KR100241833B1 - Vehicle stability control device to distinguish road surface friction coefficient - Google Patents

Abstract

A stability control apparatus for a vehicle having a vehicle body and front and rear wheels includes means for determining the propensity of the vehicle body to drift out to make an amount of drift out condition increasing with an increase in the drift out tendency; Means for detecting lateral acceleration of the vehicle body; Brake means for selectively applying a variable braking force to each wheel; Control means for controlling the brake means to variably apply a braking force to each wheel, wherein the control means controls the brake means on the basis of the amount of drift out state to brake the rear wheels at a higher intensity as the amount of drift out state increases. At the same time, if the lateral acceleration is actually small, a correction is made to actually eliminate the participation of the drift-out state amount in the rear brake control.

Description

Vehicle stability control device to distinguish road surface friction coefficient

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to behavior control of a vehicle in order to improve driving stability of the vehicle, and more particularly, to a stability control device for distinguishing road surfaces of roads having different friction coefficient values in regions driven by left and right wheels. Such road conditions are referred to herein as split μ.

When a vehicle such as an automobile is excessively manipulated on a curved road or a corner, the side force applied to the vehicle body as a centrifugal force may increase without limitation with the increase of the vehicle speed and steering angle, while the tire grip force that keeps the vehicle on the road surface ( Because of the limited tire grip force, especially on slippery wet roads, it is easy to become a “drift-out”, an unstable phenomenon in which the front wheels slide out of the turn due to the concentration of tire grip force.

There are numerous efforts to suppress spin and / or drift out in vehicles such as automobiles. For example, in Japanese Patent Laid-Open No. 6-24304, controlled braking force is applied to each wheel by a feedback control system so that the actual yaw rate of the vehicle body is calculated based on the target yaw rate calculated based on the driving conditions of the vehicle including the steering condition. Explain what is matched.

The drift-out of the vehicle driven along the winding course is effectively suppressed, especially by braking the vehicle at the rear wheels, so that the applied centrifugal force is reduced by decelerating the vehicle, and when the rear wheel is braked, the lateral vector component of the tire grip force of the rear wheels is braked. Reduced by the addition of the generated front and rear vector components, the total vector of available tire grip forces is limited and as the rear wheels slide outwards as they concentrate in all directions, thus driving the traveling vehicle inwards against the drift out. Let's do it.

However, if the vehicle equipped with the drift-out suppression control device is accelerated or braked while the road friction coefficient value is driven along a straight-line split μ road with respect to the left and right rear wheels, the vehicle will turn to either side of the road. For example, assuming that the road exhibits a relatively low coefficient of friction for the left wheel of the vehicle and a relatively high coefficient of friction for the right wheel of the vehicle, the vehicle actually turns to the right when braking from the rear wheels and the driver is almost unconscious. Steer the body to the left to maintain the straight course of the body. According to such steering operation, the drift out control is activated based on the difference between the steering angle detected by the steering angle sensor and the steering angle calculated from the vehicle speed detected by the yaw rate detected by the yaw rate sensor and the vehicle speed sensor. If applied, a difference occurs in the steering angle for operating the drift out control. However, in this case, if the vehicle is driven along the bending course, the centrifugal force to be applied to the vehicle body is not applied to the vehicle body, so that the drift-out suppressor, that is, the automatic braking of the rear wheels, becomes useless or rather it is not desirable to ensure the stable operation of the vehicle. Will not.

In view of the above problems associated with the drift out inhibitor, the main object of the present invention is to provide an improved stability control device for a vehicle which overcomes the above problems.

In order to achieve the above object, in the vehicle stability control device having a front wheel and a rear wheel,

Means for determining the tendency of the vehicle body to drift out to create a drift-out quantity that generally increases with increasing drift out tendency:

Means for detecting the lateral acceleration of the vehicle body:

Brake means for selectively applying variable braking force to each wheel:

A control means for controlling the brake means to variably apply the braking force to each wheel,

Here, the control means controls the brake means based on the amount of the drift out state to control the rear wheel with higher intensity as the amount of the drift out state increases, and at the same time, if the lateral acceleration is actually small, Make a modification that actually eliminates participation.

