JP3285434B2 - Vehicle slip control device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a slip control device for a vehicle, and more particularly to a slip control device for a vehicle capable of achieving both braking performance and steering performance during turning braking of the vehicle.

[0002]

2. Description of the Related Art Conventionally, as one related to slip control during turning braking of a vehicle, for example, Japanese Patent Application Laid-Open No. Sho 62-253560.
There is something shown in the issue. In the device disclosed in this publication, when the steering angle of the steering wheel is small, a high slip ratio (20%) is obtained so as to obtain a high friction coefficient μ.
%). On the other hand, when the steering angle is large, the brake pressure control that aims at a low slip ratio is performed. This is because the cornering force that affects the steering performance takes a larger value as the slip ratio is smaller, so that when turning with a large steering angle, the slip ratio is controlled to be lower to improve the steering performance.

[0003]

However, the above-mentioned conventional apparatus has problems to be improved in the following two points. First, in the conventional device, when the steering angle of the steering wheel is large, the target slip ratio is reduced only in accordance with the condition that the steering angle is large. Here, when the slip ratio is reduced, it is possible to improve the steering performance, but on the other hand, the friction coefficient μ between the road surface and the wheels
, The braking performance decreases. For this reason, if the target slip ratio is uniformly reduced according to the steering angle as in the conventional device, there may be cases where the braking performance must be excessively sacrificed.

[0004] Further, in the conventional device, since the friction coefficient μ between the road surface and the wheels due to the road surface condition is not considered at all, it is insufficient in terms of achieving both the steering performance and the braking performance. In other words, when the friction coefficient μ of the road surface itself is high, the level of the cornering force is originally high, so if the target slip ratio is reduced because the steering angle is large, the steering is too effective, but the braking performance is reduced, There is a problem that the braking distance is extended.

SUMMARY OF THE INVENTION The present invention has been made in view of the above points, and has been made in consideration of the friction coefficient of the road surface itself, and without excessively sacrificing one of the steering performance and braking performance of the vehicle. It is an object of the present invention to provide a vehicle slip control device capable of achieving both steering performance and braking performance during braking.

[0006]

In order to achieve the above object, a vehicle slip control device according to the present invention comprises means for determining wheel speeds of respective left and right wheels of a vehicle, and means for determining a vehicle body speed of the vehicle. Adjusting means for adjusting the brake pressures of the left and right wheels, respectively, and when the wheel speeds of the left and right wheels fall below a reference speed set based on the vehicle body speed, the adjusting means adjusts the brake pressure of the wheels. A vehicle slip control device comprising: a control unit for holding or reducing pressure; determining a steering speed of a steering wheel, and determining whether or not the vehicle is suddenly steered based on the steering speed; and a traveling road surface of the vehicle. Friction coefficient estimating means for estimating a friction coefficient between the vehicle and the wheel, and correcting the reference speed to a high speed at the time of sudden steering determination by the determining means. And a correction means for reducing a correction amount to a higher speed with respect to the reference speed when the friction coefficient estimated by the friction coefficient estimation means is larger than when the friction coefficient is smaller than the friction coefficient. It is characterized by.

[0007]

In the vehicle slip control device configured as described above, first, when it is determined that the vehicle is suddenly steered based on the steering speed of the steering wheel, the reference speed for reducing or maintaining the brake pressure is determined. Correct to a higher speed. Here, when the steering angle of the steering wheel changes abruptly, it is considered that there is a strong demand for the driver to steer the vehicle. Accordingly, the correction of the reference speed to a high speed, that is, the reduction of the target slip ratio, in order to improve the steering performance only at the time of the rapid steering determination, makes it possible to minimize the reduction in the braking performance.

When the friction coefficient estimating means estimates that the friction coefficient is high, the correction amount for increasing the reference speed to a high speed is reduced. Accordingly, when the friction coefficient is high, it is possible to prevent the phenomenon that the steering is excessively effective and also suppress the extension of the braking distance.

