JPH07132787A - Vehicle collision preventing device - Google Patents

Abstract

PURPOSE:To improve mu estimation precision by regulating the output fluctuation of an internal combustion engine during estimation of mu in a vehicle collision preventing device which is operated to set deceleration during automatic braking by estimating a road friction factor mu when automatic braking processing is effected. CONSTITUTION:Based on signals from a car speed sensor 10 and a distance meansurement sensor 12, it is monitored by a computing control device 30 whether a safety distance is maintained between and a preceding vehicle. When an intercar distance is reduced to a value lower than a safety distance, slow braking is effected by an automatic braking device 26 and estimation of muis executed based on a brake oil pressure, wheel acceleration, and a wheel slip factor. When an intercar distance is further decreased, an alarm is sounded by an alarm unit 24 and a brake force generated to estimated mu is generated by an automatic control device 26. To improve mu estimation precision, a throttle valve is fully closed by a throttle actuator 28 during slow braking.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a vehicle collision prevention device, and in particular, when performing automatic braking processing to prevent a vehicle rear-end collision accident with an obstacle in front of the vehicle, the road surface friction coefficient is estimated to reduce the reduction during automatic braking. The present invention relates to a vehicle collision prevention device that sets a speed.

[0002]

2. Description of the Related Art With the increase in vehicle accidents in recent years, various devices have been proposed to prevent a vehicle rear-end collision accident. As such a device, for example, the danger of a collision is predicted based on the distance from the own vehicle to a front obstacle such as a preceding vehicle, the relative speed between the two, and the own vehicle speed, and an alarm or automatic warning is given to the driver. There are those that perform processing such as braking.

In this case, for example, if automatic braking is to be executed immediately before a collision, the automatic braking process should be started depending on the relative speed between the two, the vehicle speed of the vehicle, the condition of the road surface on which the vehicle is running, and the like. There is a difference. This is because the faster the relative speed and the vehicle speed, the longer the braking distance is required to avoid collision, and the smaller the friction coefficient μ of the road surface, the smaller the deceleration that can be generated and the longer the braking distance is.

Therefore, in order to put such a vehicle collision prevention device into practical use, it is necessary to accurately estimate the friction coefficient μ of the road surface during traveling, for example, Japanese Patent Laid-Open No. 4-36.
Japanese Laid-Open Patent Publication No. 2453 discloses that the preliminary braking is performed by a pumping brake in order to detect the friction coefficient μ before the main braking by the automatic braking.

This device focuses on the fact that the wheel acceleration during braking is determined by the braking torque applied from the brake mechanism and the frictional force generated between the wheel and the road surface. The wheel acceleration generated on the wheels is detected, and the friction coefficient μ of the road surface is calculated based on the detected value.

In this case, when the vehicle is stopped by the automatic braking, the deceleration is set on the basis of the road surface condition estimated immediately before that, and the highly accurate automatic braking process can be executed.

[0007]

However, the above-mentioned conventional device is premised on that only the braking torque generated by the brake mechanism and the frictional force generated between the wheel and the road surface are applied to the wheel during preliminary braking. There is. However, in addition to these external forces, the output torque generated by the internal combustion engine is applied to the wheels, and when the output torque fluctuates, the friction coefficient of the road surface cannot be accurately estimated.

Further, the abnormal approach to the front obstacle for which the automatic braking process is determined is often due to the driver's carelessness. Therefore, when preliminary braking is performed to estimate the friction coefficient μ, It is highly possible that the driver is operating the accelerator.

For this reason, the estimation accuracy of the friction coefficient μ by the above-mentioned conventional device is not always good, and there is a problem that an error may occur depending on the operating condition of the vehicle.

The present invention has been made in view of the above points, and when the execution of automatic braking is determined and the preliminary braking is performed to estimate the friction coefficient μ of the road surface, the output of the internal combustion engine is output. It is an object of the present invention to provide a vehicle collision prevention device that can solve the above problems by holding a torque at a constant value.