If the lateral acceleration is actually small when operating the stability control of the vehicle to suppress the drift out of the vehicle by relying on selectively applying variable braking to the rear wheel according to the amount of drift out condition indicating the vehicle's tendency to drift out By actuating to make a correction that actually eliminates the participation of the drift-out state amount in the brake control, it is clearly avoided that the stability control device that suppresses the drift-out of the vehicle actually adversely affects the driving behavior of the vehicle on the straight split mu road.

In the above stability control device, if the lateral acceleration is smaller than the predetermined threshold value, it may be determined that the lateral acceleration is actually small.

By appropriately determining the magnitude of such a threshold value, the drift out suppression control is appropriately interrupted only when it is actually unnecessary, while when executed, the advantage of the drift out suppression control can be fully utilized.

Alternatively, in the stability control apparatus described above, if the lateral acceleration is less than the predetermined threshold value of the ratio of the lateral acceleration to the front and rear acceleration of the vehicle body, it may be determined that the lateral acceleration is actually small.

Judging the split μ state of the road surface based on how small the lateral acceleration is actually by this arrangement makes the lateral acceleration closer to theoretical considering the braking magnitude generated by the split μ state.

Further, in the above stability control device, if the lateral acceleration is less than the predetermined threshold value of the ratio of the lateral acceleration to the drift-out state amount, it may be determined that the lateral acceleration is actually small.

With such an arrangement, even if the vehicle is actually traveling off the straight course, it is possible to use the judgment of the split μ state of the road surface, in which the component of the lateral acceleration due to the turning of the vehicle is drifted out of the lateral acceleration detected by the lateral acceleration sensor. This is because it is compensated by dividing by the state quantity.

The stability control device includes vehicle speed detecting means, yaw rate detecting means of the vehicle body, and steering angle detecting means, wherein the control means is a steering angle detected by the steering angle detecting means and a vehicle speed detected by the vehicle speed detecting means. And the drift-out state amount as an absolute value of the difference between the steering angles calculated based on the yaw rate detected by the yaw rate.

Operation of the above-described stability control device and the functions and advantages available thereby will become apparent from the following description of embodiments with reference to the drawings.

1 is a schematic diagram of hydraulic circuit means and electric control means in an embodiment of a stability control device according to the invention;

2 is a flow diagram of an embodiment of a stability control routine implemented by the apparatus of the present invention.

3 is a flowchart detailing the steps of modifying the amount of drift out state for control by the routine of FIG.

4 is a flowchart detailing the steps of modifying the amount of drift out state for control by the routine of FIG.

5 is a map showing the relationship between the drift out state amount for control and the target total slip ratio.

6 is a map showing the relationship between the total slip ratio and the duty ratio of the rear wheels for controlling the brakes of the rear wheels.

* Explanation of symbols for main parts of the drawings

10: hydraulic circuit means 12: brake pedal

14: master cylinder 16: hydro booster

20: left front wheel brake pressure control means

22: right front wheel brake pressure control means

24: proportional valve

28,50FL, 50FR: 3 port-2 position switchable electromagnetic control valve

54FL, 54FR: Normal Open On-Off Valve

56FL, 56FR: Normally Closed On-Off Valve

64RL, 64RR: Wheel Cylinders

Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings.

First, referring to FIG. 1 schematically showing an embodiment of the stability control device of the present invention with respect to the configuration of the hydraulic circuit means and the electric control means, the hydraulic circuit means 10 is a brake pedal 12 in which the driver steps on the foot 12. And a master cylinder 14 for generating a master cylinder pressure upon stepping-on of the brake pedal 12, and a hydro-booster 16 for generating a booster pressure. A manual brake pressure source means.

The hydraulic circuit means 10 also has a powered brake pressure source means comprising a reservoir 36 and a brake fluid pump 40, which brake fluid pump supplies pressurized brake fluid to the passage 38, and An accumulator 46 is connected to the passage so that a stable accumulator pressure for automatic brake control described below can be used in the passage 38. The accumulator pressure is also supplied to the hydro booster 16 as a pressure source for generating the booster pressure, which has the same pressure performance as the master cylinder pressure depending on the stepping performance of the brake pedal 12, but will be described below. Such pressure performance can be maintained even while the brake fluid is consumed by the series connection of the normally open on-off valve and the normally closed on-off valve to obtain the required brake pressure.

