 54, the wheel cylinder pressure decreases to the pressure of the reservoir 58 (reservoir pressure), which is approximately atmospheric pressure. Further, when both valves are controlled to be closed, the wheel cylinder pressure is maintained.

The braking force applied to the brake disc by the wheel cylinder 56 is detected by a pressure increasing time during which the high hydraulic pressure of the master cylinder 48 is supplied, a pressure reducing time during which the low hydraulic pressure of the reservoir 58 is supplied, and a pressure sensor. Depends on master cylinder pressure. Therefore, the wheel cylinder oil pressure control unit 24 calculates the pressure increasing time and the pressure decreasing time for realizing the calculated target average braking force according to the detected master cylinder pressure, and calculates the detected master cylinder pressure and The stepwise change amount ΔP of the wheel cylinder pressure can be calculated from the pressure increase time and the pressure decrease time.

Next, the operation of the first embodiment will be described. When the wheel cylinder oil pressure control unit 24 in FIG. 12 issues a pressure increase command or a pressure decrease command for changing the wheel cylinder pressure in a stepwise manner to the control valve 50, the synchronization signal and the wheel cylinder pressure are changed at the stepwise change point. The stepwise change amount ΔP is transmitted to the step response detection unit 21.

The step response detecting section 21 detects the step response component of the wheel speed detected by the wheel speed detecting section 20 by using the time point delayed by a predetermined time from the input time point of the synchronization signal as the detection start time point. From Δ
The time change characteristic normalized by P is calculated.

Here, the step response detecting section 21 operates as shown in FIG.
First when configured in the manner of a 6, time change characteristic of the frequency components in a band including the resonance frequency f ₁ during the tire grip is detected. In addition, the second embodiment of FIG.
In the third embodiment, the frequency value or time width of the main frequency component of the step response component is calculated.

Next, in the road surface μ gradient calculation unit 22, the μ gradient search unit 27 refers to the table 28 to search for a road surface μ gradient corresponding to the calculated time change characteristic. At this time, the road μ gradient corresponding to the vehicle speed estimated based on the wheel speed of each wheel is selected.

[0092] For example, if you increase the stepwise braking force, as shown in the conceptual diagram of FIG. 19, the wheel speed damping vibrations in a band including the resonance frequency f _1, the attenuation rate during slip, when the tire grip It becomes larger than the attenuation rate. Thus, when the step response detection unit 21 is configured in the first mode, the road surface μ gradient can be obtained from the data of the table 28 prepared corresponding to the detected attenuation rate. At that time, as shown in the figure, as the vehicle speed increases,
Since the damping rate increases during both slipping and gripping, the vehicle speed dependency can be compensated by referring to the data in the table 28 corresponding to not only the damping rate but also the vehicle speed.

Then, the target braking force calculation unit 23 calculates a target average braking force based on the calculated road surface μ gradient α and transmits the calculated result to the wheel cylinder pressure control unit 24. That is, the road contact state of the tire is determined from the road surface μ gradient α,
The target average braking force is incremented if the braking force is far from the peak μ and there is room for the braking force, and if the braking force is insufficient before the peak μ, the target average braking force is decremented.

The wheel cylinder oil pressure controller 24 determines that the current braking force is smaller than the target average braking force.
In order to increase the braking force in a stepwise manner, the control valve 52 is opened to open the pressure increasing valve 50 for a predetermined pressure increasing time.
Command. Thus, as shown in FIG. 5, the wheel cylinder pressure is stepwise increased rapidly at time t _1, reaches the target average braking force. At this time, the wheel cylinder oil pressure control unit 24 determines the master cylinder pressure and the pressure increase time
The stepwise change amount ΔP of the wheel cylinder pressure is calculated and output. Then, the pressure increasing valve 52 is closed to maintain the wheel cylinder pressure.