[0011]

FIG. 1 is a diagram showing the principle configuration of a vehicle collision prevention device that achieves the above object. That is, as described above, the purpose is to measure the distance between the vehicle front obstacle and the braking control means M2 for controlling the automatic braking device M1 mounted on the vehicle in the slow braking mode or the rapid braking mode, as shown in FIG. When the distance to the front obstacle detected by the distance measuring means M5 is less than or equal to the first safety distance, the braking process in the slow braking mode is executed, and the distance to the front obstacle is the first safety distance. When the second safety distance shorter than the distance is equal to or less than the second safety distance, the execution determination means M7 for executing the braking processing in the sudden braking mode and the braking control means M2 for executing the braking processing in the slow braking mode, The second safety distance is provided by a road surface μ estimating means M3 for estimating the friction coefficient μ of the traveling road surface based on the braking torque generated by the automatic braking device M1 and the wheel acceleration generated on the wheels. In the vehicle collision prevention apparatus in which the setting is made in consideration of the friction coefficient μ as well, a vehicle including an engine output holding unit M8 that holds the output of the internal combustion engine constant during execution of the braking process in the slow braking mode. This is achieved by a collision prevention device.

Further, in the vehicle collision prevention device having the above-mentioned structure, the engine output holding means 8 may be constituted by a throttle fully closing means for fully closing a throttle valve provided in an intake passage of an internal combustion engine. This is effective for causing the driver to perceive abnormal approach to the front obstacle prior to the sudden braking by the braking device M1.

Further, the throttle fully closing means constituting the engine output holding means M8 receives a signal from the pedal position detecting means M9 for detecting the position of the accelerator pedal that the accelerator pedal has been returned to the fully closed position. Up to, the configuration that holds the throttle valve in the fully closed position regardless of the depression amount of the accelerator pedal, and releases the fully closed holding of the throttle valve when a signal indicating that the accelerator pedal is returned to the fully closed position is received, It is effective to prevent accelerating after the braking force by the automatic braking device M1 is released and to ensure the operability according to the driver's intention after the automatic braking.

[0014]

In the vehicle collision prevention system according to the present invention, the execution determination means is configured to detect when the distance to the front obstacle detected by the distance measuring means M5 is shorter than the first safety distance. It is determined that the slow braking mode braking process by the braking control means M2 should be executed.

At this time, since the output of the internal combustion engine is held at a constant value by the engine output holding means M8 regardless of the accelerator operation by the driver, the external force applied to the wheels during the braking process in the slow braking mode is performed. Of these, the variables that vary are the braking torque applied from the automatic braking device M1 and the frictional force generated between the wheels and the road surface.

Therefore, the road surface μ estimating means M3 estimates the road surface μ based on the braking torque generated by the braking device M1 and the wheel acceleration generated on the wheels by the braking torque during the braking process in the slow braking mode. In this case, high estimation accuracy will be ensured. As a result, the braking torque generated by the automatic braking device M1 when the braking control means M2 executes the braking process in the sudden braking mode is controlled to an ideal value with high accuracy.

Further, when the engine output holding means M8 is constituted by the throttle fully closing means, the automatic braking device M1 is actuated by the driver's carelessness and the like to start execution of the braking control in the slow braking mode. Then, the output of the internal combustion engine is reduced accordingly, and the driver's attention is called.

Further, until the throttle full closing means constituting the engine output holding means M8 receives a signal from the pedal position detecting means M9 indicating that the accelerator pedal is fully closed, the throttle valve is fully closed. According to the holding structure, the output of the internal combustion engine does not increase unless the driver releases the depression of the accelerator pedal after the automatic braking device M1 starts operating. Therefore, after the automatic braking process is completed, the vehicle is not suddenly accelerated at the same time when the braking torque by the automatic braking device M1 is released.

[0019]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT FIG. 2 is a block diagram of a vehicle collision prevention device according to an embodiment of the present invention. In the figure, a vehicle speed sensor 10
Is a sensor that detects the vehicle speed of the vehicle. Distance measuring sensor 1
Reference numeral 2 denotes a sensor for detecting the distance between the own vehicle and a front obstacle such as a preceding vehicle, which corresponds to the distance measuring means M5 described above, and emits a predetermined wave such as a laser or a millimeter wave to generate a reflected wave. It can be configured by a radar device or the like that detects a distance from the propagation time until reception.

The relative speed sensor 14 is a sensor for detecting the relative speed between the own vehicle and an obstacle ahead of it. For example, the relative speed sensor 14 emits a predetermined wave toward the front of the vehicle and superimposes it on the reflected wave from the front vehicle. The Doppler sensor can detect the relative speed based on the existing Doppler shift.