[0009]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a configuration diagram showing a system configuration of the vehicle slip control device according to the present embodiment. In FIG.
101 and 102 are wheel speed sensors for the right front wheel and the left front wheel, and 103 and 104 are wheel speed sensors for the right rear wheel and the left rear wheel. Each wheel speed sensor 101-1
04 generates a sine wave signal having a frequency corresponding to the rotation speed of each wheel.
It is taken in through the waveform shaping circuit in. The ABS computer 120 further receives a detection signal from a steering angle sensor 130 that detects the steering angle of the steering wheel, and a detection signal from a G sensor 110 that detects the longitudinal acceleration of the vehicle body. The ABS computer 120 determines a control mode (pressure increase, hold, pressure decrease) suitable for each wheel based on these detection signals.
The drive signal is output to 40.

The ABS actuator 140 includes a solenoid valve,
It is a well-known device composed of a reservoir, a pump, etc.,
FIG. 1 shows a so-called three-channel system in which the left and right front wheels adjust the brake pressure independently and the left and right rear wheels adjust the brake pressure the same. Reference numeral 150 denotes a master cylinder, which generates a brake pressure when a brake pedal is operated.

Next, the control contents of the ABS computer 120 will be described with reference to the flowchart of FIG. In FIG. 2, in step 210, the wheel speed sensors 101 to 1
The wheel speeds are calculated based on the detection signals from the wheel numbers 04, respectively. In step 220, the wheel acceleration of each wheel is calculated based on the calculated wheel speeds.

In step 230, the friction coefficient μ between the road surface of the vehicle and the wheels is determined based on the detection signal of the G sensor 110. Specifically, the acceleration detection value output from the G sensor 110 when a predetermined slip occurs on the wheel corresponds to the friction coefficient μ between the road surface of the vehicle and the wheel. The friction coefficient μ is determined in three stages of high μ, medium μ, and low μ according to the magnitude of the signal.

In step 240, the vehicle speed VSO is calculated based on the wheel speed of each wheel calculated in step 210. At this time, the one having the highest speed among the wheel speeds of the wheels is defined as the vehicle body speed VSO. In step 250, the normal target control vehicle speed when the steering angle detected by the steering angle sensor 130 is substantially zero, that is, when the vehicle is in a straight running state, is calculated. If the vehicle is straight ahead,
The slip ratio at which the friction coefficient μ becomes highest is approximately 20% (slip ratio SN in FIG. 3), and the normal target vehicle speed V
SN is obtained by the following equation.

[0014]

## EQU1 ## Normal target vehicle speed VSN = (1─0.2) × VSO In step 260, the steering angle of the steering wheel is calculated from the detection signal of the steering angle sensor 130. In the calculation of the steering angle, the steering angle position corresponding to the straight traveling state of the vehicle is set to zero degree, and the number of rotations in each of the left and right directions is calculated. In step 270, a steering angular velocity, which is a rate of change of the steering angle, is calculated based on the steering angle calculated in step 260. The steering angular velocity is calculated as an absolute value regardless of the left and right rotation directions.

In step 280, it is calculated from the steering angle calculated in step 260 how much the slip ratio at which the friction coefficient μ becomes highest is offset from that in the case of the straight running state. That is, in FIG. 3, the difference (offset) ΔSN between the slip ratio SN suitable for the straight running state and the slip ratio SNA corresponding to the high friction coefficient μ that changes according to the steering angle is determined.

FIG. 3 shows a change in the μ-S characteristic when a slip angle occurs in the wheel. FIG.
As shown in (2), when the slip angle is zero, that is, when the steering angle is zero and the vehicle is in a straight running state, the friction coefficient μ becomes maximum when the slip ratio S is about 20%. However, as the wheel slip angle increases, the maximum friction coefficient μ gradually moves in the direction in which the slip ratio S increases, and the level itself of the friction coefficient μ decreases. In the present embodiment, the slip angle is substituted by the steering angle, and the slip ratio S at which a high friction coefficient μ is obtained is determined according to the steering angle.

