JPH09170916A - Apparatus for estimating state of road surface - Google Patents

Abstract

PROBLEM TO BE SOLVED: To estimate a state of a road face highly accurately by estimating a friction coefficient of the road face, comparing the coefficient with a previously estimated value, and controlling not to update the coefficient to a lower value from the previously estimated value based on the comparison result when a driving wheel slips not larger than a predetermined value. SOLUTION: Velocities of driving wheels 14, 16 and driven wheels 10, 12 are measured by driving wheel velocity sensors 48, 50 and driven wheel velocity sensors 52, 54, which are input to an electronic control device 46. The device 46 obtains a friction coefficient of a road face from a previous velocity of the driven wheels and the present velocity of the driven wheels, and compares the coefficient with a previous value. When a present value of the friction coefficient is larger than or equal to the previous value, the friction coefficient is updated to the present value. When the present value is smaller than the previous value, it is detected whether or not a slip of the driving wheels 14, 16 obtained from a difference of velocities of the driving wheels and driven wheels is smaller than a predetermined value. If the difference is not smaller than the predetermined value, the friction coefficient is updated to the present value. If the difference is smaller than the predetermined value, the previous value is maintained. Accordingly, the friction coefficient of the road face can be estimated more highly accurately.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a road surface state estimating device for estimating the state of a road surface on which a vehicle is traveling.

[0002]

2. Description of the Related Art Conventionally, when starting or accelerating,
When a slip occurs on a drive wheel, an acceleration slip control device that controls the drive force in order to converge the drive slip to reduce the traction of the drive wheel in which the slip occurs and thereby suppress the drive slip is provided. Being developed.

In such control, in order to calculate the target rotational speed for controlling the drive wheels, it is important to estimate the state of the road surface on which the vehicle is traveling, particularly the road surface friction coefficient μ. For example, in the control device disclosed in Japanese Patent Application Laid-Open No. 2-3776, the road surface friction coefficient μ is estimated based on the amount of increase in the driven wheel speed per unit time.

[0004]

However, in the above-mentioned prior art, since the acceleration of the driven wheels becomes 0 even during the gear shift even in the acceleration state, when the road surface state is estimated based on this, the road surface friction coefficient μ becomes There is a problem that it is erroneously estimated to be 0.

This will be described with reference to the drawings. FIG. 5 qualitatively shows changes over time in the wheel speed and the road surface friction coefficient μ. In FIG. 5, the horizontal axis represents time, the upper solid line graph represents the driven wheel speed, the alternate long and short dash line graph represents the driving wheel speed, and the lower graph represents the estimated value of the road surface friction coefficient μ.

The portion of the dashed-dotted line graph above the solid line graph indicates that the drive wheel speed is higher than the driven wheel speed, and the drive wheel rotates faster, causing an acceleration slip. ing. In the part indicated by reference symbol A in the figure, the driven wheel is rotating at a constant speed, while the acceleration slip is increasing. This is because wheel spin occurred because the road surface reaction force decreased, and the road surface friction coefficient is considered to be almost zero.

On the other hand, in the portion indicated by reference numeral B in the drawing, since the power is not being transmitted to the drive wheels, so to speak, all four wheels are driven wheels, and steady traveling is performed at a constant speed. Therefore, the amount of increase in the driven wheel speed is zero.

Therefore, if it is attempted to estimate the road surface friction coefficient μ based on the amount of increase in the driven wheel speed, the road surface friction coefficient μ is not 0 in the portion B of the drawing, but is the same as the portion A of the drawing. Also in the part B, the road surface friction coefficient μ is 0
I presume.

As described above, in the conventional estimation method, even when the vehicle is traveling on a road surface having a high road surface friction coefficient μ, the engine output torque is not transmitted by the clutch operation at the time of gear shifting in a vehicle with a manual transmission. There is a possibility that the road surface friction coefficient μ may be erroneously estimated in a steady running state.

The present invention has been made in view of such conventional problems, and it is an object of the present invention to provide a road surface state estimating device capable of accurately estimating a road surface friction coefficient.

[0011]

SUMMARY OF THE INVENTION The present invention, as shown in FIG. 1, is a road surface condition estimating device for estimating the condition of a road surface on which a vehicle is traveling. Means for determining whether or not, a means for estimating the road surface friction coefficient, a means for comparing the road surface friction coefficient estimated this time with the road surface friction coefficient estimated last time, and when the slip of the drive wheels is below a predetermined value, The problem is solved by including means for restricting updating of the previously estimated road surface friction coefficient to a lower side based on the comparison result.