However, the relative speed between the own vehicle and the obstacle ahead can also be obtained by differentiating the distance data obtained by the distance measuring sensor 12 with time.
Instead of 4, a mechanism for differentiating the detection value of the distance measuring sensor 12 may be provided.

Further, the distance measuring sensor 12 and the relative velocity sensor 14 generate a wave that periodically modulates, based on the distance from the time shift of the modulation cycle and the frequency difference between the transmitted wave and the reflected wave. An FM-CW radar that detects a relative velocity, or a relative velocity based on a distance based on the time until a reflected wave is received by emitting a wave in a predetermined cycle, and a Doppler shift superimposed on the reflected wave. Can be simultaneously realized by a pulse Doppler radar or the like for detecting each of these.

The acceleration sensor 16 is a sensor for detecting acceleration / deceleration of the vehicle based on the motion state of the vehicle. Here, the acceleration / deceleration of the vehicle can also be obtained by time-differentiating the vehicle speed detected by the vehicle speed sensor 10. Therefore, instead of the acceleration sensor 16, a mechanism that differentiates the detection value of the vehicle speed sensor 10 with respect to time may be provided.

The wheel speed sensor 18 is a sensor which is provided for each wheel and generates a pulse signal or the like having a cycle corresponding to the rotation speed of the wheel, and constitutes a part of the road surface μ estimating means M3. Here, since the wheel rotation speed and the vehicle speed can be regarded as substantially the same, it is possible to substitute the vehicle speed sensor 10 with the wheel speed sensor 18.
In this case, the wheel speed sensor 18 also constitutes the vehicle speed detecting means M5 described above.

The brake oil pressure sensor 20 is a sensor for detecting the brake oil pressure supplied to the brake mechanism provided for each wheel, and constitutes a part of the road surface μ estimating means M3 as in the wheel speed sensor 18. .

The accelerator pedal sensor 22 corresponds to the pedal position detecting means M9 described above, and is a sensor for generating a signal indicating such a situation when the accelerator pedal is in the fully closed position.

The alarm device 24 is a member that gives a visual or audible alarm to the driver when it is detected that the vehicle has approached an obstacle in front of the vehicle. It is composed of a lamp and an alarm buzzer.

The automatic braking device 26 is composed of a brake mechanism arranged on each wheel, a brake hydraulic pressure generating mechanism, a brake hydraulic pressure control mechanism, etc., and supplies the brake hydraulic pressure to the brake mechanism according to a given command value. It is a device that generates a braking torque according to a command value by supplying it, and constitutes the automatic braking device M1 described above.

Further, the throttle actuator 28 is
It is a mechanism that constitutes the engine output holding means M8 as the above-mentioned throttle fully closing means, and when a predetermined drive signal is received, the throttle valve provided in the intake passage of the internal combustion engine is brought into a fully closed state. Therefore, when a predetermined drive signal is supplied to the throttle actuator 28, the output of the internal combustion engine always corresponds to the throttle fully closed regardless of the operation of the accelerator pedal.

The arithmetic and control unit 30 is mainly composed of a microcomputer, and is a main part of the vehicle collision prevention system of the present embodiment, which realizes the main parts of the braking control unit M2, the road surface μ estimating unit M3 and the execution judging unit M7. It is a department. The arithmetic and control unit 30 is provided with an input / output interface circuit in addition to a CPU as a main control unit, a ROM and a RAM as memory, and a desired detection value supplied from various sensors such as the vehicle speed sensor 10 described above. Then, the alarm device 24 and the like are controlled as necessary.

Here, the vehicle collision prevention device of this embodiment is
For example, when the vehicle improperly approaches an obstacle ahead of the vehicle due to the driver's carelessness or the like, the alarm device 24 makes the driver perceive such a situation. By automatically guiding the vehicle to stop by, the rear-end collision is surely avoided. The operation of the vehicle collision prevention device having the above structure will be described below.

In FIG. 3, the own vehicle 32 travels at the speed V ₀ at a certain time t ₀ , and the position of Δx in front of the own vehicle 32 is set to the preceding vehicle 34.
Shows that the vehicle is traveling at speed V ₁ and deceleration a ₁ . In this case, the safe distance that the own vehicle 32 should secure in relation to the preceding vehicle 34 is a distance that is guaranteed not to cause a rear-end collision with the preceding vehicle 34 during traveling, and even if that distance is secured. For example, the distance must be such that a collision with a front obstacle can be avoided if at least an immediate braking operation is started.