The first passage 18 extends from the first port of the master cylinder 14 to the left front wheel brake pressure control means 20 and the right front wheel brake pressure control means 22. The second passage 26 including the proportional valve 24 has a three-port-2 position from the second port of the master cylinder 14 toward the left rear wheel brake pressure control means 32 and the right rear wheel brake pressure control means 34. It extends via the switchable electromagnetic control valve 28, and the outlet port of the control valve is connected to the left and right rear wheel brake pressure control means 32, 34 via the common passage 30.

The brake pressure control means (20, 22) of the front left and right wheels includes wheel cylinders (48FL, 48FR) for applying a variable braking force to the front and rear wheels, a 3-port-2 position switching electromagnetic on-off valve (50FL, 50FR), A series connection of the normally open electromagnetic on-off valve (54FL, 54FR) and the normally closed electromagnetic on-off valve (56FL, 56FR) connected in series, the series connection of the normally open on-off valve and the normally closed on-off valve A passage 53 adapted to supply the accumulator pressure of the passage 38 or the pressure of the hydro booster through the three-port-2 positional electromagnetic control valve 44 (the operation thereof is described below), It is connected between the return passages 52 connected to the reservoir 36. The midpoint of the series-connected on-off valves 54FL and 56FL is connected to the port of the control valve 50FL by the connecting passage 58FL, and the midpoint of the series-connected on-off valves 54FR and 56FR is the connecting passage. It is connected to the port of the control valve 50FR by 58FR.

The brake pressure control means 32 and 34 of the left and right rear wheels have wheel cylinders 64RL and 64RR for applying braking force to the left and right rear wheels, respectively, and a normally open electromagnetic on-off valve 60RL and 60RR connected in series and a normally closed electromagnetic. An on-off valve (62RL, 62RR), the series connection of the normally open on-off valve and the normally closed on-off valve includes: a passage (30) connected through an outlet port of the control valve (28), It is connected between the return passages (52). The midpoint of the series-connected on-off valves 60RL and 62RL is connected to the wheel cylinder 64RL for applying braking force to the left rear wheel by a connecting passage 66RL, and the series-connected on-off valves 60RR and 62RR. The midpoint of is connected to the wheel cylinder 64RR for applying the braking force to the right rear wheel by the connecting passage 66RR.

The control valves 50FL and 50FR have a first position that connects the wheel cylinders 48FL and 48FR to the hand brake pressure passage 18 and separates from the connection passages 58FL and 58FR, as shown in the figure. The wheel cylinders 48FL and 48FR are separated from the passage 18 while being switched between the second positions connected to the connecting passages 58FL and 58FR, respectively.

The control valve 28 includes a passage 30 for the series-connected on-off valves 60RL and 62RL and the series-connected on-off valves 60RR and 62RR, as shown in the drawing. A first position connected to the passageway (68) and a passage (68) connected to the passageway (68) connected to the outlet port of the switching control valve (44) while separating the passageway (30) from the passageway (26). Is connected to the delivery port of the hydro booster 16 or accumulator pressure passage 38 depending on whether the control valve 44 is in the first position as shown in the figure or vice versa. ).

When the control valves 50FL, 50FR and 28 are in the first position as shown in the figure, the wheel cylinders 48FL, 48FR, 64RL, 64RR are connected with the hand brake pressure passage 18 and thus the master cylinder 14 The pressure of) is supplied to each wheel cylinder so that the driver can apply braking force to each wheel as the brake pedal 12 is pressed. When the control valve 28 is switched to the second position, while the control valve 44 is in the first position shown, the rear wheel cylinders 64RL and 64RR are boosted from the hydro booster 16 by stepping on the brake pedal. Pressure is supplied. When the control valves 50FL, 50FR, 28, 44 are switched to the second position, the normally open on-off valves of the wheel cylinders 48FL, 48FR, 64FL, 64RR are separate from the stepping of the brake pedal 12. According to the open state and the ratio of the closed state of the normally closed on-off valve, i.e., the duty ratio, of the normally open on-off valve (54FL, 54FR, 60RL, 60PR) and the normally closed on-off valve (56FL, The motorized accumulator brake pressure of the passage 38 is supplied under the control of 56FR, 62RL, 62RR.