The cornering force for turning the vehicle decreases as the slip ratio S increases, as shown in FIG. When the friction coefficient μ of the road surface decreases, the cornering force has the same degree of decrease as the slip ratio S increases, but the level itself decreases. Therefore, from the viewpoint of securing a necessary cornering force, the offset ΔSN with respect to the steering angle is determined in accordance with the friction coefficient μ of the road surface determined in step 230 from the viewpoint of securing a necessary cornering force instead of simply determining the offset ΔSN only by the steering angle.
It is desirable to change the SN.

Specifically, for example, before starting the ABS control for preventing the wheels from slipping excessively during braking, AB
The reference offset ΔSN at which the S control is started can be obtained by the following equation.

[0019]

ΔSN = steering angle ÷ ω1 × 100 where steering angle ≧ A ° steering angle = A ° If the ABS control is being performed, the friction coefficient μ of the road surface obtained in step 230, that is, high μ , Medium μ, and low μ, the offsets ΔSNH, ΔSNM, Δ
Calculate SNL.

[0020]

ΔSNH = steering angle ÷ ω2 × 100 where steering angle ≧ B ° Steering angle = B °

[0021]

ΔSNM = steering angle ÷ ω3 × 100 where steering angle ≧ C ° steering angle = C °

[0022]

ΔSNL = steering angle ÷ ω4 × 100 where steering angle ≧ D ° steering angle = D ° In the above formulas 2 to 5, ω1 to ω4 and A to D are constants, respectively, and ω2 <ω3. <Ω4 and D <C
<Relationship with B holds. The reason for setting ω2 <ω3 <ω4 is to increase the offset ΔSN for the same steering angle as the friction coefficient μ of the road surface increases. Also,
Each of A to D serves as a maximum guard of the steering angle, and stops increasing the offset ΔSN when the steering angle reaches the angle of A to D. D <C <B <
By setting to A, the lower the friction coefficient μ of the road surface, the more the offset ΔSN can be stopped at a lower value.

As shown in FIGS. 4 and 5, when the friction coefficient μ of the road surface is low, the value of the offset ΔSN and the rate of change thereof are reduced as shown in FIGS.
If the friction coefficient μ is determined to be low or low, the point at which the friction coefficient μ becomes maximum is not clear, and the cornering force changes significantly despite the small change in the friction coefficient μ due to the change in the slip ratio.

In step 290, it is determined from the steering angular velocity obtained in step 270 whether or not the driver has performed rapid steering to avoid an obstacle or the like. This sudden steering determination
As shown in FIG. 6, the steering angular speed is compared with a predetermined reference speed, and it is determined that sudden steering has started from the time when the steering angular speed becomes equal to or higher than the reference speed. Then, the abrupt steering determination is terminated when a predetermined time β has elapsed from the time when the steering angular velocity falls below the reference speed. The meaning of setting the constant time β is that the yaw rate generated in the vehicle by steering converges,
Until the vehicle is stabilized, the control with emphasis on the steering performance is continued.

In step 300, based on the offset ΔSN obtained in step 280 and the result of the sudden steering determination in step 290, the target control correction vehicle speed during turning ΔVSM is obtained from the following equation.

[0026]

[Equation 6] At the time of sudden steering determination ΔVSM = (ΔSN−ΔS)
K) $ 100 x VSO

[0027]

[Equation 7] At the time of non-rapid steering determination ΔVSM = ΔSN ÷ 100 ×
VSO Here, at the time of the sudden steering determination, the sudden steering correction amount ΔSK is subtracted from the offset ΔSN.
Is changed according to the coefficient of friction μ of the road surface obtained in step 230. Specifically, as shown in FIG. 4, the abrupt steering correction amount ΔSKL when the road surface friction coefficient is the lowest (low μ road).
Is the maximum value, and is decreased as the friction coefficient μ increases. When the friction coefficient is the highest (high μ road), the minimum value ΔSK
H.