On the other hand, when the braking force at the present time becomes larger than the target average braking force, the control valve is opened so as to open the pressure reducing valve 54 for a predetermined pressure reducing time in order to decrease the braking force in a stepwise manner. 52. Thus, as shown in FIG. 5, the wheel cylinder pressure at time t ₂
, And is controlled so as not to exceed the target average braking force. Since the wheel speed step response component is generated both during stepwise pressure increase and pressure decrease, ΔP and a synchronization signal are output to the step response detection unit 21 in any case, and the time change characteristic is calculated. . Of course, this time-varying characteristic indicates that the pressure increases stepwise (ΔP>
0) and when the pressure is reduced (ΔP <0), the road μ gradient calculating unit 22 searches for the road μ gradient by distinguishing each case.

When the current braking force is achieved to the target average braking force, when the braking force difference is large, not only one step change of the wheel cylinder pressure but also, as shown in FIG. The change may be made in a plurality of steps. Even in such a case, the road surface μ gradient is calculated from the wheel speed step response component for each stepwise change.

As described above, in the first embodiment, the braking force acting on the wheels varies stepwise so as to follow the target average braking force, and the braking force is generated by this stepwise change. A road surface μ gradient is calculated based on a time change characteristic of a wheel speed step response component, and an antilock brake operation is performed based on the gradient. Therefore, according to the present embodiment, while maintaining a smooth running state without constantly micro-exciting the wheel cylinder pressure,
At the time of braking, the road surface μ gradient can be estimated with high accuracy, and good antilock brake control can be performed. (Second Embodiment) The principle of friction state detection similar to that of the first embodiment can be applied to an EV braking / driving force control device in an electric vehicle (EV). The configuration of such an EV braking / driving force control device is described as a second embodiment in FIG.
3 is shown. Note that the same components as those of the first embodiment are denoted by the same reference numerals, and detailed description is omitted.

As shown in FIG. 13, the EV braking / driving force control device according to the second embodiment
The road μ gradient calculating unit 22b that calculates the road μ gradient α between each tire and the road based on the time change characteristic of the wheel speed step response component detected by the above, and based on the calculated road μ gradient α A target braking / driving force calculation unit 23b for calculating a target braking / driving force command to be applied to each wheel; and a torque command to a wheel motor (not shown) for realizing the calculated target braking / driving force is calculated for each wheel. And a generated torque control unit 25 that performs the control.

Of these, the generated torque control unit 25 is different from the wheel cylinder oil pressure control unit 24 according to the first embodiment in that only the braking force is controlled by the wheel cylinder oil pressure control unit 24. Since it is used, it is possible to control both the braking force and the driving force. That is, in the second embodiment, not only when the braking force changes stepwise, but also based on the time change characteristic of the wheel speed step response component generated when the driving force changes stepwise, the road surface μ gradient is determined. It is possible to calculate α. The stepwise change amount ΔT calculated by the generated torque control unit 25 is a concept including not only the braking force but also the step change amount of the driving force. In the first embodiment, the stepwise change amount ΔT corresponds to ΔP. It is.

Further, the road μ gradient calculating section 22 b
However, the table 28 stores the data of the road surface μ gradient α corresponding to the time change characteristics at the time of the step change of the braking torque and the driving torque together with the table 28. Then, data of the road surface μ gradient α corresponding to the vehicle speed and the time change characteristics are searched by distinguishing between the step change of the braking torque and the step change of the drive torque.

The target braking / driving force calculator 23b first sets the target braking / driving force corresponding to the driver's request for acceleration / deceleration. Then, the ground contact state of the tire is determined from the calculated road surface gradient α, and if the braking force has a margin, the set target braking / driving force is incremented.If the braking / driving force has no margin, the setting is performed. Decrease the set target braking / driving force.