Toggle Control Valves (50FL, 50FR, 28, 44), Normally Open On-Off Valves (54FL, 54FR, 60RL, 60RR), Normally Closed On-Off Valves (56FL, 56FR, 62RL, 62RR), and Pumps (40) Are all controlled by the electrical control means 70 as described in detail below. The electric control means 70 is composed of a microcomputer 72 and a drive circuit means 74. Although not shown in detail in FIG. 1, the microcomputer 72 generally includes a central processing unit, read only memory, random access memory, input and output port means, and a common bus interconnecting these functional elements. It may have a configuration.

The input port means of the microcomputer 72 has a signal indicating the vehicle speed V from the vehicle speed sensor 76, a signal indicating the lateral acceleration Gy of the vehicle body from the lateral acceleration sensor 78 mounted at the center of mass of the vehicle body, and yawing. Signal body indicating yaw rate γ of the vehicle body from the rate sensor 80, signal indicating steering angle θ from the steering angle sensor 82, and the vehicle body from the front and rear acceleration sensor 84 mounted at the center of mass of the vehicle body A signal indicating front and rear acceleration Gx of and a signal indicating wheel speeds (wheel circumferential speeds) Vwfl, Vwfr, Vwrl, and Vwrr of the left and right front and rear wheels from each of the wheel speed sensors 86FL-86RR are supplied. The lateral acceleration sensor 78, the yaw rate sensor 80, and the steering angle sensor 82 detect the lateral acceleration, the yaw rate, and the steering angle as positive when the vehicle turns left, respectively, and the front and rear acceleration sensors 84 Is detected as a positive forward and backward acceleration when the vehicle is accelerated in the forward direction. In general, the parameters that distinguish the vehicle's turning direction in the analysis below are considered positive when the turning is counterclockwise, respectively, when viewed from the top, and negative when the turning is clockwise.

The read-only memory device of the microcomputer 72 stores the flowcharts shown in FIGS. 2 to 4 and the maps shown in FIGS. 5 and 6. The central processing unit performs calculation based on the variables detected by the various sensors according to the flowchart and map as described below, and the spin state amount and drift out for determining and evaluating the spin state and the drift out state of the vehicle. The amount of state is obtained, and the turning behavior of the vehicle is controlled based on the evaluated state amount, and in particular, the variable braking force is selectively applied to each wheel to suppress the spin and drift out of the vehicle.

In the following, the stability control device of the present invention will be described as an embodiment of the control operation with reference to FIGS. Control in accordance with the flowchart of FIG. 2 is initiated by the closing of the ignition switch, not shown in the figure, and iteratively performed at predetermined time intervals, such as tens of microseconds.

In step 10, the signal including the vehicle speed V from the vehicle speed sensor 76 and other signals are read. If the gear ratio of the steering system is set to N and the wheel base is set to L in step 20, the steering angle is evaluated by the following equation 1 based on the yaw rate?.

[Equation 1]

θy = (γ / V) * N * L * 3.6

In step 30, the difference Δθ between the actual steering angle detected by the steering angle sensor 82 and the steering angle evaluated based on the yaw rate is calculated as in Equation 2 below.

[Equation 2]

Δθ = θ-θy

In step 40, a variable called the drift out state amount DQ is calculated based on the turning direction of the vehicle determined from the sign of the yaw rate γ so that if the vehicle turns left, the drift out state amount DQ becomes equal to Δθ, and if the vehicle turns right, the drift The out state amount DQ becomes equal to -Δθ. The drift out state amount DQ has no negative value.

In step 50, the drift out state amount DQ is modified according to FIG. 3 or FIG.