As shown in FIG. 4, on a low μ road and a middle μ road, as the offset ΔSN increases, the cornering force decreases and steering becomes difficult. Therefore, at the time of sudden steering determination, the offset ΔS by the sudden steering correction amount ΔSK
By decreasing N, the steering performance is improved. Further, on a low μ road or a middle μ road, as shown in FIG. 5, since the change in the friction coefficient μ due to the change in the slip ratio is small, even if the offset ΔSN is reduced by the sudden steering correction amount ΔSK, the friction coefficient μ The drop is slight.

On the other hand, on a high μ road, as shown in FIG. 4, the level of the cornering force is originally high. Therefore, when the correction ΔSKL at the time of the rapid steering similar to the low μ road and the middle μ road is performed, the cornering force becomes excessive. (CKL),
Steering may be too effective and steering stability may be impaired. On a high μ road, as shown in FIGS. 3 and 5, the change in the friction coefficient μ with respect to the change in the slip ratio is large.
When the offset ΔSN is reduced by the abrupt steering correction amount ΔSKL, the friction coefficient μ is greatly reduced. For this reason, in the present embodiment, the sharp steering correction amount ΔSK is set to a smaller value (ΔSKH) as the friction coefficient μ increases.
Increase in cornering force (CKH) and coefficient of friction μ
Thus, the above-mentioned adverse effects are prevented by suppressing the decrease in the temperature.

In step 310, the optimum target control vehicle speed VSM is calculated by the following equation using the normal target control vehicle speed VSN obtained in step 250 and the turning target control correction vehicle speed ΔVSM obtained in step 300.

[0031]

VSM = VSN-ΔVSM In step 320, the wheel speed of each wheel obtained in step 210 is compared with the optimum target control vehicle speed VSM or a reference speed based on the optimum target control vehicle speed VSM. By comparing the wheel acceleration of the wheel with a predetermined reference acceleration, an actuating pattern (for example, pressure increase, hold, pressure decrease) for each wheel is calculated. As an example of the calculation of the actuate pattern, for example,
When the wheel acceleration of each wheel reaches a predetermined negative reference acceleration, the brake pressure is maintained, and when the wheel speed falls below the optimum target control vehicle speed VSM, the brake pressure is reduced.
When the wheel acceleration returns, the brake pressure is maintained, and when the wheel speed returns to the optimum target control vehicle speed VSM, the brake pressure is increased. The optimum target control vehicle speed VS
Depending on the set value of M, the brake pressure may be maintained on the condition that the wheel speed falls below this VSM.

In step 330, a so-called low select control for selecting an actuating pattern having a strong locking tendency from the actuating patterns of the left and right rear wheels calculated in step 320 is performed. Then, the actuator of the rear wheel is driven by the actuated pattern selected here, and the aim is to ensure vehicle stability. In step 340, a drive signal is output to drive the ABS actuator 140 according to the activate pattern calculated in steps 320 and 330.

By the above-described control, the braking performance at the time of turning braking can be improved, and both the braking performance and the steering performance can be achieved. In addition, the present embodiment has the following effects. That is, in the present embodiment, the control target speed is not separately set for the turning inner wheel and the outer wheel, but the optimum target control vehicle speed VSM is set uniformly for all the wheels according to the turning state and the road surface condition. The vehicle does not become unstable even if the sensor 130 fails.

In the above-described embodiment, the sharp steering correction amount ΔSK is set to the minimum value ΔSKH on a high μ road.
ΔSKH = 0 may be set. Furthermore, the friction coefficient μ of the road surface
When it is determined that the steering angle is very high, it is also effective to correct ΔSK to a negative value, that is, to increase the slip ratio, in order to prevent the steering from being excessively effective. In the above-described embodiment, the friction coefficient μ of the traveling road surface of the vehicle is determined in three stages. However, when the G sensor 110 outputs the acceleration detection value linearly, this acceleration detection is performed. Assuming that the value corresponds to the friction coefficient μ of the road surface, the sudden steering correction amount ΔSK may be linearly calculated according to the acceleration detection value. The sudden steering correction amount ΔSK at that time can be obtained, for example, according to a map as shown in FIG. Note that the curves shown as A, B, and C in FIG. 7 may be selected according to the characteristics of the vehicle.

