JP2787480B2 - Vehicle anti-lock control method - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to an antilock control method for preventing locking of a wheel during braking of the wheel.

(Prior Art) In general, an anti-lock control device for a vehicle outputs an electric signal representing a wheel speed detected by a wheel speed sensor for the purpose of ensuring the steerability of a wheel, running stability and shortening a braking distance during braking. Determine the control mode of the brake fluid pressure based on it, open and close the hold valve consisting of a normally open solenoid valve and the decay valve consisting of a normally closed solenoid valve,
Thus, a control unit including a microcomputer is controlled to increase, maintain, or reduce the brake fluid pressure.

FIG. 6 shows the wheel speed Vw, wheel acceleration / deceleration dVw / dt and brake fluid pressure Pw in such antilock control.
FIG. 6 is a control state diagram showing a change of a hold signal and a decay signal DS for opening and closing a hold valve and a decay valve. Incidentally, the wheel speed Vw in FIG. 6 means a controlled wheel speed in each control channel,
In the following, this is referred to as system speed Vs.

When the brake is not operated while the vehicle is running, the brake fluid pressure Pw is not pressurized, and both the hold signal HS and the decay signal DS are OFF. Therefore, the hold valve is opened and the decay valve is closed. However, the brake fluid pressure Pw changes with time t0 due to the brake operation.
, And rapidly rises (normal mode), whereby the wheel speed Vw decreases. A reference speed Vr that follows the wheel speed Vw with a temperature difference lower by a constant speed ΔV.
Is set, and the following limit on the deceleration side with respect to the wheel speed Vw is limited to the range of -1.1 G. Therefore, the reference speed Vr is determined by the time when the wheel deceleration (negative acceleration) dVw / dt is
When a predetermined threshold value is reached at t1, for example, -1.1G,
From this point in time t1, it descends linearly with a deceleration gradient θ of -1.1G. Then close the hold valve and the hold signal HS is turned ON at the time t2 when the threshold is reached -G _max deceleration dVw / dt of the wheel represents a predetermined maximum deceleration, to hold the brake hydraulic pressure Pw.

The wheel speed Vw further decreases due to the holding of the brake fluid pressure Pw, and at time t3, the wheel speed Vw falls below the reference speed Vr.At this time t3, the decay signal DS is turned on to open the decay valve, and the brake fluid is opened. The pressure Pw starts to be reduced. Due to this decompression, the wheel speed starts to accelerate at the low peak at time t4, but at this low peak
At t4, or at time t5 when the vehicle speed has recovered from the low peak speed Vl to the increased speed Vb by an amount corresponding to 15% of the speed difference Y between the wheel speed Va and the low peak speed Vl at the decompression start time t3, the decay signal DS is generated. Turn OFF, close the decapable, end the decompression of the brake fluid pressure Pw, and maintain the brake fluid pressure Pw. At time t6, the wheel speed Vw reaches a high peak, but from this time t16, the brake fluid pressure Pw
Start pressurizing. The pressurization here is performed by turning the hold signal HS on and off in relatively small steps, so that the brake fluid pressure P
The pressurization and the holding of w are alternately repeated, whereby the brake fluid pressure Pw is gradually increased to decrease the wheel speed Vw. At the time t7, the holding mode is set, and from the time t8 (corresponding to t3), the depressurizing mode is changed again. generate. When the brake fluid pressure is gradually increased from time t6, for example, the application time is fixed.
Ts, the holding time T1 is determined based on the determination of the road surface μ,
Thereby, the pressurization rate of the gentle pressurization from the time point t6 to the time point t7 is set. The determination of the road surface μ for determining the holding time T1 is performed, for example, in the previous cycle of the antilock control (from time t3 to t6 when the previous cycle is the first cycle of the antilock control, In the case of the second cycle and thereafter, the adjustment is performed based on the deceleration gradient of the vehicle body speed in the previous gentle pressurization start point to the present gentle pressurization start point).

The periodic repetition of pressurization, holding, and depressurization of the brake fluid pressure Pw as described above allows the wheel speed Vw to be controlled and the vehicle body speed to be reduced without locking the wheels.

By the way, when such an antilock control method is applied to a vehicle, the left and right front wheels are generally set to the wheel speeds of the left front wheel and the right front wheel as control target wheel speeds, and the first and second control independent of each other. The brake fluid pressure is increased and decreased through the system.
Three systems (three channels) which select a low-speed wheel speed from the two wheel speeds (low select) and use this as a common control target wheel speed to control the brake fluid pressure through a third control system 2.) Antilock control method is widely used.