That is, according to the present invention, when it is determined that the slip of the drive wheels is equal to or less than a predetermined value, that is, it is determined that the vehicle is traveling on a road surface having a friction coefficient μ that is high to some extent, the previously estimated road surface is used. The friction coefficient and the road surface friction coefficient estimated this time are compared, and when the road surface friction coefficient estimated this time is lower, the road surface friction coefficient estimated last time is not updated,
I kept the value last time. As a result, it is possible to estimate the road friction coefficient with high accuracy even when shifting.

[0013]

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, an example of an embodiment of the present invention will be described in detail with reference to the drawings.

FIG. 2 is a schematic configuration diagram of a vehicle equipped with an acceleration slip control device including a road surface state estimating device according to the present invention.

In FIG. 2, reference numerals 10 and 12 denote left and right front wheels as driven wheels, and 14 and 16 denote left and right rear wheels as driving wheels. The output torque of the engine 18 is applied to the left and right rear wheels 14 and 16 by the transmission 20, the propeller shaft 22, the differential device 24, and the left and right drive axles 2.
It is transmitted via 6, 28. The engine 18 sucks intake air from the intake passage 30 and the surge tank 32 and is supplied with fuel from the fuel injection valve 34. The intake passage 30 is provided with a main throttle valve 36 for controlling the intake air amount. The main throttle valve 36 is connected to an accelerator pedal 38 and opens / closes in response to depression of the accelerator pedal 38.

The fuel injection valve 34 has an engine control unit 40.
The valve opening timing and the valve opening time are controlled by the control signal from, and fuel is injected and supplied to the engine 18 in an amount corresponding to the valve opening time. The fuel injection amount control by the engine control device 40 is basically performed according to the intake air amount or the intake air amount per stroke determined by the intake pipe pressure and the engine speed.

Main throttle valve 3 of intake passage 30
Sub-throttle valve 4 on the upstream side of the intake flow from 6
2 are provided. The sub-throttle valve 42 is driven to open and close by a step motor 44, and the step motor 44 controls the opening degree of the sub-throttle valve 42 according to a control signal from an electronic control unit 46 for acceleration slip control.

The electronic control unit 46 includes a general microcomputer and has drive wheel speed sensors 48, 50.
Is taken as the driving wheel speed VWR, the left and right driven wheel speed sensors 52, 54 are taken as the left and right driven wheel speeds VWF, and the transmission 20
Information about the gear shift position, information about the opening of the main throttle valve 36 from the throttle opening sensor 56, information about the rotation speed of the engine 18 calculated by the engine control device 40, and acceleration slip according to these information. It is determined whether or not the sub-throttle valve 42
A control signal for driving to open and close to a predetermined opening suitable for acceleration slip control is output to the step motor 44.

Further, the electronic control unit 46 determines whether the drive wheel slip is a predetermined value or less based on the drive wheel speed VWR and the driven wheel speed VWF fetched from the drive wheel speed sensors 48 and 50 and the driven wheel speed sensors 52 and 54. Whether or not the road surface friction coefficient μ is estimated is calculated. Further, the electronic control unit 46
Compares the previous estimated value with the current estimated value of the road surface friction coefficient,
When the drive wheel slip is equal to or less than a predetermined value, updating of the road surface friction coefficient to a lower side is restricted.

The operation of this embodiment will be described in detail below with reference to the flow chart of FIG.

In step 100 of FIG. 3, the driven wheel speed VWF and the driving wheel speed VWR are set to the driving wheel speed sensors 48, 5 and 5.
0 and the driven wheel speed sensors 52, 54 from the electronic control unit 4
Input to 6.

In the next step 110, K is a constant and T is a calculation cycle, and the driven wheel speed VWF (n-1) at the previous calculation is set.
And the driven wheel speed VWF (n) this time, the road surface friction coefficient μ
(N) is calculated by the following equation (1).

Μ (n) = K × (VWF (n) −VWF (n−1)) / T (1)

The reason why the road surface friction coefficient μ can be calculated by the equation (1) will be briefly described. Now, assuming that the vehicle body weight is m, the vehicle body acceleration is a, and the force acting on the vehicle body is F, the so-called Newton's equation of motion as shown in equation (2) is established.

Ma = F (2)

Here, when the driven wheel speed VWF is regarded as the vehicle body speed V, the vehicle body acceleration a can be regarded as shown by the equation (3) using the above symbol.