According to the routine of FIG. 3, in step 51, the absolute value of the lateral acceleration Gy detected by the lateral acceleration sensor 78 is not actually driving the vehicle along the curved road, that is, the driven vehicle actually runs the straight road. It is determined whether it is smaller than a relatively small threshold to confirm that it is being driven accordingly. If the answer is yes, then control proceeds to step 52, where the drift out state amount DQ is zero, and control returns to step 10. FIG. If the answer to step 51 is no, control proceeds to step 53, where it is determined whether the absolute value of Gy is greater than the relatively large threshold G2. If the answer is yes, then control passes to step 54 where the value of DQ is maintained as calculated in step 40. If the answer to step 53 is no, control proceeds to step 55, where the value of DQ is proportional to the value of Gy and adjusted according to Equation 3 below.

[Equation 3]

DQ = DQ * {(| Gy | -G1) / (G2-G1)}

If the lateral acceleration is judged to be actually small so that the absolute value of the lateral acceleration Gy is less than the threshold G1 which is small, while any substantial value of DQ has been computed in step 40, the actual value of such DQ is determined by the vehicle accelerating on a straight split μ road or At the same time, it is assumed that the driver is trying to steer the vehicle away from the straight course. Thus, as understood in the above process of FIG. 3, drift out control is not executed in such a state. Steps 53-55 are provided to stabilize the drift out control in the gray area between the state in which the vehicle is traveling along the straight split μ road and the state in which the vehicle is running along a clear bend.

According to the routine of FIG. 4, as the driver adjusts the vehicle so that it does not leave the straight course, the state in which the vehicle is being accelerated or braked along the straight split μ road is the calculated value of the transverse acceleration Gx or the drift-out state quantity DQ. It is judged more precisely by comparing with. So in step 61 the variable Gxyr is computed as the ratio of DQ at Gy to Gx or Gy. (In each case, it is measured not to divide by zero to establish a non-zero minimum value for the change in denominator.) In step 62, it is determined whether Gxyr is less than the appropriately defined relatively small threshold G3. By dividing Gy by Gx, the choice to eliminate false DQ due to split μ can be made according to Gy's low threshold. In other words, the comparison between the state in which the vehicle is accelerated or braked along a straight split μ road as the driver steers away from the straight course and the state in which the vehicle actually turns along the winding course is relatively apparent. A similar effect can be obtained by dividing Gy by DQ. If the answer to step 62 is YES, then control proceeds to step 63 where the value of DQ is zero and control returns to step 10. On the other hand, if the answer to step 62 is no, then control proceeds to step 64, where it is determined whether Gxyr is greater than the relatively large threshold G4. If the answer is yes, the routine ends without changing the value of DQ and proceeds to step 70, while if the answer of step 64 is no, control proceeds to step 66 and the value of DQ is expressed in Equation 4 below. Adjusted so that the value of Gxyr is proportional to the value of Gxyr for the gray region between G3 and G4.

[Equation 4]

DQ = DQ * (Gxyr-G3) / (G4-G3)

Returning to the flowchart of FIG. 2, in step 70 the target total slip ratio Rsall is determined based on the drift out state amount DQ processed in step 50 by referring to the map as shown in FIG. Next, in step 80, it is determined whether the target total slip ratio Rsall is zero or not. If the answer is yes, control returns to step 10 because in such a state no drift out control is needed.

If the answer of step 80 is no, then control proceeds to step 90, where the target total slip ratio Rsall is distributed between the target slip ratios Rsri and Rsro at the inside and outside of the turn in accordance with the appropriate distribution ratio Kr as shown in Equation (5). do.

[Equation 5]

Rsri = Rsall * kr / 100 Rsro = Rsall * (100-kr) / 100

In step 100, the target slip ratios Rsrl and Rsrr for the left and right rear wheels according to the turning direction determined by the sign of yaw rate γ are determined according to Equation 6 below when the vehicle turns left, and when the vehicle turns right, It is determined according to the equation (7).

[Equation 6]

Rsrl = Rsri Rsrr = Rsro

[Equation 7]

Rsrl = Rsro Rsrr = Rsri

In step 110, if Vb is taken as the reference wheel speed (e.g., the wheel speed of the front wheel in the turning inside), the target wheel speed Vwti (i = rl, rr) is calculated according to the following expression (8).

[Equation 8]

Vwti = Vb * (100-Rsi) / 100

In step 120, taking Vwide (differential of Vwi) as the wheel acceleration of the rear wheel and Ks as the appropriate positive coefficient, the target slip ratio SPi (i = rl, rr) is calculated according to the following equation (9).