By the way, at time t ₀ , with respect to the preceding vehicle 34 traveling at the speed V ₁ and the deceleration a ₁ , the speed V
_If the own vehicle 32 following at ₀ starts decelerating at the deceleration a ₀ after a predetermined delay time τ from the time t ₀ , if the own vehicle 32 stops after the preceding vehicle 34 stops,
The inter-vehicle distance that is shortened until the vehicle stops after time t ₀ is equal to the area S ₁ indicated by diagonal lines in FIG.

Here, the area S₁Is the time of the following car
t₀Distance to move later {V₀・ Τ + (V₀ ²/ A₀) /
2}, time t₀Distance that the preceding vehicle 34 will move later
(V₁ ²/ A₁) / 2 is equal to
Can be represented.

X _B = {V ₀ · τ + (V ₀ ² / a ₀ ) /
2} − (V ₁ ² / a ₁ ) / 2 Therefore, at time t ₀ , if the distance x shown in the following equation is secured, start deceleration at deceleration a ₀ after the delay time τ. Thus, it is guaranteed that the vehicle can be stopped with the stop distance L secured.

X = {V ₀ · τ + (V ₀ ² / a ₀ ) / 2}-(V ₁ ² / a ₁ ) / 2 + L (1) By the way, the above equation (1) is applied to the preceding vehicle 34. Deceleration a ₁
Is relatively large, and it is assumed that the own vehicle 32 must also stop following the preceding vehicle 34 in order for the following own vehicle 32 to avoid a rear-end collision. However, the preceding vehicle 3
When the deceleration a _{1 of} 4 is relatively small, both speeds may be equal in the deceleration process without stopping the vehicle, and the relative speed may be “0”.

In this case, the distance shortened from the time t ₀ until both speeds become constant, that is, the distance corresponding to the area S ₂ shown by hatching in FIG. 5, is secured at the time t ₀ . In this case, the collision is avoided, and if the distance L is secured at the time when both speeds become constant, the safety distance x can be expressed by the following equation. x
= V ₀ · T- (T-τ) ² · a ₀ / 2- (V ₁ · T-a
^{_{1 · T 2/2) +}} L ··· (2) It should be noted that, in the above formula, T
= (V ₀ −V ₁ + a ₀ · τ) / (a ₀ −a ₁ ).

Therefore, if the above variables (1) and (2) can be switched and used according to the deceleration a ₁ of the preceding vehicle 34 and various variables can be detected at any time, an appropriate safety distance according to the running condition can be obtained. It is possible to calculate x.

Here, in this embodiment, in the above equations (1) and (2), the vehicle speed V ₀ is determined by the vehicle speed sensor 10, and the moving speed V ₁ of the preceding vehicle 34 is determined by the relative speed sensor 14.
As a result, the deceleration a ₁ of the preceding vehicle 34 can be detected by the time derivative of the moving speed V ₁ . Also,
The delay time τ until the deceleration a ₀ is realized and the distance x to be secured when the vehicle is stopped or when the relative speed is “0” can be set in advance and stored in the arithmetic and control unit 30.

Therefore, if the deceleration a ₀ to be generated at the time of deceleration is determined, the calculation of the above equations (1) and (2) can be executed. When the automatic braking device 26 is operated, the vehicle collision prevention device of this embodiment performs gentle braking prior to sudden braking in order to achieve the deceleration of a ₀ , and the resulting wheel acceleration causes friction on the traveling road surface. The coefficient μ is estimated, and the maximum deceleration allowed in relation to the coefficient μ is set as a ₀ .

Then, when the friction coefficient μ is calculated, the throttle valve is fully closed by the throttle actuator 28 to limit the output fluctuation of the internal combustion engine during μ estimation, thereby improving the estimation accuracy, and thus the automatic estimation. A feature of the present invention is that collision prevention can be ensured by setting a proper braking start timing by the braking device 26 in accordance with μ.

FIG. 6 shows a flowchart of an example of a braking control routine executed by the arithmetic and control unit 30 to realize such a function.

In FIG. 6, the arithmetic and control unit 30 first initializes various parameters required for the following arithmetic processing in step 100. In the following description of parameters, all initial setting values are represented by adding "'".