A = (VWF (n) -VWF (n-1)) / T (3)

Further, the force F acting on the vehicle body can be expressed as in (4) using the road surface friction coefficient μ, where W is the load applied to the wheels.

F = μW (4)

Therefore, the above equation of motion is expressed by the following equation (5).

M (VWF (n) -VWF (n-1)) / T = μW (5)

When this is solved for μ, the following equation (6) is obtained.

Μ = (m / W) × (VWF (n) −VWF (n−1)) / T (6)

Therefore, if m / W is a constant K, the above equation (1) can be obtained.

In the next step 120, the road surface friction coefficient μ (n) calculated this time is compared with the previous calculated value μ (n-1).

As a result, when the calculated value μ (n) of this time is greater than or equal to the calculated value of the previous time, the routine proceeds to step 150, where the road surface friction coefficient μ is calculated at the calculated value μ (n) of this time.
Is updated, and μ = μ (n).

If the calculated value μ (n) of this time is smaller than the calculated value μ (n−1) of the previous time, the following step 1
At 30, it is determined whether the slip of the drive wheels 14, 16 is smaller than a predetermined value S. This is the driving wheel speed VWR and the driven wheel speed V
It is determined whether or not the difference in WF is greater than or equal to a predetermined value S. If this difference is greater than or equal to the predetermined value S, as indicated by the portion A in FIG.
It is considered that the slip has increased due to the fact that the road surface friction coefficient μ has actually decreased, and the routine proceeds to step 150, where the road surface friction coefficient μ is updated with the current estimated value μ (n).

When the difference is smaller than the predetermined value S, the previous estimated value μ (n-1) is set as the present estimated value μ (n) in the next step 140, and this is set as the road surface friction coefficient μ in step 150. Then, the previous estimated value μ (n−1) is maintained.

The effect of the control of the road surface friction coefficient estimated value explained above is shown in FIG.

Similar to FIG. 5, FIG. 4 shows the driven wheel speed VWF on the upper side, the driving wheel speed VWR on the dashed-dotted line, the estimated value of the road friction coefficient μ on the lower side, and the broken line on the upper side. The slip determination is shown.

Code C in which almost no slip occurs
In the part (2), the previous estimated value of the road surface friction coefficient μ is maintained, and it is not erroneously estimated to be 0 as in the conventional case.

After all, when the driving wheel speed VWR is smaller than the slip judgment value shown by the broken line as in the portion C, the possibility that the road surface friction coefficient μ is lowered is extremely small. Do not update (to the low side). On the other hand, as in the part D, the drive wheel speed V is determined from the slip determination value.
When the WR is large and slippage occurs, the road surface friction coefficient μ is updated.

Therefore, according to the present embodiment, it is possible to prevent a temporary steady running due to a gear shift in a vehicle with a manual transmission and an erroneous estimation of the road surface friction coefficient in a state where the acceleration is not the limit.

In this embodiment, the road surface friction coefficient is estimated on the basis of the wheel speed detected by the vehicle speed sensor, but the present invention is not limited to this. For example, an acceleration sensor or the like. May be used.

[0045]

As described above, according to the present invention,
If the drive wheel slip does not occur when estimating the road surface friction coefficient, the value estimated in this state is not updated,
Since the previous value was maintained, it became possible to more accurately estimate the road surface friction coefficient.

[Brief description of the drawings]

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

FIG. 2 is a schematic configuration diagram of a vehicle including an acceleration slip control device including a road surface state determination device according to the present invention.

FIG. 3 is a flowchart illustrating control according to the embodiment;

FIG. 4 is a diagram showing changes over time in wheel speed and road surface friction coefficient showing the effects of the present embodiment.

FIG. 5 is a diagram showing changes over time in wheel speed and road surface friction coefficient, which indicate conventional problems.

[Explanation of symbols]

 10, 12 ... Driven wheels 14, 16 ... Driven wheels 18 ... Engine 46 ... Electronic control unit 48, 50 ... Driven wheel speed sensor 52, 54 ... Driven wheel speed sensor

Claims (1)

[Claims] 1. A road surface condition estimating device for estimating a condition of a road surface on which a vehicle is traveling, means for judging whether or not a slip of a driving wheel is below a predetermined value, means for estimating a road surface friction coefficient, and this time. A means for comparing the estimated road surface friction coefficient with the previously estimated road surface friction coefficient, and when the slip of the driving wheels is equal to or less than a predetermined value, based on the comparison result, the previously estimated road surface friction coefficient A road surface state estimating device comprising: a means for restricting updating to a lower side;