[Equation 9]

SPi = Vwi-Vwti + Ks * (Vwid-Gx)

In step 130, referring to the map as shown in FIG. 6, the duty ratio for switching to the normally open on-off valves 60RL and 60RR and the normally closed on-off valves 62RL and 62RR is the target slip. Determined based on the value of the ratio SPi. In step 140, the control valves 28 and 44 are switched to the second position so that the brake pressure supplied to the rear wheel cylinders 64RL and 64RR is increased or decreased by an increment or decrease corresponding to the duty ratio Dri obtained above. Controlled.

Although the present invention has been described with respect to particular embodiments, those skilled in the art will understand that various changes may be made to the illustrated embodiments without departing from the spirit of the invention.

According to the stability control device according to the present invention, the stability of the vehicle for suppressing the drift out of the vehicle by selectively applying the variable braking to the rear wheel according to the amount of the drift out state indicating the tendency for the vehicle to drift out If the lateral acceleration is actually small when the control is activated, the stability control that suppresses the vehicle's drift-out is actually on a straight line μ road by activating a modification that actually eliminates the involvement of the draft-out condition in the rear brake control. The adverse effect on the running behavior of the vehicle is clearly avoided.

Further, in the above-described stability control device, in the embodiment in which the lateral acceleration is actually smaller when the absolute value thereof is smaller than the predetermined threshold value, the draft out suppression control is actually performed by appropriately determining the magnitude of such threshold value. Properly interrupted only when it is not necessary, on the other hand, when executed, the advantage of the draft out suppression control can be fully exploited.

Further, in the above-described stability control device, when the lateral acceleration is less than the predetermined threshold value of the absolute value of the ratio of the lateral acceleration to the front and rear acceleration of the vehicle body, in the embodiment of determining that the lateral acceleration is actually small, Determining the split μ state of the road surface based on how small the acceleration is actually made makes the lateral acceleration closer to the theoretical considering the braking magnitude generated by the split μ state.

Further, in the above-described stability control device, in the embodiment in which the lateral acceleration is actually small if the absolute value of the ratio of the lateral acceleration to the drift-out state amount is smaller than the predetermined threshold, by such an arrangement, Since the component of the lateral acceleration due to the turning of the vehicle is compensated by the lateral acceleration detected by the lateral acceleration sensor divided by the drift-out state amount, it is possible to use the judgment of the split μ state of the road even if the vehicle is actually traveling off the straight course. Can be.

Claims (5)

1. A stability control apparatus for a vehicle having a vehicle body and a front wheel and a rear wheel, comprising: means for determining the propensity of the vehicle body to drift out to make an amount of drift out condition increasing generally with an increase in the drift out tendency; Means for detecting lateral acceleration of the vehicle body; Brake means for selectively applying a variable braking force to each wheel; Control means for controlling the brake means to variably apply a braking force to each wheel, wherein the control means controls the brake means on the basis of the amount of drift out state to brake the rear wheels at a higher intensity as the amount of drift out state increases. And at the same time, if the lateral acceleration is actually a minor, the controller reliably corrects the participation of the drift-out state amount in the rear brake control. 2. The stability control device according to claim 1, wherein if the absolute value of the lateral acceleration is smaller than the predetermined threshold value, the lateral acceleration is judged to be actually small. The method of claim 1, further comprising means for detecting forward and backward acceleration of the vehicle, wherein if the absolute value of the ratio of the lateral acceleration to the forward and backward acceleration is less than the predetermined threshold, the lateral acceleration is determined to be actually small. Stability control device, characterized in that. 2. The stability control device according to claim 1, wherein the lateral acceleration is judged to be actually small when the absolute value of the ratio of the lateral acceleration to the drift-out state amount is smaller than the predetermined threshold value. 2. A vehicle according to claim 1, further comprising a vehicle speed detecting means, a yaw rate detecting means of the vehicle body, and a steering angle detecting means, wherein the control means includes a steering angle detected by the steering angle detecting means and a vehicle speed detecting means. And calculating the amount of drift out state as an absolute value of the difference between the steering angles calculated based on the detected vehicle speed and the yaw rate detected by the yaw rate.

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