Specifically, the automatic braking device 26
First safety distance x calculated as the distance at which braking should be started
₁Deceleration a used to calculate₀The default value of₀′, Destination
The distance to the traveling vehicle 34 is less than or equal to the second safety distance
After the determination is made, the desired deceleration is made by the automatic braking device 26.
a₀The initial setting value of the delay time τ until
τ ', the maximum deceleration a that can be exhibited in the current road surface condition_0max
The default value of_0max′, Impressions to be described later Asphalt road
Coefficient C of the slip ratio S of the regression line obtained for the plane ₁of
Initial setting C₁Set ′.

The deceleration initial set value a ₀ ′ is, for example, about 0.1 [G], and the maximum deceleration initial set value a _0max ′.
Is a value of about 0.6 [G], and the initial delay time setting value τ ′
Is set to, for example, 0.2 to 0.4 [second].

After completing the initial setting, Step 1
In step 02, various parameter values necessary for the following arithmetic processing are read. Specifically, the vehicle speed V ₀ of the host vehicle is measured by the vehicle speed sensor 10, and the inter-vehicle distance Δx is measured by the distance measuring sensor 12.
From the relative speed sensor 14 to the relative speed ΔV (= V ₀ −V
₁ ), the acceleration sensor 16 reads the vehicle acceleration a ₀ , the wheel speed sensor 18 reads the wheel angular velocity ω, and the brake hydraulic pressure sensor 20 reads the brake pressure P.

Next, at step 104, the above-mentioned various initial setting values and the parameter values read from various sensors are substituted into the above equation (1) or equation (2), and the automatic braking device 26 suddenly brakes. Is calculated, that is, the second safety distance x ₂ is calculated.

In this case, when it is estimated that the own vehicle and the preceding vehicle will be at the same speed due to the stop, the above equation (1) is used to predict that both will become the same speed during the deceleration process. In this case, the equation (2) is selected, and the maximum deceleration a _0MAX or the initial set value a _0MAX ′ is substituted for the deceleration to be generated.

Further, in this step 104, in addition to the calculation of the _second safety distance x ₂ , the calculation of the first safety distance x ₁ is also executed. Here, the first safety distance x ₁ is longer than the second safety distance x ₂ , and based on the current motion states of the own vehicle 32 and the preceding vehicle 34, the distance between them is the second safety distance. It is a distance at which estimation of the road surface friction coefficient μ described later can be completed before reaching x _2, and assuming that μ estimation is performed by slow braking of the initial set value a ₀ ′, the above formula (1) or (2) calculated by substituting a ₀ 'to a ₀ in the formula.

In this way, the second braking should be started.
Safety distance x₂And the first to start μ estimation by gentle braking
Safety distance x₁After calculating and, go to step 106
Distance between vehicles Δx and x detected by distance measuring sensor 12₁Ratio with
Make a comparison. And Δx> x ₁When is established
Is the alarm processing by the alarm device 24 and the automatic braking device 26.
It is determined that it is not necessary to execute the automatic braking process
After releasing the alarm and automatic braking at step 108,
Return to step 102.

On the other hand, in step 106, Δx> x ₁
Is not established, that is, when it is determined that the distance between the vehicle 32 and the preceding vehicle 34 is the first safety distance x ₁ or less, the routine proceeds to step 110, where Δx and the second safety distance x ₂
Compare with. Immediately after the condition in step 106 is not satisfied, the inter-vehicle distance Δx should be the distance between x ₁ and x ₂ .

Therefore, in this case, the condition Δ of step 110 is
It is determined that x <x ₂ is not established, and in step 114, the alarm device 24 is instructed to generate a primary alarm, and the automatic braking device 26 is instructed to execute gentle braking to the extent that the wheels are not locked. This is because the braking coefficient is executed to estimate the friction coefficient μ of the road surface.

In this routine, the present step 114 is executed.
In addition to the above processing, the characteristic is that a command for forcibly closing the throttle valve to the throttle actuator 28 is issued. This allows
μ Prevents output fluctuation of the internal combustion engine during estimation μ
The estimation accuracy of is improved. In this sense, this step 114 corresponds to the engine output holding means M8 described above together with the throttle actuator 28.