As described above, in the second embodiment, it is possible to respond to the driver's request for acceleration and deceleration and to follow the target braking / driving force suitable for the road contact state. At this time, it is possible to control the average braking / driving force while changing the braking / driving force in a stepwise manner. In various driving states such as driving and steady driving, the road surface μ gradient can be estimated with high accuracy. (Third Embodiment) FIG. 22 shows the configuration of a braking force control device according to a third embodiment. This braking force control device is based on the principle of the third and fourth aspects of the present invention, and is called "running stabilizing device" (trade name: VS).
This is realized as a C (Vehicle Stability Control) device or an antilock brake control (ABS) device.

As shown in FIG. 22, the braking force control device according to the third embodiment has a wheel speed detecting section 20 for detecting wheel speed signals of the respective wheels, and an input from the detected wheel speed signals. A pulse response detecting unit 62 that detects a wheel speed pulse response component in synchronization with the synchronization signal, and detects an amplitude characteristic of the component for each wheel, based on an amplitude characteristic of the detected wheel speed pulse response component. A road μ gradient calculating unit 63 that calculates a road μ gradient α between each tire and the road,
A target braking force calculation unit 65 that calculates a command of a target braking force to be applied to each wheel based on the calculated road surface μ gradient α;
A wheel that outputs a pulse-like wheel cylinder pressure change command at a certain timing and calculates a pressure increase / decrease command to a control valve for realizing a wheel cylinder pressure corresponding to each calculated target braking force for each wheel. And a cylinder oil pressure control section 67.

In this embodiment, the pulse-like change of the braking force acting on the wheel is realized by changing the wheel cylinder pressure in a pulse-like manner. For this reason,
The wheel cylinder oil pressure controller 67 outputs a pressure increase / decrease command for realizing the target braking force, and at a certain timing, the first pulse shown in FIG. 11C and the frictional force vibration generated by the pulse. On the other hand, a command to generate a second pulse having the opposite phase is output. Note that the second pulse amplitude is set so as to be a half cycle of the vibration component similarly to the first pulse amplitude.

In the pulse response detection section 62, the wheel cylinder oil pressure control section 67 supplies a synchronization signal indicating the start point of the first pulse change and the pulse change amount ΔP of the wheel cylinder pressure (the maximum wheel cylinder pressure after the change- Wheel cylinder pressure just before the change). The pulse response detection unit 62 detects the start point of the pulse change based on the synchronization signal, and starts detection of the pulse response component of the wheel speed after a lapse of a predetermined time from the time point or a time delay in consideration of the time point. .

FIG. 2 shows a configuration example of the pulse response detection section 62.
5 will be described. As shown in FIG. 25, the pulse response detection unit 62 includes a high frequency cutoff filter 73 for cutting off the frequency component of the high band than the resonance frequency f ₁ during the tire grip on the wheel velocity pulse response components, given the filter output samples A pole detection unit 74 that detects the first maximum point and the first minimum point based on a predetermined algorithm from the time series data discretized for each time τ, the amplitude a ₁ of the first detected maximum point and the first an amplitude detecting section 75 for detecting an amplitude a ₂ of the minimum point, the amplitude characteristic calculation unit 77 for calculating an amplitude characteristic of the impulse response component based on at least one of amplitude a ₁ and the amplitude a _2, consists You.

The amplitude characteristic calculating section 77 calculates, as the amplitude characteristic, a ₁ / Δ obtained by normalizing the amplitude a ₁ with the pulse variation ΔP.
P, and the ratio of the amplitude a ₁ for the amplitude _{a 2 (a 1 / a 2} )
And outputs at least one of them.

The road μ gradient calculating section 63 can be realized by the same configuration as the road μ gradient calculating section 22 of FIG. 14 according to the first embodiment, but as shown in FIG. The μ gradient search unit 68 according to the embodiment is configured to calculate the road μ gradient based on the estimated vehicle speed and the calculated amplitude characteristic of the wheel speed pulse response component.

That is, the table 69 shown in FIG. 24 shows the relationship between the amplitude characteristic and the road surface μ gradient α, and in order to compensate for the vehicle speed dependency, the amplitude characteristic (a ₁ / ΔP
And a ₂ / a ₁ ) are stored.