However, in the above-described anti-lock control method of independently controlling the left and right front wheels, when the brake is suddenly applied and the anti-lock control is started while traveling on a road surface (right / left split μ road) where the friction coefficient μ is largely different between left and right, As shown in FIG. 7, the control state of the front wheels on the high μ road surface is controlled with a high brake fluid pressure, and the front wheels on the low μ road surface are controlled with a low brake fluid pressure. Become. Therefore, there is a significant difference in hydraulic pressure between the left and right front wheels, and a large yaw moment is suddenly generated in the vehicle.

Also, when only the left or right front wheel enters the low μ road from the high μ uniform road (the high μ road where μ of the left and right road surfaces are substantially equal) during the antilock control, the control state diagram of FIG. As is apparent, the wheels on the low-μ road side go toward the lock, the wheel speed drops sharply, and the brake fluid pressure on the wheels is extremely relaxed. Therefore,
Also in this case, similarly to the example shown in FIG. 7, there is a problem that the difference in hydraulic pressure between the left and right front wheels increases rapidly, a large yaw moment is generated, and it becomes difficult for the driver to correct the steering wheel. .

Preventing the generation of such a yaw moment
It is thought that it is sufficient to lower the hydraulic pressure on the front wheels on the high μ road side.However, if the hydraulic pressure on the front wheels on the high μ road side is simply reduced, a new problem that the braking distance becomes longer occurs. Become.

(Object of the Invention) Accordingly, an object of the present invention is to provide an antilock control method capable of suppressing the occurrence of a sudden yaw moment during braking on a split μ road having extremely different left and right road surfaces μ.

(Constitution of the Invention) In the present invention, the wheel speed on the low-speed side of the left and right wheel speeds is shared by the two control systems before the pressure reduction start time and during a predetermined time from the pressure reduction start time in the first cycle of the antilock control. In addition to performing pressure reduction as the control target wheel speed, upon pressurization in the first cycle in the control system to which the high-speed wheel belongs after the lapse of the predetermined time, the low-speed wheel speed at the start of pressurization depends on the vehicle speed. When the pressure drops below a predetermined speed threshold value set in advance, gentle pressurization is performed at a pressurization rate having a fluid pressure increase rate that is steeper than a normal pressurization rate.

Then, when pressurizing the control system to which the high-speed side wheel belongs after the second cycle, if the low-speed side wheel speed at the time of starting pressurization has fallen below the above speed threshold, the normal pressurization is performed. The gradual pressurization is performed at a pressurization rate having a gradual increase in the liquid pressure than the rate.

(Embodiment) Hereinafter, an embodiment of the present invention will be described in detail with reference to the drawings.

FIG. 1 is a block diagram showing a three-system (three-channel) antilock control device to which the present invention is applied. The outputs of the wheel speed sensors 1 to 4 are sent to arithmetic circuits 5 to 8 to be calculated.
Signals representing the respective wheel speeds Vw1 to Vw4 are obtained. SW4 and SW5 indicate a changeover switch function. At the start of the anti-lock control, the movable contacts of these changeover switches SW4 and SW5 are at the positions shown by solid lines in FIG. 1, so that the left front wheel speed Vw1 and the right front wheel speed Vw2 are The low-speed wheel speed Vw5 is supplied to the front wheel low select circuit 17 and is selected as the first system speed and the second system speed Vs1 and Vs2, and is sent to the two control logic circuits 9 and 10. On the other hand, the lower wheel speed of the left rear wheel speed Vw3 and the right rear wheel speed Vw4 is selected by the rear wheel low select circuit 11 and sent to the third control logic circuit 12 as the third system speed Vs3. In each of the control logic circuits 9, 10, and 12, the system speeds Vs1 to Vs2 are respectively set as control target wheel speeds Vw (hereinafter, simply referred to as “wheel speeds Vw”), and the hold valve HV and the decay valve are determined based on the wheel speeds Vw. Performs DV ON / OFF control.

Signals representing the wheel speeds Vw1 to Vw4 are sent to the pseudo vehicle speed calculation circuit 13.The calculation circuit 13 sets the four wheel speeds Vw1 to Vw4 to high select and further sets the following limit for the fastest wheel speed. The speed limited to the range of ± 1G is set as the pseudo vehicle speed Vv, and each control logic circuit 9, 10,
Output to 12.

Each of the control logic circuits 9, 10, and 12 is provided with a slow pressurizing determination circuit 14, 15, 16 for determining a pressurizing rate (fluid pressure rise degree) of the slow pressurizing in the antilock control. The pressure determination circuits 14, 15, 16 are provided by the logic circuits 9, 10,
12 and connected via switches SW1, SW2 and SW3.
The switches SW1, SW2, and SW3 are turned on by the output from the control logic circuits 9, 10, and 12 for each system during the period from time t6 to time t7 shown in FIG. Controlled to be OFF.