For example, as shown in FIG. 7, the slow braking is operated so that the brake oil pressure is about 10 atm at maximum, and thereafter, at every minute time interval Δt, n (n> 3) sets of data ( Brake oil pressure Pi, wheel slip ratio Si, wheel acceleration αi) are sampled. Incidentally, i = 1, 2, ... That is, first, the brake oil pressure Pi is detected from the brake oil pressure sensor 20, then the wheel angular speed ωi detected by the wheel speed sensor 18 is time differentiated to obtain the wheel acceleration αi, and in step 118, the following equation (3) ), The wheel slip ratio Si is obtained.

Si = (V _B −V _W ) / V _B (3) Here, V _B is the speed of the vehicle at the time of the sampling, and V _W is the wheel speed (circumference) at the time of the sampling. Speed). If the wheel radius is r, Vw, ω
Between them, the relationship of V _W = r · ω is established.

When (Pi, Si, αi) is obtained in this way, these are stored as a set in step 120, and steps 102 to 120 are executed until it is determined in step 122 that the measurement of n points has been completed. The process of is repeatedly executed.

Next, based on these measurement data, the friction coefficient μ of the road surface is estimated.
In step 4, based on the output signal of the accelerator pedal sensor 22, it is determined whether the driver of the vehicle releases the accelerator pedal. Then, if the accelerator pedal is released, the routine proceeds to step 126, where the throttle valve is fully closed by the throttle actuator 28, while if the accelerator pedal is not released,
The routine proceeds to the subsequent step 128 while maintaining the fully closed state by the throttle actuator 28.

By inserting such processing, the driver can
Unless the accelerator pedal is released in response to the next alarm and slow braking, no output will be obtained from the internal combustion engine thereafter, and output torque fluctuations of the internal combustion engine during μ estimation execution can be effectively prevented, and automatic The rapid acceleration of the vehicle after releasing the braking can be effectively prevented.

Step 128 is a step of obtaining a regression line by regression analysis using Pi as dependent variables and Si and αi as independent variables, based on the n samples (Pi, Si, αi) sampled as described above. Also, step 1
30 is a step of calculating the maximum friction coefficient μ _MAX for the traveling road surface from the relationship between P, S, and α specified by the regression line. Then, step 132 is a step of calculating the maximum deceleration a _0MAX from the maximum friction coefficient μ _MAX .

The method of deriving the regression line and the method of calculating the maximum friction coefficient μ _MAX and the maximum deceleration a _{0M AX} will be described below.

As shown in FIG. 8, when the wheel 36 having the radius r is traveling on the road surface 38 at an angular velocity ω, the rotational moment of the wheel 36 in consideration of the influence of the vehicle weight and the like is I, and at the time of gentle braking. When the braking torque is fi, the vertical load on the wheel is F _T , and the ground friction force is F _Bi , F _Bi = μi × F
_{From T} , the equation of motion can be expressed as the following equation (4).

I × αi = fi−r × F _Bi = fi−r × μi × F _T (4) Generally, between the friction coefficient μ of the road surface and the wheel slip ratio S, the tire From the characteristics of performance, there is a relationship as shown in FIG. 9, and the friction coefficient μ becomes maximum at the time immediately before the wheel locks (slip ratio S = S _L = about 10%).
The value of this friction coefficient μ usually draws a maximum curve in the case of a dry asphalt road surface, and its peak value, that is, the maximum friction coefficient μ is 1.0. Further, the value of the friction coefficient μ is greatly influenced by the condition of the traveling road surface, and for example, on a road surface wet with rain, a snow road, a frozen road surface, etc., becomes a smaller curve than a dry road.

From the relationship between the friction coefficient μ and the wheel slip ratio S shown in FIG. 9, the value μ _MAX of the maximum friction coefficient μ on the road surface is also the value at the slip ratio S _L immediately before the wheel locks. While it should, the slip ratio S is, 0～S _L
Is almost proportional to the friction coefficient μ, and μi =
It can be simulated as k × Si (k is a coefficient according to the road surface condition). Therefore, the equation (4) can be rewritten as the following equation (5).

I × αi = fi−r × k × Si × F _T (5) Here, the braking torque fi is represented by the brake oil pressure Pi and r × k × F, which is a coefficient of the slip ratio Si. _T (constant if the road surface condition is constant) is C ₁ and rotational moment I
Is treated as a constant C ₂ , the above equation (5) can be expressed as the following equation (6).