Next, the operation of the third embodiment will be described. The wheel cylinder hydraulic control unit 67 of FIG.
When a pressure increasing command or a pressure decreasing command is issued to change the wheel cylinder pressure in the form of the first pulse and the second pulse of 1 (c), a synchronizing signal indicating the point of generation of the first pulse and the pulse change amount ΔP of the wheel cylinder pressure To the pulse response detector 6
Transmit to 2. At this time, the road surface friction force vibrates due to the first pulse. The amplitude value of this vibration is equal to twice the applied braking force when no slip occurs on the + side, and the friction force is saturated when the slip occurs. Smaller. Then, by the second pulse output in the opposite phase to the vibration, the subsequent vibrations are canceled and rapidly attenuated.

The pulse response detecting section 62 detects the pulse response component of the wheel speed detected by the wheel speed detecting section 20 by using the time point delayed by a predetermined time from the input time point of the synchronization signal as the detection start time point. Is calculated.

Here, the wheel speed vibration generated by the frictional force vibration due to the pulse application also shows an amplitude change corresponding to the frictional force vibration. For this reason, the amplitude characteristic (a ₁ / ΔP) detected by the pulse response detection unit 62 is such that when no slip occurs on the + side (pulse application direction), the applied braking force (proportional to the pulse change amount ΔP) Shows a value corresponding to a frictional force twice as large as On the other hand, when the slip occurs on the + side, (a ₁ / ΔP) is smaller than the value corresponding to twice the maximum frictional force and indicates a value dependent on the magnitude of the marginal braking force.

Therefore, the road μ gradient calculating section 63 can calculate the road μ gradient α having a high correlation with the amplitude characteristics as described above by searching the data of the table corresponding to the detected amplitude characteristics. . At this time, the vehicle speed dependency is compensated by selecting a road surface μ gradient according to the estimated vehicle speed.

In the above description, it is assumed that the slip state is discontinuously shifted from the completely gripped state, and the state returns to the fully gripped state. In fact, there is very little grip, and there is a slight slip.

Therefore, the frictional force does not overshoot up to twice the applied braking force, and the frictional force is attenuated to some extent even if it does not completely enter the slip state. Therefore, if the damping characteristic serving as a base when the state does not completely shift to the slip state is obtained from a ₂ / a ₁ and the amplitude characteristic is corrected, the accuracy is further improved.

Then, the target braking force calculation unit 23 calculates a target average braking force based on the calculated road surface μ gradient α, and transmits it to the wheel cylinder pressure control unit 24. For example, in the case of an ABS device, a reference value α _s which is a positive value near 0
And a deviation command for making the deviation between the road surface μ gradient α and the road surface μ gradient α equal or substantially equal to zero. Alternatively, the target braking force may be calculated based on the wheel deceleration and the like, and the target braking force may be changed according to the calculated road surface gradient α.

In the case of the VSC device, a target braking force for stably controlling the vehicle body is calculated and set based on the wheel acceleration, the yaw rate, the steering wheel operating angle, the wheel cylinder pressure, and the like. Then, the tire contact state is determined based on the road surface μ gradient α, and if the braking force has a margin, the master cylinder pressure is set as an upper limit, the set target braking force is increased, and if the braking force has no margin, the setting is performed. Decrease the set target braking force.

The wheel cylinder oil pressure controller 67
Thus, wheel cylinder pressure control for following the target braking force is executed.

As described above, in the third embodiment, a road surface frictional force is actually generated by applying a pulse-like braking force, and then the road surface μ gradient is calculated based on the pulse response component. Therefore, the margin to the slip limit can be reliably grasped, and high reliability can be obtained.