On the other hand, the outputs of the control logic circuits 9 and 10 are given to the switch switching logic circuit 18, and when a predetermined condition is satisfied by the determination method shown in the flowchart of FIG.
Switch by the output of the switch switching logic circuit 18
SW4 and SW5 are both switched to the positions indicated by the broken lines in FIG.

Next, FIG. 2 is a flowchart showing the operation of the switch switching logic circuit 18. First, in step S1, it is determined whether or not the brake is ON. If the result of the determination is "YES", the flow proceeds to the next step S2, in which the first cycle pressurization is performed in the left or right front wheel control system. It is determined whether the starting point has been reached. Until one of the front wheel systems reaches the pressurization start point, the determination result here is "N
"O", the process proceeds to step S3, and it is determined whether the left or right front wheel system has reached the decompression start point in the first cycle. Then, if the determination result is “YES”, the elapsed time T from the pressure reduction start point is incremented in step S4, and the process proceeds to the next step S5, where the time T is equal to a predetermined time T _K (for example, T _K). = determined whether a 100 mS) than, T <switch SW4 in step S6 if T _K, SW5
Are connected to the front wheel low select circuit 17 side, and the control system speeds Vs1 and Vs2 of the left and right front wheels are set to the front wheel select low speed Vw5. Further, the process proceeds when it becomes a T ≧ T _K in step S5 to step S7, switched to the position shown the movable contact of the switch SW4, SW5 together by the dashed line in FIG. 1, the system speed Vs
1 and Vs2 are set as the left and right front wheel speeds Vw1 and Vw2, respectively, and the left and right front wheels are controlled independently of each other. If the determination result of step S1 or S3 is “NO”,
In any case, the process proceeds to step S8, and T is set to zero.

FIG. 3 is a circuit for determining gentle pressurization of the first and second control systems.
15 is a flowchart illustrating the operations of 14 and 15 by taking the circuit 14 of the first control system on the high μ road side as an example when the left front wheel side is a high μ road and the right front wheel side is a low μ road. First, step S1
It is determined whether or not the split flag indicating that the vehicle is on the split μ road in step 1 is ON.Since the split flag is initially OFF, the process proceeds to step S12, where the right front wheel speed Vw2 is a predetermined speed threshold. It is determined whether the value is equal to or less than the value VT1. Here, the speed threshold value VT1 is a speed that follows the pseudo vehicle body speed Vv with a predetermined relationship, and the equation VT1 = Vv × AB (where A is in the range of 0 <A <1). The coefficient, B, is a constant speed difference, for example, A
= 0.91 and B = 8 km / h). If it is determined in step S12 that Vw2> VT1, the first gentle pressurizing process is performed in step S13 at a normal pressurizing rate (holding time in gentle pressurization = T1). Also, if Vw2 ≦ VT1 in step S2,
It is determined that the road is a left / right split μ road, the split flag is turned on in step S14, and the process proceeds to step S15. In this step S15, it is determined whether or not the antilock control cycle of the own system (the left front wheel system) is the first cycle. If the determination result is "YES", the normal pressurization rate is determined in the next step S16. The second gentle pressurization process is performed at a pressurizing rate (holding time in gentle pressurization = T2, T2 <T1) having a steeper fluid pressure increase degree. On the other hand, if it is determined in step S15 that the current time is after the second cycle, step S1
Proceeding to 7, it is determined whether or not pressurization has been started for the right front wheel belonging to another system. If it is determined in step S17 that pressurization has been started, only one wheel (in this case, the right front wheel) has entered the low μ road from the high μ uniform road. The third gentle pressurizing process is performed at a pressurizing rate (holding time in gentle pressurization = T3, T3> T1) having a degree of increase in the fluid pressure more slowly than the pressurizing rate of (1). If the determination result of step S17 is “YES”, the process proceeds to step S13.
If the split flag is ON in step S11, the process proceeds directly to step S15.

The split flag is set at the decompression start point of each cycle.
It is turned off.

FIG. 4 shows a control state at the time of traveling on the left and right split μ roads executed according to the above-described flowchart, and unless the right or left control system has reached the pressurization start point of the first cycle, Until the predetermined time T _K elapses from the decompression start point (before t10 shown in the figure), the system speeds Vs1 and Vs2 of the left and right front wheels are changed to the front wheel select low speed.
Vw5. After the lapse of the predetermined time Tk (after the second cycle), the left and right front wheel speeds Vw1 and Vw2 are used as the system speeds Vs1 and Vs2 to perform left and right independent hydraulic pressure control. If the speed is equal to or lower than the predetermined speed threshold value VT1, it is determined that the road is a right and left split μ road, and the split flag is turned on to control the high μ road side control system. A second gentle pressurizing process is performed at a pressurizing rate having a steep increase in hydraulic pressure to secure a necessary brake hydraulic pressure.