Pi = C ₁ × Si + C ₂ × αi (6) Then, the n sets of (Pi, Si, αi) stored in step 120 are substituted into the equation (6), and C is calculated by the least squares method. ₁ and C ₂ are obtained, and the regression line shown in the following equation (7) is derived.

P = C ₁ × S + C ₂ × α (7) The method of deriving the regression line by the least squares method is as follows.
For example, a publicly known method detailed in "Modern control engineering" (Hideaki Kano, Nikkan Kogyo Shimbun) is used.

On the other hand, similarly to the above, a regression line is derived in advance for a dry asphalt road surface, a coefficient C ₁ ′ of the slip ratio S is obtained, and the value is used as a value for generating the maximum friction coefficient μ = 1.0. If so, C ₁ is proportional to k, that is, to μ, that is, the maximum friction coefficient μ _MAX of the current road surface is calculated by the following equation (8) using the known value C ₁ ′.
You can ask for

Μ _MAX = C ₁ / C ₁ ′ (8) That is, the regression line shown in the above equation (7) and the above (8)
By using the relation of the equation, the maximum friction coefficient μ _MAX of the traveling road surface can be obtained from the brake oil pressure P during the slow braking, the slip ratio S of the wheel, and the wheel acceleration α. Executed to calculate μ _MAX .

When the maximum friction coefficient is μ _MAX , the maximum braking force that can be generated without locking the wheels can be obtained as μ _max × F _{T in} relation to the vertical load F _{T of the} wheels. On the other hand, in order to prevent the wheels from locking when the deceleration a ₀ occurs, if the dispersed weight of the vehicle weight on each wheel is M, a road frictional force of M × a ₀ or more is required. Here, if gravitational acceleration is g, F _T = M
Since xg, the condition for the wheels not to lock can be expressed by the following equation (9).

M × a ₀ ≦ μ _MAX × M × g (9) Therefore, the maximum deceleration a that can be generated during vehicle deceleration
_0MAX can be _obtained by the following equation (10), and in step 132, the calculation is performed by such a method.

A _0MAX = μ _max × g (10) In this way, the external force applied to the wheel during the slow braking is
When only the braking torque caused by the brake hydraulic pressure P and the torque caused by the road friction force are used, the maximum friction coefficient μ _MAX and the maximum deceleration can be accurately calculated from the brake hydraulic pressure P, the wheel slip ratio S, and the wheel acceleration α. a _0MAX can be calculated.

In the vehicle collision prevention system according to this embodiment, the throttle valve is fully closed during execution during gentle braking.
The situation is such that the output fluctuation of the internal combustion engine does not occur, and it is guaranteed that the external force applied to the wheels is only the braking torque and the torque due to the road surface frictional force.

Therefore, due to the accelerator operation by the vehicle driver,
Without always a_0MAXCan be calculated and is shown in FIG.
The processing of steps 102 to 132 in the routine is repeated.
The above is executed every time the process of step 104 is executed.
In the formula (1) or the formula (2), a ₀Was calculated accurately
a_0MAXWas substituted, and the condition of the current road surface was properly reflected.
Second safety distance x₂Is calculated.

As a result, in step 110, Δ
When it is determined that x <x ₂ is satisfied, step 112 is executed, and the secondary alarm by the alarm device 24 and the automatic braking device 26 are executed.
When the sudden braking by is realized, the rear-end collision with the preceding vehicle 34 can be surely avoided.

As described above, the vehicle collision prevention system according to the present embodiment improves the estimation accuracy of the friction coefficient μ by
This has the effect of improving the reliability of the vehicle collision prevention device.

Further, in this embodiment, as described above,
As long as the accelerator pedal is not released after the execution of the slow braking, the internal combustion engine does not generate an output, and the driver can be made aware that the execution of the slow braking has started. It is possible to prevent a situation in which sudden acceleration occurs.

That is, when the driver notices an abnormal approach to the preceding vehicle 34 and takes appropriate measures, the driver perceives the situation while maintaining a mechanism capable of recovering the driving characteristics in line with the driver's intention. It also has the feature that the safety is improved when it is not done.

Incidentally, the mechanism for holding the output of the internal combustion engine at a constant value is realized by fixing the throttle valve by the throttle actuator 28, and particularly by fully closing the throttle valve in the above-mentioned embodiment. The present invention is not limited to this, and as long as a diesel engine can be maintained at a constant output value, such as by controlling the fuel supply amount to be fixed, it is possible to eliminate the influence thereof and perform μ estimation with high accuracy.

[0079]

As described above, according to the first aspect of the invention, the output of the internal combustion engine does not fluctuate while the road surface μ estimating means estimates the friction coefficient μ of the traveling road surface. By eliminating the influence of the output, μ estimation can be executed with high accuracy from the braking torque and the wheel acceleration that occur during gentle braking.

Further, according to the second aspect of the present invention, the output of the internal combustion engine is reduced, so that the driver can perceive that the execution of the slow braking mode of the automatic braking process is started, and the automatic braking process is performed. Prior to the sudden braking, it is possible to obtain an opportunity to take appropriate measures against an abnormal approach to a front obstacle.

Further, according to the invention described in claim 3, since the output of the internal combustion engine does not interlock with the accelerator pedal unless the driver releases the depression of the accelerator pedal after the operation of the automatic braking device is started, Even if the accelerator pedal is depressed at the end of the braking process, the vehicle will not suddenly accelerate due to it. Further, once the depression of the accelerator pedal is released, the operation by the accelerator pedal becomes effective again, and the driver's intended driving can be restored.

[Brief description of drawings]

FIG. 1 is a principle view of a vehicle collision prevention device according to the present invention.

FIG. 2 is an overall configuration diagram of an embodiment of a vehicle collision prevention device according to the present invention.

FIG. 3 is an explanatory diagram showing a positional relationship between a host vehicle and a preceding vehicle.

FIG. 4 is a diagram (No. 1) for explaining a method of calculating a safety stop distance.

FIG. 5 is a diagram (part 2) for explaining a method of calculating a safety stop distance.

FIG. 6 is a flowchart of an example of a braking control routine executed by the arithmetic and control unit of this embodiment.

FIG. 7 is a diagram showing a supply pattern of brake hydraulic pressure during gentle braking.

FIG. 8 is a diagram for explaining a state of an external force applied to a wheel during braking.

FIG. 9 is a diagram showing a relationship between a slip ratio of a wheel and a coefficient of friction between a road surface and the wheel.

[Explanation of symbols]

 M1 automatic braking device M2 braking control device M3 road surface μ estimating means M5 distance measuring means M7 execution determining means M8 engine output holding means M9 pedal position detecting means 10 vehicle speed sensor 12 distance measuring sensor 18 wheel speed sensor 20 brake oil pressure sensor 22 accelerator pedal sensor 22 24 alarm device 26 automatic braking device 28 throttle actuator 30 arithmetic and control unit 32 own vehicle 34 preceding vehicle

Claims (3)

[Claims] 1. A braking control means for controlling an automatic braking device mounted on a vehicle in a slow braking mode or a rapid braking mode, and a front obstacle detected by a distance measuring means for measuring a distance to an obstacle ahead of the vehicle. When the distance to the front obstacle is equal to or less than the first safety distance, the braking process in the slow braking mode is executed, and the distance to the front obstacle is equal to or less than the second safety distance shorter than the first safety distance. When the braking control unit executes the braking process in the slow braking mode, the braking torque generated by the automatic braking device and the wheels generated on the wheels when the braking process in the gentle braking mode is executed. A vehicle collision prevention system, comprising: a road surface μ estimating means for estimating a friction coefficient μ of a traveling road surface based on acceleration and a setting of the second safety distance in consideration of the friction coefficient μ. The vehicle collision prevention device, wherein the stop device includes an engine output holding unit that holds the output of the internal combustion engine constant while the braking process in the slow braking mode is being executed. 2. The vehicle collision prevention device according to claim 1, wherein the engine output holding means is constituted by throttle fully closing means for fully closing a throttle valve provided in an intake passage of an internal combustion engine. . 3. The engine output holding means is constituted by throttle full closing means for fully closing a throttle valve provided in an intake passage of an internal combustion engine, and the throttle full closing means detects the position of an accelerator pedal. Until the pedal position detecting means receives a signal indicating that the accelerator pedal is returned to the fully closed position, the throttle valve is held at the fully closed position regardless of the depression amount of the accelerator pedal, and the accelerator pedal is at the fully closed position. The vehicle collision prevention device according to claim 1, wherein when the signal indicating that the throttle valve has been returned to the vehicle is received, the throttle valve is released from the fully closed state.