Further, even if the braking force suddenly increases at the rise of the pulse due to the application of the pulse-like braking force and a slip occurs only for a short period of time, the braking force sharply decreases at the fall of the pulse, and immediately Since the road surface friction force in the opposite direction is applied, it is possible to easily return to the grip state. Therefore, the influence on the vehicle running can be minimized. Furthermore, since the braking force of the second pulse for attenuating the frictional force vibration is applied after the first pulse, the frictional force vibration becomes only one cycle, and the influence on the vehicle running can be further suppressed.

As described above, in the present embodiment, the road surface μ gradient can be extremely increased without applying a great influence on the vehicle running only by applying a pulse-like braking force without constantly exciting the braking / driving force. Accuracy can be estimated, and better vehicle stabilization control can be performed.

Further, as shown in FIG. 23, the present embodiment can be realized as a road μ gradient calculating device applied to an electric vehicle. In this case, instead of the wheel cylinder oil pressure controller 67, a pulse braking / driving force generator 64 capable of changing the braking force and the driving force in a pulsed manner is used.

According to the road surface μ gradient calculating device shown in FIG. 23, not only the braking force but also the driving force can be changed in a stepwise manner. μ gradient can be estimated with high accuracy.

Although the embodiments of the present invention have been described above, the present invention is not limited to the above-described examples, and can be arbitrarily and suitably changed without departing from the gist of the present invention.

For example, in the above-described embodiment, the friction state to be calculated is the road surface μ gradient α. However, the present invention is not limited to this. Can be calculated as long as it is a physical quantity relating to the ease of slipping between the wheel speed and the time variation characteristic or the amplitude characteristic of the wheel speed vibration.

The ABS device according to the first embodiment can be realized as a VSC device.

[0127]

As described above, according to the first and second aspects of the present invention, the braking / driving force acting on the wheel is changed in a predetermined change state, and the wheel speed is changed by the predetermined change in the braking / driving force. The damping characteristic of the response component is detected, and the friction state between the wheel and the road surface is calculated based on the damping characteristic. The effect that the calculation can be performed with high accuracy is obtained.

According to the third and fourth aspects of the present invention, the braking / driving force acting on the wheels is changed stepwise.
The frictional state is calculated based on the time change characteristic of the wheel speed step response component that is correlated with the frictional state between the tire and the road surface. -In various running states such as steady running, the effect that each friction state can be calculated with high accuracy can be obtained.

In particular, according to the fourth aspect of the present invention, it is possible to control to follow the target braking / driving force while changing the braking / driving force in a stepwise manner. High-accuracy target following control of braking / driving force can be performed without adding hardware.

According to the fifth and sixth aspects of the present invention, by applying a pulse-like braking / driving force, a road surface frictional force is actually generated, and then the frictional force based on the pulse response component is generated. Since the state is calculated, the margin to the slip limit can be reliably grasped, and high calculation accuracy can be obtained.
This has the effect.

Further, according to the fifth and sixth aspects of the present invention, since the applied braking / driving force is changed in a pulse shape, even if a slip occurs, it is possible to easily return to the grip state, and After the application of one pulse, the braking / driving force of the second pulse having the opposite phase to the frictional force vibration is applied.
The effect that the frictional force vibration after this is attenuated and the influence on the vehicle running can be minimized is obtained. As a result, there is an effect that the frictional state can be calculated with high accuracy without always slightly exciting the braking / driving force and without affecting the traveling of the vehicle.

[Brief description of the drawings]

FIG. 1 is a block diagram showing a configuration of the present invention.

FIG. 2 is a diagram showing a dynamic model equivalent to a wheel resonance system according to the present invention.

FIG. 3 is a diagram showing a friction characteristic between a tire and a road surface in the wheel resonance system according to the present invention.

FIG. 4 is a conceptual diagram of a vibration model according to the present invention.

FIG. 5 is a diagram showing a flow of control of a wheel cylinder pressure when a braking force is changed in a stepwise manner and detection of a wheel speed step response component.

FIG. 6 shows a time change characteristic of a wheel speed step response component,
FIG. 9 is an experimental result for explaining a relationship between a tire and a road surface and a wheel speed signal and a vehicle speed when a brake is applied from an initial vehicle speed of 10 rad / s on a road surface having a friction coefficient μ = 0.25. FIG. 6 is a diagram showing a time change of the data.

FIG. 7 shows a time change characteristic of a wheel speed step response component,
FIG. 4 is an experimental result for explaining a relationship between a tire and a road surface, and shows a wheel speed signal and a vehicle speed when a brake is applied from an initial vehicle speed of 20 rad / s on a road surface having a friction coefficient μ = 0.1. FIG. 6 is a diagram showing a time change of the data.

FIG. 8 shows a time change characteristic of a wheel speed step response component,
FIG. 9 is an experimental result for explaining the relationship with the friction state between the tire and the road surface, and shows a wheel speed signal and a vehicle speed when braking is performed from an initial vehicle speed of 20 rad / s on a road surface having a friction coefficient μ = 0.25. FIG. 6 is a diagram showing a time change of the data.

FIG. 9 shows a time change characteristic of a wheel speed step response component,
FIG. 9 is an experimental result for explaining the relationship between the tire and the road surface frictional state, and shows a wheel speed signal and a vehicle speed when braking is performed from an initial vehicle speed of 20 rad / s on a road surface having a friction coefficient μ = 0.3. FIG. 6 is a diagram showing a time change of the data.

FIG. 10 is a block diagram showing a configuration of the present invention.

11A and 11B are diagrams showing a time change of a road surface frictional force and a wheel speed vibration when a pulse-like braking / driving force is applied to a wheel, wherein FIG. (b) is a slip state in the application direction (+) when one pulse is input, and (c) is a road surface frictional force and wheel speed vibration in a slip state in the application direction when one pulse and a pulse having an opposite phase are input. Are shown over time.

FIG. 12 is a block diagram showing a configuration of the antilock brake control device according to the first embodiment of the present invention.

FIG. 13 is a block diagram illustrating a configuration of an EV braking / driving force control device according to a second embodiment of the present invention.

FIG. 14 is a block diagram illustrating a configuration of a road surface μ gradient calculating unit according to the first embodiment of the present invention.

FIG. 15 is a block diagram illustrating a configuration of a target braking force calculation unit according to the first embodiment of the present invention.

FIG. 16 is a block diagram showing a configuration of a first mode of the step response detection section according to the first embodiment of the present invention.

FIG. 17 is a block diagram illustrating a configuration of a third mode of the step response detection unit according to the first embodiment of the present invention.

FIG. 18 is a block diagram illustrating a configuration of a fourth mode of the step response detection unit according to the first embodiment of the present invention.

FIG. 19 is a diagram schematically illustrating a damping tendency of a wheel speed step response component for each friction state and for each vehicle speed.

FIG. 20 is a block diagram illustrating a hardware configuration of a brake unit of the antilock brake control device according to the first embodiment of the present invention.

FIG. 21 is a diagram showing a command signal that changes stepwise in the target tracking control of the braking force.

FIG. 22 is a block diagram illustrating a configuration of a VSC device or an ABS device according to a third embodiment of the present invention.

FIG. 23 is a block diagram showing a configuration of an EV road surface μ gradient calculating device according to a third embodiment of the present invention.

FIG. 24 is a block diagram illustrating a configuration of a road μ gradient calculating unit according to a third embodiment of the present invention.

FIG. 25 is a block diagram illustrating a configuration of a pulse response detection unit according to a third embodiment of the present invention.

[Explanation of symbols]

 Reference Signs List 20 wheel speed detecting section 21 step response detecting section 22 road μ gradient calculating section 23 target braking force calculating section 23b target braking / driving force calculating section 24 wheel cylinder oil pressure controlling section 25 generated torque controlling section 62 pulse response detecting section 63 road surface μ gradient calculating Unit 64 pulse braking / driving force generation unit 65 target braking force calculation unit 67 wheel cylinder oil pressure control unit

 ──────────────────────────────────────────────────続 き Continued on the front page (72) Inventor Koji Umeno 41 Toyoda Central Research Institute, Inc. 41 Toyota Central Research Institute, Inc. (72) Inventor Satoshi Sugai 41 Toyota Central Research Institute, Inc.

Claims (6)

[Claims] 1. A wheel speed detecting means for detecting a wheel speed, a braking / driving force control means for changing a braking / driving force acting on a wheel in a predetermined change state, and a wheel speed based on a predetermined change in the braking / driving force. A friction state calculating device including: damping characteristic detecting means for detecting a damping characteristic of a response component; and calculating means for calculating a friction state between a wheel and a road surface based on the damping characteristic. 2. A wheel speed detecting means for detecting a wheel speed, a braking / driving force controlling means for changing a braking / driving force acting on a wheel in a predetermined change state, Damping characteristic detecting means for detecting a damping characteristic of a response component, calculating means for calculating a friction state between a wheel and a road surface based on the damping characteristic, and a target control corresponding to the friction state calculated by the calculating means. Target braking / driving force calculating means for calculating the driving force, and braking / driving force control means for changing the target braking / driving force so that the braking / driving force acting on the wheels follows the target braking / driving force. Control device. 3. A wheel speed detecting means for detecting a wheel speed, a braking / driving force control means for changing a braking / driving force acting on a wheel in a stepwise manner, and a wheel speed detected by the wheel speed detecting means.
Step response detecting means for detecting a time change characteristic of a wheel speed step response component when the braking / driving force is stepwise changed by the braking / driving force control means; and a wheel speed step response detected by the step response detecting means. Calculating means for calculating the frictional state between the tire and the road surface based on the time-varying characteristics of the components. 4. A wheel speed detecting means for detecting a wheel speed, and a wheel speed detected by the wheel speed detecting means,
A step response detecting means for detecting a time change characteristic of a wheel speed step response component when the braking / driving force acting on the wheel is changed stepwise; and a time of the wheel speed step response component detected by the step response detecting means. Calculating means for calculating a friction state between the tire and the road surface based on the change characteristic; target braking / driving force calculating means for calculating a target braking / driving force corresponding to the friction state calculated by the calculating means; A braking / driving force control unit that changes the braking / driving force so that the braking / driving force acting on the target follows the target braking / driving force. 5. A wheel speed detecting means for detecting a wheel speed, a pulse-shaped braking / driving force for oscillating a frictional force generated between a tire and a road surface, and a pulse-shaped braking / driving force generated by the pulse-shaped braking / driving force. A pulse-shaped braking / driving force having an opposite phase to the vibration of the frictional force, and a pulse braking / driving force generating means for generating, from the wheel speed detected by the wheel speed detecting means,
Pulse response detecting means for detecting an amplitude characteristic of a wheel speed pulse response component when a pulsed braking / driving force is applied by the pulse braking / driving force generating means; and a wheel speed pulse response detected by the pulse response detecting means. Calculating means for calculating the frictional state between the tire and the road surface based on the amplitude characteristics of the components. 6. A wheel speed detecting means for detecting a wheel speed, and a wheel speed detected by the wheel speed detecting means,
Pulse response detection means for detecting the amplitude characteristics of the wheel speed pulse response component when a pulsed braking / driving force is applied, based on the amplitude characteristics of the wheel speed pulse response component detected by the pulse response detection means, Calculating means for calculating the friction state between the tire and the road surface; target braking / driving force calculating means for calculating a target braking / driving force corresponding to the friction state calculated by the calculating means; braking / driving force acting on the wheels Controls the braking / driving force so as to follow the target braking / driving force, and vibrates a frictional force generated between a tire and a road surface; and a pulse-shaped braking / driving force. A braking / driving force control device including: a pulse-shaped braking / driving force having a phase opposite to the vibration of the frictional force generated by the force;