On the other hand, FIG. 5 shows a control state in a case where only one of the left and right front wheels enters the low μ road from the high μ uniform road during the antilock control. If one of the front wheels is traveling on a high μ road, but the other front wheel has entered the low μ road from the high μ road and the wheel speed has dropped significantly,
The split flag is turned on when the wheel speed of the roadside front wheel falls below the predetermined speed threshold value VT1 at time t11 shown in FIG. Then, when the pressurization of the system on the low μ road side has not been started, the pressurization on the system on the high μ road side is performed by the third gradual increase by the pressurization rate having a gradual increase in the fluid pressure than the normal pressurization rate. Pressure treatment. By performing this processing, the difference between the hydraulic pressures of the left and right two systems of the front wheels is suppressed, and the occurrence of the yaw moment is prevented.

In this embodiment, for the left and right front wheels, the left and right wheel speeds are set as control target wheel speeds, and for the left and right rear wheels, the rear wheel select low speed is set as the rear wheel control target wheel speed, and the control is performed independently. However, the present invention is not limited to this. For example, for the left and right front wheels, the front wheel select low speed is set to the front wheel control target wheel speed, and for the left and right rear wheels, the left and right Of the rear wheels in a three-system anti-lock control device that uses the wheel speed of the vehicle as the control target wheel speed, or a four-system anti-lock control method that uses the respective wheel speeds as the control target wheel speeds for four wheels It is.

(Effects of the Invention) As is clear from the above description, according to the present invention, when the vehicle enters the anti-lock control state while traveling on the split μ road, the wheels on the high μ road side are controlled in the first control cycle. If the speed is set to gentle pressurization with a steeper pressurization rate than normal pressurization, and if the vehicle enters the split μ road during control, the wheel control on the high μ road side will be more gentle than normal pressurization. Slow pressurization with a rate prevents the generation of sudden yaw moment due to braking while preventing an increase in braking distance, thereby facilitating course correction by steering wheel operation and ensuring directional stability can do.

[Brief description of the drawings]

FIG. 1 is a block diagram of a three-system antilock control device to which the present invention is applied, FIG. 2 is a flowchart showing the operation of the switch switching logic circuit, FIG. 4 and 5 are explanatory diagrams of the present invention, FIG. 6 is a control state diagram of the antilock control, and FIGS. 7 and 8 are diagrams showing the operation of the conventional antilock control method. 1-4 wheel speed sensors 5-8 arithmetic circuits 9, 10, 12 control logic circuit 11 rear wheel low select circuit 13 pseudo vehicle speed arithmetic circuits 14-16 Circuit 17: Front wheel low select circuit

──────────────────────────────────────────────────続 き Continuing on the front page (72) Yoshiaki Hirobe 5-4-1, Higashi 5-chome, Hanyu City, Saitama Prefecture Within the Development Headquarters of Akebono Brake Industry Co., Ltd. (72) Hideo Akima Kamiodanaka, Nakahara-ku, Kawasaki City, Kanagawa Prefecture 1015 Fujitsu Co., Ltd. (72) Inventor Mori Bunri 1015 Ueodanaka, Nakahara-ku, Kawasaki City, Kanagawa Prefecture Fujitsu Co., Ltd. (56) References JP-A-58-164460 (JP, A) JP-A-61-166673 (JP, A) JP-A-1-103565 (JP, A) JP-A-55-11976 (JP, A) JP-A-49-56083 (JP, A) JP-A-61-81261 (JP, A) ( 58) Field surveyed (Int.Cl. ⁶ , DB name) B60T 8/58

Claims (1)

(57) [Claims] The brake fluid pressure is increased and decreased through two independent control systems using the respective wheel speeds as control target wheel speeds for two left and right wheels, and the brake fluid pressure is controlled by anti-lock control. In the anti-lock control method for a vehicle, in which the pressure is gradually increased at a first pressure rate having a predetermined fluid pressure increase degree, the pressure is reduced before a pressure reduction start time in a first cycle of the anti-lock control and Until a predetermined time from the decompression start time, the low-speed wheel speed of the left and right wheel speeds is reduced as a control target wheel speed common to the two control systems, and the high-speed wheel speed after the predetermined time elapses. At the time of pressurization in the first cycle in the control system to which the wheel belongs, the wheel speed on the low speed side at the time of the start of pressurization depends on the vehicle speed. If the pressure drops below the set speed threshold, the pressure is gradually increased at a second pressure rate having a steeper fluid pressure rise rate than the first pressure rate. At the time of pressurization in the control system to which the high-speed wheel belongs after the second cycle of control, if the low-speed wheel speed at the time of starting pressurization has fallen below the speed threshold, the first An anti-lock control method for a vehicle, characterized in that gentle pressurization is performed at a third pressurization rate having a degree of fluid pressure increase that is slower than the pressurization rate.