Further, the friction coefficient μ of the traveling road surface of the vehicle is
The estimation can be performed without using the G sensor 110.
For example, the friction coefficient μ of the road surface is estimated from the change in the vehicle speed calculated in step 240, the degree of decrease in the wheel speed with respect to the amount of increase in the brake pressure, the degree of restoration of the wheel speed with respect to the amount of decrease in the brake pressure, and the like. Is possible.

[0036]

As described in detail above, in the present invention,
Since the reference speed is corrected to a high speed only at the time of the sudden steering determination, it is possible to improve the steering performance according to the driver's request and to suppress the decrease in the braking performance to a necessary minimum. Also,
When it is estimated that the friction coefficient is high, the amount of correction to a higher speed than the reference speed is reduced, so that it is possible to prevent the phenomenon that the steering is too effective and also suppress the extension of the braking distance. Therefore, according to the vehicle slip control device of the present invention, both steering performance and braking performance can be achieved at the time of vehicle turning braking regardless of the friction coefficient of the road surface itself.

[Brief description of the drawings]

FIG. 1 is a configuration diagram showing a system configuration of a vehicle slip control device according to an embodiment of the present invention.

FIG. 2 is a flowchart illustrating control executed by an ABS computer shown in FIG. 1;

FIG. 3 is a characteristic diagram showing a change in μ-S characteristic during turning of the vehicle.

FIG. 4 is a characteristic diagram showing a relationship between a slip ratio and a cornering force.

FIG. 5 is a characteristic diagram showing a μ-S characteristic according to a friction coefficient of a road surface.

FIG. 6 is an explanatory diagram for explaining a determination method of a sudden steering determination.

FIG. 7 is a characteristic diagram showing a relationship between a friction coefficient μ of a road surface and an abrupt steering correction amount ΔSK.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 101 Right front wheel speed sensor 102 Left front wheel speed sensor 103 Right rear wheel speed sensor 104 Left rear wheel speed sensor 110 G sensor 120 ABS computer 130 Steering angle sensor 140 ABS actuator 150 Master cylinder

──────────────────────────────────────────────────続 き Continuing from the front page (72) Inventor Takahiro Goshima 1-1-1, Showa-cho, Kariya-shi, Aichi Japan Inside Denso Corporation (72) Inventor Fumio Nakagawa 1-Toyota-cho, Toyota-shi, Aichi Prefecture Inside Toyota Motor Corporation (56) reference Patent flat 4-46857 (JP, a) JP flat 4-110265 (JP, a) JP Akira 62-253560 (JP, a) (58 ) investigated the field (Int.Cl. ⁷ B60T 8/00 B60T 8/32-8/96

Claims (1)

(57) [Claims] 1. A means for determining wheel speeds for left and right wheels of a vehicle, a means for determining vehicle body speeds of the vehicle, an adjusting means for adjusting brake pressures of the left and right wheels, respectively; And a control means for holding or reducing the brake pressure of the wheel by the adjusting means when the vehicle speed falls below a reference speed set based on the vehicle body speed. Determining means for detecting a speed and determining whether or not the vehicle is suddenly steered based on the steering speed; friction coefficient estimating means for estimating a friction coefficient between a traveling road surface of the vehicle and wheels; and sudden steering determination by the determining means. Sometimes, while correcting the reference speed to a high speed, if the friction coefficient estimated by the friction coefficient estimating means is large, Compared to smaller than Re, vehicle slip control apparatus characterized by comprising a correction means for reducing the correction amount in the high speed to the